PRETREATMENT REQUIREMENTS FOR MEMBRANE BIOREACTORS

Adequate pretreatment including fine screening is essential to the stable, long-term operation of membrane bioreactors (MBR) used to treat municipal wastewater. The amount of screenings generated by a screen with 1-2 mm size openings ranges between 10-25 dry mg/L. The cost of fine screening represents less than 3% of the total investment cost for a MBR-based wastewater treatment facility. Case studies for three large MBR plants are presented illustrating that the membranes are free of trash and sludge accumulation after a cumulative 9 years of operation. Finally, concepts for mixed liquor screening are presented and the pros and cons of this approach are analyzed.