Effects of reactor configuration on the performance of static-bed submerged media anaerobic reactors

Chiang, Chow-Feng
Major Professor
Richard R. Dague
Committee Member
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Civil, Construction, and Environmental Engineering

Three different configurations of cylindrical submerged media anaerobic reactors (SMARs) with packing volumes of 85 L were operated at 35°C for 415 days with COD loading rates varying from 1 to 12 g/L/d and three retention times of 0.5, 1, and 2 days. A synthetic waste consisting of a milk solution with a mineral supplement was used for the feed;Tracer studies on clean-bed and dirty-bed SMARs indicate that reactor configuration, biogas mixing, and biomass accumulation all have a significant effect on SMAR hydraulics and cause short-circuiting. The actual retention time can be reduced to as low as 0.6 of the theoretical retention time;Based on the isothermal energy dissipation theory, the higher hydrostatic pressures resulting from higher SMAR heights increases self-induced biogas mixing and improves the contact efficiency between substrate and organisms;Based on TCOD removal rate, the tallest SMAR performed slightly better at COD loading rates above 4 g/L/d. At COD loading rates equal to or below 4 g/L/d, there was little difference in TCOD removal rate between the three SMARs;The acetoclastic methanogenic activity (AMA) test developed in this study is reproducible within 6.5% at a mean of 0.39 L CH[subscript]4 (STP)/gm VSS/d. For VSS less than 1 g/L, a higher AMA is associated with lower VSS concentrations. For VSS greater than 1 g/L, AMA varies within a narrow range of 0.1 to 0.2 L CH[subscript]4 (STP)/gm VSS/d;Exit gas recycle at a ratio of 3.5-7.0% of exit gas flowrate resulted in a 5-13% increase in the methane content of the exit gas at a COD loading rate of about 10 g/L/d and a detention time of about 2 days. This suggests that, at high loading rates, hydrogen dissolution rate may be the rate-limiting step in anaerobic digestion.