Kinetics of growth, substrate utilization and sulfide toxicity for propionate, acetate, and hydrogen utilizers in anaerobic systems

Batch reactors and serum bottles were used to determine kinetics of growth, substrate utilization, and sulfide inhibition [dissolved sulfide (DS) and hydrogen sulfide (H2S)] in anaerobic systems fed propionate and sulfate. Thermodynamic analyses indicated six major groups of organisms were active in such systems: incomplete propionate oxidation by sulfate-reducing bacteria (SRB), propionate fermentation to acetate and hydrogen, acetate-oxidizing SRB, aceticlastic methanogenesis, hydrogenotrophic SRB, and hydrogenotrophic methanogens. Kinetic parameters determined for each of these groups were bacterial yield, decay coefficient, maximum specific substrate utilization coefficient, half-velocity constant, and inhibition coefficient (uncompetitive). Results indicated that the kinetic and thermodynamic advantages of acetate-utilizing SRB were erased by their sensitivity to sulfide toxicity. In addition, propionate fermenters were also very sensitive to sulfide toxicity. These results help to explain why methanogenesis from complex substrates occurs even in the presence of high concentrations of DS and H2S.