The sorption of algal organic matter by extracellular polymeric substances: Trade-offs in disinfection byproduct formation influenced by divalent ions

Abstract

Disinfection by-products (DBPs), formed from biofilm extracellular polymeric substances (EPS) and organic matter during regular disinfection practices in drinking water distribution systems, poses a potential threat to drinking water safety. However, the diverse DBP formations induced by the intertwined algal organic matter (AOM) and bacterial EPS remains elusive. In this study, we show substantial variations in EPS and DBP formation patterns driven by AOM biosorption with divalent ions (Ca²⁺ and Mg²⁺). Divalent ions in bulk water can significantly inhibit carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs) formation. Mechanistically, divalent ions promote the complexation of negative charged groups and thus inhibit C-DBP formation, while the hindering chlorine substitution of hydrogen atoms on α‑carbon and amine groups reduces N-DBP formation. Conversely, Ca²⁺ and Mg²⁺ could facilitate biosorption processes that increased the yields of C-DBPs and N-DBPs. Both EPS and AOM provide halogenated reactive sites for DBP formation, exhibiting diverse aromatic substances and unsaturated (lignin and tannins) compounds. Our results highlight divalent ions acting as a fundamental driving force in DBP formation, suggesting the need for cautious monitoring of divalent ions in karst water.

Keywords: Algal organic matter; Disinfection by-products; Divalent ions; Extracellular polymeric substances; Karst water.