The quantity of wastewater produced in the United Arab Emirates (UAE) is rising drastically and given the scarcity of water in the region, there is a clear need to reuse this resource. Kirsty Tuxford reveals the latest technological developments, which provide for wastewater treatment with minimal impact on the environment
With a desert climate and classification by the UN as a water-stressed region, one might expect the UAE to lead on water conservation matters but as the Dubai School of Government said in its 2011 report, the behaviour of residents means that usage per capita is twice the global average.
The Dubai School of Government report is fairly damning: “The luxury lifestyle and lack of conservation measures amongst residents has resulted in high levels of water usage and waste. It has been reported that in the UAE, per capita water usage is 550 litres per person per day, as compared to a global national average of 250 litres per person each day.”
Some reports put water use in villas with gardens as high as 1,700 litres per person, per day. Consequently, wastewater generation is rising steeply. The Statistics Centre in Abu Dhabi reported that wastewater fed into treatment plants increased 69.6 percent between 2005 and 2011 reaching 1,356.05 MCM in 2011. Yet despite the rise in wastewater produced, treated wastewater meets less than 10 percent of Abu Dhabi city’s total water demand with desalinated water (79 percent) and groundwater (12 percent) at the core of water production in the region (2012 figures).
According to the Masdar Institute of Science and Technology in Abu Dhabi, water demand in Abu Dhabi has been projected to grow by 43 percent between 2011 and 2016. This trend is likely to be seen across the UAE, especially in the most populated emirates. So how are urban planners going to ensure that capacity keeps up with demand?
“There is no other way to produce potable water besides desalination in Abu Dhabi and the UAE, where there are very limited freshwater resources,” explains Dr Farrukh Ahmad, Associate Professor of Water and Environmental Engineering at Masdar Institute of Science and Technology. “Once the desalinated water is used, it results in the generation of municipal wastewater, and so the wastewater treatment processes can be used to recover non-potable but usable water from the municipal wastewater.”
The grey water produced after wastewater is treated is not fit for human consumption and is more suited to irrigation, or use in district cooling centres, where non-potable water can be utlilised.
Ahmad is amongst those advocating wider use of treated wastewater as it could potentially make a big dent in the UAE’s carbon and energy expenditure. “Recovering [usable non-potable] water from municipal wastewater will cost only a fraction of the costs for desalination. Hence, if functions such as industrial water use and district cooling and the quality of water they demand can be identified, then wastewater treatment operations can be used to supply them with usable water,” he adds. “This should also reduce the demand for desalinated potable water because that is the type of water they currently use.”
Lowering desalinated water demand would also reduce energy consumption and the associated carbon emissions from the desalination process.
“As you can imagine, the coupling of desalination and water recovery from wastewater will keep water, originally recovered from seawater, for a much longer time in the urban water cycle,” says Ahmad.
The risks of re-using water
One of the challenges of using wastewater is trusting that the technology can deliver a treated product that does not have adverse environmental or health consequences if for example it is used for irrigation.
The ReSource Institute for Low Entropy Systems (RILES) in the US has conducted significant research into treated wastewater. RILES claims that effluent from sewage treatment plants, regardless of the level of treatment and disinfection, can cause pollution that is harmful to life. While treatment plants reduce conventional pollutants (suspended solids, oxygen-demanding substances, pH, oil and grease, and faecal coliform bacteria), they do not remove metals and organic chemicals.
A transgender fish may sound like the creation of science fiction, but studies in the US have indicated that there are what are termed ‘intersex’ fish off the Southern California coast and in the Colorado and Potomac rivers because of the chemicals in the treated sewage that has been discharged into the water. The reason male fish are developing female organs are the chemicals and endocrine disrupting compounds, including oestrogen from birth control pills and hormone replacements.
Micro pollutants tend to persist in treated wastewater because conventional treatment processes, such as activated sludge treatment and membrane bioreactors, do not target their removal. Research is still ongoing as to exactly which organisms in treated wastewater are harmful and how to remove them.
