Modified Monod Model Research Articles

Phosphorus Threshold for the Growth of Microcystis wesenbergii, Microcystis aeruginosa, and Chlorella vulgaris Based on the Monod Formula

The outbreak of algae in freshwater bodies poses an important threat to aquatic ecosystems, making finding an effective method for controlling algal blooms imperative. Numerous key factors influence algal bloom outbreaks, with nutrient levels in the water body being the decisive factor. Current research regarding the effect of nutrient levels on algal growth shows that phosphorus is a nutrient that influences algal blooms. Herein, we propose the concept of a modified Monod model for the relationship between algal specific growth rate and phosphorus concentration. Through this improved Monod model, we inferred that the phosphorus concentration at a specific growth rate of zero is the lower threshold of phosphorus concentration that limits algal growth and can effectively control algal outbreaks. This lower threshold is denoted as S′. On the basis of this concept, we designed algal growth experiments. Our results provided an equation that effectively describes the relationship between algal growth and nutrient concentration. When three algal species grow under phosphorus-limited conditions, the corresponding phosphorus concentrations at which they maintain a growth rate of 0 are 0.0565, 0.0386, and 0.0205 mg/L as reflected by the following order of their S′ values: Microcystis wesenbergii S′ < Microcystis aeruginosa S′ < Chlorella vulgaris S′. Furthermore, with the increase in phosphorus concentration, the growth of M. aeruginosa becomes faster than that of M. wesenbergii and C. vulgaris. Consequently, M. aeruginosa becomes the dominant population in the water, leading to its predominance in algal blooms. This situation explains the common occurrence of cyanobacterial blooms. Our findings provide a theoretical basis for regulating the concentration of phosphorus to control algal outbreaks. Therefore, our study is of great importance for controlling the eutrophication of water bodies.

Developing an integrated mathematical model of fermentation-pervaporation system for bioethanol production

This study presents a novel integrated model to describe the fermentation-pervaporation system for bioethanol recovery. The proposed model incorporates the effects of by-product inhibition on the fermentation process and variation in feed concentration during the pervaporation process. The model is based on a modified Monod model to describe the fermentation process and the solution diffusion model for the pervaporation process, which can predict the concentrations of biomass, glucose, and ethanol in the bioreactor, as well as the partial flux of ethanol and water, total flux, the volume of permeate, and concentration of ethanol permeate. Simulation results showed that the proposed modified Monod model outperforms the conventional Monod model in predicting biomass, glucose, and ethanol concentrations due to its ability to consider the inhibitory effect of by-products with low mean absolute prediction error values of 4.1%, 12.6 and 5.2%. Moreover, the inclusion of the byproduct inhibitory effect in the fermentation model improved the accuracy of the integrated model in predicting the bioethanol permeation flux by 7.9%. The proposed integrated model provides a useful tool for designing and optimizing fermentation-pervaporation systems for bioethanol recovery to promote the adoption of continuous fermentation at the industrial scale.

The efficient utilization of thiocyanate on simultaneous removal of ammonium and nitrate through thiosulfate-driven autotrophic denitrifiers and anammox

The efficient utilization of thiocyanate remain be an important bottleneck in the low-cost nitrogen removal for wastewaters containing thiocyanate. The study aimed to investigate the feasibility of thiocyanate in removal of nitrate and ammonium through anammox (AN) and thiosulfate-driven autotrophic denitrifiers (TSAD). The results showed that removal of nitrate and ammonium were achieved rapidly utilizing thiocyanate, which was attributed to degradation of thiocyanate by TSAD and cooperation with AN. The utilization efficiency of thiocyanate in nitrogen removal was increased by 250% due to the microbial cooperation. Excess thiocyanate and ammonium did not influence the nitrogen removal amount. However, the nitrogen removal were affected obviously by the biomass ratio (XAN/XTSAD) between AN and TSAD Moreover, the dynamics related to removal of pollutants was described successfully by a modified Monod model with time constraints. These findings offer an insight for efficient utilization of thiocyanate in nitrogen removal via microbial cooperation.

