Experts in filtration and separation

We advance and disseminate knowledge in the design and use of filtration and separation techniques in industry, commerce and other walks of life.

Volume 7, Issue 1 Abstracts from the FILTRATION journal

OVERVIEW AND RECENT DEVELOPMENTS IN EFFECTIVE PARTICLE DECONTAMINATION BY WASHING PROCESSES
H. Anlauf (pages 20-25)

Washing of disperse solid systems is a widely used and complex operation that is embedded in the process chain. The target of the washing operation can be either the purification of the solid particles or to recover the substances dissolved in the liquid as completely as possible. In many cases hazardous substances have to be removed from solid waste materials before depositing them. Washing is often not only a question of environmental protection but also a possibility for the recovery of valuable substances to recycle them in the process and decrease the demand of raw materials. Since the washing step is mostly integrated into other process operations, it is subject to numerous demands exceeding by far the primary demands, like good separation results and a low specific wash liquid demand. Because of the phenomenology and limits of different washing processes it is difficult to choose the appropriate washing process. Additionally, the transport mechanisms of some washing processes are not yet sufficiently understood.

A broad overview of the existing washing processes, the numerous parameters, and the demands they have to meet is given. Included here are well known examples from different separation technologies for permeation and dilution washing in co-current or counter-current mode as well as new highly efficient and recently developed washing processes. Based on a categorization of the washing processes and the classification of these processes according to their macroscopic transport phenomena, one can compare the existing washing processes and show their individual limits. This can be used as a rough guideline for the choice of an appropriate washing process within the complete process chain of solid/liquid separation.

POLYMERIC AND CERAMIC NANOFIBRES
J. Steffens (pages 26-28)

Nanofibre is a broad phrase generally referring to a fibre with a diameter less than 1 μm. While glass fibres have existed in the sub-micron range for some time and polymeric meltblown fibres are just beginning to break the micron barrier, 0.25 μm diameter electrospun nanofibres have been manufactured and used commercially for air filtration applications for more than twenty years. Several value-added nonwoven applications, including filtration, barrier fabrics, wipes, personal care, medical and pharmaceutical applications may benefit from the interesting technical properties of commercially available nanofibres and nanofibre webs.

This paper is a review of the electrospinning process for making nanofibres and nonwoven nanofibre webs from synthetic fibre-forming polymers. The resulting physical characteristics of nanofibre webs will be discussed. In order to provide a useful context for the nonwovens industry, nanofibre webs will be compared to both meltblown and spunbond nonwovens. The description and comparison of the properties should provide product designers in the nonwovens industry with the tools to generate product and applications ideas about new uses for nanofibres.

THREE STEPS TO A NEW FILTRATION QUALITY: MODERNISATION OF FILTER PLANTS BY REVAMPING
T. Langeloh and R. Bott (pages 29-32)

The standard job of a filter is to separate solids from a liquid and to provide: (a) well dewatered dry filter cakes; (b) clear, particle-free filtrate; (c) washed, clean filter cakes; (d) high and constant liquid and solids flow rates; (e) easy to handle bulks; in a reliable operation without failures e.g. by a clogged or damaged filter cloth. However, filter plants are often not operated under optimum conditions and the results often do not meet the requirements. The discrepancy becomes critical if a filter is used up to its capacity limit or beyond its capability, because of increased production rates, higher quality requirements, the introduction of modern process control or a change of product characteristics, for example, the particle size distribution.

In this situation the decision has to be made whether the production target shall be reached with a new filter or even with retrofitting of the existing filter plant. To answer the question it is necessary to assess the potential of improvement and to have concrete ideas as to which specific measures have to be taken for an effective filter upgrading. For this reason BOKELA developed a 3-step optimisation programme for drum, disc, belt, pan, cartridge, leaf filters or filter presses which is clearly structured in 3 phases with exactly defined decision points. According to the programme numerous filter plants have been already optimised in different industries leading to improved product qualities and operational reliability and capacity increases up to 100%.

EVALUATION OF ELECTROSTATIC FILTER MEDIA FOR AEROSOL SAMPLING AND ANALYSIS
M.M. Abdel-Salam (pages 33-40)

Aerosol particles are released into the atmosphere by different processes with significant effects on human health. During the last few decades there has been increasing interest in the measurement of aerosol particles using a wide range of different aerosol samplers and aerosol filtration is a widely used method for measuring airborne particles. Electrostatic filters have the advantage of high aerosol collection efficiency accompanied by low resistance to airflow when compared to the traditional high resistance fibrous and membrane filters commonly used in aerosol sampling.

This paper investigates the suitability of 3M electrostatic filter media for aerosol sampling and analysis in comparison to some conventional aerosol sampling filters, such as glass fibre and membrane filters. The areas investigated include resistance to airflow, aerosol collection efficiency, loading capacity, weight stability and chemical properties. The 3M electrostatic filter media was found to be suitable for aerosol sampling and analysis (gravimetric and elemental chemical analyses) and was as good as the traditional filters widely used in aerosol sampling.

MEASUREMENT OF BIOAEROSOL FILTRATION EFFICIENCY IN AN ASHRAE 52.2 FILTER TEST FACILITY
W. Tang, M.A. Ramakrishnan, S. Goyal and T. Kuehn (pages 40-44)

A real-time monitor of bioaerosols, Fluorescence Laser Aerodynamic Particle Sizer (FLAPS), was evaluated for its ability to detect bioaerosols and measure bioaerosol filtration efficiency. Biological spores (Bacillus subtilis and Cladosporium sphaerospermum) were aerosolized and injected into a wind tunnel based on ASHRAE Standard 52.2. The sensitivity of the FLAPS was adjusted by the photomultiplier tube (PMT) gain to distinguish between bioaerosols and non-biological aerosols such as polystyrene latex and potassium chloride particles. Suspensions of biological spores were carefully prepared to remove interference with culture media. Aerosol concentrations upstream and downstream of a clean synthetic media filter (MERV-14) with electrostatic charge were monitored by FLAPS and by an Andersen impactor. The calculated filtration efficiency from the measurement of FLAPS was 96% for B. subtilis and 100% for C. sphaerospermum. These results agree with those obtained with the Andersen impactor (91% for B. subtilis and 99.5% for C. sphaerospermum).

PULSED ELECTRIC FIELD ASSISTED SOLID/LIQUID EXPRESSION OF AGRO-FOOD MATERIALS: TOWARDS A NOVEL ENVIRONMENTALLY FRIENDLY TECHNOLOGY E. Vorobiev, L. Praporscic and N. Lebovka (pages 45-49)

In this paper we analyse the kinetics and mechanisms of solid/liquid expression combined with a pulsed electric field (PEF). Experiments were performed with raw agro-food materials (slices of fresh carrots and apples, whole grapes), and with agro-food wastes. The layer of particles was formed in the laboratory filter press cell, connected to a PEF generator. The PEF treatment of different intensity (<1000 V/cm) and duration (10-300 ms) was applied before solid/liquid expression (as a pretreatment) or during expression (intermediate treatment).

The PEF application caused electropermeabilisation of cell membranes and enhanced considerably the solid/liquid expression from studied agro-food materials (from 30-50% before treatment to 70-85% after the treatment). The simplified empirical model of solid/liquid expression fitted the experimental data well for both untreated and electrically treated materials. The PEF treatment also influenced the quality of juices expressed from raw materials. The PEF treated juices were more limpid and pure compared to the untreated juices, probably due to selectivity of extraction from electrically permeated cells. Such juices can be purified and clarified more easily than untreated juices. Therefore, it can be speculated that the novel technology comprising the combination of PEF and solid/liquid expression will generate less quantity of industrial wastes compared to existing transformation technologies.

PARTICULATE EMISSIONS FROM FILTER-BASED GAS CLEANING DEVICES AND THEIR CHARACTERIZATION ACCORDING TO PM2.5 CRITERIA
G. Kasper, J. Binnig and J. Meyer (pages 49-54)

We report on a study of particle emissions from pulse-jet cleaned filter media and filter ageing effects of up to 10,000 cycles, which were obtained in laboratory tests on a VDI test rig, using two measurement systems adapted specifically to determine size selective data according to PM2.5. Time resolved measurements were made with an optical particle counter recalibrated (for the test dusts Pural SB and NF) to directly read dust mass vs. aerodynamic diameter according to the PM2.5 transmission curve. In parallel, a cyclone was used as pre-separator in combination with an analytical filter to obtained emitted dust mass averaged over a number of cycles.

Regarding PM2.5 emission levels, one can draw different conclusions from the same data, depending on whether total emissions per cycle or average concentrations per cycle are reported. The results also illustrate how ageing depends on the type of dust and the duration of ageing cycles. Ageing progressed more rapidly with the coarse, free flowing dust. The 5 s ageing cycles prescribed by VDI and ASTM protocols are too short.

THE PRESSURE-DRIVEN MEMBRANE BIOREACTOR vs. THE ION EXCHANGE MEMBRANE BIOREACTOR FOR THE REMOVAL OF TOXIC ANIONS FROM DRINKING WATER SUPPLIES: ADVANTAGES AND LIMITATIONS
S. Velizarov, A. Barreiros, C.T. Matos, M.A. Reis and J.G. Crespo (pages 54-58)

Two membrane bioreactor configurations, the pressure-driven membrane bioreactor and the ion exchange membrane bioreactor (IEMB), were tested for the removal of toxic oxyanions from drinking water. The results based on a case study – nitrate removal at a treated water production rate of 30 L m-2 h-1 – showed that in both bioreactors the desired water quality in terms of nitrate and nitrite can be achieved. The pressure-driven membrane bioreactor allows for possibly higher water production rates and uses relatively cheaper membranes, however, the water quality control in terms of TOC requires on-line monitoring and a strict regulation of the carbon source addition. This configuration also requires an initial start-up period before achieving a steady state operation because the water and microbial culture are in direct contact.

The ion exchange membrane bioreactor offers the advantage of selectively removing the target anion and producing TOC-free water with practically no initial start-up period. Due to the physical separation of the microbial culture from the water stream, the very low diffusion coefficient of ethanol through the Neosepta ACS membrane used, and the membrane-attached biofilm acting as an additional reactive barrier to ethanol penetration, secondary pollution of the treated water was avoided. The development of cheaper anion exchange membrane (possibly in a hollow fibre form) would make the IEMB process economically competitive.

LINKING DEWATERING PARAMETERS FROM TRADITIONAL, FLUID MECHANICAL AND GEOTECHNICAL THEORIES
R. de Kretser and P. Scales (pages 60-66)

Due to the wide range of research fields requiring an understanding of solid/liquid separation, a range of theories and parameter sets have evolved in parallel. Discussion of the approach from one field of research is seldom discussed in the context of the other. This paper attempts a reconciliation of the key approaches in terms of their respective similarities, advantages and inter-conversion of the key parameters on which they are based. The advantages of such a reconciliation both enables a greater understanding of dewatering in general and provides the ability to readily convert data or utilise test methods from one field of research within another.

Keywords: Specific cake resistance; hindered settling factor; flux density; compressive yield stress; solids stress; consolidation coefficient; permeability; compressibility.

NANOFLUIDICS IN FILTRATION AND PARTICLE PROCESSING
H. Nirschl, R. Wengeler and B. Schäfer (pages 67-74)

The subject of this paper is to give an insight into the fluid dynamics when nanoscale or submicron particles are handled in filtration or separation processes. The differences of the forces on particles in macroscale and nanoscale are presented and discussed in detail. The differences can be separated according to particle-particle interaction, the interaction with the surrounding fluid and the influences of external fields. It is evident that the behaviour of nanoparticles suspended in a fluid depends strongly on the surface properties of the suspended material.

As examples, the flow through a nanoscale packed bed and the dispersion process of nanoscale particles is discussed. It is shown that the permeation through a nanoscale structure is influenced by electrostatic and electroviscous effects. Electrostatic effects have an influence on the aggregate structure while the electroviscous effects directly influence the permeation.

Keywords: Nanofluidics; nanoparticles; electrostatic and electroviscous effects; packed bed; suspension.

INVESTIGATION OF FILTRATION CONDITIONS FOR NANOFILTRATION OF REACTIVE DYE PRINTING WASTEWATER
N.P.R. Andersen, M.L. Christensen, K. Keiding and I. Petrinić (pages 75-81)

One of the major problems concerning textile wastewaters is the coloured effluent from rinsing and washing processes. Although the dye concentration is low, compared to many other chemicals found in this type of wastewater, the water quality is insufficient for reuse or discharge. Application of nanofiltration and reverse osmosis to reduce or remove dyestuff from reactive dyeing operations has been widely explored in the literature and is now applied in many plants worldwide. Less attention, however, has been paid to the membrane filtration of reactive dye printing wastewater containing high amounts of thickeners (alginate).

In this study synthetic wastewater, with a composition similar to reactive dye printing wastewater produced during the washing of printed fabric, has been subjected to nanofiltration. The effects of dye, thickener and salt concentration on the separation efficiency and permeate flux has been investigated. All experiments were carried out with an NFT-50 membrane in a plate and frame module applying constant crossflow and filtration pressures ranging from 200 to 1500 kPa.

The results showed that the presence of alginate in the wastewater markedly decreased the permeate flux compared to wastewater without alginate but with the same amount of dye and salts. Calculations indicated that the reduced permeate flux originated exclusively from concentration polarization (CP) and not membrane fouling. The retention of dye was high (>99%) at all pressures, while the retention of salt, expressed as retained conductivity, increased with pressure from 65% at 200 kPa to 85% at 700 kPa (crossflow 240 L/h). However, at higher pressure and crossflow the retention of salt decreased due to more pronounced CP. Thus, for the filtration of reactive dye printing wastewater, a high retention of dye and salt could be obtained at filtration pressures that were significantly lower than those normally used when filtering textile wastewaters.

Keywords: Nanofiltration; alginate; retention efficiencies; process optimisation; water reuse.

