Improved Filtration Performance Research Articles

Tailoring bimodal protein fabrics for enhanced air filtration performance

Natural material-based nanofiber air filters promise to minimize any adverse impacts on the environment after use, but the nanofiber structure causes poor airflow performance, i.e. high airflow resistance. Constructing bimodal structures reduces airflow resistance without compromising removal efficiency but has been rarely studied for natural nanofiber air filters. In this study, we fabricate bimodal protein fabric air filters and carefully tailor their bimodal structure to achieve higher removal efficiency with significantly lowered airflow resistance. The bimodal structures are generated by co-spinning of denatured zein protein in two solvent systems, via controlling the protein denaturation degree and fiber shape/size. The bimodal structures with bimodal diameter distributions are then carefully adjusted by varying the feed rates. It is revealed that a bimodal fabric shows an optimized filtration performance when the fiber diameters locate at 2.44 and 0.13 μm, reducing the airflow resistance by up to 56.47 Pa (from 84.97 Pa to 28.5 Pa) with a high PM2.5 removal efficiency of 98.43%. The bimodal fabric treated with TX-100 shows a further improved filtration performance of filtering PM0.3 of 97.01% and PM2.5 of 99.15% at an ultralow airflow resistance of 21.1 Pa. Moreover, the treated bimodal fabric presents better long-term performance and higher removal efficiency in a humid environment. This work develops a simple and viable method for fabricating and tailoring bimodal air filters made of abundant natural protein for broad applications.

Tailoring microstructure of polysulfone membranes via novel hexagonal ZnO particles to achieve improved filtration performance

Incorporation of nanofillers into polymeric membranes has been the trend in the realm of membrane research owing to the improvements in many filtration characteristics with the modifications of membrane structure, morphology and bulk properties. The major drawback of the nanoparticle embedded membrane is the uncontrollable agglomeration, which could be mitigated by tailoring microstructure of the matrix by using designed nanoparticles. In the present study, polysulfone (PSf) based ultrafiltration membranes incorporated with designed MicNo® platelets composed of strongly bonded ZnO nanoparticles were prepared as single- and double-layer membranes using immersion precipitation technique. Filtration performance, morphological and bulk properties of the novel composite membranes containing MicNo® powders of varying amounts (0.01–1%, wt.) and particle sizes were determined in comparison to those of pristine PSf membrane. Single-layer composite membrane containing 0.5% MicNo® exhibited the greatest permeance improvement of 74% and a marked enhancement of 116% could be achieved with double-layer membrane system containing 0.5% and 0.1% MicNo® in the upper and bottom layers, respectively. The results demonstrated that MicNo® powders were successfully distributed throughout the membrane matrix without any surface imperfections owing to the well alignment of ZnO particles on their hexagonal platelet surfaces, which prevented the agglomeration of primary ZnO particles that ensured a more efficient hydrophilic surface generation in the membrane.

Enhancement of flocculant-aided filtration performance of coal tailings under alternating low and high shear rates

Although flocculation has been widely applied to improve filtration performance before filtered dry stack tailings storage, it is still a challenge to create flocculated aggregates having desired characteristics which are both conducive to improving the filtration rate and reducing the filter cake moisture content. In this paper, the alternate shear conditions were investigated to enhance flocculant-aided filtration performance of coal tailings. The focused beam reflectance measurement (FBRM) was used as an in-situ monitor to measure the floc size under different shear conditions in the presence of anionic polyacrylamide. Compared with single shear conditions, sequenced flocculation produced stronger flocs. It was also found that the flocs formed under two cycles of high (1192.8 s−1) and low (637.6 s−1) shear rates were the strongest and contained fewer particles and small flocs. The particle vision measurement (PVM) was used to analyze the effects of alternate shear conditions on floc morphological characteristics. It was observed that the floc structure became more compact with the number of cycles. Lastly, the filtration experiments were conducted to determine the filtration performance of coal tailings. The results showed that the coal tailings had the best comprehensive filtration performance under the sequenced flocculation with two cycles of high and low shear rates, the filtration time was 12.17 min, which was very close to the fastest 12.03 min of single low shear rate, and 21.2% of cake moisture content was about the same as the minimum 21.1%. The filtration outcomes were consistent with that given by FBRM and PVM.

