Study On Remediation Of Phenanthrene Contaminated Soil By Fe²⁺-heat-activated Persulfate Combined With Microorganisms

Polycyclic Aromatic Hydrocarbons,as typical persistent organic pollutants,widely exist in soil and other environmental media,and the remediation of PAH-contaminated soil has attracted much attention due to toxic,teratogenic and mutagenic effects.The method of chemical oxidation pretreatment combined with microbial remediation can effectively shorten the treatment period and improve the removal effect of pollutants.In this thesis,the simulated phenanthrene-contaminated acidic red soil was used as the object,and Fe²⁺-heat-activated activated sodium persulfate combined with microorganisms was used to remediate the phenanthrene-contaminated soil,the process and mechanism of persulfate oxidation of phenanthrene and the influence on soil physicochemical properties were explored,combined with acid-resistant PAHs-degrading bacteria domesticated with phenanthrene and pyrene as model pollutants,detect the degradation performance,soil properties and microbial community structure recovery in the bioremediation stage,obtain the optimal process conditions for persulfate oxidation-bioremediation,and explore new ideas and methods for combined persulfate-microbial restoration.Acid-resistant PAHs-degrading bacteria obtained by directed domestication of coking wastewater bacterial source,the results of 16S r RNA sequencing showed that the number of species in the community decreased significantly after domestication,and the phylum level was dominated by Proteobacteria;At the genus level,Klebsiella and Pseudomonas dominated,with relative abundances of 75.4%and 23.6%,respectively.After 7 days of culture,the degradation rates of PHE and PYR were95.17%and 57.06%when the p H was 3.9,and the corresponding degradation rates were 97.65%and 70.0%under neutral conditions.Three strains of PAHs-degrading bacteria were isolated and purified.Among them,the degradation rates of Y2-Klebsiella＿pneumoniae to PHE and PYR were 97.2%and 43.9%at low p H,respectively.The degradation rates of PHE and PYR under neutral conditions were85.2%and 41.4%,respectively.After acclimation,the degradation effect was better under acidic conditions.Electron paramagnetic resonance results of the oxidation process showed that·OH and SO₄^-·radicals existed in the Fe²⁺activation stage,and only·OH existed during heat activation.The oxidation intermediates identified by GC-MS mainly include（1,1’-biphenyl）-2,2’-dicarbaldehyde,2-ethyl-6-methoxynaphthalene,dibutyl phthalate,etc.,which speculated that the following degradation pathways exist simultaneously in PHE oxidation:1)SO₄^-·and·OH attack the 9,10 sites of phenanthrene to generate（1,1’-biphenyl）-2,2’-dicarbaldehyde,which is further oxidized by oxidative decarboxylation and ring opening and finally mineralized to CO₂ and H₂O;2)SO₄^-·and·OH attack the 2,3 sites of phenanthrene,oxidatively open the ring to form 2-ethyl-6-methoxynaphthalene,and then re-oxidize to form naphthoic acid,which is further reacted and finally mineralized..The combined effect of sodium persulfate and microorganisms in remediation of PHE-contaminated soil is remarkable.Under the condition of oxidant dosage of 3.47%（w/w）,the bioremediation of PHE for 90 days has the best effect,and the inoculation group with acid-resistant bacteria has obvious advantages in the first 28 days,in the late stage of bioremediation,indigenous microorganisms also showed good remediation potential,the degradation rates of PHE at 90d in the inoculated group and the indigenous group were 98.83%and 99.24%,respectively.When the oxidant dosage was 6.94%（w/w）,the residual PHE concentration in the 23-day oxidation-bioremediation soil was lower than the industrial land standard of 50 mg/kg.Degradation of the remaining PHE.PHE degradation rate and dehydrogenase activity showed that the effect of inoculating acid-fast bacteria was significant when the oxidant was high.Compared with the original soil,the microbial community structure of3.47%w/w PS oxidation combined with microbial remediation changed greatly,and the diversity and richness of the microbial community in the treatment group inoculated with acid-resistant bacteria were significantly higher than those in the uninoculated group and the original soil.The dominant bacterial phylum in the indigenous group was Proteobacteria,with a relative abundance of 91.76%,and the dominant phylum in the exogenous bacterial group were Proteobacteria（30.39%）,Actinomycetes（25.72%）,Acidobacteria（13.76%）and Firmicutes（10.92%）.It shows that the addition of exogenous bacteria can improve the degradation effect of pollutants in the early stage of bioremediation,shorten the restoration period,and enable microorganisms to quickly adapt to the soil environment after persulfate oxidation,promote the recovery of microbial communities,and improve soil biodiversity and stability.Compared with microbial remediation alone,persulfate can first oxidizes part of the phenanthrene into available intermediate products that are easy to use,providing more degradation substrates for subsequent microbial recovery,so that the recovery of both exogenous bacteria and indigenous microorganisms can be accelerated in the microbial stage,the remediation period was shortened and the remediation performance of soil organic pollution was improved.