Model of steady-state-biofilm kinetics

A steady-state biofilm is defined as one that has neither net growth nor decay over time. The model, developed for steady-state-biofilm kinetics with a single substrate, couples the flux of substrate into a biofilm to the mass (or thickness) of biofilm that would exist at steady-state for a given bulk substrate concentration. Based on kinetic and energetic constraints, this model predicts for a single substrate that a steady-state bulk concentration, S_min, exists below which a steady-state biofilm cannot exist. Thus, in the absence of adsorption of bacteria from the bulk water and for substrate concentration below S_min, substrate flux and biofilm thickness are zero. Equations are provided for calculating the steady-state substrate flux and biofilm thickness for S greater than S_min. An example is provided to demonstrate the use of the steadystate model.     

Biodegradation Kinetic Studies on Phenol in Internal Draft Tube (Inverse Fluidized Bed) Biofilm Reactor Using Pseudomonas fluorescens: Performance Evaluation of Biofilm and Biomass Characteristics

The bioremediation potential of Pseudomonas fluorescens was studied in an internal draft tube (inverse fluidized bed) biofilm reactor (IDTBR) under batch recirculation conditions using synthetic phenol of various concentrations (400, 600, 800, 1000, and 1200 mg/L). The performance of IDTBR was investigated and the characteristics of biomass and biofilm were determined by evaluating biofilm dry density and thickness, bioparticle density, suspended and attached biomass concentration, chemical oxygen demand, and phenol removal efficiency. Biodegradation kinetics had been studied for the suspended biomass culture and biofilm systems. Suspended biomass followed substrate inhibition kinetics, and the experimental data fitted well with the Haldane model. The correlation coefficient, R ², and root-mean-square error (RMSE) obtained for the Haldane model with respect to specific growth rate were .9389 and .00729, respectively, and with respect to specific phenol consumption rate were .9259 and .00972, respectively. It was also observed experimentally that biofilm overcame substrate inhibition effect and fitted the same to the Monod model (R ² = .9831, RMSE = .00884 for specific growth rate and R ² = .9686, RMSE = .00912 for specific phenol consumption rate).     

Evaluation of steady-state-biofilm kinetics

Laboratory-scale biofilm reactors were used to evaluate a model of the kinetics of steady-state biofilm and the concept that there is a minimum concentration, S_min, below which no steady-state activity can occur. With acetate as the ratelimiting substrate, the steady-state concept of S_min was verified for naturally grown biofilms. Substrate removal and biofilm thickness declined rapidly as the substrate concentration approached S_min, which was 0.66 mg/liter for acetate. Using independently derived kinetic parameters, the model of steady-state-biofilm kinetics successfully predicted substrate utilization and biofilm thickness without the need for fitting factors. The results imply that organic materials may persist in water and wastewater, in part, because they are too low in concentration to supply sufficient energy to sustain the microorganisms.     

Growth simulation of Hansenula polymorpha

Summary Cultivation of Hansenula polymorpha with substrate ethanol in a bench-scale tower loop reactor was simulated by means of a distributed parameter model with regard to the dissolved oxygen and substrate in the medium, oxygen and CO₂ in the gas phase, and a lumped parameter model with regard to the cell mass. Space and time independence of the substrate and oxygen limiting constants of the Monod model, K_S and K_O, was assumed. Time variations of the yield coefficients, Y_X/S and Y_X/O, were allowed for.     

Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics

Abstract

Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU⁺), resulting in an effective roughness height (k_s) of 8.8?mm, significantly larger than the physical thickness of the biofilm (1.7?±?0.5?mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, C_f, of the biofilm was 9.0?×?10^?3 compared with 2.9?×?10^?3 for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.     

Substrate consumption and excess sludge reduction of activated sludge in the presence of uncouplers: a modeling approach

A mathematical model with a consideration of energy spilling is developed to describe the activated sludge in the presence of different levels of metabolic uncouplers. The consumption of substrate and oxygen via energy spilling process is modeled with a Monod term, which is dependent on substrate and inhibitor. The sensitivity of the developed model is analyzed. Three parameters, maximum specific growth rate (μ _max), energy spilling coefficient (q _max), and sludge yield coefficient (Y _H) are estimated with experimental data of different studies. The values of μ _max, q _max, and Y _H are found to be 6.72 day^-1, 5.52 day^-1, and 0.60 mg COD mg^-1 COD for 2, 4-dinitrophenol and 7.20 day^-1, 1.58 day^-1, and 0.62 mg COD mg^-1 COD for 2, 4-dichlorophenol. Substrate degradation and sludge yield could be predicted with this model. The activated sludge process in the presence of uncouplers that is described more reasonably by the new model with a consideration of energy spilling. The effects of uncouplers on substrate consumption inhibition and excess sludge reduction in activated sludge are quantified with this model.     

