Longer Residence Time Research Articles

Large eddy simulation of soot evolution in turbulent nonpremixed bluff body flames

Large Eddy Simulation (LES) is utilized to investigate soot evolution in a series of turbulent nonpremixed bluff body flames featuring different bluff body diameters. The modeling framework relies on recent development in the soot subfilter Probability Density Function (PDF) model that can correctly account for the distribution of soot with respect to mixture fraction, correcting errors in previous soot subfilter PDF models that significantly overpredict soot oxidation. With the previous soot subfilter PDF model, no soot was observed outside of the recirculation zone in past studies on similar bluff body flames. Results obtained with the current LES modeling approach compare favorably with the experimental measurements of the flow field and the soot volume fraction. Notably, the current LES modeling approach correctly predicts large soot volume fractions in the recirculation zone, a decrease in the soot volume fraction through the high-strain neck region, and then an increase again in the downstream jet-like region. Consistent with the experimental measurements, the larger bluff body diameter, with its larger recirculation zone with longer residence times, generates more soot in the recirculation zone and also more soot in the high-strain neck region. Analysis of the soot volume fraction source terms lead to mechanistic understanding of soot evolution in the entirety of the bluff body flames. Most of the soot generated in the recirculation zone is oxidized but some escapes unoxidized and is passively transported through the neck region. Virtually no new soot forms in the downstream jet-like region, and the increase in the soot volume fraction in the jet-like region is due to acetylene-based surface growth of the soot transported through the neck region. This mechanism could not be predicted with the previous soot subfilter PDF model, with the recent soot subfilter PDF model being critical in the understanding of this basic mechanism.

Development of a novel oral complex lipid emulsion containing triptolide for targeting pancreatic cancer

Triptolide (TP), a diterpenoid triepoxide, exhibits strong anti-cancer activities, especially against pancreatic cancer, but its clinical application is limited by organ toxicity. TP was combined with diammonium glycyrrhizinate (DG), as a cytoprotective agent, in a novel oral complex lipid emulsion (TP/DG-CLE) to increase the therapeutic index of TP against pancreatic cancer. The emulsion was produced by subjecting phospholipid and active components to high shear conditions using high-pressure homogenisation resulting in droplets of essentially neutral or small positive charge and consistent size below 200 nm. Pharmacokinetic studies in Sprague Dawley rats revealed an AUC(0–8 h) of TP following oral dosing of TP/DG-CLE that was fourfold higher than that achieved for TP/DG suspension, demonstrating significantly higher TP bioavailability and longer residence time in the bloodstream. Tissue distribution data obtained in mice demonstrated that TP/DG-CLE having a TP/DG weight ratio of 1:22.5 preferentially accumulated in the pancreas. Moreover, toxicology assays in rats provided indications of minor liver damage following daily administration of the emulsion for two weeks. Together these studies establish complex lipid emulsions containing TP and DG as a promising oral formulation for treatment of pancreatic cancer and establish a platform for developing new chemotherapeutic treatments.

Experimental and kinetic study of heavy metals transformation in supercritical water gasification of oily sludge

As an industrial organic waste, oily sludge can be transformed into valuable syngas by supercritical water gasification (SCWG) technology. The transformation behaviors of heavy metals in SCWG of oily sludge must be considered to prevent the secondary pollution attributed to the high contents of heavy metals in oily sludge. In this work, the gasification products distribution after SCWG of oily sludge in a batch reactor under different reaction conditions (550–700 °C, 1–15 min) was studied. The distributions of heavy metals (Cu, Cr and Zn) in different forms including acid-soluble and exchangeable fraction (F1), reducible fraction (F2), oxidizable fraction (F3), residual fraction (F4) and heavy metal ions in liquid residues (M+) were presented and the transformation trend of those five fractions during the SCWG process was demonstrated. A reaction pathway and quantitative kinetic model of Zn transformation in SCWG were proposed. The results indicated that gas yield was enhanced at higher reaction temperature and longer residence time. Heavy metals in oily sludge were mainly composed of F3 and M+, they tended to deposit in F4 with increasing reaction temperature and residence time, which was stable and environmentally harmless. F3 showed better reactivity than F2 and contributed more to the formation of F4. Enhancing the transformation of Zn ions in liquid residues to more stable forms was necessary. This study highlighted that SCWG of oily sludge could realize energy utilization and heavy metals stabilization.

