Membrane Bioreactors: Results of Low Power Use Design Procedures

The use of membrane bioreactors (MBR) continues to increase across the world. In dry countries such as Australia, they become the foundation technology for reclaimed water production facilities. However, there is a perception that an MBR uses significantly more energy than a conventional continuous wastewater treatment facility and this is incompatible with greenhouse gas concerns especially in Australia where a carbon tax is potentially going to be legislated. This paper reports on the performance of MBRs commissioned in the Australian City of Cairns, North Queensland, with particular reference to the nutrient removal performance and the measured power consumption in comparison to conventional processes with clarification and tertiary filtration. The MBRs were designed in accordance with design procedures outlined in 2008 which support the principle of avoiding high recycle rates between the membrane tank and the aeration zone of the main process bioreactor as this raises the MLSS concentration increasing the power required for process aeration. The design procedure integrates the performance requirements for BNR and the physical requirements for membranes to enable the design to be optimised with respect to reactor size and power requirements.