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

2000-1

PUblished papers: Volume 1, Issue 4

Author(s) Title, page numbers and abstract
S. Weir and G.M. Moody TRENDS IN THE DEVELOPMENT OF FLOCCULANTS AS AIDS TO SOLID/LIQUID SEPARATION (pages 11-12)

bullet Abstract

bullet Trends in the development of commercially available flocculants and their utility have been identified. Increased molecular weight flocculants are finding use in the alumina industry and for sewage sludge pre-treatment. Highly crosslinked flocculants offer benefits in performance for sewage sludge dewatering, whilst the use of encapsulated flocculant technology is leading to enhanced performance for the dewatering of coal slurries. In biotechnology, fermentation cell broth separation is enhanced by low molecular weight flocculants.

R. Reed SOME APPLICATIONS OF MEMBRANE TECHNOLOGY TO BEER PRODUCTION: CROSSFLOW MICROFILTRATION FOR BEER CLARIFICATION AND HYDROPHOBIC MEMBRANES FOR THE TRANSFER OF GASES TO/FROM BEER (pages 13-17)

bullet Abstract

bullet This article summarises work carried out under the direction of the author whilst working for Brewing Research International on the application of crossflow microfiltration for beer clarification and hydrophobic membranes for the control of gas content in beer.

In the case of crossflow filtration of beer, technical issues surrounding the impact of fouling on the removal of critical components form the beer can largely be overcome by selection of appropriate membranes and backflushing. However, commercial considerations have prevented full-scale implementation. Hydrophobic membranes are in commercial use for the addition of nitrogen and the removal of oxygen and excess carbon dioxide from beer.

B.M. Verdegan, P. Herman et al. ENGINE OIL FILTRATION – TECHNICAL RESPONSES TO CHANGING CUSTOMER NEEDS (pages 17-19)

bullet Abstract

bullet Engine owners are increasingly aware that oil filters not only protect against wear, but also play a major role in improving engine reliability, improving fuel economy, controlling costs and protecting the environment. This has resulted in trends towards extended service intervals and the need for environmentally responsible filters.

This paper discusses these trends, focusing on four technologies developed to meet these needs: venturi combination filters, cone-stack centrifuges, incinerable filters and in-place cleanable oil filters.

K.C. Plumb and A. McLeish CLEAN IN PLACE DUST COLLECTS WITH SINTERED METAL ELEMENTS (pages 20-23)

bullet Abstract

bullet This article covers the use of sintered metal filter elements within dust collectors connected to pharmaceutical equipment. The dust collectors have a reverse air jet system and contain a number of filter elements. These are used to collect product powders that can then be transferred back into the process. Sintered metal elements have been used to allow the whole system to be cleaned in place using water or solvent and this in turn overcomes the need to break the primary containment of the equipment. The requirements of the reverse air jet system within the collector and in place cleaning techniques can be conflicting, however the resulting problems have been overcome. Those systems that are now operational have indicated that systems using sintered metal filter elements can be validated and meet with the requirements of the pharmaceutical industry.

A. Jena and K. Gupta A NOVEL TECHNIQUE FOR CHARACTERIZATION OF PORE STRUCTURE OF CERAMIC MEMBRANES (pages 23-26)

bullet Abstract

bullet Ceramic membranes find extensive applications because of their corrosion resistance and high temperature resistance. Pore characteristics of the modern ceramic membranes are controlled by the composite nature of their structure. A new technique has been developed that may be used to characterize such membranes. The membrane sample is soaked in a liquid that fills all the pores in the sample. Air pressure on one side of the sample is increased so as to remove the liquid from the pores. Because the pores in the coating are usually much smaller that those in the base material, the flow rate becomes a measure of the pore characteristics of the coating. A completely automated instrument is used to record gas pressure and flow rate. These data are analysed to find the largest pore size, mean pore size, pore size distribution, gas and liquid permeability, and surface area. Data obtained with a ceramic membrane are presented. Besides being appropriate, this technique has many operational advantages.

V. Kochergin and R.W. Howe MEMBRANE FILTRATION OF RAW BEET JUICE (pages 26-30)

bullet Abstract

bullet Over the past thirty years many sugar technologists have researched and evaluated the use of membrane technology within the sugar industry. The unit processes in which membranes may be applicable are clarification, purification, concentration and colour removal. Although there are opportunities for membrane technology in the sugar industry, the initiatives to date have generally proven to be uneconomical and unreliable to introduce on a larger scale. More recently, Amalgamated Research Inc. (ARi) sponsored by nine sugar companies worldwide have been researching a particular application of membrane technology which when coupled with chromatographic separation offers a potential re-configuration of the beet sugar process. Were the development of this technology to be successful then it could provide an alternative juice purification technique for consideration. Although at an early stage in its development the process offers improvements in efficiency, operating costs and environmental impact.

The purpose of this paper is to present the process and economic factors that need consideration for applications of membrane filtration in the sugar industry.