Structure-Kinetic Relationship Studies for the Development of Long Residence Time LpxC Inhibitors.

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a promising drug target in Gram-negative bacteria. Previously, we described a correlation between the residence time of inhibitors on Pseudomonas aeruginosa LpxC (paLpxC) and the post-antibiotic effect (PAE) caused by the inhibitors on the growth of P. aeruginosa. Given that drugs with prolonged activity following compound removal may have advantages in dosing regimens, we have explored the structure-kinetic relationship for paLpxC inhibition by analogues of the pyridone methylsulfone PF5081090 (1) originally developed by Pfizer. Several analogues have longer residence times on paLpxC than 1 (41 min) including PT913, which has a residence time of 124 min. PT913 also has a PAE of 4 h, extending the original correlation observed between residence time and PAE. Collectively, the studies provide a platform for the rational modulation of paLpxC inhibitor residence time and the potential development of antibacterial agents that cause prolonged suppression of bacterial growth.

Stable isotope profiles of soil organic carbon in forested and grassland landscapes in the Lake Alaotra basin (Madagascar): insights in past vegetation changes

Abstract. The extent to which the central highlands of Madagascar were once covered by forests is still a matter of debate: while reconstructing past environments is inherently difficult, the debate is further hampered by the fact that the evidence documenting land cover changes and their effects on carbon and sediment dynamics in Madagascar has hitherto mainly been derived from lake coring studies. Such studies provide an integrated view over relatively large areas but do not provide information on how land-use change affects hillslopes in terms of carbon and sediment dynamics. Such information would not only be complementary to lake inventories but may also help to correctly interpret lake sediment data. Carbon stable isotope ratios (δ13C) are particularly useful tracers to study the past dynamics of soil carbon over time spans ranging from years to millennia and thus to understand the consequences of land-use change over such time spans. We analysed soil profiles down to a depth of 2 m from pristine forests and grasslands in the Lake Alaotra region in central Madagascar. Along grassland hillslopes, soil organic carbon (SOC) content was low, from 0.4 % to 1.7 % in the top layer, and decreased rapidly to ca. 0.2 % below 100 cm depth. The current vegetation predominantly consists of C4 grasses (δ13C ∼ −13 ‰), yet topsoil δ13C-OC ranges between −23.0 ‰ and −15.8 ‰, and most profiles show a decrease in δ13C-OC with depth. This contrasts with our observations in the C3-dominated forest profiles, which show a typical profile whereby δ13C values increase slightly with depth. Moreover, the SOC stock of grasslands was ∼ 55.6 % lower than along the forested hillslopes for the upper 0–30 cm layer. δ13C values in grassland and forest profiles converge to similar values (within 2.0 ± 1.8 ‰) at depths below ∼ 80 cm, suggesting that the grasslands in the Lake Alaotra region have indeed developed on soils formerly covered by a tree vegetation dominated by C3 plants. We also observed that the percent of modern carbon (pMC) of the bulk OC in the top, middle and lower middle positions of grasslands was less than 85 % near the surface. This could reflect a combination of (i) the long residence time of forest OC in the soil, (ii) the slow replacement rate of grassland-derived OC (iii) and the substantial erosion of the top positions towards the valley position of grasslands. At the valley positions under grassland, the upper 80 cm contains higher amounts of recent grass-derived OC in comparison to the hillslope positions. This is likely to be related to the higher productivity of the grassland valleys (due to higher moisture and nutrient availability), and the deposition of OC that was eroded further upslope may also have contributed. The method we applied, which is based on the large difference in δ13C values between the two major photosynthetic pathways (C3 and C4) in (sub-)tropical terrestrial environments, provides a relatively straightforward approach to quantitatively determine changing vegetation cover, and we advocate for its broader application across Madagascar to better understand the island's vegetation history.