IMPROVING CFD SIMULATIONS OF LUBRICANT OIL FIBROUS FILTER MEDIA
M.J. Lehmann and P.K. Hermar (pages 82-86)

Modelling lubricant oil filter media and its particle collection efficiency is still a demanding but elusive goal. Two key areas of difficulty are the availability of appropriate models for particle collections in simulation programs and the characterisation of the fibrous media. The widely used CFD program FLUENT calculates particle tracks based on the motion of the mass point of a particle. Consequently a particle is only counted as deposited when its centre hits a fibre surface. This model is not appropriate for liquid filtration modelling, as the dominant collection mechanism is interception. Therefore, we enhanced FLUENT by our own subroutines to account for the perimeter of a particle and its distance to a fibre surface which resulted in improved prediction of efficiency for particle removal from liquids.

The challenge to model the fibrous structure of the media remains. Many recent studies attempt to model the 3D fibre structure in 2D by random placement of cylinder cross sections vs. the prior over-simplified approach using perfectly spaced fibres. However, this approach still does not generate a realistic structure and still over predicts pressure drop. So the current work investigates the influence of semi-randomly arranged fibre structures. The resulting fibre structures are more realistic than those created by fully-random placement. Simulations comparing the pressure drop and collection efficiency of these types of structures are shown.

The results demonstrate the effect of the different kinds of simulated 2D fibre structures on pressure drop and collection efficiency. A shift from fully random to semi-random structures results in changes to flow patterns and generally leads to a significant decrease of pressure drop. Furthermore, changing from a staggered fibre grid to more locally aggregated fibre structures increases the media usage through its depth. However, moving from fully random to semi-random structures causes decreases in collection efficiency. The results and discussion briefly illustrate these effects and the challenges for future media modelling.

Keywords: CFD-simulation; fibrous filter; filter media; filter design; modelling.

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Volume 7, Issue 2

DEFINITE AND QUICK CHARACTERISATION OF FRACTIONAL SEPARATION EFFICIENCIES IN UNKNOWN AEROSOL CONCENTRATIONS
M. Schmidt (pages 106-108)

In many applications, besides the laboratory, there exists a need for the exact characterisation of filters and separators, e.g. in the fields of lubrication oil separation, blow-by oil separation, automotive and engine air filters and compressed air filters. As the aerosol concentration in the different processes may change rapidly, a quick particle characterisation upstream and downstream of the filter is required.

Other problems arising are the different measurement conditions of the application with regard to, for example, the temperature, type of aerosol and pressure conditions during the process. In the past, a user tried to cover at least the problem of varying aerosol concentrations by using two particle counters upstream and downstream of the filter to perform simultaneous measurements. The difficulty in doing so is the exact comparison (calibration) of the two counters with regard to their classification accuracy, resolution and counting efficiency.

Palas® has developed the new aerosol spectrometer welas® 3000 with two integrated sensors for upstream and downstream which allow quasi-simultaneous particle size and particle concentration measurements to be carried out. The sensors may be equipped with different sizes of measuring volume in order to obtain optimised results with regard to different concentrations in a short time. Since the electrical parts, such as the lamp source and optical receiving unit of the scattered light, are the same, the device parameters of the two sensors, such as classification accuracy, resolution and counting efficiency, are the same as well.

The sensors are connected to the control unit via optical fibres. Thus, it is possible to switch quickly between upstream and downstream without losses in the sample lines by simply using an optical switch of the light connection to the sensors. The welas® system may be equipped with internal heating up to 120°C and an aerosol cuvette that is pressure resistant to 10 bar. Hence, the system can be used for the previously mentioned applications. This paper will focus on measurement results, e.g. in the field of lubrication oil separation and on measurements at pressures up to 10 bar with varying upstream concentrations.

CFD ANALYSIS ON THE EFFECT OF CALENDERING OF FILTER CLOTH ON TRANSIENT CHARACTERISTICS OF CAKE FILTRATION
K-L Tung (pages 109-112)

The effects of a filter fabric calendering treatment and the permeability of filaments with regard to the particle deposition phenomena onto or into filter fabrics at the initial stage of filtration are conducted quantitatively using a microscopic forces analysis. The flow pattern and the resistance to fluid flow in the calendered interstices were obtained numerically using the fluid flow software FLUENT™. Based upon numerical data for the continuous phase, a program was devised to simulate the transient behaviours of pore clogging and cake formation by way of the Lagrangian approach. This estimates the change of filtrate clarity during the initial stage of filtration for various calendered fabric porosities and various filament permeabilities.

Results show that in the case of tightly woven filter cloths the flow is predominantly through the yarns of the cloth, while flow will generally be directed around the yarns of a loosely woven cloth, especially if the yarn is twisted tightly. Therefore, filtrations with tightly woven but loosely twisted yarn can increase the unfavourable, but inevitable, clogging problem. The simulated results further show that although the filtration resistance of woven filter fabric increases after calendering, the permeability is rectified and the clogging of the filter pores is also improved. After the calendering of the filter fabric has taken place, only the cake formation mode (in accordance with the law of blocking for all types of pore) is evident. The critical concentration proposed by previous investigators is not observed for calendered filter fabrics.

NEW ISO STANDARDS FOR COMPRESSED AIR ANALYSIS AND FILTER TESTING
S. Smith (pages 112-116)

A large number of the International Standards used within the compressed air industry are either in the process of regeneration or are due for review. In addition, the first complement of compressed air filter testing standards, ISO 12500 Parts 1 & 2, are nearing finalisation with Part 3, Particulates, in development. Further, there are proposals to develop three additional standards for inclusion in the ISO 12500 series. This paper provides an up to date review of the position regarding these standards and details the proposed methodology for ISO 12500-3 coarse particulates testing.

RECYCLING OF PROCESS WATER USING MICROFILTRATION AND NOVEL COMPOSITE FILTER MEDIA S.
Volooj, C. Carr and R. Lydon (pages 117-123)

In this study dyebath recycling and decolourisation using a dual-flocculant system combined with microfiltration has been examined, and typically above 90% of dye removal was achieved. The effects of fluorine treatment on the surface and filtration performance properties of the composite filter media have been investigated, and filtrates with less turbidity and cakes with lower moisture contents were observed. XPS and contact angle measurement techniques were used to characterise the nature of the modification imparted by the fluorine treatment.

APPLICABILITY OF FABRIC FILTERS IN AIR POLLUTION CONTROL (APC) FOR WASTE INCINERATION PLANTS – LONG-TERM EXPERIENCE…
G.G. Pranghofer (pages 124-126)

Continuous development and improvement of high durability laminates led to a large number of reference applications in Waste Incinerators, the long-term performance of PTFE membrane filters in various configurations and different stages of APC systems is detailed. Experience has been obtained over 20 years in all stages of flue gas cleaning, e.g. collectors downstream from the boiler, downstream spray dryers and in end-of-pipe filter systems, covering a temperature range in the collector of 100 – 250°C. The results of the performance in different incineration plants is provided in this paper, including retention rates of PM 2.5, dioxins, heavy metals and, in combination with absorbents, of acidic components (SO2, HCl, HF) in compliance with BAT and the European Regulation (Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on the incineration of waste).

COMPARISON OF DIFFERENT FILTER AID PERMEABILITY TEST METHODS
W. Li, C. Kiser, Q. Richard and E. Mayer (pages 127-132)

Permeability is an important specification for evaluation and selection of filter aid products. However, there has not been a standard filter aid permeability test method in the US. Permeability results published by different companies may not be comparable due to different apparatus, filter paper, cake formation, sample amount, sample preparation, and different driving force used. The objectives of the study in this paper were to (i) investigate factors affecting permeability results in different filter aid testing methods, and (ii) develop a method and procedure providing consistent testing results on different testing apparatus. Three permeability test methods, three grades of rice hull ash and two grades of diatomaceous filter aids were involved in the study. It was found that filter paper or clogging of filter paper, testing pressure, sample preparation are critical factors affecting permeability results. A tight, low resistant and not easy to clog filter paper should be chosen for a permeability test. The testing pressure should be chosen carefully considering the compactibility of samples to be tested. Recommendations on other testing conditions are also given in the paper.

PHYSICAL MEASUREMENT OF PORES BY GLASS BEAD CHALLENGE TESTING
G. Rideal (pages 132-137)

Pore size measurement by the indirect method of porometry can produce varying results, especially for larger pores in excess of about 100 μm. Consequently, ‘bubble point’ rated filters often fail to stop the expected particles in real situations. Historical labelling of filters, and even nominal ISO standard specifications can therefore be very misleading. In this work, narrow particle size distribution glass microspheres from a few microns to several hundred microns were used as challenge particles to assess a number of filter media. A new Sonic filter tester could perform the test in 1 minute in the dry state. The challenge test results were unaffected by the porosity of the samples, unlike the porometry results where large variations were seen. In other examples, a sintered polymer air filter rated at 5 μm had a filter cut point of 140 μm while a nonwoven sand screen used in petroleum extraction rated at 125 μm had a cut point of 395 μm. Recovering and analysing trapped microspheres within the pore structure can be used to measure pore size distribution and also reveal subtle internal details in woven filter media.

TESTING FILTER MEDIA FOR LIQUID FILTRATION
R.J. Wakeman (pages 138-147)

Filter media exist in many forms and with a wide range of properties that are relevant to the filtration process. Not all media have to meet the same requirements when in service and different industries place differing demands on the media. This leads to the need and development of standards that are industry specific in some cases, or media design specific in others. The range of media available is overviewed together with some of the test methods that relate to the ability of a medium to capture contaminants from a liquid stream (other methods that relate to, for example, mechanical properties of the medium are outside the scope of this paper). Integrated within the overview are the standards that have been written by associations with responsibility for representing best practice in particular industries or by national/international standards organisations. Some directions of current research that may underpin future standards are indicated.

NON-WOVEN FABRICS AS SOLID/LIQUID SEPARATION MEDIA IN A MEMBRANE BIOREACTOR
W-K. Chang, S-H. Chuang, A.Y-J. Hu and M-C. Chang (pages 149-153)

The characteristics of non-woven fabrics as solid/liquid separation media in a MBR application have been studied in this paper. To understand the effect of particle properties on filtration performance, inorganic and microbial particle filtrations were studied simultaneously. The results showed that there was no significant decline of permeate flux during 120 h operation for inorganic particle filtration. Comparatively, non-woven fabrics were fouled rapidly for microbial particle filtration and significant decline in permeate flux was observed during experimental periods. However, low effluent suspended solids was achieved rapidly due to the denser cake layer on the fabric surface. This study has demonstrated that non-woven fabric materials could be used as solid/liquid separation media in membrane bioreactors for wastewater treatment. An appropriate operating strategy, like optimum operating flux and fouling control, is needed for long-term stable operation.

Keywords: Membrane bioreactor; filtration; fouling; non-wovens; solid/liquid separation; wastewater.

MEASURING PARTICLE DEPOSITION WITHIN FIBROUS FILTER MEDIA BY MAGNETIC RESONANCE IMAGING
J. Hoferer, E.H. Hardy, J. Meyer and G. Kasper (pages 154-158)

This paper describes the application of magnetic resonance imaging (MRI) to obtain information on local particle mass deposition within fibrous filter media. The experimental set-up used for on-line loading experiments is also detailed. The required procedure to initially gather information on filter structure without destroying it, which is required when the same filter medium is later loaded with particles, is briefly presented as is the particle size distribution of the particle material used to load the filter in comparison to a conventional test dust. Preliminary results are discussed for recording the loading process within a medium by visualizing the local deposited mass at various loading stages. By using this non-destructive measuring technique which first allows measurement of the internal fibre structure followed by loading of the medium, it will be possible to compare the data with results of simulations and thereby allow validation of kinetic filter models.

Keywords: Depth filtration; fibrous filter; gas filtration; MRI; particle deposition.

FILTERABILITY AND AGEING OF CRYSTALLINE POTASSIUM SULPHATE SALTED-OUT WITH ETHANOL AND ACETONE
M. Louhi-Kultanen, A. Llansana Arnalot, L. Nyström and J. Kallas (pages 159-167)

The desupersaturation and ageing of a solid/liquid suspension consisting of crystalline and dissolved potassium sulphate, co-solvent water and an anti-solvent, i.e. acetone or ethanol, were investigated based on image analysis, measurements of electronic conductivity and determination of certain filterability parameters. The crystals were produced by salting-out precipitation at 25°C. The samples were taken after addition of the anti-solvent in a semi-batch process by pumping the precipitant at constant flow rate or in a batch process by adding all the anti-solvent at the beginning of the precipitation process. The studied ageing time was 60 mins. Ostwald ripening theory was utilized to compare the ripening tendency in the studied solvent systems. The precipitation conditions were changed by altering the flow rate of the precipitant. The solution composition was changed by adding sulphuric acid to decrease the pH from a neutral solution pH equal to 6.2. Ageing for 60 mins. decreased the cake resistances of both studied precipitant systems whereas cake porosities varied only slightly between fresh and aged precipitate cakes.

Keywords: Filterability; ageing; stability; out-salting precipitation; potassium sulphate; desupersaturation.

TUBE SETTLERS FOR THE ENHANCEMENT OF SETTLING TANK CAPACITY
K. Fujisaki and M. Terashi (pages 168-172)

A new type settler has been developed and its usefulness was confirmed experimentally. The device arranges inclined parallel plates in the vertical direction, contrary to the usual horizontal arrangement. In this method, the separated clear water is removed directly by suction from the top end of the parallel plates. For the removal of clear water, the right and left edges of the plates are closed in order to make a tube with a rectangular cross section. These are the unique and original features of the equipment. The treatment capacity is proportional to the number of settling tubes set in the suspension, since each settling tube acts as a small settling tank. The new settling tube module was set in a final settling tank and over a wide range of sediment concentration the relationship between the suction velocity and suspended sediment concentration of effluent was investigated. Based on the results of these on-site experiments, it is demonstrated that the new tube settler system is very effective for the enhancement of settling tank capacity. A numerical estimation of the application of this system to a practical settling tank also confirms the effectiveness of the device.

Keywords: Lamella settler; settling tank; tube settler; sedimentation; thickening; clarification; sewage secondary effluent; activated sludge.

