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.
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