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

ABSTRACT

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 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 S₂O₈²⁻) with a HRT of 129 min resulted in stable residual concentrations of S₂O₈²⁻ 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” (TU_a) was determined to be 1.41, which indicated that the effluent was acceptable for being discharged into an aquatic ecosystem.

KEYWORDS:

• Acute toxicity
• continuous stirred tank reactor (CSTR)
• industrial wastewater
• sodium persulfate
• sulfate radical

Funding

This study was funded by the Ministry of Science and Technology (MOST) of Taiwan under the College Student Participation in MOST Research Project No. 104-2815-C-005-077-E.