Biochar modification to enhance arsenic removal from water: a review

Arsenic (As) contamination is a major threat to drinking water quality throughout the world, and the development of appropriate remediation methods is critical. Adsorption is considered the most effective method for remediation of As-contaminated water. Biochar is a promising adsorbent and widely discussed for As removal due to its potential low cost and environmental friendliness. However, pristine biochar generally exhibited relatively low adsorption capacity for As mainly due to the electrostatic repulsion between the negatively charged biochar and As. Biochar modification, especially metal modification, was developed to boost the adsorption capacity for As. A systematic analysis of As removal as affected by biochar properties and modification will be of great help for As removal. This paper presents a comprehensive review on As removal by biochars from different feedstock, preparation procedures, and modification methods, with a major focus on the possible mechanisms of interaction between As and biochar. Biochar derived from sewage sludge exhibited relatively high adsorption capacity for As. Considering energy conservation, biochars prepared at 401-500 °C were more favorable in adsorbing As. Fe-modified biochar was the most popular modified biochar for As remediation due to its low cost and high efficiency. In addition, the limitations of the current studies and future perspectives are presented. The aim of this review is to provide guidance for the preparation of low-cost, environmentally friendly, and high efficiency biochar for the remediation of As-contaminated water.