- The Filtration Society - http://www.filtsoc.org -

2003

Published papers: Volume 3, Issue 4

Author(s) Title, page numbers and abstract
M. Rowlands, I. Schnieders and B. Heinz

NANOWEB® – THE ROUTE TO HIGH PERFORMANCE FILTER MEDIA (pages 191-193)

bullet Abstract

bullet The ever increasing demand for higher performance filter media continues to challenge development engineers throughout the supply chain. Over the decades, there have been several step-changes in filtration technology including glass microfibre, spun-bonds, meltblowns, tribo-electric charged media and multi-layer structures. These major technology steps have been interspersed with a lot of small, incremental improvements.In recent years, the need for increasingly efficient media has driven a desire to develop sub-micron synthetic media – especially in applications where glass microfibre is undesirable. The use of Nanoweb® to achieve a further reduction in fibre diameter is potentially the next significant step-change in universally available filtration technology.

S. Volooj, C. Carr and R. Lydon

INVESTIGATIONS INTO THE RECYCLING OF PROCESS WATER USING PRESSURE FILTRATION AND NEW FILTER MEDIA (pages 194-197)

bullet Abstract

bullet In this study the potential recycling of textile dyehouse water using pressure filtration and composite filter media has been examined. The recycling of hydrogen peroxide bleach baths has been demonstrated, with the benefits of cashmere fibre strength retention and whiteness improvements observed. A preliminary evaluation of acid dyebath recycling for keratin fibres has demonstrated that residual colour can be removed.

I. Townsend

DESIGN CONSIDERATIONS FOR AUTOMATIC PRESSURE FILTRATION OF FLOTATION CONCENTRATES (pages 198-203)

bullet Abstract

bullet Most major concentrators built in recent years have incorporated pressure filtration for dewatering of flotation concentrates. Plant expansions and upgrades frequently replace old vacuum filters with pressure filters. Reasons for the selection of pressure filtration are described, including developments to meet the current and future needs of the mining industry. Next, factors contributing to a successful pressure filter installation are considered. These include filtration testing, effective integration of batch equipment into a continuous process, selection and dimensioning of ancillary equipment, and plant layout considerations.

T. Stott and I. Boxall ADVANCES IN HOT GAS FILTRATION (pages 204-211)

bullet Abstract

bullet The environment and pollution are high on the agenda today, and the required standards are continually increasing, which means that operators of industrial processes have to ensure that any gaseous or liquid by-product is free from harmful contaminants. Where the effluent is gaseous it is often also hot and this imposes particularly stringent demands on the Particulate Control Device (PCD) which is employed. The paper reviews some of the PCD’s that are available, and the requirements for them, and identifies a technology which has the potential to be a significant step forward in the field.

A. Walker

OPTIMISING PRECOAT USAGE ON A ROTARY DRUM VACUUM FILTER (pages 211-215)

bullet Abstract

bullet Unlike the more conventional scraper, belt or string discharge rotary drum vacuum filters (RDVF), the precoated RDVF has an additional overhead with the usage of precoat in both the frequency of re-coating (labour and time) and the cost of the precoat powder. Optimising the filter will yield a higher throughput per tonne of precoat, although determining the ideal operating parameters can sometimes be difficult with a full-scale unit. It is not always practical, nor wanted, to undertake optimising tests on a production filter as maintaining a steady filtration rate is often of prime importance.Extended laboratory-scale or pilot-scale trials can provide useful data for existing filtration systems, as well as in the validation and development of new processes. This paper explains the principle of optimising precoat usage for a steady-state system, and is particularly relevant to extended laboratory-scale test work.

N. Pearson OBTAINING DATA FOR SIZING CENTRIFUGES (pages 216-221)

bullet Abstract

bullet Previous papers have discussed the various methods used by a process laboratory to evaluate whether a material is suitable for separation by a centrifuge, either by outward filtration (basket machines) or by accelerated sedimentation. This paper looks in more detail how the Laboratory moves forward from simply deciding what centrifuge may (or may not) be applicable, to obtaining enough information to allow the full size machine to be designed and a process guarantee to be offered.The subject is vast and to avoid too many generalities this paper will concentrate on sedimenting type centrifuges and more specifically one of the most common types, the countercurrent, solid-bowl decanter centrifuge. Although the paper specifically refers to the decanter centrifuge, the same general approach is also used for other types of sedimenting and outward-filtration centrifuges.

