Suspended Particles Research Articles

Growth, Filtration and Respiration Under Superfluous Feeding in Single-Osculum Halichondria panicea Sponges

Filter-feeding sponges capture suspended food particles from ambient water, but little is known about the response of sponges to high food concentrations causing superfluous feeding. Here, through several experimental assays, we studied the relationship between algal concentration in the water column, filtration rate, respiration rate, and specific growth rate in single-osculum Halichondria panicea demosponge explants. Laboratory experiments showed that sponge explants filter the ambient seawater at a maximum rate when exposed to naturally (low) algal concentrations, whereas high algal concentrations resulted in superfluous feeding and reduced filtration rates. Explants maintained at algal concentrations above the incipient overloading concentration level showed that growth rates were in fair agreement with the maximum possible weight-specific growth rate of about 4% d−1. Although the filtration rate became reduced due to overloading, the oxygen extraction efficiency increased, and therefore superfluous feeding did not cause reduced growth. This suggests that H. panicea and probably other sponges have adapted to low algal concentrations, displaying continuous maximum filtration rates. Osculum closure reflects a protection mechanism rather than a physiological regulatory response to high algal concentrations.

Temporally resolved concentration profiling via computationally limited, distributed sensor nodes

AbstractAccurate mapping of chemical concentrations in reactor networks remains an obstacle to establish complete systems‐level insight and control. This issue extends beyond traditional reactor design to biological and other inaccessible systems of interest. Recent developments in novel materials with non‐volatile memory allow autonomous sensor nodes to record information with minimal external supervision. Integrating these materials in solution suspended particles demonstrates the unique potential for diffuse measurements of chemical data at the microscale. In this study, we establish a generalized workflow for the simulated deployment of time aware particle sensors (TAPS) in ideal reactor systems to measure analyte profiles, using Gillespie kinetic Monte Carlo algorithms (KMC). Our results show that computationally‐limited, chemically sensitive tracer particles capable of timestamping an analyte detection event can provide accurate analyte profiles throughout multistage reactors in an ensemble fashion.

Using the Burning of Polymer Compounds to Determine the Applicability of the Acoustic Method in Fire Extinguishing

In order to achieve the objective of the work—an experimental study of the capabilities of the acoustic method for extinguishing organic compounds and for ensuring environmental monitoring—the effect of the combustion of various polymers on the acoustic parameters of the medium is considered. The negative effect of the combustion of organic substances on the medium is noted. The features of the use of fire extinguishing agents are analyzed, and it is noted that the acoustic method is a promising, inexpensive, and environmentally friendly approach for use in extinguishing fires. The ideas about the capabilities of this method using the combustion of various polymers were further developed, which is the novelty of the work. As the main results, it is proposed to use the angle of incidence, concentration of suspended particles, temperature, and wave resistance of the environment as special correction factors for acoustic sensors when monitoring in a smoky space. The possibility of using the combustion parameters of organic compounds to determine the properties of acoustic waves in a smoke-filled area is shown. The perspective of implementing the results obtained in the practice of fire prevention and liquidation was observed to increase the efficiency of fire extinguishing and increase the safety of the population and personnel of special services. The proposed approach can become part of the ecological and economic innovations of municipal communities and national strategies to achieve the goals of sustainable development.

