Mineralogical Diversity of Drinking Water Treatment DWTR: A Framework for Context-Aligned Reuse in Environmental Applications

Water treatment facilities worldwide generate substantial quantities of drinking water treatment residuals (DWTR) through coagulation processes using alum, ferric chloride, polyaluminium chloride (PAC), or lime. Interest in beneficial reuse has increased markedly; however, much of the existing literature implicitly treats DWTR as a uniform material. This obscures a critical reality: coagulant chemistry governs residue mineralogy, and mineralogical differences strongly influence environmental behaviour and suitability for reuse applications. This review synthesises current knowledge on DWTR mineralogy and associated surface-chemical mechanisms and proposes a context-aligned framework for matching specific residue types to appropriate environmental applications. Alum-based DWTR, dominated by amorphous aluminium hydroxide phases, exhibits strong phosphorus binding under circumneutral conditions, supporting its use in wetlands and bioretention systems. Ferric-based DWTR, characterised by iron oxyhydroxide phases, displays greater tolerance to redox variability and a broader operational pH window, making it attractive for stormwater and intermittently flooded environments. PAC-derived and lime-based DWTR exhibit distinct buffering and precipitation behaviours that may be advantageous under variable or alkaline conditions, respectively. The proposed framework treats mineralogical diversity as a functional asset rather than a limitation, emphasising that different DWTR types are suited to distinct environmental contexts rather than a one-size-fits-all reuse strategy. Key research priorities are identified, including the need for standardised characterisation protocols, multi-site performance validation, long-term field monitoring, and integration of DWTR reuse within circular-economy and nutrient-management strategies. By explicitly linking coagulant chemistry, mineralogical properties, and environmental context, this review provides structured guidance to support more systematic, evidence-based DWTR reuse in nature-based treatment infrastructure and sustainable phosphorus management.