LAUSR

Biological sulphate reduction (BSR) is a promising low-cost treatment of acid rock drainage effluents. In this paper, the system performance and microbial ecology of a lactate supplemented BSR up-flow anaerobic packed bed reactor (UAPBR) are evaluated across reactor height and compared to a continuous stirred tank reactor (CSTR). The biomass concentrations of planktonic and biofilm communities were quantified and subsequently characterised by 16S rRNA gene amplicon sequencing. The defined microbial communities were shown to correlate with differing availability of lactate, volatile fatty acids produced from lactate degradation and sulphate concentration. The UAPBR was able to achieve near complete sulphate conversion at a 4-day hydraulic residence time (HRT) at a sulphate feed concentration of 10.41 mM (1 g/L). The high volumetric sulphate reduction rate of 0.184 mM/L.h achieved in the first third of the reactor was attributed to OTUs present in the planktonic and biofilm communities. While the scavenging of sulphate within the final third of the UAPBR was attributed to an acetate oxidising genus of SRB which was not detected in the lactate-fed CSTR. The detailed analyses of the microbial communities throughout the UAPBR and CSTR contribute to the growing understanding of the impact of the microbial communities of BSR reactors on system performance.