Depth Filtration Research Articles

Mechanistic evaluation of virus clearance by depth filtration.

Virus clearance by depth filtration has not been well-understood mechanistically due to lack of quantitative data on filter charge characteristics and absence of systematic studies. It is generally believed that both electrostatic interactions and sized based mechanical entrapment contribute to virus clearance by depth filtration. In order to establish whether the effectiveness of virus clearance correlates with the charge characteristics of a given depth filter, a counter-ion displacement technique was employed to determine the ionic capacity for several depth filters. Two depth filters (Millipore B1HC and X0HC) with significant differences in ionic capacities were selected and evaluated for their ability to eliminate viruses. The high ionic capacity X0HC filter showed complete porcine parvovirus (PPV) clearance (eliminating the spiked viruses to below the limit of detection) under low conductivity conditions (≤2.5 mS/cm), achieving a log10 reduction factor (LRF) of > 4.8. On the other hand, the low ionic capacity B1HC filter achieved only ∼2.1-3.0 LRF of PPV clearance under the same conditions. These results indicate that parvovirus clearance by these two depth filters are mainly achieved via electrostatic interactions between the filters and PPV. When much larger xenotropic murine leukemia virus (XMuLV) was used as the model virus, complete retrovirus clearance was obtained under all conditions evaluated for both depth filters, suggesting the involvement of mechanisms other than just electrostatic interactions in XMuLV clearance.

Manganese Removal by Low Cost Adsorbent from Synthetic Wastewater-A Review

Manganese (Mn) is one of the most abundant metals in Earth's crust. Manganese is present in ground water as a divalent ion (Mn 2+ ) and is considered a pollutant mainly because of its organoleptic properties. It is an essential metal for the human system and many enzymes are activated by manganese. Therefore, manganese has to be removed from some waters and wastewaters for various reasons. Conventional chemical and physical treatments for Mn(II) removal from contaminated effluent consist of precipitation, depth filtration, ion exchange, adsorption and oxidation. The adsorption technique has been found to be one of the most effective for the removal of metal ions from solution. This review focuses on preparation of adsorbent by using of low cost material to remove manganese from wastewater.

Wavy Subsurface Flow and Vertical Flow Constructed Wetlands: Effects of Aeration and Wastewater Composition on Wetland Clogging

AbstractIn this study, effects of aeration and wastewater composition were evaluated on the clogging process in four laboratory-scale wavy subsurface-flow and vertical-flow constructed wetlands (WSVFCWs) used for secondary and tertiary treatment. The relationship between the accumulated solid material and infiltration rate, the content and particle size distribution as well as the ratio of organic and inorganic matter of the accumulated material in the filter media were determined, and the mechanisms of clogging were elucidated. The clogging mainly occurred in the upper 0–40 cm layer, and the accumulated material decreased with filter depth (along the flow direction). The main particle size contributing to clogging was ∼40 μm in the WSVFCWs for secondary treatment and >110 μm in those for tertiary treatment. The accumulated material had 30–40% of organic matter. The clogging mechanisms varied as the composition of influent and aeration conditions are different in WSVFCWs. Aeration promoted the growth of...

In Situ Volumetric Filtration Physical Model to Separate Particulate Matter from Stormwater

AbstractIn the last several decades there has been a proliferation of structural best management practices (BMPs) for particulate matter (PM) sequestration. However, effective separation and continued retention of PM without washout throughout loading periods in which there is no maintenance remains challenging. In this study the physical modeling (in situ testing) of a volumetric clarifying filter (VCF) for separation and retention of PM was conducted for an urban source area (∼500 m2) in north central Florida loaded by rainfall runoff. This paper examines the event-based response of a VCF unit for 25 events (384 mm of rainfall, 117 m3 of runoff over 13 months with no maintenance), differentiating the role of volumetric sedimentation (2.3 m3 tank) and depth filtration (106 m2 of cartridge surface area). Manual sampling was conducted with a PM mass balance over the monitoring campaign. Suspended sediment concentration (SSC), suspended and settleable PM fractions, and turbidity were measured. PM was fu...

