65 research outputs found
Integrating Enzyme-Based Kinetics in Reactive Transport Models to Simulate Spatiotemporal Dynamics of Biomarkers during Chlorinated Ethene Degradation
No full textBiomarkers such as functional gene mRNA (transcripts) and proteins (enzymes) provide direct proof of metabolic regulation during the reductive dechlorination (RD) of chlorinated ethenes (CEs). Yet, current models to simulate their spatiotemporal variability are not flexible enough to mimic the homologous behavior of RDase functional genes. To this end, we developed new enzyme-based kinetics to model the concentrations of CEs together with the transcript and enzyme levels during RD. First, the model was calibrated to existing microcosm data on RD of cis-DCE. The model mirrored the tceA and vcrA gene expression and the production of their enzymes in Dehalococcoides spp. Considering tceA and vcrA as homologous instead of nonhomologous improved fitting of the mRNA time series. Second, CEs and biomarker patterns were explored as a proof of concept under groundwater flow conditions, considering degraders occurring in immobile and mobile states. Under both microcosm and flow conditions, biomarker-rate relationships were nonlinear hysteretic because tceA and vcrA acted as homologous genes. The mobile biomarkers additionally undergo advective-dispersive transport, which increases the nonlinearity and makes the observed patterns even more challenging to interpret. The model offers a thorough mechanistic description of RD while also allowing simulation of spatiotemporal dynamic patterns of various key biomarkers in aquifers
The underlying processes of evaporative changes: within the transition period in the Miombo Woodlands, Mpika, Zambia in 2018
No full textThe Miombo woodlands are characterized by a transition period which is defined as the dry period in which grasses wither, trees shed and flush their leaves a few weeks before the rainy season. It is difficult to measure evaporation, due to the influence of the plant water storage on the water availability during the dry season. The seasonal variation in the plant water storage makes it even harder, as the time lag between the plant water storage and the terrestrial groundwater storage varies between the 0 to 90 days depending on the vegetation density. (Tian et al., 2018). It is unclear why the trees prefer this early flushing strategy and what is triggering the shedding of old leaves and flushing of new leaves. It is difficult to remotely sense the variation during this period. In this report, the outputs of several evaporation products and the vegetation indices are studied and compared to see how models follow the transition period. Three models, that are chosen for the comparison use different methods to indirectly calculate the evaporation flux. The first model is the Surface Energy Balance System (SEBS), which is based on the Surface Energy Balance as the name suggests and calculates the evaporation through land-atmosphere relationships. The second model is the Global Land Evaporation Amsterdam Model (GLEAM); this model uses the water balance model to calculate the water stress factor and in return the actual evaporation. And lastly, the MODIS Terrestrial Evapotranspiration (MOD16A2) which uses the Penman-Monteith equation as a basis to separately calculate the evaporative fluxes such as transpiration, soil evaporation, and interception. The outputs of the evaporation models differ quite a lot, especially during the transition period. This is among other things due to the input variable such as vegetation indices. There are several vegetation indices such as the Normalized Difference Vegetation Index (NDVI), the Normalized Difference Infrared Index (NDII) and the Leaf Area Index (LAI). The difference in the indexes is minimal and only small timing differences can be found. This means that the output differences are not influenced by the vegetation indices. MODIS follows the trends found by the vegetation indices best as it does not have the shortcomings that GLEAM and SEBS display. GLEAM overestimates the water stress because the model doesn’t account for plant water storage. While SEBS responds well until the start of July in which the model starts to oscillate. The oscillations could be due to the slash and burn culture which happens around this time which could impact SEBS substantially due to its dependency on temperature and radiation. Even if the MODIS output is the most similar to the vegetation output, it is limited by the fact that it is average values and daily variations might be lost. As this research is based on mostly satellite images supplemented by field observations, no statements can be made about it how accurate the models are. But based on this research, the MODIS model seems to be the preferred evaporation output.ZAMSECURCivil Engineerin
