The physicochemical composition of drinking water treatment residuals (DWTRs) depends heavily on the hydrochemistry of raw water sources and the chemicals used during the coagulation-flocculation process. Iron and/or aluminum oxides and oxyhydroxides, a material with a high affinity for metals, are the main components of DWTRs and can be accompanied by clays, organic matter, and fine sand. Modeling metal sorption (or desorption) to DWTRs is needed to assess their environmental fate when released to surface waters or when their untapped reactivity toward metals is considered in reuse schemes.<br/>A geochemical model was built and implemented in PHREEQC to predict metal sorption to DWTRs. A literature review was conducted to determine the range of physicochemical characteristics of DWTRs. The reactivity of DWTRs toward metals was conceptualized via surface complexation reactions with model surfaces. The equilibrium constants for different surfaces were obtained from geochemical databases and previous reports on model systems. This approach allows an estimation of the overall metal sorption capacity of DWTRs.<br/>The model was used to assess the likely boundaries of DWTRs performance for a range of geochemical scenarios that characterize Andean watersheds. This information is useful to identify opportunities and challenges for DWTRs management and reuse in water-scarce countries, where high metal and metalloid concentrations occur.

Reuse and fate of drinking water treatment residuals (DWTRs): Using geochemical modelling to assess the sorption of metals and metalloids

ACS Fall 2021

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