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Treated Wastewater Management and Reuse in Arid Regions:
Abu Dhabi Case Study
Mohamed A. Dawoud, Osama M. Sallam and Mahmoud A. Abdelfattah
Water Resources Department, Environment Agency – Abu Dhabi, P.O. Box 45553, UAE
Email: mdawoud@ead.ae
Abstract
In arid regions treated wastewater is an environmental, social, and economic resource
that needs to be managed in appropriate way. Reusing of treated effluent that is
normally discharged to the environment from municipal wastewater treatment plants is
receiving an increasing attention as a reliable water resource. In the last three decades,
rapid economic development coupled with population growth and large agricultural
sector expansion have forced the government to rely on non-conventional water
resources such as desalination and treated wastewater as secondary sources for
irrigation water supply. Treated wastewater has the most potential as marginal water
suitable for growing forages, landscaping, fruit orchards and non-vegetative crops. In
Abu Dhabi Emirate, the annual production of treated wastewater is about 450 million
cubic meters which is about 7.2% of the total Emirate water production. Only about
60% of the treated wastewater is reused in wetlands, landscaping, and recreation areas
due to the capacity of distribution system after treatment. The aim of this paper to
discusses Abu Dhabi strategies for assessing the alternative options for reusing the
treated wastewater including irrigating agricultural crops with recycled wastewater
which has been practiced in arid and semi-arid regions through i) reviewing the present
statues of treated waste water ,ii) the need for this resource, iii)Treated Wastewater
Reuse options and vi)presenting the pilot project in Alwathba area for enhancement the
treated waste water to be suitable for crops irrigation in same time to save groundwater
which has been using currently for crops irrigation in Alwathba area The main results
and recommendation are, i) using treated waste water will save the groundwater
resources for emergences cases ,ii) continuances monitoring of treated waste water
output to ensure that it meets the required water quality standard and maintenance
measures to prevent ageing/wear and tear of plant items and iii) establishing a five year
monitoring program, which would provide independent and robust data on the
performance of the plant and the impact of polished effluent on irrigated land.
Keywords: Environment, Treated Wastewater, Abu Dhabi, UAE, Soil, Agriculture, Aquifer
Recharge.
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1. General Background
Wastewater reuse has drawn increasing attention worldwide as an integral part of water
resources management. Such a move is driven by two major forces: scarcity of
freshwater resources and heightened environmental concerns. Meanwhile, economical
considerations are also becoming increasingly important amid the introduction of
market-based mechanisms in environmental and water resources management.
Reclaimed wastewater from municipalities and industries has been used as an additional
source of water supply in many parts of the world, especially in areas where water
resources are scarce and population and economic growth is rapid.
The situation in Abu Dhabi is a typical case in point. Reclaimed wastewater can be used
for many purposes, including agricultural irrigation, groundwater recharge, car washing,
toilet flushing, urban lawn watering and recreational amenities, road cleaning, etc. Of all
the users of reclaimed wastewater, public gardens irrigation has been by far the major
user in many areas in Abu Dhabi Emirate where wastewater is reused. This is mainly
because of the large water use in irrigation, relatively low quality requirement, and
relatively low cost of infrastructure for the irrigation water supply. Reclaiming and
reusing the wastewater is not a new concept. The practice can be traced back to several
centuries ago. In the scientific literature, there are a large number of studies on
wastewater treatment from technological and engineering aspects. Concerns on health
impacts of using reclaimed wastewater, especially for irrigation and groundwater
recharge have also drawn an increasing attention in the last decade. However, studies of
the economic viability and institutions of wastewater reuse have been few.
Treated domestic effluent is a valuable extra water source that can be reused for diverse
purposes, primarily for agriculture production, aquatic life preservation, and aquifer
recharge. Groundwater enrichment with effluent is maintained primarily via Soil
Aquifer Treatment (SAT) (Quanrud et al. 2003). Advanced wastewater treatment is
required in order to maintain adequate levels of sustainable agriculture production,
decelerated Stalinization processes of the ground waters and to prevent long range
adverse effects of gradual environmental pollution (Rebhun 2004). Complying with
these challenging goals can be attained mostly by implementing the membrane
technology (Lopez et al. 2003).