Modeling of enhanced in situ biodenitrification at different scales: Integration of microbiological, hydrogeochemical, and isotope biogeochemical processes
No full textPremi Extraordinari de Doctorat concedit pels programes de doctorat de la UAB per curs acadèmic 2017-2018En aquesta tesi s'ha desenvolupat un model de transport reactiu que integra tots els processos principals i secundaris que afecten la desnitrificació in situ induïda a diferents escales de treball. Així, l'eina obtinguda relaciona els processos biològics induïts quan s'afegeix un donador d'electrons a l'aqüífer amb els processos geoquímics (interacció aigua-roca) i la geoquímica dels isòtops. A la primera part de la tesi (Capítol 2) és on s'ha desenvolupat el model conceptual i on s'han establert les relacions que existeixen entre la microbiologia i la geoquímica prèvia de l'aqüífer a escala de batch. D'altra banda, també s'ha desenvolupat el model conceptual de tota la geoquímica isotòpica associada al procés (δ15N-NO3-; δ18O-NO3- i δ13C-DIC incorporant tota la geoquímica del δ13C). En aquest sentit, s'ha desenvolupat un dels models biogeoquímics més complets de la literatura relacionats amb la desnitrificació in situ induïda. El model s'ha calibrat emprant dos experiments a escala de batch realitzats amb etanol i glucosa com a fonts de carboni externa. En tots dos casos, s'han obtingut molt bons ajustos amb les dades experimentals. A més, el model també incorpora l'acumulació de nitrit en el cas de l'experiment de la glucosa. L'avaluació dels processos geoquímics induïts per l'EIB ha posat de manifest que en funció de la font de carboni s'indueixen processos de precipitació (en el cas de l'etanol) i processos de dissolució de carbonats (en el cas de la glucosa). Aquests dos processos poden alterar la velocitat de l'aigua i crear importants problemes operacionals durant l'EIB. També s'han incorporat els processos de fraccionament isotòpic del nitrat millorant l'avaluació de l'abast de la desnitrificació en els models a escala de camp. Un cop elaborat el model biogeoquímic que estableix el model conceptual que quantifica les interaccions entre els diferents processos que hi intervenen, el model s'ha escalat a un cas de desnitrificació induïda a escala de camp en un aqüífer fracturat (Roda de Ter (Osona, Espanya)). En aquest apartat de la tesi (Capítol 3), s'ha perseguit avaluar quin era l'impacte del canvi d'escala en els paràmetres biogeoquímics. A més a més, també s'ha determinat el canvi de porositat induïda per la precipitació de calcita. Finalment, la incorporació dels isòtops al RTM ha permès comparar qualitativament i quantitativament l'extensió dels processos de desnitrificació calculats pel RTM i per l'equació de Rayleigh. Els resultats demostren que l'equació de Rayleigh descriu bé, en termes qualitatius, l'extensió de la desnitrificació, però en general la subestima entre un 60 i un 80%. Finalment, un cop avaluada l'aplicabilitat del model tant a escala de batch com a l'escala de camp, s'ha desenvolupat un model que reprodueix diferents escenaris d'injeccions de carboni orgànic en un experiment de columna de llarga durada considerant els canvis sobre les propietats hidràuliques produïts pel creixement microbià. Així, s'ha determinat que el creixement del biofilm va augmentar set cops la dispersivitat, augmentant, per tant, la heterogeneïtat del sistema i, conseqüentment, es va produir un canvi del model conceptual del flux i del transport del transport normal al transport no-Fickià. Aquesta transició es va caracteritzar emprant un model de transferència simple de massa. A més a més, el model de llarga durada ha permès determinar que freqüències d'injecció més espaiades en el temps produeixen un impacte menor en les propietats hidràuliques del medi. A més a més, les estratègies d'injecció amb la relació Carboni:Nitrogen per sota de l'estequiomètrica es poden emprar per a minimitzar el risc de bioclogging mantenint les taxes de degradació, sempre i quan hi hagi una població important de microorganismes.In this thesis, an integrated reactive transport model has been developed that takes into account microbiology, geochemistry, and isotope geochemistry. The first section of the thesis (Chapter 2) addresses the development of a biogeochemical model with isotope geochemistry. The goal of this chapter is the setup of the conceptual relationships among microbiology, geochemistry, and isotope geochemistry (δ15N-NO3-, δ18O-NO3-, δ13C-DIC, and all geochemistry of δ13C) during Enhanced in situ Biodenitrification. Thus, one of the most complete biogeochemical models in the literature of EIB has been developed. The model was validated with a batch-scale biodenitrification experiment