a comparative assessment of phytoremediation and …
TRANSCRIPT
A COMPARATIVE ASSESSMENT OF PHYTOREMEDIATION AND
SLOW SAND FILTRATION TECHNOLOGIES FOR THE SECONDARY
TREATMENT OF SEWAGE EFFLUENT AND PUBLIC VIEWS ON THE
USE OF TREATED EFFLUENT
BY
NAOMI ADRAKI
(10105318)
THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA,
LEGON IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR
THE AWARD OF MPHIL ENVIRONMENTAL SCIENCE DEGREE
JULY, 2014
i
DECLARATION
I, Naomi Adraki, hereby declare that except for references cited, which I have duly
acknowledged, this work is the result of my own research undertaken under supervision
of Dr. Ted Annang and Dr. Dzidzor Yirenya-Tawiah of the Institute of Environment and
Sanitation Studies (IESS) towards the award of a Master of Philosophy Degree in
Environmental Science and that this work has neither in whole or in part, been presented
anywhere for the award of any other degree.
……………………………………… …………………………….
NAOMI ADRAKI DATE
(Student)
……………………………………… …………………………….
DR. TED ANNANG DATE
(Principal supervisor)
………………………………………… …………………………….
DR. DZIDZOR YIRENYA-TAWIAH DATE
(Co-supervisor)
ii
DEDICATION
This work is dedicated to my parents, Mr. and Mrs. Gabriel Anyigbah.
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ACKNOWLEDGEMENTS
I am very grateful to the almighty God for the gift of life and for the wisdom to carry out
this research. Many thanks to my supervisors, Dr. Ted Annang and Dr. Dzidzor Yirenya-
Tawiah for their direction and support. I also wish to thank Dr. Aidan of Biogas
Technologies Ltd for his great help.
To the Environmental Unit of Valley View University, especially Mr. Solomon Adei, I
say a very big thank you for granting me permission to use your Biogas facility for this
research.
Staff and students of IESS, thank you so much.
To my family and friends, I say thank you for your support and prayers. God bless you.
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ABSTRACT
This study evaluated and compared the performance efficiency of both technologies for
treating sewage effluent from a Biogas facility at Valley View University (VVU) and
also assessed public perception about the use of the treated effluent. Samples of the
sewage effluent from the VVU Biogas facility were subjected to slow sand filtration over
a ten week period using river bed sand and gravels, and phytoremediation using two
plants, Pistia stratiotes L and Ipomoea aquatica Forsk. Pistia stratiotes survived in the
raw effluent for five days, while Ipomoea aquatica survived longer (four weeks). The
findings revealed that both plants reduce contaminant levels. However, Ipomoea aquatica
had higher removal efficiency for phosphates (16.07%) and nitrates (100%). Pistia
stratiotes on the other hand was more efficient at improving electrical conductivity
(55.45%). The study showed that both slow sand filtration and phytoremediation using
Ipomoea aquatica are equally efficient at improving turbidity and Chemical Oxygen
Demand (COD). There were significant differences in values obtained for dissolved
oxygen (DO), nitrates and phosphates. Based on the differences, SSF performed better at
removing nitrates and phosphates while Ipomoea aquatica did better at enhancing
dissolved oxygen. No significant differences were recorded for electrical conductivity
(EC), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), colour, and
Biochemical Oxygen Demand (BOD). However, when the means were compared, SSF
was better at removing TSS, BOD and colour whilst Ipomoea aquatica was better at
removing EC and TDS. Both technologies were successful at reducing microbial load.
This study also revealed that the parameters analyzed on the effluent discharged from the
VVU Biogas facility fell within acceptable guidelines with the exception of EC. Majority
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of respondents agree that water is a scarce resource and that the Millennium
Development Goal (MDG) on water cannot be achieved. Majority of people interviewed
support the use of wastewater for medium contact options such as fire-fighting (71.6%),
industry (52.9%), construction of buildings (71.6%), toilet flushing (81.4%), commercial
car wash (46.1%), public parks and sports field irrigation (54.9%). Support for high
contact options such as swimming pool, aquifer augmentation and laundry was low;
10.7%, 29.4% and 34.3% respectively and this is because respondents consider the
treated water to be detrimental to health. Respondents supported the idea of wastewater
reuse for reasons of water conservation and minimization of dependency on treated water
whilst environmental protection ranked as the least frequent response. Education is
needed to sensitize the public on treatment and use of wastewater.
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LIST OF ABBREVIATIONS
AAS Atomic absorption spectrophotometry
ANOVA Analysis of variance
BOD Biochemical oxygen demand
COD Chemical oxygen demand
DO Dissolved oxygen
EC Electrical conductivity
FC Faecal coliforms
GEPA Ghana Environmental Protection Agency
SSF Slow sand filtration
TC Total coliforms
TDS Total dissolved solids
TSS Total suspended solids
VVU Valley View University
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TABLE OF CONTENTS
Content Page
DECLARATION ................................................................................................................. i
DEDICATION .................................................................................................................... ii
ACKNOWLEDGEMENTS ............................................................................................... iii
ABSTRACT ....................................................................................................................... iv
LIST OF ABBREVIATIONS ............................................................................................ vi
TABLE OF CONTENTS .................................................................................................. vii
LIST OF PLATES .............................................................................................................. x
LIST OF FIGURES ........................................................................................................... xi
LIST OF TABLES ........................................................................................................... xiv
CHAPTER ONE ................................................................................................................. 1
1.0 INTRODUCTION AND LITERATURE REVIEW .................................................... 1
CHAPTER TWO .............................................................................................................. 21
MATERIALS AND METHODS ...................................................................................... 21
2.1 Study site ................................................................................................................. 21
2.2 Materials .................................................................................................................. 22
2.3 Sewage treatment at VVU ....................................................................................... 23
2.4 Selection of sampling sites ...................................................................................... 23
2.5 Sampling of aquatic macrophytes ........................................................................... 23
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2.6 Preparation of filter media units ............................................................................. 25
2.7 Treatment of sample containers .............................................................................. 26
2.8 Monitoring of effluent quality at sampling site ....................................................... 26
2.8 Sampling of effluent for characterization................................................................ 27
2.9 Sewage effluent collection and experimental procedure ......................................... 28
2.9.1 Sewage effluent collection ................................................................................ 28
2.9.2 Slow Sand filtration (SSF) ................................................................................ 29
2.10 Phytoremediation ............................................................................................... 31
2.11 Laboratory analyses............................................................................................... 34
2.11.1 Physico-chemical analyses of raw and treated effluents ................................ 34
2.11.10 Analyses of Bacteriological Parameters of raw and treated effluents .......... 39
2.12 Social survey ......................................................................................................... 41
CHAPTER THREE .......................................................................................................... 42
3.0 RESULTS................................................................................................................ 42
3.1 Quality of sewage effluent from VVU biogas facility ............................................ 42
3.2 Phytoremediation using Pistia stratiotes and Ipomoea aquatica ............................ 43
3.3 Nitrogen and phosphorus uptake by plants ............................................................. 46
3.4 Contaminant removal efficiency of Ipomoea aquatica and Pistia stratiotes .......... 47
3.5 Weekly variations in water quality parameters after treatment with Ipomoea
aquatica ......................................................................................................................... 49
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3.6 Performance of Slow Sand Filtration ...................................................................... 53
3.7 Comparison of phytoremediation using Ipomoea aquatica and slow sand filtration
(SSF) technologies ........................................................................................................ 59
3.8 Microbial load ......................................................................................................... 80
3.9 Comparison of efficiency of experimental sand filter to the filtration system of the
Biogas plant ................................................................................................................... 82
3.10 Quality assessment of safety of treated effluent for disposal/reuse ...................... 83
3.11 Public perceptions on water scarcity and the reuse of wastewater ....................... 87
3.11.1 Demographic background of respondents .......................................................... 87
3.11.2 Environmental perceptions ................................................................................. 87
CHAPTER FOUR ........................................................................................................... 102
4.0 DISCUSSION ....................................................................................................... 102
CHAPTER FIVE ............................................................................................................ 119
5.0 CONCLUSIONS ................................................................................................... 119
REFERENCES ............................................................................................................... 122
APPENDICES ................................................................................................................ 133
x
LIST OF PLATES
Plate 1: Kpong Head Pond showing aquatic plants .......................................................... 22
Plate 2: Biogas facility of Valley View University .......................................................... 24
Plate 3: Filter media units; (a) gravels (5-10mm diameter), (b) coarse sand (2-3mm
diameter), (c) fine sand (0.4mm diameter) .......................................................... 25
Plate 4: Sampling effluent from intermediary chamber for characterization ................... 28
Plate 5: Slow Sand Filtration experimental set up at the greenhouse .............................. 29
Plate 6: Pistia stratiotes in different dilutions of effluent ................................................. 33
Plate 7: Ipomoea aquatica planted in sewage effluent ..................................................... 33
Plate 8: Condition of Pistia stratiotes days after planting in sewage effluent ................. 43
Plate 9: Condition of Ipomoea aquatica days after planting in sewage effluent .............. 43
Plate 10: Sewage effluent before (A) and after treatment (B) with Pistia stratiotes ........ 44
Plate 11: Sewage effluent before (a) and after treatment (b) with Ipomoea aquatica ...... 45
Plate 12: Sewage effluent before (A) and after seventh week (B) of slow sand filtration 58
xi
LIST OF FIGURES
Fig 1: Location map of study area .................................................................................... 21
Fig 2: Cross-section of slow sand filter media for Slow Sand Filtration of effluent ........ 30
Fig 3: Phosphate removal efficiency of Ipomoea aquatica and Pistia stratiotes ............. 47
Fig 4: Nitrate removal efficiency of Ipomoea aquatica and Pistia stratiotes ................... 47
Fig 5: COD removal efficiency of Ipomoea aquatica and Pistia stratiotes ..................... 48
Fig 6: EC removal efficiency of Ipomoea aquatica and Pistia stratiotes......................... 48
Fig 7: Concentration of dissolved oxygen (DO) in effluent after every week of treatment
with Ipomoea aquatica ........................................................................................ 49
Fig 8: Biochemical Oxygen Demand (BOD) of effluent after every week of treatment
with Ipomoea aquatica ........................................................................................ 50
Fig 9: Chemical Oxygen Demand (COD) of effluent after every week of treatment with
Ipomoeaaquatica ................................................................................................. 50
Fig 10: Electrical conductivity (EC) of effluent after every week of treatment with
Ipomoea aquatica ................................................................................................ 51
Fig 11: Total Dissolved Solids (TDS) of effluent after every week of treatment with
Ipomoea aquatica ............................................................................................... 51
Fig 12: Concentration of phosphates in effluent after every week of treatment with
Ipomoea aquatica ................................................................................................ 52
Fig 13: Concentration of nitrates in effluent after every week of treatment with Ipomoea
aquatica ............................................................................................................... 52
Fig 14: Rate of filtration through experimental sand filter ............................................... 53
Fig 15: Weekly variations in turbidity of effluent treated using SSF method .................. 54
Fig 16: Weekly variations in electrical conductivity (EC) of effluent treated using SSF 54
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Fig 17: Weekly variations in concentration of total dissolved solids (TDS) in effluent
treated using SSF ................................................................................................. 55
Fig 18: Weekly variations in concentration of Total Suspended Solids (TSS) in effluent
treated using SSF ................................................................................................. 55
Fig 19: Weekly variations in concentration of nitrates in effluent treated using SSF ...... 56
Fig 20: Weekly variations in concentration of phosphates in effluent treated using SSF 56
Fig 21: Weekly variations in concentration of dissolved oxygen in effluent treated using
SSF ...................................................................................................................... 57
Fig 22: Weekly variations in Biochemical Oxygen Demand (BOD) of effluent treated
using SSF ............................................................................................................. 57
Fig 23: Weekly variations in Chemical Oxygen Demand (COD) of effluent treated using
SSF ...................................................................................................................... 58
Fig 24: Source of water for domestic use by respondents ................................................ 88
Fig 25: Proportion of respondents who consider water to be a scarce resource ............... 89
Fig 26: Causes of water scarcity stated by respondents .................................................... 89
Fig 27: Sources of wastewater stated by respondents ....................................................... 90
Fig 28: How wastewater is generated by respondents ...................................................... 90
Fig 29: Uses of wastewater generated at home ................................................................. 91
Fig 30: Type of toilet facilty respondents have access to ................................................. 92
Fig 31: Methods of disposal of sewage as stated by respondents ..................................... 93
Fig 32: Respondents reasons for supporting wastewater reuse ........................................ 94
Fig 33: Types of health risks associated with wastewater reuse as stated by respondents 95
Fig 34: Respondents response on how health risks can be minimized ............................. 96
xiii
Fig 35: Response of respondents to the use of treated wastewater for irrigation of food
crops .................................................................................................................... 97
Fig 36: Response of respondents to the use of treated wastewater for fire fighting ......... 98
Fig 37: Response of respondents to the use of treated wastewater for industry ............... 98
Fig 38: Response of respondents to the use of treated wastewater for construction of
buildings .............................................................................................................. 99
Fig 39: Response of respondents to the use of treated wastewater for swimming pool ... 99
Fig 40: Response of respondents to the use of trated wastewater for aquifer augmentation
........................................................................................................................... 100
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LIST OF TABLES
Table 1: Quality of sewage effluent from intermediary chamber (A) and final outlet (B)
of the Valley View University (VVU) Biogas facility. .................................... 42
Table 2: Phosphorus and nitrogen accumulation in Ipomoea aquatica and Pistia stratiotes
at the end of experiment ................................................................................... 46
Table 3: Comparison of p H of effluent treated using SSF with effluent from treatment
with Ipomoea aquatica ..................................................................................... 60
Table 4: Comparison of the concentration of dissolved oxygen (DO) of effluent treated
using SSF with effluent treated with Ipomoea aquatica ................................. 61
Table 5: Comparison of turbidity of effluent treated using SSF with effluent from
treatment with Ipomoea aquatica ..................................................................... 63
Table 6: Comparison of EC of effluent treated with SSF with effluent from treatment
with Ipomoea aquatica ..................................................................................... 65
Table 7: Comparison of concentration Total Dissolved Solids (TDS) of effluent treated
using SSF with effluent from treatment with Ipomoea aquatica ..................... 67
Table 8: Comparison of concentration of Total Suspended solids (TSS) of effluent treated
using SSF with effluent from treatment with Ipomoea aquatica ..................... 69
Table 9: Comparison of colour of effluent treated using SSF with effluent from treatment
with Ipomoea aquatica ..................................................................................... 71
Table 10: Comparison of concentration of nitrates in effluent treated using SSF with
effluent treated using Ipomoea aquatica .......................................................... 73
Table 11: Comparison of phosphate concentration in effluent treated using SSF with
effluent from treatment with Ipomoea aquatica ............................................... 75
Table 12: Comparison of Biochemical Oxygen Demand (BOD) of effluent treated with
SSF with effluent from treatment with Ipomoea aquatica ............................... 77
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Table 13: Comparison of Chemical Oxygen Demand (COD) of effluent treated using SSF
with effluent from treatment with Ipomoea aquatica ...................................... 79
Table 14: Microbiological characteristics of sewage effluent before and after treatment 80
Table 15: Comparison of the quality of effluent for ten weeks of SSF to quality of
effluent passing through the filtration system of the VVU Biogas plant ......... 82
Table 16: Assessment of safety of effluent treated using SSF for disposal/reuse ............ 83
Table 17: Assessment of the quality of effluent treated using Pistia stratiotes for
disposal/use ...................................................................................................... 84
Table 18: Assessment of the quality of effluent treated using Ipomoea aquatica for
disposal/ use ..................................................................................................... 86
Table 19: Demographic characteristics of respondents .................................................... 87
1
CHAPTER ONE
1.0 INTRODUCTION AND LITERATURE REVIEW
All around the world, the demand for water resources is accelerating with increasing
population growth. Most water bodies are under threat due to pollution. It is becoming
increasingly important to seek alternative sources of water to meet the demand of the ever
increasing global population. Increasing demands on water resources for domestic,
commercial, industrial and agricultural purposes have made wastewater reclamation an
attractive option for conserving and extending available water supplies. Thus, wastewater
reclamation and reuse have become essential components of water resource management
plans throughout the world.
One of the major water resource management concerns throughout the world is the safe
disposal of sewage. In many countries especially the developing ones, disposal of raw
untreated sewage into natural waters is a common practice. This poses a great hazard for
the environment and a health risk for both human and animal life.
In recent years, sewage treatment strategies have been shifted to one of the most
promising methods i.e. biological anaerobic treatment. This method is capable of treating
sewage to produce renewable energy (biogas), leaving behind an effluent which is
usually discarded. This effluent is a substantial water resource that has to be sustainably
managed, rather than discarded.
Sewage effluent is composed of compounds of agricultural value including organic
matter, nitrogen, phosphorus and a lesser amount of calcium, sulphur and magnesium. It
may also contain pollutants such as heavy metals, organic pollutants and pathogens
2
which may have significant adverse effects on human health and the environment, thus
limiting its use. However, further treatment of the effluent can produce a high quality
effluent for use.
Treatment technologies for wastewater need to be appropriate and sustainable. They
should also be efficient but less costly and easy to operate and maintain. In developing
countries with warm climates such as Ghana, natural systems are considered more
suitable.
Slow Sand filtration (SSF) and phytoremediation are natural treatment systems that can
be used for treatment of wastewater. These technologies have proven to reduce
contaminant levels to tolerable levels. Materials needed for the use of these technologies
are readily available.
