| Anaerobic chemostats were operated in a semi-batch mode to produce sulfide for heavy metal precipitation. Glucose, acetic acid, and methanol were used as a carbon source for microbial growth. With methanol and acetic acid, the average concentrations of biologically produced sulfide were 4 and 6 mM total sulfide, respectively, but COD reductions were mainly due to methanogenic activity with 65-81% methane gas composition. The maximum substrate utilization rates (k) of COD reduction in the methanol and acetate chemostats with sulfate addition were greater than those without sulfate addition.; With glucose, the highest sulfide of 8 mM was produced but COD reduction was very low and only 1% methane gas was produced. The fact that sulfate did not inhibit methanogenesis, when fed with acetic acid, suggests that the major inhibition occurred in acetogenesis from glucose. The sulfate reductions after 12 hr. were 1.89, 0.27, and 0.14 mg SO{dollar}sb4{dollar} reduced per mg COD reduced for glucose, acetic acid, and methanol, respectively. This means that higher-molecular-weight organics are preferred for biological sulfate reduction over lower-molecular-weight ones.; Dual organic substrates (glucose plus acetic acid) were used to study biological sulfate reduction coupled with biogas production. The results show that dual organics did not exhibit extreme inhibition on methane formation as did glucose alone. Instead, they helped methanogens work in harmony with acid formers as well as sulfate reducers to remove COD through biogas production. However, the optimum G/Ac COD ratio of which both sulfate reduction and biogas production are optimized appeared to be in the range of 0.5-1.; Direct copper addition to the chemostat decreased sulfide level and, also, COD reduction rate. However, in the copper-pretreated-addition chemostat, the COD reduction was even higher than that of control, suggesting the stimulatory effect of the residual copper upon methanogenesis.; The treatability study of copper sulfide precipitation indicated that with biological sulfide, the copper removal efficiency was better than that with inorganic sulfide for all different S/Cu ratios over a broad pH range. |
