Competitive reaction kinetics of sulfate-reducing bacteria and methanogenic bacteria in anaerobic filters

Abstract

A kinetic model for the anaerobic filter (AF) that takes into account the mass fractions of sulfate-reducing bacteria (SRB) ( f SRB) and methanogenic bacteria (MB) ( f MB) and an inhibiting effect of H 2S on bacterial groups is proposed. When the acetate-fed AFs were maintained at the low organic loading rate of 2.5 kg COD/m 3 d, variations of the influent COD / SO 4 2 - ratio (0.5–3.0) does not materially affect the acetate removal efficiency (all varying between 98.1% and 99.7%). With an increase in influent COD / SO 4 2 - ratio, both the biofilm thickness and the specific substrate utilization rate decreased slightly but f SRB decreased markedly. The estimated results of f SRB and f MB showed that SRB out-competed MB for bacterial growth if the influent COD / SO 4 2 - ratio was maintained at less than 1.3, whereas MB out-competed SRB for bacterial growth if the influent COD / SO 4 2 - ratio was maintained at greater than 2.0. The specific substrate utilization rate of SRB (0.19–0.24 mg acetate/mg VSS d) was lower than that of MB (0.31–0.59 mg acetate/mg VSS d). The estimated kinetic parameters disclosed that the affinity of acetate to MB was higher and unionized H 2S imposed a greater inhibiting effect on MB. The model simulation results (acetate and sulfate removal) agreed well with the experimental results.