Instantaneous Concentration Research Articles

In Situ Study on Biodegradation Differences Between Dissolved Phenanthrene and Methylphenanthrene Using First Derivative Synchronous Fluorescence Spectrometry With Double Scans.

A rapid and highly sensitive first derivative synchronous fluorescence spectrometry with double scans was successfully optimized for the simultaneous determination of dissolved phenanthrene (Phe), 1-methylphenanthrene (1-MP), and 3-methylphenanthrene (3-MP) and their metabolites such as 1-hydroxy-2-naphthoic acid (1H2NA) and salicylic acid (SA) in the biodegradation processes of Phe, 1-MP, and 3-MP by Novosphingobium pentaromativorans US6-1. Δλ of 55 and 109 nm were selected for Phe, 1-MP, 3-MP, 1H2NA, and SA, respectively. The intensities of the first derivative synchronous fluorescence detected at λex of 289, 292, 291, 354, and 312 nm for Phe, 1-MP, 3-MP, 1H2NA, and SA varied linearly with the concentrations of them in the ranges of 0.20 × 10-7-44.89 × 10-7, 0.20 × 10-7-13.04 × 10-7, 0.20 × 10-7-13.04 × 10-7, 0.22 × 10-7-76.30 × 10-7, and 0.11 × 10-7-52.00 × 10-7 mol/L. The limits of detection were 0.11 × 10-9, 0.30 × 10-9, 0.27 × 10-9, 0.33 × 10-9, and 2.90 × 10-9 mol/L for Phe, 1-MP, 3-MP, 1H2NA, and SA, respectively, with RSD less than 2%. The method was successfully applied in situ to detect the instantaneous concentrations of the PAHs and their metabolites, especially SA, during their biodegradation processes under simulated conditions in the lab. The results demonstrated that the upper metabolic pathways of 1-MP and 3-MP by US6-1 were distinctly different from that of Phe owing to steric hindrance of the methyl group.

Tribochemical behavior of GaN in electro-fenton system base on bimetallic micro-electrolytic catalysts

In the electro-Fenton system, prolonged operation of the electro-Fenton catalyst can lead to the accumulation of significant amounts of Fe3+, resulting in concentration polarization phenomena that inhibit the progression of the electro-Fenton reaction, thereby adversely affecting the chemical mechanical polishing of GaN. This study introduces non-ferrous metal ions (Mn2+/Cu+/Ce3+) into the conventional electro-Fenton system, which primarily utilizes Fe2+ as the catalytic ion. By leveraging the principles of galvanic cells and Fenton-like reactions, we accelerate the electron exchange among different metal ions, thus enhancing the instantaneous concentration rate of electro-Fenton catalytic ions and the oxidation rate of GaN. Through tribological experiments involving GaN, it is evident that bi-metallic micro-electrolytic catalysts achieve a higher catalytic oxidation efficiency compared to their monometallic counterparts. Notably, the combination of Fe2+ and Ce3+ exhibits the most pronounced synergistic effect. This provides valuable insights for the design of composite catalytic media within the electro-Fenton framework.

CNN for scalar-source distance estimation in grid-generated turbulence

Countermeasures against material leakage in industrial plants call for rapid leak source estimation techniques based on limited downstream information. Assuming that such scalar diffusion occurs in a turbulent environment, it is necessary to extract features from its instantaneous local concentration distribution and estimate the distance from the observation point to the source. To this end, we proposed an estimation method using a supervised deep learning of a convolutional neural network (CNN) and investigated its estimation performance in grid-generated turbulence fields. The grid turbulence fields were reproduced by direct numerical simulations at three Reynolds numbers (Re), and the CNN was trained using two-dimensional distribution images of passive scalars downstream. We confirmed that the images large enough to cover the spatial integral length scales of the scalar resulted in high estimation accuracy. For images with a coarsened brightness gradation, the small-scale feature of scalar fluctuations was lost, and the CNN attained a low estimation accuracy. By training the CNN with high-Re images, a high estimation accuracy was obtained, even for low-Re images. The opposite case (low-Re training and high-Re estimation) yielded low accuracy, where the CNN significantly underestimated the distance against the source. Based on these results, we discussed the generalizability and essential features to be learned by the CNN.

