Journal of Chemical Technology and Biotechnology, Vol.82, No.2, 158-164, 2007
Modelling a sequencing batch reactor to treat the supernatant from anaerobic digestion of the organic fraction of municipal solid waste
In this study, a lab-scale sequencing batch reactor (SBR) has been tested to remove chemical oxygen demand (COD) and NH4+-N from the supernatant of anaerobic digestion of the organic fraction of municipal solid waste. This supernatant was characterized by a high ammonium concentration (1.1 g NH4+-N L-1) and an important content of slowly biodegradable and/or recalcitrant COD (4.8 g total COD L-1). Optimum SBR operating sequence was reached when working with 3 cycles per day, 30 degrees C, SRT 12 days and HRT 3 days. During the time sequence, two aerobic/anoxic steps were performed to avoid alkalinity restrictions. Oxygen supply and working pH range were controlled to promote the nitrification over nitrite. Under steady state conditions, COD and nitrogen removal efficiencies of more than 65% and 98%, respectively, were achieved. A closed intermittent-flow respirometer was used to characterize and model the SBR performance. The activated sludge model ASM1 was modified to describe the biological nitrogen removal over nitrite, including the inhibition of nitrification by unionized ammonia and nitrous acid concentrations, the pH dependency of both autotrophic and heterotrophic biomass, pH calculation and the oxygen supply and stripping of CO2 and NH3. Once calibrated by respirometry, the proposed model showed very good agreement between experimental and simulated data.