A new method combining hydrothermal carbonization and mechanical compression in-situ for sewage sludge dewatering: Bench-scale verification

In recent era, hydrothermal carbonization is an effective technology of sewage sludge dewatering. In this paper, hydrothermal carbonization coupled with mechanical compression in situ for sewage sludge dewatering has been proposed as state-of-the-art method. Different operating modes and conditions (temperature, residence time, and mechanical pressure) of hydrothermal pretreatment were investigated. The results showed that mechanical compression in situ under hot condition has revealed a significant benefit compared with other modes, resulted in a reduction of 27.7-59.6 %of the moisture content. After hydrothermal pretreatment at temperatures of 160-240 degrees C, the moisture content decreased about 30-60% and the solid yield decreased from 94.2% to 61.8% within 60 min. The HHV of hydrochar increased about 11.25% while the HHV for pressed hydrochar showed a decrease of 9.98-42.16% after in situ mechanical compression. Moreover, a kinetic model was presented based on the lumped components. The measured and the simulated masses are in a good arrangement. The average weighted absolute difference is 3.53%, while the average absolute difference is 1.08 g with parameter values k(0) = 8004.5 min(-1) and E-a = 31,506 J/mol. This new method is applicable to achieve pressed hydrochar with higher solid contents in contrast to the other drying methods.