“Without delving too deeply into the science of wastewater treatment, it is safe to say that the by-products can cause significant damage to the environment,” says Stan Wehbe, Director of Water and Environmental Engineering, at Waagner Biro Gulf in the UAE, which specialises in wastewater treatment. “The conventional way of treating sludge involves separating the sludge from the wastewater – a complicated process using a lot of energy. The final steps involve adding chemicals such as polymers, which are toxic to humans. In addition, a wastewater lagoon can quickly develop bacteria and viruses.”
Masdar’s Dr Ahmad is currently running several projects on the re-use of water, including an investigation into sustainable water treatment processes; water quality monitoring for chemical byproducts and micropollutants and health risks associated with water reuse; and water quality monitoring for pathogens and health risks associated with water reuse. The results of a study on carcinogens caused by pollutants have recently been published and other studies are due to be published within 12 months.
Xylem, a water technology company with operations in more than 150 countries, has a number of projects in the Middle East to produce treated wastewater for use in irrigation – for example at the Doha South Sewage Treatment Works in Qatar and the Sulaibiya Project in Kuwait.
Depending on the quality of the wastewater to be treated (influent) and the quality of the product water (effluent), Xylem has found a way to remove some of the harmful micropollutants that are left in wastewater after treatment. “Our WEDECO brand ozone generators form a complete Advanced Oxidation Process (AOP) solution that removes Endocrine Disrupting Compounds (EDCs), which result from the use of pharmaceuticals and personal care products,” explains Tom Glover, Vice President, Communications at Xylem. “The AOP solution is also capable of killing pathogens and mitigating bromate formation as a carcinogenic by-product.”
In fact, wastewater treatment need not even involve the use of chemicals at all. “It is possible to use UV treatment technology, which accomplishes wastewater disinfection without the need for chemicals,” adds Glover.
A sustainable solution
New technology in water recycling is already being employed in the UAE with more environmentally friendly results. This alternative takes the form of reed beds which naturally recycle wastewater and Waagner Biro Gulf are pioneers in the Middle East.
Initially introduced in Europe, the idea behind reed bed technology is to filter water through different basins of sand and gravel filters planted by reeds (see box). The roots of the plants open channels in the sand to allow a permanent vertical percolation of the wastewater. Inside the specific soil filter, the microbial processes stimulate the natural breakdown of polluting compounds. This is possible due to the special characteristics of wetland plants, such as reeds, which transfer substantial amounts of atmospheric oxygen through to their root systems encouraging an extraordinary quantity and species diversity of micro-organisms to flourish around their roots. Organic pollutants are broken down as a food source by the micro-organisms whilst other contaminants, such as metals, are fixed in humic acid and cation exchange bonds in the soil or mineral substrates in which these plants are rooted.
There are several reed beds now set up in the UAE following academic studies of their viability. “The reed beds are all aiming to meet Abu Dhabi Sewage and Services Standards (ADSSC) and the first one has already achieved this,” explains Wehbe. “There will hopefully be more to come.”
There are several reasons why reed beds could be a more appealling option for cities than traditional wastewater treatment factories, including the fact that they are cheaper to build and operate. “They use less energy,” says Wehbe. “Also, the materials used are locally produced, they are simple to operate and maintain and they create a mescoclimate–meaning that they reduce heat. They are also a great habitat for birds and the reeds can be re-used as animal feed or as an eco-concrete.”
The scope for the use of reed bed treated water is broad–the technology can be used in both domestic and industrial environments–including for domestic sewage disposal.
For industrial sludge treatment, reed beds offer a cheaper and easier system compared to conventional sludge processes, which rely on decanting basins, press filters, centrifuges and drying chemicals. Reed planting doubles the microbiological activity (degradation and conversion of organic substances) compared to unplanted sludge dewatering beds.
