Elimination of micropollutants by the solar/chlorine process: contribution of reactive species and formation risk of NDMA

Abstract

Diuron, a persistent organic herbicide, was effectively degraded by the solar/chlorine process in this study. The solar/chlorine process could not only produce HO˙ (hydroxyl radicals) and reactive chlorine species (RCS), but also O₃. They are the major contributors to diuron degradation at different solution pH values (6–8). Natural organic matter (NOM), NO₂⁻ and a high dosage of Cl⁻, NO₃⁻, and HCO₃⁻ could inhibit the efficiency of diuron degradation. Moreover, a possible degradation pathway of diuron was proposed, which gives detailed reactions in the solar/chlorine process. The co-existence of NO₂⁻ in diuron degradation has risks of producing N-nitrosodimethylamine (NDMA). Finally, the ecotoxicity of diuron and its oxidation byproducts was reduced overall according to the calculated results from the Ecological Structure Activity Relationships (ECOSAR) program. But the toxicity of the products is still very high. For that, the solar/chlorine process should be of concern when it is used for diuron degradation.