TRANSACTIONS PAPERS
E.S. Tarleton and S.A. Morgan AN EXPERIMENTAL STUDY OF ABRUPT CHANGES IN CAKE STRUCTURE DURING DEAD-END PRESSURE FILTRATION (pages 93-100)

bullet Abstract

bullet An automated apparatus has been used to obtain experimental data for the dead-end, constant pressure filtration of aqueous zinc sulphide suspensions. The apparatus and particulate/suspension properties are described and filtration data typical of that acquired during the investigation are presented. The conditions under which intuitively unexpected changes in cake structure occur are identified. It is shown how filtration parameters such as pressure, filter cell diameter and particulate dispersion all influence the onset of both irreversible and essentially reversible changes in cake structure and how these changes induce disturbances in the expected filtrate flow. Analyses of the experimental data and their relation to previous studies suggest that more localised changes in cake structure are responsible for the effects observed. The most probable mechanism is the migration of particle fines within a forming cake leading to the establishment of preferential flow channels; alternative mechanisms are also presented and discussed.

It is concluded that an abrupt change in cake form is more likely during the filtration of suspensions containing loosely networked particles and when filter cell dimensions are larger.

Keywords: Filtration; tomography; structured solids; networked particles; cake collapse; compressibility.

M. Mota, J.A. Teixeira, W.R. Bowen and A. Yelshin BINARY SPHERICAL PARTICLE MIXED BEDS: POROSITY AND PERMEABILITY RELATIONSHIP MEASUREMENT (pages 101-106)

bullet Abstract

bullet A continuous function relating the porosity of a mixture, ε, and the large particle volume fraction, xD, on binary mixtures of spherical particles has been established. The incorporation of the proposed porosity model into the conventional Kozeny-Carman equation gives a good agreement between the measured and the predicted permeability vs. xD. Based on this relationship and on the dependence of ε vs. xD a model predicting tortuosity and permeability was obtained, having demonstrated that the tortuosity may significantly alter the permeability of a mixed bed. The proposed model shows that the simulated permeability curve presents a minimum for xD values that are specified by the particle size ratios. The proposed model may be useful for the analysis of transport phenomena in granular beds as well as in engineering applications.

Keywords: Mixed beds; porosity; tortuosity; permeability; modelling; experiment.

W. Koch, W. Höflinger, E. Pongratz and D. Oechsle MULTIPLE- AND SINGLE-PASS OPERATION IN A CONTINUOUS PRESSURE FILTER WITH ROTATING DISCS AND CAKE THICKNESS LIMITATION BY SCRAPERS (pages 107-110)

bullet Abstract

bullet In this paper the differences between multiple- pass and single- pass operation were investigated for a continuous pressure filter with rotating discs and cake thickness limitation by a knife scraper. The filtration principle of the investigated pressure filter is similar to the thin-cake filter described in1-4. However, the filter investigated in this paper works with rotating filter discs and stationary scrapers. In many cases single-pass operation is designed on the basis of multiple-pass operation tests at laboratory scale. It is therefore interesting to clarify the differences in the cake build-up mechanism and the resulting cake resistances for these different modes of operation in order to estimate failures when single-pass operation is designed on the basis of multiple-pass tests. The results of the filtration experiments in multiple-pass and single-pass operation showed that the formation of the filter cake essentially depends on the rotation speed of the filter discs. At high rotation speeds the limitation of the filter cake thickness occurs due to turbulence effects and the effect of particle segregation dominates the filter cake formation. Hence, the constant amount of fine particles in the feed throughout filtration for single-pass operation (due to a larger total volume of suspension to be filtered compared with multiple-pass operation) leads to increased deposition of fine particles in the filter cake. At low rotation speeds the limitation of the cake thickness changes from turbulence effects to the cutting action at the scraper edge, hence the filter cake thickness becomes greater than at higher rotation speeds.

Furthermore, the effect of particle segregation influences the filter cake formation less than at higher rotation speeds because of the lack of vertical particle movement relative to the disc surface in laminar crossflow conditions between the filter discs. At low rotation speeds equal cake resistances occur, while at high rotation speeds the cake resistance is higher for single-pass operation compared with multiple-pass operation.

Keywords: Continuous cake building filtration; rotating discs; scrapers; cake thickness limitation.

D. Condie, C. Veal, R. Amal and I. Tsui Improving understanding of the effect of floc properties on the vacuum filtration of fine coal (pages 111-116)

bullet Abstract

bullet Despite the widespread use of polymer flocculants, their application to enhance the vacuum filtration of fine (-0.5+0 mm) coal is still poorly understood. In this paper small angle light scattering was used for determining the size and structure of conditioned coal flocs and the results correlated with cake moisture from bench-scale vacuum filtration tests. Floc size was characterised primarily as the proportion of the solids passing 25 m m, since these finest particles exert most influence on filter performance. Floc structure was characterised by a fractal scattering exponent (FSE), which was assumed to be a measure of floc compactness. The work has provided a new insight into the relationships between floc conditioning, floc properties, cake properties and filtration behaviour. Ultimately this might form the basis of an on-line technique for maximising filter performance.

