Treatment of arsenic-laden water plant sludge by anaerobic digestion

Abstract

Coprecipitation of arsenic by alum or iron salts produces a large quantity of arsenic-laden sludge (an average of 6.10 g As/dm3 of sludge on dry basis) in conventional arsenic removal plant (ARP). This toxic sludge, along with acclimated composite organic waste slurry containing a mixture of partially digested liquefied market waste, primary sludge of sewage treatment plant, and liquefied water hyacinth at 1-10% by volume of the total, was anaerobically digested for a period of 30-50 days. The maximum removal of arsenic was obtained as 99.69% at a digestion period of 50 days. The minimum biogas generation at 30 days digestion period was found to be 0.560 m3 (at standard temperature and pressure) per cubic meter of composite feed slurry at 10% of ARP sludge. The results show that presence of arsenic in adequately acclimated composite feed sludge does not significantly inhibit the anaerobic digestion process. It may thus be stated that anaerobic digestion of arsenic-laden composite organic waste sludge could be a viable option for the safe and cost-effective disposal of arsenic-laden sludge available from existing arsenic removal water plants in arsenic affected areas. © 2010 ASCE.