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Complexity International Journal (CIJ)

Volume 23, Issue 3, August-Sept 2019,

Available online at http://cij.org.in/Currentvolumeissue3.aspx

Impact Factor (2019): 5.6 www.cij.org.in ISSN Online: 1320-0682.

http://cij.org.in 84 [email protected]/[email protected]

SEWAGE TREATMENT PLANT AND ITS EFFECTS ON

SURROUNDINGS

J. RAMYA REDDY*, CH.BABU**

PG SCHOLAR*,ASSISTANT PROFESSOR**

GANDHI ACADEMY OF TECHNICAL EDUCATION

(Approved by A.I.C.T.E, New Delhi Affiliated to JNTUH) Ramapuram(V), Chilukuru(M), Suryapet District, T.S-508206

ABSTRACT:An increase in world human population, along with extensive growth of

industrialization and agriculture, have culminated in the production and accumulation of huge

quantities of waste around the world. This waste is solid, liquid and gaseous in nature. The spread

of disease-causing microorganisms, endotoxins, smells and particulate matter in the environment is

an inescapable consequence of waste generation and waste management. Thus, the risk of

infections associated with Sewage treatment plants (STPs) has become of a particular importance

in recent decades. Sewage and unstable sludge contain various pathogens such as viruses, bacteria,

and human and animal parasites. These pathogens can invade into the surrounding air in sewage

mist of droplets, which is produced during aeration or general flow of the sewage. Bioaerosols

produced during sewage treatment can therefore become a likely health hazard to the workers,

working in such plants or to residents of the surrounding areas. This project is primarily has two

objectives, firstly, to characterize the type of pathogens and other polluting elements in the air

surrounding the STP, and, secondly, suggestion of different methods to reduce and arrest such

aerosols from being released into the air. The quantum of people’s exposure to airborne endotoxin,

fungi, bacteria and other allergens might change significantly based upon the category and the

capability of a plant, type of the amenities, performed activities and meteorological conditions. This

project is implanted by taking samples of air near an STP and from areas where effect of STP is

low. Comparison is performed to gauge the different compounds present near a STP. The STP

taken for this project is the one besides Hussain Sagar, the reason for choosing this STP is that

there is huge number of people living near it and can have grave consequences for them. To

further develop the project as part of future work the suggested reduction methods have to be

applied and compared to identify the best method for reduction of bioaerosols.

Keywords: Sewage treatment plant, bioaerosol, pathogens, viruses, air borne diseases

I. INTRODUCTION

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Recent awarenesses about the risks posed by airborne microorganisms are the reason for the

enormous development of aeromicrobiology. However, it seems that there is no

internationally accepted threshold limit value for biological contamination of air (1). This is a

complex problem involving many interactions, among others, individual immunity system.

Therefore, the ascertainment of microorganisms presence, especially as indicators in the air at

a given site, is generally accepted as synonymous with the term ―range emission‖ of the

tested facility and an estimation of the potential risk zone (2). Atmospheric air, having

limited self-purification ability, is an important component of the environment, so that there

is a need for its maximum protection. It should consist primarily in reducing emission into the

atmosphere, since air pollutants occurring there may be transferred by the wind over very

large distances (3-11). According to Griffin et al. (5), bioaerosols can be transported within

and between continents on upper air currents. Some culturable microorganisms have been

detected as high in the earth’s atmosphere as 20,000 m. Papke et al. (12) showed that

microbes were viable even after being transported several thousand kilometres and were

capable of causing an infection (e.g. the epidemic of meningitis, which spread from the

African belt to Scandinavian countries). The microorganisms found in the air are usually

accidental and commensal. They appear as the large number of sporulating forms, such as

bacteria’ endospores and spores of fungi. Less numerous are the pathogenic microorganisms;

however, they pose a direct threat to human and animal health. Contamination of the air by

microorganisms, including pathogenic ones, generates from various sources, both natural,

such as water, soil or rotting plants and animal remains, and anthropogenic, including

municipal landfills and sewage treatment plants. Pathogens, mainly found in excreta (13,14),

and secretions of patients are transferred in general by sewage and municipal waste from

households and hospitals, creating unspecified health hazard in the surroundings of WWTPs.

