Remediation Of Polychlorinated Biphenyls(PCBs) Contaminated Soils By US-fenton Process

In this paper, the Ultrasound-Fenton (US-Fenton) combined oxidation technology was applied to the removal process of PCBs, then the degradation effect and degradation kinetics were studied.The experiment firstly compared the removal efficiency of PCBs executed by three different methods: Fenton, ultrasound and the combination of Fenton and ultrasound. The results confirmed the synergy effects between the two oxidation techniques that the efficiency of US-Fenton reached to 70.41%, significantly higher than the single use of Fenton (51.08%) or ultrasonic oxidation (30.44%).Secondly, the experiments explored the different influences from different factors,which including water/soil ratio, H2O2 dosing quantity, H2O2/Fe2+mole ratio, pH, ultrasonic power and ultrasonic time, to the removal efficiency of polychlorinated biphenyls in soil samples by single factor control method. Thirdly, the response surface method(RSM) is adopted to optimize comprehensively the fore said factors. The experimental results demonstrated that the best PCBs removal rate(85.80%) is gained under the conditions of soil/water rate at 1.54, H2O2 dosing amount=3.54 g kg-1,H2O2/Fe2+ mole ratio=2:1, pH at 3.08, ultrasonic power=12.16 KW·kg-1 and 8.16 of the reaction time. The significance of five factors on the removal rate is ultrasound power >H2O2 dosage > pH >water/soil ratio >ultrasound time, and some of the factors have interaction with each other.Then the kinetic process of PCBs degradation was analyzed under the optimum experimental parameters. And the kinetic equation of US-Fenton method for the degradation of PCBs in soil was obtained by mathematical calculation:-d[PCBs/PCBs]/dt=328.03eEa/RT[Fe2+]0.09[H2O2]0.39[P]0.41[PCBs]0.15 It can be seen that the degradation kinetics of PCBs is a pseudo-first-order reaction, which means the reaction is easily and rapidly occurred.Based on the results of GC-MS detection to recognize the products of the PCBs degradation is O-Xylene, P-Xylene and 1-chloro-Hexane.And the possible pathways of the degradation of PCBs is proposed at last,which is dechlorinated first and break C=C link and turn into a low toxic straight chain structure.