Cross‐linked boron nitride‐piperazine amide thin film nanocomposite membranes for rejection and concentration of per‐ and poly‐fluoroalkyl substances (PFAS)

Per- and poly-fluoroalkyl substances (PFAS)-contaminated wastewaters present major public health risks given the PFAS thermo-chemical stability and its demonstrated adverse impacts on aquatic life, extended to the entire food chain. To date, remediation of PFAS-contaminated wastewaters have been mainly undertaken with poorly cost-effective strategies, involving multi-step processes. Advanced separation systems enabling the selective capture and concentration of PFAS must be developed. In this work, the potential of nanofiltration (NF) membranes to reject short chain length PFAS, potassium nonafluoro-1-butanesulfonate (C4F9SO3K), is demonstrated with both bare polymeric and amine functionalized-boron nitride BN(NH2) nanosheet-decorated membranes. The BN(NH2)-decorated membranes exhibited almost 1.04 times higher permeation upon C4F9SO3K filtration compared to the bare poly(piperazine amide) (PPA) membranes (53 versus 26 L m−2 h−1), while maintaining very high C4F9SO3K rejection levels above 93%. A commercial membrane exhibited similar permeation to BN(NH2)-decorated membrane, but only retained ∼65% of the C4F9SO3K. The improved filtration performance of the BN(NH2)-decorated membrane was rationalized based on advanced characterization results to its enhanced wettability and negative charge density, resulting in weak interactions between the C4F9SO3K and BN(NH2) nanosheets. This communication demonstrates the role and potential of fine surface modifications of NF membranes to support improved separation performance towards PFAS removal.

Mitigating membrane fouling in a high solid food waste thermophilic anaerobic membrane bioreactor by incorporating fixed bed bio-carriers

Hybrid anaerobic membrane bioreactor (Hy-AnMBR) was developed by incorporating polyurethane sponge carriers to mitigate membrane fouling. The results showed that the membrane fouling was well controlled in Hy-AnMBR from the aspects of sludge property and membrane filtration performance. The solid concentration, including TS and MLSS in the Hy-AnMBR was reduced after introducing the fixed bed carrier, which was 13% and 20% lower than the control AnMBR (Con-AnMBR), and this resulted in improved filtration performance. The scanning electron microscope (SEM) photograph showed that membrane pores could still be observed on the Hy-AnMBR surface, indicating that the cake layer fouling of the Hy-AnMBR was less than the Con-AnMBR. The increase of the EPS and SMP promoted the acceleration of the membrane fouling rate. Analysis through confocal laser scanning microscopy (CLSM) and membrane cleaning revealed that adding sponge carriers mitigated 3.3%–9% pore-blocking, and the total membrane resistance in the Hy-AnMBR was reduced by 52% compared to the Con-AnMBR. Chemical cleaning was essential for pollutant removal, and membrane permeability recovery was more than 97%.

Improvement of Filtration Performance of Foam Ceramics Using External Electric Field

To enhance filtration performance of foam ceramics, effects of electric field on filtration performance of foam ceramics were studied. Results show that external electric field can change the wettability between melt and foam ceramics and can improve filtration performance of foam ceramics. Meanwhile, chemical composition of melt is not affected by external electric field.

Membrane-Based Harvesting Processes for Microalgae and Their Valuable-Related Molecules: A Review.

