| 1. |
- Andersson, Anna, 1990-
(author)
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Uncharted Waters : Non-target analysis of disinfection by-products in drinking water
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Disinfection by-products (DBPs) are potentially toxic compounds formed when drinking water is treated with disinfectants, such as chlorine or chloramine. A large proportion of the exposure to DBPs is still unknown and the health risks observed through epidemiological studies cannot be explained by DBPs known today. In this thesis, a part of the unknown DBP fraction is investigated, covering a wide range of non-volatile, chlorine/bromine-containing DBPs. The goals were to investigate how the compositions of these DBPs differ between water treatment plants, how their occurrence changes in the distribution system until reaching consumers and how new treatment techniques can reduce their formation and toxicity. To analyze unknown DBPs, a non-targeted approach adopting ultra-high-resolution mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), was used, where the mass of molecules is measured with such accuracy that the elemental composition of individual DBPs can be calculated. A panel of bioassays was used to assess the combined toxic effects from these DBP mixtures. The results show that the formation of these DBPs to a large extent was specific to each water treatment plant and that local conditions influenced DBP formation, based on e.g., the abundance of organic material with certain chemical structures, bromide and disinfection procedure and agent (chlorine or chloramine). The DBPs were detected in both chlorinated and chloraminated water and in all tap water samples, demonstrating that they are part of human exposure. The number of DBP formulae decreased and the DBP composition changed between drinking water treatment and consumer taps, suggesting that DBP exposure to consumers is not necessarily resembling measurements at the treatment plants. Evaluation of new treatment techniques showed that suspended ion exchange and ozonation have potential to decrease the formation and toxic effects of DBPs and that the removal of organic matter can influence qualitative aspects of DBP formation, such as the proportions of chlorine-containing (less toxic) versus bromine-containing (more toxic) DBPs. Through increased knowledge about the role and relevance of non-volatile DBPs, this work can contribute to future monitoring and actions to reduce the health risks associated with DBPs in chlorinated or chloraminated drinking water.
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| 2. |
- Ekstrand, Eva-Maria, 1985-
(author)
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Anaerobic digestion in the kraft pulp and paper industry : Challenges and possibilities for implementation
- 2019
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Doctoral thesis (other academic/artistic)abstract
- The pulp and paper industry is a large producer of wastewater and sludge, putting high pressure on waste treatment. In addition, more rigorous environmental legislation for pollution control and demands to increase the use of renewable energy have put further pressure on the pulp and paper industry’s waste treatment, where anaerobic digestion (AD) and the production of methane could pose a solution. Kraft pulping makes up 80% of the world production of virgin wood pulp, thus, the wastewaters from this sector represent a large unused potential for methane production.There are three main types of substrates available for AD at pulp and paper mills, the wastewaters, the primary sludge/fibre sludge, and the waste activated sludge. AD treatment of these streams has been associated with several challenges, such as the presence of inhibiting compounds or low degradability during AD. The aim of this thesis was to experimentally address these challenges and potentials, focusing on wastes from kraft mills.Methane potential batch tests showed that many wastewater streams still posed challenges to AD, but the alkaline elemental chlorine-free bleaching stream and the condensate effluents had good methane potentials. Further, the methane potential of kraft mill fibre sludge was high, and co-digestion of kraft mill fibre sludge and waste activated sludge was feasible in stirred tank reactors with sludge recirculation. By increasing the organic loading in a pilot-scale activated sludge facility and thereby lowering the sludge age, the degradability of the waste activated sludge was improved. The higher wastewater treatment capacity achieved by this method provides an opportunity for the mills to increase their pulp and paper production. Further, by dewatering the digestate after AD and returning the liquid to the activated sludge treatment, costs for nutrient supplementation can be reduced.In conclusion, the thesis shows that AD of wastes from the kraft pulp and paper industry was feasible and carried many benefits regarding the generation of methane as a renewable energy carrier, improved wastewater treatment and reduced costs. Different strategies on how AD may be implemented in the kraft pulp and paper industry were formulated and discussed.
