Sulfide tolerance enhancement using direct interspecies electron transfer in an electrical energy prompted Up-flow anaerobic sludge blanket (UASB) reactor

The treatment of sulfate rich wastewater leads to the failure of anaerobic digestion process due to high sulfide generation. Sulfide toxicity for the anaerobic digestion process is one the major concern that needs to overcome in order to recover the methanogenic potential of the sulfate-rich wastewater. In the present study, we tried to enhance the sulfide tolerance by promoting direct interspecies electron transfer (DIET) via electrical energy input (EEI). Two different operational conditions have been set to study the effect of sulfide on methanogenic process using up-flow anaerobic sludge blanket (UASB) reactor, comprising one control and one EEI reactor with an applied voltage of 0.6 V. The operation was continued for 194 days under different COD/SO4 2- ratios. The EEI reactor exhibited maximum performance of 2.3 L CH4/L/d at the COD/SO4 2- of 5 which is 15 % higher than the control. The free sulfide concentration were 251 and 283 mg S2-/L in control and EEI reactors, exceeding the inhibition threshold (50-200 mg S2-/L). Only EEI reactor could keep its advanced performance, by acquiring 12 and 15% higher sulfate removal and CH4 productivity respectively than control reactor. Form this study, it can be claimed that DIET stimulation has potential for enriching efficient sulfate-metabolizing microbes. Furthermore, microbiological studies can enhance the depth of the mechanism and unearthed the reason behind the sulfide tolerance system supported by DIET promoting reactor.