Increased Residence Time Research Articles

Reduction of Submicron-Sized Aerosols by Aerodynamically Assisted Electrical Attraction with Micron-Sized Aerosols

A vortex generator was installed inside an electric agglomeration device to apply aerodynamic agglomeration in the same space as electric agglomeration. Computational fluid dynamics simulation was utilized to assess the combined effects of electric and aerodynamic agglomeration, and this was subsequently validated through experiments. The discrete phase model was used to track particle trajectories. The results showed that both the aerodynamic agglomeration through the vortex generator and the electric agglomeration through the electric field were effective. When these two agglomerations existed individually in series, the total removal efficiency for submicron particles was 32.5%. However, when they coexisted in the same space, the efficiency increased to 50%. This increase is attributed to the increase in residence time when the vortex generator was added to a space with an electric field. This led to particles being exposed to the electric field for a longer duration, thus generating a synergistic effect.

Pollutant emission during pyrolysis of waste wind turbine blades: Nitrogen-containing components and polycyclic aromatic hydrocarbons

Serious attention was lacked for various pollutants formed in both gas and tar phase during pyrolysis recycling of waste wind turbine blades (WWTB), especially for components of carcinogenic bisphenol A (BPA) and potentially toxic polycyclic aromatic hydrocarbons (PAHs) in tar. Pyrolysis temperature within 400–600 °C would significantly impact pollutant formations. Additionally, CO2 had a potential to mitigate pollutants emission as an economic alternative for N2. This article investigated the influence of these factors on nitrogenous and PAHs components during WWTB pyrolysis through fixed bed and thermogravimetric experiments. The results showed that NO2 was dominated in nitrogen containing pollutants and was related to the evolution of pyrrole nitrogen oxides. It was found 550 °C as a turning temperature, at which the polycondensation reaction appeared significantly. This resulted in a markedly increase for toxic N-PAHs in tar. At this temperature, CO2 could be used to mitigate nitrogen pollutants. 25% CO2 reduced NOX emission about 26% and selectively promoted NH3 releasing to over 4.3 times and depressed HCN generating to 0.6 times. Moreover, the primary depolymerization product of organic pact in WWTB was BPA. Increasing residence time, temperature and CO2 concentration were beneficial for converting hazardous BPA to high valued P-Isopropenylphenol (IPP). The value of IPP:BPA could increase to over 2 in this experiment. It was aimed to provide not only an evaluation for the yield and migration of pollutants, but also an cleaner recycling solution through graded pyrolysis WWTB to mitigate pollution and maximize the value of by-products.

An Experimental Investigation into Ammonia Oxidation and NOx Emission in a Packed-Bed of Quartz Particles

ABSTRACT The effect of temperature, initial NH3 concentration, equivalence ratio, and flowrate on the characteristics of ammonia (NH3) oxidation and associated NOx formation in a fixed-bed reactor packed with quartz particles has been systematically investigated with a stream of NH3 and O2 in He over a range of furnace set temperatures (900 K – 1400 K), initial NH3 concentrations (2% – 10%), equivalence ratios (ɸ = 0.8, 0.9, 1.0, 1.1), and total flowrates (145 mL/min, 289 mL/min, and 434 mL/min). Benchmark flow reactor experiments, without the quartz particles in the reactor under otherwise similar conditions, were previously performed and served as a reference case for this work. Compared to the flow reactor results, the packed-bed data indicated a lower reaction onset temperature and more gradual NH3 conversion across the temperature range. Both packed-bed and flow reactor experiments indicated that decreasing flowrate, thus increasing residence time, resulted in greater NH3 conversion. NH3 conversion in the fixed-bed reactor was similar for all equivalence ratios at temperatures ≤1200 K, above which NH3 conversion increased with decreasing equivalence ratio, a trend broadly aligned with previous flow reactor experiments. For all conditions examined, NO was the major NOx component and NO2 was insignificant. Across the range of equivalence ratios, NO emission was low, yet noticeable, from 900 K – 1100 K, before spiking at 1200 K. Above 1200 K, NO emissions decreased before drastically increasing again at 1400 K under fuel-lean conditions. At temperatures ≤1300 K, NO was generally found to decrease with decreasing equivalence ratio, while at 1400 K, NO increased with decreasing equivalence ratio. NO emissions were significantly lower in the packed-bed compared to the flow reactor scenario at temperatures ≥1300 K.

