Filtration Period Research Articles

Iron–molybdenum bimetals incorporated montmorillonite-based catalytic ceramic membrane for heterogenous Fenton reaction towards the degradation of micropollutants in water

This study developed an innovative material approach that integrated Fenton catalysis with membrane filtration in a single system using iron–molybdenum bimetal oxides (FeMoO) incorporated montmorillonite (MMT)-based ceramic membrane (FeMoMMTCM) to achieve continuous Fenton reaction for water purification. The embedded bimetallic FeMoO catalyst created abundant active Fe(II) sites on the external and internal surfaces of the ceramic membrane (CM) for H2O2 activation. Using naproxen (NPX) as a model micropollutant in water, the FeMoMMTCM/H2O2 system achieved a 98.6 % removal of NPX (10 mg/L) within a filtration period of 3.4 min through the membrane, in comparison to a 17.5 % removal by FeMoMMTCM filtration with no H2O2 dosing and a 21.1 % removal by the FeMoO-less MMTCM/H2O2 system. The catalytic membrane demonstrated its high NPX removal efficiency over multiple cycles, retaining its effectiveness even in the presence of co-existing ions and organic matter in the water matrix. Furthermore, the FeMoMMTCM/H2O2 system was able to remove nearly 70 % of residual organic pollutants from the actual secondary wastewater effluent. The quenching tests and electro-paramagnetic resonance (EPR) detection confirmed the generation of hydroxyl (OH) and superoxide (O2−) radicals from H2O2. The excellent catalytic performance can be attributed to the Fe-Mo bimetallic catalyst, in which the active Mo(VI)/Mo(IV) cycle can facilitate the Fe(II)/Fe(III) cycle for continuous Fenton reaction. The cost analysis indicates that the low-cost MMT and its low sintering temperature for ceramics would greatly decrease the cost of MMTCM (243.1 US$/m2 vs. 541.5 US$/m2 of alumina-based CM). Overall, the research presents a technical strategy for the fabrication of highly cost-effective catalytic membranes with Fenton reaction for removing micropollutants from water.

Temporal resistance fluctuations during the initial filtration period of colloidal matter filtration

Membrane filtration processes with flux reversal for backwashing are employed to manage fouling during colloidal fluid treatment. This flux reversal accompanies filtration cycles where the total resistance increases over time. However, little is known about the initial phase of filtration. We focus on early filtration phase and present a microfluidic filtration system that allows precise observation of filtration resistances under constant flux or constant pressure operation for soft matter dead-end filtration with subsequent percolation of pure solvent. We identified temporal hydraulic resistance fluctuations during the start-up phase, which significantly differed from the steady-state condition. We focus on the experimental filtration of soft core–shell poly(N-isopropylacrylamide)-co-acrylic-acid microgels and observed a distinct peak in filter cake resistance with a subsequent reduction down to 50% of the initial peak resistance. To comprehend the phenomenon, we complement the experiments with temporal and spatial confocal microscopy studies linking cake compression and cake density gradients to its resistance. By comparing filtration, dialysis, and centrifugation as different microgel purification methods, we discover microgel shell degradation leading to detached polymer chains permeating in the downstream which causes the observed resistance reduction. This result demonstrates the permeation-induced degradation of macromolecular colloids during membrane filtration.

Predatory Bdellovibrio-and-like organism mixtures on efficient MBR in-situ membrane fouling diminishment and mechanisms

ABSTRACT Membrane fouling is a major hindrance that restricts the application of membrane bioreactors (MBRs). Bdellovibrio-and-like organisms (BALOs), as obligatory parasitic bacteria, prey upon various bacteria. In this study, the BALO mixtures were screened and found more effective in membrane fouling mitigation compared to the single BALO species and extended the membrane filtration period by as long as 33.3%. The higher BALO diversity reduced the potential foulants generation in the activated sludge by decreasing the sludge viscosity as high as 13.8 ± 0.6% than the pure culture of BALO. Meanwhile, the mixed BALOs demonstrated superior biofilm predation capabilities, with the content of soluble microbial products and extracellular polymeric substances on the biofilm decreasing by 26.1 ± 0.5% and 38.3 ± 0.2% as the most compared to the single BALO species involved system. Additionally, the BALO mixtures expanded the single strains’ host lysis spectrum of both the activated sludge and biofilm. The abundance of membrane-fouling-related bacteria such as Flavobacterium, Rhodobacter, and Labilithrix and pioneer bacteria such as Sphingorhabdus and Pseudomonas was significantly reduced. In summary, this study disclosed the significantly better membrane fouling mitigation effects of the BALOs with higher diversity, suggesting that the expansion of the host range is crucial for the further application of BALOs to enhance the anti-fouling performance of the MBR system.

Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability.

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.

Building a simple multivariable filtration model to predict irreversible fouling when directly filtering municipal wastewater

This paper describes a simple generic model designed to predict membrane fouling in municipal wastewater (MWW) treatment. The work was conducted using data from a direct membrane filtration demo-system (middle/long-term filtration periods of about 35 – 124 days) to calibrate the model. Two influents were treated by the demo-system: raw pre-treated MWW and primary settler supernatant from a full-scale MWW treatment plant. A resistance-in-series mathematical model structure was proposed considering fouling due to two different mechanisms: persistent cake layer formation (from suspended material) and pore blocking (from soluble and colloidal compounds). The proposed model represented transmembrane pressure dynamics at different operating solids concentrations (around 1, 2.6, 6 and 11 gL−1) using 7 model parameters, achieving 7–28 mbar differences between the experimental data and model predictions in all cases (calculated as the root mean square error). The model was also able to match the results from two different influents (raw MWW and primary settler supernatant) by modifying 3 of the 7 parameters while low uncertainties were obtained in long-term filtrations, demonstrating its robustness. This model thus provides a good potential to generate reasonable membrane fouling predictions while its simple and open structure makes it easy to implement with complementary materials. Further research will be carried out to enhance the model’s precision and validate its potential for optimizing filtration and fouling control processes.

Effects of granule disintegration and sludge re-aggregation on fouling behaviors and bio-cake formation in aerobic granular sludge membrane bioreactor (AGMBR)

The contribution of granules to membrane fouling alleviation in aerobic granular sludge-membrane bioreactor (AGMBR) has been increasingly investigated, yet the inoculated granules in MBR are more unstable than those in conventional AGS system and thus in-depth insight into the effects of the mutual transformation between granules and flocs on membrane fouling as well as corresponding bio-cake formation is necessary. Herein, we found that the disintegration of granules was accompanied by the release of soluble microbial products (SMP) and the increase of microbial diversity. The re-granulation phase occurred when granules gradually re-dominated the sludge system with the growth of biomass and the massive secretion of extracellular polymeric substances (EPS), corresponding to the declined microbial diversity and stable pollutants removal (COD: 93.45–98 %, TN: 21.06–36.86 %). Compared with the granule disintegration phase, less flocs deposition and fewer contents of SMP containing high molecular weight (>100 kDa) compounds in bio-cakes in the re-granulation phase resulted in the longer filtration period, as evidenced by lower attractive interaction energies between sludge foulants and membranes according to extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Microbial community analysis demonstrated higher relative abundance of filamentous bacteria (Thiothrix) and lower relative abundance of denitrifiers (e.g, Hydrogenophag, Trichococcus, Arenimonas, Acinetobacter) in bio-cakes in the re-granulation phase. Besides, the genera Thiothrix, norank_f__env.OPS_17 and Aeromonas may be responsible for the organic foulants accumulation on membrane surface. More importantly, stronger positive correlations among microbial populations between bio-cake and suspended sludge in the re-granulation phase indicated the lower propensity of membrane fouling. The systematic insights into the effects of granules disintegration and sludge re-aggregation on fouling layer may have important implications for the future development of membrane fouling control in AGMBR system.

