Remediation Of Soil Contaminated By Organic Pollutants Using Tween 80 And Electrochemical Advanced Oxidation Processes

Soil contaminated by petroleum-hydrocarbons is a serious environmental problem since it is toxic to agriculture and human.And the polycyclic aromatic hydrocarbons（PAHs）in petroleum-hydrocarbons possess teratogenicity,carcinogenicity,mutagenicity,low volatility and poor solubility properties,which are persistent in soil and difficult to be degraded.Hence,effective methods are essential to remedy soil contaminated by petroleum-hydrocarbons and PAHs.Among various remediation methods,soil washing（SW）combined with surfactant is a promising techniques since it is economical,effective approach.This technology promotes the transformation of contaminants from soil to aqueous solution,which is especially applied for heavy contaminated soil.However,soil washing solution highly loaded with surfactant and contaminants is produced.Therefore,effective treatment of soil washing solution is a challenge for promoting the application of surfactants and the remediation of contaminated soil.The combination of soil washing process and electrochemical advanced oxidation processes（EAOPs）is an effective technique for the remediation of contaminated soil.In this paper,Tween 80 was applied as surfactant during soil washing process.EAOPs including electrolysis oxidation（EO）,electro-Fenton（EF）,sulfate radical-based advanced oxidation processes（SR-AOPs）were investigated in the degradation of petroleum-hydrocarbons in soil washing solution.Besides,a potential advanced oxidation process in which active chlorine exists was applied for treating soil washing solution which contains phenanthrene（PHE）and Tween 80.This investigation is constituted of five experimental parts as follows.（1）The Tween 80 was applied as surfactant to remedy soil highly contaminated with diesel.The concentration of diesel was determined by using fluorescence which is a stable and fast quantification method based on the fluorescence characteristic of diesel.Besides,Tween 80 was quantified by fluorescence based on the formation of micelles between 6-（p-toluidino）naphthalene-2-sulfonic acid（TNS）and Tween 80.During soil washing process,the use of Tween 80 enhanced the removal of diesel from soil.The effects of various parameters,including clay content,soil washing time,Tween 80 concentration,the soil dosage and washing times,indicate that the percentage of diesel extraction declined with the increase of clay content and soil dosage.With the washing time varied from 30 min to 180 min,the percentage of diesel extraction increased from 66.7%to 88.2%.The percentage of diesel extraction declined to 83.5%when the washing time further increased to 240 min.Diesel extraction percentage was improved with increase of Tween 80 concentration.Under conditions of 20%clay,180 min washing time,10 g soil with 100 m L soil washing solution,about 75.2%,80.0%and 87.9%the diesel extraction percentage were achieved with 5.0,7.5,10.0 g L^-1 Tween 80 after two times of soil washing,respectively.（2）Electro-oxidation（EO）and electro-Fenton（EF）were further applied for the treatment of soil washing solution which is highly loaded with Tween 80 and diesel.Under conditions of 180 min washing time,10 g soil with 100 m L surfactant solution and two times of soil washing,about 75.2%,80.0%and 87.9%of diesel was extracted from soil with 5.0,7.5 and 10.0 g L^-1 Tween 80.The degradation of diesel in soil washing effluent was carried out by two EAOPs,EO and EF using boron-doped diamond（BDD）anode and carbon felt cathode cell.After 360 min EO treatment,72.7-83.0%of diesel was removed from the effluent after soil washing with 5.0-10.0g L^-1 Tween 80 while higher removal efficiencies（77.7-87.2%）were attained with EF process.The results of parallel factor analysis（PARAFAC）of excitation emission matrix（EEM）fluorescence spectroscopy indicate that the fluorescent intensity of component 3（C3,Ex/Em 210/290 nm）increased,the component 1（C1,Ex/Em270/310 nm）and component 2（C2,Ex/Em 230/330 nm）were significantly removed after treatment of EO and EF.（3）EC/Fe²⁺/PDS based on sulfate radicals activated by EC and Fe²⁺were applied to treat soil washing solution which includes Tween 80 and diesel.Compared with water,the addition of Tween 80 obviously promote the extracted efficiency of diesel.The 72.8%of diesel was extracted with Tween 80(2.5 g L^-1)and a constant soil to liquid ratio(1:10 g m L^-1)after 180 min.In EC/Fe²⁺/PDS process,the application of platinum anode resulted in higher diesel removal than tantalum or ruthenium anodes.The elimination of diesel was promoted with decreasing initial p H and increasing electricity intensity.Diesel removal was initially promoted and then decreased with increasing of PDS concentration or Fe²⁺dosage.Under optimum conditions,88.6%diesel removal efficiency was obtained at 120 min and 67.4%Tween 80 could be recycled.In addition,excitation emission matrix（EEM）fluorescence spectroscopy indicates that removal efficiency of diesel in EC/Fe²⁺/PDS processe is higher than that of EC process.In EC/Fe²⁺/PDS,the results of electron paramagnetic resonance（EPR）indicate that^·OH and SO₄^·-resulted in the elimination of diesel.（4）EC combined with NaCl（EC/NaCl）was applied for treatment of soil washing solution containing PHE(5 mg L^-1)and Tween 80(5 g L^-1).Under optimum conditions,50 m M NaCl,0.5 A current,p H₀ 6.14,Ti/Ru O₂-Ir O₂ anode and graphite plate cathode,95.9%PHE was removed and decay of Tween 80 was only 14.2%at 90min.Besides,the influences of several parameters including current,NaCl concentration,p H and cathode materials were investigated.Furthermore,the detection of the active chlorine concentration and quenching experiments suggested that active clorine and radicals were active species in degrading PHE.Two groups of EC/NaCl experiments carried out in divided electrochemical reactor which anode and cathode chambers were divided by the cation-exchange membrane.The results indicated that DSA anode play primary effect on the degradation of organic contaminants.（5）Electrochemically process assisted ultraviolet（UV）irradiation and the salt（NaCl）was further applied to degrade the PHE in soil washing.Besides,with the removal of PHE,the Tween 80 decay was also analyzed.Under optimum conditions of 50 m M NaCl,50 m M Na₂SO₄,0.5 A current intensity,3W UV power,6.14 p H₀,Ti/Ru O₂-Ir O₂ anode and graphite cathode,96.5%of PHE was eliminated and 35.3%of Tween 80 was decayed at 60 min.The removal of PHE increased with the increase of current intensity or NaCl concentration.It was enhanced with lower initial p H.Moreover,the analysis of chlorine concentration and scavenger experiments in electrochemical processes indicated that the active chlorine in situ and reactive radicals genenrated in EC/UV/NaCl process achieved the degradation of PHE in soil washing solution.