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Item Measurement of local effective diffusivity in heterogeneous biofilms(1998-11) Beyenal, Haluk; Tanyolac, A.; Lewandowski, ZbigniewWe have developed a novel technique to measure local effective diffusivity distribution in heterogeneous biofilms. Mobile microelectrodes (tip diameter 10 μm) and the limiting current technique were employed to measure the effective diffusivity of electroactive species introduced to natural and artificial biofilms. We calibrated the microelectrodes in artificial biofilms of known effective diffusivity and known density. In mixed population biofilms, local effective diffusivity varied from one location to another and decreased toward the bottom of the biofilm. We related local effective diffusivity to local biofilm density using an empirical equation. Surface-averaged biomass density depended on liquid flow velocity at which the biofilms were grown. The higher the flow velocity, the denser were the biofilms. Our technique permits fast evaluation of local effective diffusivity and biofilm density in heterogeneous biofilms.Item Spatial relations between bacteria and metal surfaces(1997) Little, Brenda J.; Wagner, Patricia A.; Lewandowski, ZbigniewItem Quantifying biofilm structure(1999) Lewandowski, Zbigniew; Webb, D.; Hamilton, Martin A.; Harkin, GaryThis article defines some quantitative parameters for describing the structure of a biofilm. The parameters can be calculated from a two-dimensional cross-sectional image on a plane parallel to the substratum within an in situ biofilm. Such images can be acquired using a confocal scanning laser microscope (CSLM). The parameters will eventually be used for eliciting relationships between the biofilm's structure and its biochemical function, and for computer model evaluation. The results shown here indicate that the structural parameters appear to be reaching steady-state conditions as the biofilm grows to a steady state.Item Electrochemical concepts and techniques in the study of stainless steel ennoblement(1998) Dickinson, Wayne H.; Lewandowski, ZbigniewItem An electrochemical technique to measure local flow velocity in biofilms(1998-12) Xia, Fan; Beyenal, Haluk; Lewandowski, ZbigniewThe limiting current technique and a mobile microelectrode were used to measure local flow velocity in biofilms. The microelectrode was calibrated using the particle tracking technique in conjunction with confocal scanning laser microscopy (CSLM). A relationship between the limiting current density and the local flow velocity was found using nonlinear regression. This relationship was the same whether biofilm was present or not. Therefore, we used the measurements of limiting current density to evaluate flow velocity distribution around biofilm clusters. The flow velocity distribution was affected by the geometry of interstitial voids and by their orientation with respect to the flow direction in the main conduit. Flow velocity measurements using the limiting current technique were faster than similar measurements using particle tracking with confocal scanning laser microscopy.Item The accuracy of oxygen flux measurements using microelectrodes(1998-12) Rasmussen, Kjetil; Lewandowski, ZbigniewAn electrochemical analog of a biofilm was constructed to test the accuracy of oxygen flux measurements using microelectrodes. We used a cathodically polarized graphite felt attached to the bottom of a flat plate open channel reactor as the reactive surface consuming oxygen. The oxygen flux to the felt was calculated from the polarization current. Microelectrodes were used to measure the oxygen profiles above and within the graphite felt. From the shape of the oxygen profile we evaluated the oxygen flux to the graphite felt. This provided us with two sets of data, the true oxygen flux, calculated from polarization current, and the oxygen flux estimated from microelectrode measurements. Comparing these two fluxes, for different flow velocities, showed that the fluxes evaluated from the polarization current were different from those evaluated from the oxygen profiles. The differences were likely caused by the presence of the microelectrode in the mass boundary layer and/or by the simplifying assumptions accepted in computational procedures employed to calculate oxygen fluxes. For low flow velocities, between zero and 1.0 cm s−1, the differences were velocity sensitive; the higher the flow velocity, the bigger the difference. For higher flow velocities, between 1 cm s−1 and 3 cm s−1, the flux of oxygen estimated from the microelectrode measurements was consistently approximately 80% higher than the true oxygen flux estimated from the polarization