PDADMAC flocculation of Chinese hamster ovary cells: Enabling a centrifuge-less harvest process for monoclonal antibodies

High titer (>10 g/L) monoclonal antibody (mAb) cell culture processes are typically achieved by maintaining high viable cell densities over longer culture durations. A corresponding increase in the solids and sub-micron cellular debris particle levels are also observed. This higher burden of solids (≥15%) and sub-micron particles typically exceeds the capabilities of a continuous centrifuge to effectively remove the solids without a substantial loss of product and/or the capacity of the harvest filtration train (depth filter followed by membrane filter) used to clarify the centrate. We discuss here the use of a novel and simple two-polymer flocculation method used to harvest mAb from high cell mass cell culture processes. The addition of the polycationic polymer, poly diallyldimethylammonium chloride (PDADMAC) to the cell culture broth flocculates negatively-charged cells and cellular debris via an ionic interaction mechanism. Incorporation of a non-ionic polymer such as polyethylene glycol (PEG) into the PDADMAC flocculation results in larger flocculated particles with faster settling rate compared to PDADMAC-only flocculation. PDADMAC also flocculates the negatively-charged sub-micron particles to produce a feed stream with a significantly higher harvest filter train throughput compared to a typical centrifuged harvest feed stream. Cell culture process variability such as lactate production, cellular debris and cellular densities were investigated to determine the effect on flocculation. Since PDADMAC is cytotoxic, purification process clearance and toxicity assessment were performed.

Cellulose-based filter aids increase the capacity of depth filters during the downstream processing of plant-derived biopharmaceutical proteins.

Downstream processing (DSP) is a major cost factor during the production of biopharmaceutical proteins. Clarification can account for ∼40% of these costs, especially when a large amount of dispersed particulate material is generated, such as during the extraction of intracellular proteins from plants. Filter capacity can be increased (and DSP costs reduced) by using flocculants. Here we show that cellulose-based filter aids can enhance the positive effect of flocculants by improving depth filter capacity even further. A design-of-experiments (DoE) approach was used to identify the optimal size and concentration of filter aids, at different values of pH and conductivity, for the clarification of tobacco leaf extracts during the production of a monoclonal antibody and a fluorescent protein. Filter aids ∼28 or ∼100 μm in length at concentrations of ∼10 and ∼5 g L(-1) respectively were most efficient in combination with a strong cationic flocculant, but were ineffective without the flocculant. The filter aids increased depth filter capacity by 35-fold compared to an additive-free extract reaching ∼1000 L m(-2) without affecting the target proteins. Thus, filter aids can be used to reduce production costs of plant-derived biopharmaceuticals while the DoE approach enabled the identification of robust process conditions.

All-Optical NRZ-to-PRZ Format Conversion Limitations Using Notch Filters

In this paper all-optical non-return to zero to pseudo-return to zero format conversion limitations, using optical notch filters, are evaluated numerically. Open source simulation toolbox Optilux was used for simulations. Gauss and short term integrator notch filter performance and full width half maximum bandwidth impact on format conversion at transmission speed up to 40 Gbit/s was compared. Then format conversion performance was evaluated in a cascade of single ring microring resonators. Results show that large depth of an optical notch filter can cause two pulses generation at the edges of input pulses and lead to clock signal degradation.DOI: http://dx.doi.org/10.5755/j01.eee.21.1.9807

Depth Filtration With Microfiber Cloth Enhances Performance of Ultrafiltration as Pretreatment to Seawater Desalination Systems

Depth Filtration With Microfiber Cloth Enhances Performance of Ultrafiltration as Pretreatment to Seawater Desalination Systems

Multiple Regression Model of a Soak-Away Rain Garden in Singapore

Under the possible hydrological conditions, with a design hyetograph of 3-month average rainfall intensities of Singapore, multiple regression equations on hydrological processes, specifically on overflow volume, average vertical ex-filtration rate and horizontal flow coefficient, of a soak-away rain garden are established based on simulated results of a mathematical model. The model that is based on Richard’s equation is developed using COMSOL Multiphysics. The regression equation on overflow volume and the regression equation on log of horizontal flow coefficient show a very strong relationship with the independent variables (saturated hydraulic conductivity of the filter media, saturated hydraulic conductivity of the in-situ soil, depth to groundwater table, and surface area of the soak-away rain garden). The coefficients of determination of the fitted equations on overflow volume and log of horizontal flow coefficient were 0.992 and 0.986, respectively. However, the regression equation on average vertical ex-filtration rate has high p-values (p-values > significance level, α = 0.01) for saturated hydraulic conductivity of the in-situ soil and surface area of the soak-away rain garden. Thus, forward stepwise regression was used to develop the best regression equation on average vertical ex-filtration rate with saturated hydraulic conductivity of the filter media and depth to groundwater table. The coefficient of determination of the fitted equation was found to be 0.911. These easy to use regression equations will be of great utility for local mangers in the design of soak-away rain gardens.