Study on the construction and filtration characteristics of a Triple-Layer granular bed filter

Granular bed filtration is a high-temperature dust removal technology with unique advantages. In this paper, through the fluidization tests, the densities and granule sizes of the triple-layer filter granules were optimally matched, and a triple-layer granular bed filter was constructed, which could be fluidized in layers and meet the requirement for removing ash deposited in the layers by fluidization without destroying the triple-layer structure. The whole-bed filtration tests at room and high temperatures showed that the triple-layer granular bed filter which consisted of cenosphere layer, desert yellow sand layer and 304 stainless steel shot layer had lower total pressure drop and outlet dust concentration, and higher filtration efficiency than the dual-layer granular bed filter which consisted of cenosphere layer and baozhu sand layer. The separated-bed filtration tests at high temperature found that the upper filter layer experienced the deep-bed, transition and surface filtration periods. The middle and lower filter layers didn’t experience the surface filtration period and the grade filtration efficiency curves were “V” shapes, with the lowest efficiency for particles around 1.3 μm.

Angular vibrations for fouling control during ultrafiltration of microalgae in a spiral wound module

Previous studies have shown that vibration- or rotation-based techniques can effectively mitigate the fouling and concentration polarization during membrane filtration. However, it is difficult to incorporate these active enhancement techniques with spiral wound modules (SWMs), which are widely employed in drinking water and wastewater treatment. In this work a prototype membrane system was developed to accommodate angular vibrations with a modified SWM. With this prototype system, a series of filtration experiments were designed and implemented to investigate the effect of angular vibrations on the ultrafiltration algal fouling process in an SWM. The experimental results indicate that the algal fouling in an SWM can be effectively controlled (up to ∼28.5 % at 15 Hz) by applying angular vibrations in conjunction with appropriate operating conditions; the underlying mechanisms are discussed using a mathematical model that accounts for the relative motion between the fluid and membrane when they are subject to external accelerations, related to the vibration frequency, filtration period and position along coiled membrane leaves. A quantitative analysis is also presented to demonstrate the potential of using angular oscillations to control the algal fouling in an SWM with a lower energy consumption compared to the conventional method of increasing the cross-flow rate.

Polyelectrolyte multilayers modification of nanofiltration membranes to improve selective separation of mono- and multivalent cations in seawater brine

Nowadays, brine produced in the Reverse Osmosis (RO) seawater desalination plants is a significant and largely untapped source of critical minerals and metals, which is usually discharged into the seas as wastewater. As a front face stage in the brine mining process, nanofiltration (NF) membranes can be used to separate brine stream into monovalent and multivalent ion-rich streams. Since high separation factors are required in seawater RO brine, polyelectrolyte multilayers with Layer-by-Layer (LbL) technique were used in this study to modify commercial polyamide NF membranes and improve their performance. Two common polyelectrolytes, poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated onto two poly-piperazine polyamide NF membranes (NF270 and Desal-5 DL). The effects of the bilayers number and the outer layer charge on membranes’ performance were studied using two crossflow filtration setups with two different membrane sizes to find the membrane with the higher monovalent/multivalent separation factor. Desal-5 DL membrane coated with 5.5 bilayers provided the highest selectivity factors for mono/multivalent cations (> 21), the highest average rejection of multivalent cations group (about 95.7%) for short-term experiments. Another interesting result was the increase in water permeance of the Desal-5 DL membrane after it was coated with 5.5 bLs (indicating more than 20% improvement in pure water permeance). In addition, the stability test with brines at 20 bar showed that this membrane was stable over an extended period of filtration (22 hours) with an even higher selectivity factor of 34 and multivalent cations rejection of 97.7% on average.

An all-protein aerogel with a nanofiber/foam structure for versatile air filtration

Structural design plays a vital role in advancement of multifunctional air filters. We here report a novel design of an all-protein aerogel with a unique hybrid nanofiber/foam structure, demonstrating versatile filtration capabilities, i.e. being able to capture oils & organic chemicals, toxic gaseous molecules, and particulate matter (PM), at a low pressure drop. The aerogel is made from two abundant natural proteins: zein and gelatin, by freeze-drying. The electrospun zein nanofibers dispersed within the hybrid zein/gelatin aerogel provide a large specific surface area and hydrophobicity, enabling high filtration efficiency even under a humid environment. The gelatin foam structure constructs a skeleton of the hybrid aerogel, extending the filtration capacities for capturing air pollutants. In addition, the optimal Z1/G1-3 aerogel sample exhibits high filtration efficiency of 99.24 % for PM2.5 and 95.54 % for PM0.3 at a low pressure drop of 54.76 Pa. More significantly, the Z1/G1-3 air filter presents exceptional filtration performance even when subjected to a high airflow rate of 10 L/min or after a continuous 120-min filtration period. This work proposes a novel air filter design that integrates eco-friendliness and multifunctional filtration features.

