Thermal Treatment of Pulb and Paper Mill Biosludge and Digestate to Enhance their Anaerobic Digestibility

Anaerobic digestion of pulp and paper mill biosludge has the potential to reduce sludge disposal costs and generate energy through biogas production. Thermal treatment can couple with anaerobic digestion to enhance the sludge digestibility. Conventionally, thermal pretreatment of biosludge is used by the industry. In this study, three possible thermal treatment-assisted anaerobic digestion configurations were compared: 1. Thermal pretreatment of biosludge; 2. Digestate thermal treatment; 3. Digestate thermal treatment and only recycling the hydrolysate. The thermal pretreatment (1) of biosludge at the theoretical optimal conditions (170o C for 1 h) did not extend the ultimate biogas yield. The digestate thermal treatment (2) increased the rate and extent of the biogas production; a synergistic effect on biogas production was observed by co-digesting biosludge and treated digestate. Only recycling the hydrolysate (3) is recommended if the thermal treatment is conducted at high intensities such as the one at 210o C for 30 min.M.A.S