Biomineralization of indium to indium selenide by anaerobic granular sludge in the presence of selenium oxyanions for sustainable recovery

This study examined simultaneous removal of indium (In(III)) and selenium oxyanions (Se(IV) and Se(VI)) using anaerobic granular sludge in batch and sequencing batch experiments. The indium removal efficiency was very high (>95%) throughout the experimental period, whereas the selenite removal values (78.9–98.2%) were considerably higher than the values obtained for selenate removal (15.5–70.0%) in the absence of In(III). The presence of In(III), however, increased the selenite and selenate removal efficiency to values up to 96–98%. The removal mechanism involved adsorption onto granular sludge followed by biomineralization to indium selenide. The presence of indium selenide in granular sludge treating indium and either of the selenium oxyanions was confirmed by SEM-EDX, XRD and XPS analysis. The granular sludge biomass exposed to only indium, mineralized it to form indium hydroxide. The microbial community analysis showed dominance of methanogenic microorganism in the granular sludge exposed to different combinations of indium and selenium. This study demonstrated the potential of anaerobic granular sludge biomass for production of indium selenide from co-mineralization of indium in the presence of selenium oxyanions Se(IV) and Se(VI) which provides an alternative novel strategy for its recovery from waste streams.