COMPLEX TECHNOLOGY OF THE CLEANING OF AGGLOMERATION GASES FROM DUST AND HARMFUL GASES WITH OBTAINING A GOOD PRODUCT

The purpose of the work is to improve the design of the dust-catching device of the sintering machine, to increase the efficiency of catching charged dust particles in laminar layers near the precipitating elements, the configuration and location of the elements of the precipitating elements, to establish the dependence of the effective (calculated) drift speed of charged dispersed particles on the speed of the medium being cleaned, with classical the process of electrogas purification and the combined flow of gases in electrofilters. It was established that the combined movement of gases in a modular unit ensures the charging of the entire population of dust particles to the limit values ​​by organizing a highly turbulent flow and keeping dust particles in the zones with the greatest tension in the corona charge covers, as well as effective trapping of charged dust particles in laminar layers near the precipitating elements . Mathematical modeling of the deposition block was carried out in order to optimize the configuration. The main dependences of the number and mutual location of precipitating elements to ensure maximum dust deposition were established. Studies of gas medium velocity spectra in models of new electrostatic precipitators have been carried out. The optimal live cross-sections of the aerodynamic partitions are determined to ensure favorable conditions for charging suspended particles and uniform distribution of the cleaned flow through the catching holes. The MV-2 modular type electric gas purification device with a capacity of 30 thousand nm3/h has been developed, based on innovative developments in the field of KEIT (combined electro-ion gas purification technology) in the field of conversion and control of cascade energy and aerodynamics of turbulent and laminar flows during inertial deposition dispersed suspension of flue gases. An apparatus for cleaning gases from a sinter machine with a capacity of up to 400,000 nm3/h is proposed. with an efficiency of 99 %, for replacing existing equipment (multicyclones). "MV-2JS" electric device was developed. This is a plasma-catalytic reactor, which allows you to produce the necessary amount of ozone in a low-cost way to oxidize the harmful components (SO2, NOx, CO) of the outgoing gases. The use of this device allows, in addition to the cleaning of flue gases from harmful gas impurities, to obtain commercial products (fertilizers, gypsum, sulfuric acid, etc.) at the output and to completely get rid of solid and liquid waste during gas desulfurization.

Differential Effects of Polyvinyl Chloride Microplastics and Kaolin Particles on Gut Immunity of Mussels at Environmental Concentrations

Both microplastics (MPs) and kaolin are marine suspended particles capable of influencing the physiology of bivalve mollusks. However, the current research on MPs lacks the analysis of their own physical and chemical toxicity, and the comparative study of the toxicity of microplastics and natural suspended particles (NSPs) in aquatic environment. In this work, three experiments are layered, with Experiment 1 directly comparing MPs PVC and kaolin and showing that MPs have greater deleterious effects on thick-shelled mussels than kaolin, with the exception of physical damage and effects on gut microorganisms. As the presence or absence of chemicals may be the main difference between MPs and kaolin, in Experiment 2 the toxicity drivers of MPs PVC itself were investigated, demonstrating that the chemicals in MPs are indeed toxic and that the harmful effects of MPs on mussels may be due to the superposition of their own physical and chemical toxicity. Finally, in Experiment 3 mussels were exposed to the chemicals in MPs and kaolin in a composite and found that the toxicity of the composite exposure was greater than that of the single exposure to kaolin, suggesting that the chemicals may be the main factor contributing to the difference in toxicity between MPs and kaolin. In conclusion, this work addresses the lack of a natural particle control group in current studies of MPs, confirms that the toxicity drivers of MPs are due to both physical and chemical factors, highlights the role of natural suspended particles in the environment, and provides new insights for evaluating the toxic effects of MPs in the natural marine environment.

A spatio-temporal assessment of seawater quality in Miri-Sibuti Coral Reef: Evaluating for metal pollution, sources and dynamics

