Degradation Of P-nitrophenol By The Thermally Activated Persulfate In Soil System

Persulfate commonly used to generate SO4?- as its high solubility and stability at room temperature, can be effectively activated by initiators, including heat, UV light or transition metals. Recently, SO4?- has been one of the potential advanced oxidation processes to repair the groundwater and soil. Persulfate can be effectively activated to produce SO4?-, which can rapidly degrade the organic pollution in system. Therefore, the purposes of this study were to utilize thermal activated persulfate to degrade the PNP in soil system, investigate the degradation kinetic of PNP, and evaluate the effects of soil matrix, such as Cl-, HCO3- and HA, on the PNP degradation performance in soil. At last, we detected the concentration of intermediates of PNP during the degraded process, to propose the pathway of PNP degradation.In this study, we investigated the effects of temperature(40, 50, 60, 70, 80oC) and the initial concentration of persulfate on the degradation of PNP, meanwhile, the effect of soil matter on the PNP degradation was evaluated. The results indicated that the degradation rate of PNP was improved with the increasing of temperature and persulfate initial concentration. The resulting rate constants—measured from 40 to 80 °C— fit the Arrhenius equation, yielding an apparent activation energy of 137.29 k Jmol-1 for PNP in soil-contained system. The comparison of PNP degradation between the soil-free and contained systems showed that the PNP degradation was faster in soil-free system. The reason for this was soil presented in the system would restrain the diffusion of persulfate and SO4?-, resulting in the inhibitive effect on the PNP degradation.We investigated the influence of different HA concentration and the different molar ratio of between Cl-/ HCO3- and persulfate on the PNP degradation. The results showed that the presence of HA, Cl- or HCO3- has inhibitive effect on PNP degradation. While this inhibitive effect was promoted with the increasing of dosage of HA, Cl- or HCO3- in system. Compared to Cl-, a much more significant inhibitive effect was observed for bicarbonate ion HCO3-. Cl- or HCO3- presented in system would react with SO4?-, then weaken the oxidation capacity of SO4?-, resulting in the inhibitive effect on PNP degradation. With the addition of HA in system, the SO4?- was initially consumed by HA rather than by PNP, leaded to a lag phase on PNP degradation within 60 min.The reaction mechanism of PNP degradation by the activated persulfate was investigated on the basis of identification of intermediates by HPLC coupled with LC/MS in the study. Furthermore, the concentration of intermediates formed in the process of the PNP degradation was analyzed by HPLC. The results indicated that 2, 4-dinitrophenol(2, 4-DNP), 4-hydroxy-2', 3, 4'-trinitrobiphenyl, phenol, p-benzoquinone and maleic acid were formed in the process of the PNP degradation both in the soil-free and contained systems. The intermediates formed and accumulated in the soil-free system were degraded within a comparatively lesser reaction period than that of the soil-containing system, but the evolution tendency were identical and consistent for both the systems. The soil matter presented in the system had no impact on the reaction pathway of PNP degradation. Finally, the proposed degradation pathway of PNP by thermally activated persulfate was deduced.