| Kinetics of substrate utilization for different groups of bacteria in an anaerobic system fed propionate (HPr) and sulfate (SO{dollar}sb4){dollar} were determined using batch experiments. Six major COD flow pathways were identified based on thermodynamics: incomplete oxidation of propionate by sulfate reducing bacteria (SRB), propionate fermentation to acetate (HAc) and hydrogen (H{dollar}sb2),{dollar} HAc utilization by SRB, aceticlastic methanogenesis, H{dollar}sb2{dollar} utilization by SRB and hydrogenotrophic methanogenesis. Yield coefficients (mg VSS/mg COD) were determined to be 0.032, 0.042, 0.024, 0.039, 0.042 and 0.050, respectively. Specific substrate utilization rates (mg COD/mg VSS-day) were found to be 3.3, 3.5, 4.6, 3.6, 4.4 and 3.7, respectively. The half saturation constant, K{dollar}sb{lcub}rm s{rcub}{dollar}, was found to be 41, 27, 50 and 29 (mg COD/L), respectively, for the acid-utilizing bacteria, and {dollar}1.6times 10sp{lcub}-4{rcub}{dollar} atm and {dollar}1.9times 10sp{lcub}-4{rcub}{dollar} atm for hydrogen utilizing SRB and hydrogenotrophic methanogens, respectively. Kinetics of sulfate reduction and toxicity due to dissolved sulfide (DS) and hydrogen sulfide (H{dollar}sb2{dollar}S) were studied using serum bottles. Uncompetitive inhibition appeared to best describe the inhibition due to sulfide. Values of inhibition coefficients (K{dollar}sb{lcub}rm i{rcub}{dollar} in mg S/L) for DS for the six groups listed above were: 681, 53, 35, 222, 422 and 1430, respectively. Corresponding K{dollar}sb{lcub}rm i{rcub}{dollar} values for H{dollar}sb2{dollar}S were 194, 25, 8, 108, 140 and 625, respectively. Acetate-utilizing SRB and propionate fermenters were found to be the most sensitive to sulfide toxicity. A model was developed for a completely mixed reactor (CSTR) and kinetic parameters determined in this research were used to compare against results from chemostats. The CSTR model was partially successful in explaining results from chemostat studies. Under stressed conditions, propionate oxidation by SRB and aceticlastic methanogenesis were the major pathways of COD utilization. Upflow anaerobic filters fed HPr and SO{dollar}sb4,{dollar} and HAc and SO{dollar}sb4{dollar} were also used in this research to compare attached-growth and complete-mix systems. The anaerobic filters were able to withstand significantly higher sulfide concentration than chemostats. Selective inhibitors BES and {dollar}beta{dollar}-fluorolacate were found to be effective at 25mM and 100 mg/L, respectively. |
