Study Of Bioaugmentation Based On Domesticated Soil Addition For The Remediation Of Phenanthrene Pollution

Polycyclic Aromatic Hydrocarbons(PAHs)pose a serious threat to food security,environment safety and human health because of their high toxicity and difficulty in degradation.It is imperative to eliminate PAHs contamination in environment.Soil microbiome plays an important role in PAHs biodegradation,however,most soil microorganisms cannot be cultured,and it is difficult to artificially construct a soil microbiome with structural stability,high adaptation,and efficient function.Therefore,soil enriched with PAHs-degrading bacteria can be considered as an additive for bioremediation of PAHs contamination.In this study,a soil enriched with a large number of phenanthrene-degrading bacteria was selected to degrade phenanthrene,and the composition of the bacterial microbial community was analyzed,the degradation characteristics of its supernatant on phenanthrene in liquid were learned,and the degradation of phenanthrene in soil by bioaugmentation were explored.Finally,the feasibility of this method was verified by phenanthrene bioremediation in the soils of two thermal power plants in Zhengzhou.The results of the study are as follows:(1)This study used phenanthrene to domesticate soil from a site in Xinyang with many years of waste incineration.It was found that the addition of domesticated soil significantly increased the degradation rate of phenanthrene in soil compared to the treatment without domesticated soil through soil cultivation experiments.The degradation rate in 28 d for phenanthrene(initial concentration,ca.50 mg·kg-1)was90.09% and the half-life of this pollutant was 1.45 d.High-throughput sequencing of soil 16 S r RNA genes showed that the domesticated soil was mainly enriched with efficient degrading bacteria of Streptomyces,Rhodococcus,Nocardioides,Sphingomonas and Mycobacterium.Meanwhile,five strains of phenanthrene degrading bacteria were also screened and isolated from the domesticated soil,which were identified molecularly as Sphingobium abikonense GHP1,Noviherbaspirillum malthae GHP2,Pseudomonas putida g HP6,Mycolicibacterium pyrenivorans GHP7,and Mycobacterium gilvum GHP8.Among them,GHP1 is able to produce biosurfactant and promote the degradation of phenanthrene.Therefore,the domesticated soil was selected as the soil for bioaugmentation.(2)The biodegradation characteristics of phenanthrene in liquids by microorganisms in bioenhanced soil were investigated by liquid culture experiments to explore the effects of temperature,p H,intermediate metabolites,and petroleum hydrocarbons on phenanthrene biodegradation.The results showed that the biodegradation efficiency of phenanthrene was the highest at 28 ℃ and p H 6.5,and it reached 58.12% at 3 d and 98.65% at 7 d.The addition of different intermediate metabolites inhibited phenanthrene degradation in different degrees,that was,catechol was the strongest inhibitor,salicylic acid was followed,and phthalic acid was the weakest.For petroleum hydrocarbons,diesel fuel promoted phenanthrene biodegradation and lubricants inhibited it.(3)Investigation of the mechanism of soil phenanthrene degradation with the addition of 10%(F10),30%(F30)and 50%(F50)bioaugmented soils,the results showed that: phenanthrene degradation in the three treatments was firstly fast and then slow down,and the higher the proportion of bioaugmented soil,the faster early degradation of phenanthrene and the higher soil DHA,CAT,PPO and FDA activities.Of which,DHA and PPO activities showed a trend of firstly increasing and then decreasing,CAT activities showed a trend of firstly increasing,then stabilizing and finally decreasing,and FDA activities showed a trend of firstly increasing,then decreasing and finally increasing.The higher the proportion of bioaugmented soils,the lower the soil Alpha diversity and the higher the relative abundance of PAHs-degrading bacteria.Correlation analysis showed that Rhodococcus and Mycobacterium play a key role in phenanthrene biodegradation in soil.Among the three treatments,the community composition of F10 was the most similar to FS(without bioaugmentation)at the end of remediation.Therefore,in terms of cost performance,operability and soil health,the treatment of F10 is recommended for practical applications,i.e.,a 10% soil percentage for bioaugmentation.(4)The results of the indoor remediation simulation experiments of phenanthrenecontaminated soils at two thermal power plants in Zhengzhou using bioaugmented soil with 10% addition showed that bioaugmentation could effectively improve the biodegradation efficiency of phenanthrene in soils of two thermal power plants,and phenanthrene(initial concentration,ca.50 mg·kg-1)in the two soils were degraded by86.54% and 74.53% in 3 d,respectively.The half-lives of phenanthrene in the two treatments were 0.61 d and 0.79 d,respectively.The community composition analysis revealed that bioaugmentation mainly promoted phenanthrene degradation by increasing the relative abundance of Mycobacterium and Rhodococcus in soil,however,their competitive advantage were lost since their relative abundance decreased when the remediation was completed.Therefore,bioaugmentation does not change the microbial community composition in the soils of the two thermal power plants in Zhengzhou,and the enhanced remediation of PAHs-contaminated soils using PAHsdomesticated soils is feasible.