Application of ozone related processes to mineralize tetramethyl ammonium hydroxide in aqueous solution

Tetramethyl ammonium hydroxide (TMAH) is an anisotropic etchant used in the wet etching process of the semiconductor industry and is hard to degrade by biotreatments when it exists in wastewater. This study evaluated the performance of a system combined with ultraviolet, magnetic catalyst (SiO ₂/Fe₃O₄) and O₃, denoted as UV/O₃, to TMAH in an aqueous solution. The mineralization efficiency of TMAH under various conditions follows the sequence: UV/O₃ > UV/H₂O₂/O₃ > H₂O ₂/SiO₂/Fe₃O₄/O₃ > H₂O₂/O₃ > SiO₂/Fe ₃O₄/O₃ > O₃ > UV/H ₂O₂. The results suggest that UV/O₃ process provides the best condition for the mineralization of TMAH (40 mg/L), resulting in 87.6% mineralization, at 60 min reaction time. Furthermore, the mineralization efficiency of SiO₂/Fe₃O₄/H ₂O₂/O₃ was significantly higher than that of O₃, H₂O₂/O₃, and UV/H ₂O₂. More than 90% of the magnetic catalyst was recovered and easily redispersed in a solution for reuse.