Dosing effect of zero valent iron (ZVI) on biomethanation and microbial community distribution as revealed by 16S rRNA high-throughput sequencing

•Potato starch processing wastewater was digested with zero valent iron (ZVI).•Methanation was enhanced in ZVI dosed reactors.•When ZVI was employed, Chloroflexi and Euryarchaeota increased by 2.46 and 3.53 times, respectively.•Microbial community shift was most pronounced in assays with 10 and 20 g/L ZVl.•Chloroflexi, Firmicutes and Euryarchaeota were most dominant phylum revealed by 16S rRNA gene sequencing.

The effect(s) of zero-valent iron (ZVI) in anaerobic digestion and its related impact on microbial community structure is still unclear. The effect of addition of 0, 1, 4, 10, 20 g/L ZVI on the microbial community structure was investigated during methanation from potato starch processing wastewater (PSPW). Methane production rate constants (k) obtained from kinetics studies indicated ZVI dosage had impacted on the methanation and microbial community structure. 16S rRNA gene sequencing revealed Chloroflexi, Firmicutes, Euryarchaeota, Bacteroidetes, Proteobacteria, and Synergistetes as dominant phyla in all samples. When ZVI was employed, Chloroflexi, Firmicutes and Euryarchaeota increased by 2.46, 1 and 3.53 times, respectively, whereas Bacteroidetes, Synergistetes, Proteobacteria and Caldiserica decreased. Growth trend was similar for populations of the genus Methanosaeta, Levilinea, Longilinea and Syntrophomonas. Microbial community shift was most pronounced in assays with 10 and 20 g/L ZVl. ZVl dosed reactors performed better at methanation as opposed to non-ZVl dosed reactor and 10 g/L ZVl was the optimum dose. The study revealed that, ZVI had impacted positively on the microbial community structure to favor and enhance both hydrolysis-acidification and methanogenesis processes during PSPW digestion.