A PREDICTION OF FATE AND TRANSPORT OF LANDFILL LEACHATE BY APPLYING PERMEABLE REACTIVE BARRIER

( Seung-whee Rhee ) 한국폐기물자원순환학회 2002 APLAS Vol.2002 No.1

The effects of PRB system on fate and solute transport of landfill leachate in subsurface formations are predicted to estimate the optimal conditions of the system design. Some of important parameters that affect the long-term, large scale transport of contaminants in PRB system are considered as hydraulic conductivity of PRB materials, thickness of PRB, length of PRB, and reaction constant in PRB in the subsurface formation of landfill site. In order to solve two-dimensional transport- reaction model in conjunction with steady state flow in PRB system that consists of a stratified subsurface formations, numerical simulation codes are developed by using the technique of Galerkin finite element method (FEM). For predicting of the concentration of contaminants through the reactive barrier, the transport- reaction equation is applied to the zone of a reactive barrier but a advection-dispersion equation is applied to the subsurface formations outside of the reactive barrier. Since the dimensionless concentration (C/Co) of 0.01 is passed the dike of landfill after 3 years, soil and goundwater of the outside landfill site can be contaminated by landfill leachate after 3 years if there is not built any protecting facilities such as a liner system or PRB systems. Horizontal distance at dimensionless concentration of 0.01 is decreased with increasing reaction constant. And that is increased with increasing hydraulic conductivity until 1×10^-6 m/s but decreased with increasing hydraulic conductivity after 1×10^-6 m/s. As the hydraulic conductivity in the reactive zone is increased, the plume of leachate is limited to the region of near the landfill site. The effect of PRB thickness on the spreading of contaminants in leachate is not better than that of other parameters. The optimal condition of PRB length is 7m. Horizontal distance at dimensionless concentration of 0.01 is dramatically decreased up to 29m as PRB length is increased up to 7m. Hence, it is realized that PRB system is very useful to protect the contamination of soil and groundwater by landfill leachate.

Nitrate reduction and its effects on trichloroethylene degradation by granular iron

Lu, Qiong,Jeen, Sung-Wook,Gui, Lai,Gillham, Robert W. Pergamon Press 2017 Water research Vol.112 No.-

<P><B>Abstract</B></P> <P>Laboratory column experiments and reactive transport modeling were performed to evaluate the reduction of nitrate and its effects on trichloroethylene (TCE) degradation by granular iron. In addition to determining degradation kinetics of TCE in the presence of nitrate, the columns used in this study were equipped with electrodes which allowed for in situ measurements of corrosion potentials of the iron material. Together with Raman spectroscopic measurements the mechanisms of decline in iron reactivity were examined. The experimental results showed that the presence of nitrate resulted in an increase in corrosion potential and the formation of thermodynamically stable passive films on the iron surface which impaired iron reactivity. The extent of the decline in iron reactivity was proportional to the nitrate concentration. Consequently, significant decreases in TCE and nitrate degradation rates and migration of degradation profiles for both compounds occurred. Furthermore, the TCE degradation kinetics deviated from the pseudo-first-order model. The results of reactive transport modeling, which related the amount of a passivating iron oxide, hematite (α-Fe<SUB>2</SUB>O<SUB>3</SUB>), to the reactivity of iron, were generally consistent with the patterns of migration of TCE and nitrate profiles observed in the column experiments. More encouragingly, the simulations successfully demonstrated the differences in performances of three columns without changing model parameters other than concentrations of nitrate in the influent. This study could be valuable in the design of iron permeable reactive barriers (PRBs) or in the development of effective maintenance procedures for PRBs treating TCE-contaminated groundwater with elevated nitrate concentrations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nitrate reduction impaired iron reactivity for trichloroethylene degradation. </LI> <LI> Nitrate reduction resulted in formation of passive films on iron surfaces. </LI> <LI> The iron reactivity decline was proportional to the nitrate concentration. </LI> <LI> Modeling can be valuable in designing of permeable reactive barriers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Exogenous Spermidine Improves Chilling Tolerance in Sweet Corn Seedlings by Regulation on Abscisic Acid, ROS and Ca2+ Pathways

Cai Shuyu,Wang Guofu,Xu Hua,Liu Jianxin,Luo Jie,Shen Yi 한국식물학회 2021 Journal of Plant Biology Vol.64 No.6

Chilling stress is a major abiotic constraint that affects sweet corn seedling establishment. Spermidine (Spd) is known to participate in the cold stress response in plants, nonetheless, the molecular mechanisms are largely unknown. The present study reported that exogenous Spd not only stimulated seedling growth but also enhanced photosynthetic attributes under chilling stress. Further analysis revealed that Spd application resulted in depressed abscisic acid (ABA) content and affected the expression of ABA-responsive genes. The augmented antioxidant enzymes activities, coupled with declined reactive oxygen species (ROS) content, were observed in response to Spd treatment under chilling stress. Moreover, Spd up-regulated the transcription levels of some Ca2+ transport-related genes. We propose that Spd contributes to cold tolerance in sweet corn seedlings via the regulation of genes involved in the ROS, ABA pathways and Ca2+ transport.

