Evaluation of various pre-treatment processes on tannery sludge for enhancement of soluble chemical oxygen demand

Overall sludge generation during the treatment of tannery wastewater is in the range of 18,200–165,200 tons per annum in India. One of the major problems faced by the tanning industry in India is the disposal of sludge. In recent years, increased attention has been given to minimization of waste sludge in wastewater treatment process. At present, each tannery is spending around Rs. 700–750 per ton for disposal of sludge into secured landfill facilities. Anaerobic digestion is one of the options for generation of biogas from primary and secondary sludge and to reduce sludge volume. In order to make anaerobic digestion more effective, pre-treatment of sludge before anaerobic digestion is the recent technological advancement employed to accelerate the rate of hydrolysis process. Various pre-treatment processes such as ozonation, sonication, hydrogen peroxide, alkaline, and alkaline thermal treatment were evaluated in the present study for increasing the soluble chemical oxygen demand separately in primary and secondary sludge generated during treatment of tannery wastewater. It was observed from the results obtained from the study that the increase in SCOD by various pre-treatments were in the order of ozonation > alkaline thermal treatment > sonication > alkaline treatment > hydrogen peroxide. The increase in the ratio of SCOD to TCOD by pre-treatments was effective for secondary sludge rather than primary sludge.