Antimony removal from wastewater by sulfate-reducing bacteria in a bench-scale upflow anaerobic packed-bed reactor

The objective of this research was to study the precipitation of Sb and the stability of Sb2S3 during treatment of synthetic Sb(V) wastewater by sulfate-reducing bacteria (SRB). We investigated the transformation and precipitation of Sb, as well as the re-dissolution of Sb2S3 under different pH and carbon sources. The results showed that the precipitation of aqueous Sb and the re-dissolution of Sb2S3 depend on the conversion between Sb(III)-S(-II) complexes and Sb2S3 precipitates. These processes were highly pH-dependent, and a decrease in pH enhanced reduction of Sb(V) and precipitation of Sb2S3 were observed. The newly formed Sb2S3 was found to be unstable and could re-dissolve through complexation with H2S due to the increase in pH. When pH decreased to approximately 6.5, Sb was almost completely transformed into Sb2S3 precipitates, and the Sb2S3 precipitates were relatively stable. Compared with lactate as a carbon source, ethanol resulted in a comparable H2S yield and a relatively low pH and was, therefore, more conducive to the removal of Sb(V). The results of this study suggest that when removing Sb(V) in wastewater by SRB, it is important to control the pH at a relatively low level.