Particulate matter in necropsy activities: experience from a health operators’ exposure monitoring campaign

BackgroundOperators in the obituary and necropsy sectors are exposed to various environmental hazards during specific tasks. Despite this exposure, occupational risks have often been underestimated, resulting in a lack of substantial evidence. The primary objectives of this study were to identify sources of chemical risk, establish procedures for monitoring and quantifying exposure during necropsy activities, and recommend adjustments to regulatory guidelines to protect the health of the operators. The study was conducted at the Legal Medicine Unit of the Umberto I General Hospital in Rome, focusing on the quantitative measurement of particulate matter (PM) exposure among at-risk operators during necropsy activities. Environmental levels of total suspended particles, PM10, PM4, PM2.5, and PM1 were assessed by evaluating the average, minimum, and maximum instantaneous indoor concentrations using an airborne analyzer.ResultsThe monitoring activities revealed that the PM concentrations were significantly lower than the recognized reference values. However, bone sawing, body removal, and cleaning were identified as high-risk maneuvers for dust suspension.ConclusionsOur study highlighted specific risks associated with necropsy activities, particularly concerning timing and certain maneuvers. These results may lead to interventions for improving current prevention procedures, implementing good practices, and developing specific guidelines to enhance operator safety.

Bacterial accumulation dynamics in runoff from extreme precipitation

Extreme precipitation can significantly influence the water quality of surface waters. However, the total amount of bacteria carried by rainfall runoff is poorly understood. Here, thirty rainfall scenarios were simulated by artificial rainfall simulators, with designed rainfall intensity ranging from 19.3 to 250 mm/h. The instantaneous concentration ranges of R2A, nutrient agar (NA) culturable bacteria, and viable bacteria in runoff depended on the types of underlying surfaces. The instantaneous bacterial concentrations in runoff generated by forest lands, grasslands and bare soil were: R2A culturable bacteria = 104.5–6.3, 104.5–6.1, 104.0–5.3 colony-forming units (CFU)/mL, NA culturable bacteria = 104.0–6.0, 103.9–5.8, 103.2–4.9 CFU/mL, and viable bacteria = 106.4–8.0, 107.0–8.9, 106.4–7.6 cells/mL. Based on the measured bacterial instantaneous concentration in runoff, cumulative dynamic models were established, and the maximum amount of culturable bacteria and viable bacteria entering water sources were estimated to be 109.38–11.31 CFU/m2 and 1011.84–13.25 cells/m2, respectively. The model fitting and the bacterial accumulation dynamics were influenced by the rainfall types (p < 0.01). Surface runoff from the underlying surface of forest lands and grasslands had a high microbial risk that persisted even during the “Drought-to-Deluge Transition”. Bacterial accumulation models provide valuable insight for predicting microbial risks in catchments during precipitation and can serve as theoretical support for further ensuring the safety of drinking water under the challenge of climate change.

Analysis of hydrogen peroxide production in pure water: Ultrahigh versus conventional dose-rate irradiation and mechanistic insights.