Abu Dhabi Emirate is an arid region where the average annual rainfall is less than
100mm. The water resources components found within the Emirate are traditional or
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conventional resources (rainfall, springs, wadis, sabkhas, lakes, ponds and groundwater)
and non-traditional or unconventional resources (desalinated water and treated
wastewater). Groundwater occurs in the Emirate as either consolidated or
unconsolidated surficial deposit aquifers or as bedrock/structural aquifers and
contributes 63.6% to the total water demand, followed by desalinated water (29.2%) and
treated wastewater (7.2%) as shown in Figure (1). Groundwater supply is decreasing
and the imbalance between supply and demand is being filled by ever increasing
amounts of desalinated water (EAD, 2009a).
Although wastewater reclamation and reuse has been recognized as a promising strategy
to alleviating water scarcity and reducing the impacts on the environment, the actual
reuse of treated wastewater is rather limited. In Abu Dhabi Emirate only 60% of the
total treated quantities are reused and the rest are discharged to environment (RSB,
2009). Increasing the reused volumes will relief the pressure in using costly desalinated
water and the over-abstracted brackish groundwater as show in Figure (2).
Figure 1: Abu Dhabi Water Resources
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Figure 2: Water use in Abu Dhabi Emirate
2. Treated Wastewater Production
2.1 Present Status
Abu Dhabi has treated domestic and municipal wastewater in centralized treatment
facilities since 1973. The Emirate has continued with its development of excellent
wastewater treatment facilities. There are now 32 wastewater treatment plants, split
equally between the Western and Eastern regions. Combined, they produce about 244.7
million m³/yr. Zakher (Al Ain) and Al Mafraq (Abu Dhabi) plants produce 94% of all
treated effluent, which is mostly used for irrigation of parks, gardens and other
recreation amenity areas. The main wastewater treatment plant serving the Abu Dhabi
city is Al Mafraq plant with a maximum design capacity of 260,000 m3/day. The main
sewage treatment plant serving Al Ain City is Zakhir plant with a maximum capacity of
54,000 m3/day. The plant is currently operating at peaks of 120,000 m
3/d, which
increases a risk of deterioration in the quality of effluent and sludge produced, as well as
the risk of by-pass influent to the percolation area at the rear of the treatment plant. The
other STPs are quite small, but because of remote urban expansion, some are now over-
loaded and are presently being prepared for upgrading (Figure 4).
Due to the increasing number and size of developmental and industrial projects planned
in the emirate of Abu Dhabi, an increase in the demand for sewage treatment plants is
expected. The main sewage treatment plants currently operating in the emirate of Abu
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Dhabi are heavily overloaded, leading to the generation of low quality treated effluent.
Furthermore, the overload could result in disposal of raw sewage in the marine
environment and/or desert. During emergency situations in the sewage treatment plant,
more than 25% of the raw sewage inflow is diverted to the marine environment creating
environmental crisis to marine quality and ecology. The Discharge point of excess
treated effluent and over flow line is located at the Musaffah Industrial Area south
channel. In 2005, the management of all STPs became the responsibility of the newly
formed Abu Dhabi Sewage Services Company (ADSSC), under the regulatory control
of the Abu Dhabi Regulation and Supervision Bureau, which is also responsible for
regulating the potable water and electricity sectors.
Figure 4: Location of Abu Dhabi Main Wastewater Treatment Facilities.
3.2 Future Wastewater Treatment Plants
A phased expansion of the sewerage system and reclamation and reuse infrastructure
has been planned to accommodate the development of Abu Dhabi. The Strategic Tunnel
Enhancement Program (STEP) will construct a sewage tunnel twenty meters below the
surface of Abu Dhabi. The building works are expected to be completed by 2013. In
addition, a private company – Al Etihad Biwater Wastewater Company – has been
licensed to construct four large wastewater treatment facilities. The first two of these at
Al Wathba will serve Abu Dhabi, and each will have a design capacity of 345,000
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m3/day. Veolia Besix holds an operating license for Wathba 2 and the Allahamah
treatment plants. As a result of this expansion, the sewerage system will be able to
collect sewage from the entire Abu Dhabi drainage area. A new pumping station will
feed this to the Mafraq and Al Wathba facilities. Two new facilities will be built for Al
Ain. The design capacity of Al Saad plant will be 92,000 m3/day and that of the Al
Hamah plant 149,500 m3/day as shown in Table (2).
