Arsenic (III) and arsenic (V) removal from acidic mine waters using an acidophilic sulfate-reducing bioreactor

Chile accounts for about one-third of the world's copper production; however, high levels of arsenic (As) in its copper concentrates have generated problems and subsequent challenges for the mining industry. In particular, the requirement of additional processing for arsenic removal from aqueous solutions from mining operations. In this technology area, cost effective biotechnological approaches for remediating this metalloid, using acidophilic sulfate reducing bacteria (SRB) can be an attractive alternative to current systems for As removal from acidic mine water. Here we describe the performance of two acidophilic continuous fed bioreactors for the removal of arsenic (III) and arsenic (V). The biofilm-based continuous bioreactors were inoculated with a mixed culture including an acidophilic sulfate reducer (Desulfosporosinus acididurans). Both bioreactors were fed with an acidic synthetic water (pH 2.1) for up to 420 days, with varying concentrations of As³⁺ and As⁵⁺ (2–150 ppm) and using glycerol as carbon and energy source. The results demonstrated that over 95% of both forms of As were removed as arsenic sulfide. The hydraulic retention times (HRT) increased up to 350 h for higher concentrations of As. Considering that the pH of the bioreactor liquor was maintained at pH 4.5 by the addition of the synthetic mine water, the increased HRT was correlated with a decrease in SRB activity. This study demonstrated the feasibility of removing As (III) and As (V) from an extremely acidic water by using a continuous acidophilic SRB bioreactor, expanding the use of this technology for the remediation of this metalloid.