Enhanced Scirpus Triqueter Phytoremediation Of Pyrene And Nickel Co-contaminated Soil With NTA-APG And Bacillus Subtilis Combined Application

Soil as one part of the ecosystem is an important gathering area of organic pollutants and heavy metals.Remediation of soils co-contaminated with polycyclic aromatic hydrocarbons(PAHs)and heavy metals(HMs)was more difficult than single contamination.Nickel(Ni),as an element along with petroleum,is frequently found to coexist with polycyclic aromatic hydrocarbon(PAH)in soil.Phytoremediation has great potential for the removal of contaminants in soils because of its low cost and green.Considering limited capabilities of plants to remove PAHs,inoculation of specific strains with degradation capacity was suggested as a strategy for improving remediation efficiency of co-contaminated soil.However,the remediation efficiency is also closely related to the availability of contaminants,which needed to be assisted by chemical reagents.At present,few research focus on the remediation efficiency of co-contaminated soil under the combined application of chemical reagents,pyrene degrading bacteria and plant.Therefore,in this paper,the plant-microorganism-chemical reagents system was constructed by combining the Scirpus triqueter,pyrene degrading bacteria and nitrilotriacetic acid-alkyl glycoside,and used for remediation of pyrene-nickel co-contaminated soil.This article also explored the contribution of plants,microbes and chemical reagents in the process of remediation.At the same time,the remediation mechanism was initially discussed based on the changes of plant growth,soil enzyme activity and morphology of pollutants.The main results were as follows:(1)One strain HD-1 with stronger biodegradability was selected from the pyrene degrading bacteria preserved in the laboratory.The degradation rate of pyrene in 7 days reached 43.2%.Moreover,bacterial strain HD-1,identified as Bacillus subtilis,showed a better tolerance to heavy metal nickel.It was found that the mixture of APG and NTA at concentration of 40 mg L-1 significantly enhanced the activation of nickel in the soil by investigating desorption of nickel from the soil with different concentrations of NTA-APG application.(2)The results of pot experiments showed the effect of chemical reagents and pyrene degrading bacteria on phytoremediation of pyrene and nickel co-contaminated soil.The Ni concentration in Scirpus triqueter of group with bacteria(PB),group with chemical reagents(PC)and group PBC increased to 100.40,80.97 and 87.77 mg kg-1 respectively when compared with that of group P(46.04 mg kg-1)without bacteria or chemical reagents.In addition,it was also found that the addition of chemical reagents and pyrene degrading bacteria could enhance the degradation of pyrene and the activity of microorganisms in contaminated soils.Especially in the presence of the three factors,the removal rate of pyrene increased from 19.52% to 59.78%.Taken together,these data indicated that phytoremediation for both pyrene and nickel in co-contaminated soil by Scirpus triqueter can be enhanced by the combined application of NTA-APG and pyrene degrading bacteria.(3)Chemical reagents and pyrene degrading bacteria had influence on the growth of Scirpus triqueter and soil enzyme activity.Changes in plant biomass indicated that the addition of chemical reagents and pyrene degrading bacteria could improve the resistance of Scirpus triqueter in co-contaminated soil.Compared with the control group(P and PB),the biomass in group with NTA-APG added(PC and PBC)increased by 12.24% and 10.66%,respectively,and when they were used with pyrene degrading bacteria together,the radial oxygen loss rate of Scirpus triqueter would increased significantly.The combined application of pyrene degrading bacteria,chemical reagents and plants could increase soil enzyme activity,especially the dehydrogenase.There was a positive correlation among dehydrogenase activity,radial oxygen loss rate and the degradation of pyrene in soil.(4)Addition of chemical reagents and pyrene degrading bacteria had a great impact on the transformation of pollutants various fractions in the soil.It was observed that Fe-Mn oxide fraction,fraction associated to organic matter and carbonates of nickel transformed to exchangeable fraction,and then absorbed and accumulated by plants with combined application.It was also observed that the other forms of pyrene transformed to bioavailable pyrene,and then degraded by microorganism.Through the interaction analysis,the relative contributions of three factors influencing pyrene dissipation were as follows: degrading bacteria > chemical reagents > plant.(5)Plants can provide a living environment for microbes.Chemical reagents can promote the transformation of pyrene,and more pyrene would be metabolized by microorganisms.On the one hand,pyrene degrading bacteria HD-1 can directly participate in the process of pyrene removal.On the other hand,it can alleviate the inhibition effects on the growth of Scirpus triqueter to some extent in the contaminated soil,and influence the removal of pyrene by influencing radial oxygen loss and soil dehydrogenase activity.A beneficial composite system could be formed due to the plant-microbes-chemical reagents interaction,which could contribute to enhance contaminated soil remediation.