3. Treated Wastewater Reuse
3.1 Present Status
Wastewater initially provided the bulk of the water for amenity and landscaping
purposes. However, as the volume increased from the 1990s supply outstripped the
irrigation systems capacity to fully utilize it. Where this occurred irrigation shortages
were made up from desalinated water. The fact that desalinated water is seven times
more expensive to produce had no impact on this allocation because it was free for
municipal uses. Thus there were few incentives to better manage the recycled water
supply or remove the constraints in the distribution network. Independent calculations
of irrigations application in the Abu Dhabi area put current use at 4,800 mm/year – at
least double the amount needed for urban greening (Dornier/GTZ, 2009). Until recently
the main drawback of the 200 km distribution network on Abu Dhabi Island was the
relatively small size of the pipes. In addition, the flows are still controlled manually and
water is not properly budgeted and storage reservoir operation (and there are 119
storage reservoirs) is haphazard – some reservoirs receive excessive flow while others
get no flow at all or very limited flows. Many of the control instruments do not function
properly and some may have been removed. ADSSC’s consultants have recommended
an irrigation network detection and leakage study which would help identifying
unknown off takes, cross connections and valve status. However, the budget for this at
AED 60,000 looks woefully inadequate.
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Table 1: Present Major Treatment Facilities in Abu Dhabi Emirate (2011). Eastern Region Abu Dhabi and Western Region
Treatment Plant Production
(million m3/yr)
Treatment Plant Production
(million m3/yr)
Al Ain - Zakher 43.80 Al Mafraaq 186.40
Al Araad 0.02 Al Khatem 0.27
Al Dhahira 0.16 Ghantout 0.24
Al Faqah 0.20 Al Maraa 2.38
Al Haiar 0.68 Mirfa Cans Factory 0.07
Al Khazna 0.39 Bainounah 0.35
Al Qoaa 0.72 Madient Zaied 3.49
Al waqan 0.46 Liwa 0.28
Al Yahr 0.08 Abu Al Abyad Island 0.12
Bu Keriayah 0.10 Sir Bani Yas Island 0.13
Remah 0.36 Ghuwaifat 0.19
Seih Ghraba 1 0.03 Ghayathi 1.23
Seih Ghraba 2 0.01 Delma 0.38
Al Shweib 0.37 Baaya-Sila 0.98
Sweihan 0.39
Wadi Fiely 0.44
Sub Total 28.2 196.5
Total TSE Production in Abu Dhabi Emirate 244.7
Source: ADSSC, 2009
Table 2: Future Major Treatment Facilities in Abu Dhabi Emirate (2011-2012).
Location Catchment Capacity m3/day Commissioning
Al Wathba 1 Abu Dhabi Island & Mainland 345,000 Q1 2011
Al Wathba 2 Abu Dhabi Island & Mainland 345,000 Mid 2012
Al Saad North Catchment Al Ain City 92,000 Q1 2011
Al Hamah South Catchment Al Ain City 149,500 Mid 2012
Total Future Additional Capacity 931,000
The irrigation network on Abu Dhabi Mainland is a combination of gravity and
pumping mains of medium to large diameters, the primary main being 183 km long plus
significantly longer secondary and tertiary irrigation distribution systems. It is not a
closed loop system but a series of transmission pipelines discharging to service
reservoirs (Figure 5). The main concern is that the capacity of the existing network and
associated infrastructure is insufficient to cope with the ever increasing recycled water
production. As on Abu Dhabi Island, a lot of the irrigation scheduling is done manually
making for less efficient balancing of supply and demand. Currently works are
underway to construct new, large diameter, transmission mains. All recycled water
output from Mafraq is monitored regularly for quality. As noted above, recycled water
quality has been deteriorating particularly with regard to high levels of salinity and
raised levels of heavy metals. The ADSSC feasibility study cautions that hardware
solutions alone will not solve the problem; better planning and management of
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operations are required. As far as can be determined from available reports there do not
appear to be any drainage congestion problems as a result of amenity irrigation. This is
primarily because half of available recycled water is disposed of at sea (Figure 4), and
that there is good urban drainage – some of it provided by the sewer system and some
from surface drainage and shallow groundwater flow to the Gulf.