Ultrahigh dose-rate radiation (UHDR) produces less hydrogen peroxide (H2O2) in pure water, as suggested by some experimental studies, and is used as an argument for the validity of the theory that FLASH spares the normal tissue due to less reactive oxygen species (ROS) production. In contrast, most Monte Carlo simulation studies suggest the opposite. We aim to unveil the effect of UHDR on H2O2 production in pure water and its underlying mechanism, to serve as a benchmark for Monte Carlo simulation. We hypothesized that the reaction of solvated electrons ( ) removing hydroxyl radicals (•OH), the precursor of H2O2, is the reason why UHDR leads to a lower G-value (molecules/100eV) for H2O2 (G[H2O2]), because: 1, the third-order reaction between and •OH is more sensitive to increased instantaneous ROS concentration by UHDR than a two-order reaction of •OH self-reaction producing H2O2; 2, has two times higher diffusion coefficient and higher reaction rate constant than that of •OH, which means would dominate the competition for •OH and benefit more from the inter-track effect of UHDR. Meanwhile, we also experimentally verify the theory of long-lived radicals causing lower G(H2O2) in conventional irradiation, which is mentioned in some simulation studies. H2O2 was measured by Amplex UltraRed assay. 430.1MeV/u carbon ions (50 and 0.1Gy/s), 9MeV electrons (600 and 0.62Gy/s), and 200kV x-ray tube (10 and 0.1Gy/s) were employed. For three kinds of water (real hypoxic: 1% O2; hypoxic: 1% O2 and 5% CO2; and normoxic: 21% O2), unbubbled and bubbled samples with N2O, the scavenger of , were irradiated by carbon ions and electrons with conventional and UHDR at different absolute dose levels. Normoxic water dissolved with sodium nitrate (NaNO3), another scavenger of , and bubbled with N2O was irradiated by x-ray to verify the results of low-LET electron beam. UHDR leads to a lower G(H2O2) than conventional irradiation. O2 and CO2 can both increase G(H2O2). N2O increases G(H2O2) of both UHDR and conventional irradiation and eliminates the difference between them for carbon ions. However, N2O decreases G(H2O2) in electron conventional irradiation but increases G(H2O2) in the case of UHDR, ending up with no dose-rate dependency of G(H2O2). Three-spilled carbon UHDR does not have a lower G(H2O2) than one-spilled UHDR. However, the electron beam shows a lower G(H2O2) for three-spilled UHDR than for one-spilled UHDR. Normoxic water with N2O or NaNO3 can both eliminate the dose rate dependency of H2O2 production for x-ray. UHDR has a lower G(H2O2) than the conventional irradiation for both high LET carbon and low LET electron and x-ray beams. Both scavengers for , N2O and NaNO3, eliminate the dose-rate dependency of G(H2O2), which suggests is the reason for decreased G(H2O2) for UHDR. Three-spilled UHDR versus one-spilled UHDR indicates that the assumption of residual radicals reducing G(H2O2) of conventional irradiation may only be valid for low LET electron beam.

Unveiling Pyrolysis Mechanisms of Waste Printed Circuit Boards Through Multiphysics Simulation

The pyrolysis process of waste printed circuit board (WPCB) with high economic benefit has been a black box problem, limiting the upgrading of pyrolysis processes. The resourcefulness and hazardous nature of WPCB will make it necessary for it to be treated properly. Multiphysics model was built to simulate the whole processes of WPCB pyrolysis and contaminants’ release. The circuit board samples containing six components were selected for pyrolysis in a tube furnace at a rate of 10[Formula: see text]C/min from room temperature to 600[Formula: see text]C, and the residual rate of Br- was determined by the oxygen bomb method. The results showed that the difference in temperature distribution could be attributed to thermal conductivity and surface area. Heat distribution would be more even from the inner material in areas where holes existed. The assembly method would affect the stress distribution around the components. Thermal stress at the pins might cause the separation of components from the substrate. The concentration of brominated contaminants was influenced by the material and assembly method. The instantaneous concentration around the pin was 3–4 times compared to the bare substrate, which was beneficial for the release and control of brominated organics. This study provided the research method for the in-depth understanding of the pyrolysis process of complex materials; and provided a basis for the upgrading of related processes.