Prediction on Filtration Period of Granular Bed Filter Used in Purifying Produced Water in Oil Field

Summary The granular bed filter can purify the water produced in the crude oil production process by adsorbing oil droplets and suspended solids. A regeneration operation is needed to clean the granular media and recover filtration capacity after a certain operation duration. Currently, filtration models are mainly used for one type of particle removal, with few applications in the filtration system of produced water containing oil droplets and suspended solids. However, the different deposition morphologies of oil droplets and suspended solids in the filter bed can affect the prediction of the filtration process. In this work, we develop a transient filtration model based on the multiphase system transport equations coupled with the filtration rate and momentum exchange equations to predict simultaneously the effluent concentration and the pressure drop buildup, which considers the effect of deposition morphologies of oil droplets and suspended solids on filtration behaviors. The model hypothesizes that particle removal occurs through deep bed filtration mechanisms, and initial filtration coefficients are predicted by trajectory analysis without relying on experimental data. After that, we propose a method for predicting the filtration period, and analyze the effect of particle size and water temperature on the filtration process. Results show that the filtration process can be divided into two major stages—the main filtration zone migration, followed by the saturation front migration. With an S-shape increase in the effluent concentration, the pressure drop of the filter bed increases in a parabolic shape. When the diameter median of suspended solids is 5 μm, and the water temperature is 20°C, the filtration period was determined to be 24 hours to meet both water quality and maximum usable pressure drop of 20 kPa. With the increase in non-Brownian suspended solid size, the interception and gravitational forces increase the removal efficiency of suspended solids, which results in a slight decrease in the removal efficiency of oil droplets and an increase in the pressure drop of the filter bed. As the water temperature increases, the viscosity of the produced water decreases, and the oil droplets and suspended solids are more easily removed, but the pressure drop of the filter bed increases. In this work, we provide new ideas and methods to properly design, operate, and manage filters in a sustainable and energy-efficient way.

Pre-ozonation for gravity-driven membrane filtration: Effects of ozone dosage and application timing on membrane flux and water quality

Gravity-driven membrane (GDM) filtration has been proposed as an alternative to sand filtration for drinking water treatment, but its low membrane flux and poor permeate quality hinder its widespread application. This study investigated the effect of pre-ozonation (with various dosages and application timings) on membrane flux, fouling layer characteristics, and permeate quality during GDM filtration of river water. Pre-ozonation with 3 mg/L ozone increased the mean membrane flux by 9–54%, resulting in approximately 30% increased water production and reduced dissolved organic carbon (DOC) and extracellular polymeric substance (EPS) production by 12–35% and 9–18%, respectively. The timing of pre-ozonation significantly affected the time-dependent flux behavior and morphological characteristics of the fouling layers. Pre-ozonation from the beginning of GDM filtration enhanced the initial flux because of organic fouling control but showed a gradual flux decline with time due to EPS accumulation and biologically inactive fouling layers. Pre-ozonation from the middle of GDM filtration period created heterogeneous and porous membrane fouling layers with high biological activity, showing increased membrane fluxes and improved permeate quality by removing DOC and assimilable organic carbon (AOC) via the combined action of ozone oxidation and biodegradation/sorption in the fouling layer. Overall, our results demonstrate pre-ozonation as a potential option to overcome the limitations of GDM filtration.