Reductive transformation of TNT by Escherichia coli resting cells: kinetic analysis

Microbial 2,4,6-trinitrotoluene (TNT) biotransformation via sequential nitro-reduction appears a ubiquitous process, but the kinetics of these transformations have been poorly understood or described. TNT transformation by Escherichia coli was monitored and a kinetic model for reductive TNT depletion was developed and experimentally calibrated in this report. Using resting cells of aerobically pregrown E. coli, TNT was quickly reduced to hydroxylaminodinitrotoluenes. The standard Michaelis–Menten model was modified to include three additional parameters: product toxicity (T _c), substrate inhibition (K _i), and intracellular reducing power (RH) limitation. Experimentally measured product toxicity (5.2 μmol TNT/mg cellular protein) closely matched the best-fit model value (2.84 μmol TNT/mg cellular protein). Parameter identifiability and reliability (k _m, K _s, T _c, and K _i) was evaluated and confirmed through sensitivity analyses and via Monte Carlo simulations. The resulting kinetic model adequately described TNT reduction kinetics by E. coli resting cells in the absence or presence of reducing power limitation.     

Modeling of carbon dioxide mass transfer behavior in attached cultivation photobioreactor using the analysis of the pH profiles

The CO₂ mass transfer model associated with growth kinetics of microalgal biofilm in attached cultivation photobioreactor was developed and verified by using the analysis of pH profiles which were in equilibrium with inorganic carbon components concentrations (CO₂, H₂CO₃, HCO₃ ⁻ and CO₃ ²⁻) in medium. Model simulation results showed that the model well presented the biofilm growth process. The overall volumetric mass transfer coefficient of CO₂ was more influenced by CO₂ concentration in aerated gas but less by gas aeration rate and medium circulation rate. Other bio-kinetic parameters related with the microalgal biofilm such as CO₂ diffusion coefficient in biofilm, Monod maximum utilization rate of CO₂, lag phase duration of biofilm and half-saturation CO₂ concentration in the biofilm were independent on operational conditions. The pH profiles provided a way to monitor the variations of inorganic carbon concentrations of medium and to regulate the cultivation of attached microalgal biofilm by CO₂ supplement.

     

Discrimination between rival laccase inhibition models from data sets with one inhibitor concentration using a penalized likelihood analysis and Akaike weights

Laccase from the white-rot fungus Fomes fomentarius was used for the biodegradation of ferulic acid (FA) in the presence of chloride anions. The initial reaction rates of substrate depletion were obtained by reverse-phase HPLC determination of remaining FA since substrate and reaction products have absorption peaks at similar wavelengths. Modelling of time-course data was accomplished by discrimination of the best enzyme inhibition equation from an initial set of seven different models based on Michaelis–Menten kinetics: competitive; uncompetitive; non-competitive; mixed; mixed hyperbolic; mixed parabolic; mixed hyperbolic and parabolic. Corrected Akaike information criterion was used to evaluate the relative merit of each kinetic model in order to rank them and find the more likely one. The discrimination results showed that the models with higher probabilities were the competitive and mixed inhibition types, but Akaike weights supported the selection of competitive inhibition (CI). After optimization by nonlinear regression, laccase kinetic parameters of FA biodegradation in the presence of chloride anions were: V_max?=?0.11?μmol?min^?1?mg^?1, K_m?=?44?μmol?L^?1 and a CI constant K_ic?=?14?mmol?L^?1.     

Comparative analysis of hydrogen-producing bacterial biofilms and granular sludge formed in continuous cultures of fermentative bacteria

A system for biohydrogen production was developed based on long-term continuous cultures grown on sugar beet molasses in packed bed reactors. In two separate cultures, consortia of fermentative bacteria developed as biofilms on granitic stones. In one of the cultures, a granular sludge was also formed. Metagenomic analysis of the microbial communities by 454-pyrosequencing of amplified 16S rDNA fragments revealed that the overall biodiversity of the hydrogen-producing cultures was quite small. The stone biofilm from the culture without granular sludge was dominated by Clostridiaceae and heterolactic fermentation bacteria, mainly Leuconostocaeae. Representatives of the Leuconostocaeae and Enterobacteriaceae were dominant in both the granules and the stone biofilm formed in the granular sludge culture. The culture containing granular sludge produced hydrogen significantly more effectively than that containing only the stone biofilm: 5.43 vs. 2.8 mol H₂/mol sucrose from molasses, respectively. The speculations that lactic acid bacteria may favor hydrogen production are discussed.     