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| 3. |
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| 4. |
- Rudberg, David, 1989-
(author)
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CO2 Emissions from Northern Lakes : Insights on regulation and spatiotemporal variability across contrasting lakes in Sweden
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Lakes cover only ~2 % of the global land area, but their connections to the surrounding catchment make them important for the global carbon cycle. A considerable amount of the carbon input to lakes is emitted to the atmosphere as carbon dioxide (CO2) through diffusive flux. This CO2 flux varies with surface water CO2 concentrations (CwCO2) and the transfer velocity of CO2 across the thin boundary layer between surface water and atmosphere (k), which both in turn depend on physical, biological, and chemical factors that interplay with lake and catchment characteristics over various time scales. Comprehensive studies of these interlinkages across lake types are rare, and current assessments of lake CO2 emissions are therefore uncertain. In this thesis, the variability and regulation of lake CO2 fluxes across a latitudinal gradient in Sweden is investigated. The thesis explores how CwCO2 and k regulate lake CO2 fluxes and how spatiotemporal patterns of CO2 fluxes vary within and across lakes.Regulation of CO2 flux at shorter temporal scales (<1 week) was dominated by k. However, the contribution from CwCO2 increased over time making it the dominant factor for seasonal CO2 flux in some lakes. Furthermore, we show that ways of assessing k in lakes may lead to bias, possibly due to inadequate consideration of processes occurring at the upper surface layer of lakes. In the three lakes where daynight variability was studied, we found consistent patterns of higher fluxes of CO2 at daytime during periods where lakes were emitting CO2. Meanwhile, the period of lake water column turnover in autumn was crucial for both day-night variability and total lake CO2 fluxes. Based on the patterns above, we have made recommendations on improved study design for representative measurements of CO2 fluxes in lakes. In addition, we produced models for estimating CO2 flux from combinations of climatic data, satellite imagery and national lake inventory data, i.e., information that is relatively easily available and thus simplify extrapolation of flux estimates to other lakes. Patterns observed across our models suggest strong climate feedbacks, which may lead to increasing CO2 fluxes from lakes at northern latitudes along with precipitation and temperature increases there. Thus, results in this thesis urges forthcoming studies to better account for spatiotemporal variability to improve upon models that can be used for large-scale estimates and future predictions of lake CO2 fluxes.
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| 5. |
- Ashiq, Muhammad Jamshaid, 1987-
(author)
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The occurrence of disinfection by-products in four Swedish drinking waterworks
- 2022
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Licentiate thesis (other academic/artistic)abstract
- Disinfection by-products (DBPs) are unwanted, potentially toxic compounds formed when drinking water is disinfected with chemical disinfectants such as chlorine or chloramine. The levels of DBPs produced depends on parameters, such as levels of natural organic matter (NOM) and the nature and concentration of chemical disinfectant used. In this thesis, the effects of two different types of chemical disinfectants, chlorine and chloramine, are investigated in terms of levels of DBP production. The goal was to investigate if chlorine disinfection produces similar levels and types of DBPs as in case of chloramination.Within the thesis work was also tested a method based on a gas chromatograph coupled with halogen selective detector (GC-XSD) to determine the known DBPs in the drinking water.The results show that the formation of DBPs at chlorine or chloramine disinfection were similar. Still, chloramine is preferably used because it produces less legally regulated DBPs.The GC-XSD worked well for the determination of DBPs in drinking water. Since XSD is very selective and specific towards halogens and easy to operate, therefore this setup not only a potential tool for routine DBPs monitoring at drinking water facilities, but it could also be used for the determination of unknow halogenated compounds.Through increased knowledge in the formation of DBPs and their determination with GC-XSD can contribute to the development of better methods to quantify known and identify unknow halogenated organic compounds in treated drinking water and reduce public exposure to potentially toxic halogenated organic compounds.