Cloth Depth Filtration of Primary Domestic Wastewater

Cloth Depth Filtration of Primary Domestic Wastewater

박테리아 제거를 위한 완속 모래여과에서 탄소나노튜브의 적용성 검토

The applicability of carbon nanotube (CNT) to slow sand filtration for the removal of bacteria was studied using scanning electron microscope and column experiments. The morphology of CNT were investigated using scanning electron microscope and the CNT looked like a skein serving bacteria favorable site for adhesion. Column experiments were performed over a range of CNT filter depth, pH, and ionic strength. Bacteria removal efficiency was found to increase from 44.15% to 99.95% as the CNT filter depth increased from 1 cm to 5 cm, and 3 cm of CNT filter depth was required for significant removal of bacteria. pH increase from 5.5 to 8.5 decreased the bacteria removal efficiency, due to the electrostatic repulsion between bacteria and CNT at higher pH. Bacteria removal efficiency decreased from 97.25% to 70.90% as the ionic strength increased from 0 mM to 50 mM. This study demonstrated that the CNT can be applied to slow sand filtration for treating microbially contaminated water.

Thermal and mechanical behavior of innovative melt-blown fabrics based on polyamide nanocomposites

A commercial organo-modified clay (OMC) was added to a polyamide 6 (PA6) matrix at various concentrations during the polymerization stage or by melt compounding in a twin-screw extruder, and the resulting pellets were used for the production of depth filters in the shape of cylindrical nonwoven webs through a melt-blown process. The processability of the investigated materials was significantly affected by nanofiller introduction. Differential scanning calorimetry revealed that OMCs play a nucleating effect on the crystallization of the polyamide matrix, with a remarkable increase in the crystallization temperature on cooling from the melt. Consequently, a parameter related to the filtering performances of the web, such as the pressure drop (Δ P) evaluated on cylindrical filters, decreased with the increase in die-to-collector distance in a more pronounced way for nanocomposite nonwovens. This behavior was related to the significant decrease of the connecting points in the networks due to the rapid cooling of the filaments on the collecting mandrel. Compressive mechanical tests evidenced how organoclay addition led to a remarkable increase of the rigidity of the web, when the data were compared at the same Δ P value, irrespectively from the preparation technique.

Complete clarification solution for processing high density cell culture harvests

Traditional clarification of mammalian cell culture typically combines multiple separation technologies to remove cells in a primary step, and colloids in a secondary step. Recent advances in mammalian expression systems have not only led to cell cultures with very high density and increased protein titers, but also to feed streams with a high proportion of solids and colloids that reduce the efficiency of the separation step. Issues with scale-up, flexibility and installation limit the attractiveness of centrifugation, whereas clarification solely by depth filtration can be costly due to high filter areas required. Therefore, an efficient manufacture process must be developed to overcome these restrictions. In this study we present a complete separation solution that combines cell harvest pretreatment with a polycationic flocculating agent (polydiallyldimethylammonium chloride or pDADMAC), followed by depth filtration using depth filters that were specifically developed for filtration of flocculated or precipitated feed streams. Multiple antibody feed streams treated with pDADMAC and subsequently filtered using pretreatment adapted depth filters resulted in improved removal of cells and colloids, increased clarification throughput, efficient reduction of DNA and high process yield. The residual level of pDADMAC in the filtrates was assessed by surface plasmon resonance spectroscopy. Overall, this next generation clarification solution presented herein led to a robust, high yield, economical separation process with enhanced impurity removal that can be readily incorporated into current clarification platforms.

Modeling of Filtration Processes-Microfiltration and Depth Filtration for Harvest of a Therapeutic Protein Expressed in Pichia pastoris at Constant Pressure.