The interest in microalgae production deals with its role as the third generation of feedstock to recover renewable energy. Today, there is a need to analyze the ultimate research and advances in recovering the microalgae biomass from the culture medium. Therefore, this review brings the current research developments (over the last three years) in the field of harvesting microalgae using membrane-based technologies (including microfiltration, ultrafiltration and forward osmosis). Initially, the principles of membrane technologies are given to outline the main parameters influencing their operation. The main strategies adopted by the research community for the harvesting of microalgae using membranes are subsequently addressed, paying particular attention to the novel achievements made for improving filtration performance and alleviating fouling. Moreover, this contribution also gives an overview of the advantages of applying membrane technologies for the efficient extraction of the high added-value compounds in microalgae cells, such as lipids, proteins and carbohydrates, which together with the production of renewable biofuels could boost the development of more sustainable and cost-effective microalgae biorefineries.

Fabrication of chitosan-aminopropylsilane graphene oxide nanocomposite hydrogel embedded PES membrane for improved filtration performance and lead separation

In the present study chitosan-aminopropylsilane graphene oxide (CS-APSGO) nanocomposite hydrogel was synthesized and utilized as a hydrophilic additive in different dosages (0.5, 1, 2 and 5 wt%) in fabrication of porous polyethersulfone (PES) membranes via the phase inversion induced process by immersion precipitation method for heavy metal ion and dye removal. The modified membranes were characterized using ATR-FTIR, AFM, SEM, water contact angle, overall porosity and mean pore radius evaluations and zeta potential measurement. The addition of CS-APSGO nanocomposite hydrogel to PES doping solutions enhanced membranes hydrophilicity and consequently pure water flux permeability. Filtration performance of the CS-APSGO embedded membranes showed promising antifouling properties during BSA filtration test (FRR> 90%) and 1 wt% membranes showed the highest pure water flux of 123.8 L/m2 h with BSA rejection more than 98% and removal capability more than 82% for lead (II) ion, 90.5% and 98.5% for C.I. Reactive Blue 50 and C.I. Reactive Green 19, respectively. Therefore, the CS-APSGO nanocomposite hydrogel blending in order to modification of PES-based membranes have a noticeable potential in improving filtration performance of blended membranes.

Fabrication of a novel PVDF based silica coated multi-walled carbon nanotube embedded membrane with improved filtration performance

In the present study, silica coated multi-walled carbon nanotubes (SiO2-CNT) were embedded into a pristine polyvinylidene fluoride (PVDF) polymer matrix to develop a novel PVDF/SiO2-CNT nanocomposite membrane. Initially, SiO2-CNT nanofillers were synthesized through sol gel method using commercial multi-walled carbon nanotubes (f-CNT) and incorporated into membrane matrix with varying loadings of 0.5%wt. and 1.0%wt. Pore former/polymer/solvent ratio was investigated to achieve the highest pure water flux and rejection in order to determine the most suitable pristine membrane recipe. Filtration performance properties such as flux, sodium alginate rejection, antifouling properties as well as the morphological characteristics such as porosity, pore size and distribution, hydrophilicity, surface roughness, functional groups, crystalline structure, thermal properties and mechanical strength of the SiO2-CNT embedded membranes fabricated with the best recipe were determined in comparison to those of pristine membrane. It has been demonstrated that incorporating hydrophilic SiO2-CNT into PVDF matrix increased the permeability from 303 to 377 L/m2h (25% increment) due to the improved dispersion of nanoparticles, which subsequently resulted in enhanced morphological properties. In addition to that, SA rejection of the pristine membrane increased from 84.5% to 90.2% and the flux recovery ratio increased from %74.2 to 94.7% with a comparatively smaller Rir value of 2.4 x 1010 m−1 by the addition of 0.5% SiO2-CNT nanofillers into the polymer matrix. Si-MWCNT impregnated nanocomposite membranes not only exhibited better filtration properties but also improved thermal stability and mechanical properties through the synergetic effect of nanotubes and silica group, which would provide in a significant increase in membrane life.