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| 6. |
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| 7. |
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| 8. |
- Šafarič, Luka, 1988-
(author)
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Anaerobic Digester Fluid Rheology and Process Efficiency : Interactions of Substrate Composition, Trace Element Availability, and Microbial Activity
- 2019
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Doctoral thesis (other academic/artistic)abstract
- As the anthropogenic greenhouse gas emissions continue imposing stress on our environment, it is becoming increasingly important to identify and implement new renewable technologies. Biogas production through anaerobic digestion has a great potential, since it links waste treatment with extraction of renewable energy, enabling circular bio-economies that are vital for a sustainable future.For biogas to have an important role as a renewable energy carrier in society, the scale of its production will need to be increased substantially. New substrates need to be introduced along with raising organic loading rates of the reactors to increase the rate of biogas production. This contributes to challenges in maintaining process stability, thus increasing the risk for process disturbances, including problems that were not commonly encountered before. These difficulties may be particularly pronounced when a broad range of new, largely untested substrates are introduced, leading to an increased heterogeneity of organic material entering the reactors. In the case of currently the most common reactor type; the continuous stirred-tank biogas reactor (CSTBR); such problems may include shifts in rheology (i.e. fluid behaviour) of the anaerobic digester sludge. This may lead to increased energy consumption and decreased digester mixing efficiencies, which in turn may lead to inefficient biogas processes, ultimately decreasing the economic and environmental viability of biogas production. Much is still unknown regarding how rheology shifts happen in biogas reactors, particularly when it comes to what role the substrate plays in rheological dynamics, as compared to the microbial community during varying levels of biogas process stability.This thesis elucidates the interactions between substrate type, microbial community and its metabolic activity, and anaerobic sludge rheology. A number of sludge samples from mesophilic and thermophilic CSTBRs digesting a broad range of substrates was analysed for their rheology. The specific effects of individual substrate types on CSTBR sludge rheology and the resulting implications for stirring power requirements and mixing efficiency were investigated. In order to also asses to which extent the microbial metabolism affects rheology at different levels of process disturbance, an experiment with a trace-element-induced inhibition of specific metabolic pathways under mesophilic reactor conditions was performed. This was used to identify the sequence of different interactions that occur in the reactor after the process begins to fail, and to evaluate how these interactions link to changes in digester sludge rheology. Finally, a case study of a disturbed thermophilic anaerobic digestion process was performed, including the monitoring of the response of rheology in relation to process stability, which was modified by changing trace element concentrations. The use of artificial substrate without polymeric compounds in both cases allowed for an evaluation of effects of the microbial community and its metabolic products on rheology without including the effects of complex substrates.The results showed that substrate type has a large effect on how different process parameters correlate with fluid behaviour. This was particularly apparent in the case of total solids and total volatile solids, which correlated well with rheological parameters for samples from reactors digesting agricultural waste, sewage sludge, paper mill waste, or food waste, but not for mesophilic co-digesters. Among the different substrates investigated, food waste was generally observed to lead to the highest limit viscosities (i.e. apparent viscosities at high shear rates, where it becomes linear and constant) of the anaerobic sludge, while digestion of paper mill waste and thermophilic co-digestion led to some of the lowest. No fluid type could be clearly coupled to a specific substrate, but it could be observed that increased solids content could generally be associated with more complex, non-Newtonian rheological behaviour. The differences in fluid characteristics between reactors corresponded to large differences in modelled stirring power requirements and mixing efficiency. The results indicated that fluids with high values of rheological parameters, such as the consistency index (K) or yield stress (τ0), would likely require more power or an adapted stirring system to achieve complete mixing. The substrates generally contributed more to the rheology characteristics of the anaerobic sludge than microbial cells on their own. Trace element-induced process disturbance initially led to the inhibition of specific microbial groups among methanogenic archaea or their syntrophic partners, which later escalated to broader inhibition of many microbial groups due to the accumulation of fermentation products. This resulted in microbial cell washout with a corresponding decrease of the contribution of the cells to anaerobic sludge rheology. A recovery of the thermophilic anaerobic digestion process was possible after the supplementation of selenium and tungsten was increased, resulting in increased propionate turnover rates, growing cell densities, and higher viscosity. Major shifts in the methanogenic community were observed, corresponding to the level of process stability. It could be concluded based on these experiments that the specific effect of microbial cells and their activity on sludge rheology were linked to cell density, which corresponded to process stability.A conceptual scheme was developed based on the studies in this thesis, defining complex interactions between substrate, microbial metabolism, and anaerobic sludge rheology in biogas processes. The possible causes of rheology shifts are visualised and discussed.
