Suspended Sediment Particles Research Articles

Speciation of cadmium in river waters at different contents (model experiment results)

The data of cadmium forms with a possible increase in technogenic load are presented. The experiments carried out made it possible to simulate the features of the redistribution of chemical forms of cadmium in river waters when it enters in concentrations exceeding the maximum permissible concentrations (MPC). It has been shown that most of the introduced cadmium can pass from dissolved to suspended form, thereby promoting the deposition of suspended particles to the bottom at low flow rates.

Incorporating memory effect into a fractional stochastic diffusion particle tracking model for suspended sediment using Malliavin-Calculus-based fractional Brownian Motion

This study aims to develop a Fractional Stochastic Diffusion Particle Tracking Model (FSDPTM) to illustrate suspended sediment’s long-term dependence (LTD) trajectories immersed in fully developed turbulent flow. Carried by eddies in the open channel, individual suspended sediment behavior exhibits dependence on its past increments. The Fractional Brownian Motion (FBM) is incorporated into the FSDPTM to account for the randomness of turbulent flow and to include the time-dependent increments as a memory effect. Additionally, to enhance the capacity for differentiating FBM, this study introduces Malliavin Calculus, the stochastic calculus of variation, to construct the square -differentiable FBM. For the numerical realizations of square differentiable FBM, the integration of fractional Gaussian white noise and Wiener–Ito Chaos expansion with the Hermite sequence is employed. The FSDPTM offers probabilistic LTD trajectories as solutions to the Ito-type Langevin equation. It also provides particle velocity, acceleration, and ensemble statistics, collectively demonstrating the application of FBM to sediment transport modeling. In conclusion, the key feature of the FSDPTM is its ability to translate LTD derived from FBM into the trajectory of suspended sediment particles in fully developed turbulent flow. Additionally, it expands the solutions from non-differentiable to square-differentiable stochastic processes.

Quantifying the impact of damming on phosphorus reallocation: Finer particles offset the reduction in soluble reactive phosphorus (SRP) by decreasing suspended sediment concentration

In this research, an innovative approach to quantify the impact of damming on phosphorus (P) reallocation between suspended sediments (SS) and water was proposed. P allocation can be described by the surface complexation model, with the impact of damming quantified by four variables: P load, suspended sediment concentration (SSC), particle size, and pH. Iron/aluminium (Fe/Al) oxide-adsorbed P (Fe/Alo-P) was identified as the exchangeable P during adsorption/desorption equilibrium with a series of heterogeneous sediment samples from two large Asian rivers, the Mekong River and the Yellow River. In both rivers, the Fe/Alo-P concentration increased from the tail towards the dam of the reservoirs, primarily attributed to the decrease in particle size from the tail towards the dam of the reservoirs. The Fe/Alo-P concentration in the Lancang River was higher than that in the Yellow River, ranging from 14.5 to 119.9 mg kg−1 and from 14.5 to 22.1 mg kg−1, respectively. The soluble reactive P (SRP) concentration decreased with decreasing SSC, while finer suspended sediment particles containing more Fe/Alo-P greatly offset the reduction in SRP concentration. When the maximum Fe/Alo-P concentration in the finest particles of SS was assumed to be 100 mg kg−1, the P equilibrium concentration (ce) decreased from 0.028 mg L−1 to 0.008 mg L−1 when the SSC decreased from 64 g L−1 to 1 g L−1 for SS with a median grain size (D50) of 32 μm and an Fe/Alo-P concentration of 11 mg kg−1. However, ce increased from 0.008 mg L−1 to 0.021 mg L−1 when the D50 of SS decreased from 32 μm to 4 μm with an SSC of 1 g L−1 and an Fe/Alo-P concentration of 76 mg kg−1 for 4-μm SS. The SRP concentration is sensitive to the Fe/Alo-P concentration in SS, and the P allocation ratio between sediments and water is comparable.