Global water crises
Fresh water is a scarce and unevenly distributed resource, not matching patterns of
human development (Corcoran et. al., 2010). According to UNDESA (2009), nearly 900
million people worldwide still do not have access to safe water. The population of the
world is increasing rapidly and is expected to grow by almost a third to over 9 billion
people in the next 40 years (UNFPA, 2009), resulting in increased water usage. The
African continent has the lowest total water supply coverage of any region in the world,
with only 64% of the population having access to improved water supply (WHO, 2000).
One other contributory factor to the water scarcity problem is water pollution. The
available water resources which should cater for the needs of the ever growing global
3
population are constantly being polluted the chief sources of water pollution being
sewage, industrial wastes, fossils, fuel and nuclear power plants (Egun, 2010).
Currently, there is increasing awareness of the impact of sewage contamination on water
bodies. According to the World Bank, the greatest challenge in the water and sanitation
sector over the next two decades will be the implementation of low cost sewage treatment
that will at the same time permit selective reuse of treated effluents for agricultural and
industrial purposes (Jhansi and Mishra, 2012)
Sewage treatment
Wastewater (sewage) treatment is an expensive process, both in terms of land required
and the energy consumed (Mekala et. al., 2008). More than 65% of sewage is treated in
developed countries (WHO and UNICEF, 2000) for various reasons, but only after
suitable treatment and guidelines are in place for recycling. In Africa, almost no sewerage
is treated (WHO and UNICEF, 2000).
Generally there is lack of sustainable options for treating sewage in many cities in
developing countries. Most cities in developing countries have an aging, inadequate or
even non-existent sewage infrastructure, unable to keep up with rising population. The
United Nations Development Programme (UNDP) reports that in 2000 only 2 % of the
cities in sub-Saharan Africa had sewage treatment and only 30 % of these were operating
satisfactorily.
The cities of Ghana are no exception to the poor sewage treatment coverage. It has been
shown that out of the 44 wastewater treatment plants in Ghana, only 20 % are working,
most of them below design standard (IMWI, 2012). Consequently, sewage sludge from
4
on-site sanitation systems (OSS) is collected and disposed-off in the raw and untreated
form indiscriminately into drainage ditches, inland waters and coastal waters. Discharge
of untreated effluent into water bodies puts at risk riparian communities which depend on
these waters for domestic and personal use (Tchobanologous et al., 2003). Biodiversity is
also affected as a result of water pollution. In many developing countries, contamination
of faecal origin appears to be responsible for many enteric diseases notably in children.
Africa has the worst statistics for cholera and child diarrhoea (Warner, 2000).WHO
reported in 2000 that in Africa, 155 children die every hour of everyday from sanitation,
hygiene and water related diseases. The number of cholera cases reported from Africa is
increasing every year. A total of 187,545 cholera cases and 8,051 deaths were officially
reported in the African Region (WHO, 2000). Recently, several cholera outbreaks were
reported in different African countries: Zimbabwe, Tanzania, Rwanda, Kenya, Angola,
Republic of Congo and Ghana due to contaminated drinking water (Bahri et al., 2012)
Most of the current sewage treatment technologies in developing countries lack
sustainability (Jhansi and Mishra, 2012). The conventional centralized system uses large
volumes of water to dilute human excreta and thereafter transports them out of the
settlement which makes this system unsustainable because apart from the fact that large
volumes of water are lost, most of the sewage is transported and deposited in water
bodies leading to contamination of the water causing public health hazards. There is also
a loss of nutrient resources of agricultural value such as nitrogen and phosphorus.
5
Another reason for the unsustainable treatment systems in developing countries is that
they are simply copied from western treatment systems without considering the
appropriateness of the technology for the culture, land and climate. Thus, many of the
implemented installations are abandoned due to high cost of running the system and
repairs (Jhansi and Mishra, 2012).
In order to achieve effective sewage treatment in developing countries, there is the need
to apply appropriate treatment technologies which are effective, simple to operate and
low cost in terms of investment, operation and maintenance.
One of the effective treatment options for developing countries is anaerobic digestion
(Jhansi and Mishra, 2012). This technology has been proven to have high treatment
efficiency and its operation requires no or very low energy.
Anaerobic digestion consists of several interdependent, complex sequential and parallel
biological reactions in the absence of oxygen in which the products from one group of
microorganisms serve as substrates for the next resulting in transformation of organic
matter (Parawira, 2004). The products resulting from the transformation are biogas and
nutrient rich effluent called digestate.
In this system, anaerobic bacteria degrade organic materials in the absence of oxygen and
produce methane and carbon dioxide. The methane can be reused as an alternative energy
source or biogas. Other benefits include a reduction of total bio-solids volume of up to
50-80% and a final effluent that is biologically stable and can serve as rich humus for
agriculture (Jhansi and Mishra, 2012). This anaerobic treatment technology can be
6
applied on a very small or a very large scale making it a sustainable option for a growing
community.
However, effluents from anaerobic reactors treating domestic sewage can rarely comply
with the emission standards. Besides the remaining fraction of particulate and soluble
organic matter, the main important constituents or components deserving attention are
nutrients and pathogens. These are not removed efficiently in the most commonly used
anaerobic reactors (Foresti, 2002).
Wastewater reuse
Current waste management practices propose that sanitation systems whenever feasible
should allow for recycling of organic matter and nutrients in human excreta (Esrey et al.,
1998). As a result, treatment strategies and technological options for sewage sludge and
solid waste have to be developed to allow the optimum recycling of nutrients and organic
matter.
One of the important and sustainable ways to reduce the impact of water scarcity and
pollution is wastewater recycling and reuse. Wastewater effluent is the most readily
available and cheapest source of additional water and provides a partial solution to the
water scarcity problem (Al-Dadah, 2013).
In recent years, the reuse of treated effluent that hitherto was discharged into the
environment from municipal wastewater treatment plants is receiving an increasing
attention as a reliable water resource. In many countries, wastewater treatment for reuse
is an important dimension of water resources planning and implementation. This is aimed
7
at releasing high quality water supplies for potable use. Some countries, such as Jordan
and Saudi Arabia, have national policies aimed at reusing all treated wastewater effluents,
thus have made considerable progress towards this end (Akpor and Muchie, 2011). In
China, sewage use in agriculture developed rapidly several decades ago and millions of
hectares are irrigated with sewage effluent (Akpor and Muchie, 2011). The general
acceptance is that wastewater use in agriculture is justified on agronomic and economic
grounds, although care must be taken to minimize adverse health and environmental
impacts (Sowers, 2009). Furthermore, wastewater reuse is increasingly becoming
important for supplementing drinking water needs in some countries around the world.
The option of reuse of wastewater is becoming necessary and possible as a result of
increased climate change, which leads to droughts and water scarcity, and the fact that
wastewater effluent discharge regulations have become stricter leading to a better water
quality (Rietveld et al., 2009).
Wastewater can be an essential resource for supporting livelihoods with proper
management. The treatment and reuse of wastewater in agriculture can provide benefits
to farmers in conserving freshwater resources, improving the integrity of the soil and
preventing discharge to surface and ground waters. In the State of California and in
Mexico, reclaimed water is used for irrigation (Corcoran et. al., 2010).
The use of raw untreated wastewater for irrigation is a common practice in Africa.
Practices range from the use of polluted surface water/raw wastewater to the piped
distribution of secondary or tertiary treated wastewater to irrigate different kinds of crops
and trees (IWMI, 2006). Due to poor transportation systems, 70-90% of the most
perishable vegetables consumed in many African cities such as Dakar, Bamako,
8
Ouagadougou, Accra, Addis Ababa and Nairobi are also grown within the city boundary,
using highly polluted water sources, mostly of domestic origin (Drechsel et al., 2006).
There are only a few countries in Africa namely South Africa, Tunisia and Namibia with
experience in planned reuse and a record of wastewater treatment plants producing a safe
effluent for irrigation. In most of the other countries, including Ghana partially treated or
untreated urban wastewater is widely used to irrigate vegetables, rice and fodder for
livestock. Wastewater irrigation, though a major economic contributor in terms of jobs
and food supply can also be a major health risk for farmers and consumers Among the
health risks of particular concern are endemic and epidemic diseases such as cholera and
typhoid (WHO, 2006).
Wastewater irrigation also raises issues related to environmental protection as its nutrient,
salt and contaminant levels can be high. However, farmers do not have a choice to use
“wastewater” or not, as it is often difficult to find clean water sources in and around most
cities. Wastewater has many advantages for farmers as it contains significant amounts of
nutrients for food crop production that reduce the need for chemical fertilizers. Organic
matter, nitrogen, phosphorus, and potassium in wastewater may improve soil fertility,
enhance plant development and increase agricultural productivity. More importantly,
however, it is a reliable water supply, usually ‘free-of-charge’, and readily available.
Wastewater reuse supports the livelihood of many farmers and traders and plays a
significant role in poverty alleviation. It also provides a niche for urban food supply
complementing rural production (Drechsel et al., 2007).
9
Other wastewater reuse options are landscape irrigation, industrial recycling and reuse,
recreational/environmental uses, groundwater recharge, habitat wetlands, non-potable
miscellaneous uses and augmentation of potable supplies (Hagare and Dharmappa, 1999).
The reuse of wastewater for the above mentioned purposes can help to conserve water.
Characteristics of wastewater
Physico-chemical characteristics
The composition of wastewater varies widely depending on the type of activity producing
the wastewater.
The physico-chemical characteristics of wastewater that are of special concern are pH,
dissolved oxygen (DO), oxygen demand (chemical and biological), solids (suspended and
dissolved), nitrogen (nitrite, nitrate and ammonia), phosphate, and metals (Larsdotter,
2006).
The hydrogen-ion concentration is an important quality parameter of both natural and
waste waters. It is used to describe the acid or base properties of wastewater. A pH less
than 7 in wastewater effluent is an indication of septic conditions while values less than 5
and greater than 10 indicate the presence of industrial wastes. An indication of extreme
pH is known to damage biological processes in biological treatment units (Gray, 2002).
Another parameter that has significant effect on the characteristics of water is dissolved
oxygen. It is required for the respiration of aerobic microorganisms. The actual quantity
of oxygen that can be present in solution is determined by the solubility, temperature,
10
partial pressure of the atmosphere and the concentration of impurities such as salinity and
suspended solids in the water (Metcalf and Eddy, 2003).
Oxygen demand, which may be in the form of Biochemical Oxygen Demand (BOD) or
Chemical Oxygen Demand (COD), is the amount of oxygen used by microorganisms as
they feed upon the organic solids in wastewater (FAO, 2007). The five day BOD (BOD5)
is the most widely used organic pollution parameter applied to wastewater. The presence
of sufficient oxygen promotes the aerobic biological decomposition of an organic waste
(Metcalf and Eddy, 2003). Although BOD test is widely used, it has a number of
limitations, which include the requirement of a high concentration of active acclimated
microorganisms and the need for treatment when dealing with toxic wastes, thus reducing
the effects of nitrifying organisms. The BOD measures only the biodegradable organics
and requires a relatively long time to obtain test results (Gray, 2002; Metcalf and Eddy,
2003) but the COD test measures the oxygen equivalent of the organic material in
wastewater that can be oxidized chemically. The ratio of COD to BOD provides a useful
guide to the proportion of organic material present in wastewaters, although some
polysaccharides, such as cellulose, can only be degraded anaerobically and so will not be
included in the BOD estimation (Metcalf and Eddy, 2003).
The amount of solids in drinking water systems has significant effects on the total solids
concentration in the raw sewage. In spite of this wastewater is normally 99.9 % water, 0.1
% of it is comprised of solids. Although there are different ways of classifying solids in
wastewater, the most common types are total dissolved solids (TDS), total suspended
solids (TSS), settleable, floatable and colloidal solids, and organic and inorganic solids.
11
Heavy metals are one of the most persistent pollutants in wastewater. Heavy and trace
metals are also of importance in water. The metals of importance in wastewater treatment
are As, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Mo, Ni, K, Se, Na, V and Zn. Living
organisms require varying amounts of some of these metals (Ca, Co, Cr, Cu, Fe, K, Mg,
Mn, Na, Ni and Zn) as nutrients (macro or micro) for proper growth. Other metals (Ag,
Al, Cd, Au, Pb and Hg) have no biological role and hence are non-essential (Hussein et
al., 2005). Heavy metals in wastewater is due to discharges from residential dwellings,
groundwater infiltration, and industrial discharges. The accumulation of these metals in
wastewater depends on many local factors, such as the type of industries in the region,
way of life and awareness of the impact on the environment through the careless disposal
of wastes (Hussein et al., 2005; Silvia et al., 2006). The danger of heavy and trace metal
pollutants in water lies in two aspects of their impact. Firstly, heavy metals have the
ability to persist in natural ecosystems for an extended period, and, secondly, they have
the ability to accumulate in successive levels of the biological food chain. Although
heavy metals are naturally present in small quantities in all aquatic environments, it is
almost exclusively through human activities that these levels are increased to toxic levels
(Nelson and Campbell, 1991). The methods for determining the concentrations of these
metals vary in complexity according to the interfering substances that may be present.
Typical methods of determining their concentrations include flame atomic absorption,
atomic absorption spectrophotometry (AAS), inductively coupled plasma (ICP), and
inductively coupled plasma (ICP)/ mass spectrometry (APHA, 2001).
Surface waters contain levels of phosphorus in various compounds, which are essential
constituents of living organisms. In natural conditions, the phosphorus concentration in
12
waters is balanced. However, when phosphorus input to waters is higher than that which
a population of living organisms can assimilate, the problem of excess phosphorus
content occurs (Rybicki, 1997). An excess content of phosphorus in receiving waters
usually leads to extensive algal growth (eutrophication). Controlling phosphorus
discharge from municipal and industrial wastewater treatment plants is a key factor in
preventing eutrophication of surface waters (Department of Natural Science, 2006). The
following groups of phosphorus compounds are of great importance in wastewater:
organic phosphates, condensed phosphates and inorganic phosphates. Although
phosphate itself does not have notable adverse health effects, phosphate levels greater
than 10 mg/L may interfere with coagulation in water treatment plants (McCasland et al.,
2008).
Nitrogen is important in wastewater management. It can have adverse effects on the
environment, since its discharge above the required limit of 10 mg/L can be undesirable
due to its ecological and health impacts (Kurosu, 2001; Amir et al., 2004). Nitrogen is
required by all organisms for the basic processes of life to make proteins, grow and
reproduce. It is recycled continually by plants and animals. Most organisms cannot use
nitrogen in the gaseous form (N) for their nutrition, so they are dependent on other
organisms to convert it into other forms (Jenkins et al., 2003). Ammonia, nitrate and
nitrite make up the inorganic forms of nitrogen (Hurse and Connor, 1999). Organic and
inorganic forms of nitrogen may cause eutrophication problems in nitrogen-limited
freshwater lakes and in estuarine and coastal waters. In the environment, ammonia is
oxidized to nitrate, creating an oxygen demand and low dissolved oxygen in surface
waters (Kurosu, 2001). Despite the fact that nitrate levels that affect infants do not pose a
13
direct threat to older children and adults, they indicate the presence of other serious
residential or agricultural contaminants, such as bacteria and pesticides (McCasland et
al., 2008). Methemoglobinemia is the most significant health problem associated with
nitrate in water. Usually, blood contains an iron-based compound (hemoglobin) that
carries oxygen, but when nitrite is present, hemoglobin can be converted to
methemoglobin, which cannot carry oxygen. Similarly, nitrogen in the form of ammonia
is toxic to fish and exerts an oxygen demand on receiving water by nitrifiers (CDC,
2002).
Microbiological characteristics
The major microorganisms found in wastewater are viruses, bacteria, fungi, protozoa and
helminthes. Although various microorganisms in water are considered to be critical
factors in contributing to numerous waterborne outbreaks, they play many beneficial
roles in wastewater influents (Kris, 2007). Traditionally, microorganisms are used in the
secondary treatment of wastewater to remove dissolved organic matter (Akpor and
Muchie, 2011). Apart from solid matter reduction, wastewater microbes are also
involved in nutrient recycling, such as phosphate, nitrogen and heavy metals. If nutrients
that are trapped in dead materials are not broken down by microbes, they will never
become available to help sustain the life of other organisms in the breakdown process.
Microorganisms are also responsible for the detoxification of acid mine drainage and
other toxins in wastewater (Ward-Paige et al., 2005). Microbial pollutants can also serve
as indicators of water quality.
The detection, isolation and identification of the different types of microbial pollutants in
wastewater are always difficult, expensive and time consuming. To avoid this, indicator
14
organisms are always used to determine the relative risk of the possible presence of a
particular pathogen in wastewater (Paillard et al., 2005). For instance, enteric bacteria,
such as coliforms, Escherichia coli, and faecal streptococci are used as indicators of
faecal contamination in water sources (Momba and Mfenyana, 2005).
Wastewater treatment
Wastewater treatment is an expensive process thus many of the underdeveloped and
developing nations of Africa and Asia have not been able to treat their wastewater to
appropriate levels and continue to use it in agriculture with deleterious long-term effects
on soil, groundwater and human health. However, many of the water scarce cities in
Europe, North America and Australia are able to treat their wastewater to appropriate
levels and recycle it in industries, residential areas, urban gardens and sports lawns.
While the lack of wastewater treatment to appropriate levels before use is a major
problem in developing countries, the high cost of wastewater recycling is the major
problem in developed countries (Mekala et. al., 2008)
The growing concern over the impact of sewage contamination on water bodies and the
increasing scarcity of water in the world along with rapid population increase in urban
areas give reasons to consider appropriate technologies for the post treatment of
anaerobic effluent in order to achieve the desired effluent quality and save receiving
water bodies.
Slow sand filtration (SSF)
The use of slow sand filtration (SSF) to improve the quality of water dates back to
hundreds of years (Bourdon et. al., 2012) and is a sustainable approach to purifying
15
water. It is a desirable technology in developing countries where water purification
capabilities are poor and in developed countries with technically advanced water
treatment plants. The use of SSF requires minimal use of chemicals, low electricity
requirements and marginal operation and startup costs.
