Shift In Particle Size Distribution Research Articles

Strategies to mitigate electrostatic charging during coffee grinding

Coffee grinding generates electrostatically charged particles, causing clumping, spark discharge, and beyond. When brewing, the particle aggregates affect liquid-solid surface accessibility, leading to variable extraction quality. Here, we study four charge mitigation strategies. De-electrification is readily achieved by adding small amounts of water to whole beans or by bombarding the grounds with ions produced from a high-voltage ionizer. While these techniques helped reduce visible mess, only water inclusion was found to impact coffee extracts prepared as espresso. Wetting whole beans with less than 0.05mL/g resulted in a marked shift in particle size distribution, by preventing clump formation and preventing fine particles from sticking to the grinder. This particle size shift results in at least a 15% higher coffee concentration for espresso extracts prepared from darker roasts. These findings encourage the widespread implementation of water use to de-electrify coffee during grinding with the benefit of increased coffee extraction efficiency.

Toward a sustainable laser powder bed fusion of Ti 6Al 4 V: Powder reuse and its effects on material properties during a single batch regime

Titanium alloy Ti6Al4V is the most used titanium alloy due to its high specific strength, ductility, corrosion resistance, and weldability. Currently, this alloy is produced with a density above 99% with laser welding-based additive manufacturing processes. However, the costs of titanium powder are high, and for critical components, the excess powder is usually not reused. In this work, we characterized the powder and additively manufactured Ti6Al4V parts by reusing the powder of a single batch to determine the impact on morphology, chemical composition, melt pool viscosity, density, microstructure, and tensile and impact strength. We aimed to determine the limits of powder reuse to increase sustainability and reduce the carbon footprint of Laser Powder Bed Fusion (L-PBF). We found that the powders pick up oxygen after each cycle to form an oxide layer up to 20 nm, causing a change in the optical and thermal properties of the titanium powders. This change affected the laser absorption and, with this, the melt pool properties. The powders reused after 18 cycles were responsible for a drop in the relative density of 0.1%. However, the tensile properties remained unchanged. The reused powders also presented a small shift in particle size distribution that did not affect the sphericity and increased flowability. In this work, we proved that the powders of Ti6Al4V alloys could be reused up to 18 cycles without any modification to the tensile properties but with a decrement in the impact strength of 30% for vertical- and 12% for horizontal stress-relieved specimens and 19% and 16% for furnace-annealed specimens, respectively.

A Convolutional Neural Network to Classify Phytoplankton Images Along the West Antarctic Peninsula

AbstractHigh-resolution optical imaging systems are quickly becoming universal tools to characterize and quantify microbial diversity in marine ecosystems. Automated classification systems such as convolutional neural networks (CNNs) are often developed to identify species within the immense number of images (e.g., millions per month) collected. The goal of our study was to develop a CNN to classify phytoplankton images collected with an Imaging FlowCytobot for the Palmer Antarctica Long-Term Ecological Research project. A relatively small CNN (~2 million parameters) was developed and trained using a subset of manually identified images, resulting in an overall test accuracy, recall, and f1-score of 93.8, 93.7, and 93.7%, respectively, on a balanced dataset. However, the f1-score dropped to 46.5% when tested on a dataset of 10,269 new images drawn from the natural environment without balancing classes. This decrease is likely due to highly imbalanced class distributions dominated by smaller, less differentiable cells, high intraclass variance, and interclass morphological similarities of cells in naturally occurring phytoplankton assemblages. As a case study to illustrate the value of the model, it was used to predict taxonomic classifications (ranging from genus to class) of phytoplankton at Palmer Station, Antarctica, from late austral spring to early autumn in 2017‐2018 and 2018‐2019. The CNN was generally able to identify important seasonal dynamics such as the shift from large centric diatoms to small pennate diatoms in both years, which is thought to be driven by increases in glacial meltwater from January to March. This shift in particle size distribution has significant implications for the ecology and biogeochemistry of these waters. Moving forward, we hope to further increase the accuracy of our model to better characterize coastal phytoplankton communities threatened by rapidly changing environmental conditions.

