A 41km ‘green’ tunnel–one of the largest and longest gravity-driven sewerage networks in the world–will ensure that odour emanating from sewerage system will be a thing of the past.

The eco-friendly 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.

About 33km that constitutes 80 per cent of the AED 5.7 billion Strategic Tunnel Enhancement Programme (STEP), has been completed as of last month (January 2013) and the rest will be completed by the end of 2015, Abdullah Ali Musleh Al Ahbabi, Chairman of Abu Dhabi Sewerage Services Company (ADSSC), announced on 4 Feb. 2013.

The deep tunnel — up to 5.5m id and starting at 27m underground and reaching a depth of 100m — will not require regular maintenance for the next 80 years. The project began in 2009.

The tunnel starting from Karama area in Abu Dhabi city to Al Watbha treatment plant will triple the capacity of Abu Dhabi’s sewerage network, said Omar Al Hashimi, Head of Assets
Department in ADSSC.

The existing system deals with 400,000m3 of sewage a day, but the new tunnel can carry 1.7Mm3 sewage, which is the expected demand by 2030, said Nasser Khalfan Al Nuaimi, Programme Management Department Manager at ADSSC.

The new tunnel will do away with 34 pumping stations in the existing system that consumes huge amount of energy, said Alan Thomson, managing director of ADSSC. They will be replaced by one pumping station at Al Watbha treatment plant, he said.

The current system has the risks of emanating odour through the 34 pumping stations but the new tunnel will end that problem, said Mohammad Ahmad Al Mansouri, a division manager at ADSSC. An inbuilt system in the tunnel will automatically extract odour from the sewage, he said.

The sewage will be carried by gravity alone with pumping required only to take the waste water to the treatment plant at Al Watbha.

About 100 per cent of sewage is currently recycled and 60 per cent is reused. The remaining 40 per cent of recycled water is dumped to the sea for lack of infrastructure but that issue will be sorted out very soon, officials said.

The STEP is also one of the largest infrastructure projects using advanced technology of global high standards in meeting environmental and sustainability considerations.

It is part of ADSSC’s five-year strategic plan initiatives in compliance with Abu Dhabi’s
vision 2030. The project is being carried out without disturbing the traffic, main roads and other infrastructure works.