Improved separation performance, anti-fouling property and durability of polyamide-based RO membrane by constructing a polyvinyl alcohol/polyquaternium-10 surface coating layer

In this work, a novel coating layer of polyvinyl alcohol (PVA)/polyquaternium-10 (PQ10) was constructed onto the surface of polyamide-based RO membrane via the method of surface coating followed by cross-linking. Permeation tests demonstrated that the incorporation of PQ10 into PVA could efficiently improve the water permeation ability of surface coating layer, showing a significant decrease of hydraulic resistance from 5.9 × 1012 m−1 of the PVA-1.0 coating layer to 2.5 × 1012 m−1 of the PVA-1.0/PQ10-0.2 coating layer. Anti-fouling performance evaluation revealed that the PVA/PQ10-coated membrane not only possessed the good anti-fouling property of the PVA-coated membrane to negatively charged foulants and protein but also exhibited more excellent anti-fouling performance to positively charged foulant due to its relatively lower surface charge density and pseudo-zwitterionic surface character. Long-term filtration tests with dye wastewater illustrated that although the initial water permeability of membrane coated with PVA-1.0/PQ10-0.2 surface layer was lower than that of the virgin RO membrane under the same operation condition, the PVA-1.0/PQ10-0.2-coated membrane exhibited a higher salt rejection, lower flux decline rate and larger cumulative volume of permeated water during a filtration period of 48.0 h. Soaking tests further demonstrated the improvement of membrane chemical durability against acid, alkaline and chlorine by the PVA/PQ10 coating layer.

The influence of multiple fouling and cleaning cycles upon the performance of polyethersulphone membrane filters during coffee extract decaffeination

Filtration processes have been applied widely in food processing industry over the recent decades and could offer a viable alternative to the use of solvents in the decaffeination process, comprising low operational costs, high selectivities and mild processing conditions. This paper reports the development and evaluation of the fouling occurring in multiple filtration cycles during the selective reduction of caffeine from coffee brews comparing the performance of (i) a commercially available synthetic tight ultrafiltration (TUF) polyethersulphone (PES) membrane (GP95PP – Alfa Laval) and (ii) a self-made mixed matrix (MMMs) PES membranes (PSCD) fabricated in-house. The effectiveness and performance of the PES MMMs was benchmarked against the commercial 2 kDa PES membranes showing promising results. A cross-flow rig was operated at transmembrane pressures of 2–9 bar and cross-flow velocities (CFV) of 0.04–0.1 m/s at 25 °C. The flux decline and recovery along with changes in the key component rejection and resistances are reported for multiple fouling and cleaning cycles. PSCD exhibited a higher permeate flux of ca. 10.5 L m-2h-1compared to the GR95PP membranes, which exhibited a permeate flux of 6.1 L m-2h-1 over the 29 h filtration period selected, at 9 bar and a CFV of 0.04 m/s. The rejection ratios of the GR95PP and PSCD membranes were monitored for three consecutive filtration cycles, and showed values ca. 30% and 35% for caffeine,> 90% and ∼90% for both polyphenols & proteins, & ∼ 80% for melanoidins, respectively. An effective cleaning protocol was reported, comprised of 0.5 wt% NaOH at 50 °C, exhibiting cleaning efficiencies (CE)> 99%. FT-IR data indicated the presence of key compounds residuals after membrane cleaning. Modification to the membrane surface occurs due to fouling, altering the hydrophobicity. Differences in filtration performance and cleanability between the two classes of membranes are identified and linked to variations in surface and structure properties.

Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale.

This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1 and 2.6 g L-1) were evaluated on a demonstration plant. Filtration periods of 2-8 h were achieved when using the MF membrane, while these increased to 34-69 days with the UF membrane. This wide difference was due to severe fouling when operating the MF membrane, which was dramatically reduced by the UF membrane. Use of raw wastewater and higher solids concentration showed a significant benefit in the filtration performance when using the UF module. The physical fouling control strategies tested (air sparging and backwashing) proved to be ineffective in controlling UF membrane fouling, although these strategies had a significant impact on MF membrane fouling, extending the operating period from some hours to 5-6 days. The fouling evaluation showed that a cake layer seemed to be the predominant reversible fouling mechanism during each independent filtration cycle. However, as continuous filtration advanced, a large accumulation of irreversible fouling appeared, which could have been related to intermediate/complete pore blocking in the case of the MF membrane, while it could have been produced by standard pore blocking in the case of the UF membrane. Organic matter represented more than 70% of this irreversible fouling in all the experimental conditions evaluated.