Coral environments are sensitive to seawater quality, and their sustenance depends on understanding the dynamics of geochemical variables, especially in trace levels. Miri-Sibuti Coral Reef National Park (MSCRNP) is a unique marine reserve in the state of Sarawak, NW Borneo, Malaysia, which attracts tourists worldwide. In this study, seawater samples were collected from MSCRNP in three different diving sites (Eve’s Garden (EG), Anemone Garden (AG) and North Siwa (NS)) at different depths for three seasons (pre-southwest monsoon (PRSWM), post-southwest monsoon (POSWM) and northeast monsoon (NEM). Insitu parameters (temperature, pH, salinity and turbidity) were measured in the field. The concentration of trace metals was determined in the water column (sea surface layer, middle layer and bottom water) using standard procedure. Statistics and pollution indices were used to identify the possible sources of metals and the pollution status of the seawater. From the analytical results, the vertical distribution of trace metal concentrations with respect to the locations and seasons was identified. pH ranging from 7.8 to 8.4 with a depth-wise increasing trend in NS during NEM. Similarly, a decreasing trend of turbidity was observed in AG and EG in all the seasons with respect to depth. A higher concentration of trace metals was observed during NEM, particularly at EG and NS. Fe, Ni and Pb are the dominant metals in all the seasons. Fe concentration varies from 789 to 1,478µg/L, averaging 1,112µg/L irrespective of seasons and locations. The suspended solids/sediments discharged by the river runoff were the main contributor to the distribution of metals. The release of metals from the suspended particles through desorption at the surface layers and the exchange of metals between water-sediment interface at the bottom water were observed. In addition, coastal development and other anthropogenic activities in this region were also contributed to the metal pollution.

Small-Scale Aqueous Suspension Preparation using Dual Centrifugation: The Effect of Process Parameters on the Sizes of Drug Particles

The dual centrifugation approach has in the recent years emerged as a powerful milling tool to prepare pharmaceutical suspensions in submicron range with a fast-milling capacity by milling 40 samples simultaneously in 2 mL vials. While there is some standardized milling conditions described in the literature when preparing aqueous suspensions with dual centrifugation, a more systematic and experimental understanding of the milling process to evaluate the impact of different process variables in the dual centrifuge on the final sizes of the suspended drug particles independent of the drug compound used. Overall, the present study demonstrated the applicability of the dual centrifuge for small-scale screening purposes and showed the impact of process parameters on the physical attributes of prepared suspensions. In the present work, the rate of size reduction on three different model compounds, i.e., cinnarizine, haloperidol, and indomethacin, was found to be mostly influenced by the milling speed, size of milling beads, and the bead loading during milling, whereas the rotor temperature did not affect the particle size profiles when stabilized with polysorbate 20 during milling with dual centrifugation. Smaller particle sizes were in general obtained at the highest milling intensity, i.e., 1500 rpm, smallest bead size, i.e., 0.2 mm, and higher bead loadings (42%, 56%, and 83%). The grinding limit of approximately 0.50 µm, 0.70 µm, and 0.35 µm for cinnarizine, haloperidol, and indomethacin, respectively, was achieved relatively fast, i.e., 30 minutes of milling at the specified conditions, compared to when suspensions were milled with larger bead sizes (i.e., 1.0 mm), lower milling intensities (e.g., 1000 rpm), and lower bead loadings (e.g., 14 or 28%). The study further confirmed that a higher milling intensity was necessary during milling of haloperidol suspensions probably due to the compounds predominantly plastic properties. Sizes of indomethacin particles increased with longer milling runs up to 240 minutes and also higher bead loadings of 56% and 83%. These observations were further supported by the color conversion from white to yellow of indomethacin suspensions which indicated generation of small quantities of amorphic material after milling with a high milling intensity. Upscale investigations showed comparable particle size profiles for all three model compounds while milling at 1500 rpm for five minutes.

Application of bioflocculants produced by Prestia megaterium for drinking water purification

Quality water is a scarce commodity in the developing countries. This paper aims to evaluate the application of bioflocculants produced by Priestia megaterium (accession number: ON184360) for drinking water purification. A total of twenty-four water samples from stream, ponds and wells were collected in sterile containers from four different Local Government Areas of Niger State, Nigeria. Each sample was treated with varying concentrations of bioflocculant and chemical flocculant (0.05, 0.1, 0.15, 0.2 and 0.5 mg L−1). The microbiological and physicochemical characteristics of the treated and untreated water were determined using standard methods. The results show that water samples from stream, ponds and wells treated with the bioflocculant significantly reduced the microbial load and the physicochemical properties of the water reduced to an acceptable limit, which has practical significance for the safety of drinking water in developing countries. The bioflocculant was effective in aggregating suspended particles and thus, proved its potential to be used as alternative flocculant in the drinking water treatment process.