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| 9. |
- Schenk, Jonathan, 1992-
(author)
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Methane dynamics in northern lakes : Insights from multi-scale observations
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Methane (CH4) is a potent greenhouse gas which is emitted to the atmosphere from both natural and anthropogenic sources. Current evidence indicates that lakes account for a large part of the global emissions of CH4, but their contribution is difficult to quantify because of large temporal and spatial variability in processes leading to CH4 fluxes from lakes to the atmosphere. Making sense of the complexity and variability of CH4 emissions from lakes requires observations covering the range of temporal and spatial scales at which these processes occur, both within and between lakes. Northern regions are of particular interest for such studies because they contain a larger number of lakes than any other region in the world and they are disproportionately affected by climate change, with possible consequences for future CH4 emissions.The aim of this thesis was to investigate patterns of CH4 dynamics and emissions in several lakes distributed in different climatic regions of Sweden, paying particular attention to spatial and temporal variability of CH4 fluxes and concentrations. Fluxes, concentrations, carbon stable isotope signature of CH4, and a range of commonly monitored lake characteristics were measured several times during one year at multiple locations in each lake. The measurements provided an extensive set of observations of CH4 concentrations and fluxes in lakes, together with possible environmental drivers. These observations were then used to investigate patterns of CH4 dynamics in northern lakes and to assess the ability of empirical and process-based models to predict CH4 concentrations and fluxes in lakes.The results indicate that simple empirical models, consisting of linear regressions between explanatory variables and CH4 fluxes and concentrations averaged over the lake surface and ice-free period of the year, can be useful in some specific cases (for example describing ebullitive fluxes from total phosphorus or chlorophyll a concentrations). However, it was also noted that using such models for extrapolation can lead to large errors, especially if the observations do not account for temporal and spatial variability of CH4 fluxes and concentrations. An example of high variability was seen in day-night measurements of CH4 fluxes in four lakes over several months. To try to compensate for some of the shortcomings of empirical models, an established process-based and one-dimensional lake model was used to simulate CH4 concentration in the water column of the studied lakes. Predictions were in good agreement with observations in several of the investigated lakes, considering that the model was not pre-calibrated for any of the lake specifically. However, it was also clear that there can be key processes that require specific consideration in process-based models, and some degree of simplification is needed, especially when detailed information on the modelled systems is not available. The simplifications and assumptions that need to be made can be informed by the study and observation of relevant processes in situ. For example, groundwater was found to potentially contribute a major part of CH4 stored in one small boreal lake using measurements of stable isotope signature of CH4 in littoral sediment and deep water of that lake, as well as in the groundwater in the mire next to it. Stable isotope measurements in five other lakes also revealed consistent differences in CH4 sources to the surface and deep zones of lakes when they are separated by thermal stratification of the water column. Such knowledge could be used in the design of numerical models of lakes with the objective to improve predictions of current and future emissions of CH4 from these environments.Overall, this thesis contributes to the current knowledge on assessment of CH4 emissions from lakes at several temporal and spatial scales. It also emphasizes critical aspects which must be considered to reduce bias in future empirical and process-based models of CH4 in lakes.
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| 10. |
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| 11. |
- Bastviken, David, Professor, 1971-, et al.
(author)
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Measuring greenhouse gas fluxes : what methods do we have versus what methods do we need?
