SELF-OSCILLATING COEXISTENCE OF METHANOGENS AND SULFATE-REDUCERS UNDER HYDROGEN-SULFIDE INHIBITION AND THE PH-REGULATING EFFECT

A simulation model of organic-matter anaerobic degradation described e arlier by the authors was used for the description of sulfate influenc e on methanogenesis. It was calibrated and verified on the experimenta l data of Parkin et al. (1990), where the anaerobic chemostats were ma intained at changing COD/S ratios from 60/1 to 2/1, with acetate as th e carbon source. The model was applied to investigate the interaction between sulfate-reducing and methane-producing bacteria. The stimulati on of the sulfate step increase showed that there was a threshold valu e of hydrogen sulfide concentration at which the system failed. When t he COD/S ratio was less than 10/1, both sulfate reduction and methane production shut down. Hydrogen sulfide and pH inhibitions were the mai n factors in the model for system failure, and the former played the r ole of trigger stimulating the positive feed-back loop between an incr ease in acetate and sulfate concentrations in the reactor and a decrea se in the pH level through microorganism activity. The simulations sho wed that there was an oscillating coexistence of MPB and SRB under the hydrogen sulfide inhibition and the pH regulating effect