Sequencing batch membrane reactor treatment: Nitrogen removal and membrane fouling evaluation

Performance of a laboratory-scale sequencing batch reactor using a membrane for effluent filtration was investigated in terms of chemical oxygen demand (COD) removal, nitrogen removal, and membrane permeability during long-term continuous operation treating synthetic wastewater. The reactor was operated with six 4-hour cycles per day consisting of 0.5, 2.0, and 1.5 hours for fill, aeration, and effluent filtration-idle, respectively. Minimal solids wasting occurred for the first 10 months of operation followed by an 8-day solids retention time (SRT) for the final 1.5 months. Membrane fouling was controlled by backwashing with aeration for 10 minutes during each cycle. A stable permeate flux of approximately 0.34 (L/m²·h)/kPa [34(L/m²·h)/bar] was achieved and was independent of mixed liquor suspended solids concentrations from 710 to 10 000 mg/L. The reactor effluent turbidity averaged less than 0.20 NTU, and more than 98% COD removal occurred. Nitrogen removal efficiency ranged from 87 to 93% through biological nitrification and denitrification. Most of the nitrate was removed during the mixed and unaerated fill period, but a significant amount of nitrogen was removed by simultaneous nitrification-denitrification (SNdN) during aeration at dissolved oxygen (DO) concentrations less than 3.0 mg/L. The SNdN removal increased with decreasing DO concentration in the reactor, although the nitrification rate was reduced at a low DO concentration. During operation with minimal solids wasting (1400-day calculated SRT), the average observed biomass yield was approximately 0.03 mg mixed liquor volatile suspended solids mg COD with an abundance of filamentous organisms in the reactor.