Retention Of Fine Particles Research Articles

Turbulence and Particle Deposition Under Steady Flow Along a Submerged Seagrass Meadow

AbstractSeagrass meadows can retain fine particles, improving water clarity and promoting carbon sequestration. Laboratory experiments were conducted to investigate the influence of velocity and meadow density on the retention of fine particles within a meadow. Vertical profiles of velocity and turbulent kinetic energy (TKE) were measured along a model meadow. The net deposition was measured using microscope slides positioned inside and outside the meadow. The deposition was correlated with the evolution of velocity along the meadow. At the leading edge, the net deposition decreased over a distance Lr, relative to the bare bed, which was associated with a region of vertical updraft and elevated TKE. Net deposition increased with the distance from the leading edge, associated with a decrease in vertical velocity and TKE. In some cases, a distinct peak in the deposition was observed at distance Lp from the leading edge, associated with a minimum in TKE. Both Lr and Lp decreased with increasing meadow density. Deposition in the fully developed region of the meadow decreased with decreasing stem density and increasing channel velocity, and for the lowest stem density and highest channel velocity the deposition in the meadow was less than that in the bare channel. Diminished deposition was linked to resuspension driven by stem‐generated turbulence. A model for canopy‐averaged TKE was validated and used to explore the range of field conditions for which TKE within a meadow would be reduced, relative to the bare bed, which would support the accumulation of fine organic material within the meadow.

武汉市15种阔叶乔木滞尘能力与叶表微形态特征

PDF HTML阅读 XML下载 导出引用 引用提醒 武汉市15种阔叶乔木滞尘能力与叶表微形态特征 DOI: 10.5846/stxb201808241808 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金青年项目（31500577）；湖北省高等学校优秀中青年科技创新团队计划项目（T201605）；2018年省级大学生创新创业计划项目（201810500055） Dust- retention capability and leaf surface micromorphology of 15 broad-leaved tree species in Wuhan Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以武汉市15种常见的阔叶乔木为研究对象，通过3级滤膜过滤法测定了各乔木单位叶面积滞留不同粒径颗粒物（TSP、PM>10、PM10、PM2.5）的质量，并通过扫描电镜观察比较了15种乔木的叶表面微形态结构，分析了微形态对植物滞尘能力的影响。结果表明：15种乔木单位叶面积的滞尘量存在显著差异（P<0.05），综合滞尘能力最强的植物为二球悬铃木、桂花和石楠，除以上3者外，女贞和广玉兰分别具有较强的滞留PM10和PM2.5的能力；加杨滞留TSP和PM>10的能力最弱，玉兰滞留PM10和PM2.5的能力最弱。各乔木单位叶面积滞留PM2.5和PM10的质量分别占总粉尘量的0.7%-8.9%和3.6%-33.9%。叶表面微结构观察表明，叶表面粗糙、褶皱较多，或被有蜡质层的植物有利于粉尘颗粒物的附着。相关性分析表明，植物单位叶面积的滞尘量与叶表面沟槽的宽度呈显著相关，上下表面沟槽宽度越小，越有利于细微颗粒物（PM2.5）的滞留，下表面沟槽宽度增加，有利于粉尘总颗粒物（TSP）的滞留。由此可见，叶表面粗糙度、蜡质含量和沟槽宽度等微形态结构是调控绿化树种叶片滞尘能力的重要因素，在武汉以治理大气粉尘污染为目标进行城市绿化时，可考虑选择二球悬铃木、桂花和石楠等滞尘能力强的树种。 Abstract:We selected 15 common broad-leaved tree species in Wuhan and quantified particles of different sizes (TSP, PM>10, PM10, PM2.5) per unit leaf area using a 3-layer membrane filtration method. To explore the influence of leaf surface micromorphology on dust-retention ability, the leaf surface micromorphology of the 15 tree species was observed by scanning electron microscopy (SEM). The results showed that there were significant differences in dust retention per unit leaf area among the 15 tree species (P<0.05). The plants with the strongest dust-retention ability were Platanus acerifolia, Osmanthus fragrans, and Photinia magnolia. In addition to, Ligustrum lucidum and Magnolia grandiflora had a strong ability to retain PM10 and PM2.5 on their leaves, respectively. Populus×canadensis had the weakest ability to retain TSP and PM>10, and Magnolia denudata had the weakest ability to retain PM10 and PM2.5. The ratio of PM2.5 and PM10 mass per unit leaf area to total dust content ranged from 0.7% to 8.9% and from 3.6% to 33.9%, respectively. Micromorphological observations of the leaf surfaces showed that rough, wrinkled leaves or a waxy layer on the leaves were conducive to the attachment of dust particles. The correlation analyses indicated that the amount of dust per unit leaf area was significantly correlated with the width of the grooves on the leaf surface. The smaller the width of grooves on the upper and lower surfaces, the more favorable the retention of fine particles (PM2.5). The larger the width of grooves on the lower surface, the more favorable the retention of total particles (TSP). Therefore, the micromorphological structure of the leaf surface (roughness, wax content, and groove width) are important factors in the dust-retention capability of greening tree species. When urban greening is carried out in Wuhan to control atmospheric dust pollution, we suggest to choose tree species with a strong dust-retention capability, such as P. acerifolia, O. fragrans, and P. magnolia. 参考文献 相似文献 引证文献

