Oxidative degradation of tetramethylammonium hydroxide (TMAH) by UV/persulfate and associated acute toxicity assessment

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.