Ozonation and peroxone oxidation of ethylenethiourea in water: operational parameter optimization and by-product identification
2015
Bottrel, S. | Amorim, C. | Ramos, V. | Romão, G. | Leao, M.
The objective of this work was to study the degradation and mineralization of ethylenethiourea (ETU) in water by ozonation at different pH values and in the presence of hydrogen peroxide. Degradation experiments were performed using an initial ETU concentration of 50 ppm for 180 min with a gas flux of 0.25 dm³ min⁻¹and an O₃production rate of 12.1 mg min⁻¹. Degradation of by-products was monitored by direct injection electrospray ionization mass spectrometry (ESI-MS), ETU concentration was determined by HPLC-UV, and its mineralization was detected by total organic carbon (TOC) analysis. Optimum degradation of ETU in water was observed at pH = 11, whereas at pH = 3, the degradation of ETU was slowest, indicating that the reaction occurred through different mechanisms. The additional effects of hydroxyl radicals formed at the highest pH can be used to explain the results obtained in this study. Peroxone experiments were carried out in the presence of 400 and 800 mg L⁻¹H₂O₂; the degradation of ETU was faster at 400 mg L⁻¹H₂O₂. This was attributed to the scavenging effect of the excess H₂O₂. ETU treatment by ozonation produced several by-products of degradation such as ethylene urea and 2-imidazoline.
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