The potent effects of polyoxometalates (POMs) on controlling sulfide and methane production from sewers

Although the dose of biocides to sewers could control sulfide and methane production, the high resistance of sulfate-reducing bacteria (SRB) to biocides would increase dosing frequency and thereby enlarge chemical costs. Polyoxometalates (POMs, Group VI oxyanion), as a specific inhibitor of SRB, has been applied for sulfide control in oil fields and anaerobic digesters, but not demonstrated in sewers. This study filled such knowledge gap and investigated its feasibility for methane alleviation. Long-term monitoring demonstrated that one-time dosing of 2 mM POMs into sewers immediately reduced sulfide production by >90 %. And the time for recovering 50 % sulfide production was beyond 20 days, which was much more outstanding than other chemicals. POMs combined with a low level of free nitrous acid (0.045 mg-N/L) could overcome the relatively low methane control of the single POMs dosing, with 80 % suppression of methanogenic activity for 30 days. Meanwhile, the POMs-based strategy reduced the average organic carbon loss by 18 %. Furthermore, the beneficial side-effect of in-sewer POMs-dosing on downstream nitrogen removal could be achieved with the confluence of sewage. Model-analysis indicated the recovery of sulfide and methane was a re-formation process of biofilms. Mechanistic study elucidated POMs broke the extracellular polymeric substances of biofilms and damaged the cell membranes due to accumulations of intracellular reactive oxygen species. This suppressed microbial metabolic activities including organics dehydrogenation, energy provision and electron transfer processes, and inhibited key enzymatic activities. Microbial community analysis suggested POMs shifted microbes towards against hydrolysis, acidogenesis, dissimilatory sulfate reduction and methanogenesis. Further, predicted functional genes revealed that metabolic pathways were mostly down-regulated by POMs. This study provided a better understanding for controlling sulfide and methane in sewers using biocides.