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Process performance of in-situ bio-methanation for co-digestion of sewage sludge and lactic acid, aiming to utilize waste poly-lactic acid as methane
No full textThis study examined hydrogen conversion efficiency and operational stability in pilot-scale in-situ bio-methanation during the co-digestion of sewage sludge and lactic acid (partially derived from waste poly-lactic acid). Parallel laboratory-scale experiments were also conducted. In the pilot, hydrogen conversion efficiency decreased from 98.9 % to 84.4 % as the hydrogen feed rate increased from 240 to 1,200 mL/LR/d. Conversely, laboratory experiments maintained efficiencies above 95 % at a feed rate of 3,600 mL/LR/d, suggesting that hydrogen gas-liquid transfer limited hydrogen conversion efficiency in the pilot. Lactic acid degradation was observed both with and without hydrogen injection in the pilot. Methane yields from the acid were 310 ± 30 and 300 ± 30 mL/g (chemical oxygen demand (COD))-added, close to the theoretical methane yield (350 mL/gCOD). These results demonstrate the importance of hydrogen gas-liquid transfer when scaling up bio-methanation processes. Moreover, they showed the potential of waste poly-lactic acid as a methane source
Simultaneous biogas upgrading and single cell protein production using hydrogen oxidizing bacteria
No full textCO2, a primary byproduct of anaerobic digestion, significantly reduces the calorific value of biogas, necessitating its enhancement through biogas upgrading to increase the CH4 content. The hydrogen oxidizing bacteria (HOB) Cupriavidus necator H16 demonstrates potential as a candidate for biological biogas upgrading due to its efficient CO2 capture and biosynthesis capabilities. Results indicated that in batch experiments, the concentration of CH4 could be elevated from 57.09 % to 98.46 % within 72 h by HOB, with a maximum CO2 assimilation efficiency of 27 mL/(L·h), meeting the requirements for biomethane. In bioreactor scale-up experiments, the CH4 concentration was increased to 94.22 % within 96 h. Beyond biogas upgrading, HOB also produces biomass usable as single cell protein (SCP), with its protein content varying between 43.75–70.83 % depending on the gas supply ratio. A total of 17 amino acids were identified, including eight essential amino acids. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) indicated that the essential amino acid content in the HOB-based protein was well-balanced, closely approximating the quality of fishmeal and pork. A techno-economic analysis revealed that the net revenue from the anaerobic digestion process could be enhanced by 48.49 % using HOB-based biogas upgrading. In contrast, biogas upgrading processes based on hydrogenotrophic methanogens (HM) resulted in a 57 % reduction in net revenue. This study establishes a carbon flow pathway from organic solid waste to biomethane and utilizable protein sources, facilitating sustainable nutrient recovery. This approach not only enhances economic benefits but also reduces carbon emissions associated with the anaerobic digestion process
Recent remediation strategies for flame <i>retardancy </i>via nanoparticles
No full textThis review article delves into the application of nanoparticles (NPs) in fire prevention, aiming to elucidate their specific contribution within the broader context of various fire prevention methods. While acknowledging established approaches such as fire safety principles, fire suppression systems, fire alarm systems, and the use of fire-retardant chemicals and safety equipment, this review focuses on the distinctive properties of NPs. The findings underscore the remarkable potential of NPs in controlling and mitigating fire propagation within both architectural structures and vehicles. Specifically, the primary emphasis lies in the impact of NPs on reducing oxygen levels, as assessed through the Limiting Oxygen Index (LOI), a subject explored by various researchers. Furthermore, this review delves into the examination of combustion reduction rates facilitated by NPs, utilizing assessments of ignition time, heat release rate (HRR), and flammability tests (UL-94) on plastic materials. Beyond these aspects, the review evaluates the multifaceted role of NPs in achieving weight reduction and establishing fire-retardant properties. Additionally, it discusses the reduction of smoke, a significant contributor to environmental pollution and health risks. Among the nanoparticles investigated in this study, SiO2, MgAl, and Nano hydrotalcite (NLDH) have respectively demonstrated the best results in weight reduction, smoke reduction, and HRR. Meanwhile, Al2O3 has been identified as one of the least effective treated nanoparticles. Collectively, these findings significantly contribute to improving safety measures and reducing fire risks across a range of industries
Comparison of different control methods on the thermally activated building system (TABS) with large energy flexibility
