Application of a mechanistic UV/hydrogen peroxide model at full-scale : sensitivity analysis, calibration and performance evaluation

Numerous mechanistic models describing the UV/H2O2 process have been proposed in literature. In this study, one of them was used to predict the behavior of a full-scale reactor. The model was calibrated and validated with non-synthetic influent using different operational conditions. A local sensitivity analysis was conducted to determine the most important operational and chemical model parameters. Based on the latter, the incident UV irradiation intensity and two kinetic rate constants were selected for mathematical estimation. Hydrogen peroxide concentration, the decadic absorption coefficient at 310 nm (UVA310, as a surrogate for natural organic matter) and pH could be satisfactorily predicted during model validation using an independent data set. It was demonstrated that quick real-time calibration is an option at less controllable full-scale conditions. Parameters that determine the initiation step, i.e. photolysis of hydrogen peroxide, have a large impact on most of the variables. Some reaction rate constants were also of importance, but nine kinetic constants did show absolutely no influence to one of the variables. Parameters related to UV shielding by NOM were of main importance. Hydrogen peroxide concentration was classified as a non-sensitive variable, in contrast to the concentration of a micro pollutant which showed to be very to extremely influential to many of the parameters. UV absorption as a NOM surrogate is a promising variable to be included in future models. Model extension by splitting up the UVA310 into a soluble and a particulate fraction seemed to be a good approach to model AOP treatment of real (waste)waters containing both dissolved and particulate (suspended) material

Modelling extinction and reignition in turbulent flames

The presented work attempts to extend the conditional moment closure method for noon-premixed. turbulent combustion to predict extinction and reignition phenomena in turbulent flames. The conditional moment closure method is one of a????class of conserved scalar modelling approaches in turbulent non-premixed combustion. where chemistry is treated as mainly dependend on the mixing of oxidizer and fuel. However. as designers of combustion devices aim for higher turbulence rates to enhance mixing and promote combustion, chemical conversion is not solely determined by the rate at which fuel and oxidizer are mixed, but kinetic effects become important. Therefore it is necessary in these cases. to consider a second variable to govern the evolution of the chemical system. This variable will parameterize the chemical conversion process from cold. mixed reactants at fixed eguivalence ratio to an eguilibrium state. Equations describing the chemical system as a function of these two variables, the conserved scalar, commonly referred to as mixture fraction and the progress variable. can be derived and constitute the doubly conditioned moment closure equations. However, solution of this set of equations is computationally expensive and key parameters describing the rate of dissipation of the progress variable, which is a reactive scalar, are not yet fully understood. By considering conditional fluctuations of the progress variable, applying simple relationships for scalar dissipation and using a pre-computed functional dependence of conditional moments on the progress variable, the effect of double conditioning on the chemical source term and on the overall chemistry predictions can be examined. The methodology is tested for its capability to predict the turbulent. piloted flames of the Sandia D-F series. These laboratory flames show an increasing degree of local extinction and reignition due to varying turbulence levels. Hence they provide an ideal benchmark for the study of models trying to predict these phenomena.Imperial Users onl

