Research On Degradation Of Polycyclic Aromatic Hydrocarbons In Contaminated Coking Soil By Persulfate Advanced Oxidation

With the acceleration of modernization in China,soil pollution is getting worse.The polluted cultivated land area accounts for more than one tenth of the total cultivated land area.At present,the treatment of PAH soil pollution is a research hotspot.Persulfate has been paid more and more attention because of its high efficiency,strong oxidation and low pollution.The main content of this paper is to explore the synergistic effect of ferrous and ultrasonic activation on the oxidative degradation of PAHs by persulfate.It is mainly divided into three parts.Firstly,it is proved that synergistic activation has synergistic effect on the degradation of PAHs,and its mechanism is discussed.Secondly,the influence of additive dosage on the synergistic activation was analyzed,and the best additive dosage index was obtained.Finally,the effects of soil particle size and other factors on activation were analyzed to further improve the oxidative degradation scheme.The main conclusions are as follows:Ferrous ion and ultrasonic were better than single activation in the degradation of PAHs by persulfate oxidation in coking polluted soil.Under the condition of ferrous ion combined with ultrasonic activation,the degradation rate of PAHs can reach 69%.Compared with single activation,it can be increased by more than 10%.The simple persulfate system can also degrade PAHs in soil,which is related to the existence of natural activators such as iron and manganese in soil.The degradation rate of PAHs in the ferrous ion and ultrasonic activation system was 69.08%,33.4%higher than that in the single persulfate system.The synergistic activation of PAHs was more significant.The quenching experiments show that sulfate radicals play an important role in the process of persulfate activation oxidation degradation of PAHs,and hydroxyl radicals play a certain role.In the quenching experiment,the degradation rate of PAHs in the TERT butanol quenching group was 54.96%,15%lower than that in the non quenching group.In the PAHs experiment,the best adding amount of oxidant is 5mmol/g,the best adding amount of ferrous ion is 3mmol/g,and the best water soil ratio is 4:1.With the increase of oxidant content,the degradation rate of PAHs gradually increased,and then tended to be gentle.When the oxidant concentration was 5mmol/g,the degradation rate reached 58.1%.After oxidative degradation,the content of benzo anthracene and benzofluoranthene in soil exceeded the standard seriously,which met the requirement of the first type of land screening value of 5.5mg/kg in China.With the increase of ferrous ion concentration,the degradation rate of PAHs increased from63.26%to 86.07%.Excessive Fe²⁺can inhibit the degradation rate of free radicals.Considering the cost and other factors,the optimal concentration of ferrous ion is 3mmol/g,and the soil water content has an effect on the degradation efficiency of PAHs.When the soil water ratio was 4:1,the degradation rate of PAHs increased to 86.07%,and its growth trend gradually slowed down.Considering the water consumption of the project,the optimal soil water ratio is determined to be 4:1.Through the experiment of other factors affecting the oxidative degradation of PAHs,it is found that the size of soil particles has no obvious influence on the system;the ultrasonic power has an important influence on the oxidative degradation of PAHs,which can not be too high or too low.Limited by the experimental conditions,the optimal ultrasonic power is determined to be 100W,and the chloride ion and bicarbonate ion can inhibit the oxidative degradation reaction,which should be paid attention for engineering application.Although the initial concentration of PAHs is different for different particle size soil,there is no significant difference in the degradation rate during the reaction,the degradation rate is between 83%and 86%.The ultrasonic power is an important factor that affects the degradation rate of PAHs in ferrous and ultrasonic activated oxidized soils.With the increase of ultrasonic power?60W¹00W⁴00W?,the degradation efficiency of PAHs increased first and then decreased.Chloride ions and bicarbonate ions can inhibit the degradation of PAHs in soil by ferrous ions and ultrasound activation.