Simultaneous Nitrification Denitrification in an Aerobic MBR Treating High Strength Pet Food Wastewater

This paper discusses nitrogen removal mechanisms in an aerobic membrane bioreactor (MBR) treating high strength pet food wastewater characterized by oil & grease, COD, BOD5, TSS, TKN, NH4-N concentrations of 2800 mg/L, 25000 mg/L, 10000 mg/L, 4500 mg/L, 1650 mg/L and 1300 mg/L respectively. An MBR operating at SRT >25 days achieved mixed liquor total suspended solids (MLTSS) concentrations >30000 mg/L with a mean particle size of 50 μm. Potentials for various nitrogen removal mechanisms in the MBR were evaluated. Even at DO of 1.3 mg/L and oxygen reduction potential (ORP) > +90, the MBR removed > 200 mg/L of influent nitrogen by simultaneous nitrification denitrification (SND) through nitrite pathway. Contrary to the general diffusion limitation hypothesis, this paper infers the nitrification and denitrifications to take place in separate sludge particles. Mass balance revealed cell synthesis, stripping and SND to remove 14%, 17% and 21% of the influent nitrogen respectively.