Sulfate removal rate and metal recovery as settling precipitates in bioreactors: Influence of electron donors

Four down-flow structured bed reactors were operated targeting biological sulfate-reduction and metal recovery. Three different electron donors were tested: glycerol (R1), lactate (R2), sucrose (R3), and a blend of the previous three organic compounds (R4) with increasing copper influent load (5, 15, and 30 mg Cu2+.L-1). Copper inhibited sulfate-reduction in R1 (15 mg Cu2+.L-1) and R3 (5 mg Cu2+.L-1), but the fermentative activity was not affected. R2 and R4 were not inhibited by copper influent. R2 provided the highest sulfate reduction (1767.3 ± 240.1 mg SO42- L day-1), but R4 yielded highest metal recovery as precipitates (24.8 g FSS L-1, 25% Fe2+, 5% Cu2+). 16S rDNA sequencing indicates that the blend of electron donor did not foster higher diversity of sulfate-reducing bacteria in R4. These results suggest that the electron donor influences not only biological sulfate reduction, but also metal toxicity thresholds and metal removal and recovery mechanisms.