Ultrathin Polydopamine-Graphene Oxide Hybrid Coatings on Polymer Filters with Improved Filtration Performance and Functionalities.

Thin polymer fiber mats, in particular those made of nonwoven polypropylene (PP) fibers, are extensively used for medical and industrial filtration. The recent pandemic has increased the demand for the fabrication of protective masks. The nonwoven PP filter has limitations in filtration efficiency and lacks advanced functionalities. Here, we propose a simple, effective, and low-cost method to functionalize PP filters and endow antimicrobial and photothermal properties. Our approach is based on the deposition of an ultrathin hybrid coating composed of graphene oxide (GO) and polydopamine on the surface of PP filters by spray-coating. The complementary properties and synergic effects of GO and polydopamine in the ultrathin coating improved the filtration efficiency of the PP filter by 20% with little change in pressure drop. Single component coatings did not result in similar improvements in performance. The ultrathin coating also makes the surface of the filter more hydrophilic with negative charges. The photothermal property of GO enables a rapid temperature increase of the surface-coated filter upon light irradiation for easy sterilization. Furthermore, cationic polymer brushes can be grafted to the ultrathin hybrid coating, which adds the highly desired antimicrobial property to the PP filters for their more effective protection against microorganisms.

Rapid and eco-friendly technique for surface modification of TFC RO membrane for improved filtration performance

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane’s polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39⁰ (unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2 plasma treatment to improve RO membrane performance.

Physico-chemical features of acid decomposition of dolomite

The results of studies of the physico-chemical regularities of the acid decomposition of magnesium-containing raw materials are presented and the optimal technological mode of the individual stages of obtaining magnesium sulfate is determined. It has been established that the process of obtaining magnesium sulfate based on dolomite includes the following stages: decomposition of magnesium-containing raw materials with sulfuric acid; filtration of the resulting suspension with separation of calcium sulfate and insoluble residue and subsequent washing; crystallization and separation of magnesium sulfate; drying the target product. The main technological parameters that determine the stage of sulfuric acid decomposition are: the rate of sulfuric acid, the duration of decomposition, the method and procedure for introducing reagents, the content of magnesium sulfate in the liquid phase of the suspension. In this case, the concentration of sulfuric acid cannot be considered as the main technological parameter, since its numerical value is selected depending on the value of the final content of magnesium sulfate in the liquid phase, which in turn is determined by its solubility in water. It has been proven that the use of a flocculant at the decomposition stage provides an increased filtration rate, improved filtration performance, as well as keeping the filter cloth uncontaminated. The results of chemical and X-ray phase analyzes confirmed that magnesium sulfate obtained from domestic dolomite raw materials in its composition corresponds to magnesium sulfate obtained from foreign types of magnesium-containing raw materials - magnesite, brucite - and fully complies with the requirements of TU 2141016-32496445-00 “Magnesium sulfate”.

Tailoring Microstructure of Polysulfone Membranes via Novel Hexagonal ZnO Particles to Achieve Improved Filtration Performance

Tailoring Microstructure of Polysulfone Membranes via Novel Hexagonal ZnO Particles to Achieve Improved Filtration Performance

Fabrication of Poly(lactic acid) filter media via the meltblowing process and their filtration performances: A comparative study with polypropylene meltblown

Poly(Lactic acid) (PLA) is considered as a promising alternative for petroleum-based synthetic plastic under the rising concerns over the environmental sustainability of polypropylene (PP) filter materials. To adapt PLA for the meltblown filter media production, it is necessary to establish how PLA polymer properties affect the meltblown process, media structure and filtration performance. We investigated the processability and effects of processing parameters on PLA meltblown structures and filtration performances in an industrially relevant setting by utilizing a commercially available low molecular weight PLA resin and a Reicofil meltblowing production line. We were able to fabricate PLA meltblown media comparable with PP meltblown media both in structures and filtration performances. Increasing airflow rate and decrease throughput reduced fiber diameter of PLA meltblown, but at the given processing condition, PLA meltblown tends to have larger fiber diameters than PP meltblown. However, larger diameter did not deteriorate the filtration efficiency of PLA meltblown. Interestingly, the filtration efficiency of PLA meltblown is higher than those of PP meltblown with similar fiber diameters. We also found the solidity of PLA meltblown lower than that of PP meltblown. This further improved filtration performance by improving air permeability. The quality factors of PLA meltblowns were more than double of PP meltblowns’ quality factors when fiber sizes are similar. PLA also exhibited comparable chargeability and charge stability with PP when corona charged.

