Sustainable deployment of drinking water treatment residual-derived adsorbents: From synthesis optimization to fixed-bed regeneration and life cycle assessment.

Abstract

Potable water treatment residuals are a largely underutilized, mineral-rich waste stream with considerable potential for conversion into high-value functional materials. These residuals are predominantly composed of aluminium/iron (hydr)oxide and aluminosilicate mineral phases generated during coagulation, together with residual natural organic matter carried over from the source water. This study presents a deployment-oriented valorization pathway converting residual solids into regenerable, pelletized fixed-bed adsorbents, integrating materials optimization, continuous-flow performance, regeneration, and life-cycle assessment. Residual solids were ZnCl2-activated under a factorial design and pelletized into mechanically stable media. Activation is performed ex situ, as a dedicated post-collection processing step that converts the as-generated residual into a functional adsorbent, rather than occurring within the water treatment process itself. Fixed-bed experiments under application-oriented laboratory conditions showed predictable breakthrough behavior and sub-linear responses to hydraulic loading, bed height, and influent concentration, indicating that transport limitations, rather than intrinsic kinetics, dominate performance. Two dyes with contrasting charge characteristics served as probe contaminants. Regeneration was the key determinant of long-term viability: acetone:water preserved dynamic capacity via non-electrostatic pore disruption, while electrochemical regeneration achieved high capacity retention through electrically driven transport and desorption despite a persistent irreversible fraction. Life-cycle assessment showed regeneration rapidly lowers environmental burdens per liter treated by extending service life, while end-of-life management strongly shapes impact distribution, with brick incorporation offering the most balanced profile. This work advances residual-solid valorization beyond proof-of-concept adsorption, linking process design, regeneration, and environmental consequence into a transferable framework for waste-derived adsorbents.