No full textThermally Activated Building Systems (TABS) has great energy flexibility potential for the effective demand response, but the inherent large thermal inertia creates challenges for the control. Model Predictive Control (MPC) can improve the control efficiency while achieving certain objectives. However, the modeling mechanism of the TABS thermal behavior can lead to the difference in the controller performances. In this study, the white-box model, grey-box model, and black-box model based MPCs (referred to as W-MPC, G-MPC, and B-MPC) are developed and analyzed in depth for a case TABS with high heat flexibility potential. The performances of MPC strategies are investigated together with the baseline Rule Based Control (RBC) strategy under normal conditions as well as a variety of uncertainty events. In general, MPC strategies show better performance compared to the RBC. The prediction-based control can effectively maintain the indoor temperature within the constraints considering the uncertain disturbances and the gradual outdoor climate change. Moreover, MPC strategies help to increase the cost savings due to the effective load shifting by 30%-50%, and enhance the flexible energy utilization by 14%-29%. In terms of the comparison among the different MPC strategies, W-MPC shows better performance in the room temperature control, which reduces the violation of the indoor temperature constraint by 30% and 15% compared to G-MPC and B-MPC, respectively. G-MPC shows slight superiority concerning the economy and flexible energy usage. The normalized cost saving of G-MPC is approximately 3% and 8% lower compared to the W-MPC and B-MPC, respectively, while the utilization efficiencies of the flexible energy are approximately 6% and 12% higher
High-performance nonflammable gel polymer electrolyte with 3D interpenetrating network for advanced lithium-ion batteries
No full textConcurrently attaining elevated safety and electrochemical performance in the realm of high-energy–density batteries represents a considerable challenge. Drawing inspiration from the synergistic flame-retardant concept of the P-Si element, a reactive phosphorus-containing flame retardant was meticulously devised that in conjunction with a nano octa-arm crosslinker featuring Si-O-Si and vinyl groups, collectively establishing a star-shaped crosslinked framework to resolve the issue of matrix compatibility and achieving the polymer matrix with intrinsic flame retardancy. Hence, a non-flammable composite gel polymer electrolyte (GPE) was fabricated. The composite GPE-based batteries, encompassing LiFePO4||Li, NCM523||Li and LiFePO4||Graphite, all exhibit commendable cyclic stability under 1C. Furthermore, deriving from the collaborative flame retardant characteristic, pouch cells incorporating the composite GPE displayed remarkable non-flammability and safety characteristics in various tests such as nail penetration, mechanical abuse and ignition scenarios, showcasing a notable 63.3 % reduction in maximum surface temperature. Intriguingly, the insights arising from Molecular Dynamics (MD) simulations indicate the migration mechanism for Li+ within a three-dimensional interpenetrating network, hence unmasking that feasible intra-chain hops of Li+ play a pivotal role
Impedimetric detection of chloride ions using two symmetric Ag/AgCl electrodes
No full textThe suitability of Ag/AgCl electrodes for specific detection of chloride ions in aqueous gels is investigated. In contrast to potentiometric sensors, we use an impedimetric approach and avoid the need for a separate reference electrode through a symmetric two-electrode configuration. As such, electrochemical impedance spectroscopy is employed to characterise the response of the Ag/AgCl electrodes in contact with gels at various hydration levels containing different types as well as concentrations of salt. In order to extract quantitative information related to e.g. the ion concentration and mobility from the impedance spectra, an equivalent circuit model is fitted to the data. Here, we develop a simple equivalent circuit model related to the physical parameters of the system, which can be reduced to a modified Randles circuit with only few circuit elements. Importantly, even though the equivalent circuit model contains the same elements as a Randles circuit, their physical origin is different. Systematic variations of ion mobility, ion concentration, and type of ions allow us to evaluate the relationship between those physical properties and the resulting fitting parameters of the modified Randles circuit. This finally enables us to determine chloride concentrations in complex liquids, containing other salts and long chain molecules.</p
Predicting individual thermal preferences in an office: assessing the performance of mixed-effects models