Hydrogen production and elemental migration during supercritical water gasification of food waste digestate

The rapid growth of food waste (FW) is a huge challenge on a global scale, and anaerobic digestion is one of the most commonly used methods to deal with food waste, and the increasing amount of food waste digestate (FWD) produced by anaerobic digestion also poses a huge challenge to waste management. This paper explores supercritical water gasification (SCWG) as a valuable and innovative strategy for the conversion of FWD into H2-rich syngas. The research focuses on analyzing the effects of reaction temperature and residence time on syngas production, gas composition, element migration (C, N and P) during the SCWG process. Experimental results show that as the reaction temperature increases from 400 °C to 500 °C, the total syngas yield increases significantly, from 2.4 mol/kg to 9.7 mol/kg, especially the yields of H2, CO2, and CH4. As the reaction temperature increases and the residence time increases, the migration of carbon from the solid and liquid phases to the gas phase accelerates with increasing temperature and residence time, resulting in a higher proportion of carbon in the gas phase. In terms of liquid phase composition, nitrogenous compounds are significantly converted into ammonium (NH4+-N) at higher temperatures. In addition, the organic phosphorus is observed transferring into inorganic phosphorus, which are mainly apatite. This study explores the scalability of SCWG and its potential for the production of clean fuels, thereby contributing to the sustainable management of FWD.

CFD simulation of liquid-liquid extraction mechanism and enhancement schemes in microchannels based on three mass transfer models

Microreactors are highly efficient devices with a large specific surface area to improve the mass transfer efficiency. In this paper, a comprehensive three-dimensional CFD model was constructed based on three mass transfer theories to simulate the liquid-liquid two-phase flow and mass transfer process in a microchannel reactor, and two enhancement schemes were proposed. The multiphase flow and mass transfer characteristics were investigated by visualization and extraction experiments. The results indicated that the extraction efficiencies (E) and overall mass transfer coefficients (KLa) calculated by the penetration model and surface renewal model were within ±15 % errors compared to the experimental values. Moreover, E primarily increases with the increase of fluid residence time, while KLa increases with increasing flow rate. As the flow rate increases from 0.3 ml/min to 1.5 ml/min, E decreases by 15 %, and KLa rises from 0.78 s⁻¹ to 2.65 s⁻¹. Whereas the channel width decreases from 0.8 mm to 0.3 mm, E decreases by 3 %, and KLa rises from 0.44 s⁻¹ to 2.77 s⁻¹. Finally, microchannel with necked structure and baffles in mixing zone both improve the mass transfer efficient to some extent.

Examining the efficacy of biological filters in the removal of agricultural pesticides and nutrient elements from agricultural drainage water

The high water consumption in agriculture has led to an obvious water crisis in this sector, and the use of unconventional water sources, especially agricultural drains, is considered necessary. For this purpose, the present study was carried out to evaluate the efficiency of biological filters with different types of substrates for treating agricultural wastewater in Khuzestan province, located in the south of Iran, to use receptive resources and reuse them in agriculture. Next, the efficiency of four types of biological filters for treating agricultural drainage water with different retention times was evaluated. Sawdust, cotton stalks, wheat straw, stubble, and rice husk were used as filters. Qualitative factors included agricultural pesticides (Atrazine, Randup, Paraquat, and 2, 4-D) and nutrients (nitrate, nitrogen, phosphate, and phosphorus). By examining the trend of increasing the retention time and the corresponding removal percentage, it was observed that the retention time has a direct relationship with the amount of removal efficiency of nutrients and agricultural toxins. As the residence time increases, the average amount of nutrient compounds in different filters decreases, and their removal percentage increases. The highest removal percentage of nitrate, total nitrogen, phosphate, and total phosphorus was 74.03, 71.66, 57.97, and 61.85% in the sawdust filter and was assigned to 10 days. The highest percentage of removal of Atrazine, Tofudi, Paraquat, and Roundup toxins with a removal efficiency of 91.73, 84.27, 89.81, and 88.46% was also observed in the treatment of sawdust for 10 days. The sawdust filter showed a good performance in removing the parameters of agricultural toxins and nutrient compounds in a retention time of 10 days compared to other filters and retention times. As a general result, the sawdust filter can be cited as a reliable substrate with acceptable efficiency compared to other filters.

