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237 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: [email protected] 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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237

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: [email protected]

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.

233

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

237

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

237

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

237

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

232

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.

237

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

237

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

277

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

277

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.

277

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

273

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)

277

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.

277

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.

277

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

272

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

277

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

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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.

References

Angelakis A.N.; Marecos D. M., Bontoux L.; Asano,T. (1999), The Status of

wastewater reuse practices in the Mediterranean basin: need for guidelines.-

Water Research, Volume (33), No.10 pp. 2201-2217, Elsevier Science.

Asano T., (1998), Wastewater Reclamation and Reuse, Water Quality Management

Library, Volume 10, Technomic Publishing Company, Lancaster, Pennsylvania.

Asano T., and Levine A. D. (1996): Wastewater Reclamation, Recycling And Reuse:

Past, Present, And Future, Water Science and Technology, Vol. 33 No. 10-11,

pp.1-14

Dorneir/GYZ. 2009. Al Ain Groundwater Rise Study, Final Report, Regulation and

Supervision Bureau, Abu Dhabi Emirate, UAE.

EAD, 2009a.Soil Survey of Abu Dhabi Emirate – Extensive Survey. Environment

Agency - Abu Dhabi, United Arab Emirates, Volume I, pp. xx + 506.

EAD, 2009b. Abu Dhabi Water Master Plan. Environment Agency – Abu Dhabi.

Available at: http://www.ead.ae/en/elibrary/ (Last accessed: March 2012).

Quanrud, D. M., Arnold, R. G., Lansey, K. E., Begay, C., Ela, W. & Gandolfi, A. J.

2003 Fate of effluent organic matter during soil aquifer treatment:

biodegradability, chlorine reactivity and genotoxicity. Journal Water Health 01,

33–45.

Lopez, A., Pollice A., Laera G., Lonigr A., Rubino A. & Passino R. 2005 Reuse of

tertiary membrane filtered municipal wastewater for irrigation of vegetable

crops. Paper presented at the IWA Specialty Conference on Wastewater

Reclamation and Reuse for Sustainability, WRRS2005, 8–11 November 2005,

Korea.

Rebhun, M. 2004 Desalination of reclaimed wastewater to prevent salinisation of soils

and groundwater. Desalination 160(2), 143–149.

RSB (Regulation and Supervision Bureau). 2009 Annual Report, Abu Dhabi, UAE.

USDA-NRCS. 1999. Soil Taxonomy. A Basic System of Soil Classification for Making

and Interpreting Soil Surveys.USDA Agriculture Handbook No. 436. U.S.

Government Print Office, Washington, DC. Available at: ftp://ftp-

277

fc.sc.egov.usda.gov/NSSC/Soil_Taxonomy/tax.pdf (Last accessed: February

2012.

USDA-NRCS. 2004. Soil Survey Laboratory Methods Manual, Soil Survey

Investigations Report No. 42. U.S. Department of Agriculture, Natural

Resources Conservation Service, National Soil Survey Center. Available at:

ftp://ftp-

fc.sc.egov.usda.gov/NSSC/Lab_Methods_Manual/SSIR42_2004_print.pdf (Last

accessed: February 2012).

USDA-NRCS. 2010. Keys to Soil Taxonomy, 11thedition.USDA–Natural Resources

Conservation Service, Washington, DC. Available at:

http://soils.usda.gov/technical/classification/tax_keys/ (Last accessed: February

2012).