1,721,061 research outputs found
Flow induced vibrations, drag force, and pressure drop in conduits covered with biofilm
No full textBiofilm was grown in closed conduit reactors under turbulent flow conditions. Structural development of the biofilm suggests that individual microcolonies behave like blunt bodies shedding vortices. The microcolonies assumed elongated forms, termed "streamers", possibly because of an exerted pressure drag force. The streamers when entrained in the water flow vibrated rapidly dissipating kinetic energy from the bulk liquid. The energy was transferred through the biofilm causing the underlying microcolonies to oscillate. The measured pressure drop was partially attributed to the loss of energy due to these flow induced vibrations and oscillations
Liquid flow in heterogeneous biofilms
No full textLiquid flow was studied in aerobic biofilms, consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. Fluorescein microinjection was used as a qualitative technique to determine the presence of flow in cell clusters and voids. Flow velocity profiles were determined by tracking fluorescent latex spheres using confocal microscopy. Liquid was flowing through the voids and was stagnant in the cell clusters. Consequently, in voids both diffusion and convection may contribute to mass transfer, whereas in cell clusters diffusion is the dominant factor. The flow velocity in the biofilm depended on the average flow velocity of the bulk liquid. The velocity profiles in biofilms were linear and the velocity was zero at the substratum surface. The velocity gradients within biofilms were 50% of that near walls without biofilm coverage. The influence of the biofilm roughness on the flow velocity profiles was similar to that caused by rigid roughness elements
Liquid flow and mass transport in heterogeneous biofilms
No full textConvective mass transport in heterogeneous biofilms, consisting of cell clusters and voids, was investigated using oxygen microelectrodes. Oxygen concentration profiles were measured and contour plots constructed at different (average) flow velocities (Uavg). The profiles were used to determine the thickness of the mass transfer boundary layer (δh) above the voids and the cell clusters. The δh above the biofilm was inversely related to flow, as expected, and decreased exponentially with increasing flow velocity. However, the δh above the voids decreased more rapidly than the δh above the cell clusters resulting in two distinct situations; at low flow velocities the oxygen contours were parallel to the substratum but at high velocities were parallel to the irregular biofilm surface. It was concluded that at low flow velocities the biofilm could be modeled one-dimensionally, with fluxes perpendicular to the substratum and the exchange area being equal to the substratum area, but at higher velocities biofilm voids facilitate mass transport and a more complex, three-dimensional model would be more appropriate. In this latter case fluxes are multidirectional, and the exchange area is equal to that of the convoluted biofilm surface
Paper 222. Internal mass transport in heterogenous biofilms - recent advances
No full textProceedings of NACE '95, Orlando, Fl
Measurement of local diffusion coefficients in biofilms by microinjection and confocal microscopy
No full textA new technique for the determination of local diffusion coefficients in biofilms is described. It is based on the microinjection of fluorescent dyes and quantitative analysis of the subsequent plume formation using confocal laser microscopy. The diffusion coefficients of fluorescein (MW 332), TRITC-IgG (MW 150000) and phycoerythrin (MW 240000) were measured in the cell clusters and interstitial voids of a heterogeneous biofilm. The diffusivities measured in the voids were close to the theoretical values in water. Fluorescein had the same diffusivity in cell clusters, voids, and sterile medium. TRITC-IgG did not diffuse in cell clusters, presumably due to binding to the cell cluster matrix. After treatment of the biofilm with bovine serum albumin, binding capacity decreased and the diffusion coefficient could be measured. The diffusivity of phycoerythrin in cell clusters was impeded by 41%, compared to interstitial voids. From the diffusion data of phycoerythrin it was further calculated that the cell cluster matrix had the characteristics of a gel with 0.6 nm thick fibers and pore diameters of 80 nm. (c) 1997 John Wiley & Sons, Inc
The formation of migratory ripples in a mixed species bacterial biofilm growing in turbulent flow
