A Ca-Rich Biochar Derived from Food Waste Digestate with Exceptional Adsorption Capacity for Arsenic (Iii) Removal Via a Cooperative Mechanism

Abstract

Arsenic contamination in water is an international environmental issue. Biochar adsorption is often considered a promising way for removing As from contaminated water due to its low-cost and environmental friendliness. However, the poor adsorption capacity limits the application of pristine biochar, and various modification methods are proposed to improve this shortcoming, which inevitably brings some new environmental problems. Herein, pristine Ca-rich biochar with excellent arsenic adsorption performance was prepared through one-step pyrolysis of food waste digestate. The results demonstrated that the biochar obtained at 800 °C (CDBC8) exhibited better specific surface area and absorption capacity of As than that of biochar prepared at other temperature, with the maximum As adsorption capacity of 69.03 mg/g, which was much higher than previously reported pristine biochars, even some modified biochars. This is attributed to the considerable portion of CaO and carbon in CDBC8. The adsorption process was best modeled by Langmuir model and the pseudo-second-order kinetic model. Furthermore, the removal mechanism of As was discussed in-depth. The complexation, precipitation, oxidation, and electrostatic attraction participated in the adsorption, and their contributions were significantly impacted by the pH of the solution. This work presents the great potential of this Ca-rich biochar for wastewater remediation, and also provides a feasible way for the rational utilization of food waste digestate.

Keywords: As(III) removal, Adsorption, food waste digestate, calcium-rich biochar