Performance of an inclined-plate membrane bioreactor at zero excess sludge discharge

The inclined-plate membrane bioreactor (iPMBR) is investigated on a pilot scale for 123 days of municipal wastewater treatment at zero excess sludge discharge. Results indicated that at hydraulic retention time of 6 h, average removals of chemical oxygen demand (COD), ammonia nitrogen and turbidity were 92.1, 93 and 99.9%, resulting in daily averages of 12.6 mgCOD/L, 1.3 mgNH3-N/L and 0.03 NTU, respectively. At return sludge recycle ratio of 300%, total nitrogen removal averaged 71.7% and daily averages in the permeate was about 8.86 mgTN/L that is lower than the maximum contaminant level (i.e., 10 mgTN/L) allowed by USEPA National Primary Drinking Water Regulations. The inclined-plates were in the presence of intermittent air blowing much effective to confine concentrated sludge within the anoxic tank. The sludge concentration difference between anoxic and aerobic tanks were found to be adjustable from 0.1 to 13.1 g/L in terms of mixed liquor suspended solids. The mechanism of anoxic sludge sedimentation/separation was discussed. The effect of air blowing was examined from the viewpoint of diffuser type, air flowrate and ON/OFF cycles. Tests were also conducted to explore the evolution of weir sludge concentration over one blowing cycle.