Thermal behavior of coated powder during directed energy deposition (DED)

In powder-based additive manufacturing (AM), the quality of the feedstock material is critical for obtaining enhanced mechanical properties. Recently, the application of coated powders during directed energy deposition (DED) has been prompted by the goal of fabricating composite and functional materials in-situ. The complex temperature and momentum fields established during DED render direct experimental characterization of coated powder behavior challenging. To address this challenge, this study reports on the thermal behavior of coated powders during interactions with the molten pool by constructing three-dimensional heat transfer and phase distribution models using the finite elements method (FEM). Transient temperature and phase distributions were calculated for coated and uncoated stainless steel 316L and ZnAl powders under various particle size, coating thickness, molten pool temperature, and coating material conditions. Particle residence time values were extracted from the calculations, defined as time spent by the particle before a phase change. The results show large variations in particle residence time (85 μs to 2670 μs for stainless steel 316L particles, and 48 μs to infinity for ZnAl particles) as a function of the variables considered, especially the thermal diffusivity of the coating materials, thereby highlighting the potential value of coatings as an additional design parameter in DED. Significant increases in particle residence time for both stainless steel 316L and ZnAl particles were found when contact angle increases from 0° (submergence regime) to 180° (floating regime).

Low-energy thermo-chemical conversion processes of municipal wet waste

Hydrothermal carbonization (HTC) is a low-energy thermochemical process that converts wet biomass into a carbon-rich solid, commonly called hydrochar, for use in a variety of areas, such as soil amendment, biofuels or to produce carbon-based materials. The purpose of this paper is to increase knowledge for the economic valorization of municipal wet waste, considered as a raw material to obtain high value-added products through an HTC process and an additional chemical activation procedure. In the first part of the work, a 4.5-liter batch reactor was designed, built, and used in the HTC experimental campaign by varying the main process parameters, namely reaction time, amount and type of organic waste (e.g. vegetables, fruits, bread, pasta), water concentration, temperature and pressure. In addition, some experiments were conducted by applying the steam explosion technique at the end of the HTC process. The HTC results showed that in biomass with high water content, increasing residence time decreases the hydrochar yield. Considering a dry heterogeneous waste with high carbon content, the yields at the end of the process are much higher. In the second part of this work, the hydrochar samples were treated with a high-temperature activation process based on the use of KOH, obtaining activated carbon. Particularly, the best results were achieved by using high KOH: hydrochar ratios, resulting in high-quality activated carbons with good porosity and a high surface area of 2890 m2/g. Finally, an energy analysis was carried out to evaluate how to make the whole process cost-effective.

Response of hydrodynamic environment to land reclamation in Sanmen Bay, China over the last half-century

Sanmen Bay (SMB) is one of the important harbors in Zhejiang Province. It is a semi-enclosed shallow bay that has undergone large-scale land reclamation activities. Long-term reclamation has changed the hydrodynamic conditions of SMB, such as tide, residual current, tidal prism, water exchange capacity, and tidal asymmetry. In this study, three typical periods of numerical models, based on historical charts and remote sensing, were established to investigate the influence of reclamation activities on the hydrodynamic conditions of SMB from 1971 to 2020. These model results reveal that the amplitude and phase of M2, the main tidal components in SMB, decreased by ~0.1–0.3 m and ~ 5°–15°, respectively, over the last half-century. Additionally, under the influence of ~200 km2 reclamation, many hydrodynamic conditions in SMB also changed. This includes the reduction of a residual current and tidal prism, an increase in residence time, and a change in tidal asymmetry characteristics. The residence time in nearby Xiayangtu exhibited a downward trend from 2003 to 2020, because land reclamation squeezed, and thus, enhanced the residual current eddy. The water-exchange capacity of the bay became weaker with the reduction of tidal prism to one-third and an increase in residence time. The tidal asymmetry characteristic of SMB changed from half of flood dominant to fully flood dominant by the influence of shoreline and bathymetry, which raised the flood risk. Research on the response of the hydrodynamic environment to reclamation activities in SMB reminds the local government to reassess the impact of land reclamation on the hydrodynamic environment.

