Trichloronitromethane (TCNM) is a nitrogenous disinfection byproduct featuring high cytotoxicity and genotoxicity. Previous research showed that wastewater effluents enriched in organic nitrogen feature high TCNM formation potential (TCNM-FP), and that nitrite generally promotes TCNM formation during chlorination. In watersheds with high wastewater and nitrite impacts, the organic and inorganic nitrogen species can be transformed by sunlight as they travel from the discharge points to downstream water intakes. However, it remains unclear whether this process also alters the TCNM-FP. In this study, we evaluated the effects of sunlight irradiation on the TCNM-FP of wastewater effluents in the presence of various concentrations of nitrite. First, two nitrified and two non-nitrified effluents from four wastewater treatment plants were sampled multiple times over 18 months, and the TCNM-FP was measured before and after sunlight irradiation. After 8 h irradiation under simulated sunlight, TCNM-FP was attenuated by 17–47% in 8 out of 12 samples. Longer irradiation (up to 36 h) further decreased TCNM-FP in a non-nitrified effluent, but increased TCNM-FP in a nitrified effluent by 3-fold between 8 and 36 h. Secondly, when nitrite was spiked into effluents, sunlight irradiation increased the TCNM-FP. For example, in the presence of 1 mg N/L nitrite, TCNM-FP increased by 1.1–3.6 µg/mg C after 8 h irradiation. The effect of combined nitrite and sunlight was more pronounced in nitrified effluents than in non-nitrified effluents. Lastly, the increase of TCNM-FP by combined nitrite-sunlight effect was also observed for four model TCNM precursors (humic acid, tryptophan, tyrosine, and phenol) relevant to wastewater. Humic acid and tryptophan were associated with higher increase in TCNM-FP than tyrosine and phenol after sunlight irradiation.

Combination of sunlight and nitrite increases trichloronitromethane formation from wastewater effluents

2019 Spring National Meeting

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