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Monod Kinetics (monod + kinetics)
Selected AbstractsComputer programs for estimating substrate flux into steady-state biofilms from pseudoanalytical solutionsCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2002Chetan T. Goudar Abstract Fixed-film processes employing microorganisms attached to an inert surface (biofilms) are widely used for biological treatment of municipal and industrial wastewater. For optimal design and analysis of these processes, mathematical models are necessary that describe the dynamics of contaminant transport within these biofilms and the associated contaminant utilization by the microorganisms. However, these governing equations that typically involve Fickian diffusion for contaminant transport and Monod kinetics for contaminant utilization are inherently nonlinear and have no closed form solutions except under special conditions. This can restrict their use in the classroom as cumbersome numerical techniques must be used for their solution. This problem is well documented in the literature and several authors have presented pseudoanalytical solutions that replace numerical solutions with algebraic equations. In the present study, we present pseudoanalytical solution-based computer programs for estimating substrate flux and biofilm thickness for a steady-state biofilm. Depending upon the intended end use, these programs can either partially or totally automate the solution process. In the partial automation mode, they can serve to enhance student understanding of important concepts related to steady-state biofilms, while complete automation can help bring more challenging and realistic problems associated with steady-state biofilms into the classroom. The programs have been tested on MATLAB version 5.0 and are available as freeware for educational purposes. © 2002 Wiley Periodicals, Inc. Comput Appl Eng Educ 10: 26,32, 2002; Published online in Wiley InterScience (www.interscience.wiley.com.); DOI 10.1002/cae.10017 [source] Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoirENVIRONMENTAL MICROBIOLOGY, Issue 9 2006Karel, imek Summary We investigated net growth rates of distinct bacterioplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus availability by analysing eight in situ manipulation experiments, conducted between 1997 and 2003, in the canyon-shaped ,ímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phosphorus limitation (range of soluble reactive phosphorus concentrations , SRP, 0.7,96 µg l,1). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate constants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betaproteobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabilities for possible life strategies of different bacterial phylogenetic lineages are discussed. [source] Diffusion and Monod kinetics to determine in vivo human corneal oxygen-consumption rate during soft contact-lens wearJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Mahendra Chhabra Abstract The rate of oxygen consumption is an important parameter to assess the physiology of the human cornea. Metabolism of oxygen in the cornea is influenced by contact-lens-induced hypoxia, diseases such as diabetes, surgery, and drug treatment. Therefore, estimation of in vivo corneal oxygen-consumption rate is essential for gauging adequate oxygen supply to the cornea. Phosphorescence quenching of a dye coated on the posterior of a soft contact lens provides a powerful technique to measure tear-film oxygen tension (Harvitt and Bonanno, Invest Ophthalmol Vis Sci 1996;37:1026,1036; Bonanno et al., Invest Ophthalmol Vis Sci 2002;43:371,376). Unfortunately, previous work in establishing oxygen-consumption kinetics from transient postlens tear-film oxygen tensions relies on the simplistic assumption of a constant corneal-consumption rate. A more realistic model of corneal metabolism is needed to obtain reliable oxygen-consumption kinetics. Here, physiologically relevant nonlinear Monod kinetics is adopted for describing the local oxygen-consumption rate, thus avoiding aphysical negative oxygen tensions in the cornea. We incorporate Monod kinetics in an unsteady-state reactive-diffusion model for the cornea contact-lens system to determine tear-film oxygen tension as a function of time when changing from closed-eye to open-eye condition. The model was fit to available experimental data of in vivo human postlens tear-film oxygen tension to determine the corneal oxygen-consumption rate. Reliance on corneal oxygen diffusivity and solubility data obtained from rabbits is no longer requisite. Excellent agreement is obtained between the proposed model and experiment. We calculate the spatial-averaged in vivo human maximum corneal oxygen-consumption rate as Q = 1.05 × 10,4 mL/(cm3 s). The calculated Monod constant is Km = 2.2 mmHg. