Enhanced Degradation And Ecotoxicity Of Polycyclic Aromatic Hydrocarbons Contaminated Soil By Low Temperature Plasma

The application of low temperature plasma technology in remediation of soil pollution has the advantages of simple operation,short treatment time,high efficiency of pollutant removal,no pollution,no residue and no selectivity.At present,the mechanism of remediation of soil contamination by low temperature plasma is not well studied,and the mechanism is not thorough enough.The technology is still in the laboratory stage.In this study,the performance of atmospheric pressure cold plasma in repairing PAHs-contaminated soils was studied by using B[a]P as the representative of PAHs,and plasma parameters,soil parameters and so on.The degradation regularity of PAHs-contaminated soils was also explored.The active groups in discharge plasma were detected by multi-channel optical fiber spectrometer.The degradation products of PAHs in soil were analyzed by FTIR and HPGC/MS,and the degradation mechanism was revealed.Soil environmental quality and plant toxicity tests before and after plasma treatment were conducted to study the effects of plasma treatment on soil organic matter reduction and soil microbial activity reduction,and to clarify the ecological risk effect of plasma treatment on soil pollution remediation.The main results are as follows:(1)B[a]P contaminated soil was remediated by dielectric barrier discharge(DBD)plasma.The degradation characteristics of B[a]P in soil were investigated by means of discharge gas parameters,soil type parameters and pollution concentration parameters.The results showed that with the increase of plasma irradiation time,B[a]P of different contamination concentrations in both soils decreased significantly.After 50 minutes of plasma treatment,the degradation efficiency of initial low concentration pollution treatment is better than that of initial high concentration pollution treatment under different carrier gas conditions.The degradation efficiency of each pollution treatment of sandy fluvo-aquic soil is higher than that of each pollution treatment of fluvo-aquic soil.The degradation of B[a]P in soil conforms to the first-order dynamic reaction model.The degradation gradient of B[a]P in different carrier gases was oxygen>air>nitrogen.Oxygen free radicals are mainly generated by plasma discharge in oxygen atmosphere,nitrogen free radicals are mainly generated in nitrogen atmosphere,and oxygen free radicals,nitrogen free radicals and hydroxyl free radicals are mainly generated in air atmosphere.The more oxygen-containing substances in plasma discharge environment,the stronger their oxidation ability.(2)B[a]P degradation products were analyzed by multi-channel optical fiber spectrometer,high performance gas chromatography-mass spectrometry(HPGC-MS),Fourier transform infrared spectroscopy(FTIR)and total organic carbon analyzer(TOC),and the remediation mechanism of soil B[a]P pollution was discussed.The results showed that there were no new peaks in the infrared spectra,only the original peak intensity changed,and the formation of intermediate products was not detected in the mass spectra.It may be that plasma decomposes organic pollutants into small molecular substances such as CO2 and H2O.With the increase of plasma discharge time,the organic carbon content of all contaminated soils decreased,among which nitrogen plasma was the least,mainly because of its weakest oxidation ability;the microbial carbon and nitrogen content of all contaminated soils decreased significantly,exceeding 50%,indicating that plasma remediation of soil organic pollution would have certain impact on soil microbial environment.(3)Soil culture experiments were conducted to determine the germination and growth of alfalfa and the activity of enzymes,and to infer the possible ecological risk effects in the process of plasma remediation of soil organic matter.The results showed that compared with the control,the growth of plants was better after plasma remediation of contaminated soils,but with the increase of treatment time,the growth of plants declined.The results showed that the microbial and enzymatic environments of soil changed and plant growth was inhibited to some extent by plasma remediation.