Long‐term stability of phosphate sorbed on an allophanic Andosol and a synthesized allophane

AbstractAllophane and ferrihydrite are the main hosts of phosphate in allophanic Andosols, which are vital soil resources that support high human population densities. However, the sorption mechanism of phosphate on allophane has not been elucidated, unlike that of ferrihydrite. In particular, the effects of residence time on phosphate sorbed on allophane remain unclear. Therefore, the objectives of this study were to (1) understand the effect of residence time on the stability of phosphate sorbed on allophanic Andosol and allophane by desorption experiments using arsenate and (2) elucidate the sorption mechanism of phosphate on allophane using solid‐state 31P nuclear magnetic resonance (NMR). Consequently, the slow sorption of phosphate onto allophanic Andosol, allophane, and ferrihydrite continued for approximately 150 days. The ratio of total desorbable phosphate to phosphate sorbed onto the allophanic Andosol and allophane decreased with increasing residence time. In other words, phosphate sorption on allophanic Andosol and allophane was more irreversible with increasing residence time. The NMR spectra and X‐ray diffraction patterns showed that the molecular environment of phosphate sorbed onto allophane and ferrihydrite did not change at any residence time. Therefore, the slow sorption and irreversibility of phosphate were caused not by surface precipitation but by internal diffusion. In addition, the NMR spectra showed that most of the phosphate sorbed on allophane was present as inner‐sphere complexes.

Adaptive evolution of carbapenem-resistant hypervirulent Klebsiella pneumoniae in the urinary tract of a single patient

The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) is a growing concern due to its high mortality and limited treatment options. Although hypermucoviscosity is crucial for CR-hvKp infection, the role of changes in bacterial mucoviscosity in the host colonization and persistence of CR-hvKp is not clearly defined. Herein, we observed a phenotypic switch of CR-hvKp from a hypermucoviscous to a hypomucoviscous state in a patient with scrotal abscess and urinary tract infection (UTI). This switch was attributed to decreased expression of rmpADC, the regulator of mucoid phenotype, caused by deletion of the upstream insertion sequence ISKpn26. Postswitching, the hypomucoid variant showed a 9.0-fold decrease in mice sepsis mortality, a >170.0-fold reduction in the ability to evade macrophage phagocytosis in vitro, and an 11.2- to 40.9-fold drop in growth rate in normal mouse serum. Conversely, it exhibited an increased residence time in the mouse urinary tract (21 vs. 6 d), as well as a 216.4-fold boost in adhesion to bladder epithelial cells and a 48.7% enhancement in biofilm production. Notably, the CR-hvKp mucoid switch was reproduced in an antibiotic-free mouse UTI model. The in vivo generation of hypomucoid variants was primarily associated with defective or low expression of rmpADC or capsule synthesis gene wcaJ, mediated by ISKpn26 insertion/deletion or base-pair insertion. The spontaneous hypomucoid variants also outcompeted hypermucoid bacteria in the mouse urinary tract. Collectively, the ISKpn26-associated mucoid switch in CR-hvKp signifies the antibiotic-independent host adaptive evolution, providing insights into the role of mucoid switch in the persistence of CR-hvKp.

Effects of flame impingement on the stability and NO/CO emissions of laminar premixed methane-ammonia impinging flame