하천 유해화학물 유입사고 대응을 위한 2차원 오염물질 혼합모형 개발

학위논문(석사)--서울대학교 대학원 :공과대학 건설환경공학부,2019. 8. 서일원.한국의 하천들은 하수처리시설과 취수시설이 혼재되어있어 수질오염사고가 발생할 가능성이 높다. 최근 신소재 공학 등 첨단산업이 발전하게 되면서 유해화학물질의 유입문제는 더욱 대두되고 있으며, 실제로 최근 유해화학물질 유입사고 발생건수가 늘어나고 있다. 또한 국내 취수량의 90%가 지표수에서 취수한다는 점을 고려하였을 때, 하천오염사고는 식수오염, 관개수 오염 등 형태의 즉각적인 피해로 이어지게 되므로 적절한 대응책이 필요하다. 특히 중-대하천에 유해화학물질이 유출되는 사고에 대해서는 주요지점(취수장, 친수지구 등)에 마다 그 특징에 따른 적절한 조치가 필요하다. 이러한 사고에 대비하여 환경부는 유해화학물질 유입사고대응체계를 구축하여 대응하고 있다. 본 연구에서는 이러한 대응체계에 탑재 가능한 FEM기반 2차원 유해화학물질의 거동 해석 모형을 개발하였으며, 개발된 모형의 효율적인 운영을 위한 반응항의 유의성 판별 알고리즘의 프레임을 제시하였다. 서울대학교에서 개발한 2차원 수질해석 모형인 CTM-2D를 기반으로 생화학적반응, 휘발 그리고 흡탈착 메커니즘을 고려한 유해화학물질 해석 모형을 개발하였다. 각 반응 메커니즘은 1차 반응항으로 구성되며 사고에 즉각적으로 대비하기 위해 각 메커니즘의 매개변수들을 구축된 DB를 통해 추정할 수 있도록 여러가지 추정식을 탑재하였다. 물-토양 분배계수를 추정하기 위하여 Karickhoff (1981)가 제안한 물-옥탄올 분배계수와 물-유기탄소 분배계수 회귀식을 사용하였으며, 휘발계수를 추정하기 위해 Dobbins (1964)의 회귀식을 사용하였으며, 생화학적 반응계수는 문헌들의 값을 사용하였다. 구축된 반응항들을 검증하기 위해 해석해와 모형의 결과값을 비교하였으며, 0.1% 미만의 오차를 보여 모형의 타당성이 입증되었다. 또한 개발된 모형을 효율적으로 운영하기 위해 각 입력변수의 민감도 분석을 사용한 유의성 판별 알고리즘을 제시하고, 이를 이용해 유의하지 않은 항을 제거하여 계산소요시간이 단축할 수 있도록 하였다. 본 알고리즘의 첫째 과정은 미리 업데이트된 수리모형의 결과 값을 이용하여 유입지점으로부터 주입지점까지의 유하거리 및 평균 유속 그리고 평균 수심을 산정한다. 그 다음 구축된 지형 특성 자료를 이용해 단순화된 가상 직사각수로를 구축하고, 반응항의 매개변수를 유의하지 않은 값을 시작으로 매개변수의 값을 올려가며 결과에 유의한 변화를 가져오는 임계 값을 산정한다. 그 다음 구해진 임계 값과 실제 유입된 물질의 매개변수를 비교하여 유의한 메커니즘을 판별하고 모의를 수행하게 된다. 개발된 모형과 유의성 판별 알고리즘을 낙동강 중상류에 있는 낙동고령보와 달성보 사이의 금호강 합류부 구간의 가상 유해화학물질 유입사고를 가정하여 적용하고, 그 결과를 분석함으로 적용성을 검토하였다. 금호강 합류부의 죽곡 배수장에서 사고가 발생하여 톨루엔이 유출되었다고 가정하여, 4 km 유하거리 낙동강 합류지점에 있는 화원 양수장을 주요지점으로 설정해 모의를 수행하였다. 수리모의를 위해 첨단기술 기반 하천 운영 및 관리 선진화 연구단에서 2016년에 측량한 하상자료가 사용되었으며, 국가수자원관리 종합정보시스템(WAMIS)의 유황자료를 사용하였다. 또한 유의성 판별 알고리즘의 적용성 검토를 위해 3가지 조건으로 모의를 진행하였다. 적용성 검토를 위해 앞서 언급한 유의한 반응항만 고려한 모의를 포함해 총 3가지 케이스를 비교하였다((1)모든 반응항이 미반영된 결과, (2)유의한 메커니즘만 반영된 결과, (3)모든 메커니즘이 반영된 결과). 사고대비 물질 38종 중 휘발 및 생화학반응이 유의하게 판별된 염화메틸 물질을 대상으로 모의를 진행하였으며, 모든 메커니즘을 반영하지 않은 결과와 유의한 메커니즘을 반영한 결과 는 첨두농도에서 약 100 %의 변화를 보였고, 체류시간은 약 2시간 정도의 차이로 약 33 % 변화를 보였다. 이는 사고 시 대처 방안에 고려해야 할 차이로 볼 수 있다. 또한 유의한 메커니즘만 반영한 결과와 유의하지 않은 메커니즘까지 모두 반영한 결과를 비교하였을 때 첨두농도에서 0.002 ppm 차이, 체류시간에서는 약 13분 가량의 차이를 보였으며, 이는 유의한 메커니즘만 반영한 결과 대비 약 3 % 정도의 변화를 보였으며, 사고 대응책은 보수적인 판단이 필요함을 고려하였을 때, 허용 가능한 차이로 볼 수 있다. 따라서 이는 주어진 조건의 시나리오 상황에서 제시된 유의성 판별이 타당함을 보였다. 또한 계산소요시간이 1/4로 줄어들어 신속한 대응책이 필요한 하천유입사고발생 시 보다 적절한 대응책을 마련할 수 있을 것으로 기대된다. 따라서 하천에 유해화학물질 유입사고가 일어날 시 본 연구에서 개발한 유해화학물질 거동해석모형과 제시한 유의성 판별 알고리즘을 이용해 보다 신속한 대비가 가능할 것으로 기대된다.The pollutant spill accidents in rivers more frequently occur since the high-tech industries are growing up in recent years. The accident can lead direct damages to human society such as contaminating drinking water and irrigation water. In Korea, the damage will be more significant since 90% of quantity of water intake is from surface waters. Therefore, response measures are needed to respond to pollutant spills in rivers. Some accidents, however, cannot be treated by direct measures such as chemical treatment and blocking the river water. Therefore, it is necessary to cope with passive countermeasures by expecting the spatiotemporal distribution of the pollutants. Ministry of Environment has operated 2 type of response systems for it. One of them is developed for the 4 main rivers, and another is developed for tributaries of 4 main rivers. Nonetheless, those systems were appraised as difficult to operate since they adopted foreign water quality model. In this study, two-dimensional pollutant transport model for response, which is called CTM-2DT, was developed based on FEM, and an algorithm for identifying the significant reaction was proposed. CTM-2DT is a toxicant analysis version of CTM-2D which is two-dimensional water quality model developed by Seoul National University. CTM-2DT can represent mechanisms of volatilization, adsorption/desorption, and biochemical reactions. Each reaction mechanisms were expressed as first reaction terms, so each term requires an equilibrium concentration and rate of change. Additionally, parameter estimation equations of each terms were installed so that the parameters be obtained through database in order to prepare for the accident