- 2022
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Conference paper (other academic/artistic)abstract
- Appropriate methods to measure greenhouse gas (GHG) fluxes are critical for our ability to detect fluxes, understand regulation, make adequate priorities for climate change mitigation efforts, and verify that these efforts are effective. Ideally, we need reliable, accessible, and affordable measurements at relevant scales. We surveyed present GHG flux measurement methods, identified from an analysis of >11000 scientific publications and a questionnaire to sector professionals and analysed method pros and cons versus needs for novel methodology. While existing methods are well-suited for addressing certain questions, this presentation presents fundamental limitations relative to GHG flux measurement needs for verifiable and transparent action to mitigate many types of emissions. Cost and non-academic accessibility are key aspects, along with fundamental measurement performance. These method limitations contribute to the difficulties in verifying GHG mitigation efforts for transparency and accountability under the Paris agreement. Resolving this mismatch between method capacity and societal needs is urgently needed for effective climate mitigation. This type of methodological mismatch is common but seems to get high priority in other knowledge domains. The obvious need to prioritize development of accurate diagnosis methods for effective treatments in healthcare is one example. This presentation provides guidance regarding the need to prioritize the development of novel GHG flux measurement methods.
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| 12. |
- Domènech-Gil, Guillem, Mr. Doctor, et al.
(author)
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Efficient Methane Monitoring with Low-Cost Chemical Sensorsand Machine Learning
- 2024
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Conference paper (peer-reviewed)abstract
- We present a method to monitor methane at atmospheric concentrations with errors inthe order of tens of parts per billion. We use machine learning techniques and periodic calibrationswith reference equipment to quantify methane from the readings of an electronic nose. The resultsobtained demonstrate versatile and robust solution that outputs adequate concentrations in a varietyof different cases studied, including indoor and outdoor environments with emissions arising fromnatural or anthropogenic sources. Our strategy opens the path to a wide-spread use of low-costsensor system networks for greenhouse gas monitoring.
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| 13. |
- Domènech-Gil, Guillem, Mr. Doctor, et al.
(author)
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Electronic Nose for Improved Environmental Methane Monitoring
- 2024
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In: Environmental Science and Technology. - : AMER CHEMICAL SOC. - 0013-936X .- 1520-5851. ; 58, s. 352-361
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Journal article (peer-reviewed)abstract
- Reducing emissions of the key greenhouse gas methane (CH4) is increasingly highlighted as being important to mitigate climate change. Effective emission reductions require cost-effective ways to measure CH4 to detect sources and verify that mitigation efforts work. We present here a novel approach to measure methane at atmospheric concentrations by means of a low-cost electronic nose strategy where the readings of a few sensors are combined, leading to errors down to 33 ppb and coefficients of determination, R-2, up to 0.91 for in situ measurements. Data from methane, temperature, humidity, and atmospheric pressure sensors were used in customized machine learning models to account for environmental cross-effects and quantify methane in the ppm-ppb range both in indoor and outdoor conditions. The electronic nose strategy was confirmed to be versatile with improved accuracy when more reference data were supplied to the quantification model. Our results pave the way toward the use of networks of low-cost sensor systems for the monitoring of greenhouse gases.
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| 14. |
- Jansen, Joachim, 1989-, et al.
(author)
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Global increase in methane production under future warming of lake bottom waters
- 2022
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In: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:18, s. 5427-5440
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Journal article (peer-reviewed)abstract
- Lakes are significant emitters of methane to the atmosphere, and thus are important components of the global methane budget. Methane is typically produced in lake sediments, with the rate of methane production being strongly temperature dependent. Local and regional studies highlight the risk of increasing methane production under future climate change, but a global estimate is not currently available. Here, we project changes in global lake bottom temperatures and sediment methane production rates from 1901 to 2099. By the end of the 21st century, lake bottom temperatures are projected to increase globally, by an average of 0.86-2.60 degrees C under Representative Concentration Pathways (RCPs) 2.6-8.5, with greater warming projected at lower latitudes. This future warming of bottom waters will likely result in an increase in methane production rates of 13%-40% by the end of the century, with many low-latitude lakes experiencing an increase of up to 17 times the historical (1970-1999) global average under RCP 8.5. The projected increase in methane production will likely lead to higher emissions from lakes, although the exact magnitude of the emission increase requires more detailed regional studies.
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| 15. |
- Karlson, Martin, 1980-, et al.