No full textMultiple studies suggested that existing thermal comfort models inadequately predict occupants' individual thermal preferences. Personalised comfort models offer an alternative to conventional comfort models aiming to forecast individual's thermal preference. Implementation of these personalised models in occupant-centric control of heating, ventilation, and air-conditioning (HVAC) systems can enhance their performance.A promising technique for personalised comfort modelling is mixed-effects (ME) modelling. A ME model accounts for fixed effects, representing the trends in the general sample, and for random effects, representing variations of specific clusters in the data. In contrast to fixed-effects (FE) models, ME models can capture individual differences. However, its effectiveness in predicting occupants' thermal preferences based on field measurement data, as well as the influence of variations in ME models on prediction accuracy, remains to be thoroughly investigated.This study aims to assess the prediction accuracy of ME models in contrast to FE models using field measurement data, including thermal preference votes from 30 unique occupants. The prediction performance was evaluated across three testing scenarios, each representing a different application of the models. Furthermore, two random effect structures were tested for the ME model: an intercept-only model and an intercept and slope model. The results show that ME models, in comparison to FE models, achieve an improved prediction performance of 8.0 % on average and up to 28.4 % for individual occupants. Moreover, the addition of a random slope to the ME resulted in deteriorated predictions. Finally, occupants’ individual variations were determined with an uncertainty of 6 % after 20 observations
CFD modeling of a modern wood stove - soot formation
No full textWood stoves are important domestic heating appliances using renewable bioenergy. However, the emission of Particulate Matter (PM) is the major concern for the application of wood stoves. Thus, improvements in the design of wood stoves are required for the reduction of PM emissions (mainly soot) to fulfill the increasingly stringent pollutant emission limits. To achieve low PM emission of the wood stove, a 3D steady-state CFD model is used to simulate the wood stove with a focus on soot formation in this study. The model is evaluated with the experimental data, the results of which show that the CFD model provides a reasonable prediction of wood stove experiments, indicating that the CFD model can be used as an efficient tool to optimize the design of the wood stove. The model is further used to study the effects of injection direction and mass flow rate of the tertiary air on the soot particle emission. It is found that the horizontal- and down-direction injectors can effectively reduce soot formation and an optimized tertiary air mass flow rate exists in the modern wood stove system. These conclusions are very useful in designing and developing the intelligent control system of the modern wood stove
Dynamic tank-in-series modelling and simulation of gas-liquid interaction in trickle bed reactor designed for gas fermentation
No full textTrickle bed reactors (TBR), historically utilized in petroleum processing and wastewater treatment, now extend their applicability in biological gas conversions, including syngas biomethanation for renewable methane production. Despite operational benefits, optimizing TBR design and scale-up demands a good understanding of the reactor’s hydraulic behavior and mass transfer phenomena. This study’s novelty is TBR’s hydraulic characterization in respect to liquid and gas flowrates and simulation of the gas-liquid interaction by a dynamic gas-liquid transfer model. Residence time distribution (RTD) experiments in 220 mL lab- and 5000 mL pilot-scale TBRs with co-current flow of gas and liquid were conducted to determine the liquid and gas working volume and the number of tanks for a dynamic tank-in-series (TIS) model. RTD experiments revealed 2 – 6 tanks for varying liquid flowrate (constant gas flowrate) and 5 – 8 tanks for varying gas flowrate (constant liquid flowrate). A dimensionless equation, fitted to RTD experimental data, predicted the liquid working volume of a TBR at various liquid flowrates and reactor configurations. TBR simulation by TIS model considering 8 well mixed gas and liquid phase tanks connected in series, resulted in an excellent model validation with an R2 at 0.99. Finally, the model simulated the mass transfer kinetics of H2, CO, and CO2 in water under varying gas and liquid flowrates for lab- and pilot-scale TBRs. Simulation results showed increased dissolved gas concentration with higher gas flowrate (constant liquid flowrate) for both scales TBR. It was also noticeable that under constant gas flowrate, the dissolved gas concentration initially decreased (0.01 < ReL < 17), then increased (17 < ReL < 34), and again decreased (34 < ReL < 105). This behavior was the same for both scales TBR and revealed an optimum ReL value irrespective of TBR size
Strategies for mitigating organic micropollutants in drinking water
