Study On Electric Field Enhanced Bioremediation Of Petroleum-hydrocarbon Contaminated Soils

The issue of oil contaminated soils is becoming increasingly prominent,which seriously threatens human health and ecological system.To solve the environmental problem,bioremediation is a green and economic soil remediation technology.However,bioremediation is commomly inefficient due to the low bioavailability of contaminants,nutrients and electron acceptors in the soil,which is the key problem in the process of bioremediation.To overcome the above problem,a electric field enhanced bioremediation technique coupling electric fields to bioremediation was constructed in this paper,then the coupling and strengthening mechanism of the remediation process was investigated and engineering tests were carried out to verify the actual performance of the coupling technology.Firstly,starting with the selection and acclimation of petroleum-degrading bacteria,microbial consortia with high-efficiency petroleum hydrocarbon degradation function were obtained,mainly including Stenotrophomonas,Pseudomonas and Bacillus.In order to maintain biological activity in the soil,the additive solution was optimized for improving soil properties.Furthermore,by optimizing the applying mode and voltage gradient of electric field,the problem of soil acidification and alkalization caused by effects of direct current electric fields could be overcomed using sinusoidal alternating current electric fields and the optimal voltage gradient proved to be 50 V/m.In above optimized conditions,21-day remediation experiments of petroleum-hydrocarbon polluted soils were conducted.The removal efficiency in the electric field enhanced bioremediation reached 31.6%,which was 2.3 times of the biodegradation efficiency.In the long-period experiment,the electric field enhanced bioremediation showed good operating stability.By supplementing the soil additive solution in time to ensure sufficient nutrients and electron acceptors,the concentration of petroleum hydrocarbon pollutants reached the soil remediation standard(below 1000 mg/kg_{dry soil})after 119days,and the removal rate was 22.0 mg/kg_{dry soil} per day.Secondly,by comparing the growth and metabolism function of petroleum-degrading microbial consortia under aerobic and anaerobic conditions,it was found that petroleum hydrocarbon pollutants were removed mainly through aerobic degradation.In the 21-day treatments of petroleum-hydrocarbon contaminated soils,the remediation efficiency in the electric field enhanced bioremediation was 31.6%,far exceeding the simple sum of electrokinetic remediation efficiency（5.5%）and biodegradation efficiency（13.7%）.Meanwhile,the microbial diversity was improved and the microbial community（mainly some species belonged to Firmicutes）were enriched by the effect of electric fields.The above results showed that there were synergistic strengthening and coupling effects in the electric field enhanced bioremediation.Oxygen evolution reaction,electrochemical oxidation,electrodynamic effect and current thermal effect,which were induced by electric field,could synergistically promote the growth and metabolism function of microorganisms,thereby improving the pollutant degradation efficiency.Finally,the field trial based on the optimized electric field enhanced bioremediation was carried out.A pilot plant with the dimension of 1.6×1.1×1 m（length×width×height）was designed and constructed to remedy soils polluted with petroleum hydrocarbon pollutants in one chemical industry field and the pollutant removal rate in the actual remediation process was 8.4 mg/kg_{dry soil} per day.All in all,it was demonstrated that the electric field enhanced bioremediation technique had synergistic enhancement effects in the remediation process,which could provide theoretical and technical support for the remediation of petroleum-hydrocarbon contaminated soil.