Internal loading regulates the phosphorus concentration in a diversion input shallow lake in the semi-humid region of North China: Differentiated processes in littoral wetland and open water areas

Diversion input lakes usually have a low catchment area/lake area ratio and pulsing pollution input. Various pollutants might accumulate in the lake continuously owing to the concentration effect under high evaporation but low precipitation over the entire area, typically for sedimentary cyclic elements such as phosphorus (P). However, the detailed transportation, sedimentation, and internal release mechanisms of P in the diversion input lakes remain unclear. This study conducted a year-long investigation of the littoral wetlands and open water areas of the shallow Lake Hengshui in the semi-humid region of North China. Results revealed that the average total P concentrations in the water and surficial sediment reached as high as 0.202 mg L−1 and 878.21 mg kg−1 in summer. The high water P levels in the lake were mainly regulated by the high internal P loading during summer and autumn, with the internal P loading being approximately nine times the external P loading. The littoral wetland area serves as a higher sedimentation sink and release source of P than the open water area. The concentrated P was continuously transported to the littoral wetland area through detritus burial, coprecipitation, and deposition of suspended particles. The release of P was mainly controlled by the dissolution of redox-sensitive Fe-P and Org-P at high temperatures and organic matter mineralization in the sediment, accompanied by the potential release capacity of apatite P (Ca-P). Future management of eutrophication and P levels in similar diversion input lakes should pay more attention to the high internal P loading in the sediment and the differentiated sedimentation and release processes in the littoral wetland and open water areas.

Summary of Experiments and Influencing Factors of Sediment Settling Velocity in Still Water

Sediment deposition significantly impacts soil erosion processes, consequently influencing the geographical morphology and surrounding environments of reservoirs and estuaries. Given the intricate nature of sediment deposition, it is imperative to consolidate and analyze existing research findings. Presently, studies on sediment settling velocity primarily employ theoretical, laboratory, and field experimentation methods. Theoretical approaches, rooted in mechanics, examine the various forces acting on sediment particles in water to derive settling velocity equations. However, they often overlook external factors like temperature, salinity, organic matter, and pH. Although laboratory experiments scrutinize the influence of these external factors on sedimentation velocity, sediment settling is not solely influenced by individual factors but rather by their collective interplay. Field observations offer the most accurate depiction of sediment deposition rates. However, the equipment used in such experiments may disrupt the natural sedimentation process and damage flocs. Moreover, measurements of sediment particle size from different instruments yield varied results. Additionally, this paper synthesizes the impact of suspended sediment concentration, particle size, shape, temperature, salinity, and organic matter on sediment settling velocity. Future research should focus on innovating new laboratory observation methods for sediment settling velocity and utilizing advanced scientific and technological tools for on-site measurements to provide valuable insights for further investigation into sediment settling velocity.

Effect of hydrological variability on suspended sediment load at a river junction: a case study

Abstract Confluences act as crucial intersection in a fluvial system as they regulate the flow, sediment, and geomorphological stability. Two of the natural occurrences that have an effect on hydro-morphological processes that characterize the channel are sediment movement and stream discharge. However, assessments of suspended sediment distribution patterns across channel confluences and functions of tributaries on sediment transfer in downstream streams are still inadequately explored. To fulfil this, a year-long field investigation was conducted around river confluence at various time scales during the hydrological season. The bathymetry of the confluence was performed using digital echo-sounding equipment, electro-magnetic current meter, and differential global positioning equipment. This study uses in situ measurement and empirical techniques to quantify the spatiotemporal distribution of suspended sediment particles. Furthermore, Yang's formula was used to analyze the sediment concentration, and several statistical standards were employed to establish a differentiation between predicted and observed data. The results illustrated that a good agreement has been achieved among the calculated and measured statistics based on the correlation coefficient value. According to the findings, 8% fewer errors in the quantification of suspended sediment were induced in the tributary than in the main river because of the very low flow of the tributary. The present ramifications can help increase our database and understanding of the dynamics of major river confluences.

Analysis of environmental transport of suspended sediment particles in a tidal wetland flow under the effect of floating vegetation absorption