Modeling the Biodegradation Kinetics of Perchlorate in the Presence of Oxygen and Nitrate as Competing Electron Acceptors

A mathematical model was developed to describe the biodegradation kinetics of perchlorate in the presence of nitrate and oxygen as competing electron acceptors. The rate of perchlorate degradation is described as a function of the electron donor (acetate) degradation rate, the concentration of the alternate electron acceptors, and rates of biomass growth and decay. The kinetics of biomass growth are described using a modified Monod model, and inhibition factors are incorporated to describe the influence of oxygen and nitrate on perchlorate degradation. In order to develop input parameters for the model, a series of batch biodegradation studies were performed using Azospira suillum JPLRND, a perchlorate-degrading strain isolated from groundwater. This strain is capable of utilizing oxygen, nitrate, or perchlorate as terminal electron acceptors. The maximum specific growth rate (μ_max) and half-saturation constant (K _S ^don) for the bacterium when utilizing either perchlorate or nitrate were similar; 0.16 per h and 158 mg acetate/L, respectively. However, these parameters were different when the strain was growing on oxygen. In this case, μ_max and K _S ^don were 0.22 per h and 119 mg acetate/L, respectively. The batch experiments also revealed that nitrate inhibits perchlorate biodegradation by this strain. This finding was incorporated into the model by applying an inhibition coefficient (K _i ^nit) value of 25 mg nitrate/L. Combined with appropriate groundwater transport models, this model can be used to predict perchlorate biodegradation during in situ remediation efforts.     

Erodibility and erosion patterns of mudflat sediments investigated using an annular flume

Laboratory flume experiments were carried out, to measure the effect of biota on erodibility of mudflat sediments. The experiments sought to reproduce the environment of the lower mudflat at Hythe, Southampton Water, Southern England; this is characterised by fine grain-size and a surface layer of very fluid mud. Natural sediments were used to produce settled beds in the Lab Carousel, an annular flume of 2 m diameter. The following bed conditions were investigated diatom biofilms; the addition of cockles (Cerastoderma edule); and abiotic sediment, obtained by the addition of sodium hypochlorite. The erosion threshold (τ_crit, calculated with the TKE method) was in the range 0.02–0.20 Pa. Bioconsolidation increased τ_crit considerably: compared to the abiotic sediment experiment, τ_crit was 5–10 times higher depending on the biofilm development. The relationship between τ_crit and water content of sediment (the best proxy for sediment compaction) was as good, or better than between τ_crit and chlorophyll a (proxy for biofilm development). When cockles were introduced, τ_crit was significantly lower (reduction by 50–75% compared with the diatom biofilm experiments), reflecting the surface disturbance by the bivalves. The biofilm erosion was characterised by a patchy pattern: the bed surface stayed mainly uneroded and erosion was visible only on a few elongated patches commencing at some weakness points of the biofilm, then progressing downstream. The results illustrate the importance of the surface heterogeneity: the irregularities of a natural bed (weak points of the biofilm, bioturbations, microrelief, larger roughness elements like shells or algae, etc.) have a determinant effect on the erodibility of biofilms. Such characteristics may have more influence than biofilm strength, because the erosion starts from the weaker areas.     

Biofilm diatom community structure: Influence of temporal and substratum variability

Abstract

Diatoms, which are early autotrophic colonisers, are an important constituent of the biofouling community in the marine environment. The effects of substratum and temporal variations on the fouling diatom community structure in a monsoon-influenced tropical estuary were studied. Fibreglass and glass coupons were exposed every month for a period of 4 days and the diatom population sampled at 24 h intervals, over a period of 14 months. The planktonic diatom community structure differed from the biofilm community. Pennate diatoms dominated the biofilms whilst centric diatoms were dominant in the water column. Among the biofilm diatoms, species belonging to the genera Navicula, Amphora, Nitzschia, Pleurosigma and Thalassionema were dominant. On certain occasions, the influence of planktonic blooms was also seen on the biofilm community. A comparative study of biofilms formed on the two substrata revealed significant differences in density and diversity. However species composition was almost constant. In addition to substratum variations, the biofilm diatom community structure also showed significant seasonal variations, which were attributed to physico-chemical and biological changes in both the water and substratum. Temporal variations in the tychopelagic diatoms of the water were also observed to exert an influence on the biofilm diatom community. Variations in diatom communities may determine the functional ecosystem of the benthic environment.     

Analytical effectiveness calculations concerning the degradation of an inhibitive substrate by a steady-state biofilm

A reaction engineering model for the degradation of an inhibitory substrate by a steady-state biofilm is presented. The model describes both the metabolic rate controlling behavior of this substrate in the biofilm and the effect of diffusion limitation caused by an arbitrary substrate on the active biofilm thickness. An analytical expression for the biocatalyst effectiveness factor is presented on the basis of Pirt kinetics for cell maintenance, first order substrate inhibition kinetics, and zero order substrate consumption kinetics. The proposed expression for the biocatalyst effectiveness factor is much more convenient to incorporate into a macroreactor model than the numerical alternatives. Simple criteria are presented to check the applicability of the model in case of true Monod kinetics. The analytical solution is expected to be particularly applicable to processes where a low soluble organic substrate controls the biomass growth, a situation which is often met in wastewater purification processes of industrial importance. The degradation of phenol by Pseudomonas sp. is treated as an example. (c) 1993 John Wiley & Sons, Inc.     