Sewage concentration via a graphene oxide modified thin-film nanocomposite forward osmosis membrane: Enhanced performance and mitigated fouling

• The GO modified TFN-FO membrane shows improved filtration performance. • The GO modified TFN-FO membrane shows an enhanced antifouling property. • The GO modified FO membrane has high and stable sewage concentration performance. • High water flux recovery rates can be achieved by simple membrane cleaning. Upstream intensification of wastewater pre-treatment could improve the efficiency of the biological wastewater treatment process by separating and concentrating the organic matter. Forward osmosis (FO) technology is a potential upstream intensification strategy for sewage concentration. Herein, a high-performance graphene oxide (GO) modified TFN-FO membrane was fabricated and evaluated. The GO modified TFN-FO membrane showed 41% enhancement in water flux without weakening the selectivity property, due to the improved membrane hydrophilicity, thinner polyamide layer and facilitated water transportation by GO. The enhanced filtration performance and antifouling property of the TFN-FO membrane were confirmed by using simulative foulant solution and raw sewage as feed solutions. Moreover, a 41 h semi-continuous filtration experiment was conducted for sewage concentration using real raw sewage as the feed solution. Results indicated that the TFN-FO membrane achieved 4.6 times sewage concentration with high rejection of ammonia, nitrogen and organics. In addition, with a simple in-line water cleaning-in-place (CIP) process, most of the pollutants could be washed off from the surface of the TFN-FO membrane in 15 min and ~ 90% water flux could be recovered after each cleaning cycle. This work demonstrates the potential application of TFN-FO membranes for sewage wastewater concentration.

An optimization approach for fabricating electrospun nanofiber air filters with minimized pressure drop for indoor PM2.5 control

Electrospun nanofiber air filters can achieve remarkable particle filtration efficiency with low pressure drop. Therefore, they can potentially be installed in buildings for reducing indoor PM2.5 concentrations. To improve filtration performance, this study developed a design and fabrication approach for electrospun nanofiber air filters with minimized pressure drop under a target PM2.5 filtration efficiency. First, this research developed semi-empirical models for calculating the pressure drop and PM2.5 filtration efficiency of nylon electrospun nanofiber filters using the fabrication parameters of electrospinning time and nylon concentration. With the developed models, this investigation then proposed an optimization approach to minimize the pressure drop under a given PM2.5 filtration efficiency and air velocity. For a given air velocity and PM2.5 filtration efficiency, one can minimize the pressure drop by finding the optimal solution concentration, while the target PM2.5 filtration efficiency can be achieved through adjustment of the electrospinning time. Furthermore, the proposed optimization approach successfully minimized the pressure drop for 110 out of the 125 cases, with an average pressure drop reduction of 32.7%. Finally, this research numerically studied the performance of a window screen coated with the optimized nanofiber filter in reducing indoor PM2.5 of outdoor origin.