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Development and simulation studies of an unsteady state biofilter model for the treatment of cyclic air emissions of an ,-pinene gas streamJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2005Christina Dirk-Faitakis Abstract This paper describes the development and simulation of an unsteady state biofilter model used to predict dynamic behaviour of cyclically-operated biofilters and compares it with experimental results obtained from three, parallel, bench-scale biofilters treating both periodically fluctuating concentrations and constant concentrations of an ,-pinene-laden gas stream. The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclic biofilters operating at short cycle periods (ie, in the order of minutes and hours). Steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 h cycle period, the dynamic model compared well with experimental results. For long cycle periods (ie, hours and days), removal efficiency decreased after periods of non-loading: the longer the period of non-loading, the poorer the biofilter's performance at the re-commencement of pollutant loading. At longer time scales the model did not effectively predict transient behaviour, as adsorption and changes in kinetic parameters were not accounted for. Modelling results showed that similar biofiltration performance for the cyclic and constant concentration biofiltration of ,-pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically-operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, Cg, max/Cg, relative value of the half-saturation constant in the Monod expression, Ks, and effective diffusivity of ,-pinene in the biofilm, De. Copyright © 2005 Society of Chemical Industry [source] Microbial competition: Study of global branching phenomenaAICHE JOURNAL, Issue 2 2000Abdelhamid Ajbar The stability characteristics of a bioreactor with cell recycle involving the competition between microbial cultures are investigated. The unstructured model, based on Andrew's inhibitory kinetics, involves the pure and simple competition between two microorganisms for a single pollutant. The singularity theory used for this study allows an in-depth analysis of both the static and dynamic bifurcation mechanisms occurring in the system. The hysteresis with five solutions is the highest singularity the system can exhibit. With inhibitory kinetic expressions, the model can also predict self-sustained oscillations for a wide range of parameters. The analysis of clean feed conditions shows that the model cannot exhibit periodic behavior regardless of the growth kinetics model. Analytical criteria are also derived for the coexistence of the competing cultures and for the prevention of wash-out conditions. The stability characteristics for Monod kinetics, derived as a limiting case of the inhibitory kinetic expressions, are incorporated in the general framework offered by the singularity theory. [source] Basic equations of mass transfer through biocatalytic membrane layerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Endre Nagy Abstract The diffusive and convective mass transport through biocatalytic membrane layer (membrane bioreactor), without and with biochemical reactions, have been investigated. Similarly to the two-film theory for gas-liquid system with diffusive mass transport, only, mass transfer rates have been developed for the biocatalytic membrane layer and for the concentration boundary layer on the feed side of the membrane. Overall mass transfer coefficient has also been defined involving the two-layer, simultaneous mass transfer, namely the mass transfer through the concentration boundary layer and biocatalytic membrane layer. The effect of the convective velocity (Pe number) and the biochemical reaction rate, namely first-order and zero-order reactions as limiting cases of the Monod kinetics, are demonstrated on the mass transfer coefficients accompanied by chemical reaction and on the concentration profiles. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Modeling and Biokinetics in Anaerobic Acidogenesis of Starch-Processing Wastewater to Acetic AcidBIOTECHNOLOGY PROGRESS, Issue 2 2004Johng-Hwa Ahn Starch-processing wastewater was anaerobically treated to produce acetic acid in laboratory-scale, continuously stirred tank reactors. The optimal conditions, in which the maximum acetic acid production occurred, were 0.56 d hydraulic retention time, pH 5.9, and 36.1 °C. Acetic acid production at the optimum conditions was 672 ± 20 mg total organic carbonequivalent L,1, which indicated a 75% conversion efficiency of influent total organic carbon into acetic acid. A fourth order Runge-Kutta approximation was used to determine the Monod kinetics of the acidogens by using unsteady-state data from continuous unsteady-state experiments at the optimum conditions. The model outputs and experimental data fit together satisfactorily, suggesting that the unsteady-state approach was appropriate for the evaluation of acidogenic biokinetics. These included ,m, Ks, Y, and kd, which were evaluated as being 0.13 h,1, 25 mg total carbohydrate (TC) L,1, 0.38 mg volatile suspended solid mg,1 TC, and 0.002 h,1, respectively. [source] Analysis of the Activated Sludge Process in an MBR under Starvation ConditionsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2006M. Vukovic Abstract An aerobic membrane bioreactor (MBR) at complete biomass retention was studied over a period of time under starvation conditions. Kinetic parameters were determined in a no-feed batch test. The decay rate of activated sludge, kd = 0.05,d,1, was determined by tracking the decrease of MLSS. The ratio of MLVSS/MLSS was in the range 0.76,0.85. The pH values were between 7.02 and 8.23. As a function of different initial concentrations of MLSS, specific nitrification rates qN, decreased from 4.23 to 0.02,mg-N/(g,MLVSS,d) and specific biodegradation rates qb increased from 0.23 to 1.90,mg-COD/(g,MLVSS,d). From experimental data the kinetic constants for respiration, which followed Monod kinetics, were determined as qO2max = 9.8,mg-O2/(g,MLVSS,h), Kx = 2.9,g/dm3. Additionally, a linear correlation between MLSS and mean floc size was found to exist during the biodegradation process. [source] | |||||||||||||