Minimalno prerađen paradajz pomoću jednostavno razvijenog uređaja za filtraciju - obična so i biljno ulje mogu očuvati koncentrat paradajza

In attempt to produce and preserve tomato concentrate, without destroying some useful nutrients, in a rural area where there is no electricity, a minimal processing method is necessary. In this study, a simple filtration unit was developed. Fresh tomatoes (Solanum lycopersicum) (3.50 kg) were bought, cleaned and blended. Initial moisture content (MC) of the slurry (3.0 g) was determined and 3.0 kg slurry filtered. The amounts of concentrate, filtrate and filtration period were noted. Initial MC of the concentrate was also found. A mixture of concentrate (200 g), vegetable oil (30 ml) and salt (12.0 g) was prepared for preservation as sample A. This was re-prepared but with 10.0 and 8.0 g of salt as samples B and C. pH, colour and lycopene content of the test samples were found before and during preservation at a week-interval for 2 months in duplicates. The results showed that the initial MC of the fresh tomato / slurry and concentrate were 93.5 and 73.3%, respectively. Test sample pH before preservation was 4.22. Sample A recorded 18.79% decrease in pH while B and C had 9.2% and 54% increase in pH, respectively. Visual observation after 8th week of preservation showed that the tomato concentrate was still reddish but colour change (∆E) from the colorimeter revealed that sample A had the least value of 6.09 while B and C were 7.31 and 8.53, respectively. Initial lycopene concentration was 14.11 mg /100 g product. After preservation, Sample A had the least decrease (19.63%) compared to sample B (29.91% decrease) and sample C (33.3% decrease). Hence, common salt (12.0 g) and vegetable oil (30 ml) were able to maintain the acid content and minimize the reduction in lycopene content in the tomato concentrate.

Performance of polycarbonate, cellulose nitrate and polyethersulfone filtering membranes for culture-independent microbiota analysis of clean waters

Demineralized and disinfected waters may have very low microbial loads, requiring that large volumes of water are filtered to recover enough biomass for further analysis. Extended filtration periods, often interrupted by clogging, are a major limiting factor to concentrate samples’ microbiota for further examination, besides hindering the work pace. In this study, we investigated the performance of three types of filtering membranes – polycarbonate (PC), cellulose nitrate (CN), and polyethersulfone (PES) with 0.22 µm pore size for culture-independent microbiological analysis (quantitative PCR of seven housekeeping and integrase genes) of tap water, recirculating tap water in a bottle washing loop, and of demineralized water. Compared to PC membranes, CN or PES required lower filtration periods, although had slightly lower DNA extraction yields. However, genes abundance per volume of water was, in general, not significantly different. The exception was observed for bottle washing water in which PC membranes supported significantly higher quantification values than PES membranes. These differences were lower than ∼ 0.5 log-units and did not hamper the distinction of the types of water based on genes profile. Also, the type of membrane did not significantly affect the profile of the bacterial community determined for tap and demineralized water. A major conclusion is that CN membranes, cheaper, allowing shorter filtration periods, and producing results that are not significantly different from those obtained with PC or PES, can be a good alternative to analyze waters with low biomass loads.

Experimental Studies of PowerCore Filters and Pleated Filter Baffles.

The material most commonly used to filter and clean the intake air of vehicle internal combustion engines is pleated filter paper, which in most cases is shaped in the form of a cylinder or panel. The production technology has a low cost and is not complicated. In addition to high separation efficiency and filtration performance, pleated filter media are required to have low initial pressure drop, which depends on the geometry of the bed. Much research has been conducted in this area. Dust accumulated in the filter bed causes an increase in pressure drop, which is the cause of deformation and sticking of pleats. The lack of stability of the pleats, the need to strengthen them, and the need to obtain small sizes while achieving high efficiency and accuracy of filtration of engine intake air was the reason for the development of a different design and a new technology for making filter cartridges called PowerCore. The distinctive feature of these filters is axial flow in one direction of the air stream, which avoids turbulence and thus minimizes pressure drop. This paper presents a comparative analysis of a standard PowerCore and PowerCore G2 filter bed and two cylindrical filters with a pleated filter bed made of cellulose and polyester. The conditions and methodology of experimental testing of filters with test dust are presented. During the tests, the characteristics of separation efficiency and filtration performance, as well as pressure drop as a function of the mass of dust retained on the filter of two PowerCore filters and two cylindrical filters were performed. Three specimens of test filters with the same filtration area were made from each sample of filter bed. The results showed that in each test of the filter bed, there is an initial filtration period characterized by low (96–98%) initial separation efficiency and the presence of large (dpmax) dust grains. As the dust loading of the bed increases, the separation efficiency and filtration performance obtain higher and higher values. The initial period of filtration ends when the conventional value (99.9%) of separation efficiency is reached. The duration of this period depends on the type of filter bed and for the PowerCore G2 filter ends for a dust loading of km = 33.1 g/m2, and for the cellulose filter for km = 117.3 g/m2. During the initial period, the air behind the PowerCore G2 filter contains grains with sizes in the range of dpmax = 9–16 µm. Behind the cellulose filter, dust grains are much larger, dpmax = 17–35 µm. The total operating time of the PowerCore G2 filter, limited by the achievement of the permittivity resistance Δpwdop = 3 kPa, is twice that of the other filter compositions tested.