Slow Sand Filtration operates by allowing untreated water to slowly percolate through a
bed of porous sand, with the influent water source introduced over the top surface of the
filter area, and effluent collected and drained from the bottom. The ability of SSF
method to purify water is the result of several mechanisms that occur during filtration. It
requires a continuous filtration of raw water through the sand bed. As the raw water
filters through the sand grains, particles in the raw water are removed by transport and
attachment processes such as adsorption and ion exchange. The most basic transport
mechanism that occurs in SSF is the straining of particles out of the water by the sand
grains. Straining occurs when the particles in the water larger than the voids in the sand
grains become trapped and lodged in the sand bed. As more and more particles become
lodged in the sand bed, the pore size between the sand gains and the particles decrease,
allowing for a larger percentage of particles in the water to be removed. The majority of
this screening process occurs at the surface of the filter. Sedimentation of the particles
onto the sand grains is another transport mechanism. The settling action occurs as
gravity forces the particles to move downward onto the top surfaces of the sand grains.
Since the flow rate through SSF is gradual, the particles will remain settled on top of the
sand grains and removed from the effluent of the SSF system.
The sedimentation removal of the particles is enhanced by attachment processes. Once
the particle has made contact with the sand grains, Van der Waals forces can help
16
maintain that particle on the sand grain. Another and stronger attachment mechanism is
the adhesion of particles to the “schmutzdecke” layer or “dirt cover”. The
“schmutzdecke” layer consists of the organic matter that settles on the filter surface and
becomes the breeding ground for bacteria and microorganisms. As the “schmutzdecke”
layer develops it becomes a sticky, gelatinous film and adheres a great deal of the
particles from the raw water. The layer takes several weeks to form and can consist of
bacteria, fungi, protozoa, algae, and microscopic aquatic organisms, once fully
developed. The organic matter in the raw water is trapped by the “schmutzdecke” layer
and utilized by the bacteria and microorganisms as a food source, thus reducing the
organic matter into water, carbon dioxide, and inorganic salts. The “schmutzdecke” layer
provides the primary means for eliminating organic matter in the slow sand filtered
effluent.
The transport and attachment processes in an established SSF have the ability to greatly
improve the quality of the raw water. No other single process in typical drinking water
treatment plants has the ability to improve the physical, chemical, and bacteriological
quality of the raw water as an established Slow sand filter (Bourdon et. al, 2012).
Phytoremediation
Phytoremediation is defined as the efficient use of plants to remove, detoxify or
immobilize environmental contaminants in a growth matrix (soil, water or sediments)
through the natural, biological, chemical or physical activities and processes of plants
(Peuke and Rennenberg, 2005). Phytoremediation techniques require very low costs to
carry out (Jamil et. al., 2009). The method is widely recognized and accepted as an
17
ecologically responsible alternative to the environmentally destructive chemical
remediation methods (Ahmadpour et. al., 2010). Aquatic macrophytes can effectively
reduce total nitrogen, total phosphorus and chemical oxygen demand (Sooknah and
Wilkie 2004).
The principles of phytoremediation system are to clean up contaminated water which
includes the identification and implementation of efficient aquatic plant, uptake of
dissolved nutrients and metals by growing plants and the harvest and beneficial use of the
plant biomass produced from the remediation system (Lu, 2010). The most important
factor in implementing phytoremediation is the selection of an appropriate plant (Stefani
et.al, 2011) which should have high uptake of both organic and inorganic pollutants and
grow well in polluted water. The uptake and accumulation of pollutants vary from plant
to plant and from species to species within a genus (Singh et. al., 2003). The economic
success of phytoremediation largely depends on photosynthetic activity and growth rate
of plants (Xia and Ma, 2006) and low to moderate amount of pollution (Jamuna and
Noorjahan, 2009).
Numerous aquatic plants have demonstrated considerable potential for nutrient removal
from various types of wastewaters (Sooknah and Wilkie, 2004). Some of the aquatic
plants used in the treatment of wastewater include Water hyacinth (Eichhornia
crassipes), water lettuce (Pistia stratiotes), duckweed (Lemna sp.), Bulrush (Typha sp),
Vetiver grass (Chrysopogon zizanioides) and common reed (Phragmites australis)
(Piyush et. al., 2012). In this study, Ipomoea aquatica and Pistia stratiotes were used.
18
Water lettuce (Pistia stratiotes L)
Pistia stratiotes L is a floating perennial commonly called water lettuce belonging to the
family Araceae. It floats on the surface of water and its roots hang submerged beneath
floating leaves (Dipu et. al., 2011). The leaves can be up to 14 cm long and have no stem.
They are light green with parallel veins, wavy margins and are covered in short hairs
which form basket-like structures and help in trapping air bubbles, increasing the
buoyancy of the plants. The flowers are dioecious and are hidden in the middle of the
plant among the leaves. The plant can reproduce both sexually and vegetatively (Dipu et.
al., 2011).
Water lettuce has a minimum growth at temperature 15°C (Kasselmann, 1995). Fonkou
et.al., (2002) stated that the water lettuce doubles its biomass in just over five days,
triples it in ten days, quadruples it in twenty days and has its original biomass multiplied
by a factor of nine in less than one month. This indicates that the maximum period to
allow the plant in the system is twenty five days (Piyush et. al., 2012).
In the tropics, water lettuce is used in phytoremediation systems because compared to
native plants; it shows higher nutrient removal efficiency with increased nutrient uptake
capacity, fast growth rate and big biomass production (Reddy and Sutton, 1984).
Water spinach (Ipomoea aquatica Forsk)
Ipomoea aquatica is a semi-aquatic tropical plant grown as a leaf vegetable belonging to
the family Convolvulaceae. It is a very good source of nutrients (Visitacion et. al., 2011)
and acts as a good metal and toxin accumulator (Teerakun and Reungsang, 2005).
19
Public perception and acceptance of wastewater reuse
A successful implementation of a wastewater reuse project is dependent not only on its
economic and environmental feasibility but mainly on the support and acceptability of the
general public that ultimately patronize and might be affected by the reuse project. Reuse
schemes may face public opposition resulting from a combination of prejudiced beliefs,
fear, attitudes, lack of knowledge and general distrust often resulting from the frequent
failures of wastewater treatment facilities worldwide (Jeffrey and Temple, 1999).
Results from several surveys on public attitudes toward wastewater reuse options have
been published, the data collected mainly in the United States of America, Western
Europe and Australia. Results of these surveys indicate that, a large majority of the public
support water reuse as a concept and public support for reuse decreases as the degree of
contact with the reclaimed water increases. Crook (2003) reported that in the US the
public generally supports non-potable reuse while acceptance of potable reuse is
problematic, with typically less than 50% support. . Much less information is available
regarding the attitude toward the issue in other regions and under different environmental
and climatic conditions (Friedler et. al., 2006)
The primary concerns of the public are costs and public health protection, thus uses that
result in financial gains and involve minimal degree of contact with the reclaimed water
are favoured (Friedler et. al., 2006).
20
Objectives
The main objective of this study was to assess performance efficiency of slow sand
filtration and phytoremediation for effective secondary treatment of sewage effluent from
a biogas plant
The specific objectives were to:
1. characterize the sewage effluent after anaerobic digestion of sewage in the
Biogas facility of Valley View University (VVU)
2. conduct phytoremediation using two macrophyte species namely Pistia statiotes
and Ipomoea aquatica to identify the better macrophyte for the uptake of specific
pollutants
3. conduct slow sand filtration of the raw effluent using river bed sand
4. compare the experimental slow sand filter to the filtration system of the biogas
facility
5. evaluate and compare the performance of slow sand filtration and
phytoremediation technologies in treating sewage effluent
6. assess the safety of the treated effluent for disposal and/or reuse
7. assess public perception of wastewater reuse
21
CHAPTER TWO
MATERIALS AND METHODS
2.1 Study site
The study site was the Valley View University (VVU) located at Oyibi in the greater
Accra Region of Ghana.
Fig 1: Location map of study area
22
2.2 Materials
(i) Raw sewage effluent
The raw sewage effluent was obtained from the Biogas facility of the
Valley View University (VVU)
(ii) Sand and gravels for Slow Sand Filtration (SSF)
The river sand and gravels for the SSF experiment were obtained from the
Volta River at Asutuare
(iii) Aquatic macrophytes for phytoremediation were obtained from the Kpong
Head Pond
Plate 1: Kpong Head Pond showing aquatic plants
23
2.3 Sewage treatment at VVU
The method of sewage treatment at VVU is anaerobic digestion. In this system, there is a
digestor (Plate 2) where anaerobic bacteria degrade organic materials (in the absence of
oxygen) and produce methane and carbon dioxide. The methane is stored and used in the
school’s kitchen (for cooking). The effluent from the digestor is transported to an
intermediary chamber (Plate 2). From this chamber, the effluent passes into a filtration
system made of activated charcoal and then discharged into a mango plantation (Plate
3.1d)
2.4 Selection of sampling sites
The sewage effluent was obtained from the Biogas facility of the Valley View University.
Samples were taken from two points for analyses; the intermediary chamber and the final
outlet (Plate 2). Effluent samples for sand filtration and phytoremediation were collected
from the intermediary chamber (Plate 3.1)
2.5 Sampling of aquatic macrophytes
Two aquatic macrophytes namely Pistia stratiotes L and Ipomoea aquatica Forsk were
selected and identified. Pistia stratiotes is a floating species whilst Ipomoea aquatica is
an emergent species. Fresh and healthy macrophytes were collected from the Kpong
Head Pond and transported along with adequate quantity of water from the source (to
prevent wilting) to the greenhouse at the Botany Department of the University of Ghana,
Legon.
24
(a) Digestor
(b)
Filtration bed Intermediary chamber
(c) Final outlet
(d) Mango plantation
Plate 2: Biogas facility of Valley View University
25
2.6 Preparation of filter media units
Sand and gravels harvested from the Volta River at Asutuare were washed thoroughly
using ordinary tap water to remove sediments, sun dried and sieved to obtain desired
fractions. Below are the different fractions of sand and gravels used for the Slow Sand
Filtration (SSF).
Plate 3: Filter media units; (a) gravels (5-10mm diameter), (b) coarse sand (2-3mm
diameter), (c) fine sand (0.4mm diameter)
a
b
c
26
2.7 Treatment of sample containers
The following measures were adhered to in avoiding possible contamination of samples
during sampling. The sampling containers with well-fitted stoppers were pre-treated by
washing with acetone to get rid of organic substances such as grease and fat residues.
They were then washed with detergent and rinsed with de-ionised water and then soaked
in 0.1 M nitric acid solution for 48 hours. The containers were finally rinsed several times
with de-ionised water before used for taking and holding water samples. Water samples
that were not analyzed immediately at the site were transported on ice to the laboratory
where they were stored in a refrigerator below 4oC. Precautions were taken as to the
number of days the samples should be stored to avoid inaccuracy.
2.8 Monitoring of effluent quality at sampling site
Characterization of sewage effluent, both for the intermediary and final outlets was
carried out twice a month over a period of four months (February 2014-May 2014).
Reject water samples from the intermediary and final out-let points of the plant were
taken for physico-chemical analyses. Parameters including temperature, pH, conductivity,
colour, turbidity, biochemical oxygen demand (BOD), chemical oxygen demand (COD),
total suspended solids (TSS), total dissolved solids (TDS), nitrate, phosphate and heavy
metals like Pb, Cd, Cu, Ni, Zn, Fe, Cr were determined. Microbiological parameters such
as total heterotrophic bacteria (THB), total coliform and faecal coliforms were also
determined.
27
2.8 Sampling of effluent for characterization
2.8.1 Sampling for physico-chemical tests and field measurements
Cleaned 500 ml plastic bottles were filled with effluent samples from the intermediary
chamber and the final outlet. This was subsequently used in the laboratory for off-site
analyses. pH, temperature, conductivity and dissolved oxygen of the effluents were
measured in-situ.
2.8.2 Biochemical Oxygen Demand (BOD) and Dissolved Oxygen (DO) Sampling
A plain bottle and one dark bottle (painted with bitumen to prevent possibility of
photosynthetic production of oxygen) were used for sampling. The plain one was used for
dissolved oxygen sampling and the dark bottles were used for BOD sampling. The bottles
were filled with the waste water to overflow in order to avoid any air bubbles from
getting trapped in the bottles. The dissolved oxygen samples were fixed on site with 2 ml
each of Winkler 1 (Manganous chloride) and Winkler 2 (alkaline-iodide-azide reagent).
Samples, which were not analyzed within 2 hours of collection, were kept at or below
4oC but brought to 20oC before analysis in the laboratory.
2.8.3 Trace Metals Sampling
Water samples for analysis of the trace metals Iron, Cadmium, Copper Nickel, Zinc, Lead
and Chromium, were collected in plastic vials and fixed on the field with nitric acid.
They were then kept at or below 4oC but brought to 20oC before analysis in the
laboratory.
28
2.8.4 Bacteriological sampling
Glass bottles of 500 ml capacity with metal caps were used to collect the effluents at the
intermediary and final outlets. The bottles were sterilized before use and the mouths
covered with aluminium foil to avoid contamination during sample collection. The
samples were stored on ice at 4ºC and transported to the laboratory for analyses.
Plate 4: Sampling effluent from intermediary chamber for characterization
2.9 Sewage effluent collection and experimental procedure
2.9.1 Sewage effluent collection
Sewage effluent for the experiment was collected from the intermediary chamber of the
VVU Biogas facility. The effluent was collected into 40 L plastic gallons and transported
to the greenhouse at the Botany Department of the University of Ghana.
29
2.9.2 Slow Sand filtration (SSF)
2.9.2.1 Preparation of filter media
Three plastic buckets each of 100 cm height and 100 L capacity were prepared, each with
a tap fitted at the bottom to allow filtered effluent to be drained out. Two of the buckets
were used to filter the raw sewage effluent and the third was used as a control. Each
bucket was filled with gravel of 5-10 cm diameter at the bottom, coarse river sand of 2-3
mm diameter as mid layer each of 10 cm depth and fine river sand of 0.4 mm diameter at
40 cm depth. A diffusion plate was placed 10 cm above the fine sand to allow even
distribution of the raw sewage effluent on the surface of the fine sand.
Plate 5: Slow Sand Filtration experimental set up at the greenhouse
30
Fig 2: Cross-section of slow sand filter media for Slow Sand Filtration of effluent
10cm
10cm
m
40cm
Diffusion plate
Fine sand (0.4mm)
Coarse sand (2 – 3mm)
Gravels (2 – 5mm)
31
2.9.2.2 Procedure for slow sand filtration of raw effluent
Effluent was carefully poured from a bucket and allowed to percolate through the filter
media. A water column of about 10 cm height was maintained above the sand to provide
the needed pressure force to move the water through the sand bed system. The procedure
was repeated for the control using distilled water. The rate of filtration through the filter
media was determined weekly by measuring the volume of effluent per minute. Filtration
was done once every week for ten weeks.
Effluent samples and water for the control were analyzed for their various physico-
chemical and microbiological characteristics before sand filtration and filtered effluents
were also analyzed on a weekly basis for ten weeks using standard methods
2.10 Phytoremediation
2.10.1 Layout of the experiment
The design of the experiment was a completely randomized. Two different macrophytes,
namely Ipomoea aquatica and Pistia stratiotes were used. These plants were selected
because they are readily available.There were two replicates each and one control unit
using distilled water.
Trial experiments were conducted to ascertain the performance of the plants in the
sewage effluent. Two bowls of 40 L capacities were each filled with sewage effluent and
the ten each of the plants, previously rinsed with tap water were planted in the bowls. In
each bowl, twenty each of the individual plants were planted. Plant growth was observed.
32
For the actual experimental set up, Pistia stratiotes and Ipomoea aquatica plants
collected from the Kpong Head Pond were rinsed and transferred into a large bowl
containing tap water. Samples of the whole plants were oven dried at 105°C for 10 hours,
ground into powder, digested and analyzed for the nutrient content.
For each of the plants, two plastic bowls were each filled with sewage effluent to a height
of 16 cm and kept outside in the open air. A third bowl was filled with distilled water to
serve as a control.
Each plant was then put in the bowls and one week was allowed for the plants to
acclimatize to their new environment. It was observed during the first week that the Pistia
stratiotes showed signs of wilting after the fifth day. Therefore, water samples from
effluent treated with Ipomoea aquatica and Pistia stratiotes were taken after the fifth day
for analyses. Starting from the second week, samples of water from effluent treated with
Ipomoea aquatica were collected on a weekly basis for four weeks and analyzed for the
physico-chemical and microbiological characteristics. At the end of the experimental
period (five days for Pistia stratiotes and four weeks for Ipomoea aquatica), samples of
the whole plant were taken from each bowl, oven dried, ground into powder, digested and
analyzed to determine the nutrient and heavy metal content.
Dilutions of the effluent (50% and 75%) were also prepared for planting Pistia stratiotes.
This was done to determine whether Pistia stratiotes would survive for more than five
days in the diluted effluent.
The experiment was conducted in open air under natural daylight regime.
33
A B C
Plate 6: Pistia stratiotes in different dilutions of effluent
A- Pistia stratiotes in 50% dilution of effluent, B- Pistia stratiotes in 75% dilution of
effluent, C- Pistia stratiotes in distilled water (control)
Plate 7: Ipomoea aquatica planted in sewage effluent
34
2.11 Laboratory analyses
Physico-chemical analyses were carried out at the Ecological Laboratory of the
University of Ghana. Bacteriological analyses for Total coliforms, Total Heterotrophic
Bacteria (THB) and faecal coliforms were undertaken at the Microbiological Laboratory
at the Soil Science Department of the University of Ghana. The physico-chemical
parameters determined included pH , temperature, conductivity, turbidity, dissolved
oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD),
total suspended solids (TSS), total dissolved solids (TDS), colour, phosphate and nitrate.
