Assessing strategies to improve the efficacy and efficiency of direct filtration plants facing changes in source water quality from anthropogenic and climatic pressures

Abstract

Lake recovery from acidification and climatic drivers are causing increasing concentrations of natural organic matter (NOM) in surface waters across North American and Europe. These shifts in source water quality have caused challenges in the drinking water treatment industry, particularly in direct filtration plants, which are sensitive to changes in influent water quality. There is a need for immediate treatment strategies to address the increasing organic load while sustainable solutions are developed. The presented research investigated the impacts of partially substituting aluminum sulphate (alum) with a high charge density cationic polyelectrolyte on NOM removal and unit filter run volume (UFRV) in a direct filtration pilot plant. Various combinations of alum (10–12 mg/L) and polyelectrolyte (0–1 mg/L) were compared to the current full-scale plant dose of 12 mg/L of alum. The impacts of increasing the effective size of the filter media from 0.9 mm to 1.3 mm on NOM removal and UFRV were also studied. The partial substitution of alum with polyelectrolyte did not significantly impact total organic carbon (TOC) removal, which was consistent around 35–40 %, or TOC residual concentrations, which were approximately 2.1–2.3 mg/L. The UFRV was not impacted by the partial substitution of alum with polyelectrolyte, but increasing the effective size did improve the UFRV by 3 to 16 m3/m2 without impacting the effluent water quality. Additionally, the research highlighted the importance of understanding projected trends in the concentration and character of source water NOM for sustainable drinking water treatment design.