Filter Media Research Articles

Development of a methodology for studying microbiological contamination of office indoor air by analyzing air handling unit filters - Application to a low-energy building

Bioaerosols can alter the air quality, affecting differently people depending on their health status. Methods to sample bioaerosols are limited in terms of sampling time and air volumes. This study evaluated a new methodology to sample airborne microorganisms in buildings, using the air handling unit (AHU) filters and filtration media sampling discs (FMSD). Filtration media with FMSD of different natures were tested at the laboratory, and characterized by their air permeability, particle collection efficiency and the airflow distribution on their surface. Filtration media with FMSD of the same nature had best properties with a sampling particle efficiency of the FMSD of 50 %. This sampling methodology was applied on a building AHU, and FMSD were collected each month during one year. Airborne microorganisms collected by the FMSD were analyzed by culture and nucleic acids based methods (qPCR and Next-Generation sequencing). FMSD methodology gave results for all of those identification methods. Most of the bacteria orders identified by 16 S sequencing were Rhodobacterales (Paracoccus), Pseudomonadales and Cyanobacteria. For fungi, the most represented orders were Agaricales, Polyporales and Hymenochaetales. This sampling methodology has also made it possible to detect small size airborne microorganisms like viruses including two Coronaviruses. This study has shown the potential of using AHU filters to sample the airborne microorganisms in buildings.

Gravity‐driven packed bed filter, with copper‐impregnated activated carbon, for continuous water disinfection in absence of electricity

AbstractAvailability of safe drinking water is a major concern in many parts of the world. While many filtration units operating on various principles are available to combat this, most require electricity, which may not be consistently available in such areas. In the present study, we have designed and demonstrated a water disinfection system that can operate purely on gravity, without any electricity. For this, a potassium hydroxide modified copper‐impregnated activated carbon (KOH‐Cu‐AC) hybrid was used as a filter medium for disinfection, because it is less expensive, with performance comparable to previously reported hybrids containing silver. To maintain a constant water flow rate under gravity, during disinfection, a Mariotte bottle was used as the reservoir of the contaminated water. Using this and a constant head between the bottle and the treated water exit point, the required water‐filter contact time of 25 min (for decontamination) is maintained in the filter column, regardless of tank‐fill level. The demonstrated lab‐scale system can perform disinfection of simulated contaminated water (with an initial concentration of 104 CFU mL−1 Escherichia coli), for at least 6 h, with a flow rate of 150 mL h−1. The disinfection performance from the gravity‐based filter was further validated with the conventional pump‐driven filter, used for continuous disinfection of drinking water. Equivalence of results between pump‐ and gravity‐driven operations helps us to eliminate the need for power, without any compromise in disinfection efficacy. Finally, copper concentration from treated water (106 ppb at steady state) remains very well within the safe limit (1000 ppb as per USEPA guideline). Hence, the lab‐scale design of gravity‐based packed bed filter will be useful for domestic and community‐based supply of safe drinking water in resource‐constrained areas, because it eliminated electricity requirement of conventional power‐driven systems.Practitioner Points Cost‐effective KOH‐Cu‐AC hybrid is developed as a disinfection material. Mariotte bottle used for maintaining constant disinfected water flow rate works without any electrical power supply. This system can be used for getting on‐spot, continuous disinfected water supply. The concentration of copper in the treated water is well within the safety limit. It can be applicable in rural and remote areas (no electric power source) as well as natural calamity‐affected areas.

