The cohesive strength of microbial biofilms cultivated on a rotating disc has been measured using fluid dynamic gauging (FDG). The thickness of heterotrophic mixed culture biofilms was found to depend on substrate concentration and shear force at the biofilm surface during the cultivation. For high substrate concentrations and low shear forces the biofilm thickness increased to several 100 microm within 7 days. Low substrate concentration and higher shear forces yielded thin biofilms of about 100 microm thickness. Independent from cultivation conditions and thickness of the biofilms their cohesive strength ranged between 6.0 and 7.7 N m(-2). The ratio between cohesive strength measured with FDG and shear forces applied during biofilm cultivation have ranged from 200 to 1,100. Higher concentrations of iron in the cultivation media has a positive effect on the stability of the biofilms cultivated. By using the CLSM technique a stable base biofilm with a high amount of stained EPS glycoconjugates could be visualized after gauging. The thickness of the base biofilm was about 100 microm for all biofilms cultivated and was not removable under the applied shear conditions used during FDG.

Structure and shear strength of microbial biofilms as determined with confocal laser scanning microscopy and fluid dynamic gauging using a novel rotating disc biofilm reactor

In recent years, the advances in microbiology show that biofilms are structurally complex, dynamic and adaptable systems including attributes of multicellular organisms and miscellaneous ecosystems. One may distinguish between beneficial and harmful biofilms appearing in daily life as well as various industrial processes. In order to advance the growth of the former or prevent the latter type of biofilm, a detailed understanding of its properties is indispensable. Besides microbiological aspects, this concerns the determination of mechanical characteristics, which provides the basis for material modelling. In the present paper the existing experimental methods that have been proposed since the 1980s are reviewed and critically discussed with respect to their usefulness and applicability to develop numerical modelling approaches.

Recent advances in mechanical characterisation of biofilm and their significance for material modelling

Fluid dynamic gauging for measuring the strength of soft deposits

On-line fouling/cleaning detection by measuring electric resistance-equipment development and application to milk fouling detection and chemical cleaning monitoring

Investigation of alkaline cleaning-in-place of whey protein deposits using dynamic gauging

This paper describes the development of a novel proximity gauging technique for soft deposits, exploiting a siphon effect. This non-contact technique has the capability to measure the thickness of soft deposits on a surface in situ and in real time. A theoretical model of performance has been developed and its validity demonstrated by calibration experiments. Local thickness measurements of soft deposits such as whey protein deposit, supermarket butter and sticky foam on metal surfaces had an accuracy of ±20 μm for a deposit thickness of 500 to 1000 μm. The potential of this technique for on-line monitoring of fouling and cleaning processes in liquid environments is demonstrated by preliminary studies of alkali (NaOH) cleaning of whey protein deposits from stainless steel surfaces.



On decrit dans cet article la mise au point d'une nouvelle technique de jaugeage de proximite pour des depots mous, exploitant un effet siphon. Cette technique sans contact a la capacite de mesurer l'epaisseur de depots mous sur une surface in situ et en temps reel. Un modele de performance theorique a ete developpe et sa validite est demontree par des experiences de calibration. Des mesures d'epaisseur locales de depots mous tels que des depots de proteines de petit-lait, du beurre de supermarche et de la mousse collante sur des surfaces metalliques ont une precision de ±20 μm pour une epaisseur de depot de 500 a 1000 μm. Le potentiel de cette technique pour la surveillance en continu des precedes de refoulement et de nettoyage dans des environ-nements liquides est demontre par des etudes prelim-inaires de nettoyage a la soude (NaOH) de depots de proteines de petit-lait sur des surfaces d'acier inoxydable.

N. Macleod

Papers

Development of a novel non-contact proximity gauge for thickness measurement of soft deposits and its application in fouling studies