Application of micro-filtration and ultra-filtration membranes for water reclamation has grown significantly in recently years due to lower foot print and stable product water quality. For membrane bioreactor (MBR) application, it is critical to improve the sludge quality to allow membrane systems to operate at higher flux without significant trans-membrane pressure (TMP) increase. It was found that quality of mixed liquor can be enhanced by hydrocyclone to improve the operating flux of MBR. When the membrane system was exposed to a dense particle fraction of the mixed liquor after installation of hydrocyclone, TMP was found to be stable at 16–18 kPa for approximately 8 months while operating at net flux 25 L/m2-hr (LMH). Then, TMP gradually increased to 21 kPa in the next 6 months and sharply increased to 35 kPa toward the end of this investigation. It means TMP was relatively stable without any need of recovery cleaning for over one year of operation. The improvement of MBR performance by introducing a hydrocyclone could be due to removal of unwanted mixed liquor as overflow. The dense component of the mixed liquor as overflow of hydrocyclone should be retained in the MBR system.

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