Purification Effect of Fish–Algae Coupling on Nitrogen and Phosphorus in Shrimp Aquaculture Effluent

As the scale of shrimp aquaculture continues to expand, the environmental impacts of shrimp effluents have become increasingly severe. The purification of aquaculture effluents can no longer be overlooked. Effectively reducing the discharge of aquaculture wastewater and mitigating its potential pollution risks to the surrounding aquatic ecological environment are key issues that need to be addressed to promote the industry’s development towards a greener, more environmentally friendly, and sustainable path. This study explored the purification effect of the integration of tilapia and Spirulina on tail water from a zero-water-exchange aquaculture of whiteleg shrimp (Litopenaeus vannamei) in seawater, with the aim of assessing the growth performance of tilapia and the efficacy of the fish–algae integration in purifying tail water from the perspective of tail water resource utilisation. The study found that the removal rates of the biofloc sedimentation volume and total suspended particle concentration in the fish–algae group were 42.6% and 29.6%, respectively. The removal rates of phosphate and total phosphorus in the fish–algae group were 26.3% and 20.8%, respectively. Research indicates that tilapia effectively removes suspended organic matter from water. Introducing Spirulina into this water body aids in the removal of soluble nitrogen and phosphorus from the effluent, and tilapia exhibit a favourable feeding response to Spirulina.

Cascaded frameworks in underwater optical image restoration

Optical imaging and vision technology have become crucial research topics in the field of underwater and ocean scenes. These technologies play a vital role in advancing underwater exploration, scientific research, and smart aquaculture. Despite their importance, optical systems face substantial challenges in complex water environments, especially in turbid conditions where light absorption and scattering by water and suspended particles drastically reduce the quality of captured images. This degradation highlights the need for sophisticated image restoration algorithms that can effectively recover the quality of images impaired by turbid water conditions. Cascaded frameworks, which incorporate multiple modules, including that of color correction, detail enhancement, and information fusion, have emerged as particularly efficacious, offering significant improvements over traditional direct or end-to-end restoration methods. This review elaborates on the comparative benefits of various cascading structures — serial, parallel, and hybrid — and examines different restoration algorithms that utilize intrinsic image features, physical models, prior knowledge, and deep learning technologies. Furthermore, it provides a comprehensive overview of publicly available datasets and evaluation metrics, both referential and non-referential, which are crucial for developing, validating, and optimizing underwater image restoration algorithms. Additionally, by conducting experimental comparative studies of several open restoration algorithms, the effectiveness and applicability of different methods are validated. Finally, the review proposes potential research directions, aiming to deliver valuable insights to scholars in underwater application and computer vision, thereby inspiring innovative research initiatives that could further enhance the capabilities of underwater optical imaging.

Numerical Simulation of the Distribution Patterns of Particle Deposition on the Vertical Wall Behind Near-Wall Heat Source

Near-wall heat sources have a crucial part to play in the process of particle deposition. Thus, this study investigates the impact of the near-wall heat source on the distribution patterns of particle deposition on the vertical wall behind the heat source, taking into account the variability in heat source temperatures and distances from the vertical wall. A model based on the Eulerian–Lagrangian method was established for tracking the motion trajectories of 1000 particles with a density of 1400 kg/m3 and a particle size range of 0.01–10.0 μm. The temperature field, airflow field, and particle deposition distribution in six cases were analyzed. It was shown that the heat source temperature significantly affectis the temperature field, airflow field, and particle deposition distribution on the vertical wall behind the heat source. This study demonstrated that as the temperature rises, the quantity of particles deposited in the upper-right region of the vertical wall decreases more noticeably. The quantity of particles deposited onto the vertical wall is inversely related to the distance between the near-wall heat source and the vertical wall. On one hand, the deposition distribution law serves as a foundation for advancing the technology aimed at removing suspended particles via thermal plumes. On the other hand, it provides critical insights for addressing the challenges associated with harmful particle deposition linked to the attachment effects of thermal plumes.