High-Fidelity Velocity and Concentration Measurements of Turbulent Buoyant Jets

Accurate models of turbulent buoyant flows are essential for the design of the cooling circuit of nuclear reactors and passive safety systems. However, available models fail to fully capture the physics of turbulent mixing when buoyancy becomes predominant with respect to momentum. Therefore, high-fidelity experiments of well-controlled fundamental flows are needed to develop and validate more accurate models. We analyze experiments of positive and negative turbulent buoyant jets, both in uniform and stratified environments, with the aim of understanding the thermal hydraulics of turbulent mixing with variable density and providing high-fidelity data for the development and validation of turbulence models. Non-intrusive, simultaneous particle image velocimetry and laser-induced fluorescence measurements were carried out to acquire instantaneous velocity and concentration fields on a vertical section parallel to the axis of a jet in the self-similar region. The refractive index matching method was applied to measure high-resolution buoyant jets with up to 8.6% density difference. These data are free of the typical errors that characterize optical measurements of buoyancy-driven flows (e.g. natural and mixed convection) where the refractive index of the fluid is inhomogeneous throughout the measurement domain. Turbulent statistics and entrainment of buoyant jets in uniform and stratified environments are presented. These data are compared with non-buoyant jets in a uniform environment, as a reference to investigate the effects of buoyancy and stratification on turbulent mixing. The results will be used for the assessment of current turbulence models and as a basis for the development of a new model that captures turbulent mixing.

Real-time concentration detection of Al dust using GRU-based Kalman filtering approach

Kalman filter algorithms have been widely used in dust environment concentration detection systems. However, in industrial environments, methods such as KF and median filtering usually require about 10 s of detection time, which cannot meet the requirements of online real-time detection. For this reason, this present study proposes a framework that combines a gated recirculation unit (GRU) with the KF method to achieve online real-time detection of dust concentration. In this framework, the GRU is mainly responsible for handling dynamic and nonlinear characteristics and capturing instantaneous concentration trends. On the other hand, the Kalman filter utilizes its superior state estimation capability to provide more accurate system state estimation by fusing real-time predictions from GRU and sensor measurements. The results show that the KFGRU method is superior to the conventional linear filtering method with a response time of less than 2 s and can detect dust concentration online in real-time. In terms of prediction accuracy, the deviation value of the curve processed by the KFGRU method is only 0.334, which is a significant breakthrough compared with the Kalman filter algorithm 0.755, the sliding average method 0.843, and the median filter method 0.849 (the smaller the deviation value, the higher the prediction accuracy). This study provides a comprehensive and innovative approach for dust concentration monitoring in dust reduction and explosion suppression systems, which not only meets the real-time requirement but also makes important progress in explosion safety management. This will provide more reliable and advanced technical support for dust control and safety in industrial production processes.

Dual Functional Antibacterial-Antioxidant Core/Shell Alginate/Poly(ε-caprolactone) Nanofiber Membrane: A Potential Wound Dressing.

Core/shell nanofibers offer the advantage of encapsulating multiple drugs with different hydrophilicity in the core and shell, thus allowing for the controlled release of pharmaceutic agents. Specifically, the burst release of hydrophilic drugs from such fiber membranes causes an instantaneous high drug concentration, whereas a long and steady release is usually desired. Herein, we tackle the problem of the initial burst release by the generation of core/shell nanofibers with the hydrophilic antibiotic drug gentamycin loaded within a hydrophilic alginate core surrounded by a hydrophobic shell of poly(ε-caprolactone). Emulsion electrospinning was used as the nanofibrous mesh generation procedure. This process also allows for the loading of a hydrophobic compound, where we selected a natural antioxidant molecule, betulin (BTL), to detoxify the radicals. The resulting nanofibers exhibited a cylindrical shape with a core/shell structure. In vitro tests showed a controlled release of gentamicin from nanofibers via diffusion. The drug reached 93% release in an alginate hydrogel film but only 50% release in the nanofibers, suggesting its potential to minimize the initial burst release. Antibacterial tests revealed significant activity against both Gram-negative and Gram-positive bacteria. The antioxidant property of betulin was confirmed through the DPPH assay, where the incorporation of 20% BTL revealed 37.3% DPPH scavenging. The nanofibers also exhibited favorable biocompatibility in cell culture studies, and no harmful effects on cell viability were observed. Overall, this research offers a promising approach to producing core/shell nanofibrous mats with antibacterial and antioxidant properties, which could effectively address the requirements of wound dressings, including infection prevention and wound healing acceleration.