Controls on fine particle retention in experimental streams

The transport and retention of fine particulate organic matter (FPOM) in headwater streams plays a significant role in organic matter processing and represents a critical link between upstream and downstream systems. Benthic biofilms potentially alter substrate characteristics and dynamics. However, the influence of biofilm colonization on FPOM retention has not been well documented, likely due to inherent heterogeneity of natural systems. We expected that biofilm growth would either enhance or diminish FPOM retention in the streambed, whereas biofilm growth would vary depending on the underlying substrate template. We used a short-term FPOM addition technique to estimate transport distances of a fine particle analog (corn pollen: 70 μm) in four 50-m experimental streams (Q = 1.5 L/s) at the Notre Dame Linked Experimental Ecosystem Facility. Streams varied in substrate size (1-cm pea gravel vs 10-cm small cobble) and complexity (homogenous 50/50 mix vs alternating sections). We sampled streams on multiple dates over 5 mo (June–October) of biofilm colonization and senescence. While FPOM transport distances generally increased as biofilm colonization occurred, retention was variable across streams and over time. We found no consistent or simple pattern of FPOM retention in our streams. Rather, one of the strongest effects was an indirect relationship between FPOM removal and transient storage, a factor that is strongly driven by biofilm colonization. These results emphasize the dynamic feedback of the physical and biological environments influencing FPOM retention in streams.

Particle Migration and Clogging in Porous Media: A Convergent Flow Microfluidics Study

AbstractThe migration and retention of fine particles in porous media are important phenomena in natural processes and engineering applications. Migrating particles experience physicochemical interactions with carrier fluids, pore walls, and other migrating particles. The governing dimensionless ratios capture particle‐level forces, flow conditions, and geometric characteristics. This study explores micron‐size particle migration and retention in microfluidic chips during convergent radial flow, which is the prevalent flow condition in water extraction and oil production. Pore‐scale observations reveal the role of electrostatic interactions on clogging mechanisms: Glass particles experience retardation‐accumulation bridging, while quasi‐buoyant latex particles involve capture and clogging. Consequently, flow rates exert opposite effects on the clogging behavior of inertial glass particles versus electrostatically affected latex particles. Migrating particles experience a varying fluid velocity field in convergent radial flow, and clogging reflects the evolving local conditions (Nad, Ar, Stk, and Re). In particular, clogged pores alter local flow and promote further clogging nearby. Pore network model simulations suggest that such “dependent clogging” lowers the permeability of the porous medium more effectively than independent clogging at random locations.

Fine particle retention and deposition in regions of cyclonic tidal current rotation

Benthic sediments in continental shelf seas control a variety of biogeochemical processes, yet their composition, especially that of fine sediment, remains difficult to predict. Mechanisms for mud or fine sediment deposition and retention are not fully understood. Using sediment data and a hydrodynamic model of the Northwest European shelf seas, a relationship is shown to exist between fine benthic sediment composition and regions of cyclonic tidal current rotation. The reduced thickness of cyclonic tidal benthic boundary layers compared with the anticyclonic case promotes deposition of fine sediment and trapping of resuspended material. Adding the effects of the benthic boundary layer thickness, as influenced by ellipticity or not, sheds some light on the limitations of approaches only focusing on bed shear stress and sediment pathways to predict the location of mud deposits. A tidal boundary layer predictor that includes ellipticity alongside tidal current magnitude and depth was shown to spatially agree with maps of mud deposits.

