Wet scrubber systems help clear the air in Abu Dhabi

By Rick Parker

UAE officials begin upgrading two wastewater treatment plants following citizen complaints of odours from the facility. USFilter's RJ Environmental Products deliver nine LO/PRORegistered odour control wet scrubber systems to solve the problem.

A major upgrade to the sludge management and odour control systems in the Mafraq sewage treatment works in Abu Dhabi, United Arab Emirates, should eliminate offensive odours and expand treatment capacity to accommodate a growing population and industrial growth. USFilter delivered eight LO/PRORegistered odour control wet scrubber systems in March 2002, which are currently being installed in the facility's two wastewater treat-ment plants that treat an average of 210,000 m3/day of municipal and industrial wastewater. Commission-ing and system start-up will be completed this summer.

Abu Dhabi Municipality selected USFilter's RJ Environmental Products to install the scrubber systems and ten chemical storage tanks.

Fresh water is a scarce commodity in the UAE so wastewater reuse provides much of the nation's irrigation water. "Water produced by the facility bene-fits the region in so many ways, saving declining fresh water reserves and enhancing the environment," said Sahban Ali, technical manager of the Concorde Trading Company in Abu Dhabi.

For this installation, the LO/PRO systems treat an average hydrogen sulphide concentration of 100 ppm with peak concentrations up to 400 ppm and at a removal efficiency of 99.9%. This performance level must be achieved in a climate where ambient temperatures regularly exceed 50°C at near 100% relative humidity. The Abu Dhabi Municipality knew that the LO/PRO system would perform well in this extreme environment because USFilter installed two earlier systems in 1998 and 1999. The municipality specified strict chemical consumption limits.

USFilter used the patented 3-stage LO/PRO wet scrubber design to meet performance requirements. The LO/PRO system is a multi-stage packed tower wet scrubber system with a patented process and configuration designed to minimise chemical consumption and footprint. Sodium hydroxide (caustic) is used in the first and second stages, and a mixture of sodium hydroxide and sodium hypochlorite (bleach) is used in the third stage. Approximately 80% to 90% of the hydrogen sulphide is removed in the first two stages, thereby reducing the quantity of sodium hypochlorite required to achieve 99.9% removal. The design allows the three stages to be combined in a single rectangular vessel, which minimises the footprint and allows un-reacted chemicals from Stages 2 and 3 to overflow into Stage 1 to minimise chemical waste. Softened water supplies each system to minimise scaling and improve system operation.

The Mafraq STW odour control system consists of eight LO/PRO systems ranging in capacity from 3,000 cfm to 24,500 cfm. The scrubbers will treat odours from the headworks operations, primary settling tanks and sludge consolidation tanks.

A separate LO/PRO odour control system for the main pump station (MPS-5A) will arrive by June 2002.

Author's note

Rick Parker is the operations manager at USFilter's RJ Environmental Products, located in Poway, California, USA.