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Volume 7, Issue 3 Abstracts from the FILTRATION journal

CHARACTERISATION OF PARTICLE PENETRATION AND DUST HOLDING CAPACITY OF SURFACE TREATED NEEDLEFELTS
W. Hoeflinger, H. Rud and G. Mauschitz (pages 196-200)

For surface treated filter media porosity properties at and just below the filter surface are essential to particle penetration and particle clogging behaviour. In order to compare different surface treated filter media it is necessary to develop suitable parameters and measuring devices regarding these porosity properties. In this work a transmission microscope together with image analysis software was used to determine a so called hydraulic diameter and a pore volume equivalent, which can be measures for comparing the particle penetration and the particle holding capacity of different surface treated filter media. The experimental verification was performed with a gas/particle system filtered using different surface treated filter media. Generally, the parameters for comparing different surface treated filter media should be also applicable to liquid/particle systems, but for correctness this needs further experimental verification.

DESIGN CONSIDERATIONS FOR CRANKCASE VENTILATION SYSTEMS TO MEET FUTURE DIESEL ENGINE EMISSION REGULATIONS
P. Banerjee, B. Verdegan, B. Schwandt, C. Holm and S. Heckel (pages 201-205)

Successful application of crankcase ventilation (CV) systems to diesel engines is critical for engine manufacturers to meet future emission requirements. This paper discusses the challenges associated with filtering crankcase blow-by and explains the technical considerations for designing a CV system for specific engine platforms. The paper also compares the performance of CV systems from various filter manufacturers using common performance metrics and presents our approach for optimizing CV system design to support diesel engine manufacturers’ efforts to meet emission requirements of 2007 and beyond.

STREAMING CURRENT MONITORING (SCM) OF INDUSTRIAL FLOCCULATION PROCESSES
E. Mayer (pages 206-214)

Conventional wastewater (WW) treatment usually involves coagulation or polymer flocculation prior to clarification by sedimentation or dewatering by filter presses, belt filter presses, or centrifuges. Polymer dosage control is critical for optimum performance as well as reducing costs. Many devices have been developed over the years to measure both floc size as well as the excess charge in solution. The Water Environment Federation (WEF) has recently conducted a research program on three such devices that concluded the Streaming Current Monitor (SCM) has the most merit. This paper will discuss this relatively new technology and how it was applied in a rigorous fashion to industrial flocculation processes. Case histories will be presented that highlight its usefulness.

MEMBRANE FILTRATION CONCEPT AND CATALYTIC FILTRATION
G.G. Pranghofer (pages 214-219)

Various technologies have been developed for the control of Poly-Chlorinated-Di-benzo- Dioxins and -Furans (PCDD/F). In flue gas cleaning systems of municipal waste incineration plants the most commonly used methods are (i) adsorption technology by utilizing pulverized activated carbon (PAC) or lignite coke (Herdofenkoks, HOK) in fabric filters, and (ii) catalytic destruction by means of a selective catalytic reactor system (SCR). The adsorption technology is well proven but does not destroy the PCDD/F; they are collected on the surface of the carbon particles and disposed of with the fly ash. SCR systems destroy PCDD/F but cannot control particulate matter. About 10 years ago a new system was developed which is an evolution of two proven technologies: catalysis and surface filtration.

The new system developed for the control of Poly-Chlorinated-Di-benzo- Dioxins and -Furans (PCDD/F) consists of an ePTFE (Poly-Tetra-Flouro-Ethylene) membrane and a catalytic felt substrate. In this paper the catalysis and surface filtration principles are detailed. Performance results in different incineration plants are provided. PCDD/F concentrations up to 10 ng ITEQ/m³ in the raw gas have been reduced well below the limit of < 0.1 ng ITEQ/m³.

NANOFILTRATION – A METHOD FOR SOLUTE REMOVAL FROM LIQUID HYDROCARBONS
E.S. Tarleton and J.P. Robinson (pages 220-225)

In relation to potential applications in hydrocarbon processing, the separation characteristics of a dense polydimethylsiloxane (PDMS) membrane were studied using alkyl and aromatic solvents and low-polarity, sulphur bearing, organometallic (OM) and poly-nuclear aromatic (PNA) solute compounds. Solute rejection was found to be dependent on trans-membrane pressure, crossflow rate (hydrodynamic conditions), solute size and the degree of swelling induced by the solvent. Rejection increased progressively with pressure whilst a threshold condition was observed above which further increases in crossflow had a negligible influence on rejection. Measurements over the molecular weight range 84-612 g/mol showed the membrane to have a cut-off in the region 350-400 g/mol to all but one of the tested PNA compounds (rubrene). An additional correlation using molecular dimensions instead of molecular weight showed the cut-off size to be in the region of 1-2 nm, with all data falling on a well defined rejection/size curve.

Solvent type influenced membrane swelling to an extent dependent on the relative magnitude of the solubility parameters for the solvent and PDMS; similar values led to more swelling, higher fluxes and lower rejections. Results support the concept of viscous solvent flow whilst solute transport could be either predominantly viscous or a combination of viscous and diffusive. With larger molecules a size exclusion mechanism was dominant.

MEASUREMENT OF THE EFFICIENCY OF DEPTH FILTERS FOR WATER TREATMENT
M. Zielina and L. Hejduk (pages 225-228)

Conventional granular filters have been widely used in drinking water treatment technology since the first half of the previous century. Numerous laboratory experiments and theoretical analysis of depth filtration have been done by many researchers, but there are still no satisfactory complete mathematical models to calculate the hydraulic head loss and the effluent quality during the whole process. While transport of suspended particles in the filter medium is quite well recognized, the ability to predict the adhesion efficiency is poor. For this reason, and because of variable conditions in filter plants, continuous observation of the filtrate quality and head loss are practically the only possibility for predicting accurate results. In most filter plants “on-line” information about the efficiency of the suspended solid removal is estimated using turbidity sensors. The interpretation of the turbidity (especially nephelometric) is quite complex and difficult without detailed information about the suspension. Laser particle size analyzers give interpretative information about the suspension and removal efficiency through the filter, but its application in drinking water treatment plants remains limited.

A laboratory set-up has been designed and built, which includes filtration by a 3 m deep column together with the inflow system for preparing the suspension in raw water. Several experiments were performed in the laboratory set-up and in the full scale water treatment plant for various flow rates, medium heights, grain stratifications and suspensions. The filter efficiency change versus time was analyzed with the laser particle size instrument and the turbidimeter. The significant differences between results depending on the measuring method were observed and compared to the theory. An interpretation of the predicted filter efficiency on the basis of both methods is proposed.

CLEAN PRODUCTION AND SIGNIFICANT ENERGY SAVINGS WITH A HYBRID SEPARATION PROCESS – HI-BAR STEAM PRESSURE FILTRATION
T. Langeloh and R. Bott (pages 228-233)

Hi-Bar steam pressure filtration is an innovative hybrid separation process which combines mechanical and thermal dewatering. This advanced variant of continuous pressure filtration enables a simplified separation process design with lower emissions and significant energy savings. The process is currently establishing itself in the chemical, pharmaceutical, food and life science industry particularly for the demanding applications of filtration, washing and dewatering of high value products.

INFLUENCE OF LEAKS IN SURFACE FILTERS ON PARTICULATE EMISSIONS
B. Bach and E. Schmidt (pages 235-239)

Compliance with severe limit values of dust emissions is a main characteristic of surface filters that is due to the high particle collection efficiency of surface filters. Besides regular operation it is necessary to consider phenomena such as a “pinhole” bypass in surface filters to ensure the above mentioned compliance with the limit values at all times. “Pinhole” bypass is suspected to be the main mechanism concerning particle penetration through leaks in installed filters.

Experimental research has been carried out to observe and understand “pinhole” bypass and the behaviour of pinholes with filtration time. To work out the influence of different filtration conditions, the parameters pinhole diameter, filter face velocity and dust cake thickness were varied.

The results can be explained using formulae that are usually used to the calculate volumetric flow rates of orifice gauges. The experiments and calculations lead to the conclusions that bigger pinholes decrease the collection efficiency and higher filter face velocities increase the collection efficiency of pinholed filter media. Worst case clean gas concentrations can be calculated by the theoretical model provided.

Keywords: Solid/gas separation; surface filtration; filter efficiency.

PERFORMANCE OF BAGHOUSE DUST COLLECTORS IN THE WOODWORKING INDUSTRY
D. Bémer, X. Simon, R. Régnier, I. Subra and B. Honnert (pages 240-247)

Baghouse dust collectors are frequently used in the woodworking industry for the removal of dust that causes several diseases, including a number of serious ones. Common practice involves resorting to air recycling after filtration, which enables the costs associated with air heating to be curtailed. However, performance of dust collectors must be ascertained, given the dangerous nature of the dust and the low concentration limit value in recycled air (≤ 0.2 mg m-3). Measurements were carried out on installations that exhibit different characteristics (e.g. age, design, airflow, filtration process, etc.). Filtration efficiency was measured using two methods, namely tracing with a fluorescent aerosol and optical counting. Downstream concentration was determined by isokinetic sampling and gravimetry.

Tests allowed the authors to validate and improve the tracing method. Measurements generally revealed low wood dust concentrations that were usually below the established limit (0.2 mg m-3). An exception was during cleaning phases although the concentration remained low (< 1 mg m-3). On the other hand, air recycling reintroduces sub-micronic wood dust particles into the workshop for which the effects on health remain unknown. Keywords: Aerosol; filtration; fluorescein; baghouse filter; wood dust.

CONTINUOUS METAL RECOVERY PROCESS USING POLYMER ENHANCED ULTRAFILTRATION
J. Sabaté, M. Pujolà, J. Llorens and P. Marco (pages 248-250)

The separation of metals from aqueous streams by continuous polymer enhanced ultrafiltration (PEUF) was modelled in order to understand, evaluate and optimise the feasibility of the process. The mathematical model developed has three sections: mass balances, equilibrium of metal-polymer complexation and rules for UF membrane separation. On the one hand, the model allows an examination of the influence of physico-chemical variables (affinity between the metal ion and the complexing polymer groups) and engineering parameters (mainly expended acid and base reagents, amount of polymer used and recycling stream flow) on the quality and productivity of the treated water stream. On the other hand, a suitable representation of the simulation results has been shown to be helpful in choosing operation parameter values that lead to the stable output of treated water with the desired quality and productivity.

Keywords: Metal; recovery; ultrafiltration; continuous; simulation.

STATISTICAL MODELLING OF THE PORE STRUCTURE OF STOCHASTIC FIBRE NETWORKS
W.W. Sampson (pages 251-254)

A model is presented that accounts for the influence of grammage and porosity on the pore radius distribution in stochastic fibre networks. The influence of fibre width on the mean pore radius of two-dimensional random networks is derived. The model shows that increasing grammage and decreasing porosity decreases the mean pore radius in random and non-random networks. The standard deviation of pore radii is shown to be proportional to the mean in agreement with experimental observation; the proportionality is shown to be sensitive to the uniformity of the constituent layers of multiplanar structures.

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Volume 7, Issue 4 Abstracts from the FILTRATION journal

PERFORMANCE OF PRESSURISED AGRICULTURAL VEHICLE CABS AGAINST PESTICIDES – AEROSOL TESTING METHOD
D. Bémer, I. Subra, M.T. Lecler, J.P. Larrat and D. Schaeffner (pages 282-285)

A method for determining the efficiency of a vehicle cab for agricultural tractors with respect to an aerosol has been developed. The method has been used to evaluate the efficiency of two cabs differing in their filtration system (medium and high efficiency filters) and ventilation designs. For the cab fitted with the high-efficiency filter, the measured efficiency was corrected according to the aerosol internal source. Results obtained for the cab fitted with a medium performance filter revealed an efficiency higher than that of the filter itself. This increase in efficiency is achieved by partially recycling the air through the filter. Results obtained for the cab fitted with a very high performance filter were contrary, inasmuch as the measured efficiency was lower than that of the filter itself. Measurements of the aerosol were taken near a tractor cab during pesticide application in an orchard. A tracing method was applied to determine cab efficiency, as well as concentration and particle size distribution of the pesticide aerosol.

WHO ARE THE CULPRITS? – POTENTIAL CONTAMINANTS OF FOODS AND BEVERAGES
G. Shama (pages 286-290)

The ‘culprits’ of the title are actually extremely diverse, and include both living organisms and what might be referred to as ‘complex biochemical agents’. This last, somewhat contrived, term is intended to cover viruses, viroids and prions. These latter may be thought of as occupying the evolutionary gap between molecules and living organisms.

All of these agents have the ability to contaminate foods and beverages, and the potential to cause food poisoning in different ways and with various degrees of severity ranging from mild enteric discomfort to death. Whilst methods of detection for known pathogens continue to improve, it is also the unknown that we need to be constantly vigilant over. The nature of the unknown is literally unknowable, but some guidance as to what new types of foodborne agents might emerge in the future may be gained by considerations of recent discoveries in microbiology that are helping to (re)define the boundaries of the possible. Consequently, whilst primarily focussing on well-characterised foodborne pathogens, some speculation about the ‘next generation’ has also been included where strictly relevant.

MINIMISING THE PRESSURE DROP ACROSS FILTERS WITH MULTI-CYLINDRICAL FILTER TUBES
M. Buzanowski and D. Fadda (pages 290-292)

Effective, efficient and economical removal of dust, dirt, scale, rust, and other solid foreign particles from different types of gas streams is a process requirement often encountered in the design of chemical plants, pipeline stations, gasoline plants, refineries, town border stations for distribution systems and various other industrial plants. Gas filters are used where a high degree of solids removal is required. Pressure drop, the negative factor associated with filtration, can be decreased by optimizing filter media geometry. Computational fluid dynamics (CFD) analysis is used to optimize cylindrical filters currently used as gas filters and filter separators. The computational method used in this analysis is described and its results are presented.