immediately. In order to verify the constructed reaction terms, the results of the analytical solution and the model were compared. The error was less than 0.1%, which proved the validity of the model. An algorithm for identifying significant reaction terms was proposed in order to operate the developed model efficiently. The algorithm process is as follows: (1) figuring out the hydro-conditions and topography from hydrodynamic model results, (2) constructing virtual rectangle channel based on the conditions in step 1, (3) performing one-at-a-time sensitivity analysis for each parameters of reaction terms to find critical parameter values, and (4) examining the significant reaction by comparing the critical values and target material properties, (5) conducting simulation with only significant reaction mechanisms so that the calculation time can be reduced. The developed model and algorithm were applied to assess validity of the algorithm. The virtual accident was assumed as the toxic chemical inflows into the Kumho River where joins the Nakdong River. It was assumed that methyl chloride is assumed to be introduced at Jugok drainage station, accordingly concentration-related-data were figured out at Hwawon intake station located in the downstream. The riverbed elevation referred to the survey data in 2016 by Advanced Research Center for River Operation and Management (ARCROM). And the hydraulic data referred to the National Water Resources Management Integrated Information System (WAMIS). In order to examine applicability, three cases were compared taking into account the significant mechanism mentioned above ((1) results reflecting all reaction terms, (2) results reflecting only significant mechanisms, (3) results without reactions). In case of methyl chloride, the volatilization and biochemical reactions were identified as significant mechanisms while the sorption process was not. When comparing the case 2 and 3, the residence time at the Hwawon intake station was about 33% with about 2 hours difference. Also, in case of the peak concentration, there was 100% difference. When comparing the case 1 and 2, there was 3% changes in peak concentration and residual time which can be regarded as an acceptable difference considering the need for conservative judgment. The results showed that the algorithm for identifying significant reaction is valid in the given condition. Moreover, the calculation of case 2 took only 1/4 times compared to case 1, and it is expected to provide a more appropriate countermeasure for the accidents. Therefore, it is expected that the pollutant transport model for toxic chemicals and the algorithm for identifying the significant reaction mechanism in this study help to provide quicker decision for response to the river spill accidents.1. Introduction 1 1.1 Research background and necessity 1 1.2 Objectives and methodology 6 2. Theoretical Research 8 2.1 Contaminant transport model in rivers 8 2.2.1 Two-dimensional contaminant transport model 8 2.2.2 Two-dimensional toxic chemical transport model 12 2.2 Toxicant dynamics in river 14 2.2.1 Depth-averaged advection dispersion equation 16 2.2.2 Adsorption and desorption 17 2.2.2.1 Mathematical model 17 2.2.2.2 Partitioning coefficient and rate of sorption 20 2.2.3 Deposition and resuspension 25 2.2.4 Volatilization and biochemical reaction 27 3 Model development 30 3.1 Description 30 3.1.1 Governing equations 32 3.1.2 Hydrodynamic model (HDM-2D), sediment transport model (STM-2D) 34 3.2 Model validation 38 3.2.1 Soil – water reaction 38 3.2.1.1 Validation with analytic solution (Cd - Cp) 39 3.2.1.2 Validation with analytic solution (Cd - Cpb) 43 3.2.2 Validation of volatile term 46 3.2.2.1 Continuous injection in rectangle channel 46 3.2.2.2 Validation with analytic solution 48 3.3 Algorithm for identifying significant reactions 50 4. Application 53 4.1 Study site 53 4.2 Critical values of reaction parameters 57 4.3 Results 60 5. Conclusion 65 References 67 Korean Abstract 75 Appendix A. Mixing layer 78 Appendix B – Flow conditions of study site 80 Appendix C. List of Accidental materials 81Maste

