| Soil was contaminated by organic pollutants and heavy metals,which caused by the exploitation of new energy,and the co-contaminated soil endangered human health and became a hotspot and difficulty in the field of soil environmental remediation research.The bioremediation enhanced by electric field was a new kind of combined remediation technology for remediation of soil contaminated by inorganic,organic or their mixed pollutants.In this study,the soil contaminated by petroleum hydrocarbon and heavy metals in Changning-Weiyuan,Sichuan province was taken as the research object.And the simulated contaminated soil with 9,075 mg·kg-1 total petroleum hydrocarbon(TPH)concentration and 446.5 mg·kg-1 heavy metal nickel(Ni)was prepared for the treatment object.The high-efficiency tolerant heavy metals and petroleum hydrocarbon-degrading bacteria strain were screend out and the conditions of electrokinetic remediation were optimized.The remediation effect of bioremediation enhanced by electric field technology on co-contaminated soil was studied.At the same time,the migration mechanism of mixed pollutants in soil by electric field and natural leaching was investigated.The main research results of this study are as follows:(1)A petroleum-degrading strain with the resistance to heavy metal nickel(Ni)was isolated from the soil heavily-polluted areas around a shale gas wells in Changning-Weiyuan,Sichuan Province.After observation of the strain and colony,physiological and biochemical experiments and 16S rDNA analysis,the strain was identified as Citrobacter farmeri strain and named Citrobacter farmeri strain M1.The strain has a wide pH growth range,and it can grow well at the pH range of 7～9.It also can grow well in the range of salt concentration from 1%to 5%,and has certain alkali resistance.When the salt concentration exceeds 5%,the growth of the strain was inhibited,and the strain belongs to the strain with high salinity tolerance.The optimal growth temperature of this strain was 30℃,the optimal growth pH was from 7 to 9,the optimal C:N was 10:1,and the maximum salt tolerance was up to 5%.In liquid medium,Citrobacter farmeri strain M1 had a good degradation and removal efficiency on petroleum hydrocarbon and nickel,respectively.During the experimental data by shaking flask of 7 days,the degradation rate of crude oil of this strain reached 35.65%,the removal rate and adsorption rate of heavy metal Ni2+reached 56.64%and 54.16%,respectively.Meanwhile the resistance to nickel reached 350 mg·L-1.(2)By the optimizing the conditions of bioremediation enhanced by electric field and according to the comprehensive degradation of petroleum hydrocarbon and removal efficiency of heavy metals,the remediation effect was better than others when the electrode materials of cathode and anode were graphite plate and titanium plate,respectively and the electric field intensity was 1 V·cm-1.Under the condition of different electrode material repair,the saturated hydrocarbon was the most easily degraded,the organic binding state was the most reduced,and the residue state was gradually accumulated.(3)Selective ion-exchange membranes coupled with bioremediation enhanced by electric filed were used for remediate soil contaminated by petroleum hydrocarbon and heavy metals.The use of selective ion exchange membrane could maintain the pH of soil near neutral,which was conducive to the degradation of petroleum hydrocarbon by microorganisms and the migration and transformation of heavy metals by electric field.Under the optimal condition of remediation for co-contaminated soil,the removal rate of TPH and heavy metal Ni reached 77.4%and 58.5%,respectively.The exchangeable of heavy metals was easier to be transferred and transformed and the saturated hydrocarbons were more easily biodegraded among petroleum hydrocarbon components.The application of electric field could enhance the activity of soil dehydrogenase and stimulate the removal of petroleum hydrocarbon by petroleum hydrocarbon degrading bacteria.Citrobacter M1 promoted the fixation of heavy metals by reducing the exchangeable species of nickel and increasing the residual species of nickel,and gradually reduced the biological toxicity of heavy metals in soil.There was a positive correlation between the degradation rate of hydrocarbons and the population of TPH degradation bacteria(P<0.05).(4)In the case of low voltage treatment(≤1 V·cm-1),the exchangeable,carbonates-bounded and Fe and Mn oxides-bounded species of heavy metals were gradually migrated to the cathode.The organic matter-bounded was hardly affected by the voltage gradient.And the residual species accumulated gradually,which was not conducive to the migration of the residual species.At high voltage(>1 V·cm-1),the exchangeable,carbonates-bounded and Fe and Mn oxides-bounded species of heavy metals gradually accumulated near the cathode.The organic matter-bounded was also hardly affected by the voltage gradient.The residual species gradually migrated to the cathode.(5)Under intermittent leaching conditions,the water infiltration of soil column was affected by leaching amount.The greater the leaching amount was,the greater the water infiltration amount was,and the higher the soil moisture content was.By comparing the migration effects of different leaching amounts on pollutants,it was shown that the petroleum hydrocarbon and heavy metals content decreased gradually with the increase of soil column depth,and the pollutants were mainly concentrated at 5～10 cm.The relative content of saturated hydrocarbon and aromatic hydrocarbon increased gradually,and the relative content of resin-asphaltene decreased gradually with the increase of soil column depth.At a same time,the relative content of-pollutants with large carbon number gradually increased,which indicated that its migration ability in soil column was strong with the increase of soil column depth.After the pollutants moved and stabilized in the soil column,the main components of the pollutants were C27～C33.The relative content of exchangeable increased gradually,and the relative content of Fe and Mn oxides-bounded decreased gradually with the increase of soil column depth.The change of relative content of carbonate-bounded was consistent with the change of soil pH with depth.The change of the relative content of Fe and Mn oxides-bounded was consistent with the change of soil Eh with depth.The relative content of organic-bounded was consistent with petroleum hydrocarbon pollutants in soil.This paper successfully screened a strain with heavy metal resistance and petroleum hydrocarbon degradation ability.The problem that soil was easy to acidify when it was supplied with DC power has been effectively alleviated.The effect and mechanism of BioEK in simultaneous remediation of soil contaminated with heavy metals and organics and the migration and transformation of contaminants in the soil by the electric field and the natural leaching were studied.This study provided a scientific theory and basis for the practical application of bioremediation technology enhanced by electric field,especially for the remediation of soil contaminated with heavy metals and organics,which was of great significance for the treatment of complex contaminated soil and the solution of complex ecological and environmental problems. |
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