The generation, treatment, and disposal of the human and animal waste contribute to the

increase in the production of bioaerosols containing a wide variety of microbial pathogens

and related pollutants. Bioaerosols might be a vehicle for the dissemination of human and

animal pathogens from wastewater. Their presence in the air might pose a potential

epidemiological threat. This review is intended to summarize the information on bioaerosols

and highlight the significance of bioaerosols emitted during municipal waste treatment for

public health and condition of the environment. Comparing the degree of contamination with

bioaerosols generated by WWTPs which use different types of sewage treatment systems,


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seems to be particularly important. The determination of the spreading range of bioareosols

allows defining the size of the potential health hazard zone to workers of WWTPs and

inhabitants of the surrounding areas.

WASTEWATER TREATMENT PLANTS AS A SOURCE OF MICROORGANISMS

The production of urban wastewater and sludge is increasing on a global scale, because more

cities are being connected to wastewater treatment plants. Domestic and industrial

wastewaters are collected by an extensive network of sewer lines and treated at municipal

plants. Commercial and industrial establishments have to pretreat their wastewater to varying

degrees before they are released into the sewer lines. In order to eliminate the

microorganisms present in the sewage (especially in the case of the effluent from hospitals

with infectious diseases wards) disinfection processes are performed. They can be divided

into physical methods (ultrasound, UV) and chemical (chlorine gas, sodium hypochlorite,

chlorine dioxide, ozone). At the treatment plant, the wastewater undergoes: preliminary

treatment - floatables, grit and grease removal; primary treatment - gravity sedimentation to

remove suspended solids; secondary treatment - biological treatment to reduce biochemical

and chemical oxygen demand (BOD and COD respectively) and remove suspended solids;

and in many cases tertiary treatment - biological removal of nitrogen, mainly chemical or

biological removal of phosphorus, disinfection. The solid components accumulated at each

treatment stage are generally referred to as sludge or biosolids. The quantity and the

characteristics of the sludge depends on the type and volume of wastewater and the treatment

kind used (50). Sludge undergo treatment at the wastewater treatment plant before they are

used or disposed of. Two common treatments are dewatering followed by stabilization. The

dewatering procedures are air-drying, vacuum filters, centrifugation, and belt filter presses.

Stabilization processes, such as lime stabilization, anaerobic and aerobic digestion,

composting and or heat-drying, are used to reduce organic matter, pathogen levels and odours

in sludge. Recycling the sludge as an organic fertilizer is environmentally friendly, but

among the large diversity of microorganisms found in urban wastewater, some pathogens can

be present (viruses, bacteria and parasites) (51) and such microorganisms are concentrated in

sludge during the treatment of wastewater. Furthermore, some of these pathogens are known

to survive for several months in the environment (52). Chun-Ming et al. (53) observed that

some pathogenic bacteria such as E. coli O157:H7 cells survived in composting process even


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at 54 to 67°C. Therefore, monitoring of pathogens during wastewater and sludge treatment

enables to evaluate the efficiency of the process in terms of sanitization (54).

Bacteria, moulds and yeasts in the sewage and sludge

The degradation of organic substances in WWTPs is mainly a result of the activities of

aerobic and facultative anaerobic heterotrophic bacteria and heterotrophic fungi. Numerous

saprophytic and opportunistic organisms, and sometimes pathogenic or potentially pathogenic

microorganisms occur in the raw wastewater of all types of treatment plants, regardless of the

origin of sewage (55,56,57). The microflora of wastewater is as varied as the composition of

pollutants. The highest amounts and the most diverse of microorganisms are found in a

domestic sewage along with human and animal excreta, which may include bacteria:

Aeromonas, Acinetobacter, Campylobacter, Clostridium, Enterobacter, Enterococcus,

Escherichia, Klebsiella, Mycobacterium, Pantoea, Pseudomonas, Serratia, Staphylococcus,

Salmonella, Shigella and Vibrio (34,35,38,54,57-61), as well as filamentous fungi from genus

Alternaria, Aspergillus, Cladosporium, Penicillium, Trichoderma and numerous yeasts and

yeast-like fungi like Candida, Cryptococcus, Geotrichum and Rhodotorula (57,62-65).

