Application Of Surfactants To Enhance Anoxic Biodegradation Of Oil Contaminated Soil Pretreated By Chemical Oxidation

Polycyclic aromatic hydrocarbons（PAHs）and petroleum hydrocarbons（PHC）are common petroleum pollutants,and the remediation of their contaminated soil has attracted much attention.The combined remediation technology of chemical oxidation and microorganism is a promising remediation technology for PAHs/PHC contaminated soil.However,at present,most studies focus on chemical oxidation and aerobic microbial degradation,and there are few studies on the combined degradation of chemical oxidation and anoxic microorganisms.In addition,due to the low solubility of PAHs and PHC,their bioavailability is low,which limits the further degradation of PAHs and PHC.Taking PAHs and PHC contaminated soil as the research object,this paper investigated the anoxic biodegradation law of PAHs and PHC in soil after persulfate（PS）pre oxidation treatment under the condition of surfactant addition,and explored the impact of surfactant on indigenous microbial abundance and community structure.The main results are as follows:（1）The results of pre oxidation experiment showed that PS with mass concentration of 1%has good removal effect on PAHs and PHC.For PAHs and PHC,under the same mixing ratio,the solubilization effect of high concentration surfactant(3000 mg·L^-1)was better than that of low concentration surfactant(800 mg·L^-1).The solubilization effect of surfactants with the same concentration increased with the increase of the proportion of nonionic surfactant polyoxyethylene sorbitan monooleate（Tween80）in the mixed system.For PAHs contaminated soil,the solubilization of 4-ring and 5～6-ring PAHs by two concentrations of surfactants was higher than that of 3-ring PAHs.For PHC contaminated soil,the solubilization of F₁component(C₁₀～C₁₆)and F₂ component(C₁₇～C₂₃)by two concentrations of surfactants was higher than that of F₃ component(C₂₄～C₃₀).（2）For PAHs,low concentrations of surfactants promoted the anoxic biodegradation of all ring PAHs in soil,but the degradation rates of 3-and 4-ring PAHs（30.16%～47.47%and 26.00%～43.79%respectively）were significantly higher than those of 5～6-ring PAHs（5.17%～10.65%）,while high concentrations of surfactants inhibited the anoxic biodegradation of PAHs with different ring numbers.For PHC,low concentration surfactant promoted the anoxic biodegradation of PHC.The degradation rates of F₁,F₂ and F₃ components were 42.79%～57.62%,34.78%～42.70%and25.10%～40.23%,respectively.The degradation effect was inversely proportional to the length of carbon chain.The high concentration surfactant inhibited the degradation of PHC in soil under most proportion conditions,and the inhibition effect on F₁component was the most obvious.（3）In PAHs and PHC contaminated soil,the dominant bacteria at phylum level were both Proteobacteria,Firmicutes and Actinobacteria.At genus level,the dominant bacteria were Bacillus,Microcella,Dietzia,Silanimonas and Pseudomonas,Nocardioides,Streptomyces,respectively.After adding surfactants,the dominant bacteria in PAHs contaminated soil changed into Firmicutes and Proteobacteria,the dominant bacteria in PHC contaminated soil became Proteobacteria.The bacterial abundance in PAHs and PHC contaminated soil increased by 1.32～1.99 and 1.89～2.51orders of magnitude compared with that in PS oxidized soil（1%PS）for 30 days when surfactants in low concentrations were applied.And the bacterial abundance of PAHs and PHC contaminated soil decreased by 0.39～1.24 and 0.28～0.76 orders of magnitude compared with that in PS oxidized soil（1%PS）for 30 days when surfactants in high concentrations were applied.In conclusion,PS as an oxidant has a good pre oxidation effect on PAHs and PHC in soil.Low concentration of surfactant can promote the anoxic biodegradation of pollutants in soil and the growth of microorganisms after PS pre oxidation,and the degradation effect increases with the increase of the proportion of non-ionic surfactant Tween80 in the mixed system.The high concentration of surfactant inhibits the degradation of pollutants in soil and the growth of microorganisms after PS pre oxidation.