Filter Loading Research Articles

Study of structural factors of structure-resolved filter media on the particle loading performance with microscale simulation

Microstructure strongly affects the macroscopic properties of filter media. Many previous works studied the filter loading behavior with the single fiber or macroscale model using unresolved fiber networks, but the influence of pore-scale structure was not thoroughly investigated. In this paper, the dynamic dust loading process in structure-resolved filter media was studied with microscale simulations. The distribution of trapped particles in the filter media in depth and cake filtration regimes was recorded, and the evolution of pressure drop and filtration efficiency was analyzed in depth. This work systematically explored how structural factors such as filter thickness, solidity (i.e., packing density), bulk, and fiber orientation affect the dust holding capacity (DHC) of the filter media. We also investigated better composite filters based on various designed filters with multilayer, uniform, or gradient structures. The results showed that the filter L-bot with a finer fiber layer at the bottom had the highest dust loading capacity, 63.98% higher than the filter L-top with an inverted structure, followed by the gradient filter GI-lin and GI-exp with open pore structure near the inlet. Our work presents a strategy for designing innovative depth filter media with effective and prolonged service life. Our detailed simulation with structure-resolved fiber network and particle deposits provides a fundamental understanding of the dust loading process.

The Effect of Filter Media Size and Loading Rate to Filter Performance of Removing Microplastics using Rapid Sand Filter

Microplastics (MP) can pose a serious threat to the environment and human health because of their tiny size and ability to spread easily in water. One of the alternative treatments to remove MP from water is the rapid sand filter (RSF). The objective of this study was to analyze the effects of filter media size and loading rate on RSF performance in removing MP. The applied filter media was silica sand with effective sizes (ES) of 0.39 and 0.68 mm. The loading rates of filtration were 4; 6; 8 and 10 m3/m2-h. The MP samples were made from plastic bags and torn tires (artificial samples: 10 to 800 µm). This study showed that the MP removal percentage was up to 96.6% (MP size larger than 200 µm). The head loss increment for loading rates 4; 6; 8; 10 m3/m2-h was 0.16; 0.35; 0.34; 0.25 m (ES 0.39 m) and 0.10; 0.18; 0.18; 0.19 m (ES 0.68 m)), respectively. Meanwhile, the filtration cycle for loading rates 4; 6; 8; and 10 m3/m2-h was 5, 2, 2, and 1 days (ES 0.39 mm) and 9, 4, 3, and 3 days (ES 0.68 mm), respectively. The result of this study showed that the smaller the filter media size, the higher the head loss of the filter media bed. Furthermore, there is an increased head loss of the filter media bed when the loading rate is greater.

Combined beam hardening artifact correction and quantitative microanalysis of colloidal depositions in deep bed filtration experiments investigated by 3D X-ray computed microtomography

In this study we present quantitative X-ray computed microtomography measurements (μCT) of retained sub-micron-sized particles in open porous media carried out in a laboratory μCT setup. Due to the polychromatic spectrum of the used X-rays, the tomograms are affected by various non-linear artifacts, which belong to the class of beam hardening artifacts. These artifacts become more dominant, when the amount of retained particles increases and can affect wide areas of the images, making a qualitative and quantitative analysis barely possible. Furthermore, the colloidal depositions show an inhomogeneous distribution inside the filter, making a reliable material discrimination between filter and particle material challenging. We introduce a calibration method, which is capable to sufficiently remove the majority of the artifacts by linearization of the projection data and thus enabling the precise material quantification of the retained colloids in the reconstructed tomograms. While most beam hardening correction routines are only applicable to homogeneous materials, our algorithm takes into account inhomogeneous material distributions and is adapted to multi-material systems. Moreover, the method includes a material discrimination of the colloids and the filter in the raw data domain. Thus, erroneous segmentations at the interfaces between different material fractions are avoided. As a result we present quantitative concentration maps of the particle distribution inside the porous media with a resolution of < 10μm. A series of validation samples was prepared, covering a wide range of different, representative filter loading stages. The accuracy of the particle quantification was evaluated from these samples and the relative deviation of the overall contained particle mass was less than 10% in all cases, partially even less than 1%. The overall image quality due to the artifact removal was significantly improved. The local variation of the particle concentration could be well assessed from the obtained concentration maps.

