Biostimulation For The Enhanced Degradation Of Phenanthrene In Soil

Polycyclic aromatic hydrocarbons(PAHs)are a variety of organic compounds composed of two or more aromatic rings.Phenanthrene(PHE)is one of the tricyclic compounds that is persistent,genotoxic and teratogenic and has been shown to be potentially dangerous to human health.As an effective and feasible technique,mud bioreactor technology is applied to the degradation of persistent organic matter in soil.At present,most of the research on mud reactors only considers the overall efficiency,and pays less attention to the removal mechanism of pollutants and the changes of soil microbial communities before and after treatment.In this experiment,phenanthrene is the target pollutant.Based on the reaction conditions of the refinement mud reactor,the bio-stimulation method is used to stimulate the degradation activity of the indigenous flora in the soil and improve the degradation efficiency.Through high-throughput sequencing,the relationship between soil microbial community composition and diversity and pollutant degradation during remediation was explored to understand the ecological response of phenanthrene-contaminated soil to biostimulation and repair processes.The experiment collected the garden soil from the south side of Ximen,Institute of Environmental Engineering,China University of Mining and Technology.After adding 100mg/L of phenanthrene,it was added into the mud bioreactor for degradation research after aging treatment.By gradually refining the reaction conditions of the mud reactor,the ratio of carbon,nitrogen and phosphorus(100:10:1),the co-metabolite to sodium acetate(200 mg/L),the stirring speed of 220 r/min,the aeration amount of 1.5 L/min,and the surface were found.Under the condition of active agent(rhamnolipid 10mg/L)or corn oil(2g/L),when the initial concentration of phenanthrene is 100mg/L,the degradation of PHE can reach 98% after 3 days.Taking the results of the test into principal component analysis,we found that the basic operating conditions of the mud bioreactor are the main influencing factors,namely the stirring speed and the aeration amount.The addition of nutrients is a secondary factor,with nitrogen and co-metabolites having a greater impact.The effect of adding a surfactant or corn oil is relatively small.Therefore,in the application of actual contaminated site repair,the most important thing is to adjust the basic operating conditions of the mud reactor and supplement the necessary nutrients.Adding corn oil or surfactant on this basis can further promote the degradation of phenanthrene.Through the results of high-throughput sequencing,the effects of biostimulation on the microbial diversity of contaminated soils were further explored.After microbial community analysis,the relative abundance of the treated flora was reduced,and the strains were biased to be uniform.Proteobacteria,Actinobacteria and Chloroflexi are the main gates,accounting for almost 65% of the sample.Proteobacteria,Actidobacteria and Bacteroidetes constitute a stable and important component of the bacterial community structure of PAHs.Gammaproteobacteria(Bacteroides)is the most affected group of organisms.In addition,the activity of catechol dioxygenase increased under the action of biostimulation;the abundance of enzymes such as salicylate hydroxylase and protocatechuic acid 4,5-dioxygenase increased.It indicated that the bio-stimulation would change the soil bacterial community structure,increase the proportion of bacteria with PAHs degradation,and increase the activity of degradation-related enzymes.The method was applied to soil remediation of an actual PAHs contaminated site in Tianjin.The results showed that the addition of 5g / L corn oil or 10 mg / L rhamnolipid can reduce the degradation rate of most PAHs in the contaminated site to more than 45%.The addition of corn oil has a higher degradation rate of 2-3 ring PAHs,which can reach 70% in 7 days.For PAHs above 3 rings,the addition of biosurfactant has higher degradation effect,reaching 42% in 7 days.the above.