H. Saveyn, K. Weber, P. Van der Meeren and W. Stahl TWO-SIDED ELECTROFILTRATION OF YEAST SUSPENSIONS: FILTRATION KINETICS AND PHYSIOLOGICAL IMPACT (pages 224-230)

bullet Abstract

bullet Yeast (Saccharomyces cerevisiae) suspensions were filtered on a laboratory scale two-sided filter press with central suspension inlet. Electrodes were provided on both sides in order to apply an electric field during the pressure filtration stage. Cathode and anode filtration kinetics were measured and modelled according to a new model based on classical batch filtration equations and electroosmotic and electrophoretic phenomena. Both the experiments and the model revealed an improvement of the filtration kinetics. The new model proved to fit very well to the experimental data, indicating a decreasing trend in the specific cake resistance upon application of the electric field. The values of the electrophoretic mobility determined by regression analysis were in line with the expected physical values, supporting this phenomenological model.Moreover, the viability of the yeast cells at different positions in the filter cake was tested, to determine the damaging effect of electrofiltration. Untreated yeast suspension as well as electrofiltered yeast cake parts were inoculated in batch reactors and followed in time. From these experiments it became obvious that the cell concentration and cell dry mass evolution, the glucose metabolism and the Crabtree ethanol producing effect were not altered by the electrofiltration stage, indicating no negative effect on the physiology of the micro-organisms.

Keywords: Biological effect; electrodewatering; electroosmosis; electrophoresis; model; Saccharomyces cerevisiae.

F. Heese and L.D. Hall MAGNETIC RESONANCE IMAGING (MRI) FOR NON-INVASIVE VISUALISATION AND QUANTITATION OF FILTRATION AND SEPARATION PROCESSES (pages 231-236)

bullet Abstract

bullet Work from recent projects highlighting the application of magnetic resonance imaging (MRI) to the filtration and separation field are described. These include MR imaging of the internal structure of filters, determining the particle deposition pattern in a cartridge filter and qualitatively and quantitatively measuring the fluid flow fields in a blood filter. It will be shown that MRI can successfully evaluate a variety of important parameters and thus offers huge potential as a unique measurement modality to assess non-invasively many of the critical parameters before, during and after filtration.Keywords: Filtration; separation; magnetic resonance imaging; MRI.

R.J. Wakeman and P. Wu NEURAL NETWORK MODELLING OF VIBRATION FILTRATION (pages 237-244)

bullet Abstract

bullet Vibration has been considered as a method to reduce filter medium clogging and disrupt the cake during filtration. However, there is difficulty in the widespread practical application of vibration to filtration because of the absence of sufficiently understood and well-defined theory of vibration filtration. A new identification method for the cake resistance is provided for vibration filtration. It estimates accurately the development of the cake resistance during vibration filtration and provides a tool to predict the process. In addition, the neural network modelling method is used in vibration filtration to establish the mathematical relationship amongst the combined cake resistance (the resistance to fluid flow due to the packing density of the particles in the cake during vibration filtration), vibration parameters, concentration of the feed suspension and the filtration time. It can provide guidance during practical applications about such parameters as the cake discharge time and optimal vibration conditions. Keywords: Cake filtration; vibration; filter media clogging.


Published papers: Volume 3, Issue 3

Author(s) Title, page numbers and abstract
A. Bologa, H.-R. Paur and W. Baumann

REMOVAL OF SUBMICRON FLY ASH FROM A BIOMASS COMBUSTION UNIT WITH A NOVEL “CAROLA” ELECTROSTATIC COLLECTOR (pages 133-135)

bullet Abstract

bullet EU directives for PM10 and PM2.5 particles may require the development of cost-effective gas cleaning technologies for fine particles. The results of design and experimental investigations with the novel electrostatic collector CAROLA for the collection of sub-micron particles are presented. The advantages of the new equipment are discussed.