A numerical analysis of particulate matter control technology integrated with HVAC system inlet design and implications on energy consumption

This paper examines and outlines the development of a novel inlet for an air handling unit (AHU) which controls PM concentration entering mechanically ventilated buildings. The aspiration efficiency reducer (AER), can reduce the ambient PM concentrations drawn into a building ventilation system. The AER device incorporates an array of cylindrical tubed orifices, which create conditions for potential improved indoor air quality (IAQ) and energy savings. Prototypes were designed by reverse-engineering the aspiration efficiency (AE) concept, creating new inlets for AHUs using Computational Fluid Dynamics. This approach helps achieve low AE values and reduce PM concentrations entering the AHU and filter loading rates. 3D k-ω SST models were used to simulate particle laden fluid flow around an AHU with AER attachments. The investigation found that the engineering of wind flow around the AHU and its inlet resulted in lower levels of particles with diameters ≤10 μm entering the AHU. The difference in AE for particles within the PM10 range for the passive AER prototypes in comparison to a commercial rainhood ranged from 5 to 35% for various inlet designs. This translated into increased energy savings of 15.2–20.6% and extended fabric filter lifespan of up to an additional 100 hundred days until saturation. The AER has the potential to reduce energy consumption, minimise waste generation and present cost savings whilst improving IAQ, through a reduction in maintenance activities and the number of filter replacements. This novel technology requires low-capital investment to deliver environmental, energy and economic savings in this sector.

A General Framework of Polarimetric Detectors Based on Quadratic Optimization

Ship detection is an important task in civil or military applications and we can use polarimetric synthetic aperture radar (PolSAR). Many polarimetric detectors were proposed and achieved good performances in particular environments, such as optimal polarimetric detector (OPD), polarimetric whitening filter (PWF), polarimetric notch filter (PNF), polarimetric detection optimization filter (PDOF) and diagonal loading detector (DLD) etc. Up to know, the analytical links among different polarimetric detectors have not been found. In this work, the above polarimetric detectors are unified in mathematical forms and a general framework of polarimetric detectors based on quadratic optimization is presented. The mathematical forms are summarized as a trace of two matrices’ product. One is a detection transformation matrix and the other is the polarimetric covariance matrix of the pixel to be detected. We find that all these polarimetric detectors can be regarded as the optimization of such detection matrix, which is the key point of the general framework, and the difficulty turns to be a linear inseparable problem. Pocket Perceptron Linear Algorithm (PPLA) is used to solve the linear inseparable problem. In the case of low resolution, target detection is almost an indivisible problem, and multilayer perceptron (MLP) cannot provide better detection results than PPLA. In the case of high resolution, target detection becomes a nonlinear separable problem, and MLP is gradually superior to PPLA. Additionally, the optimal weights of the recent DLD are obtained to compare with other detectors in the general framework and the DLD is developed to a more general case (GDLD). The experiments validate the general framework of polarimetric detectors. Different detectors in the general framework are utilized and compared in both simulated and measured PolSAR data. The results show the optimal solution in the general framework can always reach the best performance, and the GDLD is the closest one to the optimal detector of the general framework.

How to Reduce the Exposure of Welders to an Acceptable Level: Results of the InterWeld Study.

