Every drop counts
The Al Wathba 2 wastewater treatment plant recycles precious water for the city of Abu Dhabi
The Al Wathba 2 wastewater treatment plant was built in the desert outside Abu Dhabi to manage the rapidly expanding amount of wastewater produced by the capital of the United Arab Emirates (UAE).
The facility added 300,000 m3 per day of treatment capacity when it was commissioned in 2012 by Al Wathba Veolia Besix Waste Water, a joint venture between the government of Abu Dhabi, represented by ADWEA, and two private companies – Veolia and Besix.
According to official statistics, Abu Dhabi was witnessing an average annual demographic growth of roughly 8%. A bigger population means higher demand for water and therefore more wastewater is produced.
The other main driver behind the need for the plant was that potable water produced by desalination plants was being used for greenery and landscaping and a lot of wastewater was not being recycled.
Reusing wastewater means relieving some of the demand on precious potable water, which is produced at higher cost than treated water. The water produced by the plant is mainly used for irrigation and landscaping as well as a multitude of industrial uses, like concrete mixing.
Dany Fawaz, executive managing director, Al Wathba Veolia Besix Waste Water, says there were options to consider as to the treatment technology, but in the end the joint venture opted for an advanced but robust technology based on conventional treatment rather than resorting to more advanced technology that was yet to be proven on a large scale.
“It’s the long-term cost,” Fawaz explains. “With technologies that are very advanced but not yet proven, you have a lot of risk and being the operator of the plant, we would be taking a chunk of that risk.
“Plus, with the harsh environment that we’re working in, it can’t be foreseen what the cost impact would be in the future. And we want a reliable plant that would last a minimum of 25 years if not more,” he adds.
The plant uses an advanced extended aeration technology with Carrousel® type biological tanks. It also incorporates some advanced Veolia technologies for various sub-treatment processes to enhance the efficiency.
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One of the first and biggest challenges the project faced was securing financing after the bid was won in 2008 at the start of the financial crisis, Fawaz says. On the ground there were a few other challenges that came with building a greenfield site in the middle of the desert, where there were no roads leading to it.
During the commissioning phase there was a challenge to fine tune the plant, because the quality of the incoming sewage was worse than expected. It took longer to figure out how to best configure the plant to produce clean water.
Fawaz explains: “There was a higher percentage of contaminants in the wastewater than foreseen in the design specifications. We speculate that the source was industries that were not clearly identified and which were discharging highly contaminated water into the domestic network.
“We still have challenges with sewage quality but this is pretty much under control. We are now more familiar with what to expect and have the measures in place to cope with it.”
The fact that the local population continues to grow fast means that Abu Dhabi will need more wastewater treatment capacity at some point in the future. Abu Dhabi Sewerage Service Company (ADSSC) has commissioned a masterplan that will be used to determine whether a third plant will be added at Al Wathba or built at a separate location.
There would be obvious benefits to building a new plant adjacent to the existing facility, such as sharing some existing infrastructure but, at the same time, there are other considerations which could tilt the decision towards another location altogether.
“The ADSSC network has different catchments and some of them are more difficult to connect to the STEP (Strategic Tunnel Enhancement Programme), the tunnel ADSSC is building to transport sewage from Abu Dhabi all the way to Al Wathba,” says Fawaz.
The tunnel, which is around 40 kms long and 5.5 meters in diameter at its widest point, is expected to bring a number of benefits when it is commissioned at the end of this year or early in 2016.
“We hope that the quality of the sewage we receive will be better because the tunnel will be delivering mainly domestic sewage from Abu Dhabi City and excluding some of the catchment areas where industries are relocated,” says Fawaz.
And because it uses gravity instead of pumping stations, it will reduce the amount of energy, and therefore the cost, currently required to transport sewage to the wastewater treatment plant.
“ADSSC would achieve a drastic reduction in energy consumption and in network maintenance costs,” says Fawaz. “The gravity tunnel will hopefully be maintenance free for many decades.”
- Al Wathba 2 wastewater plant
- Average flow: 300,000 m3/day
- Population equivalent: 1 million (Abu Dhabi)
- Tolerance capacity: 345,000 m3/d
- Peak flow to pre-treatment: 25,000 m3/hour
- 25 years Duration of the operation contract
- 2.5 years For design and construction of the plant