Multilevel immobilized CNT/SCN purification beads and the removal efficiency over TC[sbnd]HCl/clay composite pollutant in the underwater environment

Natural water bodies often contain a significant amount of suspended colloidal particles, which not only reduce water transparency but also have a high adsorption capacity for soluble pollutants. These composite pollutants can migrate rapidly with water flow, which are usually difficult to degrade and remove by traditional methods. Aiming at suspended contaminated waterbodies, this study introduced a multilevel loading method to prepare carbon nanotube/sulfur doped carbon nitride (CNT/SCN) composite photocatalytic purification beads. The surface of the obtained core-shell structured purification beads is loaded with CNT/SCN photocatalysts which exhibit three-dimensional conductive and porous characteristics. TCHCl was introduced as the target pollutant, and the removal efficiency of the composite purification beads under different water turbidity and hydrodynamic conditions were investigated. The results showed that during 15 h of degradation process, at the depth of 20 cm, with the flow rate of 0.015 m3/h and water turbidity of 10.3 NTU, the purification beads achieved a removal efficiency of 54.9% for tetracycline hydrochloride (TCHCl), which was 2.03 times higher than that of SCN purification beads. The three-dimensional porous structure of the surface exhibited excellent adsorption and trapping capabilities for suspended colloidal particles. The introduction of carbon nanotubes enhanced charge transfer ability of the surface layer and reduces the local charge accumulation effect caused by surface adsorption, which effectively enhances the adsorption of suspended colloid, and also significantly improved the degradation efficiency of TCHCl. This study provides a valuable insight for the engineering application of photocatalytic technology.

Improvement of Bio-Optical Characteristics of Seawater in the Southern Caspian Sea Basin Triggered by COVID-19 Lockdowns: Insights from Remote Sensing Data

Multiple studies have demonstrated that human activities have significant impacts on aquatic ecosystems, particularly in coastal areas. The COVID-19 pandemic, along with the sharp decline in industrial, transportation, and tourism activities, provided an opportunity to examine the impact of these changes on seawater quality in this study, using MODIS-Aqua satellite data, changes in key seawater quality indicators, including chlorophyll-a, dissolved organic matter, and suspended particles, were evaluated in the coastal and offshore areas of the Southern Caspian Sea basin during pre-lockdown and lockdown periods. The data analysis results showed a significant reduction in chlorophyll-a concentration in coastal areas and in dissolved organic matter in both coastal and offshore areas during the lockdown period. More specifically, this reduction was 24.9% and 40.7% for chlorophyll-a, and 22.1% and 19.5% for dissolved organic matter in coastal and offshore areas, respectively. The decline in these indicators reflects an improvement in seawater quality and a reduction in organic pollutant loads in these areas. The findings of this study highlight that reduced human activities have visibly positive effects on marine aquatic ecosystems. Therefore, continuous monitoring of bio-optical parameters changes and improving wastewater treatment processes before discharge into aquatic environments are of particular importance. This study also demonstrates that global pandemics can provide experimental opportunities to study the effects of human activities on the environment.