Elimination of microorganisms in the process of sewage treatment is the result of a

combination of physical (sedimentation, filtration, adsorption), chemical (redox potential,

toxicity, changes in the pH value) and biological factors (competition for nutrients, grazing

by protozoa, lytic activity of bacteria and bacteriophages, the production of bacteriocins)

(66,67). As Korzeniewska et al. (57) reported the numbers (CFU – colony forming units – in

1 cm3) of heterotrophic mesophilic bacteria, Enterobacteriaceae bacteria, moulds and

yeast/yeast-like fungi in untreated wastewater ranged from up to 1.9.×105– 6.4.×107, 2×105–

4×107, 1.0.×103–3.0.×103 and from 8.5.×103 to 5.0.×104, respectively. Therefore treatment of

sewage could be not only a source of emission of chemical compounds, but also many

bioaerosols which pollute atmospheric air and might become a threat to human health

(58,62,68). The character and range of the environmental effects produced by a WWTP

depend on the initial concentration of microorganisms in sewage as well as their growth

phase, emission threshold level, sewage treatment technology, aeration techniques (69,70,71),

meteorological and environmental conditions (35,57,61,72).


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Pathogenic and potentially pathogenic microorganisms in the sewage

Pathogens that are present in raw wastewater are also present, in concentrated amounts, in

unstable sludge. Concentrations and types of pathogens in treated sewage and biosolids

depend significantly on the origin of waste and the type of their purification process

(34,38,55,57,60). Although aerobic and anaerobic wastewater treatment processes reduce

bacteria number in the sewage, some pathogens can remain in the sewage outflow and the

final biosolid product. Studies have shown that aerobic and anaerobic treatment units remove

faecal coliforms from sewage with efficiency up to 90–99.9.9% (55,73). Jones (74) has also

reported a significant reduction of Campylobacter bacteria when the sewage undergoes

activated sludge treatment. The reduction of pathogens during treatment processes can vary;

depending on how precisely the process is controlled. Even with a 1–2 order of magnitude

decrease in bacterial and viral numbers, the actual concentration of microorganisms in the

treated wastewater and biosolids can still be significantly high. As Filipkowska (55),

Espigares et al. (59) and Kay et al. (56) reported, although the sewage purification system

was efficient and reduced the contamination load to the low level and removed a great

percent of indicator bacteria (even above 99%), the purified sewage could be a source of

many pathogenic bacteria in the inland waters. These bacteria are often characterized by

multiple resistance, showing a cross-resistance to multiple antibiotics simultaneously (75,76).

Examples include bacteria belonging to the family Enterobacteriaceae (77). Among them,

bacteria from Salmonella, Shigella, Escherichia, Klebsiella, Serratia, Enterobacter or

Proteus genera deserve a special attention. Since the 80s, an increase in the number of

infections caused by these bacteria has been observed. They have been found to be one of the

most important etiological agents of systemic infections (78-81). E. coli is a common cause

of urinary tract infections, Klebsiella spp. and Enterobacter spp. cause pneumonia, while all

Enterobacteriaceae are associated with blood infection (sepsis), peritonitis, and

gastrointestinal infections. Bacteria of the genus Salmonella, which produce toxins are

responsible for typhoid and paratyphoid fever. The natural habitat of these bacteria is the

gastrointestinal tract of humans and animals and the entries of infections are mainly

gastrointestinal, respiratory, urinary, biliary, wound and soft tissue. E. coli, which has the

ability to encode genes of multiple resistance, is a physiological component of the microflora

in the colon and naturally inhabits the gastrointestinal tract of humans and animals, both sick


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and healthy. Feuerpfeil and Stelzer (82) found that 80.5.% of the faeces samples of healthy

people contained coliform bacteria resistant to some antibiotics, the microorganisms were

frequently resistant to several antibiotics simultaneously. Along with these excrements,

microbes get into the domestic and municipal sewage. After having been collected in

treatment plants and even in well-functioning biological plants, huge quantities of these

bacteria get to the environment with treated sewage (83). Reinthaler et al. (84) ascertained as

many as 102 CFU/ml resistant coliform bacteria in the effluent of a large treatment plant.

About 17% of those bacteria had a six-fold resistance to antibiotics. Together with purified

sewage, they can penetrate the soil, surface water, rural groundwater supplies, municipal

drinking water and also accompanied by bioaerosols - the air. Their presence is an underlying

cause of an increasing public health problem.

