Evaluation of additive effecton anaerobic sewage sludge digestion

Abstract

An additive based on iron oxides was applied to reduce the amount of produced sludge and to increase the production and quality of biogas. The C/N ratio was 11.0–11.3 and the pH of the sludge mixture was 7.3 before the anaerobic digestion. The determined optimal dose of the additive was 0.35 g/g of sludge dry matter over 20 days. This allowed a reduction in the sludge retention time up to 6–11 days. Consequently, maximum biogas production was reached on average 1.6 times faster, volatile solids degradation increased by 56.7%, biogas production increased by 75%, specific biogas production increased by 11.5%, and methane concentration in the biogas increased by 8.4%–18.2%. When the additive was applied, the quantity of phosphate phosphorus in the supernatant was reduced by up to 19%, and hydrogen sulfide reduction efficiency in the biogas ranged between 55% and 62%. In sludge treatment facilities, using an iron oxide-based additive could reduce the dewatering and drying costs for digested sludge by up to 35% .