Workplace measurements in the past have shown that the applicable occupational exposure limits (OELs) are regularly exceeded in practice when high-emission welding processes are applied. The InterWeld pilot study was planned as part of an intervention study to show under which conditions compliance with the OEL is achievable in gas metal arc welding (GMAW) with solid wire. The investigation focussed on local exhaust ventilation, i.e. captor hoods and welding torches with integrated fume extraction. Forty tests with hand-guided GMAW were configured by experts with regard to all technical parameters and carried out by a professional welder. Effects of protective measures and process parameters on the exposure to respirable welding fumes and airborne manganese (Mn), chromium, nickel, and hexavalent chromium were investigated. Personal sampling was carried out in the welder's breathing zone outside the face shield at high flow rates (10 l min-1) in order to achieve sufficient filter loading. Particle masses and welding fume concentrations were determined by weighing the sampling filters. Metal concentrations were analysed by inductive coupled plasma mass spectrometry. In order to evaluate the effects on exposure, the measurements were performed under similar conditions. The data were analysed descriptively and with mixed linear models. For measurements below the limit of detection, the exposure level was estimated using multiple imputation. Two to five times higher exposures to respirable welding fumes and airborne metals were observed during welding of 10 mm sheets than during welding of 2- or 3-mm sheets. Welding fume and Mn exposure were reduced by 70 and 90% when on-torch extraction or a captor hood was applied. Other airborne metals were reduced to a similar extent. Modifications on welding parameters led to a reduction of exposure against respirable particles by 51 up to 54%. Although proper extraction at the point of origin and lower-emitting process variants ensure a drastic reduction in exposure, compliance with current OELs is not guaranteed. In order to ensure adequate health protection, especially at workplaces where thick sheets with long relative arc times are processed, there is a need for technical development.

Development of a Novel Gasoline Particulate Filter Loading Method Using a Burner Bench

In view of the deliberations on new Euro 7 emission standards to be introduced by 2025, original equipment manufacturers (OEMs) are already hard at work to further minimise the pollutant emissions of their vehicles. A particular challenge in this context will be compliance with new particulate number (PN) limits. It is expected that these will be tightened significantly, especially by including particulates down to 10 nm. This will lead to a substantially increased effort in the calibration of gasoline particulate filter (GPF) control systems. Therefore, it is of great interest to implement advanced methods that enable shortened and at the same time more accurate GPF calibration techniques. In this context, this study presents an innovative GPF calibration procedure that can enable a uniquely efficient development process. In doing so, some calibration work packages involving GPF soot loading and regeneration are transferred to a modern burner test bench. This approach can minimise the costly and time-consuming use of engine test benches for GPF calibration tasks. Accurate characterisation of the particulate emissions produced after a cold start by the target engine in terms of size distribution, morphology, and the following exhaust gas backpressure and burn-off rates of the soot inside the GPF provides the basis for a precise reproduction and validation process on the burner test bench. The burner test bench presented enables the generation of particulates with a geometric mean diameter (GMD) of 35 nm, exactly as they were measured in the exhaust gas of the engine. The elemental composition of the burner particulates also shows strong similarities to the particulates produced by the gasoline engine, which is further confirmed by matching burn-off rates. Furthermore, the exhaust backpressure behaviour can accurately be reproduced over the entire loading range of the GPF. By shifting GPF-related calibration tasks to the burner test bench, total filter loading times can be reduced by up to 93%.

Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration.

The aim of the study was to find out good practices for effective air distribution inside a complex shaped asbestos enclosure and for control of pressure differences between the enclosure and the surroundings. In addition, sufficient pressure difference for asbestos containment was tested. The effect of air distribution was studied in laboratory conditions by constructing an L-shaped asbestos enclosure and connecting it to a negative pressure unit. The efficiency of six different ventilation configurations was compared using a tracer decay method and the local air change indexes as the performance indicator. The sufficient negative pressure for containment was assessed by simulating person traffic to and from the enclosure and recording the pressure difference continuously. The effect of a pressure controller unit in maintaining the target pressure difference was also tested by simulating filter loadings of the negative pressure unit causing changes in the air flow rate. The results showed that high nominal air change rates alone do not guarantee good air distribution. Effective air distribution within an asbestos enclosure can be arranged by locating additional air supply openings far away from the air exhaustion point, using recirculation air with a pressure controller, or extending the exhaust location to the poorly ventilated areas. A pressure difference of at least −10 Pa is recommended to ensure a sufficient margin of safety in practical situations.

Piloting During a Pandemic

Key TakeawaysFour pilot teams shared experiences with piloting during the COVID‐19 pandemic, emphasizing that thoughtful planning streamlines the piloting process while mitigating the risk of transmitting illness.Remote access to and control of pilot equipment, along with the use of virtual communication platforms, enabled teams to successfully perform pilot‐scale studies.Operating pilot systems through the pandemic allowed teams to respond to drastic changes on a small scale to mitigate risks around full‐scale processes at the treatment plant.

