N e w s a n d V i e w s

Figure 1: Top: Fluid Sys tems 4" tape- wrapped element. Bottom: Standard

flbreglass reinforced plastic (FRP) element.

Further Informatlon from: Fluid Systems, 10054 Old Grove Road, San Diego, CA 92131, USA. Tel: +1 619 695 3840. Fax: +1 619 695 21 76.

New ge la t in f i l ter for air s a m p l i n g A new gelatin disposable filter, the SM 17528-80-ACD, is now available from Sartorius Separation Technology for use with its MD8 air sampler. Customers who purchase a sufficiently high volume of the new filters on an ongoing basis will be eligible for a free MD8 unit (worth approximately £2500).

With gelatin membrane filters, the MD8 consti tutes an airborne microorganism sampling system for accurate, reproducible and quantitative detection of airborne microorganisms in room air, whether conventionally ventilated or under laminar flow. It is particularly suitable for use in the pharmaceutical , food and processing industries and hospitals.

The new filter is an individually packed, ready-to-use, sterile uni t consist ing of a gelatin filter in a holder for the coliection of samples of airborne microbes for analysis. Made of cyrolite, a recyclable material, the holder of the new filter protects the filter during transport .

Being disposable makes it possible to maximize the advantages of the gelatin filter method (i.e. it remains moist during sampling, the volume of air filtered can be measured, it is water soluble) because handling is greatly improved, says the company.

Further Informatlon from: Sartorlus Separation Technology, Longmead Business Centre, Blenheim Road, Epson, Surrey, KT19 9QN, UK. Tel: 0372 728879. Fax: 0372 726171.

Lact ic acid s epara t ion from f e r m e n t a t i o n broths Laboratory scale and pilot plant nanofiltration and reverse osmosis experiments with fermentation broths were carried out by researchers at the Netherlands Institute for Dairy Research (J. Membrane Sol., 92, pp 185-197). They had the foliowing aims:

• to quantify lactic acid rejection and to determine whether a previously developed theoretical model could be used to predict lactic acid rejection; and

• to quantify fouling of NF membranes and to determine the major fouling mechanism.

Lactic acid is a major food preservative that can be produced either by chemical synthesis or fermentation. If the fermentat ion process is carried out without using pH adjustment, lactic acid can be removed using cellulose acetate RO membranes, bu t additional techniques are required to concentrate the dilute lactic acid stream obtained. In this application NF membranes show lower rejection for lactic acid than RO membranes, so both systems were looked at here, along with experiments with broth that w a s

ultrafiltered prior to investigation. For industrial applications a predictive model for

the lactic acid rejection of NF and RO membranes which can be used for process development or opt imizat ion is necessary. This model should take into account fouling of the membranes .

From lactic acid rejection experiments, it w a s

found that the previously-developed rejection model, based on the extended Nernst-Planck equation, could be used to quantify the rejection of RO and NF membranes. Especially at high fluxes the prediction of lactic acid rejection using parameters determined with lactic acid/water mixtures was quite good. At Iow fluxes the predicted rejection of lactic acid was usually lower.

Fouling of the spiral wound NF40 membrane could be quantified by a model in which three different resistances - - membrane resistance, initial fouling resistance and t ime-dependent fouling resistance w e r e

taken into account. In the case of a UF-broth a colloidal fouling model could be used to describe the t lme-dependent fouling, while for a broth a gel layer model was used. It was shown that during NF of an ultrafiltered fermentation broth the initial fouling resistance, resulting from concentrat ion polarization effects, was the predominant resistance. For a fermentation broth the t lme-dependent fouling becomes more important than the initial fouling resistance. This was caused mainly by protein fouling, so it was concluded that it is beneficial to remove the proteins by UF prior to NF.

Further Information from: J.M.K. Timmer, Netherlands Instltute for Dalry Research, Kernhemseweg 2, 6718 ZB Ede, the Netherlands.

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