Wetlands play an important role in maintaining many natural cycles and supporting a wide range of biodiversity. In the current world, the transport of solute in a wetland with vegetation is an essential issue in environmental, biological, geophysical, and concerned applications. Specially, floating vegetated wetland which is a buoyant platform enveloped by plants, playing a pivotal role in filtering and purifying water in aquatic ecosystems The main focus of the present research is to investigate the transport of sediment particles in a depth-dominated tidal floating vegetated wetland (FVW) flow. The characteristics of floating vegetation absorption and vegetation parameter in FVW are explained to explore the transport of sediment particles. This work’s model relies on an advection-diffusion equation, the solution of which discloses the concentration of settling particles in the water phase. Utilizing the method of moments, a set of moment equations is derived from the governing equation. The equations of moment are then solved using a finite difference implicit scheme. Further, the four moments and Hermite polynomial illustration is adopted to derive the vertical mean concentration distribution profile. The effective dispersivity and the concentration distributions of the sediment particles are illustrated for three different situations of fluid flow: steady, purely oscillatory, and periodic flow with non-zero-mean for all time. The effects of the vegetation factor, settling velocity, absorption due to floating vegetation, and other important factors on sediment transport in FVW are discussed for three different cases separately. Result shows as settling velocity (ω) increases, the influence of vegetation absorption (β) on dispersion coefficient diminishes in the steady state, and its effect on mean concentration becomes less pronounced due to the downward movement of particles. This is because vegetation absorption is stronger near the upper surface, but higher ω values lead to particle downward, reducing β′s impact. The results are described in the context of some real-world situations, as the free surface of a tidal wetland is naturally covered with plants; FVW serve as a natural water purification filter for polluted estuaries, contaminated crude oil wastewater, and so on. This study has potential to aid in water purification efforts as well as for the protection and conservation of coastal environments to limit sea level rise.

Numerical Investigation of the Two-Component Suspension Filtration in a Porous Medium Taking into Account Changes in the Characteristics of the Porous Medium

The paper explores a mathematical model of the filtration of dual-component suspension within a porous medium characterized by two distinct zones. This model encompasses mass balance equations of suspended particles, kinetic equations of deposition formation for both reversible and irreversible deposition types for each suspension component, and incorporates Darcy’s law. In order to solve the problem, we formulate a numerical algorithm for computer-based experimentation on the basis of the finite difference method. Through the analysis of numerical findings, we establish key features of two component suspension filtration within a porous medium. Furthermore, we examine the effects of model parameters on the transport and deposition of suspended particles in a two-component suspension within porous media. The polydispersity of the suspension and the multi-stage nature of deposition kinetics can induce effects that differ from those typically observed in the transport of onecomponent suspensions with single-stage particle deposition kinetics.

Mathematical Model of Three-Component Suspension Transport

Introduction. Prediction of suspension deposition zones is required to assess and minimize the negative impact on the ecosystem of the reservoir during dredging within the framework of large-scale engineering projects, prediction of suspension deposition zones is required to assess and minimize the negative impact on the ecosystem of the reservoir. It is necessary to build a mathematical model that takes into account many factors that have a significant impact on the accuracy of forecasts. The aim of the work is to construct a mathematical model of transport of multicomponent suspension, taking into account the composition of the soil (different diameter of the suspension particles), the flow velocity of the water flow, the complex geometry of the coastline and bottom, wind stresses and friction on the bottom, turbulent exchange, etc.Materials and Methods. A mathematical model for the transport of a multicomponent suspension and an approximation of the proposed continuous model with the second order of accuracy with respect to the steps of the spatial grid are described, considering the boundary conditions of the Neumann and Robin type. The approximation of the hydrodynamics model is obtained based on splitting schemes by physical processes, which guarantee fulfillment mass conservation for discrete model.Results. The proposed mathematical model formed the basis of the developed software package that allows to simulate the process of sedimentation of a multicomponent suspension. The results of the work of the software package on the model problem of sedimentation of a three-component suspension in the process of soil dumping during dredging are presented.Discussions and Conclusions. The mathematical model of transport of three-component suspension is described and software implemented. The developed software allows to simulate the process of deposition of suspended particles of various diameters on the bottom, and to evaluate its effect on the bottom topography and changes in the bottom composition. The developed software package also allows to analyze the process of sediment movement in the case of resuspension of multicomponent bottom sediments of the reservoir, which causes secondary pollution of the reservoi

From cave to spring: Understanding transport of suspended sediment particles in a fully phreatic karst conduit using particle analysis and geochemical methods