Incorporating parameter variability into Monod models of nutrient-limited growth of non-diazotrophic and diazotrophic cyanobacteria.

Models are widely used tools in aquatic science to understand the mechanism of phytoplankton growth and anticipate the occurrence of harmful algal blooms. However, model parameterization remains challenging and issues that may introduce prediction uncertainty exist. Many models use the Monod equation to predict cyanobacteria growth rate based on ambient nutrient concentrations. The half-saturation concentrations in the Monod equation varies greatly among different studies and depends on environmental conditions. In this study, we estimated the growth rate due to nutrient limitations for two cyanobacteria species (Microcystis aeruginosa and Dolichospermum flos-aquae) using a modified Monod model which allows the half-saturation concentration to vary according to initial nitrogen (N) conditions. The model is calibrated against observations from laboratory experiment where cyanobacteria growth and ambient nutrient concentrations were measured simultaneously, which is rarely done in the literature. Our results show this modified model produce better predictions on growth rate and biomass, indicating many commonly used mechanistic models may need improvement regarding phytoplankton growth representation. Furthermore, our study quantifies the flexibility in cyanobacteria growth parameter across a wide range of environmental N in eutrophic lakes thus provides important information for large-scale modelling applications.

Generalized modelling of effect of oxygenation and glucose concentration on Corynebacterium glutamicum growth and production kinetics

According to the oxygenation level, Corynebacterium glutamicum can produce several organic acids with marginal growth on glucose. A kinetic model was proposed for the C. glutamicum growth and several organic acids production during batch cultures in shake flasks, considering the effect of oxygenation level and glucose availability. In this model, the balance equations for the organic acids contained both production and consumption terms. The growth rate was described by a modified Monod model accounting for glucose consumption or organic acids reconsumption. During model building, identified kinetic parameters showed a close relationship with the kLa value. This relationship, representing a secondary black box model, was embedded in the previous model. The resulting generalized model predicted very well the experimental kinetics and observations under a very large variety of kLa conditions. Using the same methodology, a similar model was developed to describe the behavior of a mutant strain of C. glutamicum 2262 deleted of lactate dehydrogenase in microaerobiosis. With the same excellent agreement between experimental and predicted concentrations, results confirmed that our models can be applied to predict the behavior of various strains and to a large experimental domain of kLa values. It thus can be a good basis to monitor organic acid production.

Inhibition kinetics of bio-based succinic acid production by the yeast Yarrowia lipolytica

Kinetic models that describe the fermentative SA production by the yeast Yarrowialipolytica were developed for the first time. A modified Monod model considering both substrate and product inhibition based on shake flask experiments is proposed to describe the cell growth. Y. lipolytica tolerated up to 302.4 g/L glycerol, and significant decrease in SA yield and prolonged lag phase were observed with glycerol concentration above 212.0 g/L. Among the end-products investigated, acetic acid (AA) was found to have the most inhibitory effect on SA fermentation. The critical concentrations of SA and AA were 243.4 g/L and 57.9 g/L respectively. These demonstrated the greater potential of the yeast than bacterial SA producers. An unstructured model, based on a basic mass-balance of carbon, was used to describe substrate consumption, from which the cell maintenance coefficient ms was estimated to be 0.118 g/(g h). The Luedeking–Piret model was applied to describe the accumulation of organic acids, with SA and AA production following a mixed-growth-associated pattern. The values of the growth-associated term of both SA (0.386 g/g-DCW) and AA (0.208 g/g-DCW) were much higher than those of the non-growth-associated term of SA (0.013 g/(g-DCW h)) and AA (0.010 g/(g-DCW h)) respectively, indicating these products were mainly formed in tandem with yeast growth. After optimisation and validation, the model simulations match the experimental observations well, enabling elucidation of the fermentation characteristics for Y. lipolytica possible. This paper provides key insights into the improvement of SA production and the modelling of inhibition kinetics.

