Enhanced formation of carbonaceous and nitrogenous disinfection byproducts from biofilm extracellular polymeric substances undercatalysis of copper corrosion products

Abstract

Biofilm formation is ubiquitous on the corroded inner surface of water distribution pipes. Extracellular polymeric substances (EPS) secreted by biofilm microorganisms are nonnegligible precursors of disinfection byproducts (DBPs). The aim was to study the catalysis of copper corrosion products (CCPs, CuO and Cu2+) on the formation of carbonaceous and nitrogenous DBPs (C-DBPs and N-DBPs) with EPS as a precursor. Results indicate that CCPs had a remarkable enhancement on the formation of DBPs, especially N-DBPs. The enhancement by Cu2+ was mainly via homogeneous catalysis initiating from its complexation with EPS, while that by CuO was primarily through heterogeneous catalysis initiating from the polarization of Cl atom in HOCl/OCl−. The enhancement was more evident as pH increased because an alkaline condition favored the electrostatic interactions of CCPs with EPS and HOCl/OCl−. The presence of Br− weakened the enhancement, which may be attributed to that HOBr/OBr− had a much higher reaction rate than HOCl/OCl− towards the low reactive moieties in EPS. Due to more phenolic or unsaturated/conjugated groups, EPS proteins had a higher catalytic formation of DBPs than EPS polysaccharides. Among the major amino acids in EPS proteins for DBPs formation, tyrosine had the highest enhancement on the formation of trihalomethanes, while histidine had the highest catalytic formation of halogenated acetic acids, acetonitriles and acetamides. The study helps to understand the formation of DBPs by the joint actions of EPS and CCPs in drinking water distribution systems.