A. Donn

EFFLUENT TREATMENT IN THE TEXTILE INDUSTRY (pages 136-138)

bullet Abstract

bullet In many of today’s process industries there are increasing pressures to reduce the impact and cost of wastewater discharge. At the same time process water costs are increasing due to increasing supply water charges and decreased water resources available to utilities. Effluent treatment and reuse can be a solution to both these problems and membrane technology is ideally suited to providing part of that solution.

K. Järvinen and J. Hämäläine

DIRT-REPELLENT FABRICS FOR DEINKED PULP DEWATERING PROCESSES (pages 139-142)

bullet Abstract

bullet A major problem in deinking mills is fouling of the filter medium caused by stickies, printing inks and other, predominantly anionic impurities. Existing disc filter bags are mainly made from polypropylene, polyester and polyvinylidene fluoride yarns, and the dirt-repellence of these traditional materials has turned out to be insufficient.This paper presents experimental results achieved by incorporating anti-pitch monofilament yarn technology and chemical fabric surface treatment technology into the conventional waste-paper based pulp dewatering fabric manufacturing. The filtration performance, dirt-repellence and hydrophilicity/hydrophobicity of the developed fabrics were analysed. Based on the results, it is possible to enhance filter media performance by altering the surface properties of the fabric. As a conclusion, it seems that dewatering media manufactured by utilising these new developments enable pulp mills to enhance the process performance and filter media lifetime due to the improved dirt-repellence.

A. Startin and G. Elliott INDUSTRIAL EXPERIENCES WITH LOW DENSITY CERAMIC FILTER ELEMENTS (pages 143-146)

bullet Abstract

bullet Environmental legislation and the demands of process filtration duties have necessitated the development of effective barrier filter media that can operate under arduous conditions. There have been many interesting developments in recent years including needlefelts based on advanced polymers, treated fabrics, metallic filters and rigid ceramic filters. Low density ceramic filter elements were launched in the mid 80’s and were initially applied to thermal soil cleaning duties. Since then the introduction and subsequent development of a range of monolithic elements has seen application to an increasing range of pollution abatement and product collection duties.Low density ceramic filter elements offer a number of significant benefits to the end user – temperature resistance (refractoriness), corrosion resistance, high efficiency, the ability to operate under variable conditions and operational reliability. They have generally been applied to processes where the gas stream is at an elevated temperature and where low emissions from the filter plant are required. They are also particularly applicable to processes which generate fine (sub-micron) particulates that can be difficult to control efficiently and economically using established techniques such as the cyclone or electrostatic precipitator. Applications to date include coal processing, waste incineration, non-ferrous metal processing, chemicals manufacture, fluidised beds and thermal soil cleaning.

Low density ceramic elements offer a viable particulate removal solution to a broad range of processes which can utilise the benefits of the technology. This paper highlights applications where the benefits of low density ceramic filter elements have been effectively employed. One such duty involves the collection of trace amounts of catalyst intermediate from a calcining furnace. Stable operation and low emissions are critical to the process and this level of performance has been demonstrated by the ceramic filter plant.

H. van Heeren, W. Nijdam et al.

MICROFILTERS MADE WITH SEMICONDUCTOR TECHNOLOGIES: A REVOLUTION IN PARTICLE-FLUID SEPARATION (pages 147-150)

bullet Abstract

bullet The ultimate goal in membrane filtration is to achieve a membrane with a low flow resistance, a high chemical resistivity and a well-controlled pore size distribution. There is no better way of achieving these goals than using semiconductor technologies for membrane production. This industry has a long experience in volume production of products with extremely small dimensions with ongoing research towards decreasing dimensions. A few years ago, an innovative small company, Aquamarijn, introduced this technology into the world of microfiltration. The result, microsieves made out of silicon, offered very good mechanical properties and a membrane made of silicon nitride, one of the most inert materials. Thanks to the lithographic technologies employed, the pore size distribution is much narrower than can be achieved with conventional membrane fabrication methods. The absolute pore size is also very well controlled, leading to very good separation characteristics. As it is a very thin membrane, it has very low resistance to the liquid flux, making low-pressure operation possible and featuring small footprints of installation.

