Two biogas scrubbing and cogeneration – combined heat and power (CHP) plant –are scheduled for the Northern Wastewater Treatment Works and the Driefontein Wastewater Treatment Works. Until now, the biogas produced by the WWTW plants has been used to fire boilers, which maintain the temperature in the digesters. But due to the escalation in the price of electricity and the WWTP’s to date have only used Anaerobic Digestion as part of the overall process to reduce the organic load on the WWTP.

At an estimated cost of R76 787 001, the design work started in September 2011 with the civil work on the first phase of the project, NWWTW, is scheduled to start in February. The Northern WWTW is expected to be commissioned by July 2012 and work on Driefontein will commence on commissioning of the former plant. The project will generate power and recover the heat from the gas fired generators on site to run grid parallel and supply the thermal energy required to the digesters in order to maintain temperatures. The plant will have the ability to supply power to portions of the WWTP when the utility supply falls away. The power plants will be built adjacent to the digesters in order to maximise thermal recovery, and will supply about 20% of the Northern WWTW’s power. As Joburg Water invests in additional digester capacity the WWTP’s load on the grid will be reduced accordingly.

The most environmental beneficial aspect of the project is the reduced electrical demand on Eskom thereby lowering carbon emissions. Thus far, no setbacks have been identified.

PROJECT TEAM
Project design, construction and operation WEC Projects (Pty) Ltd
Biogas scrubbing Provided by Applied Filter Technology
Gas engines Supplied by Guascor
Electrical design and implementation Zest Energy
C&I and pipework Ertec