Keywords: Vacuum filtration; coal; flocculation; light scattering.

R. de Lima Isaac and C.S.B. Fitzpatrick UPFLOW DIRECT FILTRATION: PERFORMANCE EFFECTS OF DIFFERENT BACKWASH STRATEGIES (pages 117-120)

bullet Abstract

bullet The influence of backwash method on upflow direct sand filtration, followed by downflow filtration, was investigated. The influent was a kaolin suspension coagulated with aluminium sulphate. Two different backwash methods were tested: water only, at 20% expansion and simultaneous air and water at collapse-pulsing conditions. Filtrate turbidity and particle counts were monitored for filtration rates of 5 and 10 m3 h-1. The influence of backwash conditions on filtrate quality was assessed. For an influent turbidity of 20 NTU (30 mg l-1 of suspended solids plus coagulant dosage of 5 mg l-1), the upflow filter produced a high quality filtrate. For an influent turbidity of 100 NTU (150 mg l-1 of suspended solids plus an alum dose of 10 mg l-1) subsequent downflow filtration was needed to obtain acceptable filtrate quality. Particle count data during the ripening period, including size ranges for Cryptosporidium and Giardia, show the ripening period to be independent of wash regime, but the peak is higher when a combined air and water wash is used.

Keywords: Upflow direct filtration; backwashing; ripening; particle counts.


PUblished papers: Volume 1, Issue 3

Author(s) Title, page numbers and abstract
A. Urkiaga, L. de las Fuentes et al. RED WINE CLARIFICATION BY MICROFILTRATION (pages 4-7)

bullet Abstract

bullet Wine making differs from other beverage production technologies in that the quality properties of the final product are not exactly predictable as many factors (e.g. weather, soil conditions) affect grape composition. It is also subject to numerous rules and restrictions dictated by local, national and international regulations and laws, and by culture and tradition. Although different technologies have been implemented in wine manufacturing, it is still a very traditional process. One of the most common operations includes a filtration stage to remove residual yeast, solids and colloids, normally achieved by conventional depth filtration with diatomaceous earth filters. However, the used diatomaceous earth from these filters will soon be considered a hazardous waste and its disposal will involve significant costs.

Alternatively, membrane filtration is emerging as a promising technology for this purpose. Its main advantage lies in its ability to perform wine clarification/filtration/pasteurisation in a single step in continuous operation with clean in place (CIP) strategies. Its use for white and red wine clarification has become common. However, for red quality wines the maintenance of organoleptic properties in the final product restricts its application. The viability of the technology has been proved by normalised sensorial evaluation of Rioja Alavesa microfiltered red wine compared with traditionally produced wine.

B. Jefferson, A. Laine, C. Bedel, P. LeClech and S. Judd SUBMERGED MEMBRANE BIOREACTORS AND THEIR ROLE IN WASTEWATER TREATMENT AND REUSE (pages 8-9)

bullet Abstract

bullet The potential of advanced biological unit operations for the recycling of grey and black waters has been evaluated. The membrane bioreactor (MBR) demonstrated the greatest efficacy towards water recycling in terms of all the usual quality determinants. The initial flux rate through the system was 28 l m-2 h-1, which then gradually decreased to a stable level of 8 l m-2 h-1, with no further decline and so no cleaning required. This demonstrated the process to be operating under sub critical flux conditions where no irreversible fouling occurs. Wastewater recycling is emerging as an integral part of water demand management throughout the world. The major benefit associated with it is the preservation of high quality supplies, alleviating current stresses on potable resources as well as offering environmental and economic advantages. Preference in the UK is for internal water recycling such as domestic grey and black water reuse, whereby water is reused from sources local to the demand. Domestic water recycling is an attractive option in the UK due to a relatively high domestic water consumption coupled with an intensive population. Domestic water use accounts for 40% of the total water usage in the UK. Given that over half the population lives in towns of 100,000 population or greater, water recycling in urban regions is an attractive option.

C.J. Sherwin, C.T. Ta, R. Scriven and D. Richardson SEDIMENTATION TANK PERFORMANCE STUDIES USING COMPUTATIONAL FLUID DYNAMICS (pages 10-12)

bullet Abstract

bullet The performance of sedimentation tanks is studied using computational fluid dynamics (CFD). The flow and solid particle concentration profile under steady state conditions are simulated using the two-phase (solid/water) Lagrangean coupled model. Flow velocity vectors are compared with Acoustic Doppler Velocimetry (ADV) measurements. The results show qualitative agreement. A tracer test is simulated using the flow profile to obtain the residence time distribution (RTD). Simulation is carried out for both a circular final settlement tank and a rectangular primary tank.