Less Fine Particle Retention in a Restored Versus Unrestored Urban Stream: Balance Between Hyporheic Exchange, Resuspension, and Immobilization

AbstractStream restoration goals include reducing erosion and increasing hyporheic exchange to promote biogeochemical processing and improve water quality. Little is known, however, about fine particle dynamics in response to stream restoration. Fine particles (&lt;100 μm) are exchanged with transient storage areas near and within streambeds and banks. Fine particle retention directly impacts carbon and nutrient cycling by supporting benthic and hyporheic primary production, but overaccumulation of fine particle deposits can impair metabolism by burying benthic biofilms and reducing streambed permeability. We analyzed the transport and retention of water and fine particles at both the reach and local scales in a restored urban stream, 9 years postrestoration. We injected conservative solute and fine particle tracers under summer baseflow conditions and monitored their distribution between surface water, porewaters, and storage areas (i.e., biofilms, hyporheic zones, and slow surface waters). Comparison of the results to a nearby unrestored stream demonstrate that the restored reach had 10–45 times greater exchange of fine particles with transient storage zones, but 5 times lower rate of net particle immobilization. Local‐scale results showed that restoration increased fine particle exchange with short‐term storage areas but did not increase long‐term particle retention. Thus, the restored stream rapidly exchanged fine sediments with transient storage areas, but did not store fine sediments as efficiently as the unrestored stream. The decreased retention of particulate organic matter in the restored stream may reduce biogeochemical processes, such as denitrification, by not providing sufficient organic carbon or the surface area required for microbial colonization.

Fine particle retention within stream storage areas at base flow and in response to a storm event

AbstractFine particles (1–100 µm), including particulate organic carbon (POC) and fine sediment, influence stream ecological functioning because they may contain or have a high affinity to sorb nitrogen and phosphorus. These particles are immobilized within stream storage areas, especially hyporheic sediments and benthic biofilms. However, fine particles are also known to remobilize under all flow conditions. This combination of downstream transport and transient retention, influenced by stream geomorphology, controls the distribution of residence times over which fine particles influence stream ecosystems. The main objective of this study was to quantify immobilization and remobilization rates of fine particles in a third‐order sand‐and‐gravel bed stream (Difficult Run, Virginia, USA) within different geomorphic units of the stream (i.e., pool, lateral cavity, and thalweg). During our field injection experiment, a thunderstorm‐driven spate allowed us to observe fine particle dynamics during both base flow and in response to increased flow. Solute and fine particles were measured within stream surface waters, pore waters, sediment cores, and biofilms on cobbles. Measurements were taken at four different subsurface locations with varying geomorphology and at multiple depths. Approximately 68% of injected fine particles were retained during base flow until the onset of the spate. Retention was evident even after the spate, with 15.4% of the fine particles deposited during base flow still retained within benthic biofilms on cobbles and 14.9% within hyporheic sediment after the spate. Thus, through the combination of short‐term remobilization and long‐term retention, fine particles can serve as sources of carbon and nutrients to downstream ecosystems over a range of time scales.

Benthic biofilm controls on fine particle dynamics in streams

AbstractBenthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to obtain a range of biofilm characteristics. Fluorescent, 8 µm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30 min period. We measured particle concentrations using a flow cytometer and mesoscale (10 µm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition‐resuspension dynamics were determined by fitting results to a stochastic mobile‐immobile model, which showed that retention timescales for particles within the biofilm‐covered streambeds followed a power‐law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers.

Intact and broken cellulose nanocrystals as model nanoparticles to promote dewatering and fine-particle retention during papermaking

