High rate production of concentrated sulfides from metal bearing wastewater in an expanded bed hydrogenotrophic sulfate reducing bioreactor

Metallurgical wastewaters contain high concentrations of sulfate, up to 15 g L-1. Sulfate-reducing bio-reactors are employed to treat these wastewaters, reducing sulfates to sulfides which subsequently co-precipitate metals. Sulfate loading and reduction rates are typically restricted by the total H2S concentration. Sulfide stripping, sulfide precipitation and dilution are the main strategies employed to minimize inhibition by H2S, but can be adversely compromised by suboptimal sulfate reduction, clogging and additional energy costs. Here, metallurgical wastewater was treated for over 250 days using two hydrogenotrophic granular activated carbon expanded bed bioreactors without additional removal of sulfides. H2S toxicity was minimized by operating at pH 8 +/- 0.15, resulting in an average sulfate removal of 7.08 +/- 0.08 g L-1, sulfide concentrations of 2.1 +/- 0.2 g L-1 and peaks up to 2.3 +/- 0.2 g L-1. A sulfate reduction rate of 20.6 +/-& nbsp; 0.9 g L-1 d(-1) was achieved, with maxima up to 27.2 g L-1 d(-1), which is among the highest reported considering a literature review of 39 studies. The rates reported here are 6-8 times higher than those reported for other reactors without active sulfide removal and the only reported for expanded bed sulfate-reducing bioreactors using H2. By increasing the influent sulfate concentration and maintaining high sulfide concentrations, sulfate reducers were promoted while fermenters and methanogens were suppressed. Industrial wastewater containing 4.4 g L-1 sulfate, 0.036 g L-1 nitrate and various metals (As, Fe, Tl, Zn, Ni, Sb, Co and Cd) was successfully treated with all metal(loid)s, nitrates and sulfates removed below discharge limits. (C) 2022 The Authors. Published by Elsevier B.V. on behalf of Chinese Society for Environmental Sciences, Harbin Institute of Technology, Chinese Research Academy of Environmental Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study successfully treated metallurgical wastewater with high sulfate concentrations using two hydrogenotrophic granular activated carbon expanded bed bioreactors operating at pH 8 ± 0.15. The reactors achieved a high sulfate removal rate of 7.08 g L-1 and a sulfate reduction rate of 27.2 g L-1 d(-1) while effectively removing various metals, nitrates, and sulfates below discharge limits.