Comparison of the formation, filtration performance, and structural characteristic of self-forming dynamic membranes under constant transmembrane pressure and constant filtration flux

The formation and filtration of self-forming dynamic membranes (SFDMs) can be affected by multiple factors, such as the operating conditions and sludge properties in membrane bioreactors. There has been limited research on the effects of the constant transmembrane pressure and constant filtration flux on the stable filtration of dynamic membranes. In the present study, a large-pore stainless steel mesh (70 µm pore size) was used as the support material for dynamic membrane formation to explore the formation, filtration performance, and structural characteristics of two dynamic membranes, P-SFDM (filtration under constant transmembrane pressure) and J-SFDM (filtration under constant flux), with the same initial filtration flux. The results showed that the stable filtration period of J-SFDM went up to 22.5 h, which was significantly longer than that of P-SFDM (5.5 h) with a higher resistance growth speed. The blocking process of the P-SFDM membrane conformed to the complete blocking model, whereas that of the J-SFDM membrane conformed to the standard blocking model in the initial stage and follows the intermediate blocking model in the later stage. Besides, the P-SFDM cake layer had a higher extracellular polymer content and smaller particle size (106 ± 2 mg·g−1 VSS, 546 ± 63 µm) than that of the J-SFDM cake layer (89 ± 3 mg·g−1 VSS, 615 ± 51 µm). During a 39-day continuous long-term operation, the energy consumptions per ton of water for J-SFDM and P-SFDM were 0.14 kw·h·t−1 and 0.19 kw·h·t−1, respectively. The above results show that the J-SFDM has a longer stable filtration period with lower energy consumption per ton of water.

Fouling of polyethersulphone ultrafiltration membranes during the decaffeination of ground coffee brews

The production of reduced caffeine coffee beverages (so called ‘half-decaf’) has recently gained increased commercial attention. Ultrafiltration (UF) can offer a viable alternative to the use of solvents in the decaffeination process, also operating at ambient temperatures, and a low operational cost. This paper reports the development and evaluation of the fouling occurring during the selective reduction of caffeine from coffee brews using a commercially available synthetic tight ultrafiltration (TUF) polyethersulphone (PES) membrane (GP95PP – Alfa Laval) with a 2 kDa molecular weight cut off (MWCO). Performance is reported in terms of fluxes, hydraulic resistances, and component rejection ratios. A cross-flow rig was operated at transmembrane pressures of 2–9 bar and cross-flow velocities of 0.04–0.1 m/s at temperatures in the range 25–50 oC. The process is viable: a retentate is produced with a much reduced caffeine concentration whilst still rich in higher molecular weight bioactives. Commercial PES membranes (GP95PP – Alfa Laval) had a permeate flux of 6.5 L m-2 h-1 and a fouling index (FI) of ca 60%. Rejection ratios were ca 30% for caffeine, ≥ 90% for both polyphenols & proteins, & ≥ 80% for melanoidins, over a 29 hr filtration period. Membrane surface modification due to fouling takes place, altering the hydrophobicity. An effective cleaning protocol is reported comprised of 0.5% w/v NaOH at 500 C. The flux decline and recovery are reported for multiple fouling and cleaning cycles.