New insights into impact of thermal hydrolysis pretreatment temperature and time on sewage sludge: Structure and composition of sewage sludge from sewage treatment plant

Abstract

This work investigated the effects of THP temperature (140–200 °C) and time (10–60 min) on the surface morphology, pyrolysis properties, and soluble compounds of dewatered sludge. Results indicate that higher temperature and longer pretreatment time considerably improve organics hydrolysis (the SCOD content increased 1.4–2.46 times, increasing 2.46 times at 200 °C). In addition, high temperature also improved the sludge pyrolysis efficiency (the highest at 200 °C), and reduced the harmful gas release, especially HCN. Moreover, the surface morphology of the sludge changed, the gap and floccules on the surface of the sludge increased. The carbohydrate content increased the highest; approximately 91.9% at 170 °C. THP promoted the decomposition of the nitrogen compounds in the sludge and facilitated their transition to a liquid phase. The total nitrogen and ammonia nitrogen content doubled, and the organic nitrogen content decreased by 50% with time increased from 10 to 60 min.