x Abu Dhabi, UAESunday 23 July 2017

Desert challenge for reverse osmosis

Farms are on the front line in the battle to reduce the problem of high salt levels in water.

Dr Nurul Akhand, an irrigation management scientist at the ICBA, looking over hydroponic chambers.
Dr Nurul Akhand, an irrigation management scientist at the ICBA, looking over hydroponic chambers.

In a one-room building on a farm in Al Dhaid, a technician kneels over a white water pipe. The pipe, about 20cm in diameter, runs from the floor into what looks like a large water heater tank. The man takes out his mobile telephone, points its camera at a gauge fixed to the pipe and takes a photograph. He is a research assistant at the International Centre for Biosaline Agriculture (ICBA) in Dubai, and has been doing this, once a month, since last November.

His visits to this and 14 other farms around the UAE will continue throughout this year and for most of 2010. The visits are arranged by the Ministry of Environment and Water. But at some of the farms, he is hardly a welcome guest, says his supervisor, Dr Nurul Akhand, irrigation management scientist at the ICBA. That is scarcely surprising. The researcher is spearheading a project likely to result in government intervention in an issue that until now farmers have been free to manage themselves - the use of reverse-osmosis desalination units to process extracted groundwater.

The ICBA is studying the best way to extract water from the country's damaged underground aquifers without harming the environment. Its guidelines will be submitted to the ministry in September next year. The photograph the researcher has taken records the reading on the gauge, which monitors the amount of water being pumped constantly from a deep well. Some of it is used directly to irrigate the farm's date palms. They are about the only crops on the property that can handle this water, whose salt content is very high.

This has not always been the case. Once, the UAE's wells yielded sweet water but, as farming has intensified, so much has been pumped out of the aquifers that the remaining stocks have, in some places, become twice as saline as seawater. To solve this problem, farmers are increasingly turning to desalination technology. The preferred method is reverse osmosis, which involves forcing water under pressure through a membrane that lets the liquid through but retains salts and impurities.

But, as an investigation by The National highlighted, the extremely salty by-product of this process, released back into the ground, is causing problems. "There are many small-scale reverse-osmosis plants installed at farms here," says Dr Akhand. "There is no regulation." According to the Environment Agency-Abu Dhabi's water resources masterplan, in Al Ain alone there are 74 of these small-scale plants in operation.

The unit in Al Dhaid produces 160 cubic metres of potable water a day, which is used to irrigate cucumbers grown in several greenhouses. But the plant also produces concentrated salty brine. If the brine is dumped in an open pit, as is very often the case, it leaches deep into the soil and pollutes the groundwater, completing a vicious circle. In addition, the brine is laden with chemicals and heavy metals ? byproducts of the desalination process ? some of which can be harmful to animals and people, even in small amounts.

"The first question is how to minimise the brine," says Dr Akhand, The 15 plants that are part of the study discharge between 16 and 400 cubic metres of brine per day. The amount produced by an individual unit depends on its efficiency, which, in turn, depends on the salt content of the intake water, the membrane itself and the amount of pressure used to force the water through the membrane. At the moment, the farmers and the private companies that install the equipment are left to decide these variables. "This is where guidelines will help," says Dr Akhand. Scientists are comparing the efficiency of all 15 units so they can work out how to achieve maximum efficiency.

The study will also recommend the type of anti-scalants and other chemicals allowed for use in the units and come up with the best solution for dealing with the salty brine. At the Al Dhaid farm, the salty waste liquid is used to irrigate a line of tall green conocarpus trees, native to parts of Africa and the Arabian peninsula, where they are known as damas. "They are using all the water here, there is no wastage," says Dr Akhand.

But at some of the other farms the brine is an environmental hazard. Of the 15 in the study, five dump the brine in excavation pits from which it seeps underground. At a farm in Fujairah, the brine was previously even being injected underground but that practice has been stopped and the by-product is now spilt on top of nearby sandy dunes. The scientists are taking regular soil samples at all the farms so they can track the effect of these practices over time.