Microbial community and sulphur behaviour in phototrophic reactors treating UASB effluent under different operational conditions

Two phototrophic bioreactors were applied for sulphide removal from anaerobic effluent. They were operated at different hydraulic retention times (HRTs) and packed with different materials (R1 - polypropylene rings; R2 - polyurethane sponges). The microbial communities in both reactors were investigated by 454 pyrosequencing and results revealed that they were complex and the composition and diversity were influenced by the packing material as well as by the HRT. Sequences of phototrophic purple sulphur bacteria (Chromatiaceae) and non-sulphur bacteria (Rhodopseudomonas, Rhodobacter, Rhodocista and Blastochloris) were detected in both reactors together with sequences belonging to hydrolytic/fermenting bacteria, methanotrophic, sulphate-reducing bacteria and methanogens. Higher diversity and abundances of sulphur bacteria were observed in R1 than in R2. Whereas higher abundances of non-sulphur bacteria were observed in R2 than in R1. Greater sulphide removal efficiencies were achieved in both reactors at an HRT = 12 h. An almost complete abatement of the dissolved sulphide (>90%) together with a partial conversion of sulphide to sulphur (28%) was achieved in R2-sponge operated at an HRT of 12 h. The results call attention for the potential use of phototrophic reactors for the abatement of dissolved sulphide (and possibly organic matter and methane) from the anaerobic reactors effluents.