Figure 5: TSE irrigation network in Abu Dhabi
Island
Figure 6: Treated Wastewater Production
versus Irrigation Use.
In recognition that the current levels of wastage of unacceptable, ADSSC commissioned
a special Assessment and Ownership of Green Water Infrastructure in Abu Dhabi
Emirate that was completed in 2008. Subsequently in response to an instruction from
the Executive Council another consulting firm was engaged to carry out “a feasibility
study into the addition of a “fourth stage with the use of fiber” to all large sewerage
treatment plants in Abu Dhabi”, specifically those at Abu Dhabi and Al Ain. It was
proposed in these studies that no desalinated water will be used for irrigation in the
future and that this shortfall will be made up with recycled water supplied from both
Mafraq and the proposed new plants at Al Wathba. Together these reports’
recommendations aim to:
provide the basis for the upgrading of the irrigation management in Abu Dhabi
and Al Ain
Improve the quality of recycled water to remove all risk of biological
contamination making it suitable, in principle, for unrestricted use.
The planning horizon for both studies was 2025.
Figure (7) shows all amenity and irrigation demands based upon present water
consumption and projected available supplies, and all new proposed future development
that will need amenity irrigation. These supply projections by the consultants assume
0
100,000
200,000
300,000
400,000
500,000
J J A S O N D J F M A M J J A S O N D
Irrigation use
Wastewater production
Discharged to
Environment
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that current total inflow of recycled water will remain unaffected by improvement to the
sewer system that could reduce inflow volumes by as much as 30-50%. Thus under
almost all future demand scenarios all the recycled water produced in Abu Dhabi will be
fully accounted for in the next 1-3 years.
Figure 7: Projection of future wastewater supply and demand.
4. Abu Dhabi Water Reuse Standards
Numerical standards are in the process of being agreed for the use of recycled water and
biosolids. However, numerical standards are of little value by themselves unless they
are applied and regulated within an effective framework that ensures adequate
monitoring, sampling, analysis, reporting and action. Fortunately, the regulations put
forward by the RSB provide the basis for effective control as it addresses all of the
aspects that would be expected of a modern state of the art system. Two features are
worth highlighting. The first is the requirement for a Reuse Safety Plan to be developed
by the Disposal Licensee, the Treatment Licensee and the End-User for each reuse
scheme. That is certainly a key feature of effective regulation and reflects a modern up-
to- date approach. The second is the establishment of a Reuse Review Panel that will
review operation, performance and quality standards every two years. Reuse and its
regulation is a dynamic process and regular review is an important element.
The Abu Dhabi numerical standards have been informed by international opinion and,
in particular, the WHO Guidelines for the safe use of Wastewater, Excreta and Grey
water (2006). In the WHO’s perspective recycled water treatment is one component of
an integrated risk management strategy, and they propose minimum verification
monitoring of microbial performance. The latest guidelines aim at preventing
communicable disease transmission, while optimizing resource conservation and
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recycling. They allow incremental and adaptive changes, which are cost-effective in
reducing health and environmental risks.
Abu Dhabi RSB’s Recycled Water and Biosolids Regulations of 2010 provide in-depth
details of standards that will come into force later in 2010. Schedule A provides
numerical values for Public Health Standards, P1 (general reuse), P2 (Restricted reuse),
P3 (Marine) and P4 (Land percolation system) that are to be applied to specific reuse
activities. These define both general physico-chemical characteristics along with three
important microbiological standards. It is somewhat surprising, given that the use is
mostly irrigation, that there is no standard to minimise the concentration of salts such as
TDS, SAR or conductivity. Before comparing these standards with selected
international ones it is appropriate to say that an attractive feature of the Abu Dhabi
standards is that they are relatively simple and only include relevant parameters that can
be readily measured and have meaning; by contrast many national standards include
pages of unimportant parameters that have no relevance and are an expensive
encumbrance to effective control. Also, the inclusion of the Reuse Review Panel means
that additional parameters can be added at a later stage if deemed necessary.