AbstractKarst aquifers are vulnerable to contamination, especially in the context of heavy rainfall events. Contamination is often associated with turbidity that can originate from the soil zone, infiltrating surface waters or resuspension of previously deposited sediments within the aquifer. While turbidity events can be well monitored at karst springs, related information about the sediment origin and the spatiotemporal input function usually remain unknown. Thus, the mobility and attenuation of the particulate matter and associated pollutants can hardly be determined quantitatively. A tracer test with suspended cave sediments and solute tracers for comparison has hence been performed in a karst aquifer at the Blue Spring (Blautopf) in Southern Germany. The tracers were injected in the cave system, at the beginning of a fully phreatic karst conduit, and monitored at the spring after a travel distance of 1250 m. The particle‐size distribution was monitored using a particle counter and sediment samples were filtered with 0.45‐μm cellulose acetate filters. Particles on the filter were analysed for major and trace elements as well as rare earth elements (REE) by ICP‐MS after acid digestion. Results show that (1) sediment particles were transported faster than solutes, which was interpreted as a transport in the main flow path of the conduit, whereas conservative tracers tend to diffuse into smaller fissures as well. (2) All measured particles sizes were transported at similar flow velocities. (3) A transport associated to sediment particles could be shown for all measured elements. This study presents a methodological improvement of comparative sediment tracer tests as well as deeper insights into particle and element transport processes in karst aquifers, originating from previously deposited cave sediment. Results provide deeper knowledge into transport processes of sediment‐associated contaminants, such as heavy metals which may strongly be affected by the particle size. This knowledge contributes to a better management of karst water resources in the context of turbidity events.

Fresh submarine groundwater discharge offshore Wellington (New Zealand): hydroacoustic characteristics and its influence on seafloor geomorphology

Fresh submarine groundwater discharge (FSGD) influences the biogeochemistry of coastal areas and can be a proxy for potential untapped resources of offshore freshened groundwater (OFG). In most areas however, the onshore-offshore connection and the recharge characteristics of offshore aquifers are poorly constrained, making a potential exploitation of this resource challenging. Offshore Wellington (New Zealand), a well-defined onshore aquifer system extends beneath the harbour, where substantial amounts of freshwater seep out from the ocean floor. The aquifer system has been studied in detail and recently the first attempts worldwide have been made here to use the offshore groundwater as a future source of drinking water. However, the locations and extent of FSGD as well as its influence on seafloor morphology are still poorly understood. Exact localisation of FSGD sites is essential to sample and quantify discharging waters but remains challenging due to a lack of robust and appropriate measurement procedures. Novel sensing strategies, such as the influence of seeping groundwater on hydroacoustic water column reflectivity could greatly improve the identification of groundwater discharge locations worldwide. Therefore, we use a multidisciplinary dataset and evaluate different methodologies to map the spatial extent of FSGD sites and determine their geomorphologic expressions on the seafloor of Wellington Harbour. In this study, single and multibeam hydroacoustics and towfish (temperature, salinity and turbidity) transects were combined with remotely operated vehicle (ROV) dives and sediment cores to better characterise FSGD sites. We observed several hundred seafloor depressions (pockmarks) that we attribute to continuous seepage of gas and groundwater from the seafloor. Different pockmark morphologies indicate different fluid flow regimes and the persistent flow allows even small pockmarks to remain unchanged over time, while the geomorphologic expressions of anchor scours on the seafloor diminish in the same region. Enhanced hydroacoustic reflections in the water column within and above the pockmarks indicate suspended sediment particles, which are likely kept in suspension by discharging groundwater and density boundaries.

Effect and microbial mechanism of suspended sediments particle size on nitrous oxide emission in eutrophic lakes

Suspended sediment (SPS) is an important environmental factor in eutrophic lakes, where they may play a significant role in the microbial nitrogen cycle and thus affect the N2O source and sink function. This study investigated the correlation and corresponding microbial mechanisms between N2O emission fluxes and SPS particle sizes. N2O emission characteristics were investigated in four parallel operated lab-scale microcosmic systems, in which different sizes of SPS particles were inoculated (i.e., <75, 75–150, 150–300, and >300 μm). The results show that, N2O emission fluxes in the eutrophic lakes were exponentially correlated with the lake trophic level index (TLI) (R2 = 0.94, p < 0.01) and the specific surface area of the SPS (R2 = 0.38, p < 0.05). In the microcosmic systems, SPS with 75–150 μm particles had the highest N2O emission rate of 5.94 ± 0.007 μg N/L/d, which was 2.6 times that of the <75 μm particle size system. The microcosmic system with particle size >300 μm had the highest N2O reduction rate (Vmax) of 6.776 μmol/L/h, which was 16–50 times that of the other three groups. Larger particle size SPS have a smaller specific surface area, which could affect the microenvironment on SPS surface and thus affect the microbe functions. The microbial community structure results indicated that the dominant microorganisms on the SPS surface were denitrifying bacteria. The maximum (nirS + nirK)/nosZ ratio was 30.2 for the 75–150 μm system, which was nearly 2 times higher than the other systems. The >300 μm system had the highest nosZ abundance, indicating a strong ability to reduce N2O. The co-occurrence networks analysis indicated that the cooperation and competition among nitrifiers and denitrifiers determined N2O emissions. These results provide fundamental insights into the influence of SPS size on N2O emissions in eutrophic lakes.

