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

Volume 11, Issue 2

STUDY OF DEPOSITION AND SEPARATION OF SUBMICRON PARTICLES IN NANOFIBRE COMPOSITE FILTERS
Thomas Bahners and Eckhard Schollmeyer (pages 93-99)

A growing interest in the integration of nanofibres in media for surface as well as deep bed filtration can be observed. The present paper summarizes a study of the morphology of deposition and mechanisms of separation in multi-layer deep bed filters, predominantly with regard to submicron particles in liquid filtration. The considered composite filters were prepared as stacks of alternating layers of commercial nonwoven and electrospun nanofibre webs with variation in the thickness of the nanofibre layers. Analogous stacks made-up of only commercial nonwoven served for comparison. While the results indicate geometric separation purely due to pore size, as well as some contribution of impact driven separation, for micron sized particles, scanning electron microscopy (SEM) and combined X-ray spectroscopy (SEM/EDX) show deposition morphologies of submicron particles that are exclusively due to particle diffusion, i.e. statistical variation of the ideal trajectories. Particle separation/deposition mainly occurred in the nanofibre layers.

FILTER MEDIA PORE SIZE COMPARISON BETWEEN POROMETRY AND CHALLENGE TESTING USING SPHERICAL STANDARDS
Graham Rideal and Jamie Storey (pages 99-104)

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

PRODUCTION OF CONCENTRATED YOGURT USING SUPERABSORBENTS AND A PERMEABLE MEMBRANE
Abdolmajid Maskooki, Ali Ahmadpour and Masoud Rezaee (pages 105-114)

Superabsorbent polymers (SAP) are materials that absorb and retain water and aqueous solutions up to several hundred times their own weights within their structure, even under pressure. Reducing the time of dewatering by permeable membrane and superabsorbent polymers for the production of traditional concentrated yogurt was investigated. Yogurt samples were dewatered using vertical and wide bed permeable membranes with and without SAP. The effects of SAP and position of the bed on the amount of dry matter and soluble solid during reduction of moisture content were evaluated at different time intervals and continued for 180 mins.

The results showed that using polymeric superabsorbent combined with a wide bed reduced the dewatering time by one third with respect to conventional methods. At a specific time interval, using superabsorbent with a wide bed increased the dewatering efficiency by approximately 68% compared to the conventional method, while dewatering using a wide bed without SAP increased dewatering efficiency only by 10% compared to the usual vertical bed method. The dewatering process did not affect the soluble solid content of the tested yogurt. The results may be practically applicable to the industrial dewatering processes of many other foods.

FILTRATION OF NANOPARTICLES: PRESENTATION OF FANA TEST BENCH
N. Michielsen, T. Lelandais, C. Brochot and S. Bondiguel (pages 114-117)

A test bench for the analysis of air filter penetration has been developed at IRSN. The paper introduces this nano-aerosol filtration test bench (FANA) and the methodology used to measure filter penetration as accurately as possible for nanoparticles. Two configurations are compared by measuring the penetration through a metallic grid. The results obtained are identical. In addition, penetration results using two filtration velocities and a particle size range of 2.5 to 400 nm are presented for different types of filtration media (F6, F9, HEPA).

EXPERIMENTAL STUDY OF THE INFLUENCE OF PROCESS VARIABLES ON THE PERFORMANCE OF A HORIZONTAL BELT FILTER
Mikko Huhtanen, Antti Häkkinen, Bjarne Ekberg and Juha Kallas (pages 118-123)

This paper introduces an experimental study that was carried out to determine the influence of several different process variables on the performance of a horizontal vacuum belt filter. Laboratory scale tests were performed according to the multilevel full factorial design by using a conventional Buchner test unit. The investigated process variables were the volumetric feed rate of the slurry, dewatering time, amount of wash liquid used and solids concentration of the feed suspension. The parameters that were used for describing the performance of the process were the cake moisture content, production capacity of the filter and the purity of the washed filter cake. The results obtained from these tests were used to create different kinds of regression models for all of the studied responses.

Several different kinds of test designs were also extracted from the initial full factorial design for defining the minimum number of tests required to obtain satisfactory results for the investigated application. Comparison of different models showed that the amount of test work could be efficiently reduced by utilizing the statistical design of experiments and empirical modelling tools.

EVALUATION OF CONSOLIDATION-SEDIMENTATION PROPERTIES FOR THE BATCH GRAVITY SEDIMENTATION OF CONCENTRATED SUSPENSIONS
Nobuyuki Katagiri, Takeshi Hashimoto and Eiji Iritani (pages 123-128)

Consolidation-sedimentation behaviour of consolidated sediments under the action of gravity was investigated using highly concentrated suspensions of titanium dioxide particles under conditions of various pH, initial height and initial concentration. The average consolidation ratio of the consolidated sediment was analysed on the basis of the simplified analytical solution obtained using the modified Terzaghi model with the moving Lagrangian coordinate system. The modified average consolidation coefficient increased in almost direct proportion to the total volume of solids per unit cross-sectional area, which changes the driving force of consolidation-sedimentation due to the overlying weight of the solid particles. The variations with time of the height of the consolidated sediment were adequately modelled using the analytical solution describing the average consolidation ratio with the aid of the relation that the equilibrium height was represented by a power function of the total volume of solids for a specified pH.