A low-cost and efficient adsorbent, based on sewage sludge, was prepared by hydrothermal carbonization. The sludge-hydrochar was prepared at different temperatures (160, 190, 220, and 250℃) and different reaction times (1, 4, 8, and 16 h). It was applied to the adsorption of methylene blue (MB) in water. This study analyzed the structure and physicochemical properties of hydrochar by BET, FT-IR, and zero charge points. In addition, we investigated the optimum hydrothermal conditions for the preparation of adsorbents and adsorption properties for MB by experiments. Studies have shown that 190℃ and 4 h were the best hydrothermal conditions for the preparation of adsorbent (SS190-4). SS190-4 has the largest specific surface area (11.916 m2·g-1) and the best removal rate (96.44%) for methylene blue (MB). The adsorption of MB is more favorable when the solution is alkaline. The adsorption conforms to the Langmuir isotherm equation, and the maximum model adsorption capacity for MB is 400 mg·g-1. When the concentration of hydrochar is 0.5 g·L-1, it is more economical and reasonable. When there are coexisting ions in the solution, the adsorption capacity of hydrochar to MB is inhibited. The adsorption process of MB by hydrochar conforms to the quasi-secondary kinetic model, which is a spontaneous exothermic reaction.
Keywords: adsorbent; hydrochar; hydrothermal carbonization; methylene blue; sludge.