Improved Filtration Performance Research Articles

High flux and antifouling filtration membrane based on non-woven fabric with chitosan coating for membrane bioreactors

To prepare a high flux and antifouling filtration membrane used for submerged membrane bioreactors, non-woven fabric (NWF) was modified by coating chitosan (CS) on both internal and outer surface. Chemical structural and morphological changes were characterized. The changes of surface free energy were monitored by dynamic contact angle, which showed an increase after modification. The CS/NWF composite membranes were found to be with high flux, high effluent quality and excellent antifouling property. The results of fouling resistance distribution indicated that irreversible fouling resistance was decreased by coating CS. Especially, there were fewer gel layers existing on the outer surface. The adsorption of EPS on the NWF membrane internal surface decreased after being coated with CS. Modification improved filtration performance, and made fouling less troublesome and membrane regeneration efficient.

Development of a Phosphate - Free Reticulated Foam Filter Material for Aluminium Cast Houses

Filtration of molten aluminium using porous reticulated ceramic foam was developed in 1974 by SELEE Corporation. Since that time, there have been significant technical advances in filter bowl design and construction, preheat systems, development of fine pore size filters, development of compact two-stage filtration systems, filter gasket materials, and equipment automation. One area that has remained relatively unchanged has been the refractory filter material technology. The refractory material utilized by all of the major cast house filter suppliers is based on an alumina aggregate grain bonded with aluminium phosphate (AlPO4). This filter material, commonly referred to as “PBA” in the aluminium industry, has become an industry wide standard and accounts for nearly 99% of the filters supplied to cast houses worldwide. There are significant technical limitations of PBA filters in terms of refractory performance, as well as potential environmental, health and safety concerns. This paper describes the development of a cost effective replacement filter material that overcomes the limitations of PBA filters. The new material utilizes a low expansion – low modulus aggregate material and a non-phosphate bond. The result is a significant reduction in mechanical failures during use, improved filtration performance and elimination of the issue of potential environmental, health and safety concerns.

Effects of diesel particulate filter structural parameters on filtration performance of different size particles

In this study, microcosmic capturing mechanism of single unit on diesel engine particles is firstly studied,then, macroscopical filtration model of single porous medium bed and trap model of monolithic wall-flow diesel particulate filter (DPF) on particulate matter (PM) are developed and formulated. Effects of main DPF structural parameters on filtration performance of different size particles from diesel engines are studied. The results show that the trap efficiency of 10 nm diameter particles is highest, and the efficiency descends while the particle diameter increases. The trap efficiency will be lowest near 500 nm diameter particles, and the trap efficiency ascends with particles diameter increasing to 1μm continuously. This indicates the complex effects of diffusion, inertia and interception mechanisms on particle trap. With increasing cell density, wall thickness, diameter and length of filters, the filtration efficiencies of different size particles ascend with different extents. The trap efficiencies rapidly increase with decreasing porosity and mean pore size of filter substrates. These results are valuable for matching DPF structural parameters and improving filtration performance of DPF.

Influence of the strongly anisotropic cross-section morphology of a novel polyethersulfone microfiltration membrane on filtration performance

Polyethersulfone (PES) microfiltration membranes with remarkably improved filtration performance were recently developed. Subtle changes in the conditions of the phase separation process lead to a very pronounced anisotropic (“hour glass”-like) cross-section morphology of these novel membranes named DuraPES ®. Furthermore, due to macromolecular additives, the membranes are permanently hydrophilic. The properties and performance of the DuraPES ® membranes are compared to other membranes available on the market, such as AMC Accupor, Osmonics Micron PES, Pall Supor, Sartorius Sartopore, and Millipore Express. Parameters investigated are on the one hand focussed on membrane structure such as pore morphology (from SEM), volume porosity, trans-membrane pore size distribution, contact angles and wetting with water, and trans-membrane streaming potential. On the other hand, membrane performance is evaluated with respect to water permeability, the filtration of a protein solution and the correlated fouling, as well as other filtration tests with more complex feed solutions. Up to >10 times higher filtrate fluxes are observed for the DuraPES ® membranes as compared to the other membranes having the same nominal pore size. However, such higher performance is only achieved with the macroporous surface upstream to the feed. The overall analysis of all data shows that the significant advantages of DuraPES ® membranes resulted from their special surface and pore morphology.

Effect of Media Grain Shape on Particle Straining during Filtration

This paper investigates how straining mechanisms of angular media (crushed limestone) provide improved filtration performance compared to rounded media (river stone). Columns of granular media were set in resin, sectioned, photographed, and digitized to produce a three-dimensional model of pore space geometry. This process was repeated for four filter media, each representing different grain shapes or packing densities. From measured pore throat distributions, a stepwise particle movement model was used to estimate the maximum volume of particles that could be stored in the bulk of the filter media. The results showed that the more angular the media, the wider the range of particle sizes that could be strained in the bulk of the filter. The stepwise model was applied only to individual particles; trapping of colloidal particles was not considered. However, when individual particles are too small to be strained, the same pore throat trapping contributes to the physical capture of avalanches and flocculates. Thus the findings of this work are relevant to deep bed filtration applications where headloss results from straining, such as storm-water best management practices or soil filters.