TRANSACTIONS PAPERS
W.W.-F Leung and A.H. Shapiro AN ACCELERATING VANE APPARATUS FOR IMPROVED CLARIFICATION AND CLASSIFICATION IN DECANTER CENTRIFUGES (pages 61-67)

bullet Abstract

bullet In an improved feed accelerator system for solid bowl and screen bowl decanters, a continuous feed stream is accelerated to full tangential speed as it is laid onto a separation pool in the centrifuge bowl. The full centrifugal force thus generated provides good performance in terms of the clarification or classification of fine slurries. Conventional accelerator designs, on the other hand, have poor acceleration efficiency, resulting in lower throughput and poor process performance. The improved accelerating apparatus is installed in each port of the feed compartment. An inwardly extending baffle at the trailing face of the port counteracts the Coriolis force generated by the discharge of feed slurry through the port. As the feed moves through the vane apparatus, it gains a high velocity (that is the feed is overspeeded), so that its tangential velocity is greater than its tangential velocity at the discharge radius. Then, as the feed passes to the larger radius at the pool surface, conservation of angular momentum causes a reduction in tangential velocity and an approximate match where the feed enters the pool. Turbulence, mixing, inefficiency and wear are thereby reduced. An additional feature – a “smoothener”, spreads the feed circumferentially, thus minimising concentrated jets that impinge upon and disturb the pool surface. The more quiescent pool facilitates settling.

The technology has been thoroughly tested and proven in the laboratory. Many field installations with the vane apparatus design have demonstrated process benefits in terms of either higher throughput or better process quality in both clarification and classification applications. In cases where polymer is used for the agglomeration of fines or low-density biosolids, polymer dosage can be reduced as the floc is gently accelerated, thus minimising floc breakage.

Keywords: Feed acceleration; decanter centrifuges; overspeeding vane; Coriolis; feed ports; efficiency.

S.K. Sharma, G.F. Ijpelaar and J.C. Schippers IRON OXIDE COATING DEVELOPMENT ON FILTER MEDIA (pages 68-72)

bullet Abstract

bullet The development of an iron oxide coating on filter media is a prerequisite for effective iron removal from groundwater. The rate of development of the coating and its characteristics may be influenced by raw water quality, process conditions and characteristics of the filter media. Laboratory scale short column experiments were conducted to study the effect of pH, influent iron concentration and type of filter media on the development of iron oxide coatings on the filter media. Increases in the surface extractable iron content (SEIC) and iron(II) adsorption capacity (AC) of filter media with the coating development were measured. Coating developed faster on filter sand at pH 7.0 than at a pH 6.0. Coated sand developed at pH 6.5 and 7.0 had a higher iron(II) AC compared to coated sand developed at pH 6.0.

Coating development was faster at the influent iron concentrations of 4.0 and 6.0 mg l-1 compared to 1.0 mg l-1 and the coated sand developed at an iron concentration of 6 mg l-1 had the highest iron(II) AC. The AC for iron(II) increased rapidly with increasing SEIC until the sand was fully covered with iron oxide. Thereafter, the iron(II) AC increased very slowly despite a steady increase in the SEIC.

Among the three media tested basalt had the highest iron(II) AC and coating development was fastest on basalt followed by olivine and then sand. Conditioning of new media at higher feed water pH and/or higher iron concentration could be a strategy to reduce ripening time and to develop media with high iron(II) adsorption capacity.

Keywords: Groundwater; iron removal; iron oxide coating; adsorption capacity.

D. Tao and B.K. Parekh CERAMIC CAPILLARY FILTRATION OF ULTRAFINE COAL SLURRY (pages 73-80)

bullet Abstract

bullet Ceramic capillary vacuum filtration of ultrafine coal slurry (<0.15 mm) was investigated under various experimental conditions using a ceramic filter plate supplied by the Outokumpu Mintec Oy. Parameters examined included cake formation time, cake drying time, type and dosage of flocculants, surfactants and metal ions. Results showed that cake drying time had significant effects on cake moisture but cake formation time affected both cake moisture and solids throughput. The anionic flocculant substantially reduced cake moisture, but only slightly reduced solids throughput. The cationic flocculant provided a three fold increase in solids throughput at a dosage of 20 g t-1, while cake moisture essentially remained unchanged. Of three different types of surfactants, the cationic surfactant was most effective in reducing cake moisture and increasing solids throughput. The addition of metal ions significantly increased solids throughput, but also increased cake moisture.

The lowest cake moisture of 14% was obtained using 10 g t-1 anionic flocculant, while the highest solids throughput of 390 kg m-2 hr-1 was found using 1.0 kg t-1 cationic surfactant. All cationic reagents (cationic flocculant, surfactant and metal ions) are highly effective in increasing solids throughput of the ceramic capillary filter.

Keywords: Coal dewatering; vacuum filtration; flocculation.

