Biofilm formation by Pseudomonas fluorescens

The formation of biofilms on heat exchange surfaces was studied using water contaminated with Pseudomonas fluorescens. The rate of deposition and the maximum amount of deposit decrease as the fluid velocity increases. The processes occurring at the interface and in the biofilm appear to govern the build-up of the deposit. together with the removal (shear stress) mechanism. Values of the attachment and biological growth rates were calculated from the changes observed in the biofilm thermal resistances after suppressing the addition of nutrients to the flowing water. In both cases there is a decrease for higher velocities.JNICT. Portugal. through Project no. 8750

Reação de cultivares de cenoura a meloidogyne incognita raça 1 e Meloidogyne mayaguensis.

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Surface interactions and deposit growth in fouling of heat exchangers

Fouling of heat exchangers is a costly problem in industJ)'. There is a need for a better understanding of the phenomena involved in the build up of deposits on surfaces. The paper reviews the basic mechanisms of fouling, emphasizing their rdle in determining the overall fouling rate. Mass transfer, adhesion, chemical or biological reactions can be the rate limiting processes depending on the design and operating conditions of the heat exchanger. Reference is made to the most common types of fouling, particularly in water systems, and to their interaction with corrosion of metallic surfaces. Special attention is devoted to adhesion, since the formation of fouling layers is primarily a surface process. The main forces of adhesion and the methods fa predicting adhesion tendencies are reviewed. The paper presents and discusses data obtained in laboratory studies on fouling caused by inorganic particles, by microorganisms, and also by both of these types of foulants acting simultaneously. Synergistic phenomena (positive and negative) seem to occur when two oc more types of foulants are present in the fluid, but the final result is still unpredictable. Data on the effects of fluid velocity, temperature and surface material are also presented and discussed.(undefined

Interaction between different fouling agents in water systems

Publicado em "Heat transfer 1990 : proceedings of the Ninth International Heat Transfer Conference", Jerusalem, Israel, Vol. 5 (1990)Most of the fouling studies have been up to now focused on the build up of deposits caused by only one foulant. Although this type of research allows a more clear identification of the mechanisms involved in the formation of deposits, the study of more realistic situations is now needed. The paper reports the results of fouling tests where different fouling agents were present in water: kaolin plus magnetite particles, and bacteria (Pseudomonas jl.uorescens) plus kaolin particles. Deposit formation was monitored through heat transfer measurements. The tests were performed with water flowing at several velocities and the data were compared with previous results obtained using a single foulant. in an attempt to determine possible changes in the processes controlling the fouling rate. Increased fouling resistances and rates were observed when kaolin particles were suspended in the bacteria - - water system. The kaolin - magnetite interaction seems to decrease the final amount of deposit and, at the same time, to increase its mechanical strength. Modifications in the metabolic processes or in the adhesion forces may account for the observed changes

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

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.(undefined

Dynamics of biofilm formation

[Excerpt] Biofilms found in industrial systems are composed by living organisms such as bacteria, fungi and algae, and by non-living material such as inorganic particles and extracellular substances produced by the microorganisms. Biofilms are unwanted in heat exchangers, tubes, valves, etc. , Cthe so-called biofouling). Oppositelly, their biological activity finds a very useful application in water and wastewater treatment. The growth of microbial films on surfaces in contact with a circulating fluid involves different steps : the formation of a "conditioning film" made of organic molecules existing in the fluid ; the attachment of microorganisms to the surface, ei~her by direct contact or with the assistance of biopolymers excreted by the cells ; the growth and reproduction of the microorganisms, together with the production of a biopolymer network, at the expenses of the nutrients available in the fluid ; the sloughing off (erosion, removal> of parts of the biofilm by the action of the flowing fluid. [...]info:eu-repo/semantics/publishedVersio

Evolução dos níveis de tolerância a queima das folhas em cultivares de cenoura.

Este trabalho teve como objetivo avaliar a evolução ds cultivares de cenoura da Embrapa Hortaliças quanto à tolerância à queima das folhas.bitstream/item/57212/1/BPD-75.pd