Effect of hydraulic residence time on biological sulphate reduction and elemental sulphur recovery in a single-stage hybrid linear flow channel reactor

[Display omitted] •Simultaneous BSR and partial sulphide oxidation achieved in a single, open reactor.•High volumetric rates and sulphate conversion achieved at a low HRT of 12 h.•Semi-passive system achieved similar BSR performance to active equivalents.•Biomass retention ensured system robustness and resilience at low HRT.•Shift in lactate metabolism from oxidation to fermentation as HRT decreased. Biological sulphate reduction and partial sulphide oxidation, occurring simultaneously within the hybrid linear flow channel reactor (LFCR) were evaluated, under controlled conditions at laboratory scale, as a function of hydraulic residence time (HRT) using a synthetic media containing 1 g/L sulphate. The hybrid LFCR comprises a rectangular channel containing carbon microfibers as a support matrix for attachment of sulphate-reducing bacteria and an exposed air-liquid interface to facilitate the formation of a floating sulphur biofilm. Exposure to decreasing HRT, from 3 days to 12 h, resulted in an increase in the volumetric sulphate reduction rate (0.14 to 0.63 mmol/L.h), achieving levels typically associated with active reactors. Sulphate conversion was highest (97 %) at a 3 day HRT, decreasing to 73 % at 12 h. The highest sulphide removal efficiency (82 %) and accompanying sulphur recovery through harvesting of the floating sulphur biofilm (FSB) was observed at a 2 day HRT. The sulphur fraction not recovered through the biofilm was predominantly released within the effluent as colloidal elemental sulphur and fragments of the sulphur-rich biofilm, with minimal re-oxidation to sulphate occurring in the reactor. The hybrid LFCR technology was able to achieve high rates of sulphate reduction and effective sulphide removal within a single, semi-passive reactor unit.