TESTING ANTI-MICROBIAL EFFECTIVENESS IN POOL FILTER MEDIA
P.J. Angelini (pages 293-297)

Anti-microbial containing filter media designed for pool and spa applications have been in commercial use for five years. Currently there are two commercial suppliers of these media. The purpose of treating the filter media with an anti-microbial material is to provide a means of inhibiting bacterial growth on the surface of the filter. By doing this the service interval between cleanings will be extended.

LARGE SCALE BAG FILTRATION ENHANCED BY ELECTROSTATICS
C.-V. Rasmussen, M. Koch, H.V. Pedersen and G. Krammer (pages 297-299)

This work comprises the evaluation of industrial measurements carried out on FLSmidth Airtech (FLS A) fabric filters (FFs) positioned downstream of two different cement mills. One mill in Aalborg, Denmark features an upgraded electrostatic precipitator (ESP) into a hybrid filter where part of the electrodes were removed and filter bags were fitted in place in 2001. Here tests were carried out with and without ESP in operation. The second mill in Kunda, Estonia is exclusively equipped with a FF from start up of the plant in 2005. The filtration behaviour of the filters in different operational states is assessed using the permeability distribution (PD) method to characterize the different filtration behaviour of the cloth/dust combinations observed.

EXPERIMENTAL COMPARISON OF FRACTIONAL EFFICIENCY MEASUREMENTS ACCORDING TO ISO TS 11155-1, ISO 5011, EN 779 AND ISO CD 20564
M. Schmidt and S. Schütz (pages 300-303)

International standards – ISO TS 11155-1 for cabin air filters, EN 779 for general air ventilation filters, ISO 5011 for engine air filters or filter media, and ISO CD 20564 for crankshaft ventilation filters – are developed for the producer and user of these filters to compare their special characteristics under defined and comparable conditions.

International round robin tests according to ISO TS 11155-1/DIN 71460-1 and EN 779 accomplished by different laboratories using these test systems have previously shown large differences, especially in fractional efficiency measurements. For example, the international round robin tests according to ISO 11155-1 accomplished in 1999 and 2004 showed differences in initial fractional efficiency at 0.3 micron of up to 70%. Nonetheless, the measurement of fractional efficiency is an important tool to characterise the efficiency of filters and filter media unambiguously.

We will show that good comparisons of different test rigs according to ISO 11155-1/DIN 71460 can be achieved even when using different particle measuring systems. Additionally, we will present the comparison of two HMT-1000 Palas test rigs for blow-by filters and two Palas® test rigs for filter media testing of cabin air filters or motor air engine intake filters.

ROLE OF FLOCCULANT INJECTION AND MIXING CONDITIONS IN SLUDGE FLOCCULATION
P. Ginisty, C. Peuchot and A. Premel (pages 304-308)

This work deals with the effects of dispersion/mixing parameters on sludge flocculation efficiency before thickening on a drainage table and dewatering on a belt filter. The first part of the paper concerns sludge flocculation in an agitated tank at the laboratory scale. Camp numbers were determined. The kinetics of floc growth were followed by a Turbiscan apparatus and the efficiency of flocculation was determined by gravity drainage and CST tests. The main parameters influencing the process are the energy dispersed and the time of polymer dispersion and floc growth. Additional factors are the impeller design and polymer characteristics. Results enabled a new laboratory protocol to be defined and the optimisation of sludge flocculation. The second part of the paper concerns sludge flocculation in pipes in wastewater treatment plant.

A specific apparatus was designed to measure Camp numbers and to test different kinds of injectors, addition points and in-line mixers. The impact of the hydrodynamic conditions used during flocculation on drainage table and belt filter performances was evaluated. Results showed that Camp numbers are not sufficient to qualify hydrodynamic conditions and compromises should be found between floc growth and breakage. Even though the mechanisms of sludge flocculation were difficult to fully understand, practical and specific recommendations are made to enable optimised hydrodynamic conditions to be chosen according to site configuration.

AN IMPROVED METHOD FOR WASHING LIGNIN PRECIPITATED FROM KRAFT BLACK LIQUOR – The key to a new biofuel
F. Öhman, H. Wallmo and H. Theliander (pages 309-315)

In a previous study on the washing of lignin precipitated from kraft black liquor, problems with complete or partial plugging of the filter cake and/or filter media were encountered that resulted in uneven washing and high sodium contents in the final lignin product. This effect was ascribed to large gradients in pH and ionic strength during the washing process. Based on this understanding of the phenomenon involved, an improved method for lignin washing was developed, which gave very successful results in laboratory scale trials.

In the continuing studies on lignin separation from black liquor within the FRAM (Future Resource Adapted pulp Mill) research programme, this method was evaluated in bench scale and small pilot scale trials. These trials were equally successful and it was shown that kraft lignin with low sodium content (<0.5% by weight), high dry solids content (62.5% on average) and high calorific value (LHV 25.4 MJ/kg) could be produced. There were no particular problems encountered in scaling up the new method from laboratory scale (filter area 20 cm2) to the small pilot scale (filter area 1.7 m2). The investigated separation properties concerning filtration and washing were found to be similar for bench scale and pilot scale experiments.

EXAMPLES OF AIR FLOW PATTERNS IN FOOD PRODUCTION AREAS
D. Burfoot (pages 315-322)

Air movements can transport particles, including those containing microorganisms, around food production areas. The sources of particles may be within or outside the production area. Sources of such contamination must be restricted and the air guided such that the risk of particles landing on the food is low. Examples are given of the movements of airborne particles in chilled food factories, bakeries, and slaughterhouses. Although the level of sophistication of the air handling systems are different in each case, and the composition of the aerosols are also dissimilar, the need to maintain a good direction of air flow remains important. In general, air should flow out of the production area, and from clean areas near to the food towards lower-care areas. It will be demonstrated that providing sufficient clean air to produce a positive pressure in the production area, based on average flow rates, is not always sufficient to prevent contamination entering the production area.

THE PRODUCTION AND CERTIFICATION OF PRECISION SLOTTED SIEVE STANDARDS
G. Rideal (pages 322-324)

Calibration of slotted sieves using vernier micrometers has given rise to measurement uncertainties in the past. Calibration microspheres have been shown in a recent report to give promising results but their accuracy depends on two important factors. Firstly, the ability to accurately measure the widths of melt produced glass microspheres, which are not 100% spherical and, secondly, the need for narrow particle size distributions that give the highest resolution in the calibration process. This paper discusses the production of narrow particle size distribution glass microspheres and the development of a high precision slot device for calibrating the standards. The certified reference standards were then used to calibrate a 2.5 mm slotted sieve.

PARTICLE-PRESSURE INDUCED TRANSIENT CHANGES IN OSCILLATED PARTICLE-FLUID SYSTEMs
M. Davis and M.A. Koenders (pages 326-336)

From the general flow equations for a particle-fluid mixture both the oscillatory behaviour and the secular (that is, quasi-static) process can be derived. The two are coupled via a mean net stress component, called the particle pressure, in a rapidly agitated medium. In a septum-vibrated dead-end filter the particle pressure is generated near the septum. The secular changes that take place as the vibration is increased can be gathered in a set of coupled equations. The effects that are observed in permeation experiments are then reproduced from the theory. These include a critical point at which the flow rate rapidly increases. The rheology of a packed bed that is agitated by a cyclic strain is then investigated and its non-linear character is elucidated. The non-linear clogged septum rheology is also investigated, so as to obtain an impression of the stress dependence of the clogged septum permeability. Combining rheology and incremental secular equations of motion enable an understanding of the features of the flow rate vs. oscillation amplitude. Rough estimates of the various parameters show that the effects the theory describes are corroborated by experiments. Of special interest is the critical point, at which the flow rate through the filter increases rapidly with incremental oscillation amplitude.

ARTIFICIAL NEURAL NETWORK MODEL TO PREDICT COMPRESSION-PERMEABILITY CHARACTERISTICS OF SOLID/LIQUID SYSTEMS
M. Iwata, M.S. Jami and S. Shiojiri (pages 337-344)

A statistical modelling tool called artificial neural network (ANN) is used in this work to predict the compression-permeability (C-P) characteristics of a solid/liquid system. An extensive cake properties database containing experimental data that spans various material types, particle size distribution, flocculated and unflocculated particles has been developed and used to train two ANNs. The input parameters for the first ANN were the applied pressure and the particle size distribution whereas the output parameter was the porosity of the compressed cake. In the case of the second ANN, the input parameters were the porosity and the particle size distribution. The logarithm of the specific cake resistance multiplied by the particle true density of the cake (log (αρs)) was chosen as the output parameter of this network.

The use of porosity obtained from gravitational and centrifugal sedimentation experiments as one of the input parameters to the ANNs gave excellent results in predicting both the cake porosity and the specific cake resistance. With the help of this method, after the ANN is thoroughly trained with various slurries, the C-P characteristics of another slurry can be predicted with much less of the target slurry compared with that used in a conventional C-P test.

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Volume 8, Issue 1 Abstracts from the FILTRATION journal

AUTOMATION IN FILTRATION SYSTEMS: HOW TELEMETRY COULD IMPROVE OPERATING MARGINS FOR BOTH SUPPLIER AND OPERATOR
D. Harris (pages 34-37)

The operation of separations equipment can be labour intensive, with high consumables costs. Incorrect operation or equipment malfunction may directly impact process economics. The use of automation at the simplest level may allow better planning of scarce labour resource interventions or avoid unexpected process upsets. More sophisticated automation of the system, in combination with the selection of the right separations technology, may significantly reduce or practically eliminate the need for manual intervention in normal operation.

At the highest level, systems can be augmented with remote monitoring and telemetry, allowing installations to send operating data and requests for assistance to a central location. Through the communications network, alerted engineers can take control of the system from their desk to perform diagnostic investigations, make operational modifications, and determine when there is a requirement for physical intervention. Similar systems may also allow the effective operation of multiple pilot trials in different locations, or even different countries, with a minimum of engineering staff required for support.

Case studies are presented to describe the various approaches taken, and outline some of the cost benefits that may be achieved both by the process owner and by the equipment vendor.

NEW THINKING ON WET MAGNETIC TREATMENT OF FELDSPAR
P. Fears (pages 38-39)

Traditionally, magnetic separation has only been introduced into the processing flow sheet of a feldspar operation at the dry stage, late in the process. Flotation is used to remove most other contaminants. Now, as companies try to reduce their reliance on flotation, wet high intensity magnetic separation is proving to either partially or totally replace the need for flotation.

COMPARISON OF MEMBRANE FILTER PRESSES WITH BELT FILTER PRESSES AND CENTRIFUGEs
E. Mayer(pages 40-49)

Wastewater sludge dewatering is usually accomplished by three devices: solid-bowl decanter centrifuges, belt filter presses, and recessed filter presses (both standard and membrane (or diaphragm)). Of these, the membrane filter press produces the driest cakes (as well as the cleanest filtrate), which is best suited for land application, incineration, or further processing. As a consequence, most wastewater sludge dewatering in Europe utilizes membrane filter presses, while belt filter presses and centrifuges are primarily used in the US because of more landfill space. However, space is becoming limited and more filter presses are being utilized in the US. This paper presents an overview of membrane filter presses, where they have been used, and how they compare to centrifuges and belt filter presses via many case histories for a variety of wastewater sludges.

A NEW METHOD TO DETERMINE the PARTICULATE FILTRATION EFFICIENCY OF SUBMICRON CARTRIDGE FILTERS
C. Peuchot and N. Petillon (pages 50-55)

Submicron cartridge filters are broadly used to clarify, purify or decontaminate many liquids in several industrial fields. Such applications are the processing of ultrapure liquids for making electronic components, the cold sterilisation of wines, bioliquids and pharmaceutical solutes, and the decontamination of industrial solvents and washing liquids. Microfiltration cartridge filters, with ratings below 3 µm, are installed as prefilters and are pleated, agglomerated or wound. The performance and ability to use these prefilters are determined in laboratory conditions according to standard methods adopted by filter makers and large end users. For instance, the rating is determined using water or a mineral oil as the test fluid, ISO MTD according to ISO 12103 as a test powder, and online particle counting with light extinction instruments to count particles at various sizes upstream and downstream of the test filter to calculate its instantaneous efficiency.

Reading technical brochures of submicron filters show they are mainly characterised by their microbial rating (they are regarded as sterilising if they reduce to a given ratio the number of standard microorganisms). Very few brochures state a micron rating based on particle size and when they do, they do not refer to any test method. To answer the need of several large end users, IFTS has developed a new protocol to measure filtration efficiency during the clogging of submicron and microfiltration cartridges. This paper describes the test powder chosen, the test circuit designed, validation results, criteria and typical test results obtained for several cartridges bought on the market.

ON-LINE MONITORING AND OPTIMISATION OF BAGHOUSE FILTER OPERATIONS TO REDUCE OPERATING COSTS AND MINIMISE PARTICULATE EMISSIONS TO AIR
W. Averdieck (pages 55-58)

Operators of many industrial plant have made significant improvements in reducing particulate emissions to air by fitting high performance baghouse dust collectors. Emissions from such processes are highly abated provided the baghouse filter operates to its design condition, and the relevant control issue is to effectively monitor for changes in the condition of the bag filter associated with filter leakage and bag rupture.

ABOUT 20 YEARS OF OPERATION EXPERIENCE OF WASTEWATER FILTRATION IN GERMANY
M. Barjenbruch and T. Rolfs (pages 59-64)

In 1977, the first large-scale wastewater filtration in Germany started operating (in the city of Darsheim). The number of applications stagnated for several years, but at the beginning of the 1990s wastewater filtration units were installed due to the demand for lower effluent values to protect the water bodies. Currently, about 180 wastewater filtration plants in different technical variations are in operation. Most of them were built to observe very low phosphorous concentration values (< 0.5 mg Ptot/L). The German standards of dimensioning and design are summarized in the DWA Working Sheet A 203 (1995) “Wastewater filtration with deep bed filters after biological treatment”. After about 20 years of operation, a great number of experiences have been obtained which are presented in this report, with particular reference to the design and the operation of filtration units planned in future.