LITERATURE REVIEW

Jadhav and Savant (1975) analyzed the spent wash for its composition and reported pH as

8.00; electrical conductivity as 31 dSm-1 and nutrients such as total nitrogen as 0.14 per cent;

phosphorus as 0.12 per cent; potassium as 1.36 per cent; calcium as 0.01 per cent; magnesium

as 0.17 per cent; and COD as 1300 ppm. Verma and Dalela (1976) observed a very high

sensitivity of some fresh water fish to diluted spentwash.

Kulkarni et al., (1987) stated that spentwash was major pollutant because of its high organic

load. They considered spentwash as dilute liquid organic fertilizer with high K content and

further reported that it contained about 90 to 93 per cent water and 7 to 9 per cent solids.

Instances of large scale mortality of fish in river Gomti due to distillery effluent had been

reported by Joshi (1990). Letting distillery effluent into river Ganga resulted in high

concentration of organic matter and salts, which has been responsible for decreased pH and

increased BOD, COD and total dissolved solids in river water (Chauhan, 1991).

Problems arise due to the increase of metal ions in biosphere with continuous application

onto soils. These metals have toxic impact on metabolism of living organisms when they

exist beyond their respective safe limits in soils, vegetables and crops. These metals get their

way, through food chain, in the bodies and produce health hazard effects on animals and

human beings. According to the surveys, from public health services of under developed


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countries, large number of people has been exposed to health hazards of excess metals

through municipal water supplies (WHO, 1990, 1994, 1996). The increasing amounts of toxic

metals emitted into the biosphere, as a result of fast industrialization and urbanization, cause

permanent threatening to the ecosystem also. In various under-developed countries, untreated

sewage and industrial effluents are utilized for the cultivation of crops and vegetables

(Ibrahim and Salmon, 1992). Impact of sugar mill and distillery effluents on water quality of

river Gelabil, in Assam, during the operational periods of the mill and also after its closure

have been studied during the year 1990-91 by Baruah et al., (1993).

Joshi et al., (1994) noticed groundwater contamination by effluent with high BOD and salt

content near the lagoon sites in most of the distilleries. In some cases, particularly in

Maharashtra the color problem in groundwater was so acute that distilleries had to provide

potable water to surrounding villages. Unprocessed effluents contain heavy metals,

microorganisms and organic pollutants (Khan et al., 1994).

Bhat (1994) analyzed the distillery effluent of Ugar sugar works Ltd., Ugarkhurd and

reported that pH of raw spent wash as acidic (4.03) which increased to 7.62 during lagooning.

BOD and COD values of effluent were found to be drastically reduced by lagooning and

diluting with Krishna river water.

Joshi et al. (1996) found that the distillery effluent contained large amounts of organic matter,

N, P, K, S, Ca besides high salt load, sulfates and chlorides of K, Na and Ca. Rajukannu and

Manickam (1996) reported that spent wash was highly acidic having a pH range of 3.8 to 4.0.

The distillery effluent contains N, P, K, Ca, Mg and SO4 (Devarajan et al., 1996) and it is

thus valuable fertilizer when applied to soil through irrigation water (Zalawadia et al., 1997).

Ashok Kumar et al. (1998) conducted a field survey for assessing groundwater quality and

salinity build up in irrigated soils of Sikandarabad area of Bulandshahar district, Uttar

Pradesh as influenced by irrigation with mixed industrial effluents of various industries.

Samples of effluent from irrigated fields were collected and analyzed for different

characteristics. Annadurai et al., (1999) reviewed the data on characteristics of spent wash.

The standards are set with the assumptions that the environmental media have the capacity to

assimilate the pollution load so that no environmental problems will arise. However, when


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the assimilative capacities of the environmental media (surface water bodies or land)

reach/cross the limits, large-scale pollution of surface water and groundwater occurs. Such

instances have been recorded from industrial clusters in various parts of the country - Ambur;

Thirupathur; Vellore; Ranipet; Thuthipeth; Valayambattu and Vaniyambadi of Vellore

District, Kangeyam; Dharapuram and Vellakoil of Erode District, Tiruppur at Coimbatore

District and Karur at Karur District in Tamil Nadu (Thangarajan 1999; Sankar 2000;

Appasamy and Nelliyat 2000; Nelliyat 2003, 2005); Vadodara, Bharuch, Ankleshwar, Vapi,

Valsad, Surat, Navsari,

Ankleswar in Gujarat (Hirway 2005); Thane – Belapur in Maharashtra (Shankar et al.