A Convolutional Neural Network to Classify Phytoplankton Images Along the West Antarctic Peninsula

Abstract High-resolution optical imaging systems are quickly becoming universal tools to characterize and quantify microbial diversity in marine ecosystems. Automated classification systems such as convolutional neural networks (CNNs) are often developed to identify species within the immense number of images (e.g., millions per month) collected. The goal of our study was to develop a CNN to classify phytoplankton images collected with an Imaging FlowCytobot for the Palmer Antarctica Long-Term Ecological Research project. A relatively small CNN (~2 million parameters) was developed and trained using a subset of manually identified images, resulting in an overall test accuracy, recall, and f1-score of 93.8, 93.7, and 93.7%, respectively, on a balanced dataset. However, the f1-score dropped to 46.5% when tested on a dataset of 10,269 new images drawn from the natural environment without balancing classes. This decrease is likely due to highly imbalanced class distributions dominated by smaller, less differentiable cells, high intraclass variance, and interclass morphological similarities of cells in naturally occurring phytoplankton assemblages. As a case study to illustrate the value of the model, it was used to predict taxonomic classifications (ranging from genus to class) of phytoplankton at Palmer Station, Antarctica, from late austral spring to early autumn in 2017‐2018 and 2018‐2019. The CNN was generally able to identify important seasonal dynamics such as the shift from large centric diatoms to small pennate diatoms in both years, which is thought to be driven by increases in glacial meltwater from January to March. This shift in particle size distribution has significant implications for the ecology and biogeochemistry of these waters. Moving forward, we hope to further increase the accuracy of our model to better characterize coastal phytoplankton communities threatened by rapidly changing environmental conditions.

Insect Herbivory Caused Plant Stress Emissions Increases the Negative Radiative Forcing of Aerosols.

Plant stress in a changing climate is predicted to increase plant volatile organic compound (VOC) emissions and thus can affect the formed secondary organic aerosol (SOA) concentrations, which in turn affect the radiative properties of clouds and aerosol. However, global aerosol‐climate models do not usually consider plant stress induced VOCs in their emission schemes. In this study, we modified the monoterpene emission factors in biogenic emission model to simulate biotic stress caused by insect herbivory on needleleaf evergreen boreal and broadleaf deciduous boreal trees and studied the consequent effects on SOA formation, aerosol‐cloud interactions as well as direct radiative effects of formed SOA. Simulations were done altering the fraction of stressed and healthy trees in the latest version of ECHAM‐HAMMOZ (ECHAM6.3‐HAM2.3‐MOZ1.0) global aerosol‐climate model. Our simulations showed that increasing the extent of stress to the aforementioned tree types, substantially increased the SOA burden especially over the areas where these trees are located. This indicates that increased VOC emissions due to increasing stress enhance the SOA formation via oxidation of VOCs to low VOCs. In addition, cloud droplet number concentration at the cloud top increased with increasing extent of biotic stress. This indicates that as SOA formation increases, it further enhances the number of particles acting as cloud condensation nuclei. The increase in SOA formation also decreased both all‐sky and clear‐sky radiative forcing. This was due to a shift in particle size distributions that enhanced aerosol reflecting and scattering of incoming solar radiation.

Powder spreading, densification, and part deformation in binder jetting additive manufacturing

Binder jetting additive manufacturing (AM) can print complex structures in economical and scalable manner. Binder jetting AM comprises of deposition and weak binding of particles, known as green part, at room temperature and subsequent binder removal and sintering densification at high temperatures. However, during the densification (i.e., sintering), the part significantly deforms due to volume shrinkage. The deformation during sintering is difficult to predict, which prevents the widespread application of this technology. In this research, powder spreading simulation using discrete element method (DEM) was performed first to capture local variations in powder bed configuration. Second, finite element method (FEM) with a phenomenological continuum constitutive model was used to predict part shrinkage during the sintering process. DEM simulation showed variations in packing density, particle segregation, formation of uneven powder bed surface, and shift in particle size distribution (PSD). The sintering simulation modeled part deformation with a reasonable accuracy of 3% for solid-state sintering and intermediate liquid phase sintering. A demonstration case with non-uniform initial packing density showed that inhomogeneous green part density and PSD should be accounted for prediction of part deformation in binder jetting AM.

Applying Nanoparticle Tracking Analysis to Characterize the Polydispersity of Aggregates Resulting from Tannin-Polysaccharide Interactions in Wine-Like Media.