OXYGEN ENRICHMENT OF AIR FOR DIESEL ENGINES: A PROCESS EVALUATION STUDY
P. Chitta and B.J. Tatarchuk (pages 66-71)

Supply of oxygen enriched air helps increase reaction conversion rates and efficiencies in various combustion applications such as in diesel engines. This paper discusses the results of sorbent screening. Initially the sorbents are screened based upon nitrogen adsorption and moisture removal capacities at different activation temperatures and adsorption times. This study includes testing of the active zeolites under multiple adsorption-regeneration cycles. The results are presented as N2 and O2 adsorption isotherms. Finally, a comparative study of various cyclic adsorption-desorption processes comprising of pressure swing, temperature swing, temperature aided pressure swing and rapid pressure swing is presented. The adsorption experiments are carried out in a fixed bed reactor and the sorbents consist of molecular sieves and other cation exchanged zeolites that include LiLSX, RE-LiLSX, LiX, NaX, LiCuX, 13X, 3A, 4A and 5A types.

SIMILARITY ANALYSIS OF CONSTANT PRESSURE CAKE FILTRATION
A.K. Gholap, J. Peddieson and S. Munukutla (pages 73-79)

A similarity analysis of constant pressure cake filtration was carried out based on a single set of governing equations applicable to both the cake and slurry regions. A finite difference method was used to obtain numerical solutions for several forms of the effective diffusivity function appearing in the model. A representative set of results is presented graphically. It was found that, while details of the predicted concentration profiles were quite diffusivity function sensitive, certain qualitative features of the predictions were diffusivity function insensitive. This suggests that experimentally observed details of the behaviours of specific slurries can be matched with particular diffusivity functions while preserving qualitative features common to all slurries.

SIMULATION OF LIQUID PHASE ACCUMULATION FOR THE CENTRIFUGAL DEWATERING OF ACTIVATWD SLUDGE
M. Mota, J.A. Teixeira, G.N. Abaev, I. Yelshyna and A. Yelshin(pages 80-86)

Centrifugation of activated sludge is a frequently used dewatering process but, in spite of this, there is a need for a fitting function for moderate and high sludge concentrations. Liquid phase accumulation kinetics during centrifugation may be used as a source of information about the sedimentation properties and the governing mechanism during cake formation. For this purpose, activated sludge at different concentrations was investigated on a laboratory centrifuge with a centrifugation factor of 2667. The following sludges were used in the experiments:

(1) Activated sludge from a thickener (with and without flocculant treatment)

(2) Sludge taken after an industrial centrifuge decanter, treated with Flottweg Z62-4 flocculant and collected from a dumping pound

(3) Sludge (2) after anaerobic treatment

(4) Sludge (2) with a dispersed solid additive.

Using the experimental data for an asymptotical analysis, a dimensionless fitting function was obtained that adequately describes the dependence of liquid volume vs. time for the centrifugation of activated sludge. For the highly concentrated sludge it was found that the dewatering occurs through cake compression. Analysis of deformation models leads to the conclusion that for the compressible cake it is necessary to introduce a parameter characterising the cake plasticity dependence on the centrifugation time. The developed model was validated by fitting numerous experimental data. The main advantage of the proposed model is the possibility to fit the liquid phase accumulation kinetics during centrifugation over a wide range of activated sludge concentration values, from suspensions up to structured and paste-like cake consistency.

simulation OF LIQUID phAse ACCuMULATION FOR THE centrifugal dewatering of Activated Sludge

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Volume 8, Issue 2 Abstracts from the FILTRATION journal

SUPPRESSION OF ‘FILTER CAKE’ WITHIN A MEDIA PRESSURE FILTER BY VORTEX SURFACE SCOURING
D. Ward, S. Cupples, R. Poole and I. Owen (pages 114-119)

The findings reported in this paper demonstrate that ‘filter cake’, and its associated contribution to head loss in a media pressure filter system, can be suppressed by the employment of a swirl-inducing tangential inlet without any loss in separation efficiency. The likely mechanism for this performance enhancement is the creation of a vortex-induced crossflow scouring action which prevents cake formation. Instead of being retained as a thin, dense layer at the surface of the filter, particles are believed to be either held in motion above the bed or given the opportunity to penetrate the bed and collect over a greater bed depth, thus producing a lower contribution to overall system head loss by utilising media voidage more effectively. This further improves filter performance by reducing backwash cycle frequency and therefore the overall amount of contaminated backwash water requiring disposal.

INNOVATIVE TECHNOLOGIES IN WATER TREATMENT BASED ON ULTRAFILTRATION
T. Peters (pages 119-123)

Even though important innovations have been created in the last two decades that contributed to the realisation of a great variety of membrane-based solutions and industrial processes, there can still be further optimisation and important improvement in different areas of membrane technology. One of the areas is water treatment or purification with ultrafiltration, including drinking water, process water and waste water. Due to the different spectra of components or degrees of contamination in these liquids, a wide range of possibilities regarding the design, manufacturing and operation of related plants has had to be developed.

At one extreme are waters with a low level of contamination, that can be processed with the deadend operation mode. At the other are waste waters or process waters with a high burden of components or contaminants, that can only be treated with the crossflow operation mode. One example for an innovation in low contaminated applications is a module with capillary membranes with a much higher membrane area than usual and improved internal hydraulics based on flow dynamic calculation. At the other extreme a new system has been developed where the crossflow velocity of the liquid over the membrane is realized by pumping this liquid through nozzles into the open channel formed between two disc membrane cushions fixed as a disc cartridge.

CHARACTERIZING A FILTER MEDIUM
P.R. Johnston (pages 124-128)

In rating a filter medium for a possible filtration job, the outline approach is to determine (1) materials of construction, (2) thickness, (3) porosity, (4) viscous permeability, then (5) calculate the viscous flow averaged pore diameter from (3) and (4). For some uses a strength test must be performed. Media composed of random arrays of materials, such as mats of short fibres, sintered granules, and solvent-cast membranes, all have the same kind of pore diameter distribution – the same ratio of the standard deviation to the mean – making it possible to understand fluid extrusion measurements that seek pore size distributions.

The method of determining the bubble-point – starting with a liquid-soaked medium, forcing air against the bottom face to blow open the largest pores on the top face – is an eyeball determination and not standardized. Extending that test to blow open successively smaller pores, gives the ‘mean flow pore’ – half the pores have been blown open. Yet gas flows are then in the inertia, and sometimes Knudsen, range rather than in viscous flow. The ‘mean flow pore diameter’ is 3/4 of the viscous flow averaged pore diameter. The liquid drainage test – air on the top face forces liquid out the bottom face, but stops short of blowing gas out of the bottom face – reflects the viscous flow pore diameter distribution on the bottom face. The mercury incursion test is not useful.

THE USE OF ELECTROSTATIC FILTER MEDIA IN THE DEVELOPMENT OF A NEW PERSONAL AEROSOL SAMPLER M.M.
Abdel-Salam (pages 129-134)

Impacts of aerosol particles on human health have led to the design and development of a wide range of aerosol samplers; primarily for measuring airborne aerosol concentrations and human exposure. Many such instruments, based on a wide range of different physical principles, have emerged over the years, and some have been commercially successful. However, conventional pumped aerosol samplers still have limitations which make the personal sampling process difficult, including: high cost; high power demand; limited sampling time; and invasive to wearers due to high noise levels, heavy weight, large size, and loose tubing. The new aerosol sampler design described in this paper reduces or eliminates many of these limitations.

The new sampler design utilizes a low resistance electrostatic filter media (electret) to collect aerosol in a fan-driven system, eliminating the greater power requirement of traditional air sampling pumps. Use of electret media offers advantages in the design of an aerosol sampler. Lower filter resistance requires less power which allows use of smaller batteries and fans, and this has led to the design of an integrated electret-fan personal aerosol sampler. Besides size and weight reduction, the new sampler design also has the added benefits of quiet operation, long sampling duration, and low cost. The new personal aerosol sampler has less invasive design that allows more convenient use in home and office environments, as well as industrial and ambient environment settings.

MULTI-LAYER DEEP BED FILTER FOR MICRON/SUBMICRON SEPARATION
T. Bahners and E. Schollmeyer (pages 135-139)

The scope of the presented work was to study the separation of micron and sub-micron model particles from fluid systems by a deep-bed filter concept consisting of a multilayer stack of combined nanofibre/nonwoven layers. The nanofibres were intended to form an irregular small pore system with both high porosity and high flow properties. Nanofibres of an average diameter of 12515 nm were produced from polycaprolactone (PCL) by electro-spinning, a commercial nonwoven serving as the base of the individual layers. Polystyrene (PS) spheres suspended in water served as the model system. The model filters were characterized with regard to separation efficiency, flow rate and separation morphology.

The measurements showed a significant improvement in the separation of 2 µm particles by adding the nanofibre web. A two-layer stack of the combined filter system exhibited a separation efficiency significantly higher than 90%, which compares to 45% for a similar stack of the conventional system. While the nanofibre web reduces the flow rate, the superior performance results in a positive net effect. High separation efficiency was also found in the sub-micrometre regime. SEM analyses indicate an increased importance of impact separation in the filtration process.

EFFECT OF AERATION ON ALUM CONSUMPTION AND SETTLING CHARACTERISTICS DURING WATER TREATMENT
J.O. Babatola, T.O. Saiki and M.O. Ogedengbe (pages 140-143)

The role of aeration prior to coagulation in conventional surface water treatment was investigated. Samples of stream water, some aerated for varying periods by rigorous mixing and some unaerated, were treated with varying dosages of 1% solution of commercial alum. The samples were rapid-mixed, slow-mixed and settled. Turbidity readings and pH values were taken. The results show that pre-aeration is beneficial in terms of up to 30% saving in alum consumption and improved settling.

PREDICTION OF FILTRATION CHARACTERISTICS BY MULTIVARIATE DATA ANALYSIS
A. Häkkinen, K. Pöllänen, S.-P. Reinikainen, M. Louhi-Kultanen and L. Nyström (pages 144-153)

The behaviour of solid/liquid suspensions during filtration processes is strongly influenced by the properties of the particles and the liquid phase. Although prediction of common filtration characteristics, such as cake resistance, cake porosity and compressibility, has been studied extensively, general theoretical models that could be applied to complex real-life suspensions do not exist. Prediction of filtration characteristics has proved to be difficult even in those cases where an extensive set of experimentally obtained material data are available. This is due to the complexity of the cake formation process, which means that the number of influential variables that should be simultaneously considered in the models is large. Traditionally applied calculation and modelling techniques have been incapable of processing such large sets of input variables, which has consequently restricted the complexity of the models.

This paper introduces an alternative procedure for predicting the filtration characteristics of solid/liquid suspensions from measured material properties. Empirical models were created using multilinear partial least squares regression (N-PLS) for the experimentally determined pressure filtration parameters and the particle size and shape data obtained by an automated image analyzer. The density and dynamic viscosity of the liquid phase were also included in the models as input variables. The filtration characteristics of the test suspensions were described by four different parameters and separate models were derived for each parameter. All four models were tested with an independent set of samples in order to validate the created models. The results presented in this paper show that the procedure can be applied to create models that enable filtration characteristics to be reliably correlated with particle size and shape distributions.

N95 FACE MASK UNDER INCREASING SOLIDS LOADING AND MOISTURE
W.W.-F. Leung, J. Chung, C. Tsang and C.-H. Hung (pages 154-164)

Submicron particles can be pollutants from engine emissions (0.02-1 μm), or airborne contagious virus (0.05-0.2 μm). The N95 face mask has been employed to remove the finest particulates in the submicron range. In our filtration experiments, exhaust gas from a diesel engine laden with submicron particles was used to challenge the test N95 face mask with a gas velocity of 0.05 m/s. Measurements were taken over an extended 6 h period under heavy solids loading.

Among the three layers only the middle ‘filtration’ layer of the N95 face mask was used in the test. Over the 6 h period when solids loading generated from the engine emission increased linearly from zero to 2.83 g/m2, the pressure drop across the filter increased nonlinearly from 19.6 Pa at no loading condition to 36.0 Pa. The ratio of downstream particles (penetrating the filter) to those upstream stayed relatively constant for 0.3 μm particles, whereas for 0.05 μm particles this penetration ratio decreased rapidly from 30 to 0.2 %. The reduction in penetration of the fine particles (less than 0.1 μm) with solids loading is quite interesting.

The quality factor qf which measures benefit versus costs showed that during extended use of the N95 face mask, the qf reduced for particles greater than 0.1 μm due to constant capture efficiency yet increasing pressure drop, whereas for particles less than 0.1 μm, qf increases due to lower penetration (i.e. much higher capture efficiency) but only at modest increase in pressure drop. Unless there is excessive sweating causing the face mask to be fully wetted with liquid for which the electrical charges of the fibres are neutralized, the capture efficiency of the mask may only be reduced slightly due to the loss of electrostatic charges in attracting particles with opposite charges.

MODELLING OF DEEP BED FILTRATION WITH SCALE-DEPENDENT DIFFUSION AND SUPERFICIAL VELOCITY
A. Al-Mudhaf, A.J. Chamkha and J.M. Al-Humoud (pages 164-172)

A one-dimensional continuum deep bed filtration model with scale-dependent diffusion or dispersion coefficient and filter superficial velocity is considered. The diffusion coefficient and superficial velocity are assumed to increase according to a polynomial function with the filter longitudinal distance. A general mass transfer that characterizes particle attachment and detachment effects is considered. Since the general problem is nonlinear and possesses no analytical solutions, a numerical solution based on an efficient implicit finite-difference method is obtained. Comparisons with exact and approximate analytical solutions for special cases of the filtration model are performed and found to be in excellent agreement.

A parametric study of some physical parameters is conducted and the results are presented graphically to illustrate interesting features of the solutions. It is found that the presence of a particle detachment mechanism has significant effects on the solute concentration and specific deposit profiles at all filtration times. In addition, the scale-dependent polynomial-type diffusion coefficient and superficial velocity are predicted to yield significant changes in the solute concentration, specific deposit and filter efficiency at all filtration time stages compared with their corresponding constant cases.

