Remediation Of Polycyclic Aromatic Hydrocarbons Contaminated Soil By The Combined Use Of Alfalfa-earthworm-white Rot Fungi

Due to the anthropological activities,the pollution of polycyclic aromatic hydrocarbons(PAHs)in soil has become increasingly serious.This will affect the safety of agricultural products.Therefore,the remediation of PAHs in soil is also on the agenda.In recent years,many technologies were carried out in the remove of the PAHs in the soil.Bioremediation is attracting more and more attention for its low costs,environment-friendly.p Hytoremediation-microorganism combined remediation is one of the most important bioremediation technologies.It has been triump Hantly applied in remediation of organic contaminated soil in recent years.However,some drawbacks were found in p Hytoremediation-microorganism combined remediation.One is that this remediation is susceptible to environmental factors.The other is that this technology requires a longer time to remove the pollutant in the soil.In particular,the removal of the high ring PAHs is low by the p Hytoremediation-microorganism combined remediation.In order to improve the ability of p Hytoremediation-microorganism combined remediation to remove PAHs from soil,a combined plant-animal-microorganism remediation system was developed by adding the soil animals to the p Hytoremediation-microorganism combined remediation system.The removal mechanism and effect of polycyclic aromatic hydrocarbons(PAHs)in soil by alfalfa-earthworm-white rot fungi combined remediation systems were systematically studied by pot experiment.The main findings of this study are as follows.(1)Alfalfa,earthworm and white rot fungi could remove PAHs from soil by themselves.In the present study,p Henanthrene was taken as a representative of PAHs.The removal of p Henanthrene in soil by the effects of the alfalfa,earthworm and white rot fungi separately was studied under the different of pollution levels and soil p H.The results showed that the removal rates of p Henanthrene were significantly enhanced by the alfalfa,white rot fungi and earthworms,comparing to the control treatments.This indicates that the three organisms are the potential species in the soil biomremediation.Also,the removal rate of p Henanthrene in alfalfa,white rot fungi and earthworms decreased with the increase of pollution level.This indicates that the remediation effect of single species is not good for high pollution level.Additionally,the highest removal of p Henanthrene in soil was found in p H of soil near alkaline.(2)The alfalfa-earthworm-white rot fungi combined remediation system had a high removal efficiency of PAHs in fresh soil.In the present study,a combined remediation system was constructed by alfalfa,earthworms and white rot fungi.This system was used to remove p Henanthrene from soil.The results showed that the biomass of the three species were significant increased in the system.In particular,the biomass of the different species in two or three speices combined remediation system were significantly higher than the alone species remediation system.For the removal rates for p Henanthrene in soil,the highest removal rates were found in the system of alfalfa-earthworms-white-rot fungus.It is 93%.The following is the two species combined remediation system,and it ranged form74%to 85%.The lowest is found in the alone speices remediation system,and it ranged from 33%to 65%.The present study demonstrated that the combination of alfalfa,earthworms,and white-rot fungus is an effective way to remove p Henanthrene in the soil.The removal mechanism include three pointes.One is the alfalfa-earthworm-white rot fungi combined remediation system have many two species combined remediation system.And such two species combined remediation system work together.The second is the earthworms strengthen plant-microbial remediation.The third is that the interaction between the alfalfa,earthworms,and white-rot fungus improve,and increase soil enzyme activity.Thereby,it improves the removal of p Henanthrene from soil.(3)The factors affecting the restoration effect of alfalfa-earthworm-white rot fungi combined restoration system were identified.In order to understand the factors on the combined system of alfalfa-earthworms-white-rot fungus on the removal of PAHs in the soil,the system was determined by changing soil conditions,earthworm density,rhizobia and surfactants in this study.The results showed that the soil straw content is the main factor affecting the removal rate of p Henanthrene in soil,followed by the soil moisture content,and finally the soil p H.The results of the orthogonal experiments shown that the optimum conditions for removal of polycyclic aromatic hydrocarbons from soil are the soil moisture content,the soil straw content,and the p H,are 60%,1.0%,and 7.07,respectively.Also,increase the earthworms density(10 individual/pot),rhizobia of alfalfa(30?240×10~6 individual/pot),and the content of low concentration of nonionic surfactants,can significantly improve the system of alfalfa-earthworms-white-rot fungus on the removal of PAHs in the soil.(4)The effects of alfalfa-earthworm-white rot fungi combined remediation system on high rings PAHs in fresh soil were investigated.In this study,the benzo[a]pyrene was taken as the high rings PAHs to test the system of alfalfa-earthworms-white-rot fungus on the removal of high weigh PAHs in the soil.The results showed that the combined remediation system was more effective than single species and two species combined system in the remediation of PAHs in soils.In the fresh soil,the content of benzo[a]pyrene was 50mg/kg,the removal rate was higher(69%),while in 100mg/kg,the removal rate was lower(42%).This indicates that the system of alfalfa-earthworms-white-rot fungus has obvious effect on soil remediation of medium polluted PAHs.(5)The effects of alfalfa-earthworm-white rot fungi combined remediation system on PAHs in aged soil were evaluated.Study on aging mechanism,further approach to practical application,p Henanthrene and benzo[a]pyrene were used as target low and high ring PAH to test system of alfalfa-earthworms-white-rot fungus on the removal of the aged PAHs in the soil,respectively.The result showed that there were 82%and 34.6%of p Henanthrene and benzo[a]pyrene,respectively,were removed in the aged soil by system of alfalfa-earthworms-white-rot fungus.These rates were increased by 49%and 28.3%,respectively,comparing to the natural removal rates.Therefore,the combined remediation system of alfalfa-earthworms-white-rot fungus can significantly improve the removal efficiency of PAHs in aged soil.In summary,the combined remediation system of alfalfa-earthworms-white-rot fungus can significantly remove PAHs in the soil.However,the removal rate of the aged high weigh PAHs was is relatively low by this system.Compared with other remediation technologies,the removal efficiency of this technology is also higher and has a certain application prospect.This study provides a new idea and basis for remediation PAHs in the soil.