Degradation of p-Nitrophenol by thermally activated persulfate in soil system

Abstract

In this work, acceleration of oxidation of p-Nitrophenol, a known soil pollutant, by thermally activated persulfate was studied for the application of soil remediation. The effect of various operating parameters viz., reaction temperature, initial concentration of persulfate, pH, and basic constituents of soil matrix Cl−, HCO3− and humic acid (HA) was systematically examined. Further, a comparative study was made between the rate of p-Nitrophenol degradation of soil-free and soil-containing systems under similar experimental conditions. The results indicated that oxidation reaction of p-Nitrophenol followed a pseudo-first-order kinetic model, and the rate constant was found to increase with increasing the temperature and the initial concentration of persulfate as well. The rate of consumption of persulfate was enhanced at elevated temperatures, and 60°C was found to be an optimum condition to activate the persulfate. The pH of the system was found to be having no significant effect on the degradation process. The constituents of soil matter presented in the system, such as Cl−, HCO3− and HA, showed negative impact on the progressive degradation of p-Nitrophenol. The presence of soil in the system made mechanical restrains to the diffusion of sulfate radicals, resulting in an inhibitive effect. The observed decline trend of p-Nitrophenol degradation with the system of HA addition was due to a partial consumption and/or deterioration of the oxidant by the dissolved organic matter. In addition, the results derived from LC/MS analysis showed that 2,4-dinitrophenol, 4-hydroxy-2′,3,4′-trinitrobiphenyl, phenol, p-benzoquinone, and maleic acid were the primary intermediates formed during the degradation of p-Nitrophenol. Accordingly, a plausible pathway for the degradation of p-Nitrophenol could be proposed, which was identical in both the soil-containing and soil-free systems.