Maria Manuela Pinheiro

Biofilm formation: hydrodynamic effects on internal diffusion and structure

Diffusion in microbial films produced by Pseudomonas fluorescens under turbulent flow conditions was studied using an inert substance (LiCl). Mass transfer coefficients in the biofilm were measured during formation of the biological deposits and for biofilms developed under different fluid velocities. Mass transfer rates in the biofilm decreased with time, and more quickly in the case of biofilms subjected to high shear stresses. The latter show lower final thicknesses and lower internal diffusivities. The so‐called “active layer”;, if it exists, does not seem to have a fixed thickness (as proposed by some authors), since it will depend on the environmental conditions, particularly on fluid velocities.

Surface interactions and deposit growth in fouling of heat exchangers

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Effect of metallic ions on the adhesion of biofilms formed by Pseudomonas fluorescens

Abstract Data on the adhesion of biofilms formed by Pseudomonas fluorescens to aluminium, copper and brass surfaces are reported in this paper. Biofilm thicknesses after 48 h were lower on the brass plates than on the other two metals. The results are compared with predictions of bacterial adhesion obtained by the method of van Oss et al. (C.J. van Oss, M.K. Chaudhury and R.J. Good, Chem. Rev., 88 (1988) 927), based on the evaluation of the change in the free energy of adhesion of the interacting systems. The presence of metallic ions released by the surfaces into the environment seemed to affect bacterial metabolism and adhesion and were taken into account to explain the discrepancies between experimental data and thermodynamic predictions. The possible effects of the extracellular polymers excreted by the bacteria on their attachment abilities are also stressed.

Biofouling in Heat Exchangers

Heat exchangers are used to transfer heat from a hot fluid to a cold fluid. In general, the two fluids flow through appropriate channels (tubes, spaces between parallel plates or between tubes) within the equipment. Solid surfaces made of metal or, less often, of some polymer (teflon, e.g.) separate the fluids.

Effect of Design and Operating Variables on Biofouling

Biofouling, like other types of fouling, may cause serious problems in heat transfer equipment. In general, the formation of deposits is dependent on several physical and chemical variables, but in what respects bioufouling other conditions have to be considered. These are related with the growth and reproduction of microorganisms in the fluid and also in the films. In this work reference is made specially to the effects on bioufouling of: fluid velocity; surface characteristics; surface and fluid temperature; pH of the fluid; nutrient concentration; presence of inorganic suspended particles