Effect of localized hydrodynamics on biofilm attachment and growth in a cross-flow filtration channel

Biofilm attachment and growth in membrane filtration systems are considerably influenced by the localized flow inside the feed channel. The present work aims to map the biofilm attachment/growth mechanism under varying flow conditions. Effect of varying clearance region (space between the spacer filament and membrane surface) on biofouling pattern is investigated by using three 3D-printed pillar spacers having different filament diameters of 340, 500, and 1000 µm while maintaining the same pillar orientation, diameter and height. Direct Numerical Simulations (DNS) and Optical Coherence Tomography (OCT) were carried out to accurately predict the local hydrodynamics behavior and in-situ monitor the biofilm formation. On spacer filaments, biofouling attachment is primarily observed in the regions where low and non-fluctuating shear stresses are present. Conversely, on membrane surface, highest biofouling attachment was observed under spacer filaments where high shear stresses are prevalent along with low clearance height. Furthermore, as filtration time progresses, the biofilm grows faster on the membrane in the center of spacer cells where low shear stress with steady hydrodynamics conditions are prevalent. The proposed hydrodynamics approach envisages a full spectrum of spacer design constraints that can lead to intrinsic biofilm mitigation while improving filtration performance of membranes based water treatment.

Aluminum Melt Filtration with Carbon Bonded Alumina Filters.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 °C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 °C and 30 min). The conventional test yielded contact angles of around 92°, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157°. Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 µm up to 50 µm and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

3D printed honeycomb-shaped feed channel spacer for membrane fouling mitigation in nanofiltration

The development of a superior feed channel spacer is one among the problems that have to be resolved to effectively mitigate foulant accumulation in the membrane system and improve filtration performance. In view of this, a novel honeycomb-shaped spacer, whose hexagonal form is the most stable and economical structure observed in nature, is proposed. 3D printing enables us to manufacture the honeycomb-shape spacer. Then, the performance of such spacer is demonstrated by comparing its filtration results with those of a standard diamond-shaped spacer in nanofiltration. The proposed structure is observed to have higher fouling mitigation performance under various fouling conditions (i.e., low and high fouling potentials and different organic foulants). Optical coherence tomography demonstrates that the foulant layer formed by utilizing honeycomb-shaped spacers (119.0 μm) is significantly thinner than that resulting from the use of standard spacers (175.5 μm); thereby, the permeate flux of the honeycomb-shaped spacers was 16.0% greater than that of the standard spacers. Hydraulic cleaning tests reveal that honeycomb-shaped spacers have a higher potential for mitigating fouling resistances driven by the concentration polarization layer (Rcp) and cake layer (Rc), leading to higher permeate production than that generated by filtration using standard spacers. The use of computational fluid dynamics simulation affords better insights into the hydrodynamic effects of these spacers on the feed channel. It is observed that honeycomb-shaped spacers have superior performance that is attributable to the generation of high-magnitude turbulent kinetic energy in the areas enclosed by spacer filaments.

Cellulose fibre- perlite depth filters with cellulose nanofibre top coating for improved filtration performance

Depth type composite filters are used to remove contaminants from liquids by combining mechanical entrapment and adsorption. Commonly, depth filters can adsorb either anionic or cationic charged contaminants, but not both, as well as filter micron-sized particles. Therefore, there is still a need to improve the existing depth filter performance. In this study, we developed a two-layer filters with enhanced functionality by spray coating an anionically charged cellulose nanofibre (CNF) layer onto a cationically charged depth filter layer. The depth filter layer was prepared via papermaking technique of vacuum filtration from wood pulp fibres, perlite adsorbent and cationic polyamide-amine epichlorohydrin (PAE) wet strength resin. The CNF coat weight ranged from 4 to 30 g per square metre (gsm). The two layer filters were proven to have triple functionality, capable of adsorbing anionic molecules in the cationic depth filter layer, while the anionic CNF layer could adsorb cationic molecules and was also a microfiltration membrane. A gradual increase in CNF coat weight improved filtration performance but decreased the filter flux. The optimum performance was found at an 8 gsm CNF coat weight, where the membrane layer rejected 80% of 5000 kDa molecular weight polyethylene glycol, at a flux of 133 Litres per square meter per hour (LMH) under 1.5 bar pressure, while still achieving a good breakthrough curve when absorbing cationic methylene blue dye.