동전기와 생물학적 복원방법을 혼용한 토양 중의 styrene 정화

Abstract

Up to recently, many researchers showed that the bioremediaton methods adopted to the soil contaminated by diverse organic compounds have excellent efficiencies and also, several of them adopted electrokinetic treatment methods to the heterogeneous and/or low-permeable soil media. They concluded that the electrokinetic treatment raises the temperature of the media(soil) and this could affect the conductivity, ion mobility, electric osmosis and adsorption reactions in the electrokinetic processes. Styrene, the target material of this paper, is one of the major raw material in the petroleum refinery industries. And so, the petrochemical complex may have the intrinsic hazard of the soil contamination by this compound. The specific circumstance might force the industry complex employ the in-situ treatment method. In this study, to treat the styrene contaminated soil, we introduced the bioremediation method utilizing the endogenous microbes and the electrokinetic process enhancing the mobility of microbes in the process. Lastly, we combined the two processes and tested the electrokinetic bioremediation method. Consequently, to treat the styrene contaminated soils of petrochemical complex, we adopted electrokinetic bioremediation method utilizing endogenous microbes. We concluded as follows; We employ the purge&trap-GC/FID method to quantify the styrene in the soil. The recovery, relative standard deviation, and detection limit of the method is 9.61~116.4%, 1.15~6.14(less 10%), and 0.6㎍/㎏( 99%). Styrene consumable microbes are identified as gram-positive Entrococcus faecium. These microbes proliferated at 25℃(15~25℃), pH of 9.0~9.8(pH of 6.8~10) and 0.05% of substrate(styrene) concentration. In electrokinetic bioremediation combined process, the temperatures of each process tended to increase with the supply of electric current(2.5~1.0mA or 0.16~0.63mA/㎠), and this thaught to be the adiabatic character of the media(soil). The microorganism culture fluid of the process seemed to raised the pH than the electrokinetic single process, but additional increase of pH, like supplement of appropriate electrolyte, needed to achieve the optimum biological condition. Electric voltage of the process showed decreasing with time because of the circulation of microorganism culture fluid. Lower voltage in constant current system meas the cut down of the operation cost(decrease of electric power). The accumulated electroosmotic flow was a little decreased, and showed good correlation with the electric current(R2=0.9818). The mobility of the contaminant(s), including electrolyte, was improved with the electric current. As the microbes traveled to anode by electrophoresis and electroosmosis, almost no microbes were detected in the cathode sector of the process. But, the microbes were abundant in the anode and intermediate sectors. The mean removal efficiencies was 42.8%, 54.5%, and 75.0% at the electric current of 2.5mA, 5mA, and 10mA, respectively and the removal efficiency showed good correlation with electric current(R2=0.9996). In comparison with bioremediation single process, the mean removal efficiencies was 120%, 140%, and 190% at the electric current of 2.5mA, 5mA, and 10mA, respectively. And in comparison with electorkinetic single process, the mean removal efficiencies was 148%, 710%, and 250% at the electric current of 2.5mA, 5mA, and 10mA, respectively. In summary, electorkinetic process using circulating endogenous microbes thought to be suitable to the treatment of styrene contaminated soil, but long-term treatment time needed to achieve the foreign purification criteria of 50㎎/㎏. In the treatment of biologically recalcitrant contaminants, the stable optimum pH condition adjustment seemed to be the major design parameter, the further research ought to be concentrated at proper pH adjustment, which might enhance the activation of microbes.