Optimizing the Hydrothermal Carbonization of Sewage Sludge—Response Surface Methodology and the Effect of Volatile Solids

This study focuses on identifying the optimum conditions of sewage sludge hydrothermal carbonization by Box–Behnken Design and effects volatile solids heating value process water load. To get insight into solid characteristics, we applied reaction temperature (190, 220, 250 °C), time (0.5, 2.25, 4 h) pH (3.9, 5, 6.1). The response surface liquid phase revealed decreasing dissolved organic carbon (DOC) concentrations with increasing from 9446 mg/L (190 °C) to 7402 (250 at h time. For same conditions, NH4-N concentration increased 754 1230 mg/L. Reaction was identified as most important parameter, whereas had only minor effects. Moreover, linear coefficients models were more decisive than interrelation quadratic coefficients. Volatile (VS) feedstock found significantly influence both load change in hydrochars. Process steadily higher VS. around 65–80% VS feedstock.