Rehabilitation Of Simulated Oil Contaminated Soil By Sodium Persulfate System

In recent years,with the rapid development of China's economy,soil pollution has become increasingly serious.In order to effectively strengthen soil control and improve people's living environment,in 2016,the state issued"Ten Articles of Soil",requiring all provinces to carry out regular surveys of soil environmental quality.Petroleum hydrocarbon?TPH?pollution has many characteristics in soil pollution,such as many kinds of pollution and so on.Chemical oxidation has become a popular technology in the existing remediation technology with the advantages of high efficiency,universality and low cost.Among many oxidants,sodium persulfate is one of the most potential oxidation technologies because of its stability,low cost and no secondary pollution.In this study,sodium persulfate system was used to remediate simulated oil-contaminated soil,and the effects of different systems on the remediation of simulated oil-contaminated soil were discussed in order to find an efficient,inexpensive and environmentally friendly compound agent.The main research contents are as follows:?1?The experiment Fe²⁺activated sodium persulfate was used to treat simulated oil contaminated soil showed that the maximum removal rate of petroleum hydrocarbons by FeSO₄·7H₂O was 33.12%,when the dosage of sodium persulfate was 3%,and the dosage of Fe²⁺activated sodium persulfate was 0.6%.The maximum removal rates of petroleum hydrocarbons reached 48.28%and 57.76%after adding citric acid and beta-cyclodextrin chelating agents,respectively.That is to say,the addition of chelating agent can effectively improve the stability of Fe²⁺in soil,so as to better activate sodium persulfate and improve the removal efficiency.Infrared spectra showed that citric acid,beta-cyclodextrin and Fe²⁺mainly coordinated on carboxyl and hydroxyl groups.Among them,the coordination effect between beta-cyclodextrin and Fe²⁺is better.Chelating agent can effectively improve the destruction of organic matter in soil by sodium persulfate.analyzing the petroleum hydrocarbon subsection found that the degradation of organic matter by sodium persulfate is a step-by-step process.Replacing part of sodium persulfate with CaO₂ can effectively solve the problem of soil acidification caused by sodium persulfate,and it improves the degradation efficiency of petroleum hydrocarbons and reduces the dosage of reagents.The kinetics study indicated that the degradation accorded with the first order kinetics.?2?Remediation of simulated oil contaminated soil by Fe⁰-C activated sodium persulfate displayed that the removal rate of petroleum hydrocarbons by Fe⁰-C activated sodium persulfate reached 46.12%when the dosage of iron and carbon was 0.1%and that of sodium persulfate was1%.The dosage of sodium persulfate was 2/3 lower than that of Fe²⁺activated sodium persulfate.Increasing the amount of iron and carbon can improve soil acidification.X-ray analysis reveals that Na₂Fe?SO₄?₂·4H₂O is mainly produced by activating sodium persulfate with Fe⁰-C.The removal rate of petroleum hydrocarbons reached 62.98%and 46.58%after adding beta-cyclodextrin and humic acid.That is to say,adding beta-cyclodextrin can improve the removal rate of petroleum hydrocarbons,while humic acid has no effect on the removal rate of petroleum hydrocarbons.Infrared spectra made clear that the main coordination of humic acid was also on carboxyl and hydroxyl groups.With the increase of Fe⁰-C dosage,the removal rate of petroleum hydrocarbons did not increase significantly.Using CaO₂ instead of sodium persulfate,the maximum removal rate was 66.62%.Fenton reagent was used to remediate contaminated soils treated by sodium persulfate system.The results showed that fractional addition could improve the removal efficiency of petroleum hydrocarbons by 20.61%.?3?The effect of sodium persulfate on the number of soil microorganisms was studied by dilution coating method.The results indicated that the addition of sodium persulfate had a negative effect on soil microorganisms,resulting in a sharp decline in the number of soil microorganisms,but it would gradually recover over time,while the addition of FeSO₄ had little effect on the number of soil microorganisms.The oxidation and acidity of sodium persulfate are the main cause for the decline of soil microorganisms.When the dosage of sodium persulfate is less than 3%,the number and activity of microorganisms can gradually recover over time,and the small molecule petroleum hydrocarbons oxidized and decomposed can be used as carbon source by microorganisms,which provides a reference for the future chemical oxidation combined with microorganisms to remediate petroleum hydrocarbon contaminated soil.In conclusion,compared with Fe²⁺activated sodium persulfate,iron-carbon activated sodium persulfate system has less dosage and better effect.The removal rate of petroleum hydrocarbons can be increased by adding beta-cyclodextrin and fractional dosage of reagents.The problem of soil acidification can be well solved by replacing part of sodium persulfate with CaO₂.Excessive dosage of chemicals and soil acidification are important factors leading to microbial population and decrease.Therefore,activation of sodium persulfate and calcium peroxide system by iron-carbon-beta-cyclodextrin not only improves the removal rate of petroleum hydrocarbons and reduces the dosage of reagents,but also improves the problem of soil acidification.Consequently,the system is conducive to the follow-up joint chemical oxidation and microbial remediation.Moreover,it provides a reference for the follow-up development of economic and environmental remediation technology of petroleum hydrocarbon contaminated soil.