Interfacial and ion-pairing catalysis for oxygen-tolerant large-scale ATRP in ab initio emulsion

A cooperative interfacial and ion-pairing catalysis, coupled with a molecular oxygen reduction reaction (ORR), to scale up an Atom Transfer Radical Polymerization of n-butyl acrylate (BA) from 20 mL to 10 L (scale-up factor = 500) in ab initio emulsion conditions is introduced. The polymerization is driven by the regeneration of [CuIL]+ through CuII/Cu0 comproportionation. [CuIL]+ simultaneously converts O2 to H2O2 (which is then degraded by sodium pyruvate) and drives the polymerization of butyl acrylate. The anionic surfactant sodium dodecyl sulfate (SDS) facilitates catalyst transport inside and outside the micelles by ion-pairing catalysis. n-Butyl acrylate polymerizations are investigated on a small scale with Cu0 wire and on a larger scale with Cu0 powder. On a 10 L scale, the polymerization yielded controlled PBA-Br (Mn = 32.3 × 103; Ð = 1.39, ∼1.64 kg) after 9 h. Chain extension of PBA-Br macroinitiators proved their livingness. An on-line electrochemical monitoring was also introduced to determine the instantaneous CuI and CuII concentrations at the Cu0 wire surface during the polymerization.

In situ synthesis of porous metal-organic frameworks NH2-UiO-66 on tea stem biochar and application in odours adsorption

Multiple odour nuisance in livestock farming is a notorious problem that has a significant impact on the living environment of surrounding communities. Adsorbents based on metal-organic framework (MOF) materials show great promise for controlling odour pollution, as they offer a high specific surface area, a controllable structure and an abundance of active sites. However, the MOF formation process is prone to problems such as pore clogging or collapse and reduced porosity, which limits its further application. In this study, a series of odour adsorbents were prepared by in situ growth of NH2-UiO-66 on tea stem biochar (TSBC) using a hydrothermal method and named UiO (Zr)-TSBCx. The physical and chemical properties and composition of UiO (Zr)-TSBCx have been systematically characterized using SEM, TEM, XRD, FT-IR, N2 adsorption-desorption and XPS. The release of odours from the pig farm effluent was monitored using in-situ continuous Proton-Transfer-Reaction Mass Spectrometry (PTR-MS), and the obtained primary compositions were tested for further adsorption. In dynamic adsorption experiments focused on butyric acid, UiO (Zr)-TSBC2 showed a high adsorption capacity of 3.99 × 105 μg/g and exceptional structural stability. UiO (Zr)-TSBC2 showed variable adsorption efficiencies for different odorous gases, with the best performance for the removal of ammonia, toluene and butyric acid. It also demonstrated the ability to rapidly mitigate instantaneous high concentrations of hydrogen sulfide (H2S), methanethiol and toluene resulting from agitation. Additionally, based on the relationship between the adsorption amount and the structural characteristics of the adsorbent as well as the nature of the odours, a possible adsorption mechanism of UiO (Zr)-TSBC2 for a variety of odours released from pig farm effluent was proposed. This work demonstrates a novel approach to promote deodorization applications in livestock and poultry farming environments by the in-situ growth of NH2-UiO-66 on biochar prepared from tea stem.