Sensitivity Analysis for Reactive Transport Model in Concrete Disposal System

Min Seok Kim,Chang Min Shin,Jong-il Yun 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

LILW disposal repository in Gyeongju, South Korea is considered with a concrete mixture that uses Ordinary Portland Cement (OPC) partially substituted with supplementary cementitious materials (SCMs). The degradation of cementitious materials that result from chemical and physical attacks is a major concern in the safety of radioactive waste disposal. We present a reactive transport model utilized as one of the geochemical simulation approaches for the timescales of concern that range from hundreds to thousands of years. The purpose of this study is to investigate the sensitivity of parameters in concrete disposal systems and to evaluate the influence of various assumptions on the chemical degradation of the systems using a reactive transport model. A reactive transport model in the concrete disposal vault was developed to evaluate the behavior of engineered barriers composed of cementitious materials. The sensitivity analysis was performed using reactive transport models through the coupling between COMSOL and PHREEQC. The databases selected for the analysis are the Thermochimie database presented by ANDRA. Among many variables considered, two variables that can highly affect chemical degradation were selected for detailed sensitivity analysis for dealing with uncertainties. This is important because the chemical degradation mechanism is generally sensitive to precipitation and diffusion coefficient. The first factor is precipitation, which might be the most important factor in chemical degradation because it acts as a calcium leaching of cementitious materials in a disposal system in a highly alkaline environment, increasing the porosity of the system. To predict the change in annual precipitation, the measurement of the precipitation observatory station in the nearest area of Gyeongju for the past 80 years was collected. The second factor is the diffusion coefficient, which plays an essential role in the durability of the concrete disposal system, promoting the decalcification of cementitious minerals, accelerating system degradation, and increasing the porosity of its system, thereby facilitating the migration of radionuclides. The diffusion coefficient values used in studies similar to this work were calculated and evaluated using the box-and-whisker method. The results of the sensitivity analyses for the reactive transport model in the concrete disposal system will be presented. The sensitivity cases show that the results obtained are much more sensitive to changes in transport parameters.

세균의 활성산소종과 활성질소종에 대한 내성에서 NADH dehydrogenase-2 결손의 효과

박희정(Hee Jeong Park),채권석(Kwon Seok Chae),방일수(Iel Soo Bang) 대한구강악안면병리학회 2010 대한구강악안면병리학회지 Vol.34 No.6

The electron transport chain (ETC) delivers electrons from many substrates to reduce molecular oxygen to water. ETC accomplishes the stepwise transfer of electrons through series of protein complexes conferring oxidation-reduction reactions with concomitant transport of proton across membrane, generating a proton gradient which leads ATP synthesis by F0F1ATPase. Bacterial ETC initiates with oxidation of NADH by NADH dehydrogenase complex (complex Ⅰ). Therefore, damage of complex Ⅰ leads to insufficient function of ETC and accumulation of NADH inside the cell. Contribution of ETC activity and its consequent changes of NADH levels to bacterial damage response against reactive oxygen and nitrogen species (ROS/RNS) has been poorly understood. In this study, by constructing ndh mutant Salmonella lacking complex Ⅰ NADH dehydrogenase 2, we evaluated the effect of ETC deficiency to bacterial resistance against ROS and RNS. The growth of ndh mutant Salmonella is impaired in the culture media containing hydrogen peroxide, but rather accelerates in the media containing nitric oxide donors. Data suggest that redox potential of NADH accumulated inside the cell by ETC blockage may affect inversely to bacterial resistance against reactive oxygen species and reactive nitrogen species.

지하수 내 질산성 질소 반응-이동 모델링을 위한 부지특이적 탈질화 계수 선정 방안에 대한 고찰

김상현,정재식,이승학,Kim, Sang Hyun,Chung, Jaeshik,Lee, Seunghak 한국지하수토양환경학회 2021 지하수토양환경 Vol.26 No.6

A simple and efficient scheme is presented that attempts to implement the site-specific denitrification rate in the reactive transport modeling for the nitrate in groundwater. A series of correlation analyses were conducted using 133 datasets obtained from different nitrate-contaminated sites to find the empirical relationships between denitrification rates and various subsurface properties. Based on Pearson's correlation analysis, the soil organic carbon concentrations showed a statistically significant correlation (r = 0.75, p < 0.05) with the denitrification rates. A linear regression was performed, which could be utilized to effectively determine the site-specific denitrification rate based on the soil organic carbon concentration of a site. The proposed method is expected to effectively replace the conventional methods which either were too complicated for practical application or impose large uncertainties that might end up with unreliable results.