using groundwater and sediment from a Roda de Ter (Osona, Spain) site and two different external organic carbon sources, i.e., ethanol and glucose. In both cases, the model fit notably well with the experimental data. Moreover, the developed model also incorporated the nitrite accumulation observed in the glucose experiment. Consideration of the water-rock interaction in the model determined that if ethanol is used as an organic carbon source, carbonate mineral precipitation is induced, whereas if glucose is used, carbonate mineral dissolution is observed. Moreover, nitrate isotope incorporation facilitated the determination of the extent of denitrification at the field scale. Finally, the incorporation of a carbon isotope flow in the model was another tool used to verify the full consistence of the model due to the central role of inorganic carbon in biodenitrification and water-rock interactions. Moreover, modeling of carbon isotope flow showed that both ethanol and glucose were inversely fractionated. After the conceptual model was carried out, it was applied to an Enhanced in situ Biodenitrification application in fractured media (also Roda de Ter (Spain)). The main goal of this chapter is to incorporate the groundwater flow equations into a previously develop biogeochemical model and to validate it in media with a complex hydrogeology. It was observed that certain batch parameters can be used directly in the field (maximum consumption rate of electron donor (kmax) and stoichiometric relationships) and that the other parameters (saturation constants (Ks) and decay (b)) should be adapted, but the modifications involved less than one order of magnitude. Moreover, the induced calcite precipitation caused a change of porosity of less than 3%. As a secondary goal, the use of the Rayleigh equation to determine the extent of EIB was also verified from a practical perspective. The model demonstrated that the Rayleigh equation underestimated the percentage of degradation by approximately 60-80% and increasingly at the fringes of the plume. Chapter 4 focuses on a model that reproduces the system under different injection conditions and with the presence of important biofilm growth. This chapter evaluates how different feeding strategies modify the hydraulic properties of the media. It was observed that a weekly feeding strategy did not modify the hydraulic properties of the media, whereas daily feeding significantly modified the dispersivity. These changes in dispersivity implied an increase in heterogeneity and a consequent change in the conceptual model of flow transport along the column from normal to non-Fickian. This transition was well characterized using a single-rate mass transfer model. Moreover, the long-term model demonstrated that use of a feeding strategy with less carbon than predicted by stoichiometry implied a reduction of biomass without a reduction in nitrate degradation rates (because of the presence of an important biomass population). Overall, the elaboration of this thesis has contributed to the knowledge of all processes involved in Enhanced in situ Biodenitrification and their quantification using numerical models. The developed model will allow improvement in the design, planning, monitoring and optimization of this technology at the field scale
Injectivity reduction in geothermal wells: Investigating the causes
No full textThis study investigated the three possible main causes of injectivity reduction in geothermal wells (suspended solids, scaling, biological activity). That has been done by obtaining water samples at three operating geothermal doublet locations in the Netherlands. This paper contains new geothermal data and the interpretation of them. At the moment, injectivity reduction is the biggest and least understood issue in geothermal projects in the Netherlands. Investigating this problem is valuable for current and future geothermal injectors and essential for the upscaling of geothermal energy in the Netherlands.The three locations differ from each other in several aspects (reservoir, surface facilities, chemicals in use, injectivity reduction), which yields a good comparison. Water samples were taken at different moments in time, on different points in the geothermal systems and for different purposes: TSS, chemical composition and ATP concentrations. The data is obtained in the laboratory and used for scale analysis (using the Stream Analyzer software from OLI Studio®) and microbial kill tests to determine the influences on growth. Scientific quality and data reliability are guaranteed by multiple pre-experiments (e.g. to verify sterility of sample bottles) and extra measurements (e.g. duplo samples, oxygen concentrations). It has been found that TSS is reduced through the systems by