Abstract:The high water content is one of factors limiting cow manure treatment approach. The hydrothermal carbonization (HTC), which can convert cow manure with high water content into hydrochar, is considered as a potential approach for safe disposal and resource utilization of cow manure. Fresh cow manure was hydrothermally treated at 190℃ and 260℃ for 1h, 6h and 12h, respectively. And then the collected solid products were determined for the physicochemical properties. Based on entropyweight TOPSIS model, the agricultural value was evaluated. The aim was to investigate the effect of temperature and time on hydrochar nature, and then provide a theoretical reference for its agricultural application. The results showed that physicochemical properties of hydrochar was changed with carbonization temperature and duration. Compared with the hydrochar produced at 190℃ for 1h, carbon, total phosphorus and potassium concentrations of hydrochar produced at 260℃ for 12h were increased by 17.88%, 39.06% and 85.19%, but yield, H/C atomic ratio, O/C atomic ratio, (O+N)/C atomic ratio, ammonium nitrogen, exchangeable P and K contents were reduced by 26.65%, 24.00%, 68.42%, 64.29%, 98.91%, 89.26% and 42.30%, respectively. Meanwhile, carbonization degree was increased significantly. With high temperature and long duration, position of functional group absorption peak was varied less, intensity of oxygen functional groups absorption peak was reduced, but intensity of metalhalogen chemical compound performed an opposite trend. The higher reaction temperature and longer residence time caused less surface charges, lower pH value dependence, smaller specific pore volume and specific surface area. Overall, temperature had a large impact on hydrochar nature compared with reaction duration. Cow manure hydrochar produced at low temperature for short time was more suitable as a soil conditioner due to its higher agricultural value.