S.K. Teoh, R.B.H. Tan, D. He and C. Tien A MULTIFUNCTION TEST CELL FOR CAKE FILTRATION STUDIES (pages 81-90)

bullet Abstract

bullet A new test cell to determine filter cake properties has been developed. This multifunction test cell can serve as an accurate Compression-Permeability (C-P) cell, as well as a variable-volume filtration chamber, thereby enabling direct comparison and correlation between data. It is equipped with a computerised test system that can automatically control the operating parameters, such as the applied loading and the moving speed and vertical travel of the piston. It also provides a means for the determination of the transmitted pressure, the wall friction exerted by the filter cake, the cake displacement rate and the filtrate flow rate. The C-P test data generated from this new multifunction test cell is able to provide a reasonable prediction, within 2-15%, of the average specific resistance, obtained from the actual filtration process in the pressure range of 1 to 8 bar g.

Keywords: Cake filtration; compression-permeability cell; porosity; specific resistance; permeability.


Published papers: Volume 1, Issue 2

Author(s) Title, page numbers and abstract
N. Bugli, C. Bennett and B. Smith PERFORMANCE AND Service Life of Engine Air Cleaners (pages 7-11)

bullet Abstract

bullet Initial efficiency is one of the key performance measures of automotive engine air cleaners (EAC). Performances of EAC are generally measured and evaluated in the laboratory using standard test procedures and test dusts that may or may not represent real world conditions.

Typical laboratory performance levels of initial efficiency and dust capacity for three major air filtration technologies are presented. Service life of an EAC is related to its dust/contaminant holding capacity and its restriction rise over time. Evaluating performances of EAC in real world conditions provide meaningful data. Field evaluations are also presented for light and medium duty vehicles (passenger cars, light/medium trucks) to understand EAC performance and service life requirements.

P. Gullett and A. Hayns REMOVAL OF TOTAL HYDROCARBONS FROM WATER AND AIR (pages 12-13)

bullet Abstract

bullet In January 1996 details of laboratory filtration trials showing that Clerify TM consistently removed over 90% of total (dispersed and dissolved, in particular BTEX) hydrocarbons from water were announced to a produced water seminar in the USA. This paper is a sequel covering 36 months work and case histories since January 1996. During this time, in conjunction with major oil and gas industry operators, field trials have been completed and a wide range of filter systems have been designed, approved, fabricated and are being operated in the field.

Work has started to quantify the performance of Clerify TM as an air filter in field trials. Laboratory results show adequate air permeability and excellent adsorption and loading characteristics. Clerify TM is a filter material that chemically bonds specifically with hydrocarbons and also some other pollutants e.g. heavy metals and corrosion inhibitor. Initially, Clerify TM is processed into sheets that are converted into cartridges for use in standard oilfield filter vessels or specific units produced by AMETEK Filters.

The principal markets identified are: gas and oil facilities; leisure and commercial shipping bilge water; tanker ballast water; and industrial process water.

T.J. Ptak ADSORPTION PROCESS IN THIN ACTIVATED CARBON MEDIA (pages 14-16)

bullet Abstract

bullet Pleatable adsorption media are widely used in a variety of gaseous pollutants control applications including commercial and residential HVAC systems as well as automotive cabin air filtration. Granular activated carbon is particularly suited as an adsorbent for this application.

The objective of this paper is to evaluate the dynamics of adsorption in thin filter media made of granular activated carbon. Experimental breakthrough curves do not follow those observed in thick bed adsorption systems, suggesting that the conventional packed bed adsorption models are not applicable. Conventional theory, on the other hand, can be utilised to predict the initial performance of carbon media and to optimise filter structure.

T. Nordman, O. Ristinen, H. Kuopanportti and M. Tolonen A new air cleaning device for a sintering plant (pages 17-18)

bullet Abstract

bullet A new type of electrostatic precipitator, Ion Blast® air cleaning device, was experimentally used to de-dust a sintering plant flue gas. Instead of having a corona wire, the device is equipped with a high-voltage electrode consisting of a combination of a metal tube and several discharge rings. The rings have sharp needle electrodes and the corona discharge takes place at the tips of the needles. A high voltage of up to 150 kV is led to the discharge electrodes.

The charging in itself is similar to that taking place in traditional electrostatic precipitators, with the exception that so many ions are generated that they form an ion blast effect, which accelerates the migration velocity of dust particles towards the grounded walls of the cleaning chamber. A pilot plant device was tested in the de-dusting process of a sintering plant flue gas. The results showed that dust emissions below 10 mg/Nm3 can be achieved.

C. Peuchot
and T. Hunt
DEVELOPMENT OF ISO STANDARDS IN CONTAMINATION CONTROL AND FILTRATION OF FLUID POWER AND LUBRICATION SYSTEMS (pages 19-20)

bullet Abstract

bullet Many international standards concerning contamination control of hydraulic fluids and lubricants have been considerably revised and new ones adopted. The stimulus for these revisions is primarily the non-availability of the standard test dust ACFTD. As a new ‘dust’ was to be applied an opportunity arose for improving the quality of relevant standards by instituting more rigorous processes in size measurement and relevance to real industrial situations. An important feature has been the introduction of new secondary and on-line calibration.