5. Treated Wastewater Reuse Options
Four options were recommended for reuse of treated wastewater in Abu Dhabi:
(1) Direct use amenity plantation, landscaping and forests
(2) Direct use for agriculture
(3) For aquifer recharge
(4) District cooling
Wastewater reuse is not a recent invention. There are indicators that wastewater was
used back for irrigation in ancient Greece and in the Minan civilization (ca. 3000 – 1000
BC) (Angelakis et al., 1999; Asano and Levin, 1996). During 1950-60, interests in
applying wastewater on land in the western hemisphere as wastewater treatment
technology advanced
and quality of treated effluents steadfastly improved. Land application became a cost-
effective alternative of discharging effluent into surface water bodies (Asano T., 1998).
Figure (8) shows the percentage of total water reuse per sector for California, Florida
and Japan. It can be observed that in agricultural irrigation the water reuse overall is
highest, but strongly dependent on the regional context. In Japan the reuse for example
is highest in the industrial and commercial sector.
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Figure 8: Wastewater applications in California, Florida, and Japan.
5.1 Reuse of treated wastewater in agriculture
The integration of wastewater reuse in the existing water management master plans has
been essentially geared towards agricultural irrigation. When considering wastewater
reuse for irrigation an evaluation of the advantages, disadvantages and possible risks has
to be made. Table (3) summarizes the advantages, disadvantages and possible risks
regarding water conservation, different substances in the water and influences regarding
the soil.
5.2 Reuse of treated wastewater in aquifer recharge
Where soil and groundwater conditions are favorable for artificial recharge of
groundwater through infiltration basins, a high degree of upgrading can be achieved by
allowing treated wastewater to infiltrate into the soil and move down to the groundwater
as shown in Figure (10). The unsaturated or "vadose" zone then acts as a natural filter
and can remove essentially all suspended solids, biodegradable materials, bacteria,
viruses, and other microorganisms. Significant reductions in nitrogen, phosphorus, and
heavy metals concentrations can also be achieved.
At present there is no any injection/recharge of the tertiary treated wastewater to
groundwater aquifer system in Abu Dhabi. However this option should be studied in
details in the future. The range of potential groundwater pollutants in wastewater
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includes pathogenic microorganisms, excess nutrients and dissolved organic carbon, and
where significant industrial effluent is present, toxic heavy metals and organic
compounds. However, the actual effect on groundwater quality will vary widely with:
the pollution vulnerability of the aquifer
the quality of natural groundwater and thus its potential use
the origin of sewage effluent and thus likelihood of persistent contaminants
the quality of wastewater, and its level of treatment and dilution
the scale of wastewater infiltration compared to that of aquifer through flow
The mode of wastewater handling and land application.
Table 3: Advantages, disadvantages and possible risks of wastewater reuse.
Advantages Disadvantages Risks
Improvement of the economic
efficiency of investments in
wastewater disposal and
irrigation
Conservation of freshwater
sources
Recharge of aquifers through
infiltration water (natural
treatment)
Wastewater is normally
produced continuously
throughout the year, whereas
wastewater irrigation is mostly
limited to the growing season.
Potential harm to
groundwater due
to heavy metal,
nitrate and organic
matter
Use of the nutrients of the
wastewater (e.g. nitrogen and
phosphate)
reduction of the use of
synthetic fertilizer
improvement of soil properties
(soil fertility; higher yields)
Some substances that can be
present in wastewater in such
concentrations that they are
toxic for plants or lead to
environmental damage
Potential harm to
human health by
spreading
pathogenic germs
Reduction of treatment costs:
Soil treatment of the pre-treated
wastewater via irrigation (no
tertiary treatment necessary,
highly dependent on the source
of wastewater)
Potential harm to
the soil due to
heavy metal
accumulation and
acidification
Beneficial influence of a small
natural water cycle
Reduction of environmental
impacts (e.g. eutrophication and
minimum discharge
requirements)
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Figure 10: General schemes of wastewater reuse for aquifer recharge.
6. Al-Nahda Farm Pilot Project
The Abu Dhabi Sewerage Services Company (ADSSC) has proposed the development
of an enhanced TSE Treatment plant on the eastern boundary of the Al Nahda farms
area, near to Al Wathba (Figure 8). The new plant will provide enhanced treatment of
Treated Sewage Effluent (TSE) sourced from the Mafraq Waste Water Treatment Plant
(WWTP). The ‘enhanced’ TSE is intended for irrigation in the Al Nahda farms area,
replacing the existing groundwater supply currently in use.
Figure 8: Location map of Al Nahda farms area.
