In this study, operation and maintenance performance in two long-term operating Membrane Bioreactor (MBR) wastewater treatment facilities were investigated. One facility in Japan started its operation in 1999 showed that both effluent BOD and n-hexane extracts were less than 5 mg/L, and a cumulative replacement percentage (CR%) of membrane cartridges was 7.8% as of 2008. Another facility in the United Kingdom (UK) started its operation in 1998 showed that average effluent BOD was less than 5 mg/L and more than 5-log removal of faecal coliforms was maintained. The CR% was 6.4% as of 2008. Amongst 95 facilities in Europe, the CR% was 6.4% after 5-year operation. In order to inspect product quality of membrane cartridges after 10-year operation in the UK facility, clean water flow (CWF) rate and pore size distribution were measured. The CWF rate was approximately 100% of that of new membrane cartridge's, and the pore size distribution was well maintained at less than 0.46 μm. A microscopic observation showed some scratches on the membrane surface. However, they did not lead to deteriorate permeate quality. These data suggested that the membrane cartridges can be used as long as 10 years.
Keywords: KUBOTA submerged membrane unit, membrane bioreactor, membrane cartridge