Поле скоростей течения на участке реки Сайгон при эксплуатации противопаводковых сооружений

Introduction. Vietnam’s largest economic centre, Ho Chi Minh City, is facing riverbank erosion, one of the main causes of which is runoff. In this study, the flow velocity field of the Saigon River section is analyzed in different time periods. Materials and methods. Data on discharge, water level, river network topography and river channel were collected to set up simulation models in the programmes MIKE 11 and MIKE 21. These programmes are the main tools used in the study. Results. The current velocity in the middle of the river is 3–4 times higher than on the two banks. However, during the period between high and low tide, the current on both sides of the river has higher speed than the main stream, especially in the upper part of the winding banks, such as the part of the river from Ben Nghe sluice to Tan Thuan sluice and the section of the river from An Loi Dong police station to Thu Thiem 2 bridge. The velocity values in the studied river section in most cases exceed the allowable erosion-free velocity values of particles of channel material, river banks, and suspended sediment particles. The operation of the flood control sluices will slightly reduce the flow velocity values and also cause whirlpools in front of the sluices. Conclusions. The MIKE 11 and MIKE 21 software detailed the flow distribution of the Saigon River. The flow velocity on the Saigon River has a complex distribution and varies from period to period depending on the flood discharge from the Dau Tieng Reservoir and the tidal currents of the East Sea. The process of erosion on both sides of the river will occur regularly and continuously, so urgent measures are needed to protect the riverbank.

Simulation of sandstone formation damage caused by solid particle invasion

During the drilling and completion process, the invasion of solid particles can have a serious impact on reservoir permeability, but there is a lack of effective prediction models for its impact. We developed a prediction model of solid particle invasion damage in response to the issue of reservoir damage induced by solid particle invasion during the exploitation of sandstone reservoirs. By considering the changes in pore permeability characteristics, particle migration and rock stress-strain state are coupled. The findings reveal that as filtration duration increases, the concentration of suspended particles and sediment particles increases, resulting in a progressive reduction in formation permeability around the wellbore. The greater the filtration coefficient, the greater the quantity of particle deposition, however, this also leads to a slowdown in the growth in deposition quantity. As the diffusion rate increases, particles are more likely to deposit. The concentration of suspended particles decreases progressively as tortuosity increases, as does the concentration of sediment particles. Large saturation sedimentation in the pore throat may cause more suspended particles to deposit, lower the effective seepage channel of the pore throat, and drastically impair formation permeability. The results of the impact factor comparison showed that filtration coefficient and medium tortuosity are the key factors. Improving the temporary plugging effect of solid particles in formations with large tortuosity of pore throats can effectively reduce reservoir damage. The findings of this study can help for optimization design of solid particles in drilling fluid for reservoir protection.

Composition and Flux of Dissolved and Particulate Carbon and Nitrogen in the Lower Tocantins River

AbstractThe Tocantins River contributes ∼5% of the total flux of water to the Amazon River plume in the Atlantic Ocean. Here, we evaluate monthly variability in the composition and abundance of carbon, nitrogen, and suspended sediment in the lower reaches of the Tocantins River from 2014 to 2016. Dissolved organic carbon concentrations generally increased during periods of high discharge and are ∼1.5 times lower than average concentrations at the mouth of the Amazon River. Dissolved inorganic carbon similarly increased during periods of high discharge. Total dissolved nitrogen and individual nitrogen species followed a similar temporal pattern, increasing during high water. predominated the dissolved inorganic nitrogen pool, followed by , and , characteristic of environments with a relatively low anthropogenic impact. Dissolved fractions represented 92% of the total carbon exported and 78% of the total nitrogen exported. The suspended particulate sediment flux was 2.72 × 106 t yr−1, with fine suspended sediment dominating (71.3%). Concentrations of carbon relative to nitrogen indicate a primarily terrigenous source of organic matter and CO2 derived from in situ respiration of this material during the rainy season and a primarily algal/bacterial source of organic matter during the dry season. Considering past estimates of dissolved carbon and nitrogen fluxes from the Amazon River to the Atlantic Ocean, the Tocantins River contributes 3% and 3.7% to total fluxes to the Amazon River plume region, respectively. While this contribution is relatively small, it may be influenced by future changes to the basin's land use and hydrology.