current.Item Microelectrode measurements of local mass transport rates in heterogeneous biofilms(1998-08) Rasmussen, Kjetil; Lewandowski, ZbigniewMicroelectrodes were used to measure oxygen profiles and local mass transfer coefficient profiles in biofilm clusters and interstitial voids. Both profiles were measured at the same location in the biofilm. From the oxygen profile, the effective diffusive boundary layer thickness (DBL) was determined. The local mass transfer coefficient profiles provided information about the nature of mass transport near and within the biofilm. All profiles were measured at three different average flow velocities, 0.62, 1.53, and 2.60 cm sec−1, to determine the influence of flow velocity on mass transport. Convective mass transport was active near the biofilm/liquid interface and in the upper layers of the biofilm, independent of biofilm thickness and flow velocity. The DBL varied strongly between locations for the same flow velocities. Oxygen and local mass transfer coefficient profiles collected through a 70 μm thick cluster revealed that a cluster of that thickness did not present any significant mass transport resistance. In a 350 μm thick biofilm cluster, however, the local mass transfer coefficient decreased gradually to very low values near the substratum. This was hypothetically attributed to the decreasing effective diffusivity in deeper layers of biofilms. Interstitial voids between clusters did not seem to influence the local mass transfer coefficients significantly for flow velocities of 1.53 and 2.60 cm sec−1. At a flow velocity of 0.62 cm sec−1, interstitial voids visibly decreased the local mass transfer coefficient near the bottom. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:302–309, 1998.Item Resistance of biofilms to the catalase inhibitor 3-amino-1,2,4-triazole(1998-07) Liu, Xiping; Roe, Frank L.; Jeasaitis, A.; Lewandowski, ZbigniewConsortia of catalase positive bacteria consisting of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Klebsiella pneumoniae, in both the planktonic form and as biofilms, disproportionate hydrogen peroxide into oxygen and water. The biofilm, however, continued to disproportionate the hydrogen peroxide in the presence of the catalase inhibitor, 3-amino-1,2,4-triazole, while the planktonic organisms did not. While the bacterial catalase–peroxidase–dismutase system was probably responsible for the disproportionation of hydrogen peroxide in both cases, biofilms resisted inhibition of this enzyme system. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59: 156–162, 1998.Item Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop(1998-03) Stoodley, Paul; Lewandowski, Zbigniew; Boyle, John D.; Lappin-Scott, H. M.Mixed population biofilms consisting of Pseudomonas aeruginosa, P. fluorescens, and Klebsiella pneumoniae were grown in a flow cell under turbulent conditions with a water flow velocity of 18 cm/s (Reynolds number, Re, =1192). After 7 days the biofilms were patchy and consisted of cell clusters and streamers (filamentous structures attached to the downstream edge of the clusters) separated by interstitial channels. The cell clusters ranged in size from 25 to 750 μm in diameter. The largest clusters were approximately 85 μm thick. The streamers, which were up to 3 mm long, oscillated laterally in the flow. The motion of the streamers was recorded at various flow velocities up to 50.5 cm/s (Re 3351) using confocal scanning laser microscopy. The resulting time traces were evaluated by image analysis and fast Fourier transform analysis (FFT). The amplitude of the motion increased with flow velocity in a sigmoidal shaped curve, reaching a plateau at an average fluid flow velocity of approximately 25 cm/s (Re 1656). The motion of the streamers was possibly limited by the flexibility of the biofilm material. FFT indicated that the frequency of oscillation was directly proportional to the average flow velocity (u(ave)) below 9.5 cm/s (Re 629). At u(ave) greater than 9.5 cm/s, oscillation frequencies were above our measurable frequency range (0.12–6.7 Hz). The oscillation frequency was related to the flow velocity by the Strouhal relationship, suggesting that the oscillations were possibly caused by vortex shedding from the upstream biofilm clusters. A loss coefficient (k) was used to assess the influence of biofilm accumulation on pressure drop. The k across the flow cell colonized with biofilm was 2.2 times greater than the k across a clean flow cell. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 536-544, 1998.Item The role of biomineralization in microbiologically influenced corrosion(1998) Little, Brenda J.; Wagner, Patricia A.; Lewandowski, Zbigniew