In-line granular filtration for mitigating gypsum scaling in membrane distillation

Mineral scaling and scaling-induced wetting are major challenges for the widespread application of membrane distillation (MD) in saline wastewater treatment. For the first time, an in-line modified activated alumina (AA) granular filtration coupled with MD process was proposed to achieve effective control of gypsum scaling. Firstly, the AA modified by NaOH impregnation with tuned pore structure and surface characteristics were supplied as the filter media. The optimized MD performance was obtained using in-line filtration with modified AA (MAA) with 20 g/L NaOH and the ratio of AA and NaOH solution of 1:3 for the duration of 24 h. Compared with severe scaling without granular filter, the optimized performance with a final normalized flux higher than 0.7 and a permeate conductivity less than 5 μS/cm at 70 % water recovery was observed. The MAA with rich pore, scale-like structures and high Na loading showed a superior ability in capturing gypsum scaling due to the enhanced heterogeneous scaling and the retention of scaling. In-line granular filtration-MD was also effective in mitigating gypsum scaling and scaling-induced wetting in saline solutions (e.g., 7–12 g/L NaCl). Our findings provide guidance for surface design of granular filter media and scaling control in membrane desalination technology.

Social Media Filters and the Vestiges of the Psyche

Social Media Filters and the Vestiges of the Psyche

Iron and Manganese Removal through Adsortive Filtration based on Zeolites, at bank scale

The aim of the current study is to assess iron and manganese removal from water used for public supply through adsorptive filtration based on natural zeolites that were chemically prepared for metal removal purposes. The research was conducted at bench scale by using water samples from two water sources in Parana State. Full cycle studies were carried out; according to them, filtration was conducted, in separate, under four filter bed conditions, namely: sand, anthracite coal, zeolite without previous chlorine application and zeolite with previous chlorine application. The zeolite filtration test without previous chlorine application recorded high meaniron and manganese removal values, - 100% and 87.96%, respectively. Based on the filtration results, the zeolite filter without previous chlorine application was the best filter media among the tested beds, under the herein proposed conditions.

Understanding the transitional phase of nitrate removal in three different specialty adsorbents for stormwater treatment

Excess nitrogen input from nonpoint sources driven by hydrologic and anthropogenic disturbances has become a significant ecological challenge in receiving water bodies. Moreover, nitrate removal by cost-effective filtration media has still not performed up to expectation because of the knowledge gap in the transitional phase from physicochemical to microbiological processes. This study developed three cost-effective, sustainable, and adaptable green sorption media (GSM), namely CPS (clay–perlite with sand sorption media), ZIPGEM (zero-valent iron and perlite green environmental media), and BIPGEM (biochar, zero-valent iron, and perlite-based green environmental media), made of readily available and recyclable materials, to compare nitrate removal methods for stormwater treatment and elucidate the transitional phase. The primary adsorption mechanism was chemisorption, and subsequent biofilm growth sustained removal efficiency for a long-lasting period. Adsorption kinetics, adsorption equilibrium, material characterization, and fixed-bed column experiments with a 2-stage cultivation approach were undertaken to characterize the transitional phase in these GSM, based on breakthrough curves, maximum adsorption capacity, and microbial population dynamics for nitrification and denitrification. As shown in the column study, BIPGEM had the highest adsorption capacity (7.637 mg∙g−1), followed by ZIPGEM (2.16 mg∙g−1), and CPS (0.1798mg∙g−1). The biochar in BIPGEM provides a better cultivation environment for nitrifying and denitrifying bacteria, contributing sufficient electron donors. Biofilm production and maturation enabled the BIPGEM to maintain 30 % nitrate removal in a steady state even after 2000 h of operation in the first stage. When the biofilm reached maturation, BIPGEM’s nitrate removal percentage was up to 70 % via denitrification in the second stage.

Enhanced Air Filtration Efficiency through Electrospun PVC/PVP/MWCNTs Nanofibers: Design, Optimization, and Performance Evaluation.

