Growth characterisation of isolated indigenous iron-oxidising bacteria and their application in sludge treatment

Indigenous iron-oxidising bacteria was acclimated and isolated from the sewage sludge originated from the Yuen Long wastewater treatment plant, Hong Kong. The acclimation process was performed by amending the sludge with FeSO₄7H₂O at pH3.0 and 28°c for 23 days. The bacteria were isolated after several transfers in the improved leathen medium and were identified as Thiobacllus ferroxidans. The influence of pH, Fe²⁺ concentration and inoculum volume on the biooxidation of Fe²⁺ showed that the isolated bacteria had a strong ability in oxidizing Fe²⁺ under acidic condition. Following the inoculation of sludge with the indigenous iron-oxidising bacteria and the addition of FeSO₄7H₂O, 5.9-53% of Cr. 81-90% of Cu, 78-83% of Zn, 27-54% of Pb and 0.7-16% of Ni could be leached from the sludge. In contrast, only 3.1% of Cr, 43% of Cu, 70% of Zn, 14% of Pb and 0.6% of Ni were removed in the control receiving no inoculation and Fe²⁺ addition. The present work confirmed the effectiveness of the isolated indigenous iron-oxidising bacteria for the removal heavy metals from sewage sludge.