Towards stable operation of a dynamic membrane bioreactor (DMBR): Operational process, behavior and retention effect of dynamic membrane

• DM formation was much shortened by using a nylon mesh of 25 μm pore size
• Effluent turbidity kept low even in the DM formation stage.
• Stable flux and effective pollutants removal was achieved at 10 cm water head.
• Many substances retained in the cake layer were identified to be foulants.
• Surface brushing assisted the removal of “irremovable fouling” for DM regeneration.

An experimental study was conducted for characterizing the whole operational cycle of a dynamic membrane bioreactor (DMBR). With a nylon mesh of 25 μm pore size as support material, the filtration flux was suddenly halved within 5 min, indicating a rapid cake layer formation. Then the flux declined gradually and became stable at t=4 h, indicating the maturation of the dynamic membrane (DM) for stable operation. By periodical bottom aeration, the flux kept stable until t=24 h before physical cleaning should be conducted for DM regeneration. In such an operational cycle, effluent turbidity about 3 NTU was only detected at the start, dropped to about 0.5 NTU after 5 min and kept lower afterwards. Effective and stable removal of chemical oxygen demand (COD), ammonia, phosphorus was achieved in the 2-month continuous operation period. Although air backwashing brought about effective recovery of the flux, additional surface brushing could further remove the “irremovable fouling”. By morphological and physicochemical analysis, it was identified that the DM could retain 15.3% of COD and 10.6% of polysaccharides from the activated sludge, as well as certain amount of protein-like and humic-like substances. These membrane fouling substances should be removed by physical cleaning for DM regeneration.

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