This study presents a novel approach for creating an effective air filtration medium using electrospun nanofibers comprised of poly(vinyl chloride) (PVC), poly(vinylpyrrolidone) (PVP), and impregnated with multiwall carbon nanotubes (MWCNTs). The membrane production was optimized using an experimental design methodology, resulting in a hydrophobic membrane that exhibits excellent dispersion of MWCNTs. Scanning electron microscopy images illustrate the nanofibers' morphology, featuring an average diameter of approximately 240 nm, minimal bead formation, and optimal MWCNT dispersion. Air filtration tests conducted with NaCl nanoparticles (7-300 nm) demonstrated superior permeability (10-12 m2) and minimal pressure drop (approximately 780 Pa at a 5 LPM airflow rate) compared to other electrospun materials. Both MWCNT-impregnated samples and individual PVC/PVP nanofibers exhibited filtration efficiencies nearing 96%. These results underscore the potential of this developed material for air filtration, particularly in indoor environments, where MWCNTs effectively adsorb and maintain low levels of gaseous and particulate pollutants. This study emphasizes the design, optimization, and comprehensive performance evaluation of PVC/PVP/MWCNT nanofibers, showcasing significant advancements in filtration efficiency with high flux. The findings suggest promising applications for this composite material in advanced air purification systems.

Comparative assessment of domestic wastewater treatment via Vermifiltration through various filter bed material.

Vermifilter (VF) is considered sustainable for rural areas; however, filter media is the most important but has been explored less. This study evaluated the performance of vermifilters in treating domestic wastewater (DWW) using various filter media, including areca nutshell (AS), rice straw (RS), dry leaves (DL), and chicken eggshells (ES). We compared the results with four different reactors: R1 (AS), R2 (RS), R3 (DL), and R4 (ES). DWW was applied with a hydraulic loading rate (HLR) of 1 m3/m2/d with Eisenia fetida earthworm species. The results showed the removal of biochemical oxygen demand (BOD) by 82%, 76%, 73%, and 87%; chemical oxygen demand (COD) by 75%, 73%, 72%, and 88%; phosphate by 36%, 25%, 27%, and 50%; sulfate by 56%, 54%, 53%, and 71% in R1, R2, R3, and R4, respectively. Simultaneously, R4 experienced a fivefold reduction in total bacteria and a sixfold reduction in total coliform. Moreover, the most exceptional filter media for vermifiltration is eggshells for the earthworm's growth and treatment efficacy.

The Effect of Filter Media Grain Size on the Headloss and Backwash Duration at PT PAM Lyonnaise Jaya (PALYJA)

The Effect of Filter Media Grain Size on the Headloss and Backwash Duration at PT PAM Lyonnaise Jaya (PALYJA)

Orthophosphate uptake onto woodchips in denitrifying bioreactors is enhanced by anoxic-(anaerobic-)oxic cycling

Woodchips are widely used as a low-cost and renewable organic carbon source for denitrifying biofilms in passive nutrient removal systems. One limitation of wood-based biofiltration systems is their relatively poor removal of phosphorus (P) from subsurface drainage and stormwaters, necessitating the use of additional filter media when co-treatment of nitrogen (N) and P is required. Here, we show that anoxic-oxic cycling of woodchip media, which enhances nitrate (NO3−) removal by increasing the mobilization of organic carbon from wood, also improves orthophosphate (Pi) uptake onto woodchips. Orthophosphate removal rates in flow-through woodchip columns ranged from 0 to 34.9 μg PO43− L−1 h−1 under continuously-saturated (anoxic) conditions, and increased to 17.5 to 71.9 μg PO43− L−1 h−1 in columns undergoing drying-rewetting (oxic-anoxic) cycles. The highest Pi removal efficiencies were observed in the first 20 h after reactors were re-flooded, and were concurrent with maxima in polyphosphate kinase (ppk) gene expression by the polyphosphate accumulating organisms (PAOs) Accumulibacter spp. and Pseudomonas spp. Batch experiments confirmed that anoxic-anaerobic-oxic pre-incubation conditions led to orthophosphate uptake onto woodchips as high as 74.9 ± 0.8 mg PO43−/kg woodchip, and batch tests with autoclaved woodchips demonstrated that Pi uptake was due to biological processes and not adsorption. NO3− removal in batch tests was also greatest under oxic incubation conditions, attributed to greater carbon availability in hypoxic to anoxic zones in woodchip biofilms. While further research is needed to elucidate the mechanisms controlling enhanced Pi uptake by woodchip biofilms under anoxic-(anaerobic-)oxic cycling, these results suggest a role for enhanced Pi uptake by PAOs in a nature-based system for treatment of nonpoint source nutrients.