filters (from 35-55 mg/L in production water to <8-16 mg/L in injection water). Also, scales can potentially form (calcite before- and barite after the heat exchanger). Furthermore, biological activity in the water is initially low, but can grow over time to high levels (>500.000 microbial equivalents). Microbial growth is site-specific and correlatable to injectivity reduction. When there is microbial growth, corrosion inhibitor (CI) enhances this growth. Scale formation is possible, but has a limited likelyhood to cause significant injectivity problems. Furthermore, there is no reason for TSS to be problematic, but it can also not be excluded as possible source for injectivity reduction. Mitigation of these issues can be done by using more injection filters in a geothermal system (for further TSS reduction). Scaling inhibitor can be used preventive and a CI without nutrients (in the solvent) should be used, or a biocide should be injected simultaneously with the CI. This report is interesting for geothermal operators, researchers and anybody else interested in geothermal operations in general or more specifically in injectivity reduction.Petroleum Engineering and Geo-science
Formulation of transport in a catchment-scale conceptual model
No full textStandard conceptual hydrological models can rarely accommodate stream tracer dynamics at the catchmentscale. They rely on the generation of runoff through the propagation of a pressure wave and do not accountfor the actual advective movement of particles. Over the last years different model frameworks have beendeveloped to account for this shortcoming. The difference between the frameworks lies in whether they arebased on mixing coefficients or storage age selection functions. Both methods have shown their ability tocapture the stream chemistry response. It is however not clear how these distinct approaches compare toeach other and to reality.To provide more clarification in this matter, this research applied both frameworks separately to model thehydrological and stream water chemistry response for a specific catchment. The results are analysed usingthe concept of transit times, where information on the fluxes and states in all model components is used togenerate distributions that describe the age structure of water. By comparing the distributions generated byboth methods and by evaluating the overall model performances, more insight is gained on the two frame-works and on their ability to capture subsurface mixing dynamics.From the results of this research it is concluded that both frameworks show similar performance. They arehowever conceptually different, which might have implications for their ability to capture specific dynamics.These implications depend on the characteristics of the catchment of interest. It is still concluded howeverthat performance for each frameworks is likely to be similar. Because the model description of the MixingCoefficient framework is less complex, it is recommended to continue research with this framework
The use of subsurface for thermal energy transport in district networks
No full textThis study introduces a new concept of ATES system, which is called ATEST system, to fulfill the transport function while crossing the barriers in water transmission and pipe replacements. Firstly, analytical models were used to help understand the physical process and range the working conditions of the ATEST system. Then numerical models were used to prove the feasibility and the value of this new conceptual system. Acceptable system performance that can meet the heat demand was iterated in case simulation; and the economical advantages were identified by comparing it with traditional ATES systems. The ATEST system showed a greater practical value than the ATES system in: 1) solving the discrepancy between heat service and heat demand in space, and 2) crossing barriers where pipes cannot be buried. However, the system should be further modified in operation to acquire better performance and avoid practical problems
Verwijdering van plantpathogenen uit drainagewater door ondergrondse opslag voor veilig irrigatiewater.
No full textDe aanwezigheid van bacteriële plantpathogen in oppervlaktewater en hun verspreiding via irrigatie vormt een bedreiging voor gewasziekten. Een natuurlijke oplossing voor veilig irrigratiewater is ondergrondse opslag van water, ofwel 'manged aquifer recharge' (MAR), Drainagewater wordt opgevangen en geïnfiltreerd in brakke/zoute watervoerende lagen (aquifer), resulterend in een zoet water 'bubbel' in de ondergrond. Dit geeft agrariërs toegang tot voldoende zoet water voor de irrigratie van gewassen, zelfs in tijden van droogte
Verwijdering van plantpathogenen uit drainagewater door ondergrondse opslag voor veilig irrigatiewater.