A comparative study of activity and apparent inhibition of fungal β‐glucosidases

β‐Glucosidases (BGs) from Aspergillus fumigates, Aspergillus niger, Aspergillus oryzae, Chaetomium globosum, Emericella nidulans, Magnaporthe grisea, Neurospora crassa, and Penicillium brasilianum were purified to homogeneity, and analyzed by isothermal titration calorimetry with respect to their hydrolytic activity and its sensitivity to glucose (product) using cellobiose as substrate. Global non‐linear regression of several reactions, with or without added glucose, to a product inhibition equation enabled the concurrent derivation of the kinetic parameters k_cat, K_m, and the apparent product inhibition constant _appK_i for each of the enzymes. A more simple fit is not advisable to use as the determined _appK_i are in the same range as their K_m for some of the tested BGs and produced glucose would in these cases interfere. The highest value for k_cat was determined for A. fumigatus (768 s^?1) and the lowest was a factor 9 less. K_m varied by a factor of 3 with the lowest value determined for C. globosum (0.95 mM). The measured _appK_i varied a factor of 15; the hydrolytic activity of N. crassa being the most resistant to glucose with an apparent product inhibition constant of 10.1 mM. Determination of _appK_i using cellobiose as substrate is important as it reflects to what extent the different BGs are hydrolytically active under industrial conditions where natural substrates are hydrolyzed and the final glucose concentrations are high. Biotechnol. Bioeng. 2010;107: 943–952. © 2010 Wiley Periodicals, Inc.     

Kinetics of potato starch fermentation by Schwanniomyces castellii

The growth behaviour of Schwanniomyces castellii in slurry fermentation systems using untreated potato starch as substrate was studied in order to asses the eventual effect of the initial concentration of substrate (S_o) on cell growth rate. By applying the elementary balance method in combination with a Monod-type kinetic equation it was possible to formulate not only an unstructured model, but also the stoichiometry for such a yeast fermentation process. From a kinetic viewpoint, the Monod model was found to be redundant with respect to the pseudo-first order one, it being impossible to discriminate the contribution of v _M and K _S on the overall fermentation kinetics. Whereas the main yield coefficients appeared to be independent of S _O, the pseudo-first order rate constant was found to be inversely proportional to S _O. Therefore, cell growth appears to be controlled by the initial amount of amylolytic enzymes, that is to some extent proportional to the inoculum size, instead of the initial concentration of potato starch, at least within the experimental range of 3 to 30 g dm³.     

Multiple Approaches to Analyse the Data for Rat Brain Acetylcholinesterase Inhibition by Cyclophosphamide

Acetylcholinesterase (AChE) is an externally oriented membrane-bound enzyme and its main physiological role is termination of chemical transmission at cholinergic synapses and secretory organs by rapid hydrolysis of the neurotransmitter acetylcholine (ACh). Nevertheless, it is well known that cyclophosphamide (CP; nitrogen mustard derivative) is an eminent anticancer drug. The present work addresses multiple approaches to analyze an identical data for rat brain AChE inhibition by CP. These different angels of analysis based on two classical (Lineweaver–Burk as well as Dixon) plots, their secondary replots, a new graphical approach and general built-in equations of GOSA. Thus various kinetic constants (K _I, K _s, K _m, k _sl, V _mao, K _i, k _sli, S _lo, K _maxi, S _K0.5, k _cat and k _sp) were estimated and mode of inhibition discussed in the current study.     

Chloroperoxidase production by Caldariomyces fumago biofilms

Chloroperoxidase (CPO) is a versatile enzyme, which is secreted by the marine fungus Caldariomyces fumago (Leptoxyphium fumago). However, the application of the enzyme is hampered by its high price, which is due to the costly, labor‐intensive purification process. One challenge of the downstream process is the removal of a coproduced black pigment that forms a complex with the active enzyme. While strain development can be considered as an option to reduce the synthesis of the interfering pigment, the metabolism of the microorganism can be altered alternatively by using the biofilm growth mode of the fungus. The aim of this study was to reduce pigment formation during CPO synthesis. We investigated for the first time CPO production during C. fumago biofilm growth initiated through the presence of different microstructured stainless steel surfaces (material number: 1.4571; AISI 316Ti). CPO production by C. fumago was similar when grown as a biofilm or in suspension, whereas pigment formation was drastically reduced by cells grown on moderately structured surfaces (R_a = 0.13 ± 0.02 μm). The possibilities of biofilm growth for changing cell properties and for continuous fermentation are discussed.