Physicochemical Properties and Environmental Effects of Suspended Sediment Particles in the Largest Freshwater Lake, China

Suspended sediment particles (SSPs) act as a potential source of and sink for aquatic pollution. This study sampled six sites in Poyang Lake in August and November 2019. Changes in the physicochemical properties of SSPs were analyzed using scanning electron microscope energy-dispersive spectrometry (SEM-EDS). The results showed that SSPs consisted mainly of clay and chalk, with an average content of 39.71% and 57.52%, respectively. The average particle size distribution of SSPs in the study area ranged from 5.54 to 15.97 μm and the spatial distribution pattern showed the north lake area (I) &gt; west lake area (II) &gt; east lake area (III). The angle (K) of morphological indicators varied widely, with coefficients of variation between 0.25 and 1.23. Water-flow velocity was negatively correlated with SSP size, while suspended-solid concentration was positively correlated with SSP surface roughness. Morphological parameters, chemical composition, and correlation between each SSP form were analyzed to identify morphological distribution characteristics. Linear regression equations estimated endogenous phosphorus load in zones I, II, and III as 1027.202 mg/kg, 1265.343 mg/kg, and 1013.111 mg/kg respectively. Therefore, we conclude that the morphological differences in particulate matter, the interaction between chemical fractions, and the aqueous environment affecting the distribution of phosphorus fugitive forms, may contribute to endogenous lake pollution. These results are essential for revealing the intrinsic relationship between SSP physicochemical properties and lake eutrophication and studying other water–sediment interface processes of lake pollutants.

Numerical analysis of sediment transport and depth averaged flow velocity in non-prismatic compound channels

The flow velocity in compound open channels is greatly affected by the geometry of both the main channel (MC) and floodplain (FP). In this study, a numerical investigation of the joint effect between the FP divergence angle and the size of suspended sediment particles on sediment transport and flow depth-averaged velocity (DAV) in non-prismatic diverging compound channels was conducted. In addition, the influence of relative flow depth on the DAV in different flow directions (i.e., stream-wise and span-wise) was examined. Three divergence angles of 4.0, 6.3 and 11.3°, four sediment particle sizes of 1, 5, 50 and 500 µm and two relative depths of the FP with respect to the MC of 0.20 and 0.40 were considered during simulations. A Computational Fluid Dynamics (CFD) software ANSYS-Fluent was used to perform the required simulation scenarios and the DAV was expressed in terms of a dimensionless velocity (i.e., relative depth-averaged velocity; RDAV) to generalize the use of the obtained results. Results revealed that the span-wise RDAV gradient between the MC and FP at the middle and the end sections of the divergence reach is much larger in the case of higher divergence angle. Moreover, the presence of coarse sediment particles in the sediment-laden flow resulted in an augmentation in the fluctuations of span-wise and stream-wise RDAVs as compared to those obtained in the case of fine sediment particles. Results also showed that the span-wise RDAV gradient between the two subsections (MC and FP) increases with decreasing the relative flow depth. Sediment particle size had a considerable impact on the span-wise RDAV values, especially in the case of lower relative depth. As the sediment particle size increases, the distortion in the span-wise RDAV distribution curves increases. However, the stream-wise RDAV along the MC and FP decreases, as the sediment particle size decreases, especially in the case of higher relative depth. Based on the results, it can be concluded that the span-wise DAV gradient was greatly affected by the FP divergence angle and sediment particle size. The fluctuations in the span-wise DAV gradient were more pronounced in the case of higher divergence angles and coarser sediment particles. The stream-wise DAV distribution along the MC and FP was mainly influenced by the relative depth and sediment particle size. The stream-wise DAV dip along the MC and FP was more explicit in the case of higher relative depths and finer sediment particles.

