Operational Optimization and Mass Balances in a Two-Stage MBR Treating High Strength Pet Food Wastewater

Abstract

A two-stage membrane bioreactor (MBR) system was evaluated for the treatment of high strength pet food wastewater characterized by oil and grease, chemical oxygen demand (COD), biochemical oxygen demand (BOD )5 , total suspended solids (TSS), total Kjeldahl nitrogen (TKN), NH4 –N , and TP concentrations of 2,800, 25,000, 10,000, 4,500, 1,650, 1,300, and 370 mg∕L , respectively, to meet stringent surface discharge criteria of BOD5 , TSS, and NH4 –N of <10 mg∕L , and TP of <1 mg∕L . Pretreatment of the dissolved air flotation effluent with FeCl3 at a dose of 3.5 g∕L , corresponding to a Fe:P molar ratio of 1.3:1 affected TP, TSS, volatile suspended solids (VSS), COD, BOD5 , and TKN reductions of 88, 72, 75, 11, 11, 36, and 17%, respectively. The two-stage MBR operating at a total hydraulic retention time of 5.3 days comprising 2.5 days in the first stage and 2.8 days in the second stage, and solids retention time of 25 days in the first stage consistently met the criteria despite wide variations in influent...