Protein-coated microplastics corona complex: An underestimated risk of microplastics

Traditionally, toxicity of microplastics is ascribed to the chemicals adsorbed on them. However, microplastics can also interact with biomolecules, such as secretory proteins from aquatic organisms, and form protein-coated microplastics corona complex with unknown toxic effects. Here, we investigated the toxic effects of polystyrene microplastics (PS) and bovine serum albumin (BSA) coated PS corona complex (PS + BSA) on adult zebrafish (Danio rerio) intestines. The food intake ratio, accumulation and distribution of microplastics, histopathological changes, and molecular effects related to the antioxidant system in the intestine were studied. For the first time, we observed that PS + BSA aggregated on the inner surface of the zebrafish intestine, whereas PS dispersed. The aggregation of PS + BSA resulted in increased microplastics accumulation and longer residence time in the zebrafish intestine, which inhibited food intake and generated reactive oxygen species (ROS) in the intestine. Furthermore, the functions of the Keap1-Nrf2-ARE antioxidant signaling pathway and the activation of antioxidant enzymes were significantly affected by PS + BSA after a 21-day exposure. Ultimately, a higher accumulation of ROS and stronger inhibition of antioxidants led to more severe intestinal injury. These results suggest that the increased toxicity of protein-coated microplastics corona complex may be affected by oxidative damage and can result in the inhibition of digestion due to their aggregation and longer residence time in the intestine. Therefore, the ecological risk of microplastics may be underestimated owing to the interactive mechanisms of microplastics and protein coronas.

Remediation of Aqueous Phosphate Agricultural Runoff Using Slag and Al/Mg Modified Biochar

Slag and Al/Mg oxide modified Douglas fir biochar (AMOB) were compared for their phosphate adsorbing abilities for use individually or in combination for simulated agriculture run-off remediation in wetlands. Aqueous batch and column sorption experiments were performed for both low-cost materials. AMOB was prepared in bulk using a novel green method. Material analyses included XRD, elemental analysis, SEM, EDX, and BET. Biochar and slag have different phosphate removal mechanisms. In short residence times (≤2 h), adsorption phenomena dominate for both adsorbents. Surface area likely plays a role in adsorption performance; slag was measured to be 4.1 m2/g while biochar’s surface area was 364.1 m2/g. In longer residence times (>2 h), the slow leaching of metals (Ca, Al, and Mg) from slag continue to remove phosphate through the precipitation of metal phosphates. In 24 h, slag removed more free phosphate from the solution than AMOB. Preliminary fixed bed column adsorption of slag or AMOB alone and in tandem was performed adopting a scaled-up model that can be used to remediate agricultural runoff with high phosphate content. Additionally, a desorption study was performed to analyze the efficiency of material regeneration. While AMOB does not release any adsorbed phosphates, slag slowly releases 5.7% adsorbed phosphate over seven days.

Transport and deposition of inhaled man‐made vitreous and asbestos fibers in realistic human respiratory tract models: An in silico study

AbstractParticles longer than 5 μm and with a length/diameter ratio >3 are defined as fibers. Asbestos or other fibers are still identified in residential environments due to the emission from asbestos‐used building materials. The respiratory system is the primary route of asbestos exposure; under a longer residence time, asbestos‐related adverse health effects are inevitable. Currently, asbestos fibers have been replaced with man‐made vitreous fibers (MMVFs); however, studies have revealed some similar biological effects of MMVFs with asbestos. Therefore, MMVFs‐induced diseases need to be determined by analyzing their deposition characteristics and foci in human respiratory tracts. In this study, we used computational fluid dynamics method to investigate fibers' airflow and deposition patterns in two realistic human respiratory models. Two drag models were used to predict the deposition of uniform 1 μm (asbestos) and 3.66 μm (carbon fiber‐CF) diameter, 15–300 μm long fibers. Two drag models provided comparable results with the experimental data. Comparatively, asbestos deposition was independent of fiber length, while CF deposition increased proportionally to fiber length. The highest level of local deposition was detected in the anterior nasal cavity. The results obtained from this study can extend current knowledge of human vitreous fiber exposure‐related lung diseases.

Evolution of N2O production at lean combustion condition in NH3/H2/air premixed swirling flames

In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures.

