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

A kinetic model for the anaerobic filter (AF) that takes into account the mass fractions of sulfate-reducing bacteria (SRB) (fSRB) and methanogenic bacteria (MB) (fMB) and an inhibiting effect of H2S on bacterial groups is proposed. When the acetate-fed AFs were maintained at the low organic loading rate of 2.5 kg COD/m3 d, variations of the influent 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 ratio, both the biofilm thickness and the specific substrate utilization rate decreased slightly but fSRB decreased markedly. The estimated results of fSRB and fMB showed that SRB out-competed MB for bacterial growth if the influent ratio was maintained at less than 1.3, whereas MB out-competed SRB for bacterial growth if the influent 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 H2S imposed a greater inhibiting effect on MB. The model simulation results (acetate and sulfate removal) agreed well with the experimental results.