Interactions between grape seed tannin and either a mannoprotein or an arabinogalactan in model wine solutions of different ethanol concentrations were characterized with nanoparticle tracking analysis (NTA), UV-visible spectroscopy and dynamic light scattering (DLS). NTA results reflected a shift in particle size distribution due to aggregation. Furthermore, the light scattering intensity of each tracked particle measured by NTA demonstrated the presence of aggregates, even when a shift in particle size was not apparent. Mannoprotein and arabinogalactan behaved differently when combined with seed tannin. Mannoprotein formed large, highly light-scattering aggregates, while arabinogalactan exhibited only weak interactions with seed tannin. A 3% difference in alcohol concentration of the model solution (12 vs. 15% v/v) was sufficient to affect the interactions between mannoprotein and tannin when the tannin concentration was high. In summary, this study showed that NTA is a promising tool for measuring polydisperse samples of grape and wine macromolecules, and their aggregates under wine-like conditions. The implications for wine colloidal properties are discussed based on these results.

Grain Size Distribution Characteristics Variationin Oily Contaminated Sandy Soils Dueto Long Term Aging Effectin Al-Ahmadi Field at Kuwait

Almost three decades on, the negative environmental impacts arising from the burning of over 600 oil wells in Kuwait following the 1991 Gulf War are still evident. At the time of the incident, the Kuwaiti desert region became polluted with hydrocarbon, with a number of ‘oil lakes’ forming, causing critical harm to local land. This paper discusses the shifts in particle size distribution (PSD) found in soil taken from Kuwait’s Al-Ahmadi oil field, caused by aging sandy soil polluted with hydrocarbon. The analysis of changes in PSD was achieved using 16 contaminated and uncontaminated soil samples, with the samples undergoing PSD analysis along with Unified Classification Soil System (UCSS), Scanning Electronic Microscopy (SEM) and Gas Chromatograph Mass Spectrometer (GC-MS) analyses.The analyses revealed a significant reduction in the mean values of both sand and silty/clay particles, which fell from 44.6% to 9.0% and 7.8% to 3.4%, respectively. The analyses also showed a significant increase in the mean values of gravel particles, rising to 44.6% from 6.1%. These results obviously clarify that the overall outcome of the alteration in soil gradation was a poorer one, which may be due to bigger particles forming out of fine particles as a result of oil contamination. The results presented in this paper are intended to support the treatment (soil washing and cement stabilisation) of contaminated sandy soil based on the insights gained into how soil grain size distribution is impacted by oil contamination.

Improving the Filterability of Particles by Healing the Seed Particles

A shift in particle size distribution toward smaller particle sizes has been observed in batches of Compound A Triethanolate, an isolated intermediate of a commercially available active pharmaceutical ingredient, leading to poor deliquoring of the filter cake and longer filtration times, which compromised the overall process cycle time. In the most extreme case, product breakthrough during filtration was observed, leading to significant yield loss. Compound A Triethanolate is crystallized through antisolvent addition/distillation/cooling crystallization in ethyl acetate/water/ethanol. Laboratory experiments were carried out using representative product streams in order to identify the cause for the shift in particle size distribution, which could be attributed to excessive secondary nucleation at an early stage of the process caused by the use of seed particles that have been previously dried under agitation. While statically dried particles exhibit a smooth surface, the surface of particles dried under a...

Physico-chemical evaluation of hydrophobically modified pectin derivatives: Step toward application

Present study reports synthesis and physico-chemical evaluation of hydrophobically modified pectin derivatives, obtained by reacting of pectin with di-acyl chlorides (glutaryl and sebacoyl chloride). Depending on length of the inserted carbon chains, the acylation resulted in possible formation of mono-grafted (isolated chains) and bi-grafted (chemical gels) structures. The structural features of obtained derivatives were investigated using FTIR spectroscopy, confirming the successful synthesis. The concentrated aqueous solutions of modified pectin showed interesting rheological properties, having lower values of apparent viscosity compared to neat pectin. Since the GPC analysis indicated that no degradation occurred, the viscosity decrease was explained by more heterogeneous organization within modified pectin solutions (microparticles together with sticky polymer entanglement). A shift in particle size distribution proved that proposed modifications also affected pectin solution properties in diluted regime. The modified samples turned to be more sensible to thermal degradation than neat pectin, whereby the increasing size of flexible acyl chains attached to a polymer backbone reduced the glass transition temperature. The hydrophobicity of obtained derivatives was evaluated by sessile drop and du Nouy ring methods. It was found that acylation enhanced hydrophobicity of the pectin molecule, while hydrophobically associative character turned to be inconsistent in aqueous and non-aqueous environment.