No full textDe aanwezigheid van bacteriële plantpathogen in oppervlaktewater en hun verspreiding via irrigatie vormt een bedreiging voor gewasziekten. Een natuurlijke oplossing voor veilig irrigratiewater is ondergrondse opslag van water, ofwel 'manged aquifer recharge' (MAR), Drainagewater wordt opgevangen en geïnfiltreerd in brakke/zoute watervoerende lagen (aquifer), resulterend in een zoet water 'bubbel' in de ondergrond. Dit geeft agrariërs toegang tot voldoende zoet water voor de irrigratie van gewassen, zelfs in tijden van droogte
Pilot study and modelling of remineralization of low-temperature desalinated water by calcite filtration
No full textTo prepare for future challenges, such as possible upcoming organic micro pollutants in the source water, including traces of medicines, pesticides, and industrial by-products, it is expected that the conventional treatment does not ensure a reliable quality of drinking water. As a result, during the past few years, Oasen started to research a new treatment concept based on 100% reverse osmosis (RO) membrane filtration to provide an excellent barrier for organic micro pollutants. However, the water produced by the RO membranes, called permeate, is corrosive, bitter in taste and does not comply with the drinking water regulation standards in the Netherlands. Therefore, a certain degree of remineralisation is crucial to solve these problems and improve the water quality. A commonly used remineralisation process is to filter the desalinated water through a calcite contactor, providing the appropriate amount of bicarbonate and calcium in the water. In order to properly design and operate the calcite filters as well as to predict the final water quality, it is essential to understand the processes that occur in the filter. The aim of this study was to find the best kinetic calcite dissolution model in order to understand the calcite grains dissolution behavior inside the filter and subsequently to adequately design and operate the calcite filter. Therefore, extensive pilot research was conducted to investigate the effect of various parameters on calcite dissolution such as the calcite grain size, velocity and carbon dioxide concentration. On top of that, the dissolution was modelled based on a successful empirical expression given by Yamauchi et al. (1987). However, it was found that the effect of the flow rate on the diffusion boundary layer around the calcite grains has not been taken into account in the study carried out by Yamauchi et al. (1987). Therefore, the effect of velocity on the calcite dissolution coefficient was investigated at five different velocity ,i.e., 5, 10,15,20,30 m/h. From there, a function was developed to describe the correlation between flow rate and the dissolution rate coefficient. In order to calculate the equilibrium concentration, the chemical reactions were simulated using PhreeqPython (Phreeqc built in Python).The main difference of this study compare to previous investigations was the low temperature of the water (12 oC vs 22-40 oC) and the smaller grain size of the calcite (0.5-1.2 mm vs 1-2 and 2-3mm) which was tested. Besides that a high range of CO2 dosing (1.45- 9.5 mmol/l) was tested. As expected from theory, the dissolution rates was strongly affected by the varied parameters. It is concluded that the smaller grain size of 0.5-1.2 mm reduced the required empty bed contact time (EBCT) to15 min where operating the filter with the larger grain size of 1-2mm needs a minimum EBCT of 25 min to reach calcite equilibrium. The CO2 dosing is recommended to be less than 3 mmol/l, since the CO2 efficiency will drop under the 60% at higher CO2 concentrations. Eventually, the optimal design will be introduced for the remineralisation process at Oasen treatment plant De Hooge Boom located in Kamerik. For this purpose various operational scenarios were compared on capital and operational cost. The overall cost including, both Capital expenses (CAPEX) and Operational expenses OPEX, was estimated between € 0.048 and 0.064 per m3 for different scenario’s where 71% consists of investment cost. The total treatment cost of this design is 0.057 €/m3 and the investment cost was found to be € 1.351.000 which is 32% less than price estimated by previous study done by Oasen. Remineralisatio
Microbially mediated kinetic sulfur isotope fractionation: reactive transport modeling benchmark
No full textMicrobiallymediated sulfate reduction is a ubiquitous process inmany subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate-reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42−) over the heavier isotopologue (S34O42−). Detection of isotopic shifts has been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing heavy metal and radionuclide bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies.We developed a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction.
The benchmark problem set is comprised of three problem levels and is based on a large-scale laboratory column experimental study of organic carbon amended sulfate reduction in soils from a uranium-contaminated aquifer. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and iron-sulfide reactions are included in the problem set. This benchmark also explores the different mathematical formulations in the representation of kinetic sulfur isotope fractionation as employed in the different RTMs. Participating RTM codes are the following: CrunchTope, TOUGHREACT, PHREEQC, and PHT3D. Across all problem levels, simulation results from all RTMs demonstrate reasonable agreemen
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