Persulfate degradation of wastewater from hydrothermal carbonization of food waste catalyzed by activated carbon

Abstract

Hydrothermal carbonization (HTC) is highly acknowledged for its ability to convert wet food waste into high calorific value hydrochar at a fast rate. However, the liquid by-product from the process, named HTC wastewater, contains high level of chemical oxygen demand (COD) of 40,000–55,000 mg/L. This HTC wastewater can greatly pollute the environment if it was released without a proper treatment, and hinder the industrial application of HTC technology. In this study, hydrochar was produced via HTC process at 250 °C, and KOH activation was employed to further improve the physical structure of the hydrochar to prepare activated carbon (AC). The obtained AC had the mesoporous structure with specific surface area of 1807.42 m2/g. The AC was used to catalyze persulfate (PS) oxidation for the degradation of HTC wastewater. The experiment of catalytic persulfate degradation of HTC wastewater was designed by the central composite design (CCD) method, and optimized by using response surface method (RSM). The experimental results were statistically discussed by the analysis of variance (ANOVA). The optimal condition determined by CCD model was PS dosage = 6.20 mmol, temperature = 32.47 °C, and pH value = 3.69, achieving a COD removal efficiency of 78.94%. The hydrochar catalyzed persulfate degradation of HTC wastewater caused a great reduction of its pollution degree, which can be a promising pretreatment for HTC wastewater with minimal effort and cost.