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

Reinoso-Maset, Estela,Steefel, Carl I.,Um, Wooyong,Chorover, Jon,O'Day, Peggy A. Pergamon Press 2017 Geochimica et cosmochimica acta Vol.207 No.-

<P><B>Abstract</B></P> <P>Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium (U) concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this work, the dissolution rates of K- and Na-compreignacite (K<SUB>2</SUB>(UO<SUB>2</SUB>)<SUB>6</SUB>O<SUB>4</SUB>(OH)<SUB>6</SUB>·8H<SUB>2</SUB>O and Na<SUB>2</SUB>(UO<SUB>2</SUB>)<SUB>6</SUB>O<SUB>4</SUB>(OH)<SUB>6</SUB>·8H<SUB>2</SUB>O, respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved carbonate concentration (ca. 0.2 and 2.8mmolL<SUP>−1</SUP>). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area, and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58–87% of total U mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved U was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were 2.5–3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57·10<SUP>−10</SUP> vs. 1.28·10<SUP>−13</SUP> molm<SUP>−2</SUP> s<SUP>−1</SUP> [log <I>R</I> =−9.81 and −12.89] and 5.79·10<SUP>−10</SUP> vs. 3.71·10<SUP>−13</SUP> molm<SUP>−2</SUP> s<SUP>−1</SUP> [log <I>R</I> =−9.24 and −12.43] for K- and Na-compreignacite, respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for U mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. This study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as U in porous geomedia.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Compreignacite dissolution rates vary with the interlayer cation (Na>K). </LI> <LI> Detachment of uranyl groups from polyhedral layers is the rate-determining step. </LI> <LI> I

Reactive transport modeling on the behavior of CO₂ and SO₂ injected into deep saline aquifer

최병영(Byoung-Young Choi),채기탁(Gi-Tak Chae),김경호(Kyoung-Ho Kim),윤성택(Seong-Taek Yun) 대한지질학회 2009 지질학회지 Vol.45 No.5

Range-based truck-state transition modeling method for foldable container drayage services

Zhang, Ruiyou,Zhao, Haishu,Moon, Ilkyeong Elsevier 2018 TRANSPORTATION RESEARCH PART E-LOGISTICS AND TRANS Vol.118 No.-

<P>Manufacturing technologies of foldable containers have almost matured. The use of foldable containers might save transportation costs; however, incorporating them into drayage services also creates great challenges. The foldable container drayage (FCD) problem is formulated as a sequence-dependent multiple traveling salesman problem with time windows using a rangebased truck state transition method. An improved reactive tabu search algorithm is designed and validated to solve the FCD problem. The methodology is evaluated extensively on the basis of randomly generated instances. Compared to the use of standard containers, the use of four-in-one foldable containers can save approximately 10% on transportation costs.</P>

CO2 지중저장 주입정에서의 CO2-H2O-시멘트 반응 운송 모델링

조민기 ( Min Ki Jo ),채기탁 ( Gi Tak Chae ),최병영 ( Byoung Young Choi ),유순영 ( Soon Young Yu ),김태희 ( Tae Hee Kim ),김정찬 ( Jeong Chan Kim ) 대한지질공학회 2010 지질공학 Vol.20 No.4

CO2 지중저장에서는 대량의 CO2를 장기간 안전하게 저장하여야하기 때문에 CO2 누출이 발생할 경우 CO2 지중저장의 목적이 달성될 수 없을 뿐만 아니라 주변지역으로 CO2가 확산되어 보건/환경/생태에 큰 영향을 미칠 수 있다. CO2 주입시 주입정을 통한 누출의 가능성이 가장 높기 때문에, 본 연구에서는 관정 시멘트에 crack이 발생하였다는 가정 하에 crack으로 CO2가 누출될 경우 CO2-H2O-시멘트 간에 발생할 수 있는 화학 반응을 지구화학 모델링을 통하여 예측하였다. 모델링 결과 CO2-plume이 진행됨에 따라 시멘트 페이스트를 구성하는 portlandite와 CSH(Calcium Silicate Hydrate)가 용해되고, 2차적으로 CSH의 침전과 calcite의 침전이 발생하는 것으로 예상되었다. 약 3년 후에는 침전물의 대부분을 calcite가 차지하고 약 30년까지 침전물의 대부분을 이루게 된다. 본 연구 결과는 CO2 누출 시 주입관정 내 시멘트에서 발생할 수 있는 화학적인 변화를 이해하고, 반응 모델은 누출을 방지하기 위한 시멘트 관련 연구/개발에 응용될 수 있을 것으로 기대된다. CO2 leakage from a geological formation utilized for CO2 storage could result in failure of the facility and threaten the environment, as well as human safety and health. A reactive transport model of a CO2-H2O-cement reaction was constructed to understand chemical changes in the case of CO2 leakage through a cement crack in an injection well, which is the most probable leakage pathway during geological storage. The model results showed the dissolution of portlandite and CSH (calcium silicate hydrate) within the cement paste, and the precipitation of secondary CSH and calcite as the CO2 plume migrated along the crack. Calcite occupied most of the crack after 3 year of reaction, which could be maintained until 30 years after crack development. The present results could be applied in the development of technology to prevent CO2 leakage and to enhance the integrity of wells constructed for CO2 geological storage.