1994); Patancheru, Pashamylaram, Bollarum, Katedan, Kazipally, Visakhapatnam in Andhra

Pradesh (Shivkumar and Biksham 1995; Subba Rao et al. 1998; NGRI 1998; Gurunadha Rao

et al. 2001; Subrahmanyam and Yadaiah 2001; Behera and Reddy 2002); Ludhiana,

Amritsar, Jalandhar, Patiala, Toansa and Nangal - Ropar District in Punjab (Tiwari and

Mahapatra 1999; Ghosh 2005).

Water quality problems related to the disposal of industrial effluents on land and surface

water bodies, are generally considered as a legal problem – a violation of environmental rules

and regulations. However, Indian pollution abatement rules and regulations provide options

to industries to dispose their effluents in different environmental media, like on surface water

bodies, on land for irrigation, in public sewers or marine disposal, according to their location,

convenience and feasibility. There are different prescribed standards for different effluent

disposal options (CPCB, 2001). As far as industries are concerned, their objective is to meet

any one of those standards, which is feasible and convenient for them to discharge their

effluents.

Analytical data of distillery effluent collected from the Coimbatore alcohols and chemicals

Ltd., situated on the banks of river Bhavani were reviewed by Kailasam et al., (2001). Anil

kumar et al., (2003) studied the effect of distillery spent wash on some soil characteristics and

water. The effluent from Sri Sadilal distillery situated at Mansurpur (Dist: Muzafarnagar)

falls into the liver Kali. Chemical composition of untreated distillery spent wash and primary

treated distillery effluent was studied by Haroon and Bose (2004).


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Kolhe and Pawar (2011) collected the treated and untreated effluents samples from dairy

industry and analyzed for physico-chemical parameters like pH, temperature, color, DO,

BOD, COD, TDS, TSS, TS, Chloride Sulphate, Oil and grease.

Boom et al (Boon and Soltanpour, 1992) found the same pattern for lettuce, potato, radish

and carrot along with eighty vegetable samples. Fardy et al., (1992) determined the

concentration of Manganese in Australian vegetables such as pumpkin, potato and carrot.

Ado-Ekiti (1995) observed that concentration of Cu, Pb and Zn in lettuce, tomato stalk,

leaves and fruit tissues generally increased in the Granby and fox soils.

Heavy metals (Mn, Cd and Co) tended to accumulate more in leaves than their respective

fruits of okra, bitter guard, mint and spinach. The vegetables cultivated with fresh water in

different countries of the world such as Pakistan (Masud and Jaffar, 1997; Husaini, 2005),

Iraq (Al-Jabori et al., 1992), Italy (Fidanza et al., 2003), Poland (Gzyl, 1990), China (Haiyan

and Stuanes, 2003) and India (Phukan and Bhattacharya, 2003) were analyzed for major,

minor and trace elements and were found contamination free, with a couple of exceptions.

Growing vegetables and crops with industrial effluents for longer periods may guide to

accumulate the trace metals in soils up to toxic levels. This could be of particular importance

where vegetables are grown. Vegetables sampled from pollutant free areas contained

concentrations of metals at permissible levels (Atta et al., 1997). Spinach and cauliflower

grown with canal water had better-looking quality and taste than irrigated with effluent (Khan

et al., 1998). Normally, vegetables grown on sewage/ effluents applied soils accumulated

high concentration of metal ions like Cd, Cu, Ni, Pb and Zn.

