Anaerobic co-digestion of sewage sludge and food waste: staging and carriers enhance system performance and process stability

Sewage sludge generated during biological wastewater treatment requires adequate treatment. Anaerobic digestion of sewage sludge is preferred, yet, it is often characterized by low biogas production rates. Co-digestion of sewage sludge with food waste could improve the hydrolysis rate and nutrients balance, resulting in higher biogas production rates. In this study, single- and two-stage anaerobic reactors were operated, with and without carriers in semi-continuous mode for 205 days for assessing the expected improved biogas production rates of sewage sludge and food waste co-digestion. Mono-digestion of sewage sludge resulted in average biogas production rates of 230±31 and 538±40 mL _biogas L ^-1 d ^-1 for single- and two-stage systems with carriers, respectively. Co-digestion of sewage sludge with food waste resulted in an improved biogas production rates in both systems. Average biogas production rates of 868±114 and 1507±174 mL _biogas L ^-1 d ^-1 were measured in single- and two-stage systems, respectively, with carriers during co-digestion of food waste (30%) and sewage sludge (70%). In all cases, the addition of carriers improved biogas production, and reduced volatile fatty acid accumulation. In conclusion, two-stage co-digestion of sewage sludge and food waste with carriers achieved the highest biogas production and long-term stability.