The fluxes achievable with these sieves and the durability against chemical attack proved invaluable in several areas. However, due to their low flow resistance, process settings are much different from conventional membranes and work had to be done to optimise the product and the filtration process. At this moment feasibility in different areas like yeast cell filtration and sample analysis has been shown. Other applications are currently under investigation. This paper gives an overview of production technology, filtration process considerations and possible applications of this new type of sieve.

K. Bell WET ELECTROSTATIC PRECIPITATION – EXPERIENCE AND LEGISLATION (pages 150-153)

bullet Abstract

bullet Electrostatic precipitation has been a reliable technology since the early part of the twentieth century. Originally developed to abate serious smoke nuisances from smelters, in particular lead and zinc, they were a cost efficient way of recovering material that would otherwise be lost.

B. Hoffner, J. Heuser and W. Stahl THE EFFECT OF A RELATIVE PARTICLE MOTION DURING THE WASHING PROCESS OF GRANULAR MATERIALS (pages 156-161)

bullet Abstract

bullet The moving bed washing process in a Sedimentator combines advantageous characteristics of both cake (displacement) washing and dilution washing. It is based on a continuously flowing moving bed. Particles inside the bed move relative to each other and to adjacent walls during their vertical movement. The moving bed is penetrated in the wash chamber horizontally by a wash liquid.Washing curves are displayed for two fractions of coarse quartz sand at a constant solids flow rate in an improved apparatus. The washing process is strongly dominated by the displacement of the mother liquid leading to extremely low residual impurity contents compared to the results usually obtained in cake washing experiments.

The comparison to cake washing curves obtained at constant wash liquid flow rates and low Pe numbers reveals that the level of residual impurity is far below that obtained in cake washing results with Pe numbers of the same order of magnitude. Due to the relative particle motion in the moving bed stagnant regions within or at the adjacent walls are broken up locally and temporarily. Additionally, the negative effect of a local maldistribution of wash liquid and mother liquid flows near the boundaries is reduced.

A displacement ratio is suggested as a physically motivated efficiency measure to rate the washing results taking into account only partial ideal displacement, and partial ideal mixing. The application of reported correlations for the dispersion coefficient does not have a practical outlet at present. A qualitative comparison reveals both a significantly decreased dispersion affinity and a slightly higher sensitivity with respect to the flow conditions. A quantitative description using the dispersion model is subject to further research.

Keywords: Washing; moving bed; displacement; purification; Sedimentator.

A. Brou, L.H. Ding, and M.Y. Jaffrin Extraction and concentration of polysaccharides using a rotating disk filtration system (pages 162-168)

bullet Abstract

bullet The recovery of exopolysaccharides (EPS) produced by Sinorhizobium meliloti bacteria has been investigated using a rotating disk filtration system. The main feature of our system is the use of vanes on the disk which produces a very important increase in permeate flux and an EPS transmission rate close to 100%. During the recovery of EPS produced under standard fermentation conditions (70 h at 30°C) by microfiltration, the mass flux has been raised to 650 g h-1 m-2 using a disk equipped with 2 mm vanes rotating at 2000 rpm against 380 g h-1 m-2 with a smooth disk at the same speed. The permeate flux Jf for various disks can be correlated by the same function of the mean shear stress at the membrane (τwm0.72 at 30°C) showing that the effect of vanes is merely to increase the shear stress by raising the fluid core velocity between the membrane and the disk. With 6 mm vanes, the core fluid angular velocity was found to be 84% of disk velocity versus 45% for a smooth disk. The same device has been equipped with a PES 50 kDa membrane to concentrate EPS by ultrafiltration. Permeate fluxes were of the order of 160 L h-1 m-2 at 2000 rpm and 30°C with nearly complete EPS rejection.

Keywords: Dynamic filtration; microfiltration; ultrafiltration; exopolysaccharides; rotating disk.