Kinetic model of ethanol inhibition for Kluyveromyces marxianus CCT 7735 (UFV-3) based on the modified Monod model by Ghose & Tyagi

Kinetic model of ethanol inhibition for Kluyveromyces marxianus CCT 7735 (UFV-3) based on the modified Monod model by Ghose & Tyagi

Recovery of ammonia nitrogen and magnesium as struvite from wastewaters in coal‐fired power plant

AbstractThis paper describes a cost‐effective method for recovering ammonia nitrogen (NH4+‐N) from regeneration wastewater by using magnesium recovered from flue‐gas desulfurization (FGD) wastewater in the same coal‐fired power plant. Mg2+ was efficiently removed from FGD wastewater at pH of 11, and the settling performance of Mg (OH)2 was evidently improved by adding anionic polyacrylamide and crystal seed. For NH4+‐N removal optimization by response surface methodology, the results indicated that the molar ratio of phosphorus to nitrogen (P/N) was the more dominant parameter, and the optimum conditions were predicted at Mg/N of 1.1 and P/N of 0.7. At the optimum conditions, the predicted data of NH4+‐N removal efficiency (NRE) and residue phosphorus were 71.41% and 21.90 mg/L, and actual experimental data were 72.12% and 19.60 mg/L. The inhibitory effect of NaCl concentration on NRE matches the modified Monod model with half inhibition concentration of 89.01 g/L. Morphologic analysis confirmed that salinity inhibited the formation and growth of struvite crystals.

Biohydrogen production under hyper salinity stress by an anaerobic sequencing batch reactor with mixed culture.

BackgroundThis study investigated the effect of organic loading rate (OLR) and NaCl concentration on biohydrogen production by preheated anaerobic sludge in a lab scale anaerobic sequencing batch reactor (ASBR) fed with glucose during long time operation.MethodsDuring ASBR operation, the OLR was increased in steps from 0.5 to 5 g glucose/L.d and NaCl addition started at an OLR of 5 g glucose/L.d, to obtain NaCl concentrations in the reactor in the range of 0.5–30 g/L.ResultsWith an increasing OLR from 0.5 to 5 g glucose/L.d, the biohydrogen yield increased and reached 0.8 ± 0.4 mol H2/mol glucose at an OLR of 5 g glucose/L.d. A NaCl concentration of 0.5 g/L resulted in a higher yield of biohydrogen (1.1 ± 0.2 mol H2/mol glucose). Concentrations above 0.5 g/L NaCl led to decreasing biohydrogen yield and the lowest yield (0.3 ± 0.1 mol H2/mol glucose) was obtained at 30 g/L of NaCl. The mass balance errors for C, H, and O in all constructed stoichiometric reactions were below 5%.ConclusionsThe modified Monod model indicated that r (H2)max and Ccrit values were 23.3 mL H2/g VSS/h and 119.9 g/L, respectively. Additionally, ASBR operation at high concentrations of NaCl shifted the metabolic pathway from acidogenic toward solventogenic.

Study of ethanol fermentation reaction using Saccharomyces diastaticus in a two-tank fermentation system with cell recycling

Abstract Experimental data of ethanol fermentation in a two-tank system with cell recycling using sucrose as a substrate were investigated to establish a kinetic model that described the reaction. Flocculent yeast Saccharomyces diastaticus LORRE-316 was used as the fermenting yeast, and the fermentation medium comprised 80 g/L sucrose, 10 g/L yeast extract, 10 g/L peptone, 2 g/L potassium phosphate monobasic (KH2PO4), and 0.5 g/L magnesium sulfate heptahydrate (MgSO4·7H2O). Three models, the Monod model, the modified Monod model, and the extended-modified Monod model, were used to describe fermentation, and the extended-modified Monod model described the reaction more accurately than the other two models. The model took substrate limitations plus substrate and ethanol inhibitive effects into consideration, and was modified to include assumptions that included terms for substrates (sucrose, glucose and fructose) and product (ethanol). In addition, the ethanol concentration had a significant effect on cell growth. The results of Lineweaver–Burk plots showed that the maximum specific growth rate (μMAX) and the Monod constant (KS) were 0.72/h and 26.77 g/L, respectively. The models were suitable for describing the experimental data.