D. Ward, S. Cupples, R. Poole and I. Owen
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Volume 8, Issue 3 Abstracts from the FILTRATION journal

GUARANTEE HIGH DUST COLLECTOR EFFICIENCY AND PRESERVE PROFITS
A. Dotti (pages 194-197)

Tyco Environmental Systems, through its Goyen and Mecair brands, provides a unique service to fabricators of dust collectors and those who use them. The GOCO software accurately models the cleaning of filters in on-line reverse pulse jet applications. This tool allows the full optimisation of the dust collector’s filter cleaning system taking into account the details of the particular application. More than ten years of operation and improvement to the software have shown GOCO to be a highly effective way to eliminate risk in the design and minimise operating costs associated with filter replacements and compressed air energy.

Now, the global experience and capability of Goyen Mecair is taking the GOCO configuration a step further by supplying the complete cleaning system ready to go to the fabricator. Such capability markedly reduces the fabricator’s risk of a failed filter cleaning system.

AHLSTROM DISRUPTOR™: NANOALUMINA FIBRE WATER FILTRATION MEDIA
R. Komlenic (pages 197-201)

Historically, there have been relatively few significant changes in filter media. With its natural electrokinetic potential and the ability to function through both electroadhesion and mechanical entrapment to effectively remove viruses, bacteria and particulates at high flow rates, nanoalumina fibre based Disruptor™ technology represents one such change. It is a multifunctional depth filter medium, effective for many water polishing applications. The nanoalumina media can also be used as a support scaffold for a wide range of very fine or nanopowders to impart compound specific adsorbance.

MICROFILTRATION WITH ROTATING MEMBRANES
Y. Taamneh and S. Ripperger (pages 202-207)

In many processes in the chemical industry and in environmental techniques it is necessary to separate finely dispersed solid/liquid systems in order to get either the regenerated solids or the solid-free liquid. Membrane filtration often relies on the presence of a shear stress at the membrane surface to reduce the accumulation of foulants. In classical crossflow filtration with membrane modules, the shear stress is brought about by tangential flow along the membrane surface which leads to pressure drops. For high concentration suspensions, the shear stress to reduce fouling may be so high that the required flow rate would induce an unacceptably high pressure drop. In cases of fractionation or classification a uniform trans-membrane pressure is needed for a high efficiency separation. For the rotating disc filter, the shear stress and flow are not alike since shear stress is only a function of the rotational speed. Therefore, these filters appear to be most applicable to the filtration of high concentration suspensions. Commercially, rotating disc filters have been implemented both as membrane discs rotating between stationary baffles and as fixed membrane discs next to rotating baffles.

In the following, filters with rotating membranes will be presented and their special advantages explained. The multi shaft disc (MSD) separator is designed in such a way that the membrane discs are mounted on two hollow shafts and form a shear gap. The opposite movement of the discs enhances the shear stress over the surface of the membranes. The solid/liquid separation process using such rotating membranes is often performed as a continuous operation to ensure an uninterrupted production process and a high efficiency (high filtrate flux at minimum energy input). Experimental results with an MSD separator and centrifugal disk (CD) filter are presented. The machines could be used as a new classification technique for the separation of a fraction of very fine particles, thereby avoiding cake formation.

A STUDY OF THE MECHANISM OF WET AND DRY FILTRATION USING NIST TRACEABLE GLASS MICROSPHERES
G. Rideal, E. Roberts, A. Stewart and J. Storey (pages 207-210)

This work investigates the performance differences in filter media depending on whether the challenge test is conducted in the dry state or using a liquid suspension of microspheres. Comparisons of filter cut points between a pulsed air flow and a single pass liquid suspension method were used to investigate the mechanisms of filtration. Depth filtration effects were examined by comparing 2-dimensional filters (precision electroformed filters) to moderate depth filters (pillow fabric and needlefelts) and a 3-dimensional depth filter (water cartridge filter). No differences were found for 2-dimensional filters but significant differences in performance were found between wet and dry analysis of 3-dimensional filters. There was little evidence of secondary filtration in the suspension method for concentrations from 0.2% down to 0.025%.

DEFOULING OF POLYMERIC MEMBRANES DURING MICROFILTRATION PROCESSING USING ULTRASOUND IN VARIOUS MEMBRANE MODULES
A. Maskooki, S. Ali.Mortazavi and A. Maskooki (pages 211-217)

The cleaning effects of ultrasound on the surfaces and pores of polymeric membranes have been proved for many years. In this paper, the defouling of three kinds of membrane at various ultrasound frequencies were investigated. The three membrane modules, hollow fibre, flat sheet and spiral wound were cleaned by irradiation at 28, 45 and 100 kHz and a constant intensity of 300 W during forward flushing with ultrapure distilled water for 30 mins. after fouling by 1% skimmed milk. The statistically analyzed results showed that the best cleaning effects are obtained for the hollow fibre membrane, using all tested frequencies during the first 5 mins. of ultrasound application; this is due to the lack of barriers such as a holder or membrane support in the module design. Although cleaning effects were observed for the flat sheet membrane module using ultrasound, especially at a frequency of 28 kHz, the cleaning efficiency at the same conditions was lower than for the hollow fibre system. The stainless steel and acrylic holders used in the module design prevented sonic power from reaching the surfaces and pores of the membrane which may be mostly due to turbulence of the feed and permeate solution by ultrasonic waves. The minimum ultrasonic cleaning effects were obtained with the spiral wound membrane module in which only the outside layers were affected. This is a consequence of the special module design and the barrier effects of the configuration and membrane holders.

POLYELECTROLYTE CONDITIONING EFFECT IN SLUDGE ELECTRODEWATERING
H. Saveyn, G. Pauwels, R. Timmerman and P. Van der Meeren (pages 218-224)

Activated sludge is known to poorly dewater due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering of sludge can enhance the dewaterability by the electroosmosis effect.

A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge compared to mere pressure dewatering. It was found that application of the electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered pressure dewatering, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.

CHARACTERIZATION OF SLUDGE FILTRATION
H. Yukseler, U. Yetis and I. Tosun (pages 224-229)

Buchner funnel filtration tests using an activated sludge obtained from a nearby wastewater treatment plant are analysed in the light of the multiphase filtration theory which states that the controlling factor in filtration is not the resistance of the cake but the resistance of the cake-septum interface. Experimental results indicated that the pore size of the filter medium strongly affects the filter performance. It is concluded that up-flow Buchner funnel experiments must be carried out using an industrial scale filter medium.

A NOVEL METHOD FOR IMPROVING LOW SEPARATION PERFORMANCE OF TOLUENE FROM N-HEPTANE VIA EMULSION LIQUID MEMBRANES CONTAINING SUBSTITUTED CYCLODEXTRINS AS CARRIERS
M. Chakraborty and H.-J. Bart(pages 229-237)

The selective separation of toluene from n-heptane is investigated using unsubstituted α-cyclodextrin (αCD), β-cyclodextrin (βCD) and also with two substituted CDs as a carrier in oil/water/oil-type emulsion liquid membranes. The separation factor for toluene to n-heptane is evaluated from the extraction of an equimolar mixture of toluene and n-heptane. βCD shows the highest selectivity followed by αCD, hydroxypropyl-αCD and hydroxypropyl-βCD. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: contact time, concentration of carriers, volume fraction of the membrane phase and the relative amount of solvent. The dispersed drop sizes as well as internal droplets sizes define the interfacial contact area and are important in determining efficiency of extraction and stability of the liquid membrane. The effects of carriers and interfacial tension on dispersed phase drop size, internal droplets size and size distribution are also systematically investigated.

NUMERICAL STUDY OF FLOW AND PRESSURE CHARACTERISTICS FOR DIESEL PARTICULATE FILTERS WITH SQUARE AND TRIANGLE CHANNELS
X. Zhang (pages 238-247)

In a previous paper the effects of filter wall permeability, channel length and width, as well as inlet mass flow rate on velocity distributions and pressure loss were investigated for diesel particulate filters (DPFs) with square channels. The current study is focussed on investigations of fluid flow and pressure drops inside a comparable DPF with triangle channels. Two DPFs with equilateral triangle channels are considered: one has the same channel width as the square channel DPF and the other has the same total open frontal area. A triangle structure with the same channel width has more individual channels and larger total filter wall surface area. The total filter wall surface area is the same when both structures have the same total open frontal area.

The effects of filter wall permeability, channel length and width, as well as inlet mass flow rate were studied by 3-D numerical simulations. The velocity profiles along the centrelines of channels, as well as inside the filter wall, are compared. For the same channel width and length, triangle channels result in much lower filter wall velocity and much higher velocity along the centrelines of inlet and outlet channels which leads to higher pressure loss. For the triangle channel geometry, flow transitions are observed as wall permeability increases or channel length increases and (compared with square channels) the transitions occur at much lower wall permeability and shorter channel lengths. Flow transition is delayed for an increase of channel width. The optimal channel length for triangle channels is dependent on channel width and a correlation is given. Results show that a much smaller optimal channel length is required compared to a square channel with the same channel width. The advantages and disadvantages of using triangle channels are discussed regarding pressure loss and soot loading capacity.

A NEW METHOD TO OBTAIN INFORMATION ABOUT THE PORE SIZE DISTRIBUTION IN MICROPOROUS POLYMERIC MEMBRANES
J. Llorens, P. Marco, J. Sabaté, M. Pujolà, I. Felip and E. Plumed (pages 248-251)

Transport measurements of selected fluids through porous membranes provide information on precise statistical moments of the membrane pore-size distribution (PSD). It is assumed that membrane porosity, εT, is distributed on different pores sizes which are statistically distributed. Mean pore sizes are determined on the basis of statistical moment analysis. This paper focuses in the special case of determining PSD in microfiltration (MF) membranes from a collection of experiments that include porosity and bubble point determinations and liquid and gas permeations.

INTERDEPENDENCE OF FINE PARTICLE FILTRATION PERFORMANCE AND DUST LOAD FOR ELECTROSTATIC MEDIA
J.A. Schütz (pages 252-258)

In this paper changes of penetration and pressure drop in electrostatic filter media that are caused by the capture of fine particles from a gas stream passing through the medium are approximated by a set of fit functions. These functions are shown to provide excellent representations of experimental data obtained from an electret split-fibre medium, a highly charged tribo-electric medium and an uncharged needlefelt. The media are benchmarked by relative comparisons of respective quality factor dependencies.

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Volume 8, Issue 4 Abstracts from the FILTRATION journal

MEMBRANE BIOREACTORS (MBR) – AN ADVANCED PROCESS FOR WASTEWATER TREATMENT
C. Deakin (pages 282-285)

Public concern over health and the environment, combined with increased requirements for municipalities to reuse wastewater, have created a need for new technologies that can generate high quality effluent at low cost. Throughout the world, there are many membrane bioreactor (MBR) systems in operation with many more in the design/construction phase. These range from small to large systems, treating both municipal and industrial wastewater. Small MBR systems are often used for water reuse within commercial developments, such as office complexes or shopping malls, whereas municipalities and industries operate the larger plants.

IMPROVING SEA WATER DESALINATION WITH REVERSE OSMOSIC
T. Peters (pages 285-288)

There is an ever increasing demand for potable water and high quality water for industrial applications. The areas affected are not only the arid regions in the world with their chronic water deficiency, but also urban agglomerations and industrial centres, especially in coastal areas where the capacity limits of natural supplies have almost been reached.

One possibility of rapidly growing importance, and in some cases the only remaining option to satisfy the increasing demand for good quality potable water for an increasing population, is the desalination of seawater. For this, the membrane process reverse osmosis is used increasingly. But even if in the last three decades numerous important technological improvements have helped to create a reliable and cost effective process, developments have been implemented recently that contribute to a further reduction of water production costs. Amongst others, these are the installation of energy saving devices instead of energy recovery units, the use of ultrafiltration as a pre-filtration step, and the innovative seawater intake and partial pre-treatment Neodren that will be discussed here in detail.

TRENDS AND TECHNOLOGY RELATED TO FILTER MEDIA DEVELOPMENT
R. Lydon (pages 289-295)

It is often said that at the heart of any filter is the filter medium which determines whether a filter process will perform adequately to give the desired separation efficiency. One of the key roles of a filter medium is to create a clear separation of particulate from a liquid or gas with the minimum consumption of energy. This paper describes some of the latest developments in filter media technology.

COMPUTER SOFTWARE FOR THE AUTOMATED SPECIFICATION OF SOLID/LIQUID SEPARATION EQUIPMENT
E.S. Tarleton and R.J. Wakeman(pages 295-302)

This paper details Filter Design Software® (FDS), Windows® software for the selection and simulation of solid/liquid separation equipment as well as the analysis of test data. FDS was developed in collaboration with multi-national companies spanning a wide range of industrial sectors to provide a comprehensive calculation, education and training tool that maintains a balance between ease of use, level of knowledge conveyed and comprehensibility. FDS is a sequence of interlinked modules that can be used independently from one another. The full set of FDS modules offers many capabilities, including: a catalogue and explanation of the main operational and design features of 70+ equipment types and a procedure for ranked equipment selection; full analysis capabilities for leaf filter, jar sedimentation and expression test results to give the parameters required for scale-up and simulation of solid/liquid separation equipment; comparison of data sets from a range of tests or trials; simulation of 20+ types of vacuum and pressure filters; the ability to import data files from other software (e.g. spreadsheets); and web access to equipment suppliers.

THE IMPACT OF ECONOMIC AND COMMERCIAL ISSUES IN MUNICIPAL WASTE MANAGEMENT
J. Heath and I. Crummack (pages 303-308)

The waste management industry is a highly regulated sector. In recent years many legislative instruments have had significant effects on waste management. Two of the most important have been the Environmental Protection Act and the Landfill Directive. The Landfill Directive has led to the introduction of the Landfill tax and then Landfill Avoidance Targets (LATS). The Environmental Protection Act has lead to the Pollution Prevention Control regime under which most waste treatment facilities now have to operate.

