Effects of copper and zinc on the anaerobic co-digestion process of waste activated sludge and septic tank sludge

The effects of copper and zinc on the anaerobic co-digestion process of waste activated sludge and septic tank sludge in Hanoi were investigated. The anaerobic fermentation tests were carried out in 32 batch fermenters with 20 d of hydraulic retention time at mesophilic temperature conditions. The different metal ion concentrations (19, 40, 60, and 80 ppm) were utilized for the anaerobic experiments, respectively. Cumulative biogas and change of total solids (TS) concentrations, volatile solid (VS), chemical oxygen demand (COD) were tested during the experiments. The results revealed that the TS, VS and COD removal efficiency at 80 ppm Cu(II) were 3.95%, 9.01%, and 6.51%, respectively. Similar, this figure at 80 ppm Zn(II) was 8.44%, 13.03%, and 11.42%, respectively. The biogas yield decreased by 35.2% with 80 ppm Cu(II), decreasing 32.13% with 80 ppm Zn(II) compared with the original sample. The results showed at higher metal concentration, the digestion process was inhibited, led to the removal of organic substances and produced biogas were reduced.