Simultaneous elimination of N,N-dimethylhydrazine compounds and its oxidation by-product N-nitrosodimethylamine by UV-activated peroxymonosulfate process: Multiple-path mechanism validation and toxicity alteration

In this study, the ultraviolet/peroxymonosulfate (UV/PMS) process was found to be an efficient and safe strategy for simultaneously controlling NDMA during the degradation of N,N-dimethylhydrazine compounds, such as 1,1,1′,1′-Tetramethyl-4,4′-(methylene-di-p-phenylene) disemicarbazide (TMDS). The distinct roles of sulfate radicals (SO₄[rad]⁻), hydroxyl radicals (HO[rad]), PMS, and UV in TMDS degradation as well as NDMA formation and elimination, have been elucidated, involving the kinetics and multiple-path transformation mechanisms. Moreover, to assess the feasibility of this process, a comprehensive toxicity assessment of treated water for zebrafish embryos was conducted. Mineralization analysis and an assessment of electrical energy per order (EE/O) were performed on actual water samples. The results indicate that SO₄[rad]⁻, HO[rad], PMS, and UV together degraded TMDS, but only SO₄[rad]⁻ and PMS led to NDMA formation. UV irradiation may coordinate SO₄[rad]⁻ and HO[rad] to overcome the energy barriers of NDMA elimination by providing continuous energy. The degradation of TMDS involved hydroxylation, radical addition, bond cleavage and nitrosation. Notably, NDMA formation may be closely related to the electron transfer between SO₄[rad]⁻ or PMS and TMDS. Subsequently, the generated NDMA was controlled through photocleavage, radical addition, and hydroxylation. Additionally, the results of toxicity evaluation and EE/O analysis suggest UV/PMS is safe and has the potential for treating N,N-dimethylhydrazine compounds-containing water.