Macroscale simulation of the filtration process of porous media based on statistical capturing models

In this work, a new model for filtration is developed using statistical capturing mechanisms. The model can be used in the macroscale simulation of filtration processes and can replace the current semi-empirical models based on the Single Fibre Efficiency. To validate the new model, firstly, simulation of the filtration process itself is implemented based on the methodology developed by Fotovati et al.(Separation and Purification Technology, 2012). Secondly, the novel statistical model for particle capturing was added in ANSYS Fluent by subroutines that calculate particle capturing and its influence on the membrane parameters. This includes recalculation of local properties of the membrane according to the collected mass and particle diameter to calculate the pressure drop with respect to the filter loading. The results from the numerical simulations were compared with experimental studies found in literature and the results are in good agreement with each other.

Effect of main-stage filter media selection on the loading performance of a two-stage filtration system

This study experimentally evaluates the performance of a two-stage indoor air filtration system with the focus on main-stage filter media selection. The impact of the main-stage filter media properties on the effectiveness of adding a pre-stage filter media is compared among three main-stage filter media types commonly used in heating, ventilation, and air conditioning (HVAC) filtration system: cellulose, melt-blown, and expanded PTFE membrane. The pre-stage filter media effectiveness was found to be significantly affected by the incoming aerosol size distribution. Although counter-intuitive, having an additional pre-stage filter was found to cause a service lifetime drop for cellulose-type main-stage filters depending on incoming aerosol size distribution, while universally enhanced life spans were found for melt-blown and PTFE membrane-coated main-stage filters. The mechanism that causes a shortened service life of cellulose main-stage filter with the presence of a pre-stage filter was explored in detail and was found to be associated with the special particle loading behavior of conventional cellulose media. The rapid pressure drop increase of cellulose media in depth and transitional filtration regimes was strongly affected by the incoming aerosol size distribution, with a steeper slope (faster pressure drop increase) associated with finer particles penetrating more deeply into the inhomogeneous pores of cellulose media. The pre-stage filter alters the particle size distribution of the main-stage faces, with an increased fraction of fine particles that negatively impacts the main-stage filter loading behavior. This observation and mechanism analysis are the first time being reported, which suggests a careful selection of the combination of pre-stage and main-stage filter types with the consideration of incoming contaminant properties. It is essential for researchers and engineers in designing energy-efficient two-stage filtration systems.

Improved estimation of PM2.5 brown carbon contributions to filter light attenuation

Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S. Chemical Speciation Network (CSN) and the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network beginning in 2016. These are used to estimate PM2.5 brown carbon (BrC) contributions to light absorption at various wavelengths, a useful method for separating biomass burning contributions from other sources. Attenuation of light transmitted through the filter deviates from Beers Law as the mass of light absorbing materials increase. This study estimates the effects of these deviations with empirical adjustment factors applied to samples for CSN from 2016 to 2017 and for IMPROVE from 2016 to 2019. Accounting for the filter loading effect results in an annual average increase of ∼6–7% BrC contribution to light attenuation: from 3.6% to 10.7% for the urban, more heavily loaded CSN samples; and from 23.7% to 29.5% for the non-urban IMPROVE samples. An alternative method is examined for BrC and black carbon (BC) adjustments by calculating the Absorption Ångström Exponent (AAE) for BC (i.e., AAEBC) based on the ratios of 635nm/780nm light attenuation rather than assuming AAEBC of unity. These paired-wavelength calculations result in a median AAEBC of 0.76 for CSN and 0.8 for IMPROVE, with the majority of samples (i.e., 91% of CSN and 70% of IMPROVE) showing AAEBC<1. By assuming negligible contributions from BrC to AAE at longer wavelengths, the amount of light attenuation at shorter wavelengths (e.g., 405nm) where BrC is dominant can be calculated. The paired-wavelength method applied to the filter loading adjusted data has a greater effect on urban (fresh) than on non-urban (aged) aerosols, resulting in a factor of two increase in annual averaged BrC light attenuation (from 10.7% to 21.6%) for CSN and by a factor of 1.11 (from 29.5% to 32.7%) for IMPROVE samples. This result demonstrates the importance of particle loading and AAE correction on quantifying BrC light attenuation from multi-wavelength thermal/optical analysis.