Development and evaluation of models for assessing geochemical pollution sources with multiple reactive chemical species for sustainable use of aquifer systems: source characterization and monitoring network design

Michael designed a groundwater flow and reactive transport optimization model. He applied this model to characterize contaminant sources in Australia's first large scale uranium mine site in the Northern Territory. He identified the contamination sources to the groundwater system in the area. His findings will assist planning actions and steps needed to implement the mitigation strategy of this contaminated aquifer

Linking a simulated annealing based optimization model with PHT3D simulation model for chemically reactuve transport processes to optimally characterize unknown contaminant sources in a former mine site in Australia

Historical mining activities often lead to continuing wide spread contaminants in both groundwater and surface water in previously operational mine site areas. The contamination may continue for many years after closing down the mining activities. The essential first step for sustainable management of groundwater and development of remediation strategies is the unknown contaminant source characterization. In a mining site, there are multiple species of contaminants involving complex geochemical processes. It is difficult to identify the potential sources and pathways incorporating the chemically reactive multiple species of contaminants making the source characterization process more challenging. To address this issue, a reactive transport simulation model PHT3D is linked to a Simulated Annealing based the optimum decision model. The numerical simulation model PHT3D is utilized for numerically simulating the reactive transport process involving multiple species in the former mine site area. The simulation results from the calibrated PHT3D model are illustrated, with and without incorporating the chemical reactions. These comparisons show the utility of using a reactive, geochemical transport process’ simulation model. Performance evaluation of the linked simulation optimization methodology is evaluated for a contamination scenario in a former mine site in Queensland, Australia. These performance evaluation results illustrate the applicability of linked simulation optimization model to identify the source characteristics while using PHT3D as a numerical reactive chemical species’ transport simulation model for the hydro-geochemically complex aquifer study area

A mathematical model development for simulating in-stream processes of non-point source pollutants.

