Construction or modernization of a wastewater treatment plant (WWTP) with membrane bioreactor (MBR) technology requires selection of optimal configuration and design. The objective of this paper is to evaluate a hybrid MBR, i.e., a combination of a conventional activated sludge (CAS) process and an MBR, in comparison to a stand-alone MBR. This paper evaluates two different hybrid MBR configurations and a stand-alone MBR. The impact of these MBR configurations on operation, performance, energy consumption and economy is evaluated. A hybrid MBR operated in series provides certain operational flexibility, ensures more stable conditions for the activated sludge leading to a more stable MBR operation at energy and cost efficient conditions. Nevertheless, determination of the optimal plant configuration depends on the particular local situation.

The Membrane Bio Reactor (MBR) in Varsseveld is the first full-scale plant in the Netherlands and functions as a demonstration plant for MBR technology. It has been in operation for 5 years and many lessons have been learnt in that time. To gain experience with this new type of treatment and to demonstrate that MBR is suitable for purification of domestic wastewater in a real situation a vast research programme was undertaken. Based on the operational experiences and the research program it can be concluded that the MBR Varsseveld shows promising results. Compared to conventional activated sludge systems with sand filtration (CAS-SF), the MBR produces superior effluent quality. Energy consumption remains up to 30% higher than the CAS-SF system but there is possibility for further improvements. The cleaning philosophy, that combines a regular maintenance cleaning with 2-yearly intensive cleanings, is effective at maintaining the membranes in optimal condition. Based on the experiences with the Zenon ZW500d membranes, a membrane lifetime of up to 10 years is expected.

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