Investigation of the Effects of Torrefaction Temperature and Residence Time on the Fuel Quality of Corncobs in a Fixed-Bed Reactor

Biomass from agriculture is a promising alternative fuel due to its carbon-neutral feature. However, raw biomass does not have properties required for its direct utilization for energy generation. Torrefaction is considered as a pretreatment method to improve the properties of biomass for energy applications. This study was aimed at investigating the effects of torrefaction temperature and residence time on some physical and chemical properties of torrefied corncobs. Therefore, a fixed-bed torrefaction reactor was developed and used in the torrefaction of corncobs. The torrefaction process parameters investigated were the torrefaction temperature (200, 240, and 280 °C) and the residence time (30, 60, and 90 min). The effects of these parameters on the mass loss, grindability, chemical composition, and calorific value of biomass were investigated. It was shown that the mass loss increased with increasing torrefaction temperature and residence time. The grinding throughput of the biomass was improved by increasing both the torrefaction temperature and the residence time. Torrefaction at higher temperatures and longer residence times had greater effects on the reduction in particle size of the milled corncobs. The calorific value was highest at a torrefaction temperature of 280 °C and a residence time of 90 min. The energy yield for all treatments ranged between 92.8 and 99.2%. The results obtained in this study could be useful in the operation and design of torrefaction reactors. They also provided insight into parameters to be investigated for optimization of the torrefaction reactor.

D-VITylation: Harnessing the biology of vitamin D to improve the pharmacokinetic properties of peptides and small proteins

Peptides have great potential to be potent and specific therapeutics, yet their small size leads to rapid glomerular filtration, which severely limits therapeutic applications. Although conjugation of small proteins to large polymers typically results in longer residence times, these conjugates often have a significant loss of biological activity due to steric hindrance. Here, we improve the pharmacokinetics (PK) of peptide therapeutics by harnessing the biology of vitamin D. Attachment of a small vitamin D-based molecule (D-VITylation) protects the conjugated peptide or protein from renal clearance by virtue of reversible binding to the serum-circulating vitamin D binding protein (DBP), without compromising bioactivity. Varying the conjugation site on vitamin D affects the binding to DBP, with higher affinity corresponding to a longer plasma half-life. We also demonstrate the important contribution of the peptide to the overall PK, likely due to alternative clearance mechanisms such as protease degradation and receptor-mediated cellular uptake. With a Fab antibody fragment, for which these alternate clearance mechanisms are not significant, D-VITylation increases the half-life of elimination from 14 to 61 h in rats. The PK profile in minipigs and projected lifetime in humans suggest that D-VITylation is a viable strategy to achieve once-weekly dosing of peptide therapeutics in humans.

C–H Bond Activation and C–C Coupling of Methane on a Single Cationic Platinum Center: A Spectroscopic and Theoretical Study

We spectroscopically investigated the activation products resulting from reacting one and multiple methane molecules with Pt+ ions. Pt+ ions were formed by laser ablation of a metal target and were cooled to the electronic ground state in a supersonic expansion. The ions were then transferred to a room temperature ion trap, where they were reacted with methane at various partial pressures in an argon buffer gas. Product masses observed were [Pt,C,2H]+, [Pt,2C,4H]+, [Pt,4C,8H]+, and [Pt,2C,O,6H]+, which were mass-isolated and characterized using infrared multiple-photon dissociation (IRMPD) spectroscopy employing the free electron laser for intra-cavity experiments (FELICE). The spectra for [Pt,2C,4H]+ and [Pt,4C,8H]+ have several well-defined bands and, when compared to density functional theory-calculated spectra for several possible product structures, lead to unambiguous assignments to species with ethene ligands, proving Pt+-mediated C–C coupling involving up to four methane molecules. These findings contrast with earlier experiments where Pt+ ions were reacted in a flow-tube type reaction channel at significantly higher pressures of helium buffer gas, resulting in the formation of a Pt(CH3)2+ product. Our DFT calculations show a reaction barrier of +0.16 eV relative to the PtCH2+ + CH4 reactants that are required for C–C coupling. The different outcomes in the two experiments suggest that the higher pressure in the earlier work could kinetically trap the dimethyl product, whereas the lower pressure and longer residence times in the ion trap permit the reaction to proceed, resulting in ethene formation and dihydrogen elimination.