Kinetic modeling of substrate and product inhibition for 2,3-butanediol production by Klebsiella oxytoca

There has been a growing interest in the fermentative production of 2,3-butanediol (2,3-BD) because of its wide applications in the chemical, food, pharmaceutical, and fuel industries. In this study, we set up kinetic models to predict the behavior of Klebsiella oxytoca οldhA mutant in the batch fermentation of 2,3-BD. Modified Monod model, Luedeking-Piret model, and carbon mass balance were employed to describe the effects of substrate and end-products on cell growth, 2,3-BD production, and substrate consumption, respectively. All the parameters in the models were estimated by minimizing mean-squared errors between the model predictions and experimental data. The model predictions were in good agreement with the fermentation data. In particular, the models accurately described the inhibitory effects of by-products on the growth of K. oxytoca οldhA mutant as well as the production of 2,3-BD. Although the models cannot describe the complex metabolic phenomena, this paper may provide useful information for design and optimization of 2,3-BD fermentation process.

Evaluation of a Modified Monod Model for Predicting Algal Dynamics in Lake Tai

Several modified versions of the Monod model have been proposed to simulate algal dynamics in lakes by keeping the parent model’s advantages of simplicity and low data requirement. This study evaluated the performance of a widely-used modified Monod model in predicting algal dynamics at various time scales in Lake Tai, a typical shallow lake in east China, using multiple time series. Chlorophyll-a (Chl-a) concentration was used as a surrogate for algal (CyanoHABs: cyanobacterial harmful algal blooms) growth and the independent variables were total nitrogen (TN), total phosphorus (TP), and either water temperature or air temperature. The evaluation indicated that the model parameters could have distinctly different values, depending on whether or not constraints are imposed, time scales, and types of nutrients. The model performance varied in terms of time scales as well as magnitudes and fluctuations of Chl-a and TN or TP concentrations, achieving a relative better performance for the monthly rather than three-day time scale and for the central part rather than bays of the study lake. The model with TP as the independent variable had a better performance than the model with TN as the independent variable, regardless of the time scale used. The temperature-nutrient interactions were important for algal growth when the temporal fluctuations of these two factors were large but the interactions could become minimal otherwise.

Effect of humic substances on phosphorus removal by struvite precipitation

Humic substances (HS) are a major fraction of dissolved organic matters in wastewater. The effect of HS on phosphorus removal by struvite precipitation was investigated using synthetic wastewater under different initial pH values, Mg/P molar ratios and HS concentrations. The composition, morphology and thermal properties of harvested precipitates were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and thermo-gravimetric analysis (TGA), respectively. It showed that inhibition effect of HS reached its maximum value of 48.9% at pH 8.0, and decreased to below 10% at pH>9.0. The increase of Mg/P ratio enhanced phosphorus removal efficiency, and thus reduced the influence of HS on struvite precipitation. At pH 9.0, the inhibitory effect of initial HS concentration matched the modified Monod model with half maximum inhibition concentration of 356mgL−1, and 29% HS was removed in conjunction with struvite crystallisation. XRD analysis revealed that the crystal form of struvite precipitates was changed in the presence of HS. The morphology of harvested struvite was transformed from prismatic to pyramid owing to the coprecipitation of HS on crystal surface. TGA results revealed that the presence of HS could compromise struvite purity.

Effect of surfactant on phenanthrene metabolic kinetics by Citrobacter sp. SA01

To attain a better understanding of the effects of surfactants on the metabolic kinetics of hydrophobic organic compounds, the biodegradation of phenanthrene by Citrobacter sp. SA01 was investigated in a batch experiment containing Tween 80, sodium dodecyl benzene sulfonate and liquid mineral salt medium. The Monod model was modified to effectively describe the partition, phenanthrene biodegradation and biopolymer production. The results showed that Tween 80 and sodium dodecyl benzene sulfonate (each at 50mg/L) enhanced phenanthrene metabolism and poly-β-hydroxybutyrate production as indicated by the increasing amounts of intermediates (by 17.2% to 47.9%), and percentages of poly-β-hydroxybutyrate (by 107.3% and 33.1%) within the cell dry weight when compared to their absence. The modified Monod model was capable of predicting microbial growth, phenanthrene depletion and biopolymer production. Furthermore, the Monod kinetic coefficients were largely determined by the surfactant-enhanced partition, suggesting that partitioning is a critical process in surfactant-enhanced bioremediation of hydrophobic organic compounds.

