Treated wastewater discharges are a source of synthetic organic micropollutants to river water. Photodegradation can be an important process that controls their downstream fate. In-river photodegradation processes are influenced by aquatic dissolved organic matter (DOM) that plays a dual role by slowing direct photolysis reactions while generating photochemically-produced reactive intermediates (RIs) that can enhance compound degradation via secondary reactions. These RIs include triplet-state excited organic matter (3OM*), singlet oxygen (1O2), and hydroxyl radicals (OH●). This work examined the photodegradation of four compounds in river water, effluent, and mixtures of river water and effluent. Higher photodegradation rates for compounds undergoing indirect photodegradation with 3OM*, 1O2 and OH● were observed in effluent than for river water from upstream. Mixtures containing higher fraction of effluent showed greater degradation rates. The experimental degradation rates of cimetidine in mixtures that showed &gt;90% degradation via 1O2 pathway were lower than the calculated values. Compound degradation rates normalized to incident light intensity, were correlated with optical properties of the water. Overall, moderate contributions (&lt;25%v/v) of effluent to rivers may not alter photodegradation rates, despite the differences in chemical composition between effluent and river DOM. Optical property characteristics may hold promise to predict indirect compound degradation rates.

Photochemistry of effluent organic matter and photochemical degradation of micropollutants

251st National Meeting (2016)

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