Intensification of Acidogenic Fermentation for the Production of Biohydrogen and Volatile Fatty Acids—A Perspective

Utilising ‘wastes’ as ‘resources’ is key to a circular economy. While there are multiple routes to waste valorisation, anaerobic digestion (AD)—a biochemical means to breakdown organic wastes in the absence of oxygen—is favoured due to its capacity to handle a variety of feedstocks. Traditional AD focuses on the production of biogas and fertiliser as products; however, such low-value products combined with longer residence times and slow kinetics have paved the way to explore alternative product platforms. The intermediate steps in conventional AD—acidogenesis and acetogenesis—have the capability to produce biohydrogen and volatile fatty acids (VFA) which are gaining increased attention due to the higher energy density (than biogas) and higher market value, respectively. This review hence focusses specifically on the production of biohydrogen and VFAs from organic wastes. With the revived interest in these products, a critical analysis of recent literature is needed to establish the current status. Therefore, intensification strategies in this area involving three main streams: substrate pre-treatment, digestion parameters and product recovery are discussed in detail based on literature reported in the last decade. The techno-economic aspects and future pointers are clearly highlighted to drive research forward in relevant areas.

Throughfall drop sizes suggest canopy flowpaths vary by phenophase

Water flowpaths caused by incident rainfall onto forest canopy surfaces have a notable effect on the water budgets and chemistry of wooded ecosystems. This study revealed varying canopy flowpaths and residence times at the intra-event scale and across the phenological transition from leafed to leafless states for a set of three American beech (Fagus grandifolia Ehrh.) trees in a multilayered canopy. Simultaneous measurements of raindrops and throughfall drops by fifteen laser disdrometers over five rain events were analyzed during the transition from leafed to leafless phenophases. Throughfall was partitioned into free throughfall, splash throughfall, and canopy drip with four drop size classes. Throughfall drop size distributions and volume of each throughfall type varied at both intra-event and inter-event scales. Smaller canopy drips, <5.5 mm in diameter, were initiated earlier in rain events, whereas more rainfall accumulation was necessary to generate larger canopy drips, >5.5 mm in diameter. Smaller canopy drips were more dominant in the leafed phenophase when some structurally-mediated woody surface drip points were more muted. These results suggested throughfall from foliar surfaces generated smaller-sized canopy drip with shorter residence time, whereas throughfall from structurally-mediated woody surface drip points generated larger-sized canopy drip with longer residence time. There was also an increase in both free throughfall and splash droplets from leafed to leafless states, consistent with increased canopy gaps and direct interaction with woody surfaces in the leafless state. Based on the results, a conceptualization of the genesis and development of leaf and branch flowpaths in canopies is proposed.

Spatial Distributions of Riverine and Marine Dissolved Organic Carbon in the Western Arctic Ocean: Results From the 2018 Korean Expedition

AbstractSeasonal primary production and river discharge increases in the Arctic Ocean exert a significant influence on the dissolved organic carbon (DOC) cycle. To improve our knowledge of the spatial heterogeneity of DOC source and concentration in the rapidly changing Arctic Ocean, we investigated the distributions of riverine and marine DOC in the western Arctic Ocean during the summer of 2018. Although the surface bulk DOC concentration indicated no clear distinction in its distribution between the Chukchi Borderland (CBL)/northern Chukchi Sea (NCS) and East Siberian Sea (ESS)/Mendeleyev Ridge (MR) regions, the estimated riverine DOC concentration (28 ± 4.2 μM C) and its contribution (40 ± 5.7%) in the surface layer of the CBL/NCS region were higher than those (19 ± 5.6 μM C and 26 ± 8.5%) in the ESS/MR region, which was attributed to the accumulation of freshwater, strong stratification, and a longer residence time in the CBL/NCS region. In contrast, although marine DOC was the dominant DOC component in both the CBL/NCS and ESS/MR regions, the higher marine DOC concentration (54 ± 8.1 μM C) and its contribution (73 ± 8.2%) in the East Siberian shelf/slope region were consistent with high bacterial abundance, which was associated with extremely high surface phytoplankton blooms sustained by nutrient supply from the deep layer, suggesting that the supply of bioavailable DOC resulted in active bacterial activities. Overall, the spatial differences in water properties between the two regions had large influences on the regional distributions of riverine and marine DOC.