Filtration steps are ubiquitous in biotech processes due to the simplicity of operation, ease of scalability and the myriad of operations that they can be used for. Microfiltration, depth filtration, ultrafiltration and diafiltration are some of the most commonly used biotech unit operations. For clean feed streams, when fouling is minimal, scaling of these unit operations is performed linearly based on the filter area per unit volume of feed stream. However, for cases when considerable fouling occurs, such as the case of harvesting a therapeutic product expressed in Pichia pastoris, linear scaling may not be possible and current industrial practices involve use of 20-30% excess filter area over and above the calculated filter area to account for the uncertainty in scaling. In view of the fact that filters used for harvest are likely to have a very limited lifetime, this oversizing of the filters can add considerable cost of goods for the manufacturer. Modeling offers a way out of this conundrum. In this paper, we examine feasibility of using the various proposed models for filtration of a therapeutic product expressed in Pichia pastoris at constant pressure. It is observed that none of the individual models yield a satisfactory fit of the data, thus indicating that more than one fouling mechanism is at work. Filters with smaller pores were found to undergo fouling via complete pore blocking followed by cake filtration. On the other hand, filters with larger pores were found to undergo fouling via intermediate pore blocking followed by cake filtration. The proposed approach can be used for more accurate sizing of microfilters and depth filters.

Changes of Mechanical Properties of AlSi7Mg0.3 Cast Alloy through Filtration

Molten aluminium alloy is so active that it an easily chemically react with O2and H2O to form Al2O3 inclusions and H during melting practice. However, some other inclusions form by process. Under turbulent flow conditions, the inclusions are distributed unevenly in molten aluminium alloy. They may associate with crack or by the location of crack initiation in solidified casting. Castings containing these inclusions will probably exhibit poor ductility or toughness. Therefore, the purification of the molten aluminium alloy is one of the most important processes for improving the quality of Al-products. The inclusions in molten secondary AlSi7Mg0.3 cast alloy (without refining or modification; grain refined with 55 ppm AlTi5B1 and modified with 20, 40 and 60 ppm AlSr10) were removed using depth filtration by ceramic foam and pressed filter. The results showed that the mechanical properties through filtration changes. Ductility and UTS of the filtered tensile specimens increases. The better mechanical properties were measured by the using of pressed ceramic filter. Highest UTS and ductility was observed for samples modified with 40 ppm of Sr. Filtration with ceramic filters have very significant influence on the porosity decreasing; in the process the better effect has a pressed filter. In samples modified with 60 ppm of Sr were observed effect of over modification (mechanical properties decreased; porosity increased).

Impact of aqueous suspension drops onto non-wettable porous membranes: Hydrodynamic focusing and penetration of nanoparticles

Abstract The impacts and dynamic penetration of nanoparticle suspension drops into porous filter membranes are studied experimentally and theoretically. This type of penetration is associated with hydrodynamic focusing and is radically different from the wettability-driven imbibition. In the case of hydrodynamic focusing water can penetrate into a non-wettable porous medium at very low values of the dynamic pressure associated with drop impact. Two types of membranes are used in the experiments: (i) glass fiber filter membrane wettable by the carrier fluid (water), and (ii) polytetrafluoroethylene (PTFE) depth filter membrane, non-wettable by the carrier fluid. The nanoparticle entrainment and deposition inside the membrane bulk is used to mostly visualize the ultimate penetration fronts by observing the cut cross-sections of the membranes, albeit also provide an insight into innovative applications like circuit printing on nonwovens. The deposition patterns inside the membranes are also linked to the drop splashing patterns at their front surfaces. The experimental results confirm that during the dynamic focusing water can penetrate into a non-wettable porous medium (PTFE). Water also penetrates by the same hydrodynamic focusing mechanism into the wettable glass fiber membrane, where it additionally spreads on a much longer time scale due to the wettability-driven flow. A theory explaining hydrodynamic focusing penetration of liquid into porous medium after drop impact is proposed. It is used to explain and predict water penetration into the non-wettable filter medium after drop impact, and the results are compared with the experimental data. Also the critical thickness of non-wettable membranes determined by dissipation of the kinetic energy in flow inside membrane is evaluated and compared with the experimental data.

