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

Volume 13, Issue 1

BEHAVIOUR OF TWO FILTER MEDIA TO REMOVE ARSENIC FROM DRINKING WATER
Sofia Garrido, Martín Piña, Isaías López, Dagoberto De la O and Raymundo Rodríguez (pages 21-26)

In recent years greater importance has been attached to the arsenic (As) content in water for human consumption. The maximum permissible limits have decreased from 0.050 to 0.010 mg L-1, with protection of public health in mind. The aim of this study was to compare two filter media to remove arsenic from water of well N° 75 located in Torreon, Coahuila, with arsenic concentrations averaging from 0.070 to 0.085 mg L-1. Tests were conducted at laboratory and pilot plant scale with manganese Greensand and sand-anthracite media.

From the batch and column experiments, equilibrium conditions and adsorption constants for manganese Greensand were established. Pilot scale tests were conducted in the well at a flow rate of 0.55 L s-1 and velocities of 4, 7 and 10 m h-1 in order to evaluate the efficiency of arsenic removal. The isotherm model that gave the best fit to the experimental batch experiments results was the Langmuir isotherm, with a maximum adsorption capacity of 0.00656 mg As g-1. In the pilot scale experiments, the difference seen in performance between the manganese Greensand and sand-anthracite filters is due to the size of the grain media. It is concluded that the reduction of grain size favours the very important capacity retentive iron (Fe) hydroxides associated with As.

LONG TERM PERFORMANCE AND MONITORING OF A 10 m3 PILOT PLANT USING TEXTILE FILTER MODULES FOR DIRECT ACTIVATED SLUDGE SEPARATION
Bernhard Gahleitner, Christian Loderer, Harald Schuster and Werner Fuchs (pages 26-31)

The implementation of the Mesh system in a 10 m3 pilot plant at the local wastewater treatment plant in Tulln (Lower Austria), as an alternative process to conventional activated sludge systems (CAS) and membrane bioreactors (MBR), is presented in this study. Separation of sludge and water is performed by a self-forming dynamic membrane which is retained by a woven coarse pore textile filter. The system was operated at high fluxes of 70 L m-2 h-1 at the beginning of the test period and increased to 150 L m-2 h-1. A constantly low pressure loss between 5 and 50 mbar for all fluxes and continuous filtration periods of 3-6 weeks without chemical cleaning could be achieved. The effluent quality of the new system was monitored over a long term period (approx. 6 months) and found to be equal to the new local CAS.

A NEW EXPERIMENTAL SET-UP FOR HIGH THROUGHPUT SCREENING OF FLOCCULANTS
Arthur M.C. Janse, Pim van Hee, Johan A. Vente, Henk Robers, Ton Verkaik and Emile J.A.X. van de Sandt (pages 32-35)

In the fermentation industry frequent use is made of filtration as a unit operation to separate biomass from the continuous aqueous phase. However, filtration is hampered in many cases by the small size of the microbial cells, typically in the order of a few microns. To facilitate the filtration so called flocculation agents have been developed over the years in order to increase the average particle size. Despite their widespread use, selection of the best flocculant and accompanying flocculation recipe is still empirical, mostly based on trial and error, and therefore time consuming.

At the DSM Biotechnology Center equipment is being developed to speed up flocculant selection and the associated flocculation recipe development and optimization. The new set-up is able to test a large number of recipes (100) within a very limited timeframe (24 h) and in a highly automated manner. In this set-up, a flocculation recipe is prepared, consisting of the fermentation broth, flocculation agents like salts and organic polymers, acids or bases and/or dilution water. During additions and a flocculation period (in total 15 minutes) the particle size distribution is followed in time. After the measurement, the flocculation vessel is emptied and cleaned automatically after which the next measurement takes place.

This approach for flocculant selection is valid in the case of a strong relationship between particle size or particle size distribution and specific cake resistance. These relationships are known from other industries, but are very scarce for biotechnology processes. The paper describes the experimental set-up and its capabilities together with the first results relating the particle size (distribution) to the specific cake resistance.

PERFORMANCE AND POSSIBLE INDUSTRIAL APPLICATIONS OF A NOVEL PULSELESS FILTRATION SYSTEM
Sunil D. Sharma, Keith McLennan, Michael Dolan and Alex Ilyushechkin (pages 36-45)

Particulate separation from gas under ambient as well as hot conditions is one of the most important operations in various industries. Depending on the conditions of operation, a number of issues and challenges are associated with a conventional bag or candle filter systems which are actually semi-continuously operated with intermittent reverse cleaning of the filter element. The reverse cleaning is achieved with an additional mechanism and infrastructure on the top of the filter elements that allows pulses of the filtered gas or an inert gas at nearly twice the filtration pressure to pass through the selected filter elements. Obviously, filtration does not occur through the elements being pulse cleaned, but filtration does occur through the rest of the elements which are not pulsed. Therefore, the conventional filtration could be called a semi-continuous process which does not really have any adverse effect on the filtration process, but there are additional costs and several technical issues associated with the pulse cleaning mechanism and its adverse effect on the filter element.