Impact of FeCl3 dosing on AnMBR treatment of municipal wastewater

The long-term (90 days) impact of dosing FeCl3 on bioprocess performance and membrane performance in a pilot AnMBR fed with authentic sewage was evaluated. The addition of 26 mg/L of FeCl3 enhanced the performance of the AnMBR with respect to removal efficiencies of COD and BOD5, but did not have a significant influence on the removal efficiencies of TKN and TP and the methane yield. The membrane was operated at a constant flux of 17 LMH and its performance was significantly improved by dosing FeCl3. This was demonstrated by a reduction in the fouling that withstood scouring stresses to values lower than 5 kPa and negligible reversible fouling for the first 75 days. The superior membrane performance was consistent with the shift of particle size distribution to the particulate fraction and the reduced colloidal and soluble substances in the sludge, especially the soluble protein, carbohydrate, Ca and S. CLSM tests showed that the addition of FeCl3 resulted in a thicker foulant layer and the deposition of protein and carbohydrate on the membrane surface was significantly reduced. Therefore a more porous foulant layer was formed and this prevented the development of a strongly-attached cake layer and pore blocking. A recovery cleaning study indicated FeCl3 dosing enhanced the efficiency of the recovery cleaning protocol. The foulants formed with the Fe-dosed sludge had greater inorganic content, as 75% of the foulant resistance was removed by citric acid. The superior membrane performance during the operation combined with enhanced cleaning efficiency by FeCl3 dosing would significantly improve the sustainability of AnMBR in municipal wastewater treatment.

The effect of fine bubble aeration intensity on membrane bioreactor sludge characteristics and fouling

While most membrane bioreactor (MBR) research focuses on improving membrane filtration through air scour, backwashing and chemical cleaning to physically counteract fouling, relatively few studies have dealt with fouling prevention, e.g. minimizing the impact of operational settings that negatively impact sludge filterability. To evaluate the importance of those settings, the effects of bioreactor aeration intensity variations on membrane fouling have been studied in a lab-scale MBR setup while simultaneously monitoring a unique set of key sludge parameters. In particular, this paper focuses on the impact of shear dynamics resulting from fine air bubbles on the activated sludge quality and flocculation state, impacting membrane fouling. When augmenting the fine bubble aeration intensity both the total and irreversible fouling rate increased. Major indications for sludge filterability deterioration were found to be a shift in the particle size distribution (PSD) in the 3–300 μm range towards smaller sludge flocs, and increasing concentrations of submicron particles (10–1000 nm), soluble microbial products and biopolymers. When lowering the aeration intensity, both the sludge characteristics and fouling either went back to background values or stabilized, respectively indicating a temporary or more permanent effect, with or without time delay. The shift in PSD to smaller flocs and fragments likely increased the total fouling through the formation of a less permeable cake layer, while high concentrations of submicron particles were likely causing increased irreversible fouling through pore blocking. The insights from the performed fouling experiments can be used to optimize system operation with respect to influent dynamics.

Effect of Livestock Slurry Ozonation and Separation on pH, Particles, and Phosphate.

Applying slurry to arable land as fertilizer increases the risk of phosphorus (P) runoff and thereby increases the risk of eutrophication. Solid-liquid separation can reduce the excess application of P, and this study focused on the use of ozonation as an alternative chemical pretreatment for separation to improve P separation efficiency. Sow and cattle slurries were separated by screw press and flocculation+filtration. The screw press and flocculation liquid fractions and raw slurries were treated with no ozone or with low-, medium-, or high-ozone doses and then separated by centrifugation. The pH, particle size distribution, dry matter, and dissolved phosphate (PO) concentrations were measured. For separations without ozonation, pH increased by 0.15 to 0.87 pH units, and correlation analysis showed that the dissolved PO concentration decreased with increasing pH and particle removal efficiency. During ozonation, pH increased, and a shift in particle size distribution in the liquid fraction combined with an improved dry matter separation indicated particle aggregation. Ozonation thus affected the parameters found to affect dissolved PO separation, and at the highest ozone dose, dissolved PO separation efficiency increased by 7 to 81%. An ozonation pretreatment may therefore promote removal of dissolved PO from the liquid fraction during separation.

