MBR functioning under steady and unsteady state conditions. Impact on performances and membrane fouling dynamics

This paper presents MBR performances observed under steady and unsteady state conditions where influent and permeate flow rates were punctually and simultaneously increased. Experiments were performed in a submerged membrane bioreactor presenting a 50 L working volume. Two capillary membrane modules, M1 and M2 (Koch systems) were placed on the outside of the bioreactor in a side stream position. Air was injected below each membrane module, ensuring vertical air lift circulation. To point out the role of the air membrane on membrane fouling control, different air flow rates were practised (1.36 m(3).m(-2).L-1 and 0.45 respectively for M1 and M2). Results confirm the high capacity of MBR to withstand high loading rate variations namely because of the total biomass retention by the membrane barrier whatever the biomass flocculation state. Under continuous extensive filtration conditions (10 LMH permeate flow rate) no significant differences were observed between TMP evolution for modules M1 and M2. Nevertheless, the results highlighted the determining role of the air membrane flow rate in controlling fouling reversibility when working in intensive filtration conditions (30 LMH) without any back-washing or relaxation procedure.