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6.1 Groundwater Supply
The irrigation water currently supply for the Al Nahda farms agricultural plots is
sourced from groundwater boreholes in Liwa. The water is currently pumped over
130km through pipelines to the Al Nahda farms area. These farms have an economic
and cultural value to the Emirati population and the continued maintenance and
preservation of this land use is deemed of importance to the UAE. The aquifers in Liwa
area are often referred to as the Liwa Crescent aquifers. Over abstraction from aquifers
is a major problem in Abu Dhabi emirate, in particular from the Liwa crescent aquifers.
Over abstraction of this valuable supply has led to declining groundwater quantity and
severe deterioration in groundwater quality.
6.2 Plant and Process
As shown in Figure (9) The Mott MacDonald Feasibility Study (April 2009) identified
the minimum necessary treatment processes to achieve the required treated effluent
water quality. The minimum treatment processes identified consist of the following:
Inlet flow balancing tank: TSE from Al Mafraq WWTP would first enter the
balancing tank to balance flow quantities and prevent surges to ensure effective
treatment in the subsequent stages.
Ultrafiltration membrane treatment: The TSE will then be pumped to the
ultrafiltration process stage, which will remove particles, algae, protozoa, bacteria,
small colloids and viruses. Pre-treatment chemicals for this part of the process are
anticipated to include ammonium sulphate (dechlorination), ferric chloride
(coagulation), sodium hypochlorite (pre-chlorination), caustic soda, citric acid (pH
control). The ultrafiltration membranes would be cleaned by flushing (referred to a
‘backwashing’) the membranes with water. Periodically, sodium hypochlorite,
citric acid, caustic soda and hydrogen peroxide may be used for chemical cleaning
of the membranes.
Ultra-violet light disinfection: In the first stage of ultraviolet disinfection, photons
in UV light react directly with nucleic acids in the target organism subsequently
killing any organisms present.
Sodium hypochlorite addition: The addition of sodium hypochlorite is the final
stage of disinfection.
Plant and Process Chemicals: All chemicals will be handled, stored and disposed of
in accordance with Control of Substances Hazardous to Health (COSHH) best
practice and EAD requirements.
Plant Chemical and Reject Flows: The enhanced treatment plant will entail a number of
chemical and reject process flows.
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Figure 9: Flowchart of processes for the plant.
6.3 Incoming TSE
The inflow of TSE from the Al Mafraq WWTP transmission main will not exceed 6
mgd, Table (4) shows the average quality of TSE effluent from the Al Mafraq
Wastewater Treatment Plant in 2008 to provide an indication of what the incoming TSE
quality is likely to be.
Table 4: Average Quality of TSE from Mafraq WWTP, 2008
Parameter Unit Value Parameter Unit Value
pH units 7 Total Organic Carbon
(TOC) mg/l 5.7
Alka mg/l 53 Turbidity NTU 1.0
Hardness mg/l 453 Residual Chlorine Cl2 mg/l 1.4
Conductivity µS/cm 4700 Calcium (Ca) mg/l 83
Total Dissolved Solids (TDS) mg/l 2501 Magnesium (Mg) mg/l 67
Chlorine (Cl) mg/l 1466 Sodium (Na) mg/l 774
Ammonia (NH3N) mg/l 0.8 Nickel (Ni) mg/l 0.02
Nitrate (NO2N) mg/l 0.4 Chromium (Cr) mg/l 0.03
Nitrate (NO3N) mg/l 9.1 Cobalt (Co) mg/l 0.01
Phosphorus as Total P mg/l 6 Iron (Fe) mg/l 0.5
Sulfate (SO4-2) mg/l 169 Zinc (Zn) mg/l 0.21
Total Suspended Solids (TSS) mg/l 2.8 Cadmium (Cd) mg/l 0.05
Biological (BOD) Oxygen
Demand
mg/l 1 Copper (Cu) mg/l 0.10
Chemical (COD)
Oxygen Demand
mg/l 10
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6.4 Treated Effluent Water
The design specifications for the proposed plant stipulate that the treated water outflow
from the plant will be greater than 75% of the influent at all times, up to a maximum of
4.5 mgd. The final treated TSE quality parameters compared to the influent TSE quality
is provided in Table (5).