Much of the activity in waste management stems from local government and the statutory responsibilities of Waste Disposal Authorities (WDA’s) to deal with Municipal waste. Thus, many other central government policies have had an effect on the private waste management industry through their contracts with WDA’s. The Local Government Act encouraged the outsourcing of local government services and helped move Local Authority Waste Disposal Companies (LAWDC’s) into the private sector. This produced a massive increase in private waste management industry activity. One of the knock-on effects was to move the financing of waste disposal facilities from government to private borrowing.

While legislation still provides the over-arching constraints that the industry works around, it is the private financing that drives the economic and commercial issues in the sector. Financial constraints effectively govern anyone trying to develop projects in the sector and an understanding of these is essential if projects are to be developed successfully. For many years in the past the answer to waste disposal was landfill or public financed facilities. Now instead of landfill, the solution increasingly has to involve dedicated facilities where technology is employed to solve the waste disposal problem, be it a recycling facility or a final disposal facility such as Energy from Waste (EFW).

PRESSURE FILTER PROCESS OPTIMIZERS AND DATA ACQUISITION SYSTEMS
S. Manninen, L. Kaipia and K. Koskela (pages 308-311)

This paper introduces tools for process optimised filtration by pressure filters as used by Larox, a supplier of solutions and technology in solid/liquid separation. Automation is an essential part of the whole system and Larox filter process control is based on Programmable Logic Control (PLC). All field components are connected to the PLC by bus technology and the man-machine communication is handled by a local interface unit. The automation also contains real-time data acquisition and reporting systems.

FILTER AID PORE SIZE AND PORE STRUCTURE CHARACTERIZATION
E. Mayer and W. Li (pages 312-317)

Filter aids are powdered materials used as precoat/body feed to improve filtration rate and filtrate quality in cake filtration. There has been a trend that filter aids are added in membrane, cartridge, and sand filters to enhance operations. Screening or pre-selection of filter aids for the various filtration applications are normally based on their physical (particle size distribution, bulk density), chemical (chemical composition, crystalline silica content), and filtration specifications (cake permeability, filtrate NTU, cake density, efficiency of specific sized particles removal). Filtration properties or specifications are obtained from water tests, and are sometimes not consistent with results when applied to specific applications with actual solid/liquid samples. To fill the gap between water and actual sample test results, and to narrow filter aid selection prior to lab or field tests, it is suggested that the pore characteristics of filter aid beds should be included in filter aid product specifications.

Various types of filter aids including rice hull ash, diatomaceous earth and perlite are involved in the current study. Capillary flow porometry was used to measure pore structure data such as minimum pore size, mean flow pore size, pore size distribution and envelope surface area. The fundamentals of capillary flow porometry for filter aid powder characterization, pore characteristic results, and correlations of the pore data with particle size and filtration testing results are presented in the paper. Problems and recommendations of flow porometry for powdered filter aid characterization are also discussed.

INFLUENCE OF MEMBRANE TYPE ON FILTRATION CHARACTERISTICS AND PROTEIN REJECTION IN CROSSFLOW MICROFILTRATION
K.-J. Hwang and H.-S. Chiu (pages 317-322)

The effects of membrane morphology and operating conditions on particle fouling, filtration flux and protein rejection in crossflow microfiltration of a binary suspension are studied. Two kinds of membranes, made of polycarbonate (Isopore®) and PVDF (Durapore®), were used for filtering PMMA submicron particles/BSA binary suspensions. The cake mass, membrane fouling and filtration resistance under various filtration pressures and membrane morphologies were measured and discussed. Experimental results show that the filtration flux increases with an increase of filtration pressure. The particle blocking and fouling phenomena in the membrane pores were observed by SEM analysis.

During the early period of a filtration, the blocking mode can be explained by the complete blocking model for the Isopore® membrane, and the standard blocking model for the Durapore® membrane. After a period, the modes change to cake filtration for all membranes, and the cake resistance plays the major role in determining the overall filtration resistance. Since membrane blocking is more severe for the Isopore® membrane, more cake is formed and then lower BSA rejection obtained for the Durapore® membrane. As a result, filtration fluxes become almost the same for the tested membranes at the pseudo-steady state. The trend for BSA rejection can be explained by the BSA transport mechanism.

EQUATION OF STATE FOR POROUS MEDIA: THEORETICAL PROPERTIES OF WELL FORMED MEDIA
N.H. Andreas (pages 323-328)

The properties currently used to characterize porous media for filtration applications are shown to be interrelated via an equation of state, equation (10), which is theoretically exact for a medium which is ‘well formed’ as defined in this paper. Theoretical and experimental results are presented which corroborate the validity of the derived equation of state. The utility of the result to media manufacturers and filtration engineers is discussed in some detail via several application examples.

The proposed equation of state is a new result and relates for the first time all the variables that have a bearing on filter media engineering: porosity, specific permeability, initial bubble point, tortuosity, surface tension and wetting angle of the fluid used to measure the initial bubble point. The only additional phenomenological parameter introduced not currently in general use to characterize filter media is the ratio of the largest pore diameter to the average diameter present, equation (9), which is central to the concept of ‘well formed media’. Since the average pore diameter is what can be typically obtained from the equivalence of the pore interfacial area to the interfacial area of the constituent grain particles from which the filter media is formed, the requirement that a relationship, equation (9), must obtain and should be considered an axiomatic requirement for the manufacturing of filter media with consistent properties.

If, for example, a media manufacturer offered filter media with no necessary relationship between the average pore diameter and the largest pore diameter present and the largest pore diameter was allowed to be variable, such media would be of little value in critical filtration applications.

A STUDY OF POLYANILINE MEMBRANES FOR GAS SEPARATIONS
Y. Gupta and R.J. Wakeman(pages 329-334)

A novel method to make reproducible, defect-free, dense, self-supported polyaniline films with thicknesses between 2 and 6 μm, and polyaniline nano-film membranes with selective polyaniline layer thicknesses between 300 and 800 nm supported on a porous polyvinylidene fluoride (PVDF) substrate was developed. Undoped, self-supported polyaniline and polyaniline/PVDF composite membranes were tested to measure their transport properties for various pure gases such as H2, CO2, O2, N2, CH4, C2H4, C2H6, C3H6 and C3H8. The productivity increased almost linearly with decreasing polyaniline film thickness. The productivity values obtained for all permeating gases were significantly higher in the case of ultrathin polyaniline membranes.

The gas transport rates (GTR) for various gases were higher by a magnitude of 104 than those reported for self-supported polyaniline membranes. The pure gas selectivity values obtained for various gas pairs through self-supported polyaniline membranes were similar to those of self-supported polyaniline membranes. The permeation behaviour of binary gas mixtures (O2-N2, CO2-O2 and CO2-N2) through self-supported polyaniline membranes and polyaniline/PVDF composite membranes at various feed compositions was investigated. The pure gas and mixed gas selectivity values were similar for the non-polar mixed gas system (O2-N2 mixed gas system). The productivity (permeance) can be significantly increased by using ultrathin polyaniline membranes of higher permeability and gas flux with similar separation efficiency for various gas pairs.

PREDICTION OF PORE SIZE AND PRESSURE DROP OF POROUS WOVEN WIRE CLOTH FILTER MEDIA ON THE BASIS OF CALCULATION MODELS
S. Schütz, P. Kopf and M. Piesche (pages 335-344)

Porous woven wire cloth filter media are often used for filtration purposes with hot or chemically aggressive liquids and gases. Their regular geometric structure is the basis for specific filtration applications with distinct particle cut sizes. Despite the widespread use of these filter media the prediction of specific filtration properties is usually not possible for manufacturers.

Within the scope of this work a range of methods were developed and provided to characterize the filtration properties of woven wire cloth filter media when the most important geometric data such as wire gauge or lattice spacing of the cloths are known. First, the possibility to calculate the maximum diameter of a spherical particle which passes a wire cloth filter medium is developed due to geometric investigations based on the most important geometric filter medium parameters. In the second part the applicability of the bubble point test to determine the maximum effective pore size in a filter medium is discussed. It is shown how the bubble formation and therefore the experimental results depend on the wire cloth geometry and the bubble formation dynamics. Finally, dimensionless numbers are defined to predict the pressure drop of woven wire cloth filter media with similarity laws if characteristic geometric filter medium parameters are known.

The described methods were applied to square mesh, single plain Dutch weave, reverse plain Dutch weave and Dutch twilled weave filter media. The results of the calculation models are compared to the authors own experimental data and CFD (computational fluid dynamics) simulations as well as experiments published in the literature. In all cases the model results show good accordance with the validation data. Based on these calculation models it becomes easier for filter media manufacturers to offer products to their customers which are adequate for specific filtration tasks.

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Volume 9, Issue 1 Abstracts from the FILTRATION journal

A REVIEW OF INDUSTRIAL FLUE GAS CLEANING
T. Golesworthy (pages 23-33)

Environmental awareness has grown significantly in the last 10 to 20 years. The general public and green eco-groups have swayed public opinion through the media such that the legislators have put increasingly stringent emission limits on many industrial processes and activities. The US Environmental Protection Agency has led the way with many countries following its lead. The Environmental Protection Act in the UK is an example of new legislation that seeks to protect our environment from all known industrial pollution hazards whilst acknowledging the need for industry to remain economically viable. A necessary part of industrial activity is generating electricity, in part through the combustion of fossil fuels, managing its wastes, using processes such as incineration, and transporting materials, using fossil fuel based transport systems. Emissions to air from these activities involve a wide range of materials that can include particulate matter, oxides of nitrogen and sulphur, hydrogen chloride, volatile organic compounds, polychlorinated bi-phenyls/di-benzo furans (dioxins) and heavy metals.

A range of mature and emergent control technologies exist for the control of these pollutants including inertial separation, filtration, electrostatic separation, wet and dry scrubbing and catalysis/conversion processes. These techniques are reviewed as well as current state of the art composite gas cleaning plant for total solutions to the emission of currently prescribed pollutants

METAL SCAVENGING PURIFICATION TECHNOLOGY FOR THE PHARMACEUTICAL AND FINE CHEMICAL INDUSTRY
K. Treacher (pages 33-38)

The manufacture of pharmaceuticals in modern-day industry is becoming an ever more involved process as the chemical complexity of active ingredients increases, driven by more intelligent and intricate design. Consequently the range of synthetic techniques required is constantly expanding, with an increasing reliance on metal-based catalysis, which can deliver more efficient, selective and cleaner processes.

FILTER MEDIA PORE SIZE COMPARISON BETWEEN POROMETRY AND GLASS BEAD CHALLENGE TESTING G. Rideal and E. Mayer (pages 38-41)

The accuracy of pore size measurement by porometry has been found to be dependent on the instrument and operator. Similarly, challenge testing using ISO test dusts is dependent on both the precision of the particle analysis of the irregular shaped particles and the laboratory protocols. To overcome the ambiguity of shape, a much simpler challenge method has been developed using NIST certified, narrow particle size distribution glass beads. The new high-speed method determines the filter efficiency (cut-point) using a novel dry sonic device for pore sizes above 20 μm and a wet suspension method for pore sizes below 20 μm. This paper will compare porometry values obtained for a number of porometers after cross-validation with the new microsphere challenge test method.

A NEW CONCEPT FOR SIMULTANEOUS REDUCTION OF ALKALINITY, OIL AND UNDESIRABLE GASES SUCH AS CO2 AND H2S
J. Chen and D. Douglas (pages 42-45)

In a steam assisted gravity drain (SAGD) application to extract oil from the reservoir, lime softening is often utilized to reduce the hardness and silica concentration to meet feed water quality requirements for ‘wet steam generators’. Produced water is normally treated for recycle and reuse as feed water to the steam generator. When the produced water contains a high alkalinity concentration, the lime softening reaction will produce excessive volume of ‘wet’ sludge resulting in large capital cost for sludge dewatering, handling and disposal. This paper presents a method to reduce alkalinity concentration in produced water without excessive sludge production and discusses stripping CO2 produced from the chemical reaction. Free oil removal by induced gas flotation (IGF) is well documented, so no discussion of oil removal is presented here since the new concept focuses on the improvement of IGF to achieve the above mentioned objectives.

HOT GAS FILTRATION – A CASE STUDY HIGHLIGHTING SUCCESSFUL DIOXIN CONTROL
R. Williams (pages 45-47)

In February 2007, R Williams Consultants assisted in the commissioning of Chinook Sciences’ proprietary Air Pollution Control (APC) system which exclusively serves the RODECS® system. The RODECS® is an industrial pyrolysis system that utilizes a novel active pyrolysis concept, and is used for the full gasification of organic material from metal and industrial waste, and municipal solid waste (MSW). In this application, the RODECS® system was processing secondary aluminium painted scrap, heavily contaminated with PVC.

THE IMPACT OF ULTRAFINE BYPASS FILTRATION ON EXTENDED DRAIN INTERVALS
R. Russell and T. Gilbert (pages 48-51)

The ability of a Cleantechnics International Inc. high capacity ultrafine fluid bypass filtration system to extend lube oil and hydraulic fluid service levels was studied. Test results show a four- to six- fold increase in filter change intervals and a more than fifteen fold increase in oil change intervals. Results of installations on Class 8 trucks, heavy duty work trucks and off-road heavy equipment are presented. These results include a review of oil analysis reports from an independent oil analysis laboratory of samples taken during normal service intervals on both control and test vehicles over extended time periods. In addition to the review of oil quality, calculations reporting long term cost savings and environmental benefits of the bypass filtration system as the result of extended drain intervals and reductions in oil change related expenses (oil costs, filters, labour, equipment downtime and waste disposal) are cited.

CHANGING WASTEWATER SLUDGE CHARACTERISTICS AFFECTING THE FOULING OF A SINGLE STAGE MECHANICAL DEWATERING AND THERMAL DRYING PROCESS
B. Peeters, L. Vernimmen and W. Meeusen (pages 52-62)

At the Monsanto Europe site in Antwerp, Belgium, wastewater sludge is mechanically dewatered and thermally dried in a single compact machine. Over the years, the biosolids throughput was limited by two main bottlenecks, namely (1) high vibrations of the solid bowl decanter centrifuge, and (2) periods of daily fouling around the centrifuge cake outlet or somewhat further in the flash drier. In that case, sludge feed towards the centrifuge has to be stopped to remove product build-up by flushing.