No full textMixed-species biofilms, consisting of Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens and Stenotrophomonas maltophilia, were grown in glass flow cells under either laminar or turbulent flow. The biofilms grown in laminar flow consisted of roughly circular-shaped microcolonies separated by water channels. In contrast, biofilm microcolonies grown in turbulent flow were elongated in the downstream direction, forming filamentous 'streamers'. Moreover, biofilms growing in turbulent flow developed extensive patches of ripple-like structures between 9 and 13 days of growth. Using time-lapse microscopic imaging, we discovered that the biofilm ripples migrated downstream. The morphology and the migration velocity of the ripples varied with short-term changes in the bulk liquid flow velocity. The ripples had a maximum migration velocity of 800 micromh(-1) (2.2 x 10(-7) m s(-1)) when the liquid flow velocity was 0.5 ms(-1) (Reynolds number=1,800). This work challenges the commonly held assumption that biofilm structures remain at the same location on a surface until they eventually detach
Experimental and conceptual studies on mass transport in biofilms
No full textIt is demonstrated that the flow velocity distributions in a flat plate reactor with and without biofilm are considerably different. Flow velocity profiles perpendicular to the channel wall indicate water movement in the space occupied by the biofilm. The flow velocity does not reach zero at the biofilm surface. Water flows through the pores in the biofilm causing convective mass transport. Longitudinal profiles of the flow velocity indicate that the presence of the biofilm disturbs the flow, which increases the entry length required for fully developed viscous flow to be established. Recently it has been shown that biofilms consist of cell clusters separated by interstitial voids. This newly proposed concept of biofilm structure helps to explain these experimental observations. However, the hydrodynamics and mass transport in biofilm systems appear to be more complex than previously assumed
Relationship between mass transfer coefficient and liquid flow velocity in heterogenous biofilms using microelectrodes and confocal microscopy
No full textThe relationship between local mass transfer coefficient and fluid velocity in heterogenous biofilms was investigated by combining microelectrodes and confocal scanning laser microscopy (CSLM). The biofilms were grown for up to 7 days and consisted of cell clusters separated by interstitial channels. Mass transfer coefficient depth profiles were measured at specific locations in the cell clusters and channels at average flow velocities of 2.3 and 4.0 cm/s. Liquid flow velocity profiles were measured in the same locations using a particle tracking technique. The velocity profiles showed that flow in the open channel was laminar. There was no flow at the top surface of the biofilm cell clusters but the mass transfer coefficient was 0.01 cm/s. At the same depth in a biofilm channel, the flow velocity was 0.3 cm/s and the mass transfer coefficient was 0.017 cm/s. The mass transfer coefficient profiles in the channels were not influenced by the surrounding cell clusters. Local flow velocities were correlated with local mass transfer coefficients using a semi-theoretical mass transfer equation. The relationship between the Sherwood number (Sh,) the Reynolds number (Re,) and the Schmidt number (Sc) was found using the experimental data to find the dimensionless empirical constants (n1, n2, and m) in the equation Sh = n(1) + n(2)Re(m) Sc(1/3). The values of the constants ranged from 1.45 to 2.0 for n(1), 0.22 to 0.28 for n(2), and 0.21 to 0.60 for m. These values were similar to literature values for mass transfer in porous media. The Sherwood number for the entire flow cell was 10 when the bulk flow velocity was 2.3 cm/s and 11 when the bulk flow velocity was 4.0 cm/s. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 681-688, 1997
Hydrodynamics and kinetics in biofilm systems - recent advances and new problems
No full textApplication of microelectrode techniques, Nuclear Magnetic Resonance Imaging, and Confocal Laser Microscopy permitted analysis of hydrodynamics, kinetics, and internal structure in biofilm systems. The commonly accepted concept of one dimensional diffusion through a three compartment model (bulk solution, biofilm, and substratum) requires revision based on recent progress in understanding the internal structures of biofilms. Biofilms seem to form three dimensional porous structures with a network of interstitial voids filled with water, forming a network of channels connected with each other and with the biofilm surface. The basic unit of this structure appears to be a bacterial cluster (sometimes called microcolony)
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