Simultaneous nitrogen and phosphorus removal in a continuously fed and aerated membrane bioreactor

This research demonstrated the feasibility of simultaneous biological nitrogen and phosphorous removal in a single tank membrane bioreactor without cycling of air and/or feed through operation at a low dissolved oxygen (DO) and a high biomass concentration. Chemical oxygen demand removal efficiency was more than 98% and total nitrogen removal efficiency was 55%. Seventy-five percent of the total nitrogen removal was through simultaneous nitrification-denitrification (SND) and 25% through assimilation into the biomass. Interestingly, more than 98% phosphorous was removed and microbiological analysis showed the presence of polyphosphate-accumulating organisms in the activated sludge. The operating mixed-liquor suspended solids was between 16 and 23 g/L. The optimum DO was found to be 0.7-0.8 mg/L.