Variations in microbiome composition of sewer biofilms due to ferrous and ferric iron dosing

During transport of wastewater in force mains, sulphide and possibly methane formation take place due to prokaryotic activity. Sulphide has several detrimental effects and addition of ferrous or ferric iron for abatement by precipitation is commonly applied. Precipitation stoichiometry and efficiency of this process have been investigated in detail. However, it is largely unknown how ferrous and ferric iron influence prokaryotic populations of sewer biofilms. The microbiomes of iron-treated force main biofilms were, together with an untreated control, examined by sequencing of the 16S rDNA V3+ V4 regions. Differences in distribution and abundance of several bacterial and archaeal genera were observed, indicating that treatment with ferrous and ferric iron for sulphide abatement differentially changed sewer force main microbiomes. Furthermore, differences at the functional level (KEGG orthologs, KOs) indicate that ferrous and ferric iron treatment possibly can decrease methane formation, whereas functions related to dissimilatory sulphate reduction seemed unaffected.