Effects of oxidants on the degradation of tributyl phosphate under supercritical water oxidation conditions

The effects of additional oxidants, such as NaNO 3 , Na 2 S 2 O 3 , KClO 4 , and K 2 Cr 2 O 7 , on the supercritical water oxidation (SCWO) of tributyl phosphate (TBP) were studied. The coupling of an ionic oxidant with SCWO can effectively enhance the oxidative degradation ability of the system, thus increasing its organic-matter-removal efficiency at a reduced reaction temperature. Moreover, the addition of NaNO 3 , KClO 4 , or K 2 Cr 2 O 7 could improve this efficiency at a reaction temperature of 500 °C compared with that of the original system at 550 °C. Additionally, based on the conditions adopted in this study, the addition of either of these oxidants could reduce the final total organic carbon (TOC) of the effluent from ~ 500 to < 100 ppm. Concurrently, the ionic oxidants could effectively improve the processing capacity of the SCWO system to reduce the scale of the equipment, as well as the amount of produced wastewater. Compared with KClO 4 and Na 2 S 2 O 3 , the addition of 10 mmol/L NaNO 3 and K 2 Cr 2 O 7 to the organic feed could increase the processing capacity of the system from 4 to 10% while maintaining the TOC removal at > 99%. The effects of the ionic oxidants on the gas products, including CO 2 , CO, H 2 , and CH 4 , as well as other organic gases, have also been studied. Among these gas products, CO 2 accounted for the main gas product with a proportion of more than half. At < 500 °C, temperature significantly affected the as products (CO, H 2 , CH 4 , and other organic gases). However, the gas product was mainly CO 2 when the temperature was increased to ≥ 500 °C. This study initially revealed the enhancement effect of ionic oxidants on SCWO, which still requires further research.