(author)
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Multi‐Source Mapping of Peatland Types Using Sentinel‐1, Sentinel‐2, and Terrain Derivatives—A Comparison Between Five High‐Latitude Landscapes
- 2023
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In: Journal of Geophysical Research - Biogeosciences. - : John Wiley & Sons. - 2169-8953 .- 2169-8961. ; 128:4
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Journal article (peer-reviewed)abstract
- Mapping wetland types in northern-latitude regions with Earth Observation (EO) data is important for several practical and scientific applications, but at the same time challenging due to the variability and dynamic nature in wetland features introduced by differences in geophysical conditions. The objective of this study was to better understand the ability of Sentinel-1 radar data, Sentinel-2 optical data and terrain derivatives derived from Copernicus digital elevation model to distinguish three main peatland types, two upland classes, and surface water, in five contrasting landscapes located in the northern parts of Alaska, Canada and Scandinavia. The study also investigated the potential benefits for classification accuracy of using regional classification models constructed from region-specific training data compared to a global classification model based on pooled reference data from all five sites. Overall, the results show high promise for classifying peatland types and the three other land cover classes using the fusion approach that combined all three EO data sources (Sentinel-1, Sentinel-2 and terrain derivatives). Overall accuracy for the individual sites ranged between 79.7% and 90.3%. Class specific accuracies for the peatland types were also high overall but differed between the five sites as well as between the three classes bog, fen and swamp. A key finding is that regional classification models consistently outperformed the global classification model by producing significantly higher classification accuracies for all five sites. This suggests for progress in identifying effective approaches for continental scale peatland mapping to improve scaling of for example, hydrological- and greenhouse gas-related processes in Earth system models.
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| 16. |
- Safaric, Luka, 1988-, et al.
(author)
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Rheology, Micronutrients, and Process Disturbance in Continuous Stirred-Tank Biogas Reactors
- 2023
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In: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 62:43, s. 17372-17384
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Research review (peer-reviewed)abstract
- Anaerobic digestion (AD) is an important technology for achieving sustainability, but it faces challenges in meeting rising production demands while remaining economically profitable. One difficulty is the lack of a comprehensive understanding of the many interactions within anaerobic digesters, which makes it challenging to fully optimize them. This is particularly notable when considering the interlinked dynamics between micronutrient availability and fluid behavior. This study addresses this gap by focusing on key operational parameters affecting the efficiency of the process in continuous stirred-tank biogas reactors, which are the most used AD technology today. It does so by proposing and evaluating a novel conceptual model of the mechanisms behind how different parts of AD processes interact upon disturbance, highlighting strategies for preventing process failure. This article aims to improve our understanding of the complexity of AD biotechnology and to provide a starting point for developing advanced strategies for operational optimization.
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| 17. |
- Svensson, Teresia, 1975-, et al.
(author)
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Chlorine Distribution in Soil and Vegetation in Boreal Habitats along a Moisture Gradient from Upland Forest to Lake Margin Wetlands
- 2023
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In: Environmental Science and Technology. - : AMER CHEMICAL SOC. - 0013-936X .- 1520-5851. ; 57:30, s. 11067-11074
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Journal article (peer-reviewed)abstract
- The assumed dominance of chloride (Cl–) in terrestrial ecosystems is challenged by observations of extensive formation of organically bound Cl (Clorg), resulting in large soil Cl storage and internal cycling. Yet, little is known about the spatial distribution of Cl in ecosystems. We quantified patterns of Cl distribution in different habitats along a boreal hillslope moisture gradient ranging from relatively dry upland coniferous forests to wet discharge areas dominated by alder. We confirmed that dry habitats are important for Cl storage but found that Cl pools tended to be larger in moist and wet habitats. The storage of Clorg was less important in wet habitats, suggesting a shift in the balance between soil chlorination and dechlorination rates. Cl concentrations in the herb layer vegetation were high in wet and moist sites attributed to a shift in plant species composition, indicating plant community-dependent ecosystem Cl cycling. Mass-balance calculations showed that internal Cl cycling increased overall ecosystem Cl residence times at all sites and that plant uptake rates of Cl– were particularly high at wet sites. Our results indicate that habitat characteristics including plant communities and hydrology are key for understanding Cl cycling in the environment.
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