Modified water treatment residual serves as an adsorbent for the removal of heavy metals from water: A review

Heavy metal pollution in water has always been an environmental issue of global concern. Water treatment residual (WTR), generated during drinking water treatment processes, has proven to be a potentially cost-effective adsorbent for heavy metals. However, the application of raw WTR is restricted due to its defects. The purpose of this review is to summarize representative research on modified WTR, elucidating the impact of various modification methods on the physicochemical properties of WTR, which is rare in previous review articles. Furthermore, the review discusses the factors influencing the adsorption of WTR and the competitive adsorption among heavy metals. The main results indicate that methods such as heat treatment, acid activation, and development of composites have been successfully applied in modifying WTR, demonstrating the importance of optimizing the adsorption of WTR by altering its properties. The adsorption capacity of WTR is regulated by multiple factors, and the competitive adsorption capacity of heavy metals is proportional to ionic radius and electronegativity. Studying adsorption under conditions of multi-metal coexistence is crucial for the application of WTR in real aquatic environments. This review aims to provide valuable information for remediating heavy metal pollution and optimizing the utilization of WTR to promote global sustainable development.