Abstract
ABSTRACT: Disposal of sewage sludge (SS) is one of the problems in treatment plants; however, SS has a high-water volume and lacks some compounds and can be mixed with other biomass. The present study analyzed co-hydrothermal carbonization of sewage sludge with sawdust and corn stalk. This research aimed to optimize the process parameters, the temperature in the range of 180-300 °C, the reaction time in the range of 30-60 min, and pH in the range of 5-9 on the mass yield, energy yield, and high heat value (HHV) to increase the quality of hydrochar, and to analyze the effect of hydrothermal carbonization (HTC) on the characteristics of raw materials and hydrochar. The response surface method and Benken's box model were conducted using Design Expert 10 software. The optimal conditions for HHV, mass yield, and energy yield were 15.802 MJ/kg, 63.754%, and 67.415% respectively which occurred in the 205.358 °C, 30 min reaction time, and pH of 5. The temperature was the most influential parameter. The morphological, physicochemical, thermal, and crystalline properties of the hydrochar with the maximum HHV, mass yield and energy yield were evaluated as well. These results demonstrate that HTC is a suitable process to produce hydrochar, which can be used as a direct solid fuel. HIGHLIGHTS: • Hydrothermal carbonization of sewage sludge with sawdust and cornstalk was investigated.• Response surface optimization hydrothermal carbonization process was studied.• The morphological, physicochemical, thermal, and crystalline properties of the hydrochar are reported.• The optimal HHV was 15.802 MJ/kg.• The process can produce hydrochar which can be used for direct combustion or activated carbon.