Qadir et al., (1999) presented a comprehensive review about the metal poisoning in more than

12 vegetables, irrigated with city effluent. In general, correlation between concentration of

metals in soils and vegetables is said to be unpredictable (Kashem and Singh, 1999). They

reported that not only species differed significantly but also different anatomical parts of the

same species changed in level of contamination with Pb and Cd. Concentration of Pb and Cd

was maximum in leaves (Spinach lettuce) followed by root and tuber (radish & carrot),

cabbage (various types of cabbages & cauliflower), bulb (onion & garlic) and fruits (tomato

& nipper green bean). The city effluent is a big source of heavy metals (Ahmad and Rizvi,

2003) like Cd, Cr, Ni and Zn, which may accumulate in the edible portion of the vegetables


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and cause different diseases through human food chain. Rainwater chemistry has an impact

on adsorption-desorption reactions in the soil system, for example, an acid rain event may

trigger a significant amount of the adsorbed proportion of heavy metals/metalloids in the soil

to become mobile which otherwise would remain stable under the prevailing conditions

(Morgan and Woodland, 1990; Gao and Kwak, 1997). The physico-chemical properties of

the soils were analyzed by Tariq et al., (1995). Soil texture was mostly sandy loam, which

exhibited slight variations in the water-holding capacity.

SALIENT FEATURES OF HUSSAIN SAGAR LAKE:

The watershed of the lake extends from Kukatpally and Jeedimetla to the heart of the city and

covers parts of the Northern and Western areas of the city and its surroundings. The

watershed exhibits undulatory to rugged topography with a slope due south-South East. The

lake with the grand monolith of the Buddha near its center stands out as one of the most

picturesque spots of the city. This Buddha monolith was installed in 1992 and is 52 ft in

height. With passage of time and urban development and migration of people from other

areas, the ecology and environment of these lakes has been disturbed. The most affected

among all the lakes is the Hussain Sagar Lake. This lake has been receiving untreated waste

and industrial effluents through the four main nalahs. The lake is mainly fed by the

Kukatpally nalah, which contributes domestic and industrial effluents from the Kukatpally

industrial area. The other nalahs, Picket, Banjara and Balkapur carrying untreated waste also

have outfalls into the Hussain Sagar thereby deteriorating the water quality of the lake.

Due to the influx of polluted water into the Huissain Sagar Lake and deterioration of water

quality of the lake it is no more a resource for water supply. The lake receives its inflows

from four nalahs. The average annual rainfall of the city is 75 cm and the average run-off into

the lake is about 30 million cubic meter. A part from the rain water following domestic and

industrial waste water enter the lake as dry weather flows.


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Sl. No.

Name of the Nalah

Domestic Flow

(in Mld)

Industrial Flow

(in Mld)

Total Flow

(in Mld)

1 Kukatpally Nalah 55 15 70

2 Picket Nalah 6 --- 6

3 Banjara Nalah 6 --- 6

4 Balkapur Channel 13 --- 13

TOTAL 80 Mld 15 Mld 95 Mld

Characteristics of Sewage:


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Physical Characteristics: Odour, colour, turbidity and temperature are physical

characteristics. The septic sewage give offensive odor of hydrogen sulphide, colour is turbid

and dark resembling dirty dishwater and temperature is higher than that of the water supply

because of heat added during the utilization of water.

Chemical Characteristic: Fresh sewage is alkalic but septic sewage is acidic and the pH

varies in between 6-7. Sewage contains 0.08 to 0.1 percent solid matter in the form of

suspended, dissolved, collided and settleable. The solid sewage comprise of both organic and

in organic matter. The organic matter is 45% of total solids consists of animal and vegetable

matter, sugar, starches, cellulose, fats, kitchens, laundries etc. The inorganic matter is 55% of

solids and consists of minerals and salts such as sand, gravel, debris, dissolved salts,

chlorides, sulphates etc. Besides solids, liquids, gases like H2S, Co2 and CH4 due microbial

action are present in sewage.

Biological Characteristics: Large number of bacteria and living organisms like algae, fungi,

protozoa etc., are present in sewage. Most of these bacteria are harmless to man and help in

converting the organic compounds of sewage into simple stable organic and mineral

compounds resulting in purification of sewage. Some of the bacteria however particularly

pathogenic type are harmful and cause disease. The bacteria useful in sewage treatment are

known as metatrophic group and they are further sub-classified as aerobic, anaerobic and

facultative. Aerobic bacteria live on free oxygen of air and on dissolved oxygen in water and

convert organic compounds of sewage in to simpler, stable and un-objectionable organic and

mineral compounds resulting in purification of sewage. For example aerobic bacteria

decompose Nitrogen, Carbon, and Sulphur into stable and unobjectionable compounds of

Nitrates, Carbohydrates and Sulphates and process is known as Oxidation.

