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, S2O82-) 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 S2O82- concentration and UV strength on the UV/S2O82- process for the degradation of TMAH in a batch reactor. The results suggested that 15 watts (W) of UV-activated S2O82- at concentrations of 10 or 50mM resulted in pseudo-first-order TMAH degradation rate constants of 3.1-4.2 x 10(-2) min(-1), which was adopted for determining the hydraulic retention time (HRT) in a continuous stirred tank reactor (CSTR). The operating conditions (15W UV/10mM S2O82-) with a HRT of 129min resulted in stable residual concentrations of S2O82- and TMAH at approximately 2.6mM and 20mg 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.