Locked nucleic acid antisense inhibitor targeting apolipoprotein C-III efficiently and preferentially removes triglyceride from large very low-density lipoprotein particles in murine plasma

A 20-mer phosphorothioate antisense oligodeoxyribonucleotide having locked nucleic acids (LNA–AON) was used to reduce elevated serum triglyceride levels in mice. We repeatedly administered LNA–AON, which targets murine apolipoprotein C-III mRNA, to high-fat-fed C57Bl/6J male mice for 2 weeks. The LNA–AON showed efficient dose-dependent reductions in hepatic apolipoprotein C-III mRNA and decreased serum apolipoprotein C-III protein concentrations, along with efficient dose-dependent reductions in serum triglyceride concentrations and attenuation of fat accumulation in the liver. Through precise lipoprotein profiling analysis of sera, we found that serum reductions in triglyceride and cholesterol levels were largely a result of decreased serum very low-density lipoprotein (VLDL)-triglycerides and -cholesterol. It is noteworthy that larger VLDL particles were more susceptible to removal from blood than smaller particles, resulting in a shift in particle size distribution to smaller diameters. Histopathologically, fatty changes were markedly reduced in antisense-treated mice, while moderate granular degeneration was frequently seen the highest dose of LNA–AON. The observed granular degeneration of hepatocytes may be associated with moderate elevation in the levels of serum transaminases. In conclusion, we developed an LNA-based selective inhibitor of apolipoprotein C-III. Although it remains necessary to eliminate its potential hepatotoxicity, the present LNA–AON will be helpful for further elucidating the molecular biology of apolipoprotein C-III.

Numerical Simulation of Effects of Cloud Top Temperatures and Generating Cells on Secondary Ice Production in Stratiform Clouds with a Detailed Microphysical Model

This paper outlines a one-dimensional, heightdependent bin model with detailed microphysical processes in which ice splinters are produced by a riming process. The model is then applied to simulate the shift of particle size distribution effected by the secondary ice production process within clouds with different generating cells and cloud top temperatures. The result of model simulations reveals the general effects of cloud updrafts on increasing ice particle concentration by extending the residence time of ice particles in clouds and providing sufficiently large supercooled water droplets. The rimesplintering mechanism is more effective in clouds with lower ice seeding rates than those with higher rates. Evolutions of hydrometeor size distribution triggered by the rime-splintering mechanism indicate that the interaction between large ice particles and supercooled water drops adds a “second maximum” to the primary ice spectra.

The Effect of Uniform Particle Size Distribution on Pt Stability

The present study aims to address the effect of the uniformity of particle size distribution on Pt stability. A theoretical model based on the chemical reactions of Pt oxidation and precipitation in the membrane is presented. The incorporation of a particle size distribution function and a population balance allows the investigation of different initial particle size distributions. Initial results demonstrate the change of platinum ions concentration across the electrode and membrane and reveal the shift of particle size distribution towards larger diameters under potential hold and potential cycling simulations.

Remarkable dynamics of nanoparticles in the urban atmosphere

Abstract. Nanoparticles emitted from road traffic are the largest source of respiratory exposure for the general public living in urban areas. It has been suggested that adverse health effects of airborne particles may scale with airborne particle number, which if correct, focuses attention on the nanoparticle (less than 100 nm) size range which dominates the number count in urban areas. Urban measurements of particle size distributions have tended to show a broadly similar pattern dominated by a mode centred on 20–30 nm diameter emitted by diesel engine exhaust. In this paper we report the results of measurements of particle number concentration and size distribution made in a major London park as well as on the BT Tower, 160 m aloft. These measurements taken during the REPARTEE project (Regents Park and BT Tower experiment) show a remarkable shift in particle size distributions with major losses of the smallest particle class as particles are advected away from the traffic source. In the Park, the traffic related mode at 20–30 nm diameter is much reduced with a new mode at <10 nm. Size distribution measurements also revealed higher number concentrations of sub-50 nm particles at the BT Tower during days affected by higher turbulence as determined by Doppler Lidar measurements and are indicative of loss of nanoparticles from air aged during less turbulent conditions. These results are suggestive of nanoparticle loss by evaporation, rather than coagulation processes. The results have major implications for understanding the impacts of traffic-generated particulate matter on human health.