No full textGroundwater is an important freshwater resource, from which more than 60% of European drinking water is produced. However, increasing detections of organic micropollutants (OMPs) in both groundwater and drinking water through enhanced analytical methods, have caused an emerging concern for wholesome and healthy drinking water as we know it. The frequencies and concentrations of recently detected OMPs e.g. pesticide metabolites challenge the current water supply. Groundwater protection as a sole strategy has failed to mitigate OMPs from drinking water, and since conventional treatment is insufficient to remove OMPs, additional treatment is necessary. Meanwhile, organic materials e.g. pipes of polyethylene (PE) are increasingly implemented in the distribution systems causing migration of OMPs, which may affect the drinking water quality after treatment, during storage and distribution.The aim of this Ph.D. thesis was to identify and investigate strategies to mitigate OMPs with the focus on treatment and materials, in order to maintain security of supply and a high drinking water quality now and in the future.Since knowledge on most recently detected OMPs is limited, a simple method was suggested to theoretically assess whether they can be removed with either granular activated carbon (GAC) or membrane filtration. Predicted sorption capacities and estimations of spherical molecular sizes were validated against reported scientific literature through which cut-off criteria were identified for efficient removal. GAC filtration was not identified as an economically efficient treatment strategy for all OMPs e.g. very polar pesticides metabolites like N,N-dimethylsulfamide (DMS), since it requires a frequent exchange of GAC material. Membrane filtration could retain most OMPs, however, water loss and discharge permits are major drawbacks of this treatment strategy. The potential for biological degradation in sand filters was explored as a sustainable retrofit treatment through various batch experiments. Nevertheless, the identified removal rates were insufficient for its further application in full scale, highlighting the persistence of recently detected pesticide metabolites e.g. desphenyl-chloridazone. Pilot scale investigations of advanced oxidation process (AOP) using H2O2 and UV were optimized for the removal of pesticide metabolites (i.e. DMS, dimethachlor ESA and alachlor ESA) from drinking water. Due to the unspecific nature of the treatment strategy, formation of various transformation and by-products including nitrite, ammonium, and in some cases, nitrosamines, were observed. AOP(UV/H2O2) was inadequate as a single treatment step to produce drinking water and therefore relies on post treatment. Implementation of additional treatment comes with an increased use of resources with economic and environmental impacts for which identification and proper handling of side-effects and waste products are essential and will affect which treatment strategy deems most optimal.Obtaining a high drinking water quality through treatment, further imposes downstream requirements on the storage and distribution not to introduce new OMPs through migration from the used materials. Migration testing coupled with non-target screening methods were used to identify currently unevaluated migration from certified materials. New suspected lists were developed, which should be considered for adaptation to the positive list with appropriate maximum tolerable concentrations at tap (MTCtap). To some extent, migration tests could predict the migration in full scale using appropriate surface area to volume ratios and contact time. However, results highlighted the need for further conversion and interpretation for a more comprehensive evaluation of the accumulated migration from materials used in contact with drinking water, for which field investigations are essential.Epoxy coating used on the interior of filter tanks caused a high initial migration of toluene and bisphenol A, which was potentially further avoided through appropriate commissioning procedures in full-scale. Antioxidants and their degradation products migrated from high density (HD) PE-pipes, and some (i.e. 3,5-diterbuthyl-4-hydroxy-styrene) exceeded MTCtap in conflict with certification. Thus, monitoring once installed in the distribution system was recommended. Targeted OMPs migrating from HDPE-pipes accounted for a decreasing share of the total migration over the lifetime, hence, long-term migration is currently unevaluated by certification schemes. Field investigations showed that extensive use of HDPE-pipes and synthetic rubber materials in e.g. valves and gaskets cause migration of various OMPs into the drinking water. Commissioning procedure, avoiding long term stagnation, or reducing the accumulated use of organic materials were identified as additional mitigation measures.Overall, this PhD thesis demonstrated that mitigation of OMPs in drinking wa-ter is not trivial. The inherent physio-chemical properties and continuous de-tection of new OMPs, as well as insufficient toxicological data, challenges the formulation of appropriate objectives for intervention with the ultimate goal to reduce adverse human health effects of OMPs present in drinking water. Fur-thermore, identifying optimal mitigation strategies requires a holistic evalua-tion including both environmental impacts and related costs