Effect of biofilms on the clogging mechanisms of suspended particles in porous media during artificial recharge

Artificial recharge of groundwater is an effective technology for solving the shortage of water resources. The clogging of porous media is a bottleneck that limits the application of this technology. In this study, percolation experiments in sand columns were conducted to investigate the influence of different types of biofilms on the deposition of suspended particles and clogging evolution during artificial recharge. A unique aspect of this study is the consideration of biofilms coated on porous media when the clogging mechanisms of suspended particles in porous media are explored. At the end of the recharge process, the relative hydraulic conductivity (K’) of the porous media in descending order was Pseudomonas aeruginosa experimental group (PA) > Bacillus subtilis experimental group (BS) > mixed microbial consortium experimental group (MC) > suspended particle only group (SP). The suspended particles in SP- moved more deeply into the sand column than those in BS, PA, and MC. Electron microscopy, high-throughput sequencing, and confocal laser scanning microscopy were used to identify the mechanisms governing clogging evolution under the influence of biofilm existence. The presence of a biofilm not only alters the surface charge and physical roughness of the porous media, but also affects the electrostatic interaction between the porous media and suspended particles. Biofilms combine tightly with suspended particles by binding and adhesion, which can form tight biofilm-particle aggregations. Compared with deposition of particle-only in SP, the biofilm-particle aggregations on the surface of the porous media are more firm. The biofilm coated on the surface of porous media occupied the pore vacancy and narrowed the void space compared with that in clean sand, which induced physical straining. As the thickness of biofilm coated on the sand surface increased, the more suspended particles were deposited on the sand surface in PA. These findings provide insights into clogging under the influence of biofilms and have implications for future field-based artificial recharge.

Coffee stain effect on a fibre from axisymmetric droplets

The so-called coffee stain effect has been intensively studied over the past decades, but most of the studies have focused on sessile droplets. In this paper, we analyse the origin of the difference between the deposition of suspended particles in a sessile drop and in an axisymmetric drop deposited on a fibre. First, we model the shape of a drop on a fibre and its evaporative flux with some approximations to derive analytical calculations. Then, for pinned contact lines, we solve the hydrodynamics equations in the liquid phase under the lubrication approximation to determine the flow velocity toward the contact lines. We comment on these results by comparison to a sessile drop of similar evaporating conditions, and we show that the substrate curvature plays a role on the contact line depinning, the local evaporative flux and the liquid flow field. The competition between the advection and the Brownian motion indicates that the transport of the particles toward the contact line occurs in a volume localised in the close vicinity of the contact lines for a drop on a fibre. Thus, the fibre geometry induces a weaker accumulation of particles at the contact line compared to a sessile drop, leading to the more homogeneous deposit observed experimentally.

Threshold Recognition of Water Turbidity for Clogging Prevention during Groundwater Recharge Using Secondary Effluent from Wastewater Treatment Plant

The recharge efficiency during artificial groundwater recharge (AGR) is reduced primarily by clogging that is triggered by suspended particles. However, there are loopholes in the current standards of recharge-water quality for clogging control during AGR, and the threshold values of turbidity to prevent clogging have not been reasonably determined. In this study, secondary effluents from wastewater treatment plants (WWTPs) were injected into saturated sand columns to simulate the process of AGR. Batch experiments under different turbidity conditions were conducted, and the numerical modeling of particle transport and deposition was performed to assess the clogging processes. Theories of single-collector contact and interfacial interaction energy were applied to elucidate possible microcosmic mechanisms. The results showed that the diluted secondary effluent (SE) with turbidities of 0.540 ± 0.050, 1.09 ± 0.050, and 1.84 ± 0.060 NTU caused considerable clogging in the porous media, which decreased the relative hydraulic conductivities (K/K0) by 13.2%, 17.6%, and 83.6%, respectively. The filtered SE with a turbidity of 0.160 NTU did not cause clogging, and K/K0 was reduced by only 1.70%. The clogging was attributed to the deposition of suspended particles in the sand matrix because they have a high collision efficiency (0.007–1.98) and attachment efficiency (0.029–0.589 kBT). Finally, this paper recommends that the turbidity of the recharge water should not exceed 0.500 NTU during AGR practices.