Evaluation of the critical factors that influence the performance of a Geo-Fabric based Bio-Filter (GFBF)

Bio-filters are high-rate aerobic biological systems with porous support media for biofilm formation and filtration of suspended solids. The support media and its ability to remove contaminants decides the performance of bio-filter. Geo-fabrics, with properties like permeability and large surface area are capable of maintaining good biomass which in turn can absorb and adsorb substrate from influent to make them an attractive media for bio-filter systems. This paper investigates the critical factors that determine the performance of a Geo-Fabric based Bio-Filter (GFBF). Experiments conducted using geo-fabric of varying GSM were analyzed and optimized using Response Surface Methodology. The results indicated that by varying process variables like HRT, C:N ratio, rate of aeration and depth of filter, the geo-fabric with 500 GSM value showed improved performance compared to geo-fabric of 300 GSM and 400 GSM. The final experimental run conducted on GFBF with geo-fabric of 500 GSM at optimized value of process variables, observed 91 %, 98 %, 88 %, 90 % and 71 % removal of COD, BOD, NH3-N, turbidity and TDS respectively. GFBF are suitable for treatment plants where the amount of wastewater generated is relatively small and a complete treatment can be accomplished in one unit.

Sorting microparticle mixtures by multiple properties in a single dielectrophoretic filter

The sorting of nano- and microparticles according to different properties is an industrially highly relevant but partly unsolved problem. In this study, we investigate the sorting of a complex microparticle mixture on the basis of their different properties by insulator-based dielectrophoretic filtration at high throughput. We demonstrate here that such a high selectivity demanding sorting process is possible in a single device thanks to recent advances in the development of dielectrophoretic filters, which has been shown using simple binary mixtures in a previous study. In that study, a filter with a regular structure (mesh) is introduced with pores several orders of magnitude larger than the target particles so that the particles are trapped solely by the action of positive dielectrophoresis. In this work, we demonstrate the improvement of the filter design, by comparing the trapping behavior to an alternative, irregular porous ceramic structure as a filter medium. A significantly higher selectivity for positive dielectrophoresis could be reached using the regular mesh structure. This high selectivity enables a stepwise operation mode, combining a selective trapping step and several subsequent selective remobilization steps. A mixture of polystyrene-based particles could be sorted by size, shape, and surface coating in one pass of the filter. The proposed method is therefore a promising technique to efficiently create highly specific particle systems in the future.

Impact of pleating on the filtration performance of fibrous air filters

Pleated fibrous air filters are widely used for aerosol filtration but the impact of pleating on its filtration performance is still lacking detailed analysis. Pleating results in changes in thickness of the filter media (indentation or bulge zone) and it is generally difficult to simulate the particle filtration process of a pleat due to large difference in scale between that of the pleat and fiber. To address this problem, a dual-scale simulation method is developed in this study by combining the fiber-scale and pleat-scale models. This is achieved by incorporating the simulation results of fiber-scale models into the pleat-scale models, using the permeability coefficient and particle capture function of the porous media in the pleat model. From the fiber-scale model, it is found that the bulge zone is beneficial to improving quality factor as it could lead to a lower pressure drop. However, for the pleat-scale model, the indentation zone has a lower pressure drop than the bulge zone, resulting in a higher quality factor. This contradicts the findings of the fiber-scale model. For real applications, it has been found that pleating with indentation is more beneficial for filter performance compared to pleating with bulges. These findings help us better understand the pleating effect on filter performance and provide guidance on optimal pleating approaches.