E.D. Archer and R.W.K. Allen REVIEW PAPER: DRY SCRUBBING OF FLUE GASES (pages 169-180)

bullet Abstract

bullet Dry scrubbing owes its origins to intense industrial activity driven by the imperative to satisfy, at minimum cost, public opinion and its resultant increasingly stringent pollution control legislation. This review examines the development of dry scrubbing systems, their performance and the factors that limit their performance.Keywords: Gas filtration; flue gases; scrubbing.


Published papers: Volume 3, Issue 2

Author(s) Title, page numbers and abstract
T. Golesworthy

A Review of Industrial Flue Gas Cleaning (pages 71-79)

bullet Abstract

bullet 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 managing its wastes using processes such as incineration. Emissions to air from incineration plant 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 historically as well as current state of the art composite gas cleaning plant for total solutions to the emission of currently prescribed pollutants.

J. Heikkinen, P. Pirkonen, J. Koskinen, R. Lahtinen and A. Mahiout

METHOD FOR REMOVING HEAVY METALS FROM METAL PLATING EFFLUENTS (pages 80-84)

bullet Abstract

bullet The objective of this work was to study the removal of dissolved metals from industrial effluents. The sorption of Cu, Zn, Cr, Pb, Ni and Cd from multicomponent mixtures was studied in a flow-through column packed with different sorbents. The materials studied were peat, two types of tree bark, rock wool and wood fibres made of reclaimed (recycled) paper. The metal-containing waste waters were collected from several industrial plants representing different industrial sectors in Finland.The efficiency of the metals removal from wastewaters studied at the laboratory scale depended largely on the wastewater and the material used as the sorbent. The results from the laboratory scale experiments suggest that the following factors should be taken into account: pH of the wastewater, number of different metal ions in the wastewater, concentration of the metal ions in the wastewater, and the solid matter content in the wastewater.

This research demonstrates that easily available materials can be used to remove dissolved heavy metals from industrial effluents. At very high metal ion concentrations the system seems to be inadequate, therefore the main purpose could be polishing of conventionally treated effluents.

K. Sutherland

PHYSICAL AND BIOLOGICAL TREATMENT PROCESSES (pages 85-88)

bullet Abstract

bullet A brief introduction is given to the main processes used in the treatment of municipal and industrial wastewaters, with emphasis on the use of filtration and related techniques. The key features of each stage in the process are described together with the main problems currently troubling the sector, especially those of increasing quantities, and greater severity in the restrictions on ultimate water discharge quality. Some of the modern developments leading to solutions to these problems are highlighted.

S. Massingham DEVELOPMENT OF A ZERO DISCHARGE PROCESS FOR MDF EFFLUENT TREATMENT (pages 89-90)

bullet Abstract

bullet Conventional processes for the treatment of effluent arising from the manufacture of MDF panels fail to comply with increasingly stringent environmental requirements. Recent advances in polymer chemistry combined with membrane technology have enabled both water recovery and, more recently, solubilised organic compound recovery. The result is that a ZERO DISCHARGE system is now a reality.This case study of the first commercialised system at an MDF mill outlines the shortfalls of conventional systems, and how the benefits of the membrane system have resulted in it being viewed not as an effluent treatment plant but as process technology incorporated into the refining process.

D. Condie, B. Johnston, S. Nicol and C. Veal

RESIDUAL MOISTURE REDUCTION IN COARSE COAL CENTRIFUGES USING AIR PURGING (pages 91-94)

bullet Abstract

bullet Air purging is a novel process for reducing the moisture content of coarse coal products from vibrating basket centrifuges. The technique involves injecting a turbulent stream of compressed air, via a manifold inserted into the centrifuge, through the bed of coal particles as it is traverses the centrifuge basket. The air blows water from the coal bed into the centrate stream. Over the last few years CSIRO and Novatech Consulting have been developing air purging, with the objective of reducing residual moisture by 1 wt% compared with conventional centrifuge operation. Such a moisture reduction would provide the Australian coal industry, which is the world’s largest exporter of coal, with substantial financial savings in downstream transport and handling costs.

This paper describes the results obtained when air purging was scaled up from pilot plant (2-4 tph) to commercial (up to 70 tph) scale operation. Reductions in residual moisture close to the 1 wt% target were achieved. The costs of installing and operating air purging are predicted to be much lower than the financial savings that would accrue from lower moisture products.