2.11.1 Physico-chemical analyses of raw and treated effluents
The physico-chemical parameters were determined according to procedures outlined in
the Standard Methods for the Examination of Water and Wastewater. At the sampling
site, the effluent was collected into a plastic bucket for in-situ measurements.
Temperature, pH and conductivity were measured using a digital meter (Model YSI 63),
turbidity was measured using turbidimeter (Model HACH 2100P) NTU and Total
Dissolved Solids (TDS) was measured with a portable digital TDS meter (Model HI
99301).
2.11.2 Total Suspended Solids Analysis
The photometric (non-filterable residue) method was used. Five hundred millilitres of
sample was blended at high speed for two minutes. This was poured into a 600 ml beaker.
The sample was stirred and 25 ml immediately poured into a sample cell. The stored
programme number for suspended solids, 630, was set to a wavelength of 810 nm. A
35
sample cell filled with 25 ml distilled water served as blank. This was placed into the cell
holder and standardized. The sample was placed into the cell holder and the reading taken
in mg/l suspended solids.
2.11.3 Heavy Metal Analysis
The Atomic Absorption Spectrometry (AAS) method for heavy metals was used to
determine the level of each heavy metal in the sample. The heavy metals whose
concentrations were determined included: Cadmium (Cd), Copper (Cu), Nickel (Ni), Zinc
(Zn), Lead (Pb), Iron (Fe) and Chromium (Cr).
In flame atomic absorption spectrometry, a sample is aspirated into a flame and atomized.
A light beam is directed through the flame, into a monochromator, and onto a detector
that measures the amount of light absorbed by the atomized element in the flame.
For some metals, atomic absorption exhibits superior sensitivity over flame emission.
Because each metal has its own characteristic absorption wavelength, a source lamp
composed of that element is used; this makes the method relatively free from spectral or
radiation interferences.
The amount of energy at the characteristic wavelength absorbed in the flame is
proportional to the concentration of ion in the sample over a limited concentration range.
36
2.11.4 Dissolved Oxygen (DO)
The azide modification of the Winkler method was used for this test. Two milliliter conc.
H2SO4 was added to the samples which had already been fixed on the field with 2 ml
each of Winkler 1 (Manganous chloride) and Winkler 2 (alkaline-iodide-azide reagent).
One hundred milliliters of the sample was titrated with 0.025 M Na2S2O3 to a pale straw
colour. Two milliliters of starch solution was added and titration was continued to first
disappearance of blue colour.
Calculation:
For titration of a 100 ml sample, mg/l mg/l O2 = Vol. of M/80 thiosulphate used x 101.6
Vol. of sample used
2.11.5 Biological Oxygen Demand (BOD)
The 5-day BOD test was used. Biochemical Oxygen Demand, or BOD, measures the
amount of oxygen consumed by microorganisms in decomposing organic matter in
stream water. BOD also measures the chemical oxidation of inorganic matter (i.e. the
extraction of oxygen from water via chemical reaction). A test is used to measure the
amount of oxygen consumed by these organisms during a specific period of time (usually
5 days at 20oC).This method consists of filling with sample an airtight bottle of the
specific size and incubating it at the specific temperature for 5 days. Dissolved oxygen
was measured initially and after incubation, and the BOD was computed from the
difference between the initial and the final DO. In cases of dilution due to less amount of
oxygen, BOD was computed from the formula below:
37
Calculation: BOD5 mg/l = D1 – D2
P
Where;
D1 = DO of diluted sample immediately after preparation, mg/l
D2 = DO of diluted sample after 5 day incubation at 20 0C, mg/l
P = Decimal Volumetric fraction of sample used.
2.11.6 Nitrogen-Nitrate (NO3- -N) Analysis
The Cadmium Reduction Method using Powder Pillows was used for the determination
of nitrogen nitrate. The nitrate level in each sample was measured using Nitrate Powder
Pillows in a direct reading Hach Spectrophotometer (Model DR 2000). Twenty five (25)
ml of the sample was measured into sample cell of the spectrophotometer. One Nitraver 5
Nitrate Reagent Powder Pillow was added to the sample. The mixture was then shaken
vigorously for 1 minute. Five minutes was allowed for the solution to react. An orange
colour of the mixture indicates the presence of nitrate. After five minutes, another cell
was filled with 25 ml of only the sample (blank). The blank sample was placed in the
Spectrophotometer for calibration. The prepared sample was placed into the cell holder to
determine the nitrate concentration at 500 nm in mg/l .
2.11.7 Phosphate (PO43-) Analysis
A 25 ml of the prepared water sample was placed in the sample cell. PhosVer 3
Phosphate Powder Pillow was added to the cell content and swirled immediately to mix.
38
A two-minute reaction period was allowed. A blue colouration of the mixture indicates
the presence of phosphate. Another sample cell (the blank) was filled with 25 ml of
sample and placed into the cell holder to calibrate it. After reaction period, the prepared
sample was placed into the cell holder and the level of phosphorus was determined at 890
nm.
2.11.8 Chemical Oxygen Demand (COD)
A sample of sewage effluent (50 ml) was pipetted into a 500 ml refluxing flask. One
gram of mercuric sulphate was added to the sample and several glass beads were added to
the solution. Very slowly, 5 ml of sulphuric acid reagent was added and the flask was
swirled while adding the reagent to help dissolve the mercuric sulphate. Twenty five
millilitres of 0.250 N potassium dichromate solution was added and mixed. Distilled
water was used as the blank.The sample flask and blank flask were refluxed after which
the sample and blank were titrated with ferrous ammonium sulphate using ferroin
indicator. The COD was calculated using the following formula:
COD mg/l = (A-B) ×M×8,000
Volumeof sample, ml
Where:
A=ml of titrant used for sample
B= ml of titrant used for blank
M=normality of ferrous ammonium sulphate
39
2.11.10 Analyses of Bacteriological Parameters of raw and treated effluents
Bacteriological analyses involved the determination of total Heterotrophic Bacteria
(THB), Total Coliforms and Faecal Coliforms by the membrane filtration method. These
parameters were determined only for the raw effluent and for the effluents at the end of
the experiment.
2.11.10.1 Preparation of bacteriological media for bacteriological analyses of raw
and treated effluents
Preparation of Hicrome coliform agar
Hicrome coliform agar was used. It is a selected medium recommended for the
simultaneous detection of faecal coliforms and total coliforms in water and food samples.
Twenty eight grams (28 g) of the powder was weighed and dissolved in 1 litre of
deionized water. It was swirled to mix, sterilized by autoclaving for 15 min at 121ºC,
cooled to 47ºC and poured into petri dishes.
Preparation of nutrient agar
Twenty eight grams of the dehydrated nutrient agar powder was weighed and dispensed
in 1 litre of deionized water. The solution was allowed to soak for 10 min and sterilized
by autoclaving for 15 min at 121ºC. It was allowed to cool to 47ºC and stored in the
refrigerator.
40
Membrane Filtration Method
The filter holding assembly constructed of stainless steel and consisted of a seamless
funnel fastened to a base by a locking device. The design permitted the membrane filter
to be held securely on the porous plate of the receptacle without mechanical damage and
allowed all fluid to pass through the membrane during the filtration process. Firstly, the
receptacle was sterilized with 96% alcohol, flamed and allowed to cool. A membrane
filter of pore size 0.45 µm was gently placed on it and a filter funnel fitted unto it.
Twenty millilitres (20 ml) of the effluent samples were diluted with distilled water,
poured unto the funnel and extracted through a side tube, such that pressure could be
exerted on the membrane filter. The filter was picked gently using sterilized forceps and
placed in a petri dish containing sterilized Hicrome Coliform agar for the enumeration of
total coliforms and faecal coliforms. Another filter was placed on nutrient agar for the
enumeration of total heterotrophic bacteria. After incubation on Hicrome Coliform Agar
for 24 hours at 35ºC to 37ºC, faecal coliforms appeared dark violet. Other colonies were
counted for total heterotrophic bacteria.
The Total and Faecal coliform present in water samples were determined using the
Membrane Filter (MF) technique. Membrane filter with 0.45 µm pore size was sterilized
in a system and used to filter 100 ml of water mixed with 10 ml of the sampled water.
The results obtained from the colony counting were then multiplied by 10 to obtain the
actual count per 100 ml for faecal and total coliforms
M-Lauryl sulphate broth (LSB) was used as growth medium for the incubation of
coliforms in a petri dish. Two milliliters of the broth was poured on an absorptive pad
placed in a small Petri dish. The petri dish was then covered and inverted into ELE
41
paqualab incubator (model 50) for incubation at 37oC for total coliform and 44oC for
faecal coliform. After 24 hours, the Petri dishes were removed from the incubator and the
colonies counted and recorded in coliform forming units per 100 ml (cfu/100 ml)
2.12 Social survey
Questionnaire Administration
Questionnaires were administered to 120 randomly selected respondents. One hundred
and twenty respondents from among students and staff of the Valley View University
were selected due to the limited time for the study. During the time of the study, the
University was on vacation so there were few people on the University campus and this
accounted for the few number of respondents. One hundred and two questionnaires were
returned and the data was coded and analysed using SPSS version 20.
2.13 Statistical analyses
All data generated were double entered and cross checked for anomalies. The data was
transferred into SPSS version 20. Comparison of phytoremediation and Slow Sand
Filtration technologies was done using one-way ANOVA. The mean and percentage
increase/ reduction were calculated for each parameter using Microsoft Excel. The
questionnaires were analyzed using Statistical Package for Social Science (SPSS) version
20.
42
CHAPTER THREE
3.0 RESULTS
The results of the study are shown below
3.1 Quality of sewage effluent from VVU biogas facility
Table 1: Quality of sewage effluent from intermediary chamber (A) and final outlet
(B) of the Valley View University (VVU) Biogas facility.
Parameters analysed A B
p H 3.9-4.14 6.47-7.48
Temperature (°C) 29.2-32.4 25.2-30.3
Electrical conductivity (µs/cm) 5017-5420 3216-3603
Total dissolved solids (mg/l) 2508.5-2710 1608-1801.5
Total suspended solids (mg/l) 322-368 56-75
Colour (PtCo) 699-792 487-543
Phosphates (mg/l) 4.3-6.4 0.44-5.6
Nitrates (mg/l) 1.7-4.2 1.8-9.7
Dissolved oxygen (mg/l) 0.11-0.6 2.98-5.4
Biochemical Oxygen Demand (mg/l) 29-40 17-35
Chemical Oxygen Demand (mg/l) 224-368 64-132
Turbidity (NTU) 121-201 42-53
Zinc ND ND
Lead ND ND
Copper 0.11 0.11
Iron 0.413 0.231
Cadmium ND ND
Nickel ND ND
Chromium ND ND
Total heterotrophic bacteria (CFU/ml) 1210 1124
Total coliforms (CFU/100ml) 348 322
Faecal coliforms(CFU/100ml) 162 101
*ND: Non Detectable; A- raw effluent from intermediary chamber; B- effluent from final
outlet
The table 1 above presents detailed results of the quality of effluent from the intermediary
chamber (A) and final outlet (B) of the Valley View University Biogas facility
43
3.2 Phytoremediation using Pistia stratiotes and Ipomoea aquatica
Plant growth in raw sewage effluent
(A) (B) (C)
Plate 8: Condition of Pistia stratiotes days after planting in sewage effluent
A above represents fresh and healthy Pistia stratiotes planted in the raw sewage effluent
on the first day. Three days after planting, the plants had started wilting as shown in B
and after the fifth day all the plants had wilted (C).
A B C D
Plate 9: Condition of Ipomoea aquatica days after planting in sewage effluent
44
A above shows Ipomoea aquatica plants on the first day of planting in the raw sewage
effluent. By the third day (B), new shoots had started coming out. C and D show the
growth of the plants on the fifth and fourteen days respectively.
A B
Plate 10: Sewage effluent before (A) and after treatment (B) with Pistia stratiotes
A above is the raw sewage effluent before phytoremediation. It can be seen that some
level of treatment occurred after phytoremediation with Pistia stratiotes. The treated
effluent (B) looks clearer and less turbid than the raw effluent (A).
45
b a
Plate 11: Sewage effluent before (a) and after treatment (b) with Ipomoea aquatica
Comparing the effluent before and after treatment with Ipomoea aquatica, it can be seen
that, some purification has taken place. The treated effluent looks clearer than the raw
effluent.
46
3.3 Nitrogen and phosphorus uptake by plants
Table 2: Phosphorus and nitrogen accumulation in Ipomoea aquatica and Pistia
stratiotes at the end of experiment
Total nitrogen (%) Total phosphorus (%)
P.S I.A P.S I.A
Before the experiment 2.996 2.604 0.92 0.77
After the experiment 3.332 3.892 1.17 1.19
Percentage increase (%) 10.08 33.09 21.37 35.29
*P.S – Pistia stratiotes I.A – Ipomoea aquatica
The table above show the nitrogen and phosphorus content of Ipomoea aquatica and
Pistia stratiotes before and after the phytoremediation experiment. The results show that
both plants took up nitrogen and phosphorus. Ipomoea aquatica took up more nitrogen
and phosphorus than Pistia stratiotes.
47
3.4 Contaminant removal efficiency of Ipomoea aquatica and Pistia stratiotes
0
2
4
6
8
10
12
14
16
18
Pistia stratiotes Ipomoea aquatica
Ph
osp
hat
e R
em
ova
l e
ffic
ien
cy (
%)
Aquatic macrophyte
Fig 3: Phosphate removal efficiency of Ipomoea aquatica and Pistia stratiotes
0
20
40
60
80
100
120
Pistia stratiotes Ipomoea aquatica
Nit
rate
re
mo
val
eff
icie
ncy
(%
)
Aquatic macrophyte
Fig 4: Nitrate removal efficiency of Ipomoea aquatica and Pistia stratiotes
48
0
10
20
30
40
50
60
Pistia stratiotes Ipomoea aquatica
CO
D r
em
ova
l e
ffic
ien
cy (
%)
Aquatic macrophyte
Fig 5: COD removal efficiency of Ipomoea aquatica and Pistia stratiotes
0
10
20
30
40
50
60
Pistia stratiotes Ipomoea aquatica
EC r
em
ova
l eff
icie
ncy
(%
)
Aquatic macrophyte
Fig 6: EC removal efficiency of Ipomoea aquatica and Pistia stratiotes
49
The figures 3,4,5, and 6 show that both plants were effective at reducing contaminant
levels. However, Ipomoea aquatica reduced phosphate (16.07%), nitrates (100%) and
COD (47.8%) to lower levels whilst Pistia stratiotes reduced electrical conductivity (EC)
to lower levels (55.45%) (Fig 6) than did Ipomoea aquatica.
3.5 Weekly variations in water quality parameters after treatment with Ipomoea
aquatica
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
1 2 3 4 5
DO
(m
g/l)
Duration of experiment (week)
Fig 7: Concentration of dissolved oxygen (DO) in effluent after every week of
treatment with Ipomoea aquatica
50
0
5
10
15
20
25
30
35
40
1 2 3 4 5
BO
D (
mg/
l)
Duration of study (week)
Fig 8: Biochemical Oxygen Demand (BOD) of effluent after every week of treatment
with Ipomoea aquatica
0
50
100
150
200
250
300
350
400
1 2 3 4 5
CO
D(m
g/l)
Duration of experiment (week)
Fig 9: Chemical Oxygen Demand (COD) of effluent after every week of treatment
with Ipomoeaaquatica
51
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5
EC (
µs/
Cm
)
Duration of experiment (week)
Fig 10: Electrical conductivity (EC) of effluent after every week of treatment with
Ipomoea aquatica
0
500
1000
1500
2000
2500
3000
1 2 3 4 5
TDS
(mg/
l)
Duration of experiment (week)
Fig 11: Total Dissolved Solids (TDS) of effluent after every week of treatment with Ipomoea
aquatica
52
0
2
4
6
8
10
1 2 3 4 5
PO
4 (
mg/
l)
Duration of experiment (week)
Fig 12: Concentration of phosphates in effluent after every week of treatment with
Ipomoea aquatica
0
5
10
15
20
25
30
35
40
1 2 3 4 5
NO
3 (
mg/
l)
Duration of experiment (week)
Fig 13: Concentration of nitrates in effluent after every week of treatment with
Ipomoea aquatica
53
3.6 Performance of Slow Sand Filtration
Fig 14 below shows a decreasing rate of filtration of the raw effluent through the
experimental sand filter. Figures 15, 16, 17, 18, 22 and 23 show a decreasing trend in
turbidity, electrical conductivity (EC), total dissolved solids (TDS), total suspended
solids (TSS), Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand
(COD) respectively. The concentration of nitrates (Fig 19) decreased after first week and
increased from the second to fifth week after which it decreased till the tenth week.
Phosphate concentration (Fig 20) decreased from start of the experiment to the fourth
week after which it increased from the fifth to sixth week and decreased again from the
seventh to tenth week. Fig 21 shows an increase in dissolved oxygen (DO) after the first
week. It decreased after the second to the seventh week and then increased again to the
end of the experiment.
