The water-starved countries of the Middle East are continuously looking for new and innovative ways to supplement their water resources. The reuse of treated sewage effluent generated by municipal sewage treatment plants is already widespread across the region.
The Gulf states recycle up to 70 per cent of their treated effluent, predominantly for irrigation, and most are targeting increases in the volume of total wastewater reuse.
But there is also increasing interest in water conservation and reuse on a local level, driven to a large extent by state-backed campaigns to build more environmentally friendly buildings, especially in the emirates of Dubai and Abu Dhabi.
This has thrown the concept of recycling grey water, or untreated household wastewater, into the spotlight. But it is still a subject of much debate as the benefits of the technology are not clear cut.
Broadly speaking, the term grey water refers to water that has not been contaminated by toilet waste. It accounts for about 70 per cent of residential wastewater, with black water, or sewage water, comprising the remainder.
Grey water itself can be subdivided into two types: dark grey water, which is produced by washing machines and kitchen utilities; and light grey water, which comes from showers, bathtubs and wash basins.
The latter makes up nearly 40 per cent of all domestic wastewater and contains the least amount of pathogens and contaminants.
If separated out at the point of generation, light grey water is a valuable resource that can be used instead of drinking water for activities such as toilet flushing and irrigation.
The average household generates 586 litres a day of wastewater, according to the World Health Organisation. With toilet flushing accounting for 32 per cent of domestic water consumption, significant volumes of desalinated water could be saved through the installation of grey-water recycling technology, particularly if fitted in the basements of high-rise buildings. Using reclaimed water for toilet flushing and irrigation translates not only into additional credits for real estate developers seeking green buildings ratings but also provides savings on bills for consumers.
Grey water can be reclaimed using one of two methods, with the choice of technology determining how the water can subsequently be reused. The simplest method is to use a coarse primary treatment, often a sand filter, which screens off oil, grease and solids.
In this instance, to minimise the risk to public health, the reclaimed water can only be used for subsurface irrigation. It cannot be used for toilet flushing, so the financial advantages are lost.
Although grey water is the least contaminated component of the entire waste stream, it still has the potential to transmit disease, so care has to be taken to avoid washing heavily soiled or bloodstained clothing and nappies in basins to limit the chances of this happening. Primary treated grey water may also contain chemicals from soaps and shampoos that are harmful to certain plant species or alter the alkalinity of the soil.
But potentially more troublesome is the impact that removing 40 per cent of the waste stream could have on the operations of municipal sewerage networks if grey water recycling for irrigation becomes commonplace.
“Existing gravity sewers are designed on a certain velocity based on factors like the density of the liquid itself,” says Saad Alani, director for water and environment at Abu Dhabi-based Hyder Consulting Middle East. “If you remove half the grey water, you are left with a thick waste, which is not going to travel as designed in the network. As a result, you will have odour problems and blockages to deal with.”
The more sophisticated method of grey-water recycling involves a secondary treatment and disinfection of the water. This cleans the water to a much higher standard and means it can be used internally for toilet flushing and externally for unrestricted irrigation, car cleaning, and even for use in water features.
In addition to this flexibility in usage, the impact on the sewerage networks is much less when secondary treatment systems are employed as most of the water re-enters the waste stream after being used for toilet flushing. However, this is a more costly option than the primary treatment process.
A further consideration when assessing the benefits of grey-water recycling systems is that they require double the amount of pipe work needed by regular wastewater infrastructure, which not only adds to the capital cost of a building, but also requires more intricate designs and additional space.
For property developers who want to be seen to reduce the environmental impact of their developments but also to have water for landscaping purposes, it might be simpler to install a decentralised sewage treatment plant, which does not have an impact on the internal configurations of the building.
There is currently little economic incentive for UAE developers that intend to install an on-site sewage treatment plant to combine it with a grey-water recycling system, even though this would be the best solution environmentally. Although reusing grey water for toilet flushing would reduce by one third the amount of desalinated water consumed by a building, given the UAE’s low water tariffs – $0.008 a gallon compared with $0.012 a gallon in Germany – it would take years for the savings made on water bills to compensate for the additional capital investment needed to install two separate treatment systems, along with the extra power required to run them and the additional land requirements, which in each case can be almost 20 per cent higher.
“The issue of grey water is important,” says Alani. “However, everything is important if it comes with the right price. It has to be properly costed.”
In Jordan, the economics of grey-water recycling are overridden by the country’s chronic lack of water. In its 2008 strategy document for reforming the water sector by 2022, Jordan’s Water Resources & Irrigation Ministry says grey-water reuse has an important role to play in easing the burden on the country’s water resources. It says it will press for legislation to stipulate that all new high-rise buildings use grey water for internal non-drinking purposes, and says it will encourage properties without connections to the country’s sewer systems to practice grey-water recycling through incentive systems. Most households in the country only receive water once a week.
A private-public project funded by German government-owned development company Deutsche Gesellschaft fur Technische Zusammenarbeit, and Pontos, a subsidiary of German tap and showerhead maker Hansgrohe, is currently under way in Jordan to promote the benefits of grey-water recycling.
Under the project, Pontos has fitted a 600-litre-a-day demonstration grey-water recycling system in the basement of a house belonging to an official of Jordan’s Water Resources & Irrigation Ministry. Groups are taken to see the plant in action.
The firm has also installed a grey-water recycling plant at the Dead Sea Spa hotel. The water at the hotel is now used three times.
The Pontos system uses a three-step non-chemical treatment process. In the first stage, hair, fluff and other solids is removed using a mechanical pre-filter. This is followed by an aerobic microbiological treatment to reduce the organic content created by shampoos and other contaminants. This is a double treatment conducted in batches. In the final step, the water is disinfected with ultraviolet light.
The Dead Sea Spa hotel plant treats 15 cubic metres a day of grey water collected from bathrooms and washbasins. The pre-filter is automatically washed with some of the reclaimed water every four hours and the micro-organisms reproduce themselves so maintenance is minimal. To allow room for storage, the plant has a capacity of 33 cubic metres. The total investment cost was e100,000 ($142,000). It uses 1.5 kilowatt hours of power to treat one cubic metre of grey water and occupies a space of about 40 square metres.
Over one year, the plant will save more than 5,000 cubic metres of drinking water from being used for activities where it is not required. This alone will make only a small contribution towards reducing the kingdom’s water deficit, which was recorded at 638 million cubic metres in 2007, but if replicated across the country, it will certainly help.
“Jordan is our first country in the region but for the future this is going to be the market,” says Jan Hertlein, project manager at Pontos.
Pontos’s biggest market currently is Germany, followed by Spain. In Spain, tightening water supplies are driving the uptake of grey-water recycling systems, while in Germany, high water rates are driving demand. Hertlein says consumers pay about e5 ($7) a cubic metre for water in Germany. This compares with about e2 a cubic metre in Jordan.
The sustainable buildings movement in the UAE has done much to raise the profile of grey-water recycling in the Gulf. Applied correctly, and with environmental concerns taking precedence over cost, grey water can make a positive contribution to the region’s water balance.
However, developers will be tempted to go for the cheapest option to meet their environmental responsibilities. A combination of legislation and financial incentives is needed to ensure this does not happen, and the opportunity to make a real difference to water management in the Middle East is not lost.