Production of recombinant human growth hormone by rCHO cells in a depth filter perfusion system

Human growth hormone is a single-chain polypeptide produced commercially from recombinant animal cells as well as recombinant microorganisms. Its increased applications have requested development of highly efficient production systems using particularly animal cells. Depth filter perfusion system (DFPS) has been developed and successfully used for production of recombinant proteins such as antibodies from recombinant Chinese hamster ovary (rCHO) cells. In this study, rCHO cells expressing recombinant human growth hormone (rhGH) were successfully cultivated in the DFPS for 2,200 h. Parameters affecting the performance of the DFPS for rhGH production were investgated. The depth filter with 40 µm pores was selected for stable operation. The shifts of culture temperature and pH were tested at 37 and 33℃, and 7.2 and 7.0, respectively. In the begining of the culture, more than 80% of the seeded cells were immobilized in 200 min by medium/cell circulation. When the culture temperature was lowered from 37 to 33℃, about 50% increase of the volumetric productivity (VP) at a perfusion rate of 2.0/day was achieved, and the VP reached 168 mg/L/d at perfusion rate of 3.0/day, showing the benefit of cultures in low temperature. In contrast, when pH was shifted from 7.2 to 7.0, maintaining rhGH concentration at about 60 mg/L and decreased perfusion rate from 2.0 to 1.0/day, the VP dropped to 50%. As the DFPS showed stable and efficient production of rhGH for long-term periods from this study, it can be an attractive choice for production of rhGH from recombinant animal cells.

Filter Depth and Cofiniteness of Local Cohomology Modules Defined by a Pair of Ideals

Let I, J be ideals of a commutative Noetherian local ring (R, 𝔪) and let M be a finite R-module. The f-depth of M with respect to I is the least integer r such that [Formula: see text] is not Artinian. In this paper we show that [Formula: see text] is the least integer such that the local cohomology module with respect to a pair of ideals I, J is not Artinian. As a consequence, it follows that [Formula: see text] is (I,J)-cofinite for all [Formula: see text]. In addition, we show that for a Serre subcategory 𝖲, if [Formula: see text] belongs to 𝖲 for all i > n and if 𝔟 is an ideal of R such that [Formula: see text] belongs to 𝖲, then the module [Formula: see text] belongs to 𝖲.

A simple semi-numerical model for designing pleated air filters under dust loading

In this work, we present a semi-numerical 2-D model for predicting the instantaneous pressure drop and collection efficiency of filters made up of rectangular and triangular pleats in both depth and surface filtration regimes. Inspired from previous CFD simulations, our semi-numerical model adopts appropriate average velocity profiles in the axial and lateral directions to approximate the flow field inside rectangular and triangular pleat channels. The model therefore circumvents the need to obtain a CPU-intensive solution for the partial differential equations governing the flow through a filter, i.e., Navier–Stokes equations. The above-mentioned analytical flow field can then be used to predict the trajectory of the particles flowing through the pleat channels by numerically solving the equation of motion for each particle—a simple set of second order ordinary differential equations. With the particles trajectories obtained, the deposition location and so the dust-cake profile can be approximated. This allows one to predict the instantaneous pressure drop and collection efficiency of a filter (filter’s service life) with a CPU-time of practically zero min. The model developed in this work is aimed at providing the aerosol filtration industry with a fast, but yet fairly accurate method of designing pleated filters. A brief parametric study is presented for model demonstration. In addition, a comparison between the predictions of our model and some experimental data from literature is presented for completeness of the study.

Cofiniteness of Local Cohomology Modules

Let M be a non-zero finitely generated module over a commutative Noetherian local ring (R, 𝔪). In this paper we consider when the local cohomology modules are finitely generated. It is shown that if t ≥ 0 is an integer and [Formula: see text], then [Formula: see text] is not 𝔭-cofinite. Then we obtain a partial answer to a question raised by Huneke. Namely, if R is a complete local ring, then [Formula: see text] is finitely generated if and only if 0 ≤ n ∉ W, where [Formula: see text]. Also, we show that if J ⊆ I are 1-dimensional ideals of R, then [Formula: see text] is J-cominimax, and [Formula: see text] is finitely generated (resp., minimax) if and only if [Formula: see text] is finitely generated for all [Formula: see text] (resp., [Formula: see text]). Moreover, the concept of the J-cofiniteness dimension [Formula: see text] of M relative to I is introduced, and we explore an interrelation between [Formula: see text] and the filter depth of M in I. Finally, we show that if R is complete and dim M/IM ≠ 0, then [Formula: see text].