Remediation Of Petroleum Hydrocarbon Contaminated Soil By Persulfate Oxidation Combined With Microbial Enhancement

The demand for crude oil and its products is increasing day by day.During the processes of exploration,production,transportation,storage,and processing,petroleum can accidentally leak into the soil,causing serious harm to the ecological environment.Petroleum hydrocarbons in soil can enter animals and humans through ecological cycles and food chains,potentially causing persistent or long-term harm to human health.Therefore,the restoration of petroleum hydrocarbons in soil is urgent.Traditional chemical remediation technologies have the disadvantages of high cost and severe pollution,while bioremediation technologies have the disadvantage of long restoration periods.In contrast,combined remediation technologies have great potential for petroleum hydrocarbon-contaminated soil restoration due to their high efficiency in pollutant degradation,short cleanup time,and low restoration cost.The present study aimed to isolate highly efficient petroleum hydrocarbon-degrading bacteria from soil contaminated with high concentrations of petroleum hydrocarbons.To promote the degradation ability of dominant strains towards petroleum hydrocarbons,external nutrients were optimized.Additionally,the effects of different concentrations of sodium persulfate（PS）on the degradation of soil petroleum hydrocarbons,as well as the physical and chemical properties of the soil after restoration and its impact on the microbial community structure were studied.Finally,the study investigated the degradation efficiency of the PS system combined with microorganisms towards soil petroleum hydrocarbons,and the succession pattern of the soil microbial community structure after restoration.The main research findings are as follows:（1）An efficient and dominant strain of Aspergillus japonicus,identified through ITS sequencing,was isolated and screened from soil contaminated with petroleum.Various carbon sources,including sucrose,glucose,cyclodextrin,oxalic acid,citric acid,tartaric acid,and humic acid,were used to enhance the strain’s degradation efficiency of petroleum hydrocarbons in the soil.The addition of glucose and sucrose resulted in the highest degradation efficiency of total petroleum hydrocarbons（TPH）,reaching 37.9%and 36.1%,respectively,after 30 days.Similarly,the addition of different nitrogen sources,including sodium nitrate,potassium nitrate,ammonium chloride,ammonium nitrate,and ammonium sulfide,showed that the addition of sodium nitrate and potassium nitrate had the highest TPH degradation efficiency,reaching 37.1%and 35.3%,respectively,after 30 days.In addition,the optimal degradation efficiency was achieved by adding 12%（w/w）sucrose and 3%（w/w）sodium nitrate,resulting in a TPH degradation efficiency of 56.8%after 30days of remediation.（2）The study investigated the effect of the PS system on the degradation of petroleum hydrocarbons in soil,as well as the impact on the physicochemical properties and microbial community structure of the soil after remediation.The optimal remediation effect was achieved when the molar ratio of PS/ferrous sulfate(Fe²⁺)/citric acid（CA）was2:3:2,with a TPH degradation efficiency of 37.92%after 30 days.PS1,PS2,and PS3 were added at 40,100,and 200 mmol/kg PS,respectively,with appropriate amounts of Fe SO₄and CA.The three PS groups showed the most significant oxidative remediation of petroleum hydrocarbons in the soil during the first 14 days,with TPH degradation efficiencies ranging from 23.91%to 37.18%.After 14 days,the growth of petroleum hydrocarbon degradation efficiency became slow,with only a 2%to 3%increase in degradation efficiency.After 14 days,the PS consumption of the three PS groups for oxidative remediation exceeded 97%,indicating that basic oxidation was complete.After remediation,the p H and soil organic matter（SOM）in the soil decreased significantly,but with prolonged remediation time,the p H and SOM began to recover.The PS1 group recovered to its initial level.At the fungal phylum level,the dominant phylum in the three PS groups was Ascomycota,and the dominant fungal genus of the PS-treated soil with medium and high PS concentrations changed from Chaetomium to Penicillium compared with the untreated soil（CK）group.There were significant differences in the bacterial community structure under different remediation conditions.The bacterial community structure of the PS1 group was more similar to that of the CK group,with the dominant bacterial phylum being Proteobacteria,while the dominant bacterial phyla of the PS2 and PS3 groups were Firmicutes,and the dominant bacterial genus of the PS2 and PS3 groups was Bacillus.（3）The results showed that pre-oxidation with the PS system followed by microbial degradation was more effective than adding PS oxidation after microbial degradation.The optimal approach was to pre-oxidize with the PS system for 15 days before microbial degradation,which achieved a total TPH degradation efficiency of 72.47%after 30 days of remediation,the study examined the removal efficiency of different PS concentrations combined with microbial remediation after 15 days of treatment.When the total remediation period was 60 days,the PS2 group with a concentration of 100 mmol/kg had the highest TPH degradation efficiency,reaching 84.34%.Analysis of fungal diversity in the soil revealed that the fungal diversity and richness of the PS groups in all three combined remediation approaches were lower than that of the control group.At the fungal phylum level,the Ascomycota phylum remained the dominant fungal phylum throughout the remediation process.At the fungal genus level,the exogenous strain Aspergillus japonicus had a significantly increased relative abundance in the soil after the combined remediation,becoming the dominant fungal genus and playing a major role in petroleum hydrocarbon removal from the soil.The bacterial microbial abundance of all three PS groups in the combined remediation was lower than that of the control group,but the microbial diversity of the PS2 group with a medium concentration was higher than that of the control group.At the bacterial phylum level,the main dominant phyla of the control group were Proteobacteria and Firmicutes.After the low PS concentration PS1 group treatment,the dominant phylum changed to Firmicutes.At the bacterial genus level,the PS2 group with a medium-high concentration had the most diverse and evenly distributed dominant bacterial genera.