Arsenic removal without thio-As formation in a sulfidogenic system driven by sulfur reducing bacteria under acidic condition

Sulfidogenic treatment using sulfate-reducing bacteria has been used to remediate Acid Mine Drainage (AMD). With sulfide, As(III) can be precipitated as As₂S₃. However, thio-arsenic formation with the pH increased by sulfate reduction, and results in the failure of As(III) removal. In this study, we proposed a novel sulfidogenic system driven by sulfur reducing bacteria (S⁰RB), which worked under acidic condition to reduce elemental sulfur into sulfide without pH elevation. Then the acidic sulfide-rich effluent mixed with the arsenic-containing AMD to remove arsenic. In the long-term lab-scale test, S⁰RB activities maintained for over 100 days under acidic condition (pH 4.3). Over 99% of the influent arsenic (10 mg L⁻¹) were removed by the acidic sulfide-rich solution. The results of batch tests show that, higher As removal rate can be obtained under lower pH conditions, under the same As-to-S molar ratio. The Eh-pH plot demonstrates that, sulfide production under acidic condition avoided the formation of thio-arsenic compounds (thio-As), ensuring the high removal efficiency of As(III) from AMD.