Efficacy Testing of Personal Protective Filters on Biosafety Level 4 Positive Pressure Suits.

Introduction: Positive pressure breathing air-fed protective suits from three vendors are commonly used in biosafety level 4 (BSL-4) laboratories: they are Dover Chemturion suits (ILC Dover, DE), Delta suits (Honeywell Safety, NC), and HVO suits (HVO-ISSI-Deutschland GmbH, Germany). To address the potential risk of infectious agents being introduced through the supplied breathing air stream, some suit manufacturers incorporate protective filters on the suits themselves. However, these integrated filters are not amenable to in situ testing for efficacy verification. We have been using external filters from Matheson USA on the positive pressure suits since our BSL-4 laboratories were commissioned two decades ago. As part of our BSL-4 protective suit management program, we test these filters before them being put into use, and annually thereafter. In the past few years, we have observed these filters failing at a higher rate, as high as two out of three of the new filters tested at one point. Objective: The purpose of this study was to procure personal protective filters from other sources and validate their efficacy long-term. Methods: Filters from Respirex, HVO, and Honeywell were validated for filter integrity and filter loading. Results: Respirex filters performed well during the initial testing and periodic testing thereafter. Regular testing of the Respirex filters has now been ongoing for 30 months with continued successful performance. Conclusion: Filters from Respirex are a suitable option to protect personnel wearing positive pressure suits in BSL-4 laboratories.

Results of the evaluation of the semi-empirical model on the selection of optimal constructive and technological parameters for a granulated loading filter

Topicality. A survey of the water use system at a state-owned enterprise processing agricultural products revealed the technological processes that cause biofouling of pipelines by colloidal inclusions (mainly phytoplankton conglomerates of blue-green algae). The implementation of measures that can protect existing technological structures against the ingress of significant masses of phytoplankton is an urgent task that can be solved with the help of mechanical filters. The efficiency of previous granulated loading filters depends very much on the properties of the filter loading. When filter loading is made of foamed polystyrene granules of food brands, phytoplankton retention is quite effective due to the physical adsorption of cyanobacteria conglomerates on the surface of these granules.&#x0D; Research results. By applying the semi-empirical model developed in IWPLR of NAAS, the optimal design and technological parameters of the filter with foam polystyrene loading were selected. That enabled to develop the design of a clarifying filter - a phytoplankton retainer for the treatment of circulating water at the enterprise Chervonoslobidsky distillery.&#x0D; In the lower part of the filter the lower drainage system in the form of a false bottom is placed, equipped with hole caps. It provides the source water entry for filtration and discharge of flush water during filter washing. The granules of the filter loading are kept from floating with the false bottom of the upper drainage, which is equipped with return filters - hole caps. Filtered water is collected in the abovefiltering space between the false bottom and the upper part of the filter body, from where it is delivered through a pipeline to the consumers.&#x0D; The application of the developed filter design allows reducing the construction costs and simplifies the filter design, which in turn increases its reliability and overall service life. The practical application of this filter provided the required degree of retention of cyanobacteria cells and conglomerates from the treated water. This filter design differs from the standard with a 1.5 times increased filter loading layer. This enabled to double the duration of a filter cycle and, at the same time, did not increase the volume of flushing water, i.e. operating costs.&#x0D; Conclusions. Based on the results of the developed semi-empirical model, the design and technological parameters of granular filters for recycling of wastewater from the distilleries were determined, which became the basis for developing a new filter design for water purification from cyanobacteria cells and colonies. The high efficiency of the developed design of the clarifying filter - phytoplankton retainer was experimentally proved. The use of the developed filter increases the economic efficiency of the circulating use of the wastewater from Chervonoslobidsky distillery by 1.3 - 1.5 times compared to the market offers of mechanical filters.