B.B. Gönül and Ö. Özcan THE USE OF SURFACTANTS IN PRESSURE FILTRATION OF VERY FINE DOLOMITE AND QUARTZ MINERALS (pages 94-97)

bullet Abstract

bullet The effect of surfactants on the pressure filtration of fine grained (x50 = 15 μ m) dolomite and quartz minerals was investigated in this study. The relationship between the surfactant type, concentration and surface tension of the slurry and the filtration rate and residual moisture content of dolomite and quartz minerals was analysed. The laboratory experiments showed that all types of surfactants increased the filtration rate of minerals and decreased the residual moisture content of the cakes. In the dolomite filtration a nonionic type was the most effective reagent, in the quartz filtration an anionic surfactant was the most effective type.

J. Umbría, A. Macias-Machín, A. Lecuona and A. Espino GAS CLEANING USING AN ATOMISED ULTRA FREEZING SEPARATION UNIT (pages 100-105)

bullet Abstract

bullet This paper describes the influence of operating variables such as gas velocity, liquid velocity, dust particle size and temperature of the atomised water used in the venturi scrubber of an Atomised Ultra Freezing Separation Unit (FUA). In this device there are two different units. In the first (termed filter) a venturi scrubber cleans the polluting dust laden gas and in the second a helicoidal heat exchanger (termed condenser) volatile organic compounds (VOCs) are recovered using liquid nitrogen as a refrigerant.Dust collection was more effective when the liquid to gas ratio increased and a low atomising water temperature improved the overall dust collection efficiency by more than 34 % when the temperature decreased from 25 to 0 ºC.

Keywords: Gas cleaning; venturi scrubber; water temperature.

O. Gundogdu, M.A. Koenders, R.J. Wakeman and P. Wu PERMEATION WITH VIBRATED MEDIA: EXPERIMENTS AND MODELLING (pages 106-113)

bullet Abstract

bullet Experiments and theoretical modelling are presented on cake permeation effects with a vibrated septum in a dead-end filter configuration. The key effect is that there is a critical vibration amplitude. Below this amplitude the cake remains intact and may even densify somewhat to display increased flow resistance. Above the critical amplitude the particle-fluid mixture may fluidise. In the latter case the vibration is strongly attenuated to such a degree that it is felt in a localised region near the septum only. Under these circumstances the septum is unclogged and the permeability of the system as a whole increases dramatically. Modelling the locally fluidised state is done by considering the motion of one particle that interacts both with the septum and the rest of the cake via a rough lubrication interaction. The results of the model show that substantial loss of contact interaction between septum and particle is possible. The parameter range in which this occurs is predicted by the model and is shown to be in the right order of magnitude when compared with the experiments. Furthermore, an analysis of the completely fluidised cake is given.

Keywords: Permeation; vibration filtration; modelling.

C. Johansson and H. Theliander MEASURING CONCENTRATION AND PRESSURE PROFILES IN DEADEND FILTRATION (pages 114-120)

bullet Abstract

bullet A laboratory filter press has been constructed with the capability of producing both liquid pressure profiles and concentration profiles with respect to the height of the filter cake and time during the course of a filtration experiment. The pressure is measured at 8 heights by means of capillary tubes placed inside the formation zone of the cake. The solid material concentration is obtained by attenuation measurements using a γ-radiating 241Am source and an NaI(Tl)-scintillation detector. It is also possible to perform cake washing experiments with the piston press. Experiments on a lignin sludge, a compressible material that is difficult to filter, have been conducted and show that both the pressure and concentration measuring systems function correctly. In this paper, solid compressive pressure profiles, solidosity profiles and filtration data are presented for lignin sludge.Keywords: Cake filtration; solidosity and pressure measurements; specific resistance.


