Degradation of natural organic matter and disinfection byproducts formation by solar photolysis of free available chlorine

Environment disinfection effectively curbs transmission of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, elevated concentration of free available chlorine (FAC) in disinfectants can be discharged into surface water, generating toxic disinfection byproducts (DBPs). The impact of solar photolysis of FAC on natural organic matter (NOM) to form DBPs has not been well studied. In this work, solar photolysis of FAC was found to result in higher formation of DBPs, DBPs formation potential (DBPsFP), total organic chlorine (TOCl) and lower specific ultraviolet absorbance at 254 nm (SUVA(254)), compared to dark chlorination. In solar photolysis of FAC, formation of total DBPs was promoted by pH=8, but hindered by the addition of HCO3-, radical scavenger or deoxygenation, while addition of NO3- and NH4+ both enhanced the formation of nitrogenous DBPs. Differences in the formation of DBPs in solar photolysis of FAC under various conditions were influenced by reactive species. The formation of trichloromethane (TCM) and haloacetic acids (HAAs) in solar photolysis of FAC positively correlated with the steady-state concentrations of ClO center dot and O-3. The steady-state concentrations of (NO)-N-center dot and (NH2)-N-center dot positively correlated with the formation of halonitromethanes (HNMs). HAAs and haloacetonitriles (HANs) mainly contributed to calculated cytotoxicity of DBPs. This study demonstrates that solar photolysis of FAC may significantly impact the formation of DBPs in surface water due to extensive use of disinfectants containing FAC during SARS-CoV-2 pandemic.

Automated summary

Environment disinfection effectively reduces transmission of SARS-CoV-2 but may generate toxic disinfection byproducts (DBPs) when elevated chlorine levels are released into surface water. This study investigates the impact of solar photolysis of free available chlorine (FAC) on DBP formation and finds that solar photolysis of FAC leads to higher formation of DBPs compared to dark chlorination. Various factors such as pH, HCO3-, and reactive species influence the formation of DBPs during solar photolysis of FAC.