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

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.