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 8, Issue 4 Abstracts from the FILTRATION journal

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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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