0
100
200
300
400
500
600
700
800
1 2 3 4 5 6 7 8 9 10 11
Filt
rati
on
rat
e (
ml/
min
)
Time (week)
Fig 14: Rate of filtration through experimental sand filter
54
0
20
40
60
80
100
120
140
160
180
1 2 3 4 5 6 7 8 9 10 11
TUR
BID
ITY
(N
TU)
Time (week)
Fig 15: Weekly variations in turbidity of effluent treated using SSF method
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5 6 7 8 9 10 11
EC (
µs/
CM
)
Time (week)
Fig 16: Weekly variations in electrical conductivity (EC) of effluent treated using
SSF
55
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7 8 9 10 11
TDS
(mg/
l)
Time (week)
Fig 17: Weekly variations in concentration of total dissolved solids (TDS) in effluent
treated using SSF
0
2
4
6
8
10
12
1 2 3 4 5 6 7 8 9 10 11
nit
rate
s (m
g/l)
Time (week)
Fig 18: Weekly variations in concentration of Total Suspended Solids (TSS) in effluent
treated using SSF
56
0
1
2
3
4
5
6
1 2 3 4 5 6 7 8 9 10 11
Ph
osp
hat
es (
mg/
l)
Time (week)
Fig 19: Weekly variations in concentration of nitrates in effluent treated using SSF
Fig 20: Weekly variations in concentration of phosphates in effluent treated using
SSF
0
50
100
150
200
250
1 2 3 4 5 6 7 8 9 10 11
TSS
(mg/
l)
Time (week)
57
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10 11
DO
(m
g/l)
Time (week)
Fig 21: Weekly variations in concentration of dissolved oxygen in effluent treated
using SSF
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9 10 11
BO
D (
mg/
l)
Time (week)
Fig 22: Weekly variations in Biochemical Oxygen Demand (BOD) of effluent treated
using SSF
58
0
50
100
150
200
250
300
350
400
1 2 3 4 5 6 7 8 9 10 11
CO
D (
mg/
l)
Time (week)
Fig 23: Weekly variations in Chemical Oxygen Demand (COD) of effluent treated
using SSF
A B
Plate 12: Sewage effluent before (A) and after seventh week (B) of slow sand
filtration
59
It can be clearly seen that the effluent has been purified to a great extent. The treated
effluent looks clearer than the raw effluent (A).
3.7 Comparison of phytoremediation using Ipomoea aquatica and slow sand
filtration (SSF) technologies
One-way analysis of variance was employed in testing the hypotheses assuming normal
distribution with equal variance: Ho: mus=mui=musc=muic. H1: The mean values are all
not the same.
60
Table 3: Comparison of p H of effluent treated using SSF with effluent from
treatment with Ipomoea aquatica
Ph Week SSF Ipomoea
aquatica
Scontrol Icontrol
0 4.130 4.14 7.32 7.72
1 6.540 7.38 6.91 6.45
2 6.515 7.22 6.63 6.06
3 7.585 7.77 6.80 6.75
4 7.165 7.65 7.10 7.19
PH ANOVA Sum of Source DF Squares Mean Square F Value Pr> F Model 3 0.93173375 0.31057792 0.27 0.8457 Error 16 18.37221000 1.14826312 Corrected Total 19 19.30394375 R-Square CoeffVar Root MSE Water Mean 0.048266 15.87218 1.071570 6.751250 Source DF Anova SS Mean Square F Value Pr> F Group 3 0.93173375 0.31057792 0.27 0.8457
The ANOVA for the pH table shows that the means of all the water treatment methods
are the same. Therefore, it does not matter which water treatment method is employed
they will both yield the same results since we fail to reject the null hypothesis. The
Scheffe's Test and Student-Newman-Keuls Test also show that the means of the water
treatment method on pH are all not significantly different. This implies that both
treatment methods are effective at changing acidic conditions to neutral.
61
Table 4: Comparison of the concentration of dissolved oxygen (DO) of effluent
treated using SSF with effluent treated with Ipomoea aquatica
DO (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 1.935 0.17 6.0 6.3
1 6.100 2.10 5.5 4.3
2 5.100 3.50 4.6 4.8
3 4.250 1.90 5.3 5.5
4 3.700 4.10 4.5 6.7
DO (mg/l) ANOVA The ANOVA Procedure Dependent Variable: Water Sum of Source DF Squares Mean Square F Value Pr> F Model 3 30.27672375 10.09224125 6.51 0.0044 Error 16 24.79960000 1.54997500 Corrected Total 19 55.07632375 R-Square CoeffVar Root MSE Water Mean 0.549723 28.83400 1.244980 4.317750 Source DF Anova SS Mean Square F Value Pr> F Group 3 30.27672375 10.09224125 6.51 0.0044 Student-Newman-Keuls Test for Water NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 1.549975 Number of Means 2 3 4 Critical Range 1.6692018 2.0317383 2.2527514 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 5.5200 5 ic A A 5.1800 5 sc A A 4.2170 5 s B 2.3540 5 i
Since the p value (0.0044) of the F calculated from the DO ANOVA is less than the
significant level (0.05), there is enough evidence against the null hypothesis and it can be
62
concluded that the means are all not the same. The analysis shows that the water
treatment methods on DO (mg/l) are not the same. Therefore, Multiple Comparisons or
Post Hoc analysis was performed since the means are not the same. The Scheffe's Test
and Student-Newman-Keuls Test revealed that the treatment with Ipomoea aquatica was
the best in this case since it has the higher mean for DO (mg/l). Water with a higher DO
concentration is evident of lower contamination by aerobic microorganism and therefore
more desirable.
63
Table 5: Comparison of turbidity of effluent treated using SSF with effluent from
treatment with Ipomoea aquatica
TURBIDITY
(NTU)
Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 159.50 143.0 0.8 4.00
1 119.00 147.0 1.1 2.18
2 12.50 20.2 1.0 5.40
3 10.95 54.0 1.0 1.80
4 9.75 12.9 1.0 6.30
Turbidity ANOVA Sum of Source DF Squares Mean Square F Value Pr> F Model 3 22508.97126 7502.99042 3.19 0.0523 Error 16 37664.08492 2354.00531 Corrected Total 19 60173.05618 R-Square CoeffVar Root MSE Water Mean 0.374071 136.0231 48.51809 35.66900 Source DF Ano va SS Mean Square F Value Pr> F Group 3 22508.97126 7502.99042 3.19 0.0523 Scheffe's Test for Water Treatment NOTE: This test controls the Type I experiment wise error rate. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 2354.005 Critical Value of F 3.23887 Minimum Significant Difference 95.651 Means with the same letter are not significantly different. Scheffe’s Grouping Mean N Group A 75.42 5 i A A 62.34 5 s A A 3.94 5 ic A A 0.98 5 sc
64
The analysis of the turbidity data shows that there is no evidence against the null
hypothesis since the p-value (0.0523) is greater than the significant level (0.05). Hence,
we fail to reject the null hypothesis and conclude that all the means of the treatment
methods are the same. Post hoc analysis also confirms this assertion. This implies
turbidity of the water would not be significantly different irrespective of the treatment
method used.
65
Table 6: Comparison of EC of effluent treated with SSF with effluent from
treatment with Ipomoea aquatica
EC (µs/CM)
Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 5413.5 5365 347 309
1 3755.0 3122 345 287
2 3398.0 3105 326 276
3 2859.0 3075 355 255
4 2813.0 2030 352 231
EC (us/CM) ANOVA
Sum of Source DF Squares Mean Square F Value Pr> F Model 3 50980178.94 16993392.98 25.88 <.0001 Error 16 10504475.20 656529.70 Corrected Total 19 61484654.14 R-Square CoeffVar Root MSE Water Mean 0.829153 42.62479 810.2652 1900.925 Source DF Anova SS Mean Square F Value Pr> F Group 3 50980178.94 16993392.98 25.88 <.0001 EC (us/CM) ANOVA The ANOVA Procedure Student-Newman-Keuls Test NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 656529.7 Number of Means 2 3 4 Critical Range 1086.3598 1322.308 1466.149 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 3647.7 5 s A A 3339.4 5 i B 345.0 5 sc B B 271.6 5 ic
The EC (mg/l) data shows enough evidence that the means are all not the same since the
p-value (0.0001) of the calculated F value is less than the significant level (0.05). In view
66
of this, Post Hoc analysis was conducted to ascertain how different they are. From the
Student-Newman-Keuls Test, sand filtration method of water treatment is not
significantly different from that of treatment with Ipomoea aquatica. However, since the
mean of the sand filtration method on EC (mg/l) is higher than that of Ipomoea aquatica,
it follows that phytoremediation with Ipomoea aquatica is better in this case than the
sand filtration.
67
Table 7: Comparison of concentration Total Dissolved Solids (TDS) of effluent
treated using SSF with effluent from treatment with Ipomoea aquatica
TDS (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 2706.75 2683.0 173.5 154.5
1 1877.50 1901.0 172.5 143.5
2 1699.00 1552.5 163.0 138.0
3 1429.50 1537.5 177.5 127.5
4 1406.50 1015.0 176.0 115.5
TDS (mg/l) ANOVA Sum of Source DF Squares Mean Square F Value Pr> F Model 3 13252236.51 4417412.17 26.72 <.0001 Error 16 2645627.80 165351.74 Corrected Total 19 15897864.31 R-Square CoeffVar Root MSE Water Mean 0.833586 42.02996 406.6346 967.4875 Source DF Anova SS Mean Square F Value Pr> F Group 3 13252236.51 4417412.17 26.72 <.0001
Scheffe's Test NOTE: This test controls the Type I experiment wise error rate. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 165351.7 Critical Value of F 3.23887 Minimum Significant Difference 801.66 Means with the same letter are not significantly different. Scheffe’s Grouping Mean N Group A 1823.9 5 s A A 1737.8 5 i B 172.5 5 sc B B 135.8 5 ic
The analysis of the TDS (mg/l) data shows that there is enough evidence against the null
hypothesis in favour of the alternate one. Since the p-value (0.0001) of the F calculated is
less than the significance level (0.05), there is sufficient ground to say that the water
68
treatment methods do not produce same results. The multiple comparisons of the methods
using Student-Newman-Keuls Test shows that sand filtration and treatment with Ipomoea
aquatica are not significantly different. However, treatment with Ipomoea aquatica
reduces TDS better than sand filtration since the mean of the former is less than that of
the latter.
69
Table 8: Comparison of concentration of Total Suspended solids (TSS) of effluent
treated using SSF with effluent from treatment with Ipomoea aquatica
TSS (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 238.0 239 8 6
1 221.5 315 6 23
2 21.0 35 6 10
3 18.0 70 6 3
4 14.0 31 5 15
TSS (mg/l) ANOVA The ANOVA Procedure Sum of Source DF Squares Mean Square F Value Pr> F Model 3 65323.7375 21774.5792 2.84 0.0708 Error 16 122602.0000 7662.6250 Corrected Total 19 187925.7375 R-Square CoeffVar Root MSE Water Mean 0.347604 135.6628 87.53642 64.52500 Source DF Anova SS Mean Square F Value Pr> F Group 3 65323.73750 21774.57917 2.84 0.0708 TSS (mg/l) ANOVA The ANOVA Procedure Student-Newman-Keuls Test for Water NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 7662.625 Number of Means 2 3 4 Critical Range 117.3641 142.85459 158.39436 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 138.00 5 i A A 102.50 5 s A A 11.40 5 ic A A 6.20 5 sc
On the analysis of the TSS (mg/l), the p-value (0.0708) of the F calculated is greater than
the level of significance (0.05), hence we have insufficient evidence to reject the null
70
hypothesis and conclude that the means of the water treatment methods on the chosen
parameter are the same. Therefore, it does not matter whether sand filtration or
phytoremediation with Ipomoea aquatica method is used since both will yield the same
result . The mean of treatment with Ipomoea aquatica method on TSS (mg/l) is greater
than that of sand filtration method even though they are not significantly different. Thus
sand filtration is a better method for the removal of suspended solids.
71
Table 9: Comparison of colour of effluent treated using SSF with effluent from
treatment with Ipomoea aquatica
COLOUR (PtCo) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 731 738 7 21
1 565 218 5 20.1
2 234 718 4 19
3 217 664 4 15
4 210 334 4 10.4
Colour ANOVA The ANOVA Procedure Sum of Source DF Squares Mean Square F Value Pr> F Model 3 1072794.737 357598.246 12.28 0.0002 Error 16 465872.320 29117.020 Corrected Total 19 1538667.058 R-Square CoeffVar Root MSE Water Mean 0.697223 72.02157 170.6371 236.9250 Source DF Anova SS Mean Square F Value Pr> F Group 3 1072794.738 357598.246 12.28 0.0002 Colour ANOVA The ANOVA Procedure Student-Newman-Keuls Test for Water NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 29117.02 Number of Means 2 3 4 Critical Range 228.781 278.4703 308.76238 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 534.4 5 i A A 391.4 5 s B 17.1 5 ic B B 4.8 5 sc
The colour analysis of the water treatment methods is significantly different since the p-
value of the F calculated (0.0002) is less than the level of significance (0.05). According
72
to the Post Hoc analysis of the same data, phytoremediation and sand filtration methods
of water treatment are not significantly different. This implies that they may yield the
same result on the colour of the water. However, the mean of the phytoremediation
method on colour is greater than that of sand filtration, hence rendering the method of
sand filtration better at reducing colour.
73
Table 10: Comparison of concentration of nitrates in effluent treated using SSF with
effluent treated using Ipomoea aquatica
NO3 (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 2.65 3.2 3.5 0.5
1 1.70 0.0 1.3 0.2
2 8.45 3.4 1.0 0.0
3 9.40 1.4 1.3 0.8
4 10.70 33.6 1.5 0.3
NO3 (mg/l) The ANOVA Procedure Sum of Source DF Squares Mean Square F Value Pr> F Model 3 949361.350 316453.783 10.37 0.0005 Error 16 488479.200 30529.950 Corrected Total 19 1437840.550 R-Square CoeffVar Root MSE Water Mean 0.660269 69.15821 174.7282 252.6500 Source DF Anova SS Mean Square F Value Pr> F Group 3 949361.3500 316453.7833 10.37 0.0005 NO3 (mg/l) The ANOVA Procedure Student-Newman-Keuls Test for Water NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 30529.95 Number of Means 2 3 4 Critical Range 234.26615 285.14678 316.16513 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 534.4 5 i A A 391.4 5 s B 80.0 5 ic B B 4.8 5 sc
74
The NO3- data also shows enough evidence against the null hypothesis in favour of the
alternative implying that the means are all significantly different. This is because the p-
value of the F calculated (0.0005) is less than the level of significance (0.05). The
treatment methods have effects on the NO3 of water. Post Hoc analysis shows that sand
filtration is better at reducing nitrate concentration even though the means are not
significantly different.
75
Table 11: Comparison of phosphate concentration in effluent treated using SSF with
effluent from treatment with Ipomoea aquatica
PO4 (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 5.470 5.60 1.44 1.70
1 3.550 4.70 1.14 0.20
2 3.030 3.90 1.09 0.10
3 2.810 5.64 2.49 1.20
4 3.350 8.24 2.54 7.04
PO4 (mg/l) The ANOVA Procedure Sum of Source DF Squares Mean Square F Value Pr> F Model 3 949361.350 316453.783 10.37 0.0005 Error 16 488479.200 30529.950 Corrected Total 19 1437840.550 R-Square CoeffVar Root MSE Water Mean 0.660269 69.15821 174.7282 252.6500 Source DF Anova SS Mean Square F Value Pr> F Group 3 949361.3500 316453.7833 10.37 0.0005
Scheffe's Test NOTE: This test controls the Type I experiment wise error rate. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 30529.95 Critical Value of F 3.23887 Minimum Significant Difference 344.47 Means with the same letter are not significantly different. Scheffe’s Grouping Mean N Group A 534.4 5 i A B A 391.4 5 s B B C 80.0 5 ic C C 4.8 5 sc
There is enough evidence against the null hypothesis in favour of the alternative since the
p-value of the F calculated (0.0005) is less than the level of significance (0.05). This
76
implies that the means are all significantly different and sand filtration seems to be better
at reducing phosphate concentration than phytoremediation with Ipomoea aquatica.
77
Table 12: Comparison of Biochemical Oxygen Demand (BOD) of effluent treated
with SSF with effluent from treatment with Ipomoea aquatica
BOD (mg/l) Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 35.00 35.0 6.2 6.2
1 25.00 16.0 4.5 4.3
2 21.50 15.1 0.9 3.2
3 11.00 18.0 0.2 1.8
4 8.50 4.1 0.2 0.9
BOD (mg/l) The ANOVA Procedure Sum of Source DF Squares Mean Square F Value Pr> F Model 3 1301.869500 433.956500 6.90 0.0034 Error 16 1006.380000 62.898750 Corrected Total 19 2308.249500 R-Square CoeffVar Root MSE Water Mean 0.564007 73.06194 7.930873 10.85500 Source DF Anova SS Mean Square F Value Pr> F Group 3 1301.869500 433.956500 6.90 0.0034 BOD (mg/l) 27 Student-Newman-Keuls Test for Water NOTE: This test controls the Type I experiment wise error rate under the complete null hypothesis but not under partial null hypotheses. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 62.89875 Number of Means 2 3 4 Critical Range 10.633286 12.942746 14.350662 Means with the same letter are not significantly different. SNK Grouping Mean N Group A 20.100 5 s A A 17.640 5 i B 3.280 5 ic B B 2.400 5 sc
78
The BOD analysis shows that all the means are significantly different since the F test is in
favour of the alternative hypothesis. Since the F calculated p-value (0.0034) is less than
the significant level (0.05), there is enough evidence against the null hypothesis. In view
of this, multiple comparison analysis revealed that sand filtration and phytoremediation
with Ipomoea aquatica have mean values that are not significantly different. But the
mean BOD of water treated with Ipomoea aquatica is greater than that of sand filtration
implying making sand filtration a better method at reducing BOD.