On-road evaluation and regulatory recommendations for NOx and particle number emissions of China VI heavy-duty diesel trucks: A case study in Shenzhen

This research analyzed the real-world NOx and particle number (PN) emissions of 21 China VI heavy-duty diesel trucks (HDDTs). On-road emission conformity was first evaluated with portable emission measurement system (PEMS). Only 76.19 %, 71.43 % and 61.90 % of the vehicles passed the NOx test, PN test and both tests, respectively. The impacts of vehicle features including exhaust gas recirculation (EGR) equipment, mileage and tractive tonnage were then assessed. Results demonstrated that EGR helped reducing NOx emission factors (EFs) while increased PN EFs. Larger mileages and tractive tonnages corresponded to higher NOx and PN EFs, respectively. In-depth analyses regarding the influences of operating conditions on emissions were conducted with both numerical comparisons and statistical tests. Results proved that HDDTs generated higher NOx EFs under low speeds or large vehicle specific powers (VSPs), and higher PN EFs under high speeds or small VSPs in general. In addition, unqualified vehicles generated significantly higher NOx EFs than qualified vehicles on freeways or under speed≥40 km/h, while significant higher PN EFs were generated on suburban roads, freeways or under operating modes with positive VSPs by unqualified vehicles. The reliability and accuracy of on-board diagnostic (OBD) NOx data were finally investigated. Results revealed that 43 % of the test vehicles did not report reliable OBD data. Correlation analyses between OBD NOx and PEMS measurements further demonstrated that the consistency of instantaneous concentrations were generally low. However, sliding window averaged concentrations show better correlations, e.g., the Pearson correlation coefficients on 20s-window averaged concentrations exceeded 0.85 for most vehicles. The research results provide valuable insights into emission regulation, e.g., focusing more on medium- to high-speed operations to identify unqualified vehicles, setting higher standards to improve the quality of OBD data, and adopting window averaged OBD NOx concentrations in evaluating vehicle emission performance.

The impact of food processing on kasugamycin residues: findings and implications

ABSTRACT Food processing operations play a significant role in the residual levels. Therefore, investigations into the fate of residues on food and their by-products are necessary to ensure food safety. We established an analytical method for the determination of kasugamycin residual levels on whole citrus and processed samples obtained from two sites using high-performance liquid chromatography coupled with tandem mass spectrometry. Furthermore, risk assessment also conducted to evaluate the chronic diet risk by TMDI-NEDI model. The results suggested that the half-life of kasugamycin in whole citrus and pulp was between 8.56–13.39 days, and 10.08–13.03 days in citrus. Additionally, the effects of commercial processing (washing, squeezing, refined filtration, high temperature instantaneous sterilisation, concentration, and centrifugation) on residual were also investigated, which indicated processing factors (PFs) values decreased in all processing samples, but increased in pomace. Additionally, the potential dietary risk in citrus was systematically evaluated by two risk assessment models, the entire NEDI is lower than the maximal ADI. These results demonstrated that the entire procedure can reduce residual kasugamycin in the concentrated juice. Regrading of risk assessment models indicated that the presence of residual kasugamycin in citrus and its processing products poses a minimal risk to human health.

Influence of foaming-induced crystallization behavior on the structure of poly(butylene adipate-co-terephthalate) supercritical foamed beads

The crystallization behavior during foaming directly affects the foaming properties. For crystalline polymers, there is no consensus on the influence of the crystallization behavior during foaming process on the stabilization of the cell structure. In this work, PBAT foamed bead and unfoamed pellets were prepared by controlling the saturated temperatures in supercritical CO2, soaking step (one or two) and the depressurization rate, respectively. Double melting peaks were observed in the DSC curve of supercritical CO2 foamed PBAT beads. By comparing the outgassing rates we find that the stretching-induced crystallization caused by the rapid expansion of the gas during foaming plays an important role in the stabilization of the cells. Although the crystalline perfection or crystal size at this time is much smaller than that of the crystalline grains formed during static cooling, the rapid crystallization is effective in stabilizing the cell structure of the foamed pores. Compared to normal supercritical foaming processes, the two-step foaming process of soaking CO2 at high temperatures followed by foaming at low temperatures results in an increase in cell size and expansion ratio. At high temperatures, more CO2 diffuses into the PBAT pellets, increasing the instantaneous gas concentration in the pellets for foaming, and the rapid stretching produces stretching-induced crystallization that raises the average size of the cells, further increasing the expansion multiplicity of individual cells. The average cell size of foam beads rises from 37.8 to 48.8 µm and the expansion ratio also increases to 8.6 with saturated temperature increasing form 95 to 105°C. The two-step soaking foaming method is a more efficient way of manufacturing industrial foamed beads, allowing for the preparation of better foam beads at low temperatures.