Table 5: Typical Enhanced TSE Quality
Parameter Unit
2008 Annual
Average
Current
Mafraq TSE
Proposed
Water Quality
from Min.
Treatment
Process
Required Treated Water
Quality
95 Percentile
Value
Maximum
Permissible
Value
Conductivity µS/cm 1000 1200
Total Hardness mg/l
CaCO3 453 23
Faecal coliforms cfu/100ml <1
Total coliforms cfu/100ml <1
Aluminium (Al) mg/l 0.15 0.10
Ammonia (NH3) mg/l 0.8 0.8
Arsenic (As) mg/l 0.0075 0.005
Boron (B) mg/l 0.75 0.5
Cadmium (Ca) mg/l 0.05 0.003 0.00225 0.0015
Chloride (Cl) mg/l 1466 73 187.5 125
Chromium (Cr) mg/l 0.03 0.002 0.0375 0.025
Cobalt (Co) mg/l 0.01 0.001
Copper (Cu) mg/l 0.1 0.005 0.750 0.500
Fluoride (Fl) mg/l 1.125 0.75
Iron (Fe) mg/l 0.5 0.025 0.15 0.1
Lead (Pb) mg/l 0.0075 0.005
Manganese (Mg) mg/l 0.3 0.2
Mercury (Hg) mg/l 0.0045 0.003
Nickel (Ni) mg/l 0.2 0.010 0.0525 0.035
Nitrate (NO3) mg/l 9.1 0.455
Phosphorus (P) mg/l P 6 0.300
Selenium (Se) mg/l 0.0075 0.005
Sodium (Na) mg/l 774 39 112.5 75
Zinc (Zn) mg/l 0.21 0.011 3.75 2.5
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Table (6) demonstrates that the enhanced TSE quality will be a significant improvement
on the quality of the influent TSE from the Al Mafraq WWTP. Parameters with a noted
improvement in quality include conductivity (salinity), cadmium, chlorides, chromium,
cobalt and zinc. Significant improvements are expected for heavy metal levels in
particular. The enhanced treated TSE will then be used for irrigation of the Al Nahda
farms.
6.5 Reject Brine Disposals
The expected quantity of reject brine to be utilized for irrigation reuse purposes is 1.5
mgd. Table (7) provides the anticipated quality of the reject brine from the proposed
plant. During project development, alternative options considered for the disposal of the
reject brine included:
1. Disposal into deep aquifers by injection/pumping. This was considered costly and
impractical. Through consultation with EAD, it was identified that problems had been
encountered previously
2. It is proposed to use the reject brine from the enhanced TSE Treatment plant irrigation of
non-agricultural horticulture such as landscaping and forestry planting.
Land adjacent to the proposed enhanced TSE Treatment plant is being developed by
EAD into a Wildlife Animal Palace for animals to be relocated from Sir Bani Yas
Island. Native Arak and Araf trees will be planted. (Araf trees have salinity tolerance to
water with a TDS of around 10 000 ppm and Arak trees have salinity tolerance to water
with a TDS of around 20,000 ppm).
6.6 Soils of Al Nahda farms
The main soils commonly exist in Al Nahda agriculture farms, the project area, are
classified, according to the USDA Soil Taxonomy (USDA-NRCS, 1999 and 2010) as
Typic Torripsamments, mixed, hyperthermic (EAD, 2009b). The soils are deep, sandy
soils with mixed mineralogy. They occur on almost level plains to mega transverse and
dune fields and are widespread throughout the Abu Dhabi Emirate. They are typically
excessively drained or somewhat excessively drained and have rapid to very rapid
permeability.
The surface soil is usually loose or soft. Where the soils occur in older landscapes, there
may be a surface lag of fine to medium gravels. Complete laboratory analyses including
physical, chemical, and mineralogical characterization (USDA-NRCS, 2004) of one soil
profile representing the common soils in Al Nahda farm, Typic Torripsamments, mixed,
hyperthermic, is presented in Table 6. The texture is fine sand with low electrical
conductivity (ECe less than 2 dS/m) and negligible quantities of gypsum and
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carbonates. Other associated soils in the study area are classified as Typic Haplocalcids,
sandy, carbonatic, hyperthermic and consist of very deep or deep sand with a calcic
horizon within 100 cm depth. They occur on all landscape positions within level plains
to undulating rises. They have also been described in some older sand sheets and
interdunal depressions. Soils are well drained or somewhat excessively drained and
permeability is rapid or moderately rapid. The main soils commonly exist in Al Nahda
agriculture farms, the project area, are classified, according to the USDA Soil
Taxonomy as Typic Torripsamments, mixed, hyperthermic. They are typically
excessively drained or somewhat excessively drained and have rapid to very rapid
permeability. The texture is fine sand with low electrical conductivity (ECe less than 2
dS/m) and negligible quantities of gypsum and carbonates.