79
Table 13: Comparison of Chemical Oxygen Demand (COD) of effluent treated using
SSF with effluent from treatment with Ipomoea aquatica
COD (mg/l)
Week SSF Ipomoea
Aquatica
Scontrol Icontrol
0 368 368 256 256
1 288 192 224 160
2 240 160 192 128
3 176 96 160 64
4 144 64 128 32
The ANOVA
Sum of Source DF Squares Mean Square F Value Pr> F Model 3 33830.4000 11276.8000 1.40 0.2802 Error 16 129228.8000 8076.8000 Corrected Total 19 163059.2000 R-Square CoeffVar Root MSE Water Mean 0.207473 48.63150 89.87102 184.8000 Source DF Anova SS Mean Square F Value Pr> F Group 3 33830.40000 11276.80000 1.40 0.2802 Scheffe's Test for Water NOTE: This test controls the Type I experiment wise error rate. Alpha 0.05 Error Degrees of Freedom 16 Error Mean Square 8076.8 Critical Value of F 3.23887 Minimum Significant Difference 177.18 Means with the same letter are not significantly different. Scheffe’s Grouping Mean N Group A 243.20 5 s A A 192.00 5 sc A A 176.00 5 i A A 128.00 5 ic
The ANOVA analysis reveals that the F calculated p-value (0.2802) is greater than the
level of significance (0.05). In view of this, there is sufficient information in the data in
favour of the null hypothesis that the means of the treatment methods are the same. This
80
is also proven by the Post Hoc analysis of the data. Therefore, any method for water
treatment on COD (mg/l) may yield similar results.
3.8 Microbial load
Table 14: Microbiological characteristics of sewage effluent before and after
treatment
SAMPLE THB
CFU/ml
TC
CFU/100ml
FC
CFU/100ml
Raw sewage effluent 1210 348 162
Effluent after treatment using P.S 648 3 1
Effluent after using I.A 744 9 3
Effluent after treatment using SSF 767 0 0
P.S.: Pistia stratiotes, I.A: Ipomoea aquatica, CFU: coliform forming units, THB: Total
heterotrophic bacteria, TC: Total coliforms, FC: Faecal coliforms
Generally, there was a decrease in microbial load at the end of the experiment for both
plants as well as for the sand filter. After the tenth week of slow sand filtration, there was
zero count for total and faecal coliforms.
82
3.9 Comparison of efficiency of experimental sand filter to the filtration system of the Biogas plant
Table 15: Comparison of the quality of effluent for ten weeks of SSF to quality of effluent passing through the filtration system
of the VVU Biogas plant
WEEKLY VARIATION IN EFFLUENT QUALITY
Parameters analysed A 1 2 3 4 5 6 7 8 9 10 B
pH 4.13 6.54 6.515 7.585 7.165 6.87 6.785 6.685 6.6 6.725 7.105 6.98
Temperature (°C) 30.25 29.2 31.05 31.45 32.6 33.45 25.65 30.25 29.8 30 25.55 27.75
DO (mg/l) 1.935 6.1 5.1 4.25 3.7 3.65 3.55 4.6 5.6 5.7 5.75 4.19
BOD (mg/l) 35 25 21.5 11 8.5 7.5 5.5 4.3 2.35 1.25 1.05 26
COD (mg/l) 368 288 240 176 144 96 64 64 64 32 32 98
Turbidity (NTU) 159.5 119 12.5 10.95 9.75 9.7 11.25 7.95 7.1 6.6 5.8 47.5
Colour (PtCo) 731 565 234 217 210 206.5 199.5 199 198.5 196.5 184 515
TDS (mg/l) 2706.75 1877.5 1699 1429.5 1406.5 1374.25 1345.85 1271.5 1286.5 1274.5 1226.25 1704.8
EC (µs/cm) 5413.5 3755 3398 2859 2813 2748.5 2692 2579.5 2573 2549 2452.5 3409.5
Phosphates(mg/l) 5.47 3.55 3.03 2.81 3.35 3.97 3 2.895 2.84 2.705 2.54 3.02
Nitrates (mg/l) 2.65 1.7 8.45 9.4 10.7 8.2 5.65 4.3 4.25 4.3 3.4 5.75
TSS (mg/l) 238 221.5 21 18 14 11.5 10.5 6.5 7 5.5 5 65.5
A: Raw sewage effluent from intermediary chamber, B: effluent from the filtration system of the VVU Biogas facility
83
3.10 Quality assessment of safety of treated effluent for disposal/reuse
Table 16: Assessment of safety of effluent treated using SSF for disposal/reuse
Parameters analysed 1 2 3 4 5 6 7 8 9 10 GEPA (2004) WHO (1993)
p H 6.54 6.515 7.585 7.165 6.87 6.785 6.685 6.6 6.725 7.105 6-9 6.5-8.5
Temperature (°C) 29.2 31.05 31.45 32.6 33.45 25.65 30.25 29.8 30 25.55 < 3°C above
ambient
DO (mg/l) 6.1 5.1 4.25 3.7 3.65 3.55 4.6 5.6 5.7 5.75
BOD (mg/l) 25 21.5 11 8.5 7.5 5.5 4.3 2.35 1.25 1.05
COD (mg/l) 288 240 176 144 96 64 64 64 32 32
Turbidity (NTU) 119 12.5 10.95 9.75 9.7 11.25 7.95 7.1 6.6 5.8 75 5
Colour (PtCo) 565 234 217 210 206.5 199.5 199 198.5 196.5 184
TDS (mg/l) 1877.5 1699 1429.5 1406.5 1374.25 1345.85 1271.5 1286.5 1274.5 1226.25 1000
EC (µs/cm) 3755 3398 2859 2813 2748.5 2692 2579.5 2573 2549 2452.5 1500 700
Phosphates(mg/l) 3.55 3.03 2.81 3.35 3.97 3 2.895 2.84 2.705 2.54
Nitrates (mg/l) 1.7 8.45 9.4 10.7 8.2 5.65 4.3 4.25 4.3 3.4
TSS (mg/l) 221.5 21 18 14 11.5 10.5 6.5 7 5.5 5
Faecal coliforms
(CFU/100ml)
0 10 0
Total coliforms
(CFU/100ml)
0 400 0
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Table 17: Assessment of the quality of effluent treated using Pistia stratiotes for
disposal/use
Parameter Effluent treated
using
Pistia stratiotes
GEPA (2004)
(Max. permissible level)
for discharge into natural
waters
WHO (1993)
Max. value for drinking
water
p H 7.87 6-9 6.5-8.5
Temperature (°C) 25.1 <3°C above ambient -
DO (mg/l) 2.2 - -
BOD (mg/l) 17 - -
COD (mg/l) 224 - -
Phosphates (mg/l) 4.88 - -
Nitrates (mg/l) 1 - -
EC (µs/cm) 2975 1500 700
TDS (mg/l) 1488 1000 -
TSS (mg/l) 96 - -
Colour (PtCo) 530 - -
Turbidity (NTU) 90 75 5
Faecal coliforms
(cfu/100ml)
1 10 0
Total coliforms
(cfu/100ml)
3 400 0
Table 15 compares the experimental values to those obtained from the filtration system of
the Biogas plant. A is the raw effluent from the intermediary chamber of the Biogas
plant. A was subjected to slow sand filtration over a ten week period and the values
obtained on a weekly basis are shown. B is effluent obtained after the raw effluent went
85
through the filtration system of the biogas plant. From the table it is evident that there
were improvements in effluent quality for both the experimental filters and the filtration
system of the biogas plant.
It can be seen from table 16 that, the experimental sand filters reduced contaminants to
acceptable limits outlined by GEPA (2004) and WHO(1993) with the exception of TDS
and EC.
Table 17 above compares the quality effluent treated using Pistia stratiotes to standards
stipulated by GEPA (2004) and WHO (1993). Turbidity, EC and TDS did not meet the
standards.
86
Table 18: Assessment of the quality of effluent treated using Ipomoea aquatica for
disposal/ use
WEEK
Parameter 1 2 3 4 GEPA (2004)
WHO
(1993)
p H 7.38 7.22 7.77 7.65 6-9 6.5-8.5
Temperature (°C) 25.2 29.1 32 25.8 <3°C above
ambient
-
DO (mg/l) 2.1 3.5 1.9 4.1 - -
BOD (mg/l) 16 15.1 18 4.1 - -
COD (mg/l) 192 160 96 64 - -
Phosphates (mg/l) 4.7 3.9 5.64 8.24 - -
Nitrates (mg/l) 0 3.4 1.4 33.6 - -
EC (µs/cm) 3122 3105 3075 2030 1500 700
TDS (mg/l) 1901 1552.
5
1537.5 1015 1000 -
TSS (mg/l) 315 35 70 31 - -
Colour (PtCo) 718 664 533 334 - -
Turbidity (NTU) 147 20.2 54 12.9 75 5
Faecal coliforms (cfu/100ml) - - - 3 10 0
Total coliforms (cfu/100ml) - - - 9 400 0
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3.11 Public perceptions on water scarcity and the reuse of wastewater
3.11.1 Demographic background of respondents
A total of 120 questionnaires were administered to students and staff of the Valley View
University. One hundred and two people completed the questionnaires, 46.1% male and
54% female. From the table, it can seen that higher proportions of the respondents were
between the ages of 18-30 (72.5%) and educated to the tertiary level. Majority (86.3%).
of the respondents are single.
Table 19: Demographic characteristics of respondents
Marital status Gender Age (Years) Educational level
Single Married Male Female 18-
30
31-
40
41-
60
Above
60
SHS Tertiary Others
Frequency 89 13 47 55 74 12 14 2 15 86 1
Percentage
(%)
87.3 12.7 46.1 53.9 72.5 11.8 13.7 2 14.7 84.3 1
3.11.2 Environmental perceptions
Fig 24 below shows that out of the 102 respondents interviewed, 57.8% have access to
treated tap water whilst 23.5% use water from the borehole. 2% have their source of
water from the stream whilst 6.9% harvest rain water for domestic use. 57.8% of
respondents stated that they have regular supply of water whiles the remaining 42.2% do
not have regular access.
88
Fig 24: Source of water for domestic use by respondents
89
3.11.3 Water as a scarce resource
Fig 25: Proportion of respondents who consider water to be a scarce resource
3.11.4 Causes of water scarcity
Fig 26: Causes of water scarcity stated by respondents
90
3.11.5 Sources of wastewater
Fig 27: Sources of wastewater stated by respondents
3.11.6 How wastewater is generated
Fig 28: How wastewater is generated by respondents
91
3.11.7 Use of wastewater generated at home
Fig 29: Uses of wastewater generated at home
All respondents admitted that they generate wastewater and the major source of
wastewater mentioned is domestic washing (81%). 13.7% generate wastewater through
work activities such as washing bay, tie and dye industry, catering industry and
commercial laundry.
Majority of the respondents (61.8%) mentioned that wastewater generated at home is
thrown away (Table 4.15). 36.3% use the wastewater for flushing toilet whilst 2% use the
wastewater for irrigation purposes. This result indicates that only 38.3% of the
92
respondents conserve water by reusing wastewater. From, Table 4.18 it is observed that
57.8% of respondents have regular access to water and this may explain why most of the
respondents throw the wastewater away.
3.11.8 Type of toilet facility
Fig 30: Type of toilet facilty respondents have access to
From the figure above, 88.2% of respondents have access to a toilet facility, the main
facility being water closet. However, only 47.1% have knowledge about how the human
excreta is disposed of as shown in the table below. This suggests that many people are
not conscious of their environment
93
3.11.9 Method of sewage disposal
Fig 31: Methods of disposal of sewage as stated by respondents
Out of the 48% of respondents who have an idea about the disposal of faecal matter,
26.5% mentioned dumping in the sea as the method of sewage disposal, while 17.65%
are aware of the use of sewage for production of biogas. A small proportion of the
respondents are aware of the use of sewage for compost (4.9) and irrigation of crops
(3.9%).
94
3.11.10 Reasons for supporting wastewater reuse
Fig 32: Respondents reasons for supporting wastewater reuse
Most of the respondents (31.4%) support wastewater reuse for the reason that it will
minimize dependency on treated water. 27.5% support use of wastewater for the reason
that it conserves water. 31.4% did not specify any reason and this may correspond to the
proportion of respondents (33.3%) who had no idea about wastewater reuse (Table 4.20).
this statistics suggests that a greater proportion of people are concerned about water
scarcity and water conservation.
95
42.2% of the respondents had no idea about health risks associated with wastewater
reuse. Among the health risks associated with wastewater reuse mentioned by
respondents are cholera (27.5%), bacterial infections (23.5%) and diarrhoea (5.9%). One
person mentioned candidiasis as the health risk associated with using wastewater
particularly for flushing toilets.
3.11.11 Health risks associated with wastewater reuse
Fig 33: Types of health risks associated with wastewater reuse as stated by
respondents
96
Fig 34: Respondents response on how health risks can be minimized
Whilst 62% of the respondents stated that treating the wastewater before use would
minimize the health risks, 11.8% prefer that the use of wastewater be avoided. This
suggests that more people agree that with treatment, wastewater can be used.
97
Most of the respondents (68.6%) are of the view that the Millennium Development Goal
(7) which highlights that the proportion of the population without sustainable access to
safe drinking water and basic sanitation be halved by the year 2015 cannot be achieved
3.11.12 Uses of wastewater
3.11.12.1 Irrigation of crops
Fig 35: Response of respondents to the use of treated wastewater for irrigation of
food crops
98
3.11.12.2 Fire fighting
Fig 36: Response of respondents to the use of treated wastewater for fire fighting
3.11.12.3 Industry
Fig 37: Response of respondents to the use of treated wastewater for industry
99
3.11.12.4 Construction of buildings
Fig 38: Response of respondents to the use of treated wastewater for construction of
buildings
3.11.12.5 Swimming pool
Fig 39: Response of respondents to the use of treated wastewater for swimming pool
100
3.11.12.6 Aquifer augmentation
Fig 40: Response of respondents to the use of trated wastewater for aquifer
augmentation
Of the reuse options suggested, most people supported to the use of treated wastewater
for irrigation (70.6%), firefighting (72.6%), industry (52.9%), construction of buildings
(72.6%), toilet flushing (82.4%), public park/ sports field irrigation (54.9%) and
commercial car wash (47.1%). This may be due to the belief that these options pose little
or no threat to human health. Only 29.4% of the respondents agreed to the use of the
treated water for aquifer augmentation and 53.9% were not sure. A higher percentage of
the respondents (47.1%) disagreed with the use of treated water for general cleaning and
101
laundry and swimming pool (65.7%) probably because there is high contact and health
risks may be high if the water is not properly treated.
Most of the respondents (52.9%) would not recommend wastewater use to their
communities and this means that more education is needed to encourage people to treat
and use wastewater.
102
CHAPTER FOUR
4.0 DISCUSSION
Results of the study showed that with the exception of nitrates, dissolved oxygen (DO)
and pH, all other parameters analyzed had higher values in the effluent from intermediary
point than in effluent from the final outlet. This suggests that the filtration system of the
biogas facility reduced contaminant load although the EC and TDS did not meet Ghana
EPA emission guidelines of 1500 µS/cm and 1000 mg/l respectively. The electrical
conductivity (EC), though reduced in the final effluent (3216-3603 µs/cm) far exceeds
the 1500 µS/cm set by GEPA (2010) maximum for disposal into the environment or for
use in agriculture. The EC of effluent discharged into the mango plantation is important
since the most influential water quality guideline on crop productivity is the water
salinity hazard as measured by electrical conductivity (Hamid et. al., 2013). The primary
effect of high EC water on crop productivity is the inability of the plant to compete with
ions in the soil solution for water, a condition known as Osmotic drought (physiological
drought). The higher the EC, the lesser is the water available to plants, even though the
soil may appear to be wet. Plants can only transpire "pure" water thus usable plant water
in the soil solution decreases dramatically as EC increases. The amount of water
transpired through a crop is directly related to yield. Therefore, irrigation water with high
EC reduces yield potential (Hamid et.al, 2013). Beyond effects on the immediate crop is
the long term impact of salt loading through the irrigation water.
Nitrates were also not efficiently removed as its concentration in the filtered effluent was
higher and this may be due to the conversion of ammonia nitrogen into nitrates through a
103
denitrification process. However, this poses no problem as plants utilize nitrates for
growth.
The faecal coliforms are within the 103 -106 CFU/100 ml set by WHO (2006) for use in
agriculture and aquaculture. The faecal coliforms are also within the WHO (2006) 1000
CFU/100ml limit for restricted irrigation and the 105/100ml for unrestricted irrigation.
The dissolved oxygen recorded a high value (2.98-5.4 mg/l) after filtration and this may
be due to a reduction in population of aerobic microorganisms. The pH of effluent from
the intermediary chamber was acidic (3.9-4.14). However, after passing through the
filtration system, the pH changed (6.47-7.48) and met the Ghana EPA recommended
limit i.e. 6-9. The COD of the final effluent was also within the 250mg/l GEPA (2010)
maximum permissible level for discharge into water bodies or for use in irrigation. The
BOD was also within the GEPA maximum acceptable standard of 50 mg/l for discharge
into water bodies and WHO (1989) standard of 20-100 mg/l for irrigation or aquaculture.
The heavy metals analysed were Zn, Pb, Fe, Cd, Cr, Cu and Ni. Apart from Fe and Cu,
all other heavy metals analysed were non detectable. In the digestion process,
putrefactive bacteria are present to degrade heavy metals during hydrolysis, acetogenesis
and methanogenesis (Issah and Salifu, 2012). From the results of this experiment, it can
be inferred that, Zn, Pb, Cd, Cr, and Ni if present, were probably degraded by
putrefactive bacteria but Cu and Fe could not be degraded by the putrefactive bacteria.