The vibrations of the centrifuge were reduced by simply reducing the centrifuge bowl speed from historical 3165 rpm to 2880 rpm. But the fouling issue was harder to resolve. Through research over the years, it was shown that the fouling frequency was higher for sludge comprised of higher inorganic fractions. The inorganic fraction varied significantly over time for this particular wastewater treatment plant (WWTP) as a result of varying calcium concentrations in the wastewater. Periods of 15% inorganic fractions are followed by periods with more than 30% inorganics in the sludge flocs. Sludge settleability varied in accordance with these changes in inorganic fractions, with a higher inorganic fraction resulting in a heavier floc and a better settling ability. Spin tube tests executed in the lab, simulating cake compaction in the field, have shown that the inorganic fraction of the sludge flocs has a significant impact on cake dryness, with a higher inorganic fraction yielding a drier cake. Taking into account the fact that activated sludge goes through a sticky phase while being dried (somewhere in the range around 40-50 %DS), this implies that the centrifuge cake dryness determines timing and place in the system where the sludge is going through the sticky phase. The hypothesis is that a ‘too dry’ centrifuge cake goes through the sticky phase at an earlier stage in the next drier system where it seems to be more susceptible to product build up, for example at the point where the cake particles are leaving the centrifuge with high velocity and hit the centrifuge casing for the first time.

In that case, in periods of sludge characterised by a higher inorganic fraction, centrifugation conditions in the field have been adjusted to make the centrifuge cake again less compact and less dry. This resulted in a significantly higher capacity of the system by reducing the fouling issue

PERFORMANCE OF FILTERS WHEN LOADED WITH NaCl AND KCl PARTICLES IN LOW RELATIVE HUMIDITY ENVIRONMENTS
T.-C. Hsiao and D.-R. Chen (pages 62-71)

In this study two low efficiency cellulose filters were loaded with sodium chloride (NaCl) and potassium chloride (KCl) particles of super-micron sizes in low relative humidity (RH) environments (RH < 30%). As NaCl and KCl particles have similar material properties, such as density and crystal structure, it was believed that no difference would be observed in the filter loading curves (pressure drop vs. the loaded particle mass/volume) of particles of the same size in such low RH environments. It is shown that at 30% RH the initial penetration and the loading curves of filters loaded with NaCl and KCl particles are nearly the same. However, as the RH decreased to 15% so the loading curve of NaCl particles deviated from that of KCl. The curve of NaCl particles moved to the right of the KCl curves. In other words, with the same pressure drop, the filter can be loaded with a greater volume of NaCl particles than KCl particles. Furthermore, the influence of filter structure and particle size on the shifting of the loading curve was investigated by performing the same loading test with two different particle sizes. It was found that the observed RH effect on the loading curve was more significant for low efficiency filters loaded with large super-micron particles. SEM examination showed that the morphology of the test particles is different when RH is varied. It was concluded that a possible reason for the dissimilarity of the NaCl particle loading curve at 15% RH is the difference in the particle morphology.

CFD BASED DEVELOPMENT OF INERTIAL SEPARATORS IN OIL MIST REMOVAL FROM CRANKCASE EMISSIONS
S. Schütz, K. Kissling, G. Gorbach, A. Zink and M. Piesche (pages 71-80)

For passenger cars and heavy duty vehicles, the current tightening in exhaust gas legislation is the driving force for new developments of oil mist separators to clean blowby gases in crankcase ventilation systems. One important aspect is the limited installation space for the oil droplet separation systems, hence the development of small-scale separators is a challenging task. As there are only a few design rules for small-scale separators, computational fluid dynamics (CFD) was used for the development of two types of centrifugal separators, small cyclone separators and disc stack centrifuges.

With CFD calculations based on high quality numerical meshes, the separation efficiency, grade efficiency and pressure drop can be predicted for non-standardized, small-scale cyclone separators. Though the pressure drop should not exceed about 40 mbar with a blowby volume flow of 80 l min-1, oil droplets in the sub-micron scale can be separated partially. Concerning the disc stack centrifuge, the CFD results show that there is a non-homogeneous volume flow distribution across the different separator gaps. Depending on the operational conditions the volume flow distribution is oscillating due to flow instabilities in the outer annular gap of the disc stack centrifuge. So there exist different grade efficiency characteristics dependent on the gap position but the separation behaviour of the whole apparatus can be described by a mean grade efficiency curve. As a further result of the CFD simulations the separation characteristics of disc stack centrifuges can be described with a universal grade efficiency curve for a wide range of geometrical and operational data.

Experimental investigations on the droplet size distributions in the raw and the clean gas volume flow show a good accordance with the simulation results. Two droplet size measuring systems, a cascade impactor and a three wavelength laser spectrometer, were used to determine droplet size distributions in an experimental setup

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Volume 9, Issue 2 Abstracts from the FILTRATION journal

ELECTROPOSITIVE FILTRATION TECHNOLOGY IN AUTOMOBILE MANUFACTURING APPLICATIONS
F. Tepper, H. Frank and R. Lancaster (pages 108-111)

Argonide Corporation began as an organization focused on the production and sale of nanopowders. By definition, nanopowders are extremely small particles (less than 0.1 micron) of materials such as nickel, copper, iron, alumina, gold, etc. These materials are in demand by research and development groups within both the public and private sectors. To date, the company is still involved in this active, although limited arena. It became clear that the future success of Argonide was not in nanomaterials themselves, but in full-scale commercialization of a product based on nanotechnology. Through several years of extensive R&D, discussions with the U.S.E.P.A. (US Environmental Protection Agency), and the use of several grants from NASA, we created a nonwoven filter media.

FILTRATION TECHNOLOGY – ITS IMPACT UPON OUR LIVES AND THE ENVIRONMENT
D. Dubbin (pages 112-117)

In these times when global warming poses such a challenge for this and future generations it is perhaps worth reflecting how advances in filtration technology have impacted upon our lives and the environment in a positive way. Not for the sake of complacency, but to illustrate how we as engineers and scientists have made a real difference over the recent past and how we must re-double our efforts in the future. In this short paper the author has considered some examples of gas and liquid technology which impact upon our lives.

CLOSED LOOP CONTROLLER IN A DWELL TIME-BASED GAS FILTRATION SYSTEM
M. Marcelo, A. Malino, J. Mercurio, M. Retirado and B. Sicat (pages 117-119)

This paper reports the development of a dwell time-based closed loop controller for a gasoline exhaust filtration system. The ppm content of the gas entering a chamber is measured. Gases that fall below a set threshold are passed on to the succeeding stage without processing, while those that are above the threshold are circulated by the system to an activated filtering loop until such a time that the concentration has fallen below the threshold. The resulting dwell time in order to attain an acceptable ppm is found to be a function of the initial ppm level.

FROM WARFARE TO HEALTHCARE
J. Taylor (pages 120-122)

Activated carbon cloth was invented by the UK Ministry of Defence for protection against chemical, biological and nuclear threats. However, today the world’s largest applications are in the medical field although that is about to change. This paper is intended to give a brief introduction to the development of activated carbon cloth (ACC), its manufacture and applications including non-particulate filtration of gases and liquids. All references to activated carbon cloth are based on ZORFLEX® ACC (ZORFLEX® is a registered trademark of Chemviron Carbon Limited).

ADSORPTIVE FILTER MEDIA (AFM)
H. Patzelt (pages 123-128)

Effective control of gaseous pollution requires filtration media developed specifically to capture the smallest concentrations of a range of ‘target’ molecules. The ability to combine particle filtration materials will result in extended filter lifetime in environments containing both particulate and gaseous pollutants. The layering together of various filtration products, often termed ‘Combination Filter Media’ (Combi), allows the filter manufacturer to customise their products for greater pollution adsorption capacity in challenging environments.

INORGANIC MEMBRANES FABRICATED BY AIR PLASMA SPRAY COATING
K.-L. Tung (pages 128-132)

Environmental protection awareness and higher energy costs in recent decades have made membrane technology more economically competitive with conventional separation processes such as absorption, adsorption, distillation, or solvent extraction. While the market of the global membrane industry varies from one estimate to another, it is reported that the total sales of membrane modules, excluding the pumps, valves, instruments, or fluid pipe work external to the housing of the module, were estimated to have been just over $8 billion in 2003 and were expected to exceed $24 billion in 20081. The market forecasts include both organic polymeric membrane and inorganic ceramic or metal membranes.

CHANGES IN SLURRY CONCENTRATION DURING THE INITIAL STAGES OF FILTRATION
A. Genç and I. Tosun (pages 133-138)

The variation in slurry concentration within the filter chamber during the startup of constant pressure filtration experiments and its effect on the cake length and filtrate volume are studied. Theoretical equations relating slurry concentration to cake length and filtrate volume are developed by using the equations of continuity together with the jump conditions at the cake-slurry interface. Comparison with experimental values indicates that the change in slurry concentration within the filter chamber, especially during the initial stages of filtration, should be taken into consideration in the evaluation of model parameters from experimental data.

NANOFILTRATION: A METHOD FOR IMPROVING THE PURITY OF FUELS AND NON-AQUEOUS SOLVENTS
E.S. Tarleton and J.S. Low (pages 138-141)

This paper describes some of the principal features of solvent resistant nanofiltration and its potential in fuel processing. Experimental data for both fuel simulants and a petrol fuel are presented. The solute rejection mechanism for low polarity mixtures was size exclusion with a membrane cut-off in the region of 1-2 nm. The extent of solute rejection was dependent on the degree of membrane crosslinking, the membrane swelling induced by the feed and the filtration pressure. Nanofiltration experiments with the petrol fuel showed a good correlation with the data obtained for the fuel simulants, both in terms of permeate flux and solute rejection. Provided that higher polarity oxygenates were not present in the fuel, it was possible to remove undesirable poly-nuclear aromatic and organometallic solutes to an extent that was sufficient to significantly reduce valve deposits and emissions gases in engine tests.

INVESTIGATIONS ON THE MINIATURISATION OF PRESSURE FILTRATION PROCESSES
S. Jermann, A. Schreiner and R. Schneeberger (pages 142-147)

As a basic operation of mechanical process engineering, pressure filtration and its scale-up has been described in detail in the literature. However, the pharmaceutical development of active substances in particular calls for scale-up from relatively small quantities and is therefore dependent on conclusions from smaller filter equipment. In this study, results from laboratory Nutsche filters with filter surface areas of 1.4 cm2 and 9.6 cm2 were compared with results from a 20 cm2 Nutsche. It is shown that no reproducible and reliable data could be generated using the 1.4 cm2 Nutsche. While this was possible using the 9.6 cm2 Nutsche, the permeability was greater than with the recommended 20 cm2 Nutsche, so that a correction factor has to be introduced.

RECONSTRUCTION ALGORITHMS FOR THE INTERNAL PACKING DENSITY DISTRIBUTION OF FIBROUS FILTER MEDIA BASED ON TOMOGRAPHIC DATA
(pages 147-154)

Algorithms were developed to approximate the 3-dimensional internal packing density distributions of fibrous filter media at different levels of detail and complexity. Each algorithm uses certain input information derived from X-ray tomographic data of filter samples.

Algorithm 1 creates a binary media structure consisting of the true (i.e. tomographically determined) void distribution plus regions of uniform packing density. The average packing density of the media is maintained constant. Algorithm 2 creates a model fibrous structure of straight fibres of equal diameter and random length positioned randomly in space, while maintaining the true (i.e. tomographically determined) fibre orientation distribution. The number and length of the fibres on average adds up to the packing density of the filter. The model fibrous structure is recreated by a stationary Poisson process of convex bodies. Algorithm 3 distributes pores of random size and location within a homogeneous matrix, such that the average packing density again coincides with the true (i.e. tomographically determined) packing density. This algorithm is also based on a stationary Poisson process of convex bodies.

The capability of each algorithm to recreate the essential structural features of the media was tested against ‘reality’ by computing the respective overall pressure drop of the filter as well as the velocity distribution in the filter interior, and comparing with the results obtained for the ‘true’ packing density distribution of a sample measured by tomography. Compared to the assumption of a completely homogenous filter (which gives roughly 2 times the actual ∆p), all algorithms are closer to reality. The binary algorithm deviates in ∆p by a factor of 1.8; algorithm 3 comes within a factor of 1.6 of the true ∆p. The best approximation is by algorithm 2 which narrows the difference in ∆p to a factor of 1.4

YEAST MICROFILTRATION USING A MODIFIED SURFACE FILTER
M. Stillwell, R.G. Holdich and S. Kosvintsev (pages 155-160)

A microfilter is generally accepted as a filter capable of removing suspended material with diameter of between 0.1 and 10 μm from fluids. All filtration systems have to balance the requirement to present a high efficiency for particle removal with the intention of presenting a minimum resistance to fluid flow. These contradictory requirements have led to research on filter pore structure and shape as well as techniques for employing the filter to minimise particle deposition on top of, and within, the filter matrix. One successful filter design uses slotted pores, which pass through a lamina filter sheet, and present a non-tortuous flow channel for the pore. However, this type of filter is only feasible for pore sizes towards the top end of the microfiltration range, at least when constructed from robust engineering materials. For the filtration of fine particulates, using a microfilter, a tortuous pore channel filter is more applicable.

This paper presents the results of a series of tests using carefully sized glass beads that have been sintered under a variety of processing conditions to provide a series of microfilters. Parameters such as particle size distribution, bed depth, sintering temperature and time as well as bed support have been investigated, considering their effect on the filtration performance of sub-10 μm yeast cells suspended in water. Models for the resulting voidage of the sintered porous media and hence permeability are presented. Surface post-treatment of the glass beads by chemical means has also been investigated: investigating the influence of chemical surface properties on yeast adhesion

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