Physiochemical properties and pyrolysis behavior evaluations of hydrochar from co-hydrothermal treatment of rice straw and sewage sludge

Co-hydrothermal treatment is an effective approach to recovery the energy and fuels from organic matter in rice straw (RS) and sewage sludge (SS). In this study, the basic fuel characteristics, ash composition, the subsequent pyrolysis behavior and relevant reaction kinetic parameters of obtained hydrochar were evaluated. The results indicated that co-hydrothermal treatment improved the fuel characteristics of hydrochar with high HHV and low N and S contents. FTIR analysis indicated that the presence of the synergy between RS and SS during co-hydrothermal treatment that the organic acids from hydrolysis of hemicellulose promoted the degradation of N-containing functional groups. In addition, the ash composition analyses showed that the obtained hydrochar had high ash fusion temperature as a result of the high removal efficiency of alkali metals during co-hydrothermal treatment. Moreover, co-hydrothermal treatment can promote the pyrolysis reaction by reducing the activation energy with the synthetic effect of RS and SS during co-hydrothermal treatment process. In summary, co-hydrothermal treatment improved the physiochemical properties and promoted the pyrolysis behavior of obtained hydrochar from RS and SS.