Effects of Completely Symmetrical Electric Field on Electro-Bioremediation of Oil Contaminated Soil

Petroleum,a complex,non-polar organic pollutant that is difficult to be degraded,was employed as a target organic pollutant at the level of 50 mg /g(mass of petroleum /mass of dry soil).An electrode control apparatus capable of reversing the polarity of the electric field every 5 min by the mode of rows /columns was designed.Therefore,the apparatus established a completely symmetric electric field both in space and field intensity.The aim was to explore the effect of electro-bioremediation on the removal rate of oil contaminants using a completely symmetric electric field.The variations of available nitrogen(AN),available phosphorus(AP) and available potassium(AK) and population of oil-degrading bacteria were compared under the electric field.Results indicated that under an electric field gradient of 1 V /cm,the contents of AN,AP and AK were 1.3,1.6 and 1.2 times higher than the original contents,respectively.In addition,the electric field effect and the electrode polarity switching led to a soil pH close to neutral(6.3 ± 0.2),and a temperature increase of 2-3 ℃,and thus the number of oil-degrading bacteria increased with a maximum value of 2.3 × 109 CFU /mL under the treating time of 20 d.These factors enhanced the removal rate of oil from the soil.The degradation rate of alkane accelerated,with a removal rate of 15.73% in 60 d.The removal efficiency of oil was 35.22% after 60 days,which was 2.4 times that of the control test.