철 환원균에 의해 재생된 철을 이용한 TCE 제거

Abstract

Part I Numerical simulation was carried out to study the trichloroethylene (TCE) degradation by permeable reactive barrier (PRB), and revealed the effect of concentration of TCE, iron medium mass, and concentration of iron-reducing bacteria (IRB). Newly developed model was based on axial dispersion reactor model with chemical and biological reaction terms and was implemented using MATLAB ver. R2006A for the numerical solutions of dispersion, convection, and reactions over column length and elapsed time. The reaction terms include reactions of TCE degradation by zero-valent iron (ZVI, Fe^(0)) and ferrous iron (Fe^(2+)). TCE concentration in the column inlet was maintained as 10 mg/L. Equation for Fe^(0) degradation includes only TCE reaction term, while one for Fe^(2+) has chemical and biological reaction terms with TCE and IRB, respectively. Two coupled equations eventually modeled the change of TCE concentration in a column. At Fe^(0) column, TCE degradation rate was found to be more than 99% from 60 hours to 235 hours, and declined to less than 1% in 1,365 hours. At the Fe^(2+) and IRB mixed column, TCE degradation rate was equilibrated at 85.3% after 210 hours and kept it constant. These results imply that the ferrous iron produced by IRB has lowered the TCE degradation efficiency than ZVI but it can have higher longevity. Part Ⅱ A mathematical model was extended from previous research (Bae et al., 2008) to simulate the performance of TCE removal by using iron media filled column at various form iron media distributed conditions. The TCE solution flow at the column reactor was assumed and described as one-dimensional flow model. TCE fate and transport model was developed by dispersion-advectionreaction model, and the TCE reaction was simulated to interact with iron media. The iron media in the column was classified as zero-valent iron (ZVI), ferrous iron (Fe^(2+)), and ferric iron (Fe^(3+)). Transportation was not considered for iron media. Reaction term of TCE was developed for ZVI and ferrous iron media with interaction between TCE and these iron media by second-order kinetics. Ferric iron cannot be used as reducing agent for TCE. For the constant TCE removal by iron media, ferric iron regeneration was essential. IRB variable was provided for ferric iron reduction to ferrous iron, which can be used as reducing agent for TCE, through Monod equation with ferric iron mass per unit volume as substrate variable. By comparing various initial ZVI mass conditions with relatively lower IRB concentration, ferrous iron production was higher at high initial ZVI mass condition at early stage due to TCE removal domination by ZVI, and ferrous iron masses converged into similar values due to consumption of ZVI at later stage of reaction. With relatively higher IRB concentration, ferrous iron production rate increases with the increase of IRB concentration. ZVI oxidation rate is almost similar with every IRB concentration conditions at early stage, and it shows slight difference at later stage due to the effect of ferrous iron. TCE removal rate is critically affected by ZVI mass at early stage, while it is critically affected by ferrous iron mass at later stage. IRB concentration and total iron media mass are significant to control ferrous iron mass production at later stage of TCE removal column system. These results suggest that application of IRB is beneficial to the longevity of PRB rather than using only ZVI at PRBs, and controling IRB condition is important to control TCE removal efficiency. Part Ⅲ Permeable reactive barriers (PRBs) have been studied and applied for several decades to treat trichloroethylene (TCE) in ground-water system. Zero-vanent iron (ZVI) can be used in PRBs as reducing agent for TCE. ZVI, however, is oxidized to ferric iron (Fe^(3+)), and loss contaminant treating ability. Iron-reducing bacteria (IRB) can reduce ferric iron. as electron acceptor. to ferrous iron, while uses substrate as electron donor. Ferrous iron has TCE reducing ability. The object of the study focused on developing model parameters by experiments, apply the parameters to established model, and eventually perform estimation and assesment for the effect of iron media-PRB with IRB. Biomass batch experiment, TCE and by-products batch experiment, tracer experiment was performed for the parameter development. The ZVI-column experiment, and iron oxide column with IRB experiments were performed to experimentally investigate the TCE reduction properties at PRB when IRB is applied. The modeling based on experimental parameter values was performed to compare with the results of column experiments, and analyze the properties and estimate the expected values about TCE treatment when IRB is applied to iron media PRB. The parameters of dual Monod equation was estimated by biomass batch experiment, and the values of half iron reduction constant, half substrate oxidation constant, and maximum specific rate of biomass growth were calculated as 23.01 mg L^(-1), 211.39 mg L^(-1), and 0.011 hr^(-1), respectively. 2nd reaction rate constant of TCE and its by-products were calculated by performing TCE and its by-products batch experiment, and the values of TCE 2nd reaction rate constant by reaction between ZVI and TCE, cis-DCE 2nd reaction rate constant by reaction between ZVI and cis-DCE, VC 2nd reaction rate constant by reaction between ZVI and VC, and TCE 2nd reaction rate constant by reaction between ferrous iron and TCE with IRB were 1.234 × 10^(-8) L mg^(-1) hr^(-1), 1.310 × 10^(-8) L mg^(-1) hr^(-1), 2.351 × 10^(-8) L mg^(-1) hr^(-1), and 0.357 × 10^(-8) L mg^(-1) hr^(-1), respectively. Dispersion coefficient was estimated by tracer experiment, and its value was 0.9345 ㎠ hr^(-1). ZVI Column experiment results shows high TCE reduction rate at early time stage, and it constantly decrease through the time elapsed. ZVI column in this experiment finally loses contaminant reduction ablity when 127 hr passed until experiment commencement. When IRB is applied to iron spent column, the column's TCE reduction ability was regenerated and it constantly sustained.