Mechanism of shear-enhanced rotating-disk microfiltration for separation of microbe/protein bio-suspension

Shear-enhanced dynamic filtration is a promising approach for separating fermented biological products. In this study, we aimed to investigate the separation of bovine serum albumin (BSA) and polymethyl methacrylate (PMMA) particles in a binary suspension using rotating-disk microfiltration. Type-R and Type-RB rotating-disk configurations were designed and compared using experimental data and simulated results. The effects of operating conditions, including rotational speed and filtration pressure, on filtration flux, resistance, and protein rejection, were analyzed. Because the filter membrane rejected all the PMMA particles, the primary source of filtration resistance in the PMMA/BSA suspension was the fouling cake. Although BSA rejection increased with higher filtration pressure, it decreased as the rotational speed increased. Computational fluid dynamics simulations were used to model the flow velocity and shear stress distributions within the rotating-disk dynamic microfiltration system. The results showed that Type-RB achieved a 55 % increase in flux compared to Type-R, owing to a significant reduction in cake resistance by approximately 46 %. A proportional relationship between the mean cake mass and the ratio of qs/τw under varying operating conditions was established using a force balance model. These findings suggest that elevated shear stress significantly enhances filtration performance, with Type-RB demonstrating superior effectiveness for bio-suspension separation.

The effects of current density on the properties of HAp-Nb2O5 films electrodeposited by pulsed current

ABSTRACT The performance of electrodeposited coatings is usually very dependent on the operating conditions. Current density can have a major effect on the appearance of electrodeposits, their physical/mechanical properties and corrosion resistance. In the present study, HAp-Nb2O5 composite layers were electrodeposited on NiTi from stirred, aqueous electrolytes, containing 1 g dm−3 of suspended Nb2O5 particles at a current density of 10, 15 or 20 mA cm−2. The morphology, topography, and elemental composition of the surface were determined using FESEM, AFM, and EDS, respectively. A higher current density enhanced the content of co-deposited Nb2O5 particles but risked the formation of particle aggregation. Microhardness and corrosion, carried out by the Vickers microhardness and potentiodynamic polarization techniques, illustrated that the films electroplated at 15 mA cm−2 showed the highest corrosion resistance performance and the least Ni2+ ion leaching. The results may aid the development of high-performance coatings on NiTi in orthopaedic applications..

Electrohydrodynamic flow about a colloidal particle suspended in a non-polar fluid

Nonlinear electrokinetic phenomena, where electrically driven fluid flows depend nonlinearly on the applied voltage, are commonly encountered in aqueous suspensions of colloidal particles. A prime example is the induced-charge electro-osmosis, driven by an electric field acting on diffuse charge induced near a polarizable surface. Nonlinear electrohydrodynamic flows also occur in non-polar fluids, driven by the electric field acting on space charge induced by conductivity gradients. Here, we analyse the flows about a charge-neutral spherical solid particle in an applied uniform electric field that arise from conductivity dependence on local field intensity. The flow pattern varies with particle conductivity: while the flow about a conducting particle has a quadrupolar pattern similar to induced-charge electro-osmosis, albeit with opposite direction, the flow about an insulating particle has a more complex structure. We find that this flow induces a force on a particle near an electrode that varies non-trivially with particle conductivity: while it is repulsive for perfectly insulating particles and particles more conductive than the suspending medium, there exists a range of particle conductivities where the force is attractive. The force decays as the inverse square of the distance to the electrode and thus can dominate the dielectrophoretic attraction due to the image dipole, which falls off with the fourth power with the distance. This electrohydrodynamic lift opens new possibilities for colloidal manipulation and driven assembly by electric fields.

Analysis of the Generation and Spatiotemporal Distributions of Dust During Tunnel Construction

The dust generated during tunnel construction poses serious health risks to workers, as it not only causes respiratory obstruction but also leads to pneumoconiosis and respiratory failure after prolonged exposure. However, most existing studies focus on specific construction stages or particular particle sizes and often assume an ideal airflow, neglecting the complex flow fields, vortex effects, and dust composition variations at different stages in tunnel and mine construction. This study systematically analyzes the spatiotemporal distribution characteristics of dust at various stages of tunnel construction and proposes targeted prevention and control strategies. On the basis of measured data from three construction stages—the working face, initial support, and secondary lining stages—and SPSS 27 statistical analysis, a dynamic analysis was conducted on the concentration and distribution patterns of total suspended particulates (TSPs) and particulate matter of different sizes (PM10, PM4, PM2.5, and PM1). The results show that coarse particles dominate during the working face stage, whereas fine particles gradually accumulate during the initial support and secondary lining stages. Finally, this work establishes a dust concentration–excavation time/tunnel depth equation and proposes targeted dust control measures. These findings offer important practical value for enhancing construction safety and air quality.