Table 6: Expected Reject Brine Water Quality.
Parameter Unit Estimate of Wastewater Quality
Concentration (mg/l) Load (kg/d)
Conductivity µS/cm 18 800
Total Dissolved Solids mg/l 10 004
Total Hardness CaCO3 mg/l 1 812 12 339.7 kg/d
pH 7
Ammonia NH4 mg/l 3.2 21.8 kg/d
BOD mg/l 4
COD mg/l 40
Cadmium mg/l 0.2 1.4 kg/d
Chloride mg/l 5 864 39 933.8 kg/d
Chromium mg/l 0.12 0.8 kg/d
Cobalt mg/l 0.04 0.3 kg/d
Copper mg/l 0.4 2.7 kg/d
Iron mg/l 2.0 13.6 kg/d
Nickel mg/l 0.08 5.4 kg/d
Nitrate NO3 mg/l 36.4 247.9 kg/d
Phosphorus P mg/l 24.0 163.4 kg/d
Sodium mg/l 3 096 21 083.8 kg/d
Zinc mg/l 0.84 5.7 kg/d
277
7. Conclusion and Recommendation
The irrigation water currently supplying the Al Nahda farms agricultural plots is
sourced from groundwater boreholes in Liwa. The water is currently pumped over
130km through pipelines to the Al Nahda farms area. These farms have an
economic and cultural value to the Emirati population and the continued
maintenance and preservation of this land use is deemed of importance to the UAE.
The aquifers in Liwa area are often referred to as the Liwa Crescent aquifers. Over
abstraction from aquifers is a major problem in Abu Dhabi emirate, in particular
from the Liwa crescent aquifers. Over abstraction of this valuable supply has lead
to declining groundwater quantity and severe deterioration in groundwater quality.
The main soils commonly exist in the project area, Al Nahda agriculture farms, are
classified according to the USDA Soil Taxonomy as Typic Torripsamments, mixed,
hyperthermic. They are typically excessively drained or somewhat excessively
drained and have rapid to very rapid permeability. The texture is fine sand with low
electrical conductivity (ECe less than 2 dS/m) and negligible quantities of gypsum
and carbonates.
The enhanced TSE quality will be a significant improvement on the quality of the
influent TSE from the Al Mafraq WWTP. Parameters with a noted improvement in
quality include conductivity (salinity), cadmium, chlorides, chromium, cobalt and
zinc. Significant improvements are expected for heavy metal levels in particular.
The enhanced treated TSE will then be used for irrigation of the Al Nahda farms.
All chemicals will be handled, stored and disposed of in accordance with Control of
Substances Hazardous to Health (COSHH) best practice and EAD requirements.
The EAD irrigation reuse project proposes to install 4-5 piezometers to monitor
groundwater in the vicinity of the reject brine irrigation areas. The site has recently
had an underground storm water drainage network installed, which is anticipated to
collect any excess reject brine infiltrate.
During project development, alternative options considered for the disposal of the
reject brine included:1. Disposal into deep aquifers by injection/pumping. This was
considered costly and impractical. Through consultation with EAD, it was
identified that problems had been encountered previously, and 2. It is proposed to
use the reject brine from the enhanced TSE Treatment plant irrigation of non-
agricultural horticulture such as landscaping and forestry planting.
The key operational activities will include: monitoring TSE output to ensure that it
meets the required water quality standard and maintenance measures to prevent
ageing/wear and tear of plant items
277
Key process maintenance tasks will include: replacing ultra-filtration membrane
modules, and, Maintenance of chemical dosing pumps and tanks.
RSB recommended that establishing a five year monitoring program which would
provide independent and robust data on the performance of the plant and the impact
of polished effluent on irrigated land.
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