Previously, with ACFTD, particles had been assessed from the longest dimension, but the new dust uses each particle’s projected area. That meant that the ‘size’ of test dust particles took on a new meaning and a new value. In order not to change the respected ISO 4406 method of coding cleanliness of systems, a novel coding definition had to be devised.

Dust changes in shape have also meant test procedures having to be reassessed. For instance, the ‘multi-pass’ test (ISO 4572) is replaced by the ISO 16889 which is more precise and requires the use of a test stand which is closely validated and controlled. Similarly, for lube oil filters, ISO 4548-12 is now used.

C. Peuchot
and T. Frost
NEW EUROPEAN DRAFT STANDARDS FOR CERTIFICATION OF THE PERFORMANCE OF CARTRIDGE FILTERS AND OTHER DRINKING WATER FILTRATION MATERIALS (pages 21-22)

bullet Abstract

bullet European regulations specify more and more stringent parametric values to define the quality of drinking water. Despite advancement in municipal treatment processes, water distributed inside buildings may suffer from poor quality (e.g. odours and turbidity) due either to the age and length of the network or to the absence of adequate treatment of the many small private supplies. This leads the consumer to look for point of use and point of entry treatment devices, e.g. cartridges or activated carbon filters, UF or RO membranes, to improve the aesthetic quality and protect them against potential disease.

To clarify product specification, create the conditions for fair competition and to protect the interests of end users (by definition a neophyte in domestic water treatment equipment) some European industrialists have agreed on defining standards for the evaluation of product performance. The products include granular filter media (from carbon to diatomaceous earth), cartridge filters and membrane devices. The authors summarise progress on drafting of standards and briefly describe test methods.

TRANSACTIONS PAPERS
O. Larue, T. Mouroko-Mitoulou and E. Vorobiev FILTRATION, CAKE WASHING AND PRESSURISED ELECTROOSMOTIC DEWATERING OF A HIGHLY CONDUCTIVE SILICA SUSPENSION (pages 31-37)

bullet Abstract

bullet A pressurised electroosmotic dewatering process was investigated within a filter cycle on a highly conductive silica suspension. A lab-scale filter-press was electrically and mechanically enhanced to perform the pressurised electroosmotic dewatering under a DC electric field, after the formation and consolidation of a silica filter cake.

The suspension conductivity was too high (22 mS cm-1) to allow efficient electroosmotic dewatering. Two processes were chosen to decrease the conductivity, namely, washing of the filter cake and dilution of the suspension. The filter cycle phases were filtration followed by cake washing or filtration of the diluted suspension, pre-compression of the cake and pressurised electroosmotic dewatering. An attempt was made to minimise the energy consumption and cake water content. The influence of the filter cycle phases, the current intensity and the electrode material were also examined.

The experiments showed that cake washing was more attractive than suspension dilution since it reduced the process time and consumed less water. It was also found that filter cycle phases could be optimised to improve water removal and energy consumption.

Keywords: Silica suspension; pressurised electroosmotic dewatering; filter-press, conductivity.

W.W.-F. Leung DEWATERING BIO-SOLIDS SLUDGE WITH THE VARIGATE TM DECANTER CENTRIFUGE (pages 38-44)

bullet Abstract

bullet High-solids decanter centrifuges have been commonly employed for dewatering environmental or bio-solids sludges throughout the past decade. This paper presents an advancement of this popular technology in which a cake-flow control baffle is installed in the centrifuge to select the driest cake and reject a wetter cake. The baffle also provides high compaction pressure and increases the retention time for cake consolidation and liquid expression. A differential hydraulic head sustained across the baffle in a centrifugal field further facilitates cake conveyance. The opening of the baffle is adjustable for optimal performance depending on the rheology of the cake and the resistance to cake flow at the baffle, which is related to the feed rate to the centrifuge.

Tests on the VariGate TM decanter which was equipped with an adjustable cake baffle at a municipal wastewater treatment plant demonstrated both higher solids throughput and drier cake compared with a conventional high-solids decanter tested side-by-side on the same feed slurry.

Keywords: Decanter centrifuge; high solids; baffle; cake; bio-solids.

G.-M. Klein, J. Meier and V. Kottke USING THE SELECTIVE PARTICLE DEPOSITION DURING CROSSFLOW FILTRATION AS A NEW METHOD OF CLASSIFICATION (pages 45-49)

bullet Abstract

bullet The particle layer build-up during crossflow microfiltration has been studied experimentally. Filtration experiments have been carried out at constant transmembrane pressure and at constant filtrate flux using a polydisperse quartz powder suspension. The constant filtrate flux experiments allow an understanding of the complex and interdependent mechanisms of particle deposition during a constant transmembrane pressure experiment.

The influence of the parameters of crossflow velocity, filtrate flux, and suspension concentration, on the specific particle layer resistance, deposit mass flow density and the particle size distribution of the particle layer was studied. The influence of the density difference between the particle and the fluid on the particle deposition process was examined using bakers yeast as a biological test medium. A specially designed flat duct module that provides defined flow conditions was used for the filtration experiments. The mean particle layer thickness, and surface structure was determined off-line by means of a high resolution laser-distance-sensor.