For the UAE in particular, the wastewater produced by the oil and gas industry contains impurities such as hydrocarbons, minerals and heavy metals that need to either be injected deep into the earth or be purified. The reed bed system can treat this water biologically so that it can be re-used.
In fact, reed beds can purify wastewater generated by several industries, as well as swimming pools and lakes, and, are even incorporated in green-roofing systems with the effect of reducing air-conditioning use and enhancing air quality. Green roofs are composed of a waterproofing membrane with a root barrier, drainage pipes and sand layers planted with reeds.
The right channels
The issue though, is not merely the treatment of wastewater, but how to distribute it and also the feasibility of treating and re-using all the wastewater produced in the UAE. Mark Dehnert, Managing Director at Invent Middle East, says: “Dubai’s infrastructure in regard of water reuse is quite advanced. However, there are still individual areas that might be improved [with regards to distributing the water] and thus more water could be re-used. Though I do not think that this is the most critical thing to do, and in many cases it is neither economical nor sustainable – there is a practical limit to the theoretical idea of re-using all the sewage.”
To overcome the need to construct kilometres of piping infrastructure for the movement of sewage and treated wastewater, companies are coming up with alternative solutions. “We produce biological sewage water treatment plants under the Biototal trademark,” says Anton Semenov, GM at Union Biotal. “The units can treat sewage from residential, commercial and office buildings in the immediate vicinity, thus removing the need for an extensive piping infrastructure and avoiding the long queues of sewage disposal trucks that we currently see along some of Dubai’s roads.”
The company has plants of different capacities starting from 2m3 a day (good for a house with four to six inhabitants), up to 500m3 per day with the company’s biggest UAE project having a capacity of 2,000m3 per day, which consists of four blocks of 500m3 per day units.
“Among our clients are individuals, villa compounds, hotels, offices, hospitals, labour camps,” says Semenov. ”The good thing is that after the treatment, the water can be used for irrigation purposes, or mixed with concrete for building, and one of the biggest advantages is that there is no bad odour.”
As parts of the UAE’s sewage disposal network are feeling the strain – the queues of trucks awaiting their turn to dump sewage are a smelly reality – Union Biototal’s localised plants offer a viable solution at an affordable price. “The financial costs are actually very attractive,” says Semenov. “For individuals, the payback period ranges from six to eight years; that’s for stations with a capacity of 2 to 10 cubic metres per day. For villa compounds and other bigger projects the payback is only two to three years.”
The water treatment plants have the potential to function well in any city. “We operate in Russia (minus temperature extreme) and in the UAE (plus temperature extreme),” explains Semenov. “Our plants are designed for areas where a connection to the city sewage network is impossible or too expensive.”
To help the UAE become more efficient in the use of water resources, technology alone cannot suffice and behavioural change is also needed in terms of residents’ usage of water—as one speaker pointed out to Masdar representatives at a conference, there is no point in residents taking a 20 minute shower even if all the technology in place is geared to making Masdar carbon neutral.
But the UAE is aware of the need to find additional ways to increase its water supply, and with new developments such as reed beds, plus the research being done at the Masdar Institute of Science and Technology, local cities are on the right path to sustainability.
How reed bed technology works
• Upstream, a screen filters large solid waste, such as bottles, cans, clothes, rags and paper.
• The inflow of wastewater flows into the first collection chamber, where the pumping system pumps sequentially.
• Raw water is filtered through gravel and sand layers planted with reeds and is recovered at the bottom by a drainage system.
• The effluent is then collected in a second collection chamber where a self-priming siphon or pumping system expels sequentially by batch-feeding the water.
• The pre-treated water is oxygenated through spraying nozzles, then percolates through a second special filtering layer of sand and gravel planted with reeds. It is recovered at the bottom.
• The outflow from the water is measured through a device, where data can be stored.
• Treated effluent is collected in the final chamber. These sequences of the reed bed system operations produce water quality that is compliant with irrigation regulations.