Key Properties of Drinking Water Treatment Residuals for their Effective Reuse as Phosphate Adsorbents

Abstract Drinking Water Treatment Residuals (DWTR) are the sludge by-products produced in the drinking water treatment plants, representing a significant amount of the operational costs. Since the DWTR properties depend on the treatment system and the raw water characteristics, it is crucial to understand the key parameters to streamline the decision-making process regarding DWTR reuse. This study aimed to assess the key parameters of DWTR as an adsorbent material of phosphate ( $$\:\text{P}{\text{O}}_{\text{4}}^{\text{3-}}$$ ). To this end, seven different DWTR were subjected to physical and chemical characterization. Adsorption tests were carried out under neutral pH. Following a comprehensive analysis of the correlation between the quantitative properties and the adsorption capacity, a reliable predictor has been determined. This predictor will inform the construction of a model that will accurately predict the adsorption capacity. The characterization showed differences among the DWTR, supporting the influence of the DWTR properties. Six of the DWTR were able to adsorb $$\:\text{P}{\text{O}}_{\text{4}}^{\text{3-}}$$ , with adsorption capacities ranging between 6.7 and 44.1 mg/g. Contrary to expectations, the aluminium content was not the key parameter for the adsorption process. Instead, the crucial factor was the pH at the point of zero charge (pH PZC ). Based on this relationship, a statistical model was built, using pH PZC as a predictor of adsorption capacity ( p -value < 0.0001, R 2 = 0.735). The use of pH PZC as a predictor of the $$\:\text{P}{\text{O}}_{\text{4}}^{\text{3-}}$$ adsorption capacity of DWTR enables the reduction of the number and the costs of analytical determinations and streamlines the decision-making process for stakeholders regarding DWTR reuse.