Cellulose nanocrystals (CNCs), either in intact form or after mechanical shortening, were used as a model nanoparticle for enhancement of dewatering and fine-particle retention during lab-scale papermaking process evaluations. Cryo-crushing, using dry or wet CNCs, was performed to shorten the particles from an initial mean value of 103.1 nm to either 80.4 nm (wet crushed) or 63.4 nm (dry crushed). Papermaking-related tests were performed with the solids from 100 % recycled copy paper, which were prepared as a 0.5 % solids suspension in dilute Na2SO4 solution and then treated successively with 0.05 % of poly-diallyldimethylammonium chloride, 0.05 % of very-high-mass cationic acrylamide copolymer, and then various types and dosages of negatively charged nanoparticles. The performance of the CNCs, relative to papermaking goals, was compared to that of two colloidal silica products that are widely used in industry for this purpose. All of the nanoparticles were observed to promote both dewatering and fine-particle retention. The intact CNCs were more effective than the broken CNCs with respect to fine-particle retention. Effects on flocculation of the fiber suspension were detectable, but not large relative to the sensitivity of the test employed. Results are discussed in the light of concepts of polyelectrolyte bridges and the participation of elongated nanoparticles in completing those bridges in such a way as to form shear-sensitive attachments among solids surfaces in the suspension.

Model Tests on Dredged Soil–Filled Geocontainers Used as Containment Dikes for the Saemangeum Reclamation Project in South Korea

AbstractA geotextile tube is a type of geocontainer typically filled with sandy slurries and fine-grained dredged sediments. Its performance in strength, dewatering, fine-particle retention, and stacked stability has been studied extensively. However, very little is understood about the shape-deformation behavior of geotextile tubes. In this paper, slurry-settlement, constant head permeability, and seepage-force tests were conducted to determine the geocontainers’ geotechnical design parameters. The characteristics of the dredged fill material determined from the slurry-settlement, constant head permeability, and seepage-force tests are presented. Large-scale tests on model geotextile tubes were also conducted. A large-scale apparatus for geotextile tube–filling test simulation is introduced. The apparatus consists of a slurry mixing station, a pumping and delivery station, a geotextile tube–filling station, and a data station. The results of the model tests conducted on a transparent geobag (undrained co...

A three-dimensional model of fine particle retention during percolation through a fiber mat

Fine particles are usually retained in fiber mats by sieving. To date, no theory has combined fiber and mat characteristics into a predictive retention model. A multilayer analytical retention model developed during this study predicts retention within a thick fiber mat by modeling retention as particles pass through a series of very thin fiber mats. A suspension of 5-75 μm toner particles was percolated through rayon fiber mats. The model’s prediction approached the experimental data only when the ratio of particle diameter to fiber diameter increased toward 2.0, the upper limit within the rayon fiber mat data set. Retention was also experimentally determined on the macroscale with simulated fiber mats, through which 4-20 mm beads were dropped. The particle diameter was at least 2.2 times the fiber diameter for all of the macroscale experimental data, explaining the much better fit of the data from those experiments to the model’s predictions.

Retention and remobilization dynamics of fine particles and microorganisms in pastoral streams

Both microbial metabolism and pathogen retention and remobilization are dependent on downstream transport of fine particles, which migrate in a series of deposition and resuspension events. All fine particles, including clay minerals, particulate organic carbon, nutrients and microbes, are often considered to be transported similarly in the environment because of a lack of specific observations comparing their relative transport. We conducted a tracer injection study to compare the transport and retention of the fecal indicator bacterium Escherichia coli, synthetic inert fluorescent fine particles, and a dissolved conservative tracer. We found that the fluorescent fine particles and bacteria were transported similarly, with both having greater retention than the solute tracer. We used a stochastic model to evaluate in-stream retention and migration of the solute, fluorescent particles, and E. coli. The best-fit model parameters indicate that different stream reaches had varied retention characteristics, but always showed greater retention of fluorescent particles and E. coli compared to the solute tracer. Direct measurements within known retention areas after the injection showed that the majority of the fluorescent particles and E. coli were retained near the sediment–water interface in macrophyte stands or filtered within the top 3 cm of the streambed sediment. Both the tracer particles and E. coli were retained within these regions for multiple months following the injection experiment. The stochastic model properly captured the wide range of storage timescales and processes we observed in the stream. Our results demonstrate the importance of the streambed sediment and in-stream macrophytes as short- and long-term reservoirs for fine organic particles and microbes in streams.

