Polyurethane as an alternative support media to low-density polyethylene in fermentative-sulfidogenic reactors: Beneficial or indifferent?

Abstract

Sporadically addressed in previous studies, the removal of sulfate during fermentation has been a matter of great interest in new applications of fixed-film two-stage biodigestion as the most efficient strategy to boost methane production from a low-sulfate fermented substrate. This study assessed the use of polyurethane (PU) as the support material in a thermophilic (55 °C) fermentative/sulfidogenic fixed-film reactor subjected to different operating conditions based on the variation of the sulfate loading rate (SLR = 8.0–4.0 kg-SO42− m−3 day−1), HRT (12.0–16.0 h) and liquid upflow velocity (3.42–7.90 m h−1). A maximum sulfate removal efficiency of only 46.8 % was achieved when applying SLR and HRT of 4.0 kg-SO42− m−3 day−1 and 16.0 h, respectively, reaching a total dissolved sulfide concentration of 275 mg L−1. This poor performance resulted from two factors: the interspaced arrangement of PU pieces and the use of ethanol as the only carbon source. While the first triggered excess biomass accumulation, the latter favored the establishment of a very restricted microbial community. Only some Clostridia-like bacterial classes, Proteobacteria, and other non-SRB bacteria belonging to phyla Synergistetes and Thermotogae were identified. Hence, under the studied conditions, using PU did not enhance sulfidogenesis in the fermentative reactor.