The eco-friendly sewer main is the major part of the city’s ambitious Strategic Tunnel Enhancement Programme (STEP), costing AED 5.7bn (USD 1.6bn), which will almost triple the capacity of its sewerage network.

The STEP features three key components: 41km of deep sewer pipes, 43km of smaller diameter link sewers, and a pumping station adjacent to the Al Wathba Independent Sewerage Treatment Plants, where the major sewer main ends.

An initiative in compliance with Abu Dhabi’s Vision 2030, the project will cater to future needs arising with an increasing population.

"It is meant for the increased population of 2030; however if the population growth is slow, this system may serve until 2040 or even beyond," officials of the Abu Dhabi Sewerage Services Company (ADSSC) said on 6 October.

The company organised a ceremony to celebrate the sewer main breakthrough of the eighth TBM of the tunnel project. The final breakthrough completed the excavation of all sections of main tunnel.

The TBMs mined through mixed ground conditions of dolomitic siltstone, clay stone, mudstone, and gypsum without causing any adverse surface settlements.

Over 1,500 skilled tunnel workers were employed on all of the eight TBM drives.

With completion of the backbone of the project, the major tunnel stretching from Al Mushrif to Al Wathba, the focus has shifted to the construction of 43km long sewerage link tunnels.

About 26 per cent of the construction of sewer links is over and the rest will be completed by 2015, Alan Thomson, managing director of ADSSC, said.

The pumping station at Al Wathba, one of the biggest in the world, will replace 34 existing pumping stations across the city, he said.

The ‘green’ tunnel will drastically reduce the carbon footprint of Abu Dhabi’s sewerage system and save AED 4.2bn (USD 1.14bn) to be spent on energy and maintenance costs in the next 25 years.

The tunnel starts at 27m underground and reaches a depth of 100m. It will not require regular maintenance in its entire lifespan of 80 years.

The project began in 2009.

The existing system deals with 600,000cu.m of sewage a day, but the new tunnel can carry 1.7Mcu.m of sewage, the expected demand by 2030.

Abu Dhabi Sewerage Services Company (ADSSC) is the service provider for sewerage services and, owns and operates the sewerage network and treatment plants throughout the Emirate of Abu Dhabi. To meet growing sewerage infrastructure demands, ADSSC has developed a comprehensive plan to accommodate the projected sewage flows in future.

As part of ADSSC’s five-year strategic plan initiatives, the project is being carried out without disturbing the traffic, main roads and other infrastructure works.