Oxidative degradation of tetramethylammonium hydroxide (TMAH) by UV/persulfate and associated acute toxicity assessment
Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering | 12 May 2017
J Huang, KS Wang and C Liang
Tetramethylammonium hydroxide (TMAH) is widely used in high-tech industries as a developing agent. Ultraviolet (UV) light-activated persulfate (PS, S2O8(2-)) can be used to generate strongly oxidative sulfate radicals, and it also exhibits the potential to treat TMAH-containing wastewater. This study initially investigated the effect of S2O8(2-) concentration and UV strength on the UV/S2O8(2-) process for the degradation of TMAH in a batch reactor. The results suggested that 15 watts (W) of UV-activated S2O8(2-) at concentrations of 10 or 50 mM resulted in pseudo-first-order TMAH degradation rate constants of 3.1-4.2 × 10(-2) min(-1), which was adopted for determining the hydraulic retention time (HRT) in a continuous stirred tank reactor (CSTR). The operating conditions (15 W UV/10 mM S2O8(2-)) with a HRT of 129 min resulted in stable residual concentrations of S2O8(2-) and TMAH at approximately 2.6 mM and 20 mg L(-1) in effluent, respectively. Several TMAH degradation intermediates including trimethylamine, dimethylamine, and methylamine were also detected. The effluent was adjusted to a neutral pH and evaluated for its biological acute toxicity using Cyprinus carpio as a bioassay organism. The “bio-acute toxicity unit” (TUa) was determined to be 1.41, which indicated that the effluent was acceptable for being discharged into an aquatic ecosystem.
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