Published papers: Volume 3, Issue 1

Author(s) Title, page numbers and abstract
D.A. Patterson DETERMINATION OF BEST AVAILABLE TECHNIQUES: METHODS AND CASE EXAMPLES (pages 12-17)

bullet Abstract

bullet Under the European Integrated Pollution Prevention and Control Directive (96/61/EC) there is a need to define the best available techniques (BATs) for pollution prevention and control for a number of industries.A number of methods have been developed in Europe for determining BAT, including life cycle analysis (LCA) and multi-criteria approaches. In the UK, a simpler method has been recommended by the Environment Agency, the Scottish Environment Protection Agency and the Northern Ireland Environmental Heritage Service. This method consists of two basic components: the assessment of environmental impacts using a series of simple calculations to determine parameters such as emissions to air, emissions to surface water, global warming potential and photochemical ozone creation potential and the balancing of environmental impacts against capital and operating costs. Despite its simplicity, this methodology is modular and flexible, allowing the possibility of more advanced techniques (such as LCA) to be used in the modules to address any deficiencies.

Despite this, the method may need to be amended in the future, since the European Integrated Pollution Prevention and Control Bureau is compiling a BAT Reference (BREF) type document on the economic and cross-media effects of BAT determination, due in May 2003.

A. Merry THE USE OF ULTRAFILTRATION FOR COD REDUCTION IN PULP MILL EFFLUENT – A CASE STUDY FROM SWEDEN (pages 18-20)

bullet Abstract

bullet The Enso Stora Fine Paper mill at Nymölla in Sweden is one of the world’s largest manufacturers of bleached magnefite pulp. Commercial pressures in the early 1990’s were pushing the mill to reduce emissions of COD. The solution was to install an ultrafiltration plant reduce COD from the oxygen stage of the bleach plant by 50%.This paper describes the 18 month process of developing and refining the UF process prior to design and start-up of the full scale plant. The experience of successfully operating the plant for seven years are also discussed, and other applications that have been looked at are commented upon.

B.D. Arnold and G. C. Deka AIR FILTRATION PERFORMANCE – SOME REAL WORLD RESULTS (pages 21-23)

bullet Abstract

bullet The establishment of air filter test methods that adequately reflect actual in-use filtration performance is of great significance to the air filtration industry. A key issue in this regard is understanding the elements that impact the performance of filters in the field and developing a test which adequately simulates these elements. One crucial element is the nature of the dust that is entrained in the air to be filtered and ultimately accumulated within the filter media. It is qualitatively understood that dust properties, such as particle size distribution, affect filtration performance over time. Quantitative studies, however, are limited. This paper describes the results of studies conducted to investigate the actual in-use performance of pleat filters. Results are compared with the filtration performance described by ASHRAE 52.2 characterisation.

D. S. Liley and M. Pearse PRACTICALITIES OF FLOCCULANT SELECTION (pages 24-27)

bullet Abstract

bullet The paper describes practical aspects of selecting flocculants for solid-liquid separation using clarification, thickening and pressure belt filtration as examples. Particular attention is given to analysing the initial process requirements and obtaining a representative test substrate. Practical procedures are given and laboratory-scale simulation equipment is described.

S. Cole, P Koklitis and M. Weaver Characterisation and Optimisation of a Filter Medium containing Immobilised Activated Carbon and its Application in Large Scale Purification Processes (pages 28-34)

bullet Abstract

bullet A modern approach to the use of activated carbon in decolourisation and purification of solids and liquids at industrial scale is described. Immobilised carbon in a form that is safe and convenient to handle simplifies the process operation, reduces process time, improves safety and cleanliness, and enhances process control and consistency. Increases in process yield are also achievable. This paper outlines the background to the use of activated carbon, describes the implementation of immobilised carbon, summarises methods of qualification and presents case studies to illustrate process benefits.

F. Tepper, L. Kaledin, G. Lukasic and S.l Farrah FILTERS BASED ON BIOACTIVE NANOFIBRES (pages 34-37)

bullet Abstract

bullet Argonide produces a form of nano alumina fibre that is bioactive in that it attracts and retains virus and other macromolecules by electrostatic forces. These fibres have been incorporated into fibrous (“depth”) filters and have been found to have ~log7-8 retention for viruses even at flow rates several orders of magnitude greater than could be obtained using microporous membranes.