Improving the technology of closed water supply at agro-industrial enterprises

The article analyzes the ways to improve the water supply system at agro-industrial enterprises. It is stated that the Institute of Water Problems and Land Reclamation of NAAS proposed to improve closed water supply systems at these enterprises to spend water and energy rationally and economically by developing highly efficient wastewater treatment technology to reuse wastewater and its sediments for technological needs.&#x0D; During the work, the main tasks to be solved were the analysis of the reasons of unsatisfactory operation of traditional wastewater treatment plants and their current quality indicators and improvement of the rational technological scheme of closed water supply at the agro-industrial enterprises.&#x0D; Scientific and practical results were obtained by analyzing the operation of wastewater treatment plants of industrial enterprises dealing with agricultural products processing, their quality indicators and known methods of improving technological schemes of biological wastewater treatment.&#x0D; It was specified that traditional technology of biological wastewater treatment do not ensure the proper treatment quality, as the quality of wastewater from enterprises has significantly deteriorated due to the inflow of harmful impurities (xenobiotics, heavy metal ions, etc.) and high concentrations of organic matter, the content of which amount to: suspended solids&gt; 1000 mg/dm3, COC&gt; 10000 mgO2/dm3, BOC5&gt; 6000 mgO2/dm3, BOCcomplete&gt; 2000 mgO2/dm3, nitrogen and phosphorus ≤50 mg/dm3, which prevents the effective operation of aeration tanks.&#x0D; The practicability of improving the "bioconveyor" technology by downward filtration through fibrous loading in bioreactors and upward filtration through floating filter loading in contact and clarifying filters to increase the efficiency of wastewater treatment was scientifically substantiated.&#x0D; It was proved that this method provides high efficiency of biological wastewater treatment by reducing the amount of sediment and the absence of reverse activated sludge, and thus reducing capital and operating costs.&#x0D; Natural mechanisms of household sewage treatment with reuse of water and sediments when cultivating agricultural crops are used as much as possible are used in the specified system of water supply at agro-industrial enterprises.&#x0D; The optimal design and technological parameters of these structures are determined using the recommendations developed on the basis of our experimental research.&#x0D; The proposed technology of closed water supply at agro-industrial enterprises provides for the separation of water supplied to consumers into technical and drinking one, as well as supplements of sewage treatment plants with bioreactors and contact-clarifying filters. Such systems ensure a minimum intake of water from natural water sources having its preliminary treatment directly in water reservoir, maximum use of treated wastewater and protection of the environment against wastewater pollution.

Not so fast with the filter! Is it really in the inferior vena cava?

Inferior vena cava (IVC) filter placement can lead to rare but sometimes serious complications, including malposition of the IVC filter in a non-target vessel or organ. We present the case of a 74-year-old male who presented to our institution for a percutaneous nephrostomy tube change and was incidentally found to have two IVC filters, one of which was properly positioned in the IVC and one of which was improperly deployed in the right ascending lumbar vein. Venography through the sheath before filter loading and deployment decreases the risk of malpositioning the IVC filter.

Smoke shade as a historic proxy for elemental carbon

The blackness of aerosol filter samples, meant as a proxy for particulate mass concentration, is the earliest parameter for which monitoring data exist. The smoke shade method (developed in the late 1910s) was the standardised approach to collect samples. The blackness was visually appraised by a comparison with a set of reference sheets covered with an increasing number of layers (shades) of a suspension of carbon black (ink). Samples were assigned a shade number (SN) according to the number of shades of ink on the reference sheet with a corresponding blackness. Automated hourly sampling started in 1921. After World War II, the blackness was measured with a reflectometer and light absorption was translated to the parameter British Smoke (BrS). One unit of SN was equivalent to a specific loading of BrS of 8 μg cm−2. BrS in turn is a proxy for elemental carbon (EC) as we showed in an earlier publication, where we found that a value of BrS of 8 μg cm−2 corresponded to an EC load of 1.4 μg cm−2. SNs can thereby be translated to historic EC loadings/concentrations. In an evaluation of SN-data, we noticed that average pre-war values were mostly at the lower detection limit (one SN) and overestimated because reference sheets faded over time. Data for smog periods with their elevated SNs, however, are quite reliable and can be used for exposure estimates. After World War II, daily sampling resulted in higher filter loadings and reliable average values. Wintertime concentrations corresponding to up to 100 μg m−3 EC were reached. On the other hand, the increased loadings due to the long sampling times resulted in a decrease of the upper limit of detection to an extent that it was exceeded at most of the measuring stations during the “Great Smog” of London in 1952. In this study, we analysed SN data from this episode in depth. At one measuring site, precautions were taken to minimise the loading by using a large filter, but even then the maximum SN was at the upper limit of detection. From a one-to-one relation of BrS and gravimetric mass, established during later smog periods, we deduced that the maximum 2-day mass concentration of EC must have been around 1000 μg m−3. This value is twenty times the new EU-limit for workplace EC exposure (EU 2019) and the 24-h ambient PM10 mass concentration.

