Cr(VI) remediation with inorganic as(III) as an electron sink immobilized in a ceramic bead packed bed biofilm reactor

Abstract

Ceramic bead media Biofilm Reactor Performance was evaluated for Cr(VI) reduction utilizing As(III) as electron source with mixed culture of chemoautotrophic bacteria. The inoculant used was isolated from cow dip in Tzaneen (Limpopo Province) and WWTW Brits Northwest South Africa. Preliminary studies show that these bacteria can remove Cr(VI) up to 99 %, and oxidizing As(III) up to 90 %. A bench-scale, ceramic bead media biofilm reactor was operated until steady-state conditions was approached under a range of influent Cr(VI) concentrations ranging from (30-200) mg/L and As(III) concentration ranging from (50-340) mg/L in the ratio of 1:1.7. Hydraulic detention time of 5 hour and 17 hours was observed for optimum Cr(VI) reduction and As(III) oxidation. Result suggests that As(III) was indeed utilized as an electron donor for complete Cr(VI) removal. Parameters such as pH, ORP, temperature and dissolved oxygen concentration was seen optimal at average of 7.1, -156 mV, 31 oC and 0.92 mg/O2L. The steady-state Cr(VI) reduction efficiency was affected by the influent Cr(VI) and As(III) concentration and hydraulic detention time. Higher Cr(VI) concentration was seen in the effluent when the influent concentration was increase above 100 mg/Cr(VI)L and 170 mg/As(III)L. Similarly, at lower hydraulic detention time, Cr(VI) reduction As(III)oxidation were affected. The bioreactor showed strong resilience by recovering from Cr(VI) and As(III) overloading through reduction in influent Cr(VI) and As(III) concentrations.