Stochastic modeling of fine particulate organic carbon dynamics in rivers

The majority of particulate organic matter standing stock in streams is < 1 mm in diameter, and the mobile phase is primarily very fine particles. Such fine particles transport downstream in a series of deposition and resuspension events mediated by interactions with coarser bed sediment, yielding fine particle retention over a wide range of time scales. This retention controls the opportunity for biogeochemical processing of particulate organic carbon in streams. We present a conceptual model of particulate organic carbon transport in rivers categorized in three cyclic processes: (i) migration of fine particles from the water column to the underlying and surrounding sediments, (ii) fine particle transport and retention within the bed sediments, and (iii) resuspension of fine particles back to the water column. We developed a stochastic model to describe the transport and retention of fine suspended particles in rivers, including advective delivery of particles to the streambed, transport through pore waters, and reversible filtration within the streambed. We then apply this model to observations of fine particle transport in two small streams, and show that the stochastic mobile-immobile model supports improved interpretation of particulate organic carbon dynamics under base flow conditions. Analysis of in-stream solute and particle data shows that particles engage in multiple deposition and resuspension events during downstream transport, and that long-term retention in the streambed produces extended slow releases to the stream even during base flow conditions. We also show how multiscale stochastic modeling can be used to incorporate local observations of particle retention in predictions of whole-stream particle dynamics.

Membrane installation for enhanced up-flow anaerobic sludge blanket (UASB) performance

It is postulated that up-flow anaerobic sludge blanket (UASB) reactor efficiency can be enhanced by a membrane immersed in the reactor to operate it as an anaerobic membrane bioreactor (AnMBR) for low-strength wastewater treatment. This postulate was tested by comparing the performance with and without a hollow fiber microfiltration membrane module immersed in UASB reactors operated at two specific organic loading rates (SOLR). Results showed that membrane filtration enhanced process performance and stability, with over 90% total organic carbon (TOC) removal consistently achieved. More than 91% of the TOC removal was achieved by suspended biomass, while less than 6% was removed by membrane filtration and digestion in the membrane attached biofilm during stable AnMBRs operation. Although the membrane and its biofilm played an important role in initial stage of the high SOLR test, linear increased TOC removal by bulk sludge mainly accounted for the enhanced process performance, implying that membrane led to enhanced biological activity of the suspended sludge. The high retention of active fine sludge particles in suspension was the main reason for this significant improvement of performance and biological activity, which led to decreased SOLR with time to a theoretical optimal level around 2g COD/g MLVSS·d and the establishment of a microbial community dominated by Methanothrix-like microbes. It was concluded that UASB process performance can be enhanced by transforming such to AnMBR operation when the loading rate is too high for sufficient sludge retention, and/or when the effluent water quality demands are especially stringent.

Impact of Water Quality Parameters on the Clogging of Vertical-Flow Constructed Wetlands Treating Urban Wastewater

In theory, biological and physical clogging, induced as a result of potentially excessive formation of biomass from degradation of pollutants and retention of inert suspended fine particles, respectively, should result in a decrease of treatment performance. However, some wetlands are not prone to clogging in practice. The aim of this study was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand [COD] loading) variables on the treatment efficiency and clogging processes. Different vertical-flow constructed wetlands were constructed and operated from June 2011 until June 2012. Data from June 2011 (setting-up period) were not used. The filter with the highest COD loading performed the worst in terms of outflow COD concentration (120 mg/l) but best in terms of COD load reduction (61 %). The wetland with the largest aggregate size had the lowest mean nitrate-nitrogen outflow concentration of 1.2 mg/l. However, the results were similar regardless of aggregate size (10 versus 20 mm) and resting time (24 versus 48 h) for most water quality variables. However, different COD inflow concentrations (COD of 146 mg/l versus COD of 312 mg/l) had a significant (p < 0.05) impact on the treatment performance for COD, ammonia-nitrogen, ortho-phosphate-phosphorus and suspended solids (SS). Serious clogging phenomena impacting negatively on the treatment performance were not observed for any columns. However, a small aggregate diameter, a short contact time, a long resting time and a low COD inflow concentration were most beneficial in reducing SS accumulation within the wetland filters.