Mathematical modeling of the process of ferrum removal in a biological reactor by bacteria Gallionella and Leptothrix

This paper proposes a mathematical model for computer prediction of the process of biological deironing of groundwater in a bioreactor, taking into account the presence of two types of iron bacteria Leptothrix and Gallionella in groundwater while maintaining a constant filtration rate. An algorithm for a numerical-analytical method for solving the corresponding nonlinear boundary value problem for an inhomogeneous system of differential equations in partial derivatives of the first order has been developed. The developed model allows to use computer experiments to predict the change in time on the depth of contact loading of cleaning efficiency, distribution of bacterial biomass values ​​in both filtered water and in filter loading, mass of stationary and mobile matrix structures. Also, the proposed model allows to predict the duration of effective operation of the biological reactor of iron deironing between its washing.

Characterization of mesoscale inhomogeneity in nonwovens and its relevance in the filtration of fine mists

Structural properties in nonwoven materials, such as porosity and layer thickness, are typically spatially distributed on a micro- and mesoscale. The mesoscale inhomogeneity is visually perceived, inter alia, as the cloudiness of the nonwoven fabric or as inclusions in the bulk material. Differential box counting, which is a fractal based image analysis method, was used to assess the inhomogeneity of several wet laid nonwoven glass fiber filter media. It has been shown that the subjectively perceived extent of media inhomogeneity strongly correlates with the lacunarity of the analyzed image.The analyzed media were then tested in different configurations for their operating behavior in the filtration of oil mist. The inhomogeneity of a medium significantly affected the formation of liquid channels in the medium, more specifically the inhomogeneity of the media layer on the filter upstream side. As most droplets are deposited on the filter upstream side, liquid likely accumulates in regions of finer pore structure in the foremost media layer. Distinct oil channels that transport the coalesced liquid to the filter rear side subsequently form behind these regions. Homogeneous media that lack such regions show a depth-filter like increase of Δp before the formation of channels, i.e. the Δp curve shows an increasing gradient with filter loading, which then changes into a linear increase of Δp. When filtering at low velocities, the liquid distribution inside the media drastically changed from distinct channels to a conically tapering form towards the filter rear for a homogeneous medium and a system of many interconnected channels in an inhomogeneous medium.

Effects of temperature and relative humidity on laboratory air filter loading test by hygroscopic salts

Air filters are common control technologies of the atmosphere pollutant, which could be operated under different environments. The operating conditions include different temperatures, relative humidities, and particle states. However, typical filter testing conditions do not strictly regulate the aforementioned parameters; hence there is always a discrepancy between the lab filter testing and the actual operating conditions. Air filter loading results are valuable to predict the filter life, whereas it could be affected by testing conditions. In this study, the effects of temperature and relative humidity on the air filter loading by hygroscopic salts were studied. Potassium chloride, ammonium sulfate, and ammonium nitrate are used to represent the dry solid particles and wet particles in the atmosphere. The testing temperature covers from 5 ℃ to 50 ℃ and the testing RH covers from 30% to 75%. Importantly, the absolute humidity is considered in this study, which depends on both temperature and RH. Besides the experiments, the possible reasons that could affect the filter loading were also discussed. Based on the experiment results and theories discussed, it could be concluded that the testing RH is a major factor while the testing temperature is a minor factor, which affects the hygroscopic particle filter loading, regardless of the particle state (dry/wet). This article not only suggests the need of revising current filter testing standards by considering the air filter operating temperature and relative humidity but also offers an insight into how the atmospheric particles hygroscopicity can be linked with ambient particulate matter mitigation technologies.