Study On Remediation Of BTEX Contaminated Groundwater By Fenton's Chemical Reactive Zone

Groundwater is a kind of important water resources, which plays an important role in agriculture irrigation, mining industry and urban water supply. In recent years, some unexpected groundwater pollution accidents occurred in many countries have made people more and more concerned about groundwater pollution problems. BTEX are the common organic pollutants caused by leakage of oil fuel. Because BTEX are easy to transfer in groundwater and has risk of causing cancer, they have serious threat to ecosystems and human health.First of all, the removal effect and kinetics of oxidation treatment of BTEX by Fenton's reagent and Fenton-like reagent were quantitative investigated and compared in the groundwater by a series of experiments. The impacts of H2O2/BTEX and H2O2/Fe (molar ratio) on the removal effects were researched. Then the remediation of BTEX contaminated groundwater by Fenton's chemical reactive zone in different conditions was studied, and the remediation of polluted site was simulated in two-dimensional simulated box. the results indicate:(1) Fenton's reagent suggested strong ability to oxidize BTEX. There was impact of H2O2/BTEX and H2O2/Fe on Fenton's and Fenton-like's treatment effect. The bigger H2O2/BTEX was, the stronger the oxidizing ability was and the better the removal rate was. While using Fenton's reagent to treat BTEX, most of the contaminants were destroyed in 20min, and the concentrations maintained stability in 3h. When H2O2/BTEX=20 and H2O2/Fe=8, the removal rates could reach 100%. It took longer time to achieve maximum of efficiency while using Fenton-like reagent to treat BTEX. The concentrations maintained stability in 24h, and removal rate was lower. Because the molecular structure and initial concentrations were different, the removal rates of BTEX were differences.(2) ORP during the Fenton and Fenton-like processes rose from -44mV to 300～500mV. and pH reduced from 6-7 to about 3. The colors of whole system were yellow or brown.(3) While the concentrations of oxidizers were high, the Fenton's and Fenton-like oxidation processes of BTEX followed the second order reaction kinetic equation:1/C=kt+1/C0. The average half lives of Fenton's and Fenton-like treatment of BTEX respectively were 0.057h and 0.642h. The rate constants during the oxidation processes were:ethyl benzene>xylenes> toluene>benzene.(4) The experiment of BTEX contaminated groundwater remediation by Fenton's chemical reactive zone indicate:the concentrations of BTEX in simulated column decreased rapidly to minimum concentrations in about 2 days, then the concentrations tend to vary smoothly. The closer the sampling ports to the injection ports were, the lower the concentrations of BTEX were. The concentrations of the sampling ports'BTEX decreased where Fenton's reagent migrated to. It maintained high removal rates in the system during the early 10 days. The removal rates of BTEX in the different ports were:benzene 49%-100%, toluene 56%-100%, ethyl benzene 58%-100% and xylenes 50.1%-100%.(5) A large amount of O2 generated during the process of injecting Fenton's reagent, which made some bubbles and fractures in the column, and the DO in the injecting ports increased. The water level in the column fell, which caused the flow of outlet water in a few days. The ORP in the column rose from -60mV to 90～501mV, and the pH reduced to around 3. The colors of whole system were yellow or brown. The closer the sampling ports were to the injection ports, the higher the ORP were, and lower the pH were. The Fe(Ⅱ) and Fe(Ⅲ) concentrations rapidly declined after rose to maximum within 2 days. The results show that the ORP, pH, Fe(Ⅱ) and Fe(Ⅲ) didn't migrate downstream, which could avoid a second-pollution downstream. When the experiment ended, the Fe(Ⅱ) and Fe(Ⅲ) concentrations of the sands in the column increased, especially in the injecting ports. The sands taken out from the column were yellow.(6) While the groundwater flow rate was 0.337 m/d, due to higher groundwater flow rate, the vary trend of BTEX concentrations in each sampling hole of the simulated column were almost the same after the injection of Fenton's reagent. The concentrations rapidly decreased to lowest within 2d. It maintained high removal efficiencies in the early 5～10 days, followed by the concentration increased.Injecting Fenton's reagent twice (in Od and 5d) into the column could enhance the oxidation process. So the concentrations of BTEX in the column continued to maintain low. and slightly rose after 16d. It can be concluded that injecting Fenton's reagent for several times got the best remediation effect.(7) The results of the experiment in the two-dimensional simulated box indicate:after adding the BTEX pollution sources, the BTEX pollution plume gradually move back and down as time went by. Because the densities are lower than that of water, BTEX mainly distributed near the surface of the groundwater and the concentration decreased gradually from top to bottom. The BTEX plume distributed almost whole of the aquifer in 22h after pollution. The maximum BTEX concentrations could reach benzene 91.2mg/L, toluene 83.6mg/L, ethyl benzene 8.0mg/L m and p -xylene 63.8mg/L and o-xylene 9.8mg/L. After injecting Fenton's reagent, Fenton's chemical reactive zone formed in groundwater and the concentrations of BTEX in the aquifer decreased. After 15d the maximum concentrations were only benzene 8.3mg/L, toluene 1.3mg/L, no ethyl benzene, m and p-xylene 0.6mg/L, and o-xylene 0.6mg/L...