BIOLOGICAL REDUCTION AND REMOVALOF CR (VI) IN A HYBRID UP-FLOW ANAEROBIC SLUDGE BLANKET TREATING MUNICIPAL WASTEWATER

Document Type : Review Article

Authors

1 Water Pollution Research Department, National Research Centre, Egypt

2 Chemistry Department, Faculty of Science, Ain Shams University, Egypt

3 Holding Company for Water and Wastewater, Giza, Egypt

Abstract

The aim of this study was to emphasize the effect of hexavalent chromium Cr (VI) on the performance of a pilot hybrid up-flow anaerobic sludge blanket (H-UASB) as well as to elaborate the biological reduction and removal of Cr (VI). The H-UASB was packed with non-woven polyester fabric (NWPF) and was operated at a hydraulic retention time (HRT) of 7.5 h, organic loading rate (OLR) ranged from 0.95 to 1.53 Kg COD m3/day. The system achieved satisfactory removal rates for total suspended solids (TSS) (86.44 %), chemical oxygen demand (COD) (74.18 %) and biological oxygen demand (BOD5) (84.8%) without the addition of Cr (VI). Results indicated that feeding the reactor with different concentrations of chromium ions from 600 mg / m3.d to 6000 mg / m3.d decreased the residual concentration of Cr (VI) in the effluent to 0.019 mg/l, while the accumulation of chromium ion increased in the biobed (160 mg/kg) and in excess sludge (165.44 mg/kg). This was due to the biological reduction of Cr (VI) to Cr (III) by the action of sulphate and chromate reducing bacteria. Also, sorption and biosorption mechanisms took place in the accumulated sludge in/on the NWPF as well as excess sludge in the reactor. Increasing the concentration of Cr (VI) up to 6000 mg / m3.d partially affected the biochemical reactions of the anaerobic microorganisms and consequently decreased the removal efficiency of TSS from 86.44% to 62.06%, COD from 74.2% to 57.07% and BOD5 from 84.8% to 61.92 %.

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