Biological Sulfate Reduction Using Gaseous Substrates To Treat Acid Mine Drainage

Purpose of Review Acid mine drainage (AMD) is a serious environmental problem due to its high sulfate and heavy metal content. In comparison with the conventionally used physico-chemical methods, biological methods involving sulfate-reducing bacteria (SRB) offer a green and sustainable way to treat AMD. Biological sulfate reduction requires an efficient and low-cost electron donor. This paper overviews different gaseous substrates as electron donor that can be used for sulfate reduction to treat AMD. Recent Findings The use of gaseous substrates as electron donor for sulfate reduction is advantageous as it avoids dilution of wastewater and avoids secondary pollution problems arising from unutilized electron donor. Among the different gaseous substrates for sulfate reduction, hydrogen (H-2) is more energetically favourable to the sulfate-reducing microorganisms. Carbon monoxide (CO) is a low-cost waste gas substrate for sulfate reduction, but its toxicity limits its applications. Only a limited number of specialized slow-growing microorganisms can utilize methane (CH4) coupled to sulfate reduction under anaerobic conditions. Different gases (H-2, CO and CH4) are evaluated as potential electron donor for biological sulfate reduction to treat AMD. Several bacterial and archaeal species can use these gases as the sole electron donor for reducing sulfate to sulfide. Heavy metals present in the AMD can be removed by sulfidic precipitation although high concentrations of heavy metals can inhibit SRB activity, thus reducing the process efficiency. In addition, proper choice of the bioreactor system has a great influence on the AMD treatment efficiency by biological sulfate reduction using gaseous substrates.