Distribution Characteristics And Oxidative Remediation Of Dibutyl Phthalate In Soil

Phthalates?PAEs?are often used as plasticizers for plastic products such as agricultural mulch films.As a typical environmental hormone,once ingesting the human body it will have a serious impact on human reproductive health.PAEs are also moderately polar compounds and easily retained in the soil.Studying the distribution characteristics of PAEs in soil helps to understand the interface process of PAEs in soil and water systems,and provides a basis for PAEs pollution restoration in soil.Due to the characteristics of stabilized properties and long service life,the S₂O₈^2-oxidation system has a good application prospect in repairing PAEs pollution.It is of great significance to study the S₂O₈^2-oxidation-repaired PAEs contaminated soil to control the soil contaminated by PAEs.In this paper,dibutyl phthalate?DBP?as priority controlled substances in PAEs was selected as the research object.Then investigate the distributive regulation of DBP in the water and soil system,the factors affecting the degradation of DBP in soil by S₂O₈^2-oxidation system,and the mechanism of oxidation degradation were studied.The process of oxidation remediation was simulated in soil column,and its effects on the change of soil properties were studied by utilizing the soil in the column.The main conclusions were as follows:?1?The distribution of DBP in soil-water system was studied.Batch experiments were conducted to study the isothermal adsorption model and adsorption kinetics of DBP on experimental soils;the effects of pH,ionic strength.Dissolved organic matter?DOM?on the distribution of DBP in soil and water systems were also investigated and the retentive ability of DBP in soil was studied by simulating soil column experiments.The results revealed that the adsorption of DBP on the experimental soil was consistent with the Freundlich isotherm model?1/n?1?and the two-chamber first-order adsorption kinetics model;and values of K_F was negatively correlated with temperature,indicating that the soil adsorption to DBP was a exothermic multi-domain linear adsorption process.DBP was easier to distribute in soil phase in acidic medium and high ionic strength conditions;and DOM had two sides effects on the distribute of DBP in water and soil system.The simulated soil column experiment showed that the interception of DBP by soil column was mainly 0¹5 cm,indicated that the threat of DBP to soil was more obvious.?2?Influences of different experimental conditions to the degradation of DBP in soil by S₂O₈^2-oxidation system were investigated.Batch experiments carried out to explore the effects of pH,the molar ratio of S₂O₈^2-/Fe²⁺,and water-soil ratio oxidation system on degradation of DBP in soil.The oxidative repair process was also simulated by soil column experiment.Studies shown the low pH was more favorable for degradation reaction.Besides,the high degradation effect meted with the ratio of S₂O₈^2-/Fe²⁺and water-soil ratio were 5/1 and 1/10 respectively.The results of soil column displayed that the degradation of DBP by S₂O₈^2-oxidation system reached expected value.?3?In the aqueous phase system,the degradation reaction kinetics and oxidation mechanism were studied.The main generation medium of oxidation was analyzed according to the total degradation rate of DBP contaminated soil by oxidation system in the different Eluent?hydroxypropyl-?-cyclodextrin,anionic surfactant,cationic surfactant,nonionic surfactant?.The main active free radicals in the oxidation mechanism are SO4·and·OH.The degradation of DBP fitted with the pseudo-second-order kinetics,and the reaction process was related to the concentration of DBP and the Oxidation free radical production rate.The reaction medium results demonstrated Tween 80,which can increase dissolve and inhibit oxidation,caused the total degradation rate to increase,indicating the oxidation process in the soil and water system mainly occurred in the aqueous phase.?4?The effects of S₂O₈^2-oxidation remediation on soil physical properties was analyzed.For the oxidized soil in the soil column,the particle size and structure morphology of the soil after remediation were characterized by laser particle size analyzer and scanning electron microscopy?SEM?.These characterization results further illuminated soil and water separation performance enhanced,and particle size distribution at 128 nm after oxidation disappeared,implying the suspended matter in the soil was mainly fine clay,and the agglomeration of fine clay caused by oxidation system was the leading cause for the enhancement of soil and water separation performance.The average particle size(d₅₀)of soil decreased with increasing of soil column depth,suggesting that S₂O₈^2-oxidation system can caused the cracking of large particle size of soil.?5?The effects of S₂O₈^2-oxidative remediation on heavy metals and the forms of nitrogen and phosphorus in soil were analyzed.Heavy metal content and main nutrient elements?N,P?before and after remediation were studied by X-ray fluorescence spectrometer?XRF?and chemical extraction.Result found the content of heavy metals in soil column increased with the increase in depth of soil column,which was consistent with the change of soil particle size in soil column.Besides,the pH value of soil layers in soil column was similar,implying the changes of heavy metals content in soil column with the changes of depth in soil column were mainly caused by the decomposition of large particle size derived from S₂O₈^2-oxidation system and had no direct connections with pH.The increase of total nitrogen?TN?concentration in leachate and the augment of ammonia nitrogen content in soil caused by the oxidation system indicated the oxidation intensified soil N loss and further promoted the transformation of soil organic nitrogen to inorganic nitrogen,while the elevating concentration of total phosphorus?TP?in leachate demonstrated oxidation aggravated the loss of TP.Available phosphorus?Ava-P?was significantly correlated with exchangeable phosphorus?E_X-P?,implying the decrease of Ava-P in soil was correlated with the loss of E_X-P.