Biological oxidation of ferrous ions under acidic conditions using rotating biological contactor

Abstract

Oxidation of ferrous (Fe2+) ion to ferric (Fe3+) ion under acidic conditions can be achieved by iron oxidizing bacteria. In this research study, oxidation of Fe2+ ions by iron oxidizing bacteria was studied using a bench-scale rotating biological contactor (RBC). Experiments were conducted to investigate the effects of parameters such as hydraulic loading rate (HLR), temperature and Fe2+ concentration at pH 2.0 on Fe2+ oxidation. Oxidation of Fe2+ was observed to decrease with temperature (in the range of 5 to 23 °C). The Fe2+ oxidation rates of 35.3 g Fe2+/(m2·d) and 52.6 g Fe2+/(m2·d) were observed at 5 °C and 21 °C, respectively, at HLR of 0.014 m3/(m2·d). The Fe2+ oxidation rates increased with increase in HLR from 0.014 m3/(m2·d) to 0.055 m3/(m2·d) for a Fe2+ concentration of approximately 3200 mg/L in the RBC feed. The maximum Fe2+ oxidation rate observed in this study was 165 g Fe2+/(m2·d). Iron solids were deposited on the RBC disks and were identified as jarosite. The RBC was able to achieve 50% Fe2+ oxidation efficiency after 24 h of a process upset. Key words: rotating biological contactor, ferrous, ferric, oxidation, acidic mine drainage, hydraulic retention time, hydraulic loading rate.