Ozone Treatment of Soil Contaminated with Chlorinated Herbicides

Abstract

The soil remediation using ozonation in laboratory was studied to control the soil contaminated with chlorinated phenoxy acid herbicides. The reaction conditions and reaction kinetics were investigated. The experimental results show that different pollutant species display different degradation efficiencies under the same reaction conditions. Degradation of 4-chloro-2-methyl phenoxyacetic acid (MCPA) is faster than that of 2,4-dichlorophenoxyacetic acid(2,4-D). This is owing to the different molecular structures between MCPA and 2,4-D. Compared with 2,4-D, MCPA is more stronger in nucleophilic activity and hence more easily attacked by ozone. Soil fineness has effect on remediation of soil pollution. The more the mesh number, the thinner the quartz sand, the larger the specific surface area of solid phase is. This will increase the reaction contact area and mass transfer area and further enhance the degradation of 2,4-D in soil. Soil moisture content affects significantly degradation of MCPA at the same other conditions. Chlorinated phenoxy acid herbicides are soluble in water. Hydroxyl radical is produced by O3 decomposition after O3 transfer from gas phase to liquid phase. The number of active species increases with the soil moisture content increases. Hence, the degradation of pollutants in soil is accelerated. By comparing with the fitness situation of pseudo-first order kinetics or pseudo-zero order kinetics, it is shown that the correlation coefficients of pseudo-first order kinetics fitting MCPA degradation with different soil moisture are all above 0.90. Pseudo-first order kinetics is more suitable than pseudo-zero order kinetics to fit degradation of pollutant in soil using ozonation remediation.