Geometrical Optimization of Closed-End Cylindrical Air Filter Using CFD Simulation

This research aims to evaluate the effect of porous filter configuration on flow characteristics within filter using CFD simulation. This simulation model was chosen for comprehensive analysis that considers different variables affecting the filter performances. Dynamics of the flow and pressure drop under different flow conditions and filter geometry were studied. The Euler-Lagrangian approach was used to model multiphase flow, and the standard K-ε model was used for turbulence characterisation. Particle size distribution was characterized using Rosin-Rammler distribution. The initial status of these properties was obtained by previous experimental references and their evolution over time was simulated at the cell level of the model using User-Defined Functions (UDF). The main conclusions of the study are: i) The pressure drop increased with flow rate and thickness of the filter but decreased with increasing filter length and diameter. ii) There is no significant change in velocity ratio with the distance from the filter inlet at the filter centre line except the first 5% from the inlet and last 5% close to the end. iii) it was identified that higher radial velocity ratios imply a less particle deposition within the filter media. The results also shows that the particle loading on 290 mm filter is 50% - 60% lower than the other filters but evenly distributed across the filter. However, the pressure drop decreased with the filter length. 55mm filter that has the highest radial velocity ratio performs poorly in particle trapping.

Occurrence, Concentration, and Distribution of 35 PFASs and Their Precursors Retained in 20 Stormwater Biofilters.

Current knowledge about the fate and transport behaviors of per- and polyfluoroalkyl substances (PFASs) in urban stormwater biofilter facilities is very limited. C5-14,16 perfluoroalkyl carboxylic acids [perfluorinated carboxylic acids (PFCAs)], C4,8,10 perfluoroalkanesulfonic acids (PFSAs), methyl-perfluorooctane sulfonamide acetic acid (MeFOSAA, a PFSA precursor), and unknown C6-8 PFCA and perfluorooctanesulfonic acid precursors were frequently found in bioretention media and forebay sediments at Σ35PFAS concentrations of <0.03-19 and 0.064-16 μg/kg-DW, respectively. Unknown C6-8 PFCA precursor concentrations were up to ten times higher than the corresponding PFCAs, especially at forebays and biofilters' top layer. No significant trend could be attributed to PFAS and precursor concentrations versus depth of filter media, though PFAS concentrations were 2-3 times higher in the upper layers on average (significant difference between the upper (0-5 cm) and deepest (35-50 cm) layer). PFASs had a similar spatial concentration distribution in each filter media (no clear difference between short- and long-chain PFASs). Commercial land use and organic matter were important factors explaining the concentration variations among the biofilters and between the sampling depths, respectively. Given the comparable PFAS accumulations in deeper and superficial layers and possible increased mobility after precursor biotransformation, designing shallow-depth, nonamended sand biofilters or maintaining only the top layer may be insufficient for stormwater PFAS management.

Relating the ultrasonic and aerosol filtration properties of filters

Non-contact methods are useful to improve the quality control of particle filtration media. The purpose of this paper is to investigate the correlation between the filtration efficiency of a porous sheet and its ultrasonic properties obtained using a non-contact technique. An air-coupled ultrasonic technique is used to obtain rapid measurements without affecting the integrity of the material. High frequencies (from 0.1 to 2.5 MHz) are used to improve technique sensitivity, and transmitted waves are measured to probe the internal properties of the material. Measurements of transmission coefficient spectra (amplitude and phase) and the corresponding ultrasound velocity and attenuation coefficient at different frequencies are obtained for a set of filtration media with well-characterized properties. Results show that the ultrasonic properties of filtration media vary as a function of basis weight, and therefore filtration efficiency, for a given charge state. However, the effect of electrostatic charge on ultrasonic propagation is almost negligible, as expected. We conclude that ultrasonic transmission may provide a valuable tool for the continuous online monitoring of material quality during fabrication and as a method to tease apart mechanical and electrostatic contributions to particle filtration.