Notwithstanding this, the values recorded for Cu and Fe in the final effluent did not
104
exceed the WHO (1993) guideline maximum value for domestic use of water (2 mg/l for
Cu and 0.3 mg/l for Fe). The concentrations of Cu in the final effluent pose little threat to
the environment. This is because, when copper ends up in the soil, it strongly attaches to
organic matter and minerals. As a result, it does not travel far after release and it hardly
ever enters groundwater (Baysal et. al., 2013). Fe is not toxic to plants in aerated soils.
Contrary to a report by Foresti (2002) that effluents from anaerobic reactors treating
domestic sewage can rarely comply with the emission standards and that the main
important constituents or components deserving attention which are nutrients and
pathogens are not removed efficiently in the most commonly used anaerobic reactors, the
effluent from the VVU biogas, complies with guidelines for irrigation with the exception
of EC which exceeded the limit of 1500 µS/cm.
From the results of the phytoremediation experiment, it was observed that Pistia
stratiotes survived for only five days whilst Ipomoea aquatica survived for four weeks in
the raw sewage effluent. According to Piyush et. al. (2012), Pistia stratiotes is able to
survive in wastewater for a maximum period of 25 days. Haller et. al., (1974) reported
that Pistia Stratiotes has a higher survival rate at higher levels of electrical conductivity
(> 4000 µs/cm) but does not do well at higher COD levels. The electrical conductivity for
the raw sewage effluent used in this experiment was 5365 µS/cm which is tolerable but
the COD was 368mg/l, which may have been too high to support the growth of the plant
thus leading to the death of the plant after five days. When the raw effluent was diluted to
50% and 75%, the EC reduced to 2040 µs/cm and 1211µs/cm respectively but the COD
105
reduced to 354mg/l and 323mg/l respectively, Pistia stratiotes showed similar results, i.e.
died by the fifth day.
In the distilled water (control) which had lower EC (309 µS/cm) and COD of 256 mg/l,
Pistia stratiotes survived for two weeks even though the nitrate and phosphate
concentrations in the control were lower (0.5 mg/l and 1.7 mg/l respectively) than that in
the raw effluent (3.2 mg/l nitrates and 5.6 mg/l phosphates). This implies that Pistia
stratiotes can tolerate low nutrient levels.
Ipomoea aquatica plants developed new shoots and leaves after three days and survived
in the raw effluent for 28 days. In a study by Yu et. al. (2013) using Ipomoea aquatica to
purify biogas slurry, Ipomoea aquatica reached the highest peak of growth after 60 days.
This indicates that Ipomoea aquatica has high tolerance to contaminants and thus was
able to survive despite the high contaminant load.
The results showed that nitrogen and phosphorus were accumulated in both plants. Pistia
stratiotes accumulated less nitrogen (10.08%) and phosphorus (21.37%) than Ipomoea
aquatica (21.37%) which survived for four weeks. From the results of the experiment,
Ipomoea aquatica accumulated more nutrients at the end of the experiment than Pistia
stratiotes. This was expected since Ipomoea aquatica stayed longer in the sewage
effluent than Pistia stratiotes. Ipomoea aquatica shows much higher nutrient removal
efficiency with their high nutrient uptake capacity as shown in the figures 3 and 4 . It can
be seen that, after five days, there was a greater reduction in the concentration of
phosphates and nitrates when the raw effluent was treated with Ipomoea aquatica. Lu et.
al. (2013) reported that low concentrations of nutrients may reduce the performance of
106
plants in removing nutrients. This may be responsible for the low nutrient removal
efficiency of Pistia stratiotes.
After the first and second weeks of experiment, there was a reduction in BOD with a
corresponding increase in DO. This could be as a result of reduction in microbial activity
and photosynthesis. Photosynthesis results in greater dissolution of oxygen due to a
reduction in TDS. During the third week, a reduction in DO was observed corresponding
to a rise in BOD and this may be due to dead leaves falling back into the water and
decomposing leading to an increase in microbial activity. The microorganisms were using
up the DO in the water and that accounted for the decrease in DO. However, during the
fourth week, new shoots had sprouted and photosynthetic activity coupled with the
uptake of microorganisms by the plant led to an increase in the DO and a corresponding
decrease in the BOD.
Reduction of EC and TDS throughout the study period was due to absorption of dissolved
solids by Ipomoea aquatica.
Reduction in phosphates and nitrates is due to uptake by the plant as nutrients for growth.
The well-developed roots of aquatic plants have microbes attached to them and these help
to utilize nutrients (Wijetunga et.al, 2009). An increase in the phosphate concentration
after the second week may be due to falling leaves which decomposed and released the
phosphates back into the water.
All the nitrates were taken up after the first week of the experiment but increased again
after the second week. Some of the plants died when all the nitrogen was used up and
decomposition released the nitrates into the water which was used by the surviving plants
107
and new shoots developed. At the end of the experiment, there was an increase in
nitrogen concentration (33.6 mg/l).
The concentrations of nitrates and phosphates in the water were higher at the end of the
experiment and this suggests that most of the nutrients were released back into the water.
There was a progressive decrease in Chemical Oxygen Demand (COD) throughout the
experiment. The mean COD of the raw sewage effluent was 368 mg/l but this reduced to
64 mg/l by the end of the experiment corresponding to an 82.6% removal of COD. This
suggests that Ipomoea aquatica can assimilate COD. Decrease in COD may also be due
to an increasing DO thereby providing a better environment for oxidation. The microbes
around the roots of Ipomoea aquatica can also contribute to treatment by providing a
comfortable environment for the microbes thus removing organic matter effectively.
The filtration rate of the slow sand filter was high at the first run (733 ml/min) but
decreased with time of filter run. This is because as time went on, the sand grains settled
decreasing the voids which became clogged with particles from the raw sewage effluent.
Because of this, a drop in the filtration rate was observed. Around the fourth week, the
system started to level out with the filtration rate around 698 ml/min. At this point, the
sand was fully settled and saturated.
There was a notable positive reduction in the turbidity of the water samples after filtration
(even though turbidity was high). Turbidity decreases due to reduction in TDS and TSS.
These results agree with findings of El-Taweel (2000) that 92% of turbidity was removed
when slow sand filter was used for wastewater treatment. The major turbidity reduction
mechanism is believed to be through surface straining as predicted by Haarhoff and
108
Cleasby (1991). Excessive turbidity or cloudiness, in drinking water is aesthetically
unappealing and may also represent a health concern.
The concentration of nitrates reduced after the first run and shot up after the second week.
It reached a peak value after the fifth week and declined. An increase in concentration of
nitrates from the second week to the fifth week may be due to oxidation of ammonia
nitrogen to nitrates. After the fifth week, the growth of algae may have commenced
leading to the uptake of nitrates by the algae as nutrients for growth, thereby resulting in
a decrease in the concentration of nitrates.
A reduction in concentration of phosphates was observed until it increased from the fifth
to sixth week then a decline was observed. The reduction in phosphate concentration after
the sixth week may be due to uptake by algae growing on the surface of the filter bed.
Dissolved oxygen (DO) of raw sewage effluent was low before filtration (1.935 mg/l).
Low oxygen concentration is associated with heavy contamination by organic matter.
There was an increase in DO at the beginning of the experiment and this may be due to
the fact that the pores in the sand were filled with air and so there was a mixing of the
effluent with atmospheric oxygen. However, there was a decline after the second week
after which the concentration increased again after the 7th week. The decline was
probably due to the fact that the air pores were filled with raw effluent and microbial
activity was high. After the seventh week, enhancement of DO may be due to the
minimization of organic pollution load and microbial population due to their retention in
the filter bed and the simultaneous mixing with atmospheric oxygen.
109
Reduction in Biochemical Oxygen Demand (BOD) may be due to a reduction in the
bacterial population due to their retention on the surface of the filter bed as a result of the
formation of the dirt cover. Removal of BOD is related to the removal of TSS (Benth
et.al., 1981). A reduction in TSS was observed in this study.
The reduction in Chemical Oxygen Demand (COD) may be due to the fact that most of
the organic wastes were oxidized as they moved through the filter bed. A similar trend
was recorded by Rao et. al. (2003) when wastewater was filtered through slow sand filter.
Reduction in total suspended solids (TSS) is due to retention time of sewage effluent in
the filter bed. The sand filter primarily removes suspended solids and the effectiveness of
the filter is related to the removal of TSS (Benth et. al., 1981)
The main use of pH in water analysis is for detecting abnormal water (Tak et.al, 2012).
The initial pH of the sewage effluent used for this study was 4.04 which is acidic. The pH
of the water samples were taken (during the duration of the study) on a weekly basis.
There was an increase in pH both with the aquatic plants and with the sand filters. For
both technologies, pH ranged from 6.54 to 7.87. The increase in pH observed in effluent
treated with plants is basically attributed to the biochemical processes. Plants can absorb
anions such as NO3-, NO2
- and PO43- for their growth and, eventually resulting in the
reduction of acid forming anions leading to an increase in the pH.
Temperature is an important parameter because it affects chemical and biological
reactions and solubility of gases such as oxygen. Increasing temperature increases
reaction rates and solubility up to the point where temperature becomes high enough to
110
inhibit the activity of most microorganisms (around 35°C). During the study, the
temperature range was 25.1 - 33.45 which allows microbial activity.
An assessment of the microbial load of the effluent showed that, generally, there was a
decrease in microbial load at the end of the experiment for both plants as well as for the
sand filters. After the tenth week of filtration, there was zero count for total and faecal
coliforms. This is attributed to the fact that, the small sand grains provided a large total
surface area for biofilm growth. This biofilm, also known as dirt cover or
“schmutzdecke” layer may have resulted in the reduction in microbial load in the effluent
from the sand filter. This layer consists of the organic matter from the raw effluent that
settles on the filter surface and becomes a feeding ground for bacteria and
microorganisms. Thus, microorganisms spend longer time on the surface of the filter
resulting in a reduction in microbial load of effluent passing through the filter media.
Microbes in wastewater perform a vital role for the releasing of nutrient to the wastewater
by utilizing the organic compounds for their growth and development. Ipomoea aquatica
and Pistia stratiotes, which showed good performances with regard to pollutant removal,
had well developed root systems which facilitated the microbes to colonize well to form a
satisfactory habitat for their growth and development. A reduction in the microbial load
may be due to a migration of the microbes in the sewage effluent to the roots of the
aquatic plants used in this study. Eventually, the benefits of degradation product of
organic compounds are used by the aquatic macrophytes for their growth and
development. Therefore, it can be concluded that microbes as well as macrophytes, work
together to purify the polluted wastewater
111
A comparison of SSF and phytoremediation with Ipomoea aquatica using the one-way
ANOVA shows no significant difference in the turbidity and Chemical Oxygen Demand
(COD) of the treated effluent. This implies that if either of the two technologies is applied
in treating wastewater which is high in turbidity and COD, the same result would be
achieved.
There were significant differences in values obtained for dissolved oxygen (DO), nitrates
and phosphates. Based on these differences, SSF performed better at removing nitrates
and phosphates while Ipomoea aquatica proved better at replenishing DO. No significant
differences were recorded for electrical conductivity (EC), total dissolved solids (TDS),
total suspended solids (TSS), Biochemical Oxygen Demand (BOD) and colour. However,
when the mean values were compared, SSF was better at improving the quality of
effluent by reducing TSS, BOD and colour while Ipomoea aquatica was better at
reducing EC and TDS.
Phytoremediation using Pistia stratiotes produced an effluent which is higher in EC,
turbidity, total and faecal coliforms than the recommended values rendering the treated
effluent unsafe for domestic use and for disposal into natural water bodies. Electrical
conductivity of water is a useful and easy indicator of the salinity or total salt content of
water. Wastewater effluents often contain high amounts of dissolved salts from domestic
sewage. Build-up of salts from domestic wastes can interfere with water reuse by
municipalities, industries manufacturing textiles, paper and food products, and agriculture
for irrigation. High salt concentrations in waste effluents can increase the salinity of the
112
receiving water, which may result in adverse ecological effects on aquatic biota (Fried,
1991). Also, a very high salt concentration (> 1 000 mg/l) imparts a brackish, salty taste
to water and is discouraged because of the potential health hazard (WHO, 1979, Quality
of Domestic Water Supplies, 1998).
The effluent obtained from treatment with Pistia stratiotes had a turbidity value higher
(90 NTU) than the Ghana EPA recommended value for disposal into natural waters (75
NTU). An excessive value of turbidity is an indication of the presence of among other
things disease causing organisms and makes water purification processes difficult which
may increase treatment cost. High turbidity values are also an indication of
microbiological contamination (DWAF, 1998). This suggests that the effluent cannot be
consumed directly by human beings without treatment.
Dissolved Oxygen (DO) concentration in unpolluted water is normally about 8-10 mg/l at
25oC (DFID, 1999). Concentrations below 5.0 mg/l adversely affect aquatic life. The
treated effluent has a very low DO (2.2 mg/l) making it unsuitable for aquaculture.
For the protection of fisheries and aquatic life, the EU guidelines stipulate the BOD target
limits of 3.0-6.0 mg/l (Chapman, 1996). The high level in effluents treated with Pistia
stratiotes (17 mg/l) disqualifies the effluent for use as an aquatic ecosystem. The GEPA
(2010) proposes a BOD of 50-200 mg/l and 250-1000 mg/l COD for effluent discharge
into water bodies. This implies that considering BOD and COD, the effluent from
treatment with Pistia stratiotes can be safely discharged into water bodies.
113
The WHO safe limit for nitrate for lifetime use is 10 mg/l. Effluent treated with Pistia
stratiotes is within this limit and thus can be used for non-potable domestic purposes.
However, the effluents can be a source of eutrophication for the receiving water bodies as
the values obtained exceeded the recommended limits for no risk of 0-0.5 mg/l (DWAF,
1998).
The level of phosphate in water systems which will reduce the likelihood of algal and
other plant growth is 5µg/l (DWAF, 1998). This limit is exceeded by effluent treated with
Pistia stratiotes (4.88 mg/l). Based on this, treated effluent is not safe for disposal into
water bodies.
According to the WHO (1989) guidelines for coliform bacteria, a limit of 105 /100 ml is
recommended for unrestricted irrigation (i.e. irrigation of cereal crops, industrial crops,
fodder crops, pasture and trees) and 1000FC/100ml for restricted irrigation (irrigation of
crops likely to be eaten uncooked, sports field or public parks). The effluent from
treatment with Pistia stratiotes was well within the recommended limits and can be used
for irrigation.
In the current study, effluent obtained for each week of treatment was higher in EC,
turbidity, total and faecal coliforms than the recommended values. None of the effluents
obtained for any of the weeks is suitable for potable uses. Due to the high EC and TDS,
the effluent is unsuitable for discharge into natural water bodies and irrigation.
114
After the second week of treatment, Ipomoea aquatica reduced the turbidity to a value
lower (20.2 NTU) than the recommended value for discharge into natural waters (75
NTU). However, after the fourth week of treatment, the turbidity was still too high (12.9
NTU) for potable use (5 NTU). This implies that after two weeks of treatment of sewage
effluent with Ipomoea aquatica, the effluent can be discharged into natural waters.
For the protection of fisheries and aquatic life, the EU guidelines stipulate the BOD target
limits of 3.0-6.0 mg/l (Chapman, 1996). This is met by the effluent after the fourth week
of treatment (4.1mg/l). This means that, considering BOD, sewage effluent can be used
as an aquatic ecosystem only after the fourth week of treatment. The GEPA (2010)
proposes a BOD of 50-200 mg/l and 250-1000 mg/l COD for effluent discharge into
water bodies. This implies that considering BOD and COD, the effluent from treatment
with Ipomoea aquatica can be safely discharged into water bodies.
The effluent obtained from the first to third weeks of treatment meets the recommended
limit for nitrate for lifetime use (10 mg/l). After the fourth week, the limit was exceeded.
This means that effluents obtained from the first three weeks of treatment with Ipomoea
aquatica can be used for non-potable domestic purposes but effluent obtained after the
fourth week is not safe for lifetime use. The effluents can be a source of eutrophication
for the receiving water bodies as the values obtained exceeded the recommended limits
for no risk of 0-0.5 mg/l (DWAF, 1998). The level of phosphate in water systems which
will reduce the likelihood of algal and other plant growth is 5µg/l (DWAF, 1998). This
115
limit was exceeded by effluent treated with Ipomoea aquatica. The treated effluent is
therefore not safe for disposal into water bodies.
According to the WHO (1989) guidelines for coliform bacteria, a limit of 105 /100 ml is
recommended for unrestricted irrigation (i.e. irrigation of cereal crops, industrial crops,
fodder crops, pasture and trees) and 1000FC/100 ml for restricted irrigation (irrigation of
crops likely to be eaten uncooked, sports field or public parks). The faecal coliform count
of effluent obtained from treatment with Ipomoea aquatica is within the recommended
limits and can be used for irrigation.
In this study pH and temperature of all effluents were within the recommended limits for
domestic use, irrigation and discharge into natural waters.
Concentrations of DO below 5 mg/l adversely affect aquatic life. In this study, it was
observed that only the effluent from the first (6.1mg/l), second (5.1mg/l), eighth (5.6
mg/l), ninth (5.7mg/l) and tenth (5.75mg/l) weeks are suitable for discharge into an
aquatic environment. The EU guidelines for BOD for the protection of fisheries and
aquatic life i.e. 3.0-6.0 mg/l was met only by effluent obtained after the eighth
(2.35mg/l), ninth (1.25mg/l) and tenth (1.05 mg/l) weeks of SSF. The GEPA (2010)
proposes a BOD of 50-200 mg/l and 250-1000 mg/l COD for effluent discharge into
water bodies. The BOD for discharge into water bodies is met by all effluents.