The effect of the selective deposition of finer particles during crossflow filtration has led to a new method of wet classification of fine particles, where the particle layer is recovered as a fine product. A new classification pilot plant which incorporates membranes was put into operation and demonstrated the feasibility of the basic process steps of this new method.

Keywords: Crossflow filtration; membrane; particle deposition; classification; polydispersity; fine particles.

C.S. Chou, H.C. Lai, J. Smid, J. T. Kuo and S.S. Hsiau NUMERICAL SIMULATION AND EXPERIMENTS IN A LOUVRED MOVING BED FILTER PANEL (pages 50-57)

bullet Abstract

bullet The history of quasi-stagnant filter granule zones near the louvres in three asymmetrical louvre configurations was studied numerically and experimentally. Results of flow patterns obtained by experiments were compared with those obtained by the Discrete Element Method (DEM). Four different flow regions were observed in the moving bed using computer simulations and experiments. The vertical shift of the louvre wall considerably affected the flow patterns in a moving granular bed. In addition, increasing the exit width of the moving granular bed improved the fluidity of the granular flow between the louvred walls.

Keywords: Louvred moving bed filter; DEM; quasi-stagnant zone.


Published papers: Volume 1, Issue 1

Author(s) Title, page numbers and abstract
D. Shaw and M. Price Process and mechanical developments of a modern day filter press and its ancillary equipment to suit the requirements of industry today (pages 8-9)

bullet Abstract

bullet The Filter Press and its well proven technology as a dewatering machine is used extensively in industries covering a wide spectrum. Its application is not restricted or limited to the dewatering of biosolids, it can operate effectively in many other areas particularly in the chemical and pharmaceutical fields where complex filtration, cake washing and air drying techniques are required. In such cases, the filtered product and/or the filtrate can be recovered efficiently and economically. In such applications the filter press has been used successfully for many years, where it has proved to be reliable and consistent in its operation.

Whilst the basic filter press and its process principles are generally well known throughout industry, the modern day developments and levels of automation now available are not so well known or recognised. This paper reviews the process and mechanical developments of a modern day Filter Press.

J. Andries, Ö. Ünal, W. de Jong and P.D.J. Hoppesteyn Hot gas clean up downstream of a coal/biomass fuelled pressurised fluidised bed gasifier using ceramic channel flow filter (pages 10-11)

bullet Abstract

bullet A research programme consisting of a number of interrelated projects in the area of energy production from solids is being carried out using a 1.5 MW process development unit. The installation is equipped with a pressurised, bubbling, fluidised bed gasifier, a high temperature ceramic channel-flow filter and a gas turbine combustor.

This paper describes the experiences with the ceramic filter system during combustion and gasification experiments using coal, miscanthus and straw. The particulate removal performance, the residual pressure drop build-up and the regenerability have been determined during combustion and gasification tests with coal and biomass-coal mixtures.

W. Reimann Purification of agricultural waste water by membranes (pages 12-13)

bullet Abstract

bullet The importance of membrane technologies for waste water treatment has increased in recent years. In order to find out the application limits for liquid agricultural residues, for example by ultrafiltration and reverse osmosis, experiments were carried out on a pilot-scale. The investigations have shown that the permeability and selectivity of membranes for ultrafiltration and reverse osmosis is influenced by the concentration of organic matter, expressed by chemical oxygen demand (COD). This is caused by concentration polarisation at the membrane as a boundary layer effect.

Membrane permeability decreases with increasing concentration of organic matter in waste water, independently of the kind of waste water. Using ultrafiltration for example, COD of waste water is retained up to 92% for milkhouse waste water (feed COD = 1.26 g/l) and up to 35% for a pig slurry (feed COD = 31.6 g/l). Therefore the filtrate of ultrafiltration from waste water with a low concentration of COD can be treated by reverse osmosis to such a degree that the minimum requirements for waste water ingredients are in accordance with the German regulations.

J. Pink Storm water screening to meet the urban waste water treatment directive (pages 14-16)

bullet Abstract

bullet The Urban Waste Water Treatment Directive (UWWTD) cites screening of storm overflows, to prevent aesthetic pollution of our watercourses, as an important issue. The water companies’ asset management plans (AMP3) will be significantly attributed to the topic over the next five years. In March 1998, Huber Technology commenced trials at North West Water’s Wigan WWTW to evaluate the ROTAMAT RoK1 Storm Screen. These were carried out partly in conjunction with a trial programme operated by UKWIR CSO Research Group, and partly under its own initiative.

The first tests were with 6 mm perforations on a side weir installation. Further tests were conducted during the year with the screen mounted in a stilling pond end weir configuration and finally with a 4 mm version on a side weir installation. This paper concentrates on the performance of the screen, in side weir configuration, operating with incoming flows set at 30, 45, 60 and 100 l/s, each with continuation/spill flow splits of 0.1, 0.2, 0.4 and 0.6. The conclusions identify how current environmental demands are best served by equipment currently available.