Effect of filter microstructure on filtration characteristics in a nonwoven bag filter: A resolved CFD-DEM approach coordinated with X-ray computed tomography image

A resolved CFD-DEM was used to simulate aerosol filtration through the microstructure of nonwoven bag filter media. The filtration behavior was simulated for three filter domains with different fiber orientations obtained from X-ray CT images of a commercial bag filter. Minimal particles were collected in the filter domain with fibers oriented parallel to the main flow. However, in the filter domain with fibers oriented perpendicularly, the particles were collected by the fibers and formed a cake layer after blocking the flow path. To verify this trend, simulations were performed using a model filter in which the fiber arrangement was systematically varied. The simulation results revealed that to collect particles and form a cake layer the inter-surface distance between fibers must be smaller than the particle diameter and the fiber orientation should be perpendicular. The sieving effect is essential for particles to remain within the filter.

Developing and testing low-cost air cleaners for safer spaces during wildfires

Air cleaning reduces indoor exposure to fine particulate matter (PM2.5) during wildfire smoke events. However, resource and cost constraints may limit access to air cleaning during such an event, as both commercial devices and the higher-rated MERV filters that do-it-yourself (DIY) assemblies typically rely upon tend to be expensive and in short supply. With these constraints in mind, we developed and evaluated several configurations of a novel, DIY air cleaner that uses common household fabrics as filtration media. Clean air delivery rates (CADRs) of the devices were experimentally evaluated in two ways: first, with independent measurements of flowrates and single pass removal efficiencies, and second, via pull-down testing in a large chamber. With two layers of cotton batting fabric and a flowrate-increasing cardboard shroud attached, the device achieved particulate matter CADRs of 162, 134, and 206 m3/h in 0.02–0.3, 0.3–1, and 1–2.5 µm particle diameter bins, respectively, during chamber testing. Results indicate that these simple, inexpensive, fabric configurations can meaningfully reduce PM2.5 levels in smaller zones of a home, and thus represent a viable option for improving indoor air quality during rapid-onset air pollution events, such as wildfires.

Enhanced wastewater treatment with an AnF-AAO system for improved internal carbon source utilization

The main challenge in removing nutrients from municipal wastewater in China is the lack of available carbon sources. While hydrolysis acidification tanks can improve wastewater biodegradability by effectively utilizing internal carbon sources, high sludge concentrations are difficult to control in traditional tank variants. In this study, an innovative anaerobic filter (AnF) hydrolysis acidification reactor composed of a continuously stirred tank reactor (CSTR) and cloth media filter was designed to regulate and maintain high sludge concentrations in the hydrolysis acidifier. The reactor was used as a pretreatment unit for the anaerobic/anoxic/oxic (AAO) units and combined into an AnF-AAO system to explore the effectiveness of internal carbon source utilization in wastewater. The results indicate that as the sludge concentration in the hydrolysis acidifier increased, the hydrolysis and acidification processes became more efficient. The optimal sludge concentration was 40 g/L, which significantly increased the production of soluble chemical oxygen demand and volatile fatty acids. Above this concentration, the efficiency decreased. Compared to traditional AAO processes, the AnF-AAO system achieved superior total nitrogen and phosphorus removal with shorter hydraulic retention times and reduced sludge production by a significant amount of 35%. Due to its capacity for enhancing internal carbon source utilization, the AnF-AAO system constitutes a promising approach for sustainable urban wastewater treatment.

Experimental and CFD analysis of fluid flow through nanofiber filter media

This work presents a novel approach to investigating the slip effect in nanofiber filter media. Electrospun nanofiber media with high efficiency and low pressure drop were produced at different concentrations and durations. The surface and cross-sectional morphology of nanofiber media were studied using FE-SEM. Fiber orientation and diameter distributions were also examined. The 3D virtual nanofiber media was modeled using this information along with the experimentally measured porosity and thickness of the media. The effect of the slip phenomenon in nanofiber media was studied numerically, and the results were compared to experimental data. Excellent agreements were found between the measured and simulation results. Additionally, filtration simulations considering aerosols injected with airflow through the nanofibrous filter media were conducted by considering the slip effect, and the effect of filter structure on filtration performance (removal efficiency and pressure drop) was investigated.