Improved Filtration Performance of Continuous Alumina‐fiber‐reinforced Mullite Composites for Hot‐Gas Cleaning

The effect of filtration layer morphology on filtration performance at 673 K was investigated for continuous alumina‐fiber‐reinforced mullite composite filters that capture fly ash on their outer surfaces. Two types of filtration layers were prepared on the outer surfaces: a mono‐layer consisting of mullite agglomerated particulates and a bi‐layer, with mullite whiskers formed by a vapor‐phase reaction and strongly adhered to the particulates exposed on the outer surfaces. For filters with mono‐filtration layers, the filtration efficiency was improved slightly by increasing the filtration layer thickness. However, the maximum differential pressure increased during the filtration tests. Adhesion of whiskers to the outer surface decreased the maximum differential pressure to about one‐third less than that with the mono‐filtration layer. This low differential pressure remained constant throughout the duration of the test, with corresponding increases in filtration efficiency.

Filter media surface modification technology: state of the art

Over the last 30 years the demand from industry for filter media that exhibit an improved filtration performance and a longer operating life has grown. These demands in turn have driven the area of surface modication for fabric filter materials. With the help of Professor Richard Lydon, Filtration+Separation takes a look at the history of this technology and highlights several of the currently available finishing methods that have proven to be effective for both air and liquid filtration.

Cake dewatering of some iron ore industrial products

This paper is concerned with studying the dewatering behavior of three samples of iron ore products. The objective is to improve the industrial filtration performance by taking into account the laboratory results. Mineral samples came from the Iron Ore Quadrangle in the state of Minas Gerais, Brazil. These samples represent products from the industrial processing of hematitic ores. The samples have almost the same chemical and mineralogical compositions, but they have different size distributions and different specific surface areas. The filtration tests were performed using a modified Buchner funnel apparatus. The results indicate that size distribution and specific surface area have significant influences on dewatering behavior. For Sample 1, the addition of flocculant and/or surfactant was not essential to improving filtration performance. For Sample 3, the cake porosity and the cake thickness were influenced by the addition of the flocculant. On the other hand, the simultaneous addition of flocculant/surfactant decreased the cake formation time and reduced the cake moisture. For Samples 2 and 3, it was also observed that the industrial operation could be improved by taking into account these laboratory results.

Influence of a gas/liquid two-phase flow on the ultrafiltration and microfiltration performances: case of a ceramic flat sheet membrane

Air injection in the feed flow was used to improve filtration performance (flux, energy consumption) when applied to a ceramic flat sheet membrane during crossflow filtration of a commercially available baker’s yeast suspension. The effect of different operating parameters (gas flowrate, liquid flowrate, feed concentration) was evaluated with a horizontally and a vertically installed UF or MF membrane. At low liquid flowrates, the membrane orientation had a strong influence on the efficiency of the two-phase flow technique, with a better improvement achieved with horizontally installed membranes. In the presence of a significant cell cake layer on the membrane surface, unsteadiness was found to enhance the permeate flux by a factor of nearly 4 compared with steady microfiltration. It was also shown that the two-phase flow unsteadiness failed to disrupt completely a previously built-up deposit, even with increasing proportions of injected gas. Under the overall experimental conditions, the consumed energy per unit volume of permeate to achieve the same flux was found to be systematically lower in two-phase flow than in single-phase flow. For a given specific energy, the permeate flux could be increased by a factor of 2.

A Practical Method to Predict Steady-State Flux and Fouling in the Crossflow Microfiltration of Rough Beer with 1.40 μm Tubular Ceramic Membranes

In crossflow microfiltration (CFMF) of real food products (beer, wine, milk), fouling mechanisms and the local phenomenology associated with fouling are largely unknown and still unidentified. In this paper, an investigation has been carried out to determine the kinds of fouling and to look for a way to improve filtration performance. Different hydraulic resistances in series were measured to determine the significance of internal and external fouling in relation to operational parameters (crossflow velocity). The influence of pressure and velocity on the steady-state flux was investigated with a 1.40 μ m tubular ceramic membrane and the steady-state flux was described using an empirical equation. A working velocity range defined by a critical and an optimum velocity was determined, in which the filtration should be performed. This work gives new experimental results in rough beer CFMF and proposes an empirical equation which could be useful in the sizing of an industrial CFMF unit.

Parameterisation of horizontal leaf filters and optimisation for the filtration of beer

For process design it is necessary to analyse the flow phenomena in precoat filters. This is achieved with the use of flow visualization in models of horizontal leaf filters in different dimensions. The parameterisation of the hydrodynamics in the filter embraces variations in the construction and operating parameters. The results are then transferred to a pilot plant. This subsequently leads to an optimised filter apparatus with improved filtration performance. The channelling of the suspension flow, combined with the optimal Reynolds number and flow velocity, leads to a homogeneous flow to the filter's surface with a homogeneous build-up of the filter cake. For the filtration of beer the optimised apparatus has a larger filtrate volume per run, reduced differential pressure rise, reduced specific consumption of filter aid, water, energy and detergents.

Cross-flow filtration with and without cake formation

A neutrally buoyant model particulate suspension has been used to examine the effect of channel flow fluid mechanics on filtrate flux kinetics. The incorporation of periodically spaced central baffles is shown to improve filtration performance by a factor of about two. Direct observations of particle activity at the cake surface show that this improvement is caused by filter cake erosion due to eddy circulation around the baffles. A novel piece of apparatus has been developed to produce oscillatory flow within the channel. When these oscillations were superimposed upon a steady net flow in the presence of baffles, more than tenfold filtrate flux enhancement was found. Optical observations of the filtration process show that in this mode of operation, cake build up is completely inhibited. It was also observed that more efficient filtration occurs when gas was entrained into the channel, through the filter.

Self-cleaning depth filter uses twisted fibrous elements to improve filtration performance

The Fibrotex filter system was originally developed for the filtration of sea water as part of an offshore exploration programme. However, its superior performance, brought about by the use of twisted fibrous elements has resulted in it finding numerous other applications.