Charged movement characteristics and enhanced removal of fine particles under the electric fields coupling with turbulence from industrial flue gas

Fine particulate matters emitted from the industrial flue gas are the primary reason for the serious haze problem. The agglomeration has been proven an effective method to improve fine particle removal efficiency, but the movement characteristics in the process and their effects on the agglomeration are unclear. In this study, the agglomeration and the underlying mechanisms in the various electric fields were investigated. The results showed that the removal efficiency of fine particles can reach near 80% under the coupling effect of turbulence and cross discharge electrode, and the particle size can be increased by 30% simultaneously. The electric field intensity with cross electrode approached 650,000 V/m and higher than another three conventional electrodes with 60,000–200,000 V/m. The residence time of fine particle was extended to 0.2 s in the electric field with cross electrodes, and the deviate distance from the discharge electrode was nearly 3 times than other electrodes. The longer residence time and the more disordered movements can make fine particles carry more charge amounts and have more opportunities to finish coagulations. This study discussed the charged particles movement characteristics under the electric fields coupling with turbulence, and explored the further effects on the agglomeration and removal of fine particles. It’s designed to provide the guidance for the setting and improvement of electric fields in the dust removal equipment.

Hydrogeology of an urban weathered basement aquifer in Kampala, Uganda

Weathered basement aquifers are vital sources of drinking water in Africa. In order to better understand their role in the urban water balance, in a weathered basement aquifer in Kampala, Uganda, this study installed a transect of monitoring piezometers, carried out spring flow and high-frequency groundwater level monitoring, slug tests and hydrochemical analyses, including stable isotopes and groundwater residence time indicators. Findings showed a typical weathered basement aquifer with a 20–50-m thickness. Groundwater recharge was 3–50 mm/year, occurring during sustained rainfall. Recharge to a deep groundwater system within the saprock was slow and prolonged, while recharge to the springs on the valley slopes was quick and episodic, responding rapidly to precipitation. Springs discharged shallow groundwater, mixed with wastewater infiltrating from onsite sanitation practices and contributions from the deeper aquifer and were characterised by low flow rates (< 0.001 m3/s), low pH (<5), high nitrate values (61–190 mg/L as NO3), and residence times of <30 years. The deeper groundwater system occurred in the saprolite/saprock, had low transmissivity (< 1 × 10−5 m2/s), lower nitrate values (<20 mg/L as NO3), pH 6–6.5 and longer residence times (40–60 years). Confined groundwater conditions in the valleys were created by the presence of clay-rich alluvium and gave rise to artesian conditions where groundwater had lower nitrate concentrations. The findings provide new insights into weathered basement aquifers in the urban tropics and show that small-scale abstractions are more sustainable in the deeper groundwater system in the valleys, where confined conditions are present.

The Small-Scale Flow Field Around Dipsastraea favus Corals

Key biological processes that are related to feeding, growth, and mortality in corals and other benthic organisms, depend on the flow field around them. For example, in the absence of flow, oxygen is accumulated inside and around photoautotrophic organisms such as algae and corals, and the rate of photosynthesis is therefore reduced. When mixing by turbulence and by streamline separation is suppressed, nutrient supply is reduced and prey capture becomes insufficient. Despite the overwhelming ecological impacts of flow on corals, almost no in-situ studies focused on the hydrodynamics at the scale of the coral polyps and their tentacles. Here we report on in-situ measurements obtained by an underwater Particle Image Velocimetry (PIV) above the tentacles of the massive coral Dipsastraea favus. The tentacles in this species, approximately 5-10 mm long, extend during the night and contract during the day. A comparison was made between the flow field around the coral when the tentacles were contracted and extended. As in large-scale canopy flows such as forests or urban areas, we found that when the tentacles were extended, a mixing layer rather than a boundary layer was formed above the coral. Velocities in between the tentacles were reduced, resident time increased, and velocity instabilities developed around the tentacle tips. Our in-situ measurements under the conditions of contracted tentacles agreed well with laboratory measurements obtained above dead skeletons of D. favus. When the tentacles were extended, a velocity profile typical for canopy flows developed, having a clear inflection point near the interface between the tentacles and the layer of free flow. The relative velocity fluctuations increased up to 3.5-fold compared with the state of contracted tentacles. The highest mixing was around the distal ends of the tentacles, where knob-like spheres named acrospheres contain extremely high concentrations of nematocytes. The intense mixing, the ensuing slowing down of prey movement, and its longer residence time within that zone may augment prey capture by the coral. These findings can explain the ubiquitous occurrence of acrospheres in benthic cnidarians.