Dynamics of fines/bacterial cells accumulation in trickle-bed reactors/bioreactors—Multiscale modeling framework

Modeling the dynamics of fines/bacterial cells accumulation in gas–liquid–solid reactors/bioreactors is a difficult task which demands an improved understanding and quantification of the complex fluid dynamics, surface physical and microbiological phenomena coupled with (bio)chemistry and thermodynamic backgrounds. This contribution is offered as a step in that direction and presents two case studies with reference to modeling the complex physical and biological plugging/clogging phenomena in trickle-bed reactors/bioreactors, induced, respectively, by the retention of fine particles and by the formation of an excessive amount of biomass. The complex gas–liquid flow and space–time evolution of fines/bacterial cells capture, aggregation, detachment and migration in trickle-bed reactors/bioreactors were analyzed after a mathematical description was cast in terms of Euler–Euler two-fluid dynamic models based on the volume-average mass and momentum equations developed for multiphase systems coupled with species balance equations, solid deposit/biomass dynamics equations, filtration equations for the fines/bacterial cells and the aggregates, population balance equations for the fines/bacterial cells agglomeration.

DISSOLVED AND COLLOIDAL SUBSTANCES (DCS) AND THE CHARGE DEMAND OF PAPERMAKING PROCESS WATERS AND SUSPENSIONS: A REVIEW

Dissolved and colloidal substances (DCS) in the process waters of paper machine systems can interfere with the retention of fine particles, retard the drainage of water from the wet web, and generally hurt the intended functions of various polyelectrolytes that are added to the process. This review considers publications that have attempted to characterize the nature and effects of different DCS fractions, in addition to some of the ways that paper technologists have attempted to overcome related problems. The consequences of DCS in a paper machine system can be traced to their ability to form complexes with various polyelectrolytes. Such tendencies can be understood based on a relatively strong complexing ability of multivalent materials, depending on the macromolecular size and charge density. Continuing research is needed to more fully understand the different contributions to cationic demand in various paper machine systems and to find more efficient means of dealing with DCS.

Dynamic Behavior of Straining in Randomly Packed Beads: Experimental Study

AbstractStraining depicts the geometrical retention of fine particles within materials’ pore network. Whether or not fines can be retained depends on (1) the structure of materials’ pore network as well as (2) fines’ size distribution, manner of deposition, and retained amount. In this paper, the main results of straining tests are presented for randomly packed beads filters. The experimental program included a series of tests performed in both dry and water-saturated filters. The tests provided information on the dynamics of fines in the filters’ pore network and changes of filters’ efficiency. For instance, data supported the existence of four distinct stages: the filling of accessible cavities, the formation then clogging of the preferential pathways, the transfer of fines toward the lateral unobstructed capillaries, and eventual formation of a surface cake. The postulated mechanisms inherent to every single stage are discussed in terms of retention rate, straining length, lateral transfer, and progres...

Influences of seasonal flow regime on the fate and transport of fine particles and a dissolved solute in a New England stream

Fine particles are necessary for biogeochemical cycling but pose a risk to water quality if they are present in excess or carry sorbed contaminants. The objective of this work is to elucidate the effects of flow on the transport and retention of fine particles within a mountain stream and to compare particulate matter transport processes to those of a conservative solute tracer. We measured the migration of bromide (a conservative solute tracer) and micrometer‐sized titanium‐dioxide particles under three seasonal flow regimes in second‐order stream in Connecticut. A one‐dimensional transport model based upon the transient storage model was applied in inverse mode to the measured data to quantify solute and particle transport processes. Rates of particle movement by advection and longitudinal dispersion matched those of bromide. Transient, or temporary, storage influenced conservative solute transport, while particle storage was irreversible on the time scale of our experiments and likely dominated by deposition within the sediments of the hyporheic zone. Both solute transient storage and particle deposition increased with decreasing discharge.

Morphologies of synthetic mineral microparticles for papermaking as a function of synthetic conditions

Morphological characteristics were determined for a system of synthetic mineral microparticles (SMM), which have been developed to promote drainage of water and retention of fine particles during papermaking. Prior research, as well as our own preliminary research showed that the SMM system can have advantages in both of drainage and retention, compared with montmorillonite (bentonite), which is one of the most popular materials presently used in this kind of application. A partially gelled form of a silica-type microparticle additive is known to perform better than the corresponding sol form, in terms of fine-particle retention during papermaking. For this reason it was of interest to investigate the morphological behavior of SMM as a function of the conditions of synthesis. BET nitrogen adsorption was used to measure the surface area of SMM. The distribution of SMM particle size was investigated in the aqueous state, using a light-scattering technique. The coagulation behavior and morphology of SMM were analyzed using scanning electron microscopy (SEM). It was found that the structural characteristics of SMM particles could be explained in terms of the effects of ionic charges on colloidal stability of primary particles during formation of the SMM.