This study investigates the stable combustion range and CO/NO emissions of laminar premixed CH4-NH3 impinging flames experimentally. Effects of flame impingement on the flame stability and CO/NO formations are analyzed quantitatively. The result shows that the flame impingement improves the flame stability considerably through decelerating the unburned gases velocity in the stagnation region, with smaller nozzle-to-wall distance (H) exerting stronger improvement on the flame stability. The NO emission is increased initially but dropped finally with the increased H. This trend is ascribed to the suppressed NO productions at both small and large H due to the intensive cooling effects of cold wall and ambient air entrainment respectively in consideration of the relatively inferior reactivity of NH3. Additionally, due to the insufficient oxidizer in the fuel-rich flame, the more NH3 molecule can also facilitate the NO destruction via the DeNOx pathways at small or large H. In contrast, the CO emissions show similar variation trends with H like the NO emission for the fuel-lean and stoichiometric flames, while the CO emission has a “N” type variation trend with H for the fuel-rich flames. Since the CH4 reactivity can be improved by the NH3 addition at low temperatures, a low-temperature environment at small H due to the strong cooling effect, as well as more available NH3 in the flame, can effectively highlight the improvement of NH3 on the CH4 reactivity in the fuel-rich flame. This makes for the CO production at small H combined with the insufficient oxidizer and eventually results in the higher CO emission of the fuel-rich flame at small H. Additionally, the decreased CO emission at large H results from the improved CO oxidation that is caused by the increased residence time and more oxidizer from ambient air.

Quartz luminescence sensitivity enhanced by residence time in the critical zone

The emerging use of quartz luminescence properties to characterize Earth-surface processes shows promise, with optically stimulated luminescence (OSL) sensitivity proposed as a valuable tool for provenance or sediment history tracing. However, the geologic processes that lead to quartz sensitization remain unclear. Here we study the impact of source rock and surface processes on the luminescence properties of quartz sand from bedrock and modern and Late Pleistocene alluvium generated from a mountainous catchment in northern Utah, USA. Continuous wave and linear modulated OSL are used to characterize the luminescence sensitivity and intensity of the fast-decay component. We compare the OSL sensitivity with sand-grain provenance and with proxies for surface processes such as topographic metrics, cosmogenic 10Be-derived erosion rates, chemical weathering indices, and magnetic susceptibility. Late Pleistocene sediment has low OSL sensitivity and a weak fast-decay component, similar to bedrock samples from the source area. In contrast, modern alluvium is dominated by the fast-decay component and has higher and more variable OSL sensitivity, with no clear relationship to upstream bedrock source. There is, however, an inverse relationship between OSL sensitivity and catchment-averaged erosion rates and a positive relationship with chemical weathering indices and magnetic susceptibility. These metrics suggest that the modern alluvium has experienced increased residence time in the shallow critical zone compared to the Late Pleistocene sediments. We suggest that changes in hillslope processes between the effectively wetter, cooler Pleistocene and the dryer, warmer conditions of the Holocene enhanced the luminescence properties. The results suggest that climatic controls on rates and processes of chemical and mechanical weathering and sediment transport and residence within the critical zone are encoded in the luminescence properties of quartz sand.

Linking reservoir annual residence time to nitrogen deposition using paleolimnological techniques

In river networks, reservoirs are hotspots for nutrient transformations, providing multiple pathways for nitrogen processing. One of the less measured pathways is nitrogen deposition. Here, we investigated the decadal relationship between water residence time and nitrogen deposition using sediment cores from eight mainstem reservoirs within a river system containing two contrasting watersheds. One watershed was significantly urbanized with regulated flow and the other watershed was unregulated with extensive rural land use. We explored the relationship of sediment nitrogen concentrations across a range of residence times, land uses, and other parameters throughout this linked river-reservoir system. Results show that average annual residence time had the strongest relationship to nitrogen deposition when compared to reservoir volume, mean depth, surface area, outflow, and land use. Pigment analysis revealed that residence time influences nitrogen by allowing for longer periods of algal uptake, followed by deposition in particulate organic form. Supporting this mechanism, sedimentary C:N, with low values representing greater algal influence, expressed a strong and negative relationship with average annual residence time, as well as a positive relationship between residence time and photosynthetic pigments diagnostic of cyanobacteria, diatoms, and a combination of green algae+cyanobacteria. Furthermore, we investigated how drought conditions could alter residence times and intensify nitrogen cycling through primary productivity in reservoirs. Drought increased residence time by 45–60 %. This increase was estimated to raise sediment nitrogen concentrations by roughly 2.5–4 %.