Particulate Flow of a Viscous Fluid Driven by a Torsionally Oscillating Disk

Abstract A novel hydrodynamic model is used to study oscillatory flow of a particle-laden fluid driven by a torsionally oscillating disk. The present model is featured by a modified form of Navier–Stokes equations which is conceptually different than existing related models and enjoys relatively concise mathematical formulation. Explicit expressions are derived for the radial, azimuthal and axial velocities using the method of power series expansions of small amplitude parameter, and the derived solutions reduce to Rosenblat's earlier results for a clear fluid driven by a torsionally oscillating disk in the absence of suspended particles. The implications of the present results to dusty gases are discussed in detail with particular interest in the effects of suspended particles on the decay indexes and wavelengths of the induced oscillatory velocity fields. The results obtained in this work can be used to quantify the effects of suspended particles on particulate flow driven by a torsionally oscillating disk.

Characterization of Indoor Air Quality in a University Library: Implications Associated with Pollutant Emissions from New and Old Books and Chemicals

During a 1-year study, organic aerosol indoor air samples were collected from sites in a library in Rio de Janeiro, Brazil. Indoor air is a cause for public concern in Brazil. This study presents an indoor air survey wherein the concentrations of aliphatic hydrocarbons, phthalates, phenyl phosphates, aldehydes, limonene, organic acids, and particulate matter were determined. Acids were estimated to be ranging between 0.01 and 30.26 ng m−3, whereas furfural ranged between 0.5 and 3.6 g m−3. Compounds such as furfural, hexanal, benzaldehyde, and vanillin were only detected indoors. Results showed that total suspended particle concentrations were higher outdoors than indoors. Interestingly, 1, 1, 1-trichloro-2, 2-bischlorophenylethane (DDT), and its derivatives were also present. Pesticides are used in libraries to control paper-degrading pests. Therefore, DDT and other chemicals remain nondegraded and pollute the library rooms. This study demonstrates the relevance of monitoring indoor air quality in libraries and the pollutants that can affect the well-being of occupants. Moreover, indoor air quality monitoring can provide early warning to library managers about the effects of indoor air characteristics on unprotected and/or preserved items.

Mechanistic Modeling of Pollutant Mass Redistribution (Sorption/Desorption) in Heterogeneous Systems Explaining Unexpected Slow Kinetics.

Redistribution of pollutants between different solid phases occurs frequently in field and laboratory settings. Examples include the input of urban particles carrying pollutants into soils or rivers with suspended particles or passive sampling. Since multiple mass transfer mechanisms are involved and natural particles typically are very heterogeneous, modeling of sorption/desorption kinetics is challenging. Here, we present a semi-analytical model formulated in the Laplace domain to simulate pollutant redistribution kinetics in heterogeneous systems. The model accounts for a coupled process governed by intraparticle and external boundary layer diffusion, and it considers the heterogeneity of various sorbents (e.g., geometric shape, size, sorption capacity coefficient, and solid and porous particles). The model is validated against data of two batch experiments: (i) the redistribution of phenanthrene in spherical polyethylene particles of different sizes and (ii) redistribution of anthracene-d10 and phenanthrene in a heterogeneous sediment suspension with polyethylene passive samplers. It allows to explain the temporary overshooting of concentrations in the aqueous phase due to different kinetic controls of various particles involved (fast desorption vs. slow sorption) as well as initial fast kinetics followed by surprising long tailing in batch experiments. The approach is very flexible and can be used for many different scenarios.