Adsorption/photocatalytic degradation of Cefixime by the green Bi2WO6/g-C3N4/ZIF-67 dual S-scheme heterojunction: Artificial neural network, genetic algorithm, density functional theory, and toxicity assessments

This study investigated the photocatalytic adsorption, degradation, and mineralization of Cefixime (CFX) through hydrothermally synthesized Bi2WO6(36 %)/g-C3N4(54 %)/ZIF-67(10 %) dual S-scheme heterojunction (BCZ). Full characterization analysis for the fresh and reused photocatalyst was explored to study the formation of heterojunction, stability, and reusability of the BCZ. VB-XPS, Mott-Schottky plots, and UV–Vis DRS defined the band structure and electron transfer mechanism of BCZ. The effects of ten operating condition factors, including reaction time, initial concentration of CFX, the dosage of photocatalyst, reaction temperature, initial pH of the reaction, visible and UV intensity, and concentration of Na2SO4, NaOH, and NaCl in the reaction solution were experimentally investigated. These factors were then modeled through artificial neural networks (ANN). The number of neurons, training algorithm, and the type of activation functions in the ANN were optimized by mean squared error metric followed by the visualizations of the ANN predictions. Two cost functions (the ratio of instantaneous CFX concentration to initial CFX concentration (C/C0) and the ratio of photocatalyst dosage to the amount of CFX removed) were employed to optimize the value of these operating condition factors separately and simultaneously through single and multi-objective genetic algorithms. Coupling LC-MS results and DFT calculations, a degradation pathway for Cefixime was proposed and then analyzed by QSAR. The toxicity of the treated solution was investigated using the wheat seed culture, along with MIC and MBC testing conducted by E. coli and S. aureus, and its eco-friendliness was confirmed by TOC and COD. Furthermore, ICP-OES confirmed that BCZ is a green photocatalyst.

On efficient modelling of radical production in cavitation assisted reactors

Process intensification by cavitation is gaining widespread attention due to the benefits that the intense bubble collapse conditions can provide, yet, several knowledge gaps exist in the modelling of such systems. This work studies the numerical prediction of single bubble dynamics and the various approaches that can be employed to estimate the changes in the chemical composition of cavitating bubbles. Specific emphasis is placed on the prediction of the radical production rates during bubble collapse and the computational performance, with the aim of coupling the single bubble dynamics to flow models for reactor hydrodynamics. The results reveal that the choice of chemical reaction approach has virtually no effect on the bubble dynamics, whereas the predicted radical production rates can differ substantially. It is found that evaluating the radical production only on temperature peaks, an approach commonly followed in literature, may result in the most erroneous estimations (on average 12.8 times larger than those of the full kinetic model), while a simplified kinetic model yields more accurate predictions (2.3 times larger) at the expense of increased computational times. Continuous evaluation of the bubble content by assuming equilibrium when the bubble temperature is above a certain threshold (≈1500K) is shown to be capable of predicting total radical production values close to those estimated by solving the kinetics of a detailed reaction model (19.8% difference), as well as requiring only 22.2% more computational costs compared to simulations without chemical reaction modelling. Such an equilibrium approach is therefore recommended for future studies aiming to couple flow simulations with single bubble dynamics to accurately predict radical production rates in cavitation devices, involving numerous bubbles following different flow trajectories. Furthermore, an algebraic expression that successfully approximates the full kinetic simulation results is proposed as a function of the initial nucleus size and the time integral of the liquid pressure when it is under vapor pressure. Such a model can be applied in modelling efforts that do not require local instantaneous radical concentrations, and paves the way for efficient closure modelling of radical production in CFD simulations of hydrodynamic reactors.