E.S. Tarleton and R.C. Hadley THE APPLICATION OF MECHATRONIC PRINCIPLES IN PRESSURE FILTRATION AND ITS IMPACT ON FILTER SIMULATION (pages 40-47)

bullet Abstract

bullet This paper describes a mechatronic approach to cake filtration where automated constant, variable and stepped pressure filtrations are performed in a consistent manner without altering the inherent characteristics of a feed suspension. Experimental data for the three pressure/flow regimes are presented where cake formation is monitored by micro-pressure transducers capable of providing up to seven independent measures of liquid pressure within 3.3 mm of the filter medium surface.For constant pressure and moderately compressible talc cakes the liquid pressure increased with cake height in a non-linear manner and generally exhibited a concave profile. When a pressure step was applied following a period of constant pressure filtration, the cake structure typically required up to 30 s to reach a new pseudo-equilibrium state. During this time the reciprocal filtrate flow rate vs. filtrate volume plot was non-linear and the liquid pressures in the cake increased rapidly before remaining nearly constant. When the cake was thicker or the pressure step larger, the liquid pressure measured at 0.5 mm above the filter medium either remained constant following the increase in pressure or increased slowly over the 360 s duration of the pressure step.

The constant and step pressure data were analysed to obtain scale-up constants. These were used in process models to give good simulations of constant pressure filtrations but less accurate predictions of constant flow filtrations where pressures were under-predicted at short times and over-predicted at longer times. The latter was attributed to the time delay in cake restructuring following a pressure change.

Keywords: Cake filtration; tomography; micro-pressure transducers; scale-up; stepped pressure.

H. Niemi, J. Kallas and S. Palosaari THE OPTIMISATION OF MULTISTAGE RECYCLE ULTRAFILTRATION AND REVERSE OSMOSIS PROCESSES: AN APPLICATION FOR WASTE WATER TREATMENT (pages 48-54)

bullet Abstract

bullet The simulation and optimisation method for tubular module multistage recycle ultrafiltration and reverse osmosis processes, developed by the authors, was used to study the effect of variations in process and cost parameters on the total cost of effluent treatment. The effect of the number of recycle stages, volumetric concentration ratio (VCR), operating pressure, price of electricity, membrane cost and pay-back time of the investment on the treatment costs were studied. The processes that were investigated included the purification of oil-contaminated water using reverse osmosis and the ultrafiltration of a cutting oil emulsion. In this study the most economic processes were 2 or 3 stage processes for VCR 5 and a 6 stage process for VCR 10. No significant change in the cost was found by varying the operating pressure or the price of electricity or the cost of the membranes by approximately 20% of their initial value. Three different modes of operation, based on the distribution of the total VCR of the process between the recycle stages, were studied. The modes, in which the VCRs of the recycle stages are equal (ECR, equal concentration ratios), gave practically the same results in terms of the costs as they did for the optimisation mode (OPT). In the optimised operation, the concentration ratios of the stages were determined in order to give the minimum costs of the separation. Although both methods can be recommended, the ECR mode requires less than a second in computing time compared with optimisation that may take up to several minutes.

Keywords: Effluent treatment; oil/water separation; process design; reverse osmosis; simulation; ultrafiltration; wastewater treatment.

O. Larue and E. Vorobiev COMPARISON OF ELECTROCOAGULATION BY IRON ELECTRODES AND COAGULATION BY IRON SALTS DOSING ON LATEX SUSPENSIONS (pages 55-60)

bullet Abstract

bullet Compared to more conventional processes such as chemical dosing, electrocoagulation (EC) offers an alternative electrochemical treatment for removing colloids from wastewater. In this paper EC with iron electrodes and chemical dosing with ferrous sulphate or ferric chloride were investigated for two types of latex suspension. The results of both processes were compared through the efficiency of solid/liquid separations performed by sludge sedimentation and filtration. Preliminary testing identified the processes conditions (i.e. pH, coagulant concentration, conductivity and current density in EC) needed to provide optimum coagulation and avoid excessively high energy consumption in EC. Comparisons of the coagulation processes at their optimum conditions showed that EC generated flocs of greater size and/or density accelerated sedimentation and filtration.Keywords: Electrocoagulation; iron electrodes; chemical dosing; iron salts; latex suspensions.