Performance of biological sulphate reduction at low pH, low temperature and low hydraulic retention time

Abstract

Biological sulphate reduction (BSR) is a promising technology for the treatment of acidic, heavy metal-laden, and high sulphate concentration effluents from mining industries. BSR is a process that uses sulphate reducing bacteria to reduce sulphate to sulphide using substrates as nutrients under anaerobic conditions. The performance of BSR is dependent on several factors including pH, temperature and hydraulic retention time (HRT). In this study, the effect of the above-mentioned factors was investigated in lab-scale reactors that were mimicking a pilot plant that is operational at a coal mine. Packed bed reactors (packed with cellulosic organic matter) were operated in a continuous downflow mode. Cow manure and lucerne pellets were used as substrates and they were replenished once a week. Sulphate reducing bacteria were able to reduce sulphate at 10 °C although at lower efficiencies compared to 30 °C. Decreasing the pH from 6 to 4 did not impact sulphate reduction significantly as sulphate reduction was above 89 % at pH 4 (20 °C) for the duration of the experiment. A washout of substrates was observed when HRT was deceased from 7 d to 2 d. This lead to a sulphate reduction drop from above 98 % at 7 d to 37.5 % at 2 d before replenishing and above 80 % after replenishing. This study shows that BSR is a promising technology for the abatement of AMD.