Biochemical Oxygen Demand (BOD): The biochemical oxygen demand (BOD) is one of the

most important parameters and is a measure of organic matter present in wastewater. The

BOD is a measure of the amount of oxygen used in the respiratory process of micro

organisms in oxidizing the organic matter in the sewage and for the further metabolism of

cellular components synthesized from the wastes. One of the primary reasons for treating

sewage or waste water prior to its being returned to the water resources (stream or lake) is to


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reduce the drain of dissolved oxygen supply of the receiving body of water. The magnitude of

the BOD is related to the amount of organic material in the sewage i.e. the more oxidizable

organic material, the higher the BOD. The “strength” of sewage is expressed in terms of

BOD level.

Microbiological Characteristics: Since the composition of sewage various, it is to be

expected that the types and number of organisms will fluctuate. Fungi, Protozoa, Algae,

Bacteria and Viruses are present. Raw sewage may contain millions of bacteria per milliliter

including the coliforms, streptococeige, and anaerobic spore forming bacilli, the proteus

group and other types originating in the intestinal tract of humans. Sewage is also a potential

source of pathogenic protozoa, bacteria and viruses. The causative agents of dysentery,

cholera and typhoid fever may occur in sewage. The poliomyelitis virus, the virus of

infectious hepatitis and the Coxsackie’s viruses are excreted in the spices of infected hosts

and thus may appear in sewage, certain bacterial viruses are readily isolated from sewage.

Predominant physiological types of bacteria may shift during the course of sewage digestion.

In an anaerobic digester facultative types (Enterobacteria, Alcaligenes, Escherichia,

pseudomonas etc) predominate during initial stages. This is followed by methane producers,

which are strict anaerobes. For eg: Methanobacterium, Methanosarcina, and Methanococcus,

the organic acids produced by the facultative bacteria are metabolized by the methane

formers; the end products are methane and carbon dioxide. Large amounts of the gases are

produced in anaerobic digesters. The various process associated with treatment of sewage

bring about pronounced changes in the predominant types of organisms. The decomposition

of Nitrogen, Carbon and oxidation through the agency of the aerobic bacteria are parts of

famous Nitrogen, Carbon and Sulphur cycles. In Nitrogen cycle, the Ammonia in sewage is

oxidized first to Nitrates and then Nitrates which are final stable compounds by aerobic

bacteria. In Sulphur cycle, the Hydrogen Sulphide is oxidized by the aerobic action into

inoffensive sulphates. In Carbon cycle, the organic matter containing cellulose, starch and

sugar are transformed into carbohydrates. The above principle is used in biological process in

aeration tank. In this particular plant extended aeration with 21 hours of detention time,

extending the bacteria’s life upto endogenous respiration of the growth curve for the BOD

removal of about 9% and high – suspended solids removal is used. For good, biological


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process in aeration tank a MLSS of 3000-5000 mg/l and a dissolved oxygen level of 2 mg/l

are required and the same are being maintained.

CONCLUSIONS:The transfer of the microorganisms from wastewater to the air occurs

mainly during the mechanical (moving of raw sewage) and biological (aeration of wastewater

in bioreactor) phases of sewage purification. Allergic rhinitis and asthma, chronic bronchitis,

extrinsic allergic alveolitis, and organic dust toxic syndrome (ODTS) are major groups of

respiratory diseases associated with exposure to bioaerosols from WWTPs (44). The

exposure of sewage workers and habitants of WWTP surroundings to airborne bacteria, fungi

and endotoxin may vary depending upon the type and capacity of the facility, performed

activities and weather conditions. The flow rate and the composition of the sewage and air

humidity play a predominant role in increasing the concentrations of the bioaerosols.

According to many authors, the sites of pre-treatment and the primary clarifiers, as well as

those sites containing moving mechanical equipments for water aeration, are the steps with

the highest emission of bioaerosols. The aeration system used in the biological process

greatly affects the amount of bioaerosols generated. Moreover, wind speed and its direction

are important factors governing the bioaerosol dispersion once they are airborne.

Consequently, workers of these sites may be exposed to harmful levels of bioaerosol.

Therefore, in order to eliminate emission of bioaerosol and significant decrease of the number

of airborne microorganisms, covering grit tanks, section of raw sewage’s influent to the

primary settling tanks and aeration chambers seems to be necessary.

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