Toward a Circular Economy in Water Treatment: Upcycling Aluminum Salt-Based Water Treatment Residual into An Effective Adsorbent–Ceramsite

Coagulation is widely used in water treatment, generating large volumes of water treatment residual (WTR), most of which is aluminum salt-based water treatment residual (Al-WTR). This waste is environmentally and financially costly to manage. Al-WTR, however, can be upcycled into value-added products such as ceramsite, a porous material that can be used for adsorption or other beneficial purposes. Here, we review the fabrication processes for transforming Al-WTR into ceramsite, the strategies for enhancing its performance, and its potential environmental applications. Ceramsite has exhibited potential as an adsorbent in removing pollutants such as phosphorus and heavy metals as well as being a biofilm-supporting medium. Moreover, ceramsite has shown the effective removal of emerging pollutants from water matrices. Therefore, ceramsite represents a promising strategy for valorizing Al-WTR. Further investigations are required to improve the ceramsite performance and assess its applicability in environmental engineering. Furthermore, we also discuss the current challenges and barriers associated with the application of the Al-WTR-derived ceramsite and possible mitigation strategies. This Review aims to stimulate further research and development in sustainable WTR management, thereby contributing to the development of a circular economy in the water treatment sector.