A two-stage membrane bioreactor was used to treat dissolved-air-flotation pretreated, high-strength pet food wastewater characterized by oil and grease concentrations of 50 000 to 82 000 mg/L and total chemical oxygen demand (COD) and five-day biochemical oxygen demand (BOD 5 ) concentrations of 100 000 and 80 000 mg/L, respectively, to meet stringent surface discharge criteria (i.e., BOD 5 , total suspended solids [TSS], and ammonium-nitrogen [NH 4 1 -N] of ,10 mg/L at an overall hydraulic retention time of 6.3 days). Organic contaminants were removed primarily in the first stage, followed by almost complete removal of ammonia in the second stage. Despite a rise in poorly biodegradable COD in the second stage, overall removal of TSS, BOD 5 , COD, and ammonia was 100, 99.9, 95.2, and 99.7%, respectively, thus readily achieving the required criteria. Consistent nitrite accumulation over a period of more than 100 days, even at dissolved oxygen concentrations of more than 2.5 mg/L, was remarkable. A residual alkalinity requirement for nitrification was quantified. Membrane performance was extensively studied in this work. Water Environ. Res., 78, 661 (2006).
This study explored two stages MBR to treat DAF-pretreated high strength pet food wastewater characterized by oil & grease concentrations of up to 50,000 to 82,000 mg/L and total COD and BOD 5 concentration of 100,000 and 80,000 mg/L respectively to meet stringent surface discharge criteria i.e. BOD 5 , TSS and NH 4 -N of < 10 mg / L. As anticipated, organic contaminants were removed primarily in the 1 st stage, followed by almost complete removal of ammonia in the 2 nd stage. More then 96% of COD was removed in the 1 st stage even at hydraulic retention time of 2.8 days which was attributed to ability of the membrane to retain biomass with total suspended solids (TSS) concentration of up to 35 g/L. Overall removal of TSS, total COD, total BOD 5 and ammonia was 100%, 95.2%, 99.9% and 99.7% respectively, which rendered concentration of these parameters <10 mg/L in the final effluent. Rise in poorly biodegradable COD across the 2 nd stage reduced overall COD removal efficiency of the system. Occurrence of consistent nitrite accumulation observed over a period of more than 100 days (or >17 overall HRTs) even at dissolved oxygen (DO) concentration of more than 2.5 mg/L was remarkable. Residual alkalinity requirement for nitrification was quantified. Membrane performance in contaminant removal and its operational aspects were extensively studied in this work.
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