Amongst the generic issues are: (a) tensile strain on the filter elements during reverse cleaning with very high pressure pulse, (b) loss of filtered gas or contamination of product gas with the inert gas used for pulse cleaning, (c) cost of the pulse cleaning system, and (d) particle breakthrough via the cleaned filter element surface. There are specific issues with the filtration processes associated with specific applications, for example, corrosion of the filter element, permanent deposition on the filter and bridging, large pressure variation during filtration of a gas with a heavy loading of particles etc. In order to address some of these issues a pulseless filtration system has been developed at CSIRO. This paper describes a novel concept of pulseless filtration and compares its performance with the conventional pulsed filtration system. The paper also highlights other possible applications of the pulseless filtration system, its benefits and limitations.

NEW OPTIONS TO BETTER EVALUATE EFFICIENCY AND CAPACITY OF COMBUSTION ENGINE FUEL FILTERS
Christophe Peuchot and Nicolas Petillon (pages 46-52)

The new high pressure direct injection systems for road and off-road vehicles combustion engines have tighter clearances which make them more sensitive to fuel particulate contamination. New requirements appear on fuel cleanliness and on all components making the fuel system. To ensure correct fuel cleanliness, engine manufacturers have to specify more efficient filters. The filtration efficiency of fuel filters is traditionally evaluated by standard methods such as ISO 19438. This method is used worldwide and requires the use of a mineral oil with a viscosity of 13 mm2/s at a test temperature of 40ºC. The contaminant specified is ISO MTD according to ISO 12103-1 A3.

The experience of many test laboratories, both internal and via international round robin exercises, has shown that standard test results do not simulate real filters in modern operational conditions precisely enough. Research has been launched to study the impact of various standard test parameters (fluid viscosity, surface tension/contact angle, contaminant size distribution and concentration…) on the measured filtration efficiency and retention capacity. Other parameters related to fluid flow conditions also explain differences between laboratory test results and behaviours in actual conditions.

The paper presents results obtained at various conditions for actual diesel and petrol fuel filters and quantifies their impact on apparent behaviour. Tests performed using the low viscosity fluid ISO 4113 and ISO FTD in steady flow conditions with steady and variable contaminant concentrations are reported. A new approach, based on the principles of the European standard method EN 13443, is presented. It consists of using alternate contaminant concentrations: low ones close to that measured on industrial fuels to give efficiency results close to reality and high ones to accelerate the clogging whilst checking the downstream fuel quality is constant whatever the contamination level of the fuel to filter.

EXPERIMENTAL STUDY OF FILTER CLOGGING WITH POLYDISPERSE PARTICLES
Ryan Sothen, Yanli Chen, Pengfei Zhao and Bruce J. Tatarchuk (pages 53-57)

The influence of dust loading on pressure drop was examined for two filtration media loaded with polydisperse particles under various face velocities. Each media displayed the traditional depth and surface loading pressure drop growth found in previous research. However, this research observed a fundamental correlation between the loading coefficient and the face velocity at which the media was aged. Media loaded at lower face velocities were found to transition from the initial depth loading stage to surface loading at lower mass captured per available filtration area and possessed higher loading coefficients. These effects were the result of dendrite shaped structures being preferentially formed at lower velocities due to a shift in deposition mechanisms from impaction to interception. The dendrite shaped structures eventually caked the upper layers of the filter and prevented subsequent particles from loading into the depths of the fibrous media. Scanning electron micrographs were used to verify the cake formation.

DETERMINATION OF FILTRATION PROPERTIES OF MINERAL SUSPENSIONS FROM ANALYTICAL CENTRIFUGATION DATA
Maksym Loginov, Nikolai Lebovka and Eugene Vorobiev (pages 58-64)

This work is focused on the use of data obtained by centrifugal consolidation of mineral suspensions for the prediction of deadend filtration. The new method for analysis of centrifugal consolidation data and the evaluation of pressure dependencies of particle volume fraction, specific filtration resistance and consolidation coefficient of mineral sediments in the low and moderate pressure region (<100 kPa), is proposed.  The applicability of the method for analysis of centrifugal consolidation of different mineral suspensions (calcium carbonate, bentonite, laponite) is discussed.