Evaluation of sulfate-containing sludge stabilization and the alleviation of methanogenesis inhibitation at mesophilic temperature

Methanogenesis process is usually inhibited in the presence of sulfate because sulfate induces the sulfate-reducing bacteria (SRB) to compete with methanogenic bacteria for the same substrate and the produced sulfide has toxicity to the anaerobic microorganisms. Therefore, the possibility for controlling the competition is important for practical application of anaerobic treatment processes of sulfate-containing sludge. In this study, the activated sludge was enriched with sulfate concentration and was treated with various concentrations of nanoscale zero valent iron (nZVI) in order to evaluate the potential of nZVI for alleviating the methanogenesis inhibitation of sulfate-containing activated anaerobic sludge. Generally, due to sulfate anions, the outcomes of this study showed that a rapid accumulation of partially stabilized organic materials was observed which indicates that the whole anaerobic digestion process was ceased. The results also reveal that nZVI contributed to significant increases in methane yield. Meanwhile, SRB in the presence of nZVI can react with sulfate to produce sulfide and subsequently can be precipitated as iron insoluble sulfides due to the sulfate reduction by nZVI. The results demonstrate that nZVI was readily utilized as an electron donor for methanogenic bacteria and sulfate reduction and hence has an assuring potential in waste sludge treatment applications.