Flame confinement in biomass combustion systems for particles abatement

This work explores the use of open-pore, inert ceramic foams with different pore sizes as particle abatement systems in small biomass combustion systems. Porous foams made of silicon carbide with pore sizes 10 to 60 pores-per-inch were installed in an in-house designed combustion unit operated with wood pellets. Their effects on the temperature distribution inside the chamber, particulate and gases emissions were studied using different airflow rates in the reaction-limited regime (low equivalence ratio) to minimise stoichiometric factors. The influence of pore size, foam position with respect to the flame and space velocity were assessed. The confinement of the flame with inert foams was found to substantially modify the temperature distribution in the combustion chamber, improve the air-fuel mixture, and favour the thermal decomposition of the pellet, leading to a reduction in particulate emissions when compared to free-flame combustion at the same experimental conditions. In general, the amount of particulate matter was found to decrease by up to one order of magnitude as the pore size of the foam was reduced, while the temperature gradient in the combustion chamber was increased. Nitrogen oxides and carbon dioxide emissions were essentially unchanged, irrespectively of the pore size of the foam. It is expected that these values will be improved with longer residence times, as happens in operations with reduced excess air ratios. These results suggest that it is possible to control pollutants derived from domestic heating within the most restrictive current regulations on particulate emissions by integrating flame confinement designs with better operating practices and efficient abatement systems.

Treatment of Wastewater, Phenols and Dyes Using Novel Magnetic Torus Microreactors and Laccase Immobilized on Magnetite Nanoparticles.

In this work, the design, manufacture, and testing of three different magnetic microreactors based on torus geometries (i.e., one-loop, two-horizontal-loop, and two-vertical-loop) is explored to increase the enzyme-based transformation of dyes by laccase bio-nanocomposites, improve the particle suspension, and promote the interaction of reagents. The laccase enzyme was covalently immobilized on amino-terminated silanized magnetite nanoparticles (laccase-magnetite). The optimal configuration for the torus microreactor and the applied magnetic field was evaluated in silico with the aid of the CFD and particle tracing modules of Comsol Multiphysics®. Eriochrome Black T (EBt) dye was tested as a biotransformation model at three different concentrations, i.e., 5 mg/L, 10 mg/L, and 20 mg/L. Phenol oxidation/removal was evaluated on artificial wastewater and real wastewater. The optimal catalytic performance of the bionanocomposite was achieved in the range of pH 4 to 4.5. A parabolic movement on the particles along the microchannels was induced by the magnetic field, which led to breaking the stability of the laminar flow and improving the mixing processes. Based on the simulation and experiments conducted with the three geometries, the two-vertical-loop microreactor demonstrated a better performance mainly due to larger dead zones and a longer residence time. Additionally, the overall dye removal efficiencies for this microreactor and the laccase-magnetite bionanocomposite were 98.05%, 93.87%, and 92.74% for the three evaluated concentrations. The maximum phenol oxidation with the laccase-magnetite treatment at low concentration for the artificial wastewater was 79.89%, while its phenol removal efficiency for a large volume of real wastewater was 17.86%. Treatments with real wastewater were carried out with a larger volume, equivalent to 200 biotransformation (oxidation) operating cycles of those carried out with dyes or phenol. Taken together, our results indicate that the novel microreactors introduced here have the potential to process wastewaters rich in contaminant dyes in continuous mode with efficiencies that are attractive for a potential large-scale operation. In this regard, future work will focus on finding the requirements for scaling-up the processes and evaluating the involved environmental impact indexes, economic performance, and different device geometries and processing schemes.