TRANSACTIONS PAPERS
S. Reymann The intermediate stage of the dead-end filtration process: New insights (pages 3-7)

bullet Abstract

bullet The analysis of volume-time curves in a dead-end filtration experiment can be used to gain understanding of the cake formation process. Two limiting cases are discussed: (1) high zeta-potential, where the particles have a strong double layer interaction and (2) zero zeta-potential where the particles behave collectively as a dense gas.

For (1) the forming cake can be assigned a continuum stiffness and the shape of the volume-time curve is obtained. A micromechanical model for the continuum stiffness of the cake has been developed, which enables accurate predictions of this property. For (2) the ‘granular temperature’ theory is appropriate and characteristic features of the volume time curve are highlighted. Again very few parameters are required. A range of experiments is described which support the theoretical findings.

Keywords: Dead-end filtration; cake formation; particle interactions; granular temperature.

R.J. Wakeman and R. Kotzian Cu2+ and Cd2+ removal from aqueous solutions using lecithin enhanced ultrafiltration (pages 8-13)

bullet Abstract

bullet Copper and cadmium ions are bound to lecithin aggregates which are removed from solution using crossflow ultrafiltration. Feed solution properties such as aggregate size, zeta potential and aggregate shape have been investigated at various surfactant to metal ion ratios. The results of these analytical methods have been used to explain permeate flux profiles and rejection levels obtained during filtration trials. Energy Dispersive X-ray Analysis and Scanning Electron Microscopy were used to investigate interactions on the membrane surface.

The surfactant to metal ion ratio has been shown to have a significant effect on the steady state flux and metal ion rejection. Metal ion rejection increases with increasing surfactant to metal ion ratio, however the maximum metal ion rejection levels decrease with increasing metal ion concentration. Lecithin rejection is not affected by these factors.

Keywords: Ultrafiltration; surfactant enhanced separations; metal ion removal.

M. Beiser, W. Stahl and M. Stiborsky A summary of academic research on decanting centrifuges (pages 14-16)

bullet Abstract

bullet Recent studies have provided improved insights into the procedures for deliquoring bulk materials in decanting centrifuges. These bulk materials can be deliquored, because centrifugal forces can overcome the capillary force at the beach of the decanter.

Experiments with a transparent flow channel have shown, that the resistance of the product as opposed to the flow resistance of the gap between the screw and the bowl determines the deliquoring kinetics. From observations of the liquid flow in the flow channel, a new model for predicting the deliquoring of bulk materials in decanting centrifuges has been developed.

The second part of this article addresses the separation behaviour of sludges in decanting centrifuges. The main conclusion of this work is that the usual assumption of a solid free bowl (i.e., the theory of the equivalent clarifying area) is no longer sustainable. When separating fine grained material, a large amount of solid matter accumulates inside the bowl. This affects the operation as well as the design of such machines.

Finally, the results of studies on the residence time of the liquid phase (centrate) are presented. These studies have shown that there are essential differences in the residence time behaviour for the flow through of the decanter centrifuge when operating with pure water as opposed to with suspension.

Keywords: Decanter centrifuge; dewatering; separation; residence time distribution; drag effects; compression.

H.M. Huotari and M. Nyström Electrofiltration in industrial wastewater applications (pages 17-22)

bullet Abstract

bullet The effect of a constant dc electric field in the crossflow membrane filtration of industrial wastewater was studied. The average electrophoretic mobility of the charged particles and colloids in the samples studied was usually slightly negative. The best flux improvement in electrofiltration was achieved when filtering a sample with very high electrophoretic mobility. In that case the limiting flux could be increased many-fold. The conductivity of the samples studied was over 500 µScm-1. At such conductivities, gas was produced on the electrodes.

The flux enhancement decreased significantly when the membrane worked as an electrode and the gas was produced on the membrane. The problem did not exist when a non-conductive ceramic membrane was used and an electric field was applied across the membrane. However, the high conductivity caused high energy consumption, which is a problem of electrofiltration in industrial wastewater applications.

Keywords: Electrofiltration; fouling; wastewater; conductivity; energy consumption.

R.W.K. Allen, H.G.D. Goyder, J. Macinnes and K. Morris Fluid dynamics of the cleaning pulse in fabric filters (pages 23-28)

bullet Abstract

bullet This paper revisits the concept of the pulse jet Venturi as a pump first proposed by Bakke in 1974. Flows from the reservoir to the pulse tube and then from the nozzle to the filter bag are analysed to allow prediction, from first principles, of the characteristic curve of the Venturi pump. The models developed are compared with experimental measurements of characteristic curves. Reasonable agreement is found for operating ranges typical of operating pulse jet filters.

Keywords : Fabric filters; cleaning; venturi; pumping; modelling.