Particle grouping, a new method for reducing emission of submicron particles from diesel engines

A new vehicle-exhaust concept is described which leads to a reduced risk for the health and for the environment from particulate matter (PM). The geometry of the exhaust induces particle grouping and coagulation leading to a shift in particle size distribution, which increases the mass/number of the larger particles at the expense of the reduction in the amount of smaller ones. Such a shift in size distribution has implications with respect to particle capturing from diesel engines and other facilities, and with respect to lower residence time of particles which are emitted to the air. The theoretical basis and the supportive experiments are described. The results show that the concept is easy to apply and has significant implications with ramification to reduction of the concentration of submicron PM in main roads, and in work places.

The effect of high hydrostatic pressure on the flow behaviour of skim milk–gelatin mixtures

The flow behaviour of aqueous solutions of gelatin, and skim milk–gelatin mixtures treated by high-pressure processing (HPP) were investigated. HPP was carried out at 5 °C for 15 min, at 150 MPa, 300 MPa, 450 MPa and 600 MPa, and the gelatin concentrations were varied from 0 to 1 wt.%. Viscosity measurements showed that the HPP treatment did not affect the flow behaviour of gelatin alone, nor that of the skim milk–gelatin mixtures made with < 0.4 wt.% gelatin. However, at gelatin concentration > 0.4 wt.%, the mixtures treated with 300 and 450 MPa exhibited a peculiar flow behaviour, where at intermediate shear rates the viscosity was higher than that of the non-treated mixture or the mixtures treated at 150 MPa and 600 MPa. Particle size measurements showed that for gelled mixtures (> 0.4 wt.% gelatin) 300 MPa HPP treatment resulted in an increase in the particle size, while at all other pressure treatments (> 150 MPa), a shift in particle size distribution to lower sizes was observed. Confocal microscopy showed that these skim milk–gelatin mixtures were phase-separated with a gelatin continuous phase, this was confirmed by dynamic rheological measurements which showed that qualitatively the viscoelastic properties of the mixtures were the same. A mechanism of the effect of high-pressure treatment on the casein micelle in skim milk–gelatin mixtures is proposed. This fundamental work, dealing with the effect of high pressure on the physicochemical properties skim milk–gelatin mixtures could be relevant to the industry in several ways. Firstly, skim milk–gelatin mixtures are widely used in the dairy industry, particularly in yoghurt manufacture, where gelatine is used as a stabiliser. In addition the application of High Hydrostatic Pressure to such a system is also relevant, as this technology could be used as a substitute to the conventional heat treatment processes. Secondly, an important finding of this study is that under certain conditions of high pressure and gelatine concentration, an increase in viscosity is observed at intermediate shear-rate (between 10 and 100 s − 1 ). This is highly relevant to Industry if the system requires subsequent pumping. Thirdly, from a sensory view point, this range of shear rates (10 and 100 s − 1 ) is comparable to that experienced by a food bolus during swallowing. Thus, this effect of high pressure on the viscosity can influence sensory attribute of the skim milk–gelatin food system.

Effect of organic loading rate on a wastewater treatment process combining moving bed biofilm and membrane reactors

The effect of moving bed biofilm reactor (MBBR) loading rate on membrane fouling rate was studied in two parallel units combining MBBR and membrane reactor. Hollow fiber membranes with molecular weight cut-off of 30 kD were used. The HRTs of the MBBRs varied from 45 min to 4 h and the COD loading rates ranged from 4.1 to 26.6 g COD m(-2) d(-1). The trans-membrane pressure (TMP) was very sensitive to fluxes for the used membranes and the experiments were carried out at relatively low fluxes (3.3-5.6 l m(-2) h(-1)). Beside the test with the highest flux, there were no consistent differences in fouling rate between the low- and high-rate reactors. Also, the removal efficiencies were quite similar in both systems. The average COD removal efficiencies in the total process were 87% at 3-4 h HRT and 83% at 0.75-1 h HRT. At high loading rates, there was a shift in particle size distribution towards smaller particles in the MBBR effluents. However, 79-81% of the COD was in particles that were separated by membranes, explaining the relatively small differences in the removal efficiencies at different loading rates. The COD fractionation also indicated that the choice of membrane pore size within the range of 30 kD to 0.1 microm has very small effect on the COD removal in the MBBR/membrane process, especially with low-rate MBBRs.