Acid mine drainage (AMD) – characterized by high acidity and elevated sulfate and metal concentrations – represents a big environmental concern. Biological sulfate reduction has become an alternative to the classical physicochemical methods. In this study, domestic wastewater (DW) was tested as a cost-effective carbon-source for the remediation of AMD. Sediments from Tinto River, an extreme acidic environment with an elevated concentration of metals, were used as inoculum. Three anaerobic bioreactors with different microbial supports were fed with a 1:10 (v:v) mixture of synthetic AMD:DW. Around 50% of the organic matter present in the DW co-precipitated with the metals from the AMD previous to feeding the reactor. Therefore, the reactors had to be supplemented with an extra carbon-source (acetate) to achieve higher S elimination. Elevated removal efficiencies of chemical oxygen demand (COD) (>88%), sulfate (>75%), Fe (>85%) and other dissolved metals (>99% except for Mn) were achieved. Bacterial communities were examined through denaturing gradient gel electrophoresis and scanning electron microscopy. Higher biodiversity was found in the bioreactors compared with that of the inoculum. Dominant species belong to two metabolic groups: fermentative (Clostridium spp., Delftia spp., Paludibacter spp. and Pelotomaculum spp.) and sulfate-reducing bacteria (Desulfomonile spp., Desulfovibrio spp., Desulfosporosinus spp. and Desulfotomaculum spp.).

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