| Sulfate reducing bacteria (SRB) belong to genera of anaerobic microbes that reduce sulfate and other sulfur oxyanions (SOxy− ) to sulfide, through biologically mediated transfer of electrons, from organic (electron) donor to sulfate or other SOxy− . Different sulfur oxyanions, specifically sulfate (SO4 2−), sulfite (SO32−) and thiosulfate (S2O32−), were used as terminal electron acceptors for mixed cultures containing SRB in lab scale batch reactors, at 35°C in an anaerobic environment. The mixed cultures were inoculated from sludges of two municipal waste treatment operations. These mixed cultures were observed to reduce all three types of SOxy− using lactate or glucose as carbon/energy source. The rates of SOx y− reduction were found to be in the order of S2O 32− > SO32− >> SO42−, which is logical considering the oxidation states of S in these SOxy−. COD/SOx y− ratio (ratio of electron donor/electron acceptor) was found to have an impact on SRB activity. Theoretically required values of this ratio were calculated based on the stoichiometry for all three SOx y−. Experimental values of optimal COD/SOx y− ranges for maximum SOxy− reduction were also determined. It was observed that the theoretically required values of COD/SOxy− ratios lie within the experimentally observed optimum ranges. The observed optimum ranges of COD/SO xy− ratios for maximum total SOx y− removal efficiency were (in g of COD/g of SOx y− units) 0.5–1.3, 0.6–1.5 and 0.4–1.1 for SO42−, SO32− and S2O32− respectively. Similar ranges were observed based on the maximum removal of COD, suggesting that under the optimal conditions, SRB contributed predominantly to the consumption of carbon/energy source. |