Dependence of Biotic and Abiotic H2O2 and •OH Production on the Redox Conditions and Compositions of Sediment during Oxygenation.

Reactive oxygen species (ROS) production in O2-perturbed subsurface environments has been increasingly documented in recent years. However, the constraining conditions under which abiotic and/or biotic mechanisms predominate for ROS production remain ambiguous. Here, we demonstrate that the ROS production mechanism, biotic and abiotic, is determined by sediment redox properties and sediment compositions. Upon the oxygenation of 10 field sediments, the cumulative H2O2 concentrations reached up to 554 μmol/kg within 2 h. The autoclaving sterilization experiments showed that H2O2 could be produced by both biotic and abiotic processes depending on the redox conditions. However, only the abiotic process could produce significant levels of •OH, and the production yield was closely related to the sediment components, particularly sediment Fe(II) and organic matter. Fe(II) bound with organic matter led to high yields of H2O2 and •OH production. Sediment oxygenation contributed to the appearance of H2O2 in groundwater, with the abiotic mechanism producing higher instantaneous H2O2 concentrations than the biotic mechanism. These findings reveal that the redox conditions, compositions, and texture of sediments collectively control abiotic and biotic mechanisms for ROS production, which assists the identification of ROS production hotspots and the understanding of ROS distribution and utilization in the subsurface.

A novel method of identifying estuary high-nutrient zones for water quality management

Coastal shallow waters are highly vulnerable to pollution, often leading to the development of intricate eutrophication zones. However, accurately determining these areas poses a significant challenge due to the complex interplay of estuarine hydrodynamics and nutrient transformation. To address such issue, a novel method was proposed to identify high-nutrient zones through calculating the continuous zonation of released tracers when their instantaneous concentrations declined to 1/e of their initial values. The method was well tested using idealized estuary models with varying shape parameters, water depths and river discharges. The results consistently revealed that the boundaries of high-nutrient zones fell within the mixed zone, characterized by salinity levels of 10– 20 psu. In Shenzhen Bay, a typical shallow bay, distinct differences were observed in the concentrations of dissolved inorganic nitrogen (DIN) and PO43−. Both the 20 psu isohaline and the proposed method effectively identified the partition boundary of high DIN and PO43− in 2001–2010, but only the newly proposed method demonstrated accuracy in delineating the actual high-nutrient zone during the continuous nutrient reduction period from 2010 to 2020. This study provides a practical and feasible approach that can serve as an auxiliary decision-making tool for managing estuarine water environments, and it has potential to facilitate the implementation of timely and effective measures for pollution control.

Salt Effects on Caffeine across Concentration Regimes.

Salts affect the solvation thermodynamics of molecules of all sizes; the Hofmeister series is a prime example in which different ions lead to salting-in or salting-out of aqueous proteins. Early work of Tanford led to the discovery that the solvation of molecular surface motifs is proportional to the solvent accessible surface area (SASA), and later studies have shown that the proportionality constant varies with the salt concentration and type. Using multiscale computer simulations combined with vapor-pressure osmometry on caffeine-salt solutions, we reveal that this SASA description captures a rich set of molecular driving forces in tertiary solutions at changing solute and osmolyte concentrations. Central to the theoretical work is a new potential energy function that depends on the instantaneous surface area, salt type, and concentration. Used in, e.g., Monte Carlo simulations, this allows for a highly efficient exploration of many-body interactions and the resulting thermodynamics at elevated solute and salt concentrations.