To irrigate farms while saving water, experts look to sewage

One way to reduce the reliance of agriculture on the nation's diminishing groundwater reserves is to use treated sewage.

Plants are watered with different parts per million of salinated water at the ICBA in Dubai.

One way to reduce the reliance of agriculture on the nation's diminishing groundwater reserves is to find an alternative, and in sewage, the UAE has a largely untapped source. In effect, sewage is only water containing pollutants, and today the technology exists to render it fit even for drinking. While that might be a leap too far for many people, experts in water management say the use of treated sewage in agriculture might be viewed with less suspicion.

For this resource to be tapped, however, the country needs to upgrade its sewage treatment network, says Bassem Halabi, the group business development director at Metito Overseas, a desalination and waste water treatment company. At about 4.5 per cent, "water reuse here is extremely low compared with other parts of the world. "The priority is always for fresh water," he says. This means that investment in waste water treatment has lagged, even though treatment plants in Dubai, Sharjah and other emirates are operating much beyond their design capacities.

Industry figures show that the UAE's total waste water treatment capacity is about one million cubic metres per day, and that this will have to more than double, to 2.6 million cubic metres, over the next five to six years if the country is to keep abreast of the needs of its rising population. That expansion of capacity, says Mr Halabi, will cost about Dh9.2 billion (US$2.5 bn). Only when the pressure on the overburdened plants is relieved will it be possible to increase the quality of the treated waste they produce to the point where it can be reused for agricultural irrigation.

At present, says Mr Halabi, the effluent in places such as Dubai and Sharjah does not meet international guidelines even for open irrigation of green areas, let alone for agricultural use. Encouraging moves are afoot throughout the UAE, however. In Abu Dhabi, the Regulation and Supervision Bureau (RSB), the independent regulatory body for the emirate's water, waste water and electricity sector, is working on guidelines for the reuse of waste water.

A draft has been produced and is now being discussed with various stakeholders, but RSB officials are not yet ready to discuss details publicly. Meanwhile, the Environment Agency-Abu Dhabi (EAD) is getting ready to test the use of specially treated effluent on 220 farms in Al Nahda, about 35 kilometres from Abu Dhabi in the direction of Al Ain. The farmers, who grow vegetables, dates and fodder, currently get their water from an underground aquifer near Liwa. The water has to be pumped and transported 130 kilometres by pipe at great cost, an expense that is shouldered by the Government, says Dr Mohammed Dawoud, manager of the agency's natural resources department.

The plan is to use water from the Mafraq sewage treatment plant as a substitute for this groundwater. To eliminate all risks of contamination, the effluent will undergo further treatment with advanced membranes of the type usually used to produce drinking water. Although the water will be off-limits for drinking, it will meet the guidelines for drinking water quality set down by the World Health Organisation, Dr Dawoud says. Once the project has been completed, the extraction of groundwater for Al Nahda's farms will cease.

The decision to invest in the expensive membrane system was prompted by a desire to win over the farmers, who were initially sceptical, Dr Dawoud says. "We wanted to use a simpler form of treatment which is suitable for agriculture use, but we decided to go for the upgrade because of their concern. The product water will be drinkable." The project consultant has finalised the design, and the EAD is expected to select a contractor in a month's time.

According to Dr Nuruk Akhand, an irrigational scientist at the International Centre for Biosaline Agriculture in Dubai, Abu Dhabi emirate alone produces 750 million cubic metres of waste water that could be captured for use in agriculture. One advantage of treated sewage is that it has low salinity, making it potentially suitable for a wide range of crops. Dr Akhand says his organisation hopes the UAE authorities will award it a contract to develop a plan for using waste water in agriculture.

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