Modeling the settling and resuspension of microplastics in rivers: Effect of particle properties and flow conditions

Microplastics have numerous different shapes, affecting the fate and transport of these particles in the environment. However, theoretical models generally assume microplastics to be spherical. This study aims to develop a modeling approach that incorporates the shapes of microplastics to investigate the vertical transport of microplastics in rivers and simulate the effect of particle and flow characteristics on settling and resuspension. To achieve these aims, a mechanistic model was developed utilizing the mass-balance and hydrodynamic equations. Scenario analysis was implemented assigning different values to model parameters, such as bed shear stress, shape factor and particle size to simulate the effect of flow patterns and particle properties. The model outcomes revealed that the residence time of microplastics in the water column was longest in medium bed shear stress, whilst it was shortest in low bed shear stress. This suggests that the influence of turbulence is not unidirectional; it can both increase and decrease microplastic concentrations and residence time in the water column. According to the scenario analysis, the settling flux of microplastics was the highest for near-spherical particles and increased with the size of the particles, as well as with increasing bed shear stress. However, the resuspension of particles was primarily influenced by increasing bed shear stress, but the ranking of resuspension flux values for different shaped and sized microplastics exhibited alterations with changing flow patterns. Turbulent conditions predominantly influenced the resuspension of near-spheres and large microplastics. On the contrary, the settling of fibers and small microplastics were significantly influenced by changing flow patterns, whereas near-spheres and largest particles were least affected. The model results were sensitive to changes in shape factor developed for this model, therefore this parameter should be improved in future studies.

Simulation of anaerobic biodegradation process in a tubular bioreactor with a biofilm layer: Steady-state and unsteady-state conditions

In this paper, anaerobic biodegradation process in a tubular bioreactor with an inner biofilm layer for steady-state and unsteady-state conditions are simulated. The effects of various parameters including bioreactor diameter, fraction of active biomass transferred to liquid phase, and residence time of the liquid on bioreactor performance are examined. Simulations indicate that decreasing diameter of bioreactor leads to increasing degree of conversion of the substrate in liquid phase and decreasing dimensionless concentration of the substrate in biofilm. With an increase in the fraction of active biomass transferred to liquid, substrate concentrations in liquid and biofilm slightly vary. Increased residence time of the liquid phase results in the degree of conversion of substrate goes up, but substrate concentration in biofilm lowers a little. In addition, it is found that biomass concentration of liquid phase is boosted with decreased bioreactor diameter and increased residence time of liquid. A proportional-integral controller is designed and the tuned parameters of KP=−0.131 and KI=0.02 are obtained using genetic algorithm. It is observed that controller regulate well the degree of conversion of the substrate within 120 s for both servo and regulatory modes.

Understanding Salinity Intrusion and Residence Times in a Small-Scale Bar-Built Estuary under Drought Scenarios: The Maipo River Estuary, Central Chile

The Maipo River estuary is a low-inflow bar-built estuary that includes a protected wetland, which harbors a rich ecosystem. The estuary and wetland have been threatened by a persistent drought for more than a decade, which has resulted in greater salinity intrusion and increased residence times. Previous studies have described salinity and pollutants in estuaries; however, almost all have focused on deeper and/or wider estuaries with dimensions much larger than those of the small-scale Maipo River estuary. In this study, we used the numerical model FVCOM to simulate the dynamics of the Maipo River estuary under drought scenarios and explored the interactions between river discharge and tides in terms of saline intrusion and particle dispersal. The model was validated against observations collected during a field campaign near the river mouth. The simulations successfully reproduced the water surface elevation but underestimated salinity values, such that the vertical salinity structure observed in the field was not captured by the model in this shallow and morphologically complex estuary. Consequently, our model results provide qualitative insight related to salinity and baroclinic dynamics. Results of maximum saline intrusion showed an exponential decay with increasing river discharge, and the analysis of salinity intrusion time series revealed that droughts may cause permanent non-zero salinity levels in the estuary, potentially affecting ecological cycles. The incorporation of passive tracers showed that decreasing river discharge increases the residence time of particles by allowing the tracers to re-enter the estuary. Model results showed the formation of accumulation zones (hotspots) in the shallower zones of the estuary.

