Development of efficient system for ethanol production from paper sludge pretreated by ball milling and phosphoric acid

High-solid paper sludge was investigated for its potential to produce renewable biofuel. As a pretreatment method without consuming a large amount of energy, mechanical grinding for a comparatively short time followed by chemical swelling was used for optimal enzyme saccharification and ethanol production from paper sludge. Chemical swelling by phosphoric acid was more favorable than ball mill grinding. However, sequential pretreatment system using ball milling for 2 min and then phosphoric acid swelling for 1 h enhanced the enzyme saccharification rate and the reducing sugar productivity, 84.1% and 28.1 mg/g/h, respectively. The simultaneous saccharification and fermentation (SSF) from the sequential pretreatment system resulted to 81.5% ethanol conversion rate, the productivity being 1.27 g/L/h compared to untreated raw paper sludge which gave 54.3% ethanol conversion rate and 0.424 g/L/h productivity. Our work shows that consecutive mechanical grinding and chemical swelling are effective pretreatment methods for the enhancement of enzyme saccharification and efficient ethanol production from paper sludge.