Improving anaerobic conversion of pulp mill secondary sludge to biogas by pretreatment

We examined the effectiveness of thermal, caustic, and sonication pretreatment methods in improv - ing anaerobic conversion to biogas of secondary sludge samples obtained from a kraft mill and a sulfite mill. All three methods improved the anaerobic digestion rate and the biogas yield of the sludge samples. Thermal pretreat - ment was the most effective, followed closely by caustic pretreatment, and sonication the least. The total biogas productions per unit of chemical oxygen demand of sulfite sludge and kraft sludge samples were respectively 1.2 and 3 times higher with pretreatments than without. Also, the biogas production from the untreated sulfite mill sludge was 4 times higher than that from the untreated kraft mill sludge.This work was part of the research program on Alternative Fuels for Lime Kilns, jointly supported by the Natural Sci - ences and Engineering Research Council of Canada (NSERC); industrial members of the research consortium on Increasing Energy and Chemical Recovery Efficiency in the Kraft Pro - cess; and the following companies: Alberta Pacific, Alberta Research Council/Alberta Forestry Research Institute, DTE Petcoke, FPInnovations, Jammbco, Kiln Flame Systems, and Zellstoff Celgar