Multi-decadal geochemical evolution of drainage from underground coal mines in the Appalachian basin, USA

Coal mine drainage (CMD) in Appalachia is a widespread source of dissolved metals, SO4, and acidity that can degrade aquatic habitats and water supplies for decades following mine closure and flooding. In the bituminous coalfield of Pennsylvania, the Irwin Coal Basin (ICB) contains a series of partly to completely flooded, abandoned underground mines separated by leaky barriers within the Pittsburgh coal seam. CMD originated throughout the basin from minepool aquifers that formed after mine closures dating from 1910 to 1957. Historical and recent water quality data for eight CMD sites across the ICB, plus mineralogy and cation-exchange capacity of overburden lithologies, were analyzed to quantify important reactants and evaluate spatial and temporal water-quality trends. As overburden thickness and residence time increase along a ~ 50-km flowpath northeast to southwest in the basin, CMD becomes more alkaline, and Na concentrations increase. Since the 1970s, all eight ICB discharges have become less acidic, with exponential decreases in acidity, SO4, and Fe concentrations; only two CMD remain net-acidic (acidic pH at equilibrium). Exponential decay models that include a steady-state asymptote consistent with background groundwater chemistry and siderite equilibrium describe the early-stage, rapid contaminant concentration decay immediately after the “first flush” (initial flooding) and the progressive evolution toward late-stage background conditions. A geochemical evolution PHREEQC model indicates that spatial and temporal trends in pH, net-acidity, SO4, Fe, and major cations could be explained by the continuous dilution of first flush water by ambient groundwater combined with sustained water-mineral reactions involving pyrite and carbonates (calcite, dolomite, siderite) plus cation-exchange by clays (illite, chlorite, mixed-layer illite/smectite). These data and model results indicate that 1) cation-exchange reactions enhance calcite dissolution and alkalinity production, resulting in the evolution of CMD to Na-SO4-HCO3 type waters, and 2) siderite equilibrium could maintain dissolved Fe >16 mg/L over the next 40 years.

Bitopic Ligands Support the Presence of a Metastable Binding Site at the β2 Adrenergic Receptor.

Metastable binding sites (MBS) have been observed in a multitude of molecular dynamics simulations and can be considered low affinity allosteric binding sites (ABS) that function as stepping stones as the ligand moves toward the orthosteric binding site (OBS). Herein, we show that MBS can be utilized as ABS in ligand design, resulting in ligands with improved binding kinetics. Four homobivalent bitopic ligands (1-4) were designed by molecular docking of (S)-alprenolol ((S)-ALP) in the cocrystal structure of the β2 adrenergic receptor (β2AR) bound to the antagonist ALP. Ligand 4 displayed a potency and affinity similar to (S)-ALP, but with a >4-fold increase in residence time. The proposed binding mode was confirmed by X-ray crystallography of ligand 4 in complex with the β2AR. This ligand design principle can find applications beyond the β2AR and G protein-coupled receptors (GPCRs) as a general approach for improving the pharmacological profile of orthosteric ligands by targeting the OBS and an MBS simultaneously.

Evaluation of industrial performance of a new three phase fluidized bed flotation column-Based on product size characterization

There are still a large number of minerals processed by flotation every year, so it is extremely important to improve the flotation efficiency in industrial production. This study established an experimental test platform for new three-phase fluidized bed flotation column (TFC). The effects of different operating conditions and equipment parameters (apparent gas velocity, apparent liquid velocity, and filling height) on separation effect of coal slime were investigated. Relationship between turbulence intensity inside TFC and the flotation effect of coal slime with different particle sizes was analyzed. Results show that turbulence intensity in fluidized environment can be influenced by adjusting operating conditions to increase the probability of adhesion and collision of fine-grained particles with air bubbles. Differences of particle size distribution in the radial and axial directions of TFC are influenced by settling velocity. Increasing circulation volume can increase residence time of particles in flotation process. Micro and nano bubbles have excellent characteristics which are beneficial to particle collision and adhesion. By adjusting the parameters, it can meet needs of mineral separation and mineralization environment and realize effective recovery of slime with different particle sizes. This study was conducted by analyzing the flotation of fine particles by TFC during industrial platform testing. By evaluating the industrial performance of TFC, it provides a reference for future industrial large-scale applications.