Doctoral Degree. University of KwaZulu-Natal, Durban.In coming years, chronic water stress is inevitable owing to the unavailability of fresh water. This situation is occasioned by rapid urbanisation, climate change, rising food demand, and production. The increasing rate of water scarcity associated with water pollution problems, makes water quality management an issue of great concern. Rivers owe their existence to the relationship of rainfalls, soil properties and land use within a catchment. The entire hydrological processes that occur in the catchment area has a direct effect on occurrences and quality of the rivers there-in. A principal part of the hydrological cycle is runoff generation. Runoff characterises soil erosion, sediment transport, pollutants and chemicals all otherwise referred to as non-point source pollutants and released into water bodies. Most non-point source pollutants are generated from agricultural fields, informal settlements, mining fields, industrial areas, and roads. These sources produce increased nutrient concentrates (sewage effluent from informal settlements and fertilisers from agricultural fields) and toxic substances which alter the water quality in uncertain quantities. This affects aquatic biota and ultimately human health negatively. Non-point source pollution is a major source of water quality degradation globally and is the single most significant threat to subsurface and surface sources of usable water. Developed countries, unlike many developing countries, have long sought ways to stop the release of non-point source pollution directly into natural rivers through the establishment of best management practices but unfortunately with little success in actual practice. Numerous non-point source models exist which are basically watershed based and are limited to simulate the in-stream processes of non-point source pollution in water channels. Most existing non-point source models are site-specific, cumbersome to manipulate, need high-level operational skills and extensive data sets. Consequently, these models are difficult to use in areas apart from where they were developed and with limited data sets, as is the case with developing countries. Hence, to develop a non-point source pollution model that would adequately and effectively, simulate non-point source pollution in water bodies, towards restoring good river health is needed. This is required to enhance the proper monitoring and remediation of water sources affected by Non-Point Source Pollution especially in areas that have scarce data. Using the concept of the Hybrid Cells in Series model in this study, a hydrodynamic riverine Non-point source pollution model is conceptualized to simulate conservative pollutants in natural rivers. The Hybrid Cells in Series model was conceptualized to address the limitations identified in the classical advection dispersion model which is the foundation for all water quality modelling. The proposed model is a three-parameter model made up of three zones, which describes pure advection through time delay in a plug zone, and advection and dispersion occurring in two other thoroughly mixed zones linked in sequence. The model considers lateral inflow and pollutant loading along the river reach in addition to the point source pollutant entry and flow from upstream stations. The model equation for water quality along with hydrodynamic equation has been solved analytically using Laplace Transform. The derived mathematical formulation is appropriately coded, using FORTRAN programming language. Other components such as hyporheic exchange process and first order kinetic reaction simulations are incorporated to the proposed model. The response of these models matches the numerical solution of the classical Advection Dispersion Equation model satisfactorily when compared. The potential of the proposed model is tested using field data obtained from verifiable existing literature. A performance evaluation at 95 percent confidence is carried out. The correlation results of the observed and simulated data are seen to be in good agreement. The breakthrough curves obtained from the proposed model shows its capability to simulate Non-point source pollution transport in natural rivers effectively. The simplicity of the Hybrid Cells in Series model makes it a viable model for simulating contaminant transport from non-point sources. As the model has been validated using recorded data collected from the field for a specific tracer injection event, it is imperative to carry out investigation on changes in model parameters before, during and after storm events. However, this study adequately addressed and attempted to develop, validate new model components for simulating non-point source pollutant transport processes in stream