Change Of Toxicity And Structure Of Petroleum Resins In Electroknetic Bioremediation Process

Resin is a type of macromolecular compounds with multi-aromatic heterocyclic in petroleum. It is so difficult to be degraded in the soil that it’s toxicity increased due to the long-term accumulation,then do harm to the ecological environment and human health. Therefore, removal and toxicity reduction of resin have become urgent issues to solve in the remediation process of petroleum-contaminated soil.In this study, resin-degrading bacterium was isolated from the soil obtained from Liaohe oilfield, which was long-term contaminated by petroleum. Superior mixed bacterium was prepared for the electrokinetic bioremediation of resin-contaminated soil. During electrokinetic bioremediation process, the changes of main soil physicochemical properties, bacteria counts and degradation of resin were analyzed. Combined with seed germination rate and infrared spectroscopy of resin, the relationship between toxicity and structure of resin was described. The main results were listed as follows:(1)Three resin-degrading bacterium named J1, J4 and J5 respectively were isolated from Liaohe oilfield contaminated soil. The degradation rate of J1, J4 and J5 reached 7.92%,9.68% and 7.33% respectively after 10 days’remediation. The strains were identified as Bacillus thuringiensis, Bacillus cereus and Bacillus megaterium according to the results of morphology and the phylogenetical analyses of 16S rRNA sequence. The proportion of mixed bacterium was optimized as J1:J4:J5=0.5:2:2 by the Orthogonal Experiment Method and the degradation rate was 11.83% after 10 adys’ remediation.(2)In the electrokinetic experiment, the electroneutrality and moisture uniformity were kept under the electric field with polarity reversal. On the contrary, the anode area was meta-acidic and drier, while the cathode area was alkaline with more moisture under the electric field without polarity reversal. The electric field promoted the growth of microorganisms. Compared with the electric field without polarity reversal, the microbial population under the electric field with polarity reversal was slightly larger. The microbe quantity in the cathode area was more than the anode area under the electric field without polarity reversal.(3)The degradation rate of resin with the electrokinetic bioremediation was better than that with bioremediation or electrokinetic remediation alone. And the degradation rate of resin with electric field without polarity reversal was better than electric field with polarity reversal, which were 20.5% and 9.9% respectively after 60 days’ remediation. And in the former treatment, the degradation rate in the cathode area was larger than in the anode area, which were 26.7% and 19.7% respectively.(4)Combined wheat seed germination rate with the changes of resin’s infrared absorption peak, the results showed that toxicity of resin was lowered in the cathode area under the electrokinetic bioremediation without polarity reversal. Oxidation degree and the number of aldehyde group were reduced, the number of carboxyl group and degree of branching carbon chain were increased, the length of the side chain was shortened and the dealkylation occurred. On the contrary, in the anode area, toxicity and oxidation degree of resin were larger, the length of the side chain was increased, and the degree of aromatization was reduced. Thus, the decrease of area of carbonyl and nCH2/nCH3 and the increase of aromatic carbon rate may cause the lower toxicity of resin so that affecting the germination rate.Electroknetic bioremediation lowered the toxicity of the resin by changing the structure of resin instead of significantly reducing it’s concentration. This maybe provide a new theoretical basis for the evaluation of heavy oil contaminated soil remediation.