ADSSC purifies sewage into potable water

The Abu Dhabi Sewerage Services Company (ADSSC) has 41 treatment plants that purify all of Abu Dhabi's wastewater collected through its network of 7,000km of sewer pipes, that lies 100 metres below ground, thus alleviating the need for sewage to end up in the sea.
"Presently, Abu Dhabi produces 850 mega litres (850,000 cubic meters) of sewage per day. It all goes through three stages of treatment, and the result is water as clear as this one in the glass," Alan Thomson, Managing Director of ADSSC, told Khaleej Times daily.
"The treated wastewater ends up with zero percent impurities, being just one step away from becoming potable. That step, involving adding minerals to the purified water, is a massive investment and not yet worth it." Only a handful of countries worldwide are commercialising drinkable wastewater and although perfectly safe and clean, not many people are keen on drinking it.
"In Abu Dhabi, all treated wastewater is used for greenery and forestry irrigation. It could be perfectly safe for farming too, but our infrastructure does not allow for that (currently). If we had treatment plants near farm lands, then it could be done," Thomson pointed out.
Across the emirate, the ADSSC has 41 treatment plants that purify all of Abu Dhabi's wastewater, thus alleviating the need for sewage to end up in the sea. Yet, only 60 percent of the treated wastewater is used. Still, this saves about 12 percent of potable water, whether from ground or desalination sources.
"In the future, we plan to re-use 100 per cent of treated wastewater, which would save 20 per cent of potable water," said Thomson.
According to Thomson, four new treatment plants have been commissioned, two in Abu Dhabi with a capacity of 300 mega litres per day each, and two in Al Ain with a combined capacity of 230 mega litres per day.
Although there is sewage produced by the business and industry sectors, the majority is residential. With the emirate's population constantly growing, so does its sewerage needs. According to the ADSSC, the sewerage requirements go up by eight percent annually.
Treating wastewater does have a negative impact on the environment, since it involves the use of chemicals and electricity consumption, but the ADSSC is keeping this impact to a minimum as chemicals are only used for disinfecting treated water, otherwise the process is a natural one, using good bacteria to kill off the bad ones.
"We collect sewage using gravity. The household drains are connected to the collection pipes, which are not horizontal, but go down, deeper and deeper underground," said Thomson. "Only when they are too deep we use a pump to bring the sewage up to the treating plants." The ADSSC's greatest ongoing project, the Strategic Tunnel Enhancement Programme (Step) is meant to further improve the sewerage collection system. Started in 2008, the Dh5.6 billion project will be one of the longest gravity-driven sewerage tunnels in the world at 41km.
When completed in 2015, the Step will provide for an average wastewater flow of 800,000 cubic metres per day and it will reach an ultimate capacity of 1.7 million cubic metres per day by 2030.
Apart from the main tunnel, the Step will have 43km of link sewers, which will transport the wastewater to treatment plants. They will be used to intercept the flows from existing gravity sewers upstream of the pumping stations.