Feasibility of anaerobic digestion for contaminated rice straw inoculated with waste activated sludge

Anaerobic digestion of the heavy metal-contaminated rice straw inoculated with waste activated sludge was carried out through an orthogonal array. The results indicated that the digestion process was optimized with an inoculum to substrate ratio (I/S) of 0.25, a total solid (TS) content of 5%, and an initial pH of 7.0, with corresponding total biogas and methane yields of 745.4 and 285.2 mL/g VS, respectively. Under the optimized conditions, the bioleaching percentages of Cd and As in the biomass were 13.13% and 42.90%, respectively. According to range analysis, the biogas yield, methane yield, and bioleaching percentages of Cd and As in the biomass significantly decreased with an increase in TS content from 5% to 15%. The results suggested that anaerobic digestion with waste activated sludge was feasible for achieving both biogas production and bioleaching of heavy metals from contaminated rice straw.