Considering the COD limit for discharge into water bodies, only the effluents from the
second to tenth weeks of treatment meet the limit. The COD from effluent from the first
week of SSF exceeds the limit for discharge into water bodies.
116
Although SSF reduced EC and TDS progressively, the values obtained after the tenth
week were still too high and do not meet guidelines for irrigation, discharge into water
bodies and potable uses. The turbidity of effluent obtained from the second to tenth
weeks of SSF are within the Ghana EPA guideline for discharge into water bodies (75
NTU) but none of the effluents met the WHO guideline for drinking water (5 NTU). It is
possible that if the length of time for SSF is prolonged, the EC and turbidity would be
reduced to recommended limits.
The WHO safe limit for nitrate for lifetime use of 10 mg/l was met by effluent obtained
for all weeks of the SSF experiment with the exception of the fourth week which
recorded a value of 10.7 mg/l. The effluents obtained from all the weeks with the
exception of the fourth week can be used for domestic purposes such as toilet flushing,
laundry and cleaning of floors. However, the effluents can be a source of eutrophication
for the receiving water bodies as the values obtained exceeded the recommended limits
for no risk of 0-0.5 mg/l (DWAF, 1998). None of the effluents meet the 5 µg/l limit for
prevention of algal and other plant growth in water systems.
According to the WHO (1989) guidelines for coliform bacteria, a limit of105 /100 ml is
recommended for unrestricted irrigation (i.e. irrigation of cereal crops, industrial crops,
fodder crops, pasture and trees) and 1000FC/100ml for restricted irrigation (irrigation of
crops likely to be eaten uncooked, sports field or public parks). Effluent from the tenth
week of is well within the recommended limits and can be used for irrigation.
117
In this study, the performance of the experimental SSF was compared to that of the
filtration system of the Biogas plant. Both filtration systems changed the pH of the
effluent from acidic (4.13) to neutral. The experimental filters performed better at
replenishing the DO after the first four weeks and also after the seventh to tenth weeks.
During the fourth to sixth weeks, the filtration system of the Biogas facility performed
better.
The experimental sand filter was better at reducing the Biochemical Oxygen Demand
(BOD). After the first week of SSF the BOD was reduced to 25 mg/l which is lower than
that obtained for the filtration system of the Biogas facility (26 mg/l). EC and TDS values
were also lower after the second week of SSF than that obtained from the Biogas facility.
From the table, it can be seen that, after the tenth week, the SSF experiment was better at
enhancing DO, and reducing BOD, COD, turbidity, colour, TDS,TSS,EC, total and faecal
coliforms of the final effluent.
The results of the social survey show that the degree of close human contact is important
in determining public support of wastewater reuse. The results of this study seem to
parallel those of other studies by Bruvold (1984), EPA (1992), Crook et.al., (1994),
Freidler et al., (2006) and Hartley (2006), where high support was to low and medium
contact reuse options. In this study, medium contact options received high support. These
options are fire-fighting (71.6%), Industry (52.9%), construction of buildings (71.6%),
toilet flushing (81.4%), commercial car wash (46.1%) and public parks irrigation
(54.9%). There was low support for the high contact options such as swimming pool
118
(10.7%), aquifer augmentation (29.4%), and laundry (34.3%). Irrigation of food crops
which was considered to be a high contact option received high support (69.6%) probably
because it was perceived by the public as a medium contact option.
Most of the participants (65.7%) agreed that water is a scarce resource. Participants in the
survey who identified themselves as supporters of wastewater reuse revealed that the
most important reasons for their support minimization of dependency on treated water
(37.3%) and water conservation (36.3%) Environmental protection ranked as the third
most frequent response (26.5%). The demographic data shows that 83.3% of respondents
are educated to the tertiary level. However, only 48% are aware of how faecal matter is
disposed of. Of the disposal options, dumping into the sea and treatment to produce
biogas are well known among respondents. Very few know about the use of sewage for
irrigation and treatment to produce compost. Only 44.1% of the respondents are familiar
with the concept of wastewater reuse. These suggest that the level of environmental
awareness among the public is low.
Domenech and Sauri (2010) found out that the perception of health risks and
environmental awareness are in different degrees significant determinants of public
acceptance. According to these authors, improving the level of knowledge of health risks
and environmental awareness would reduce the risk of social refusal of wastewater
recycling.
The objectives of this study were achieved. The quality of sewage effluent from the VVU
Biogas facility was monitored. Slow sand filtration and Phytoremediation technologies
were successful at treating the raw effluent to some extent.
119
CHAPTER FIVE
5.0 CONCLUSIONS
The results of this study substantiate that phytoremediation and Slow Sand Filtration are
effective methods for the treatment of wastewater. Phytoremediation and Slow Sand
Filtration (SSF) are effective methods for treating sewage effluent. Generally, both
technologies reduce contaminant levels. However, phytoremediation with Ipomoea
aquatica is better than sand filtration at reducing EC and TDS. Sand filtration performed
better at enhancing DO whilst reducing colour, nitrates, phosphates and BOD. Both
technologies are equally effective at reducing turbidity, TSS, and COD since there was
no significant difference in mean values obtained for these parameters. Both technologies
changed the p H from acidic to neutral.
Pistia stratiotes and Ipomoea aquatica are both effective at reducing contaminant load.
However, the results of this study show that Pistia stratiotes does not survive for long in
sewage effluent. Dilution of effluent gave similar results.
Most of the parameters analysed with respect to the sewage effluent from the Valley
View University Biogas facility fell within the acceptable guidelines with the exception
of EC.
Treated effluents were of different qualities and are applicable, depending on the quality,
for use in irrigation, aquaculture and non-potable domestic uses as well as safe for
disposal into water bodies. The effluents are however not safe for potable uses.
120
Majority of respondents agree that water is a scarce resource and that the Millennium
Development Goal (MDG) on water cannot be achieved. Majority of people interviewed
support the use of wastewater for medium contact options such as fire- fighting (71.6%),
Industry (52.9%), construction of buildings (71.6%), toilet flushing (81.4%), Public parks
and sports field irrigation (54.9%). Support for high contact options such as swimming
pool, aquifer augmentation and laundry was low; 10.7%, 29.4% and 34.3% respectively
and this is because respondents consider the treated water to be detrimental to health.
Respondents supported the idea of wastewater reuse for reasons of water conservation
and minimization of dependency on treated water whilst environmental protection ranked
as the least frequent response. Education is needed to sensitize the public on treatment
and use of wastewater.
RECOMMENDATIONS
1. It is recommended that a strategy be put in place to reduce the electrical
conductivity of the effluent discharged from the VVU Biogas facility into the
mango plantation. Salt loading of the irrigated soil should be monitored
periodically due to the high EC of discharged effluent
2. Plant biomass of plants used for the phytoremediation experiment should be
reduced by methods such as anaerobic digestion, drying and disposed at a
landfill site
3. More work should be done on phytoremediation of sewage effluent using Pistia
stratiotes.
121
(B) The length of Slow Sand Filtration (SSF) experiment, if prolonged, may produce
an effluent which may be safe for potable uses. Further work should be done on
SSF using sand from different sources. The schmuzdecke layer formed on top of
the sand should be disposed at a landfill site due to the high levels of
contaminants. The SSF should also be monitored to prevent the presence of
insects and other animals.
122
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APPENDICES
Appendix one: Filtration rate through slow sand filter column
WEEK RAW SEWAGE
EFFLUENT (ml/min)
CONTROL(ml/min)
0 733 733
1 730 732
2 729 730
3 704 726
4 698 719
5 605.5 719
6 564 711
7 553 708
8 448 705
9 431 703
10 416 701
134
Appendix two: Performance of slow sand filtration (SSF)
WEEK PH TEMP (°C) TURBIDITY (NTU) EC (µs/CM) TDS (mg/l)
MEAN CO NTRO LMEAN CO NTRO LMEAN CO NTRO L MEAN CO NTRO LMEAN CO NTRO L
0 4.13 7.32 30.25 27 159.5 0.8 5413.5 347 2706.75 173.5
1 6.54 6.91 29.2 33.5 119 1.1 3755 345 1877.5 172.5
2 6.515 6.63 31.05 25.6 12.5 1 3398 326 1699 163
3 7.585 6.8 31.45 29.9 10.95 1 2859 355 1429.5 177.5
4 7.165 7.1 32.6 29.6 9.75 1 2813 352 1406.5 176
5 6.87 6.68 33.45 31.6 9.7 0.9 2748.5 345 1374.25 172.5
6 6.785 6.82 25.65 25.6 11.25 0.7 2692 339 1345.85 169.5
7 6.685 6.5 30.25 30.2 7.95 0.6 2579.5 334 1271.5 167
8 6.6 6.92 29.8 30.2 7.1 0.7 2573 323 1286.5 161.5
9 6.725 7.01 30 29.6 6.6 0.6 2549 318 1274.5 159
10 7.105 7.23 25.55 27.2 5.8 0.6 2452.5 312 1226.25 156
WEEK TSS (mg/l) CO LO R (PtCo) NO 3(mg/l) PO 4 (mg/l) DO (mg/l) BO D (mg/l) CO D (mg/l)
CO NTRO L MEAN CO NTRO LMEAN CO NTRO L MEAN CO NTRO LMEAN CO NTRO LMEAN CO NTRO LMEAN CO NTRO L MEAN CO NTRO L
0 238 8 731 7 2.65 3.5 5.47 1.44 1.935 6 35 6.2 368 256
1 221.5 6 565 5 1.7 1.3 3.55 1.14 6.1 5.5 25 4.5 288 224
2 21 6 234 4 8.45 1 3.03 1.09 5.1 4.6 21.5 0.9 240 192
3 18 6 217 4 9.4 1.3 2.81 2.49 4.25 5.3 11 0.2 176 160
4 14 5 210 4 10.7 1.5 3.35 2.54 3.7 4.5 8.5 0.2 144 128
5 11.5 4 206.5 3 8.2 1.4 3.97 2.56 3.65 5.1 7.5 0.1 96 96
6 10.5 4 199.5 0 5.65 1.2 3 1.96 3.55 6.5 5.5 0.1 64 64
7 6.5 4 199 0 4.3 0.8 2.895 1.86 4.6 6.6 4.3 0.1 64 32
8 7 4 198.5 0 4.25 0.8 2.84 1.82 5.6 6.5 2.35 0.1 64 32
9 5.5 4 196.5 1 4.3 0.6 2.705 1.76 5.7 6.3 1.25 0 32 32
10 5 3 184 0 3.4 0.6 2.54 1.62 5.75 5.9 1.05 0.1 32 32
Appendix three: Quality of effluent after treatment with Ipomoea aquatica and Pistia
stratiotes for five days
PH TEMP (°C) DO (mg/l) EC (µS/cm) TDS (mg/l)
MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL
RAW EFFLUENT 4.04 7.72 30.5 33.6 0.17 6.3 5365 309 2682.5 154.5
P.S treated effluent 7.87 6.76 25.1 29.9 2.2 3.1 2975 295 1488 147.5
I.A treated effluent 7.38 6.45 25.2 25.1 2.1 4.3 3122 287 1901 143.5
TSS (mg/l) COLOUR (PtCo) TURBIDITY (NTU) PO4 (mg/l) NO3 (mg/l) BOD (mg/l) COD (mg/l)
MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL
RAW EFFLUENT 239 6 738 21 143 4 5.6 1.7 3.2 0.5 35 6.2 368 256
P.S treated effluent 96 16 530 190 90 2.99 4.88 0.95 1 0.2 17 1.8 224 96
I.A treated effluent 315 23 718 201 147 2.18 4.7 0.2 0 0.2 16 3 192 96
135
Appendix Four: Weekly variations in water quality parameters after during treatment
with Ipomoea aquatica
PH TEMP (°C) DO (mg/l) EC (mg/l) TDS (mg/l)
WEEK MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL
0 4.14 7.72 30.5 33.6 0.17 6.3 5365 309 2683 154.5
1 7.38 6.45 25.2 25.1 2.1 4.3 3122 287 1901 143.5
2 7.22 6.06 29.1 29 3.5 4.8 3105 276 1552.5 138
3 7.77 6.75 32 32.2 1.9 5.5 3075 255 1537.5 127.5
4 7.65 7.19 25.8 22.7 4.1 6.7 2030 231 1015 115.5
TSS (mg/l) COLOUR (PtCo) TURBIDITY(NTU) (NTU) PO4 (mg/l) NO3 (mg/l) BOD (mg/l) COD (mg/l)
WEEK MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL MEAN CONTROL
0 239 6 738 21 143 4 5.6 1.7 3.2 0.5 35 6.2 368 256
1 315 23 718 20.1 147 2.18 4.7 0.2 0 0.2 16 4.3 192 160
2 35 10 664 19 20.2 5.4 3.9 0.1 3.4 0 15.1 3.2 160 128
3 70 3 533 15.2 54 1.8 5.64 1.2 1.4 0.8 18 1.8 96 64
4 31 15 334 10.4 12.9 6.3 8.24 7.04 33.6 0.3 4.1 0.9 64 32
136
Appendix Five: Questionnaire
UNIVERSITY OF GHANA
INSTITUTE FOR ENVIRONMENT AND SANITATION STUDIES (IESS)
QUESTIONNAIRE
One of the pressing environmental problems in the world today is water scarcity. It is
increasingly becoming important to seek alternative sources of water to supplement the
available water. One attractive option is wastewater treatment and reuse. This
questionnaire is designed to get your views on reuse of wastewater.
This questionnaire is solely for academic purposes and confidentiality is assured.
Please answer the following questions regarding the treatment and reuse of
wastewater.
(A) Demographic background (Please tick)
Gender M Age 18-30
F 31-40
41-50
51-60
Above 60
Highest level of education
(a)Primary
(b)JHS
© SHS
(d)Tertiary
(e)Other (Please specify)
Marital status single
Married
Widowed
Number of children……………………………………………………………
Place of residence……………………………………………………………
137
Monthly Income (GH¢) (Please tick)
Below 100
100-300
500-1000
Above 1000
(B) Environmental perceptions
1. How do you get water for domestic use? (Please tick as many options as
possible)
(a)Treated tap water
(b)Borehole
© River/stream
(d)Rain water harvesting
(e) Other (please specify)………………………………..
2. Do you have regular access to water? Yes/ No
3. If yes, how regular is your supply of water?
(a) Daily
(b) Once a week
(c) Once a month
(d) Other (please specify)……………………………………….
4. Do you consider water to be a scarce resource? Yes/No
5. What are some of the causes of water scarcity you know about? (Please tick
as many options as applicable)
(a) Water pollution
(b) Drought
(c) Depletion of aquifers
(d) Others (please
specify)……………………………………………………………………
………………………………………………………………………………
………………
6. What do you understand by the term “wastewater”?
(a) Any dirty and unclean water
(b) Water which has already been used
138
(c) Water which cannot be used any longer
(d) Others (please
specify)……………………………………………………………………
………………………………………………………………………………
…………….
7. What are some of the sources of wastewater you know about? (Please tick as
many options as applicable)
(a) Domestic washing
(b) Sewage
© Washing bay
(e) Industries
(f) Rainfall run off
(g) Others (please specify)
………………………………………………………………………………
………………………………………………………………………………
………………
8. Do you generate wastewater? Yes/No
9. If Yes, how do you generate wastewater?
(a) Domestic washing
(b) Work activities
(c) Others (please
specify)……………………………………………………………………
………………………………………………………………………………
………………
10. What do you do with wastewater generated at home? (Please tick as many
options as applicable)
(a) Throw it away
(b) Flushing toilet
(c) Irrigation
(d) Others (please
specify)……………………………………………………………………
………..
139
11. Do you have access to a toilet facility? Yes/No
If yes, indicate (by ticking) which toilet facility you have access to.
(a) Water closet
(b) KVIP
(c) Pit latrine
(d) Open defecation
12. Do you have any idea about how the faecalmatter generated by humans is
disposed off? Yes/ No
13. If yes, please indicate (by ticking), the methods of disposal you know about
(a) Dumping into the sea
(b) Irrigation of crops
(c) Treatment to produce compost
(d) Treatment to produce Biogas
(e) Others (please
specify)…………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
……………………….
14. Are you familiar with the concept of wastewater reuse? Yes /No
15. Do you support the idea of wastewater reuse? Yes/No
16. If yes, what are your reasons for supporting wastewater reuse? (Please tickas
many options as applicable)
a. Wastewater reuse is good for the environment
b. Wastewater reuse conserves water
c. Wastewater reuse will minimize dependency on treated water
17. Do you know of any health risks associated with wastewater reuse? Yes/No
18. If yes, please indicate (by ticking) the health risks you know about
(a) Cholera
(b) Bacterial infections
(c) Diarrhoea
(d) Others (please
specify)……………………………………………………………………
………………………………………………………………………………
…………….
19. Do you know how the health risks mentioned above can be minimized or
prevented? Yes/No
(a) By treating water before use
140
(b) Avoiding the use of wastewater
(c) Others (please
specify)………………………………………………………………………………
………………………………………………………………………………………
……………….
20. The Millenium Development Goal 7 targets that the proportion of the
population without sustainable access to safe drinking water and basic
sanitation be halved by the year 2015. Can this be achieved? Yes/No
21. Please indicate ( by ticking) whether you support the following options for
wastewater reuse
Wastewater
reuse option
Strongly
agree
Agree Not
sure
disagree Strongly
disagree
Irrigation of
food crops
Fire fighting
Industry
Construction of
buildings
Toilet flushing
Public
park/sports field
irrigation
Commercial car
wash
Swimming pool
Aquifer
augmentation
General
cleaning and
laundry
22. Would you recommend wastewater use to your community? Yes/No