Inhibitory effects of sulfide on nitrifying biomass in the anaerobic–anoxic–aerobic wastewater treatment process

AbstractBACKGROUNDLong pipeline transportation of wastewater usually generates high concentration of sulfide; however, information on nitrification inhibition by sulfide in the anaerobic–anoxic–aerobic (AAO) process is still scarce. This study focused on how sulfide could inhibit nitrification activity in the AAO process, and the inhibitory effect of initial sulfide concentration and anaerobic exposure time on the behavior of nitrifying biomass.RESULTSThe net maximum specific growth rate (μAUT‐bAUT) was, respectively, 0.06 ± 0.01 and 0.31 ± 0.03 d−1 at 15 and 20°C in a full‐scale AAO wastewater treatment plant for long‐pipeline transported wastewater. The μAUT‐bAUT was not affected by 6.2 mg L−1 sulfide under aerated condition, but reduced by 75.9% after unaerated exposure for 0.5 h. The first‐order kinetic constant of sulfide inhibition under anaerobic conditions was 0.658 h−1, and half maximal inhibition concentration of sulfide on nitrification was 36.0 and 10.0 mg L−1 after 1.0 h and 1.5 h anaerobic exposure, respectively.CONCLUSIONNitrifying biomass was sensitive to the presence of sulfide under anaerobic conditions. The inhibitory reaction of sulfide on nitrifying biomass under anaerobic conditions conformed to the first‐order kinetic reaction, while the effect of initial sulfide concentration on nitrification inhibition matched the modified Monod model. © 2013 Society of Chemical Industry

Modelling of kinetics of microbial degradation of simulated leachate from tobacco dust waste

AbstractThis paper presents a kinetic analysis of the biodegradation of organic pollutants in a batch bioreactor and investigates the kinetic properties of activated sludge using different mathematical models. The treatment was conducted for different initial concentrations of leachate from 500 mg dm−3 to 5000 mg dm−3 and initial concentrations of activated sludge from 1.84 g dm−3 to 6.62 g dm−3 over 48 h. Four different kinetic models were applied to the data. The kinetic analysis was performed with the traditional Monod model, the modified Monod model with endogenous metabolism, the Haldane model, and the Haldane model extended to include endogenous metabolic consumption and known as the Endo-Haldane model. Kinetic parameters for each model were determined using differential analysis and the Nelder-Mead method of non-linear regression. The lowest deviations and very good matches with the experimental data were achieved using the Endo-Haldane model. This indicated that this model best described the process of biodegradation of leachate from tobacco waste composting. This is due to this model incorporating the effects both of inhibition and endogenous metabolism.

Growth and Physiological Features of Cyanobacterium Anabaena sp. Strain PCC 7120 in a Glucose-Mixotrophic Culture

Mixotrophic growth is one potential mode for mass culture of microalgae and cyanobacteria particularly suitable for the production of high value bioactive compounds and fine chemicals. The typical heterocystous cyanobacterium Anabaena sp. PCC 7120 was grown in the presence of exogenous glucose in light. Glucose improved the cell growth evidently, the maximal specific growth rate under mixotrophic condition (0.38 d( 1) being 1.6-fold of that of photoautotrophic growth. Mixotrophy caused a variation in cellular pigment composition, increasing the content of chlorophyll a and decreasing the contents of carotenoid and phycobiliprotein relative to chlorophyll a. Fluorescence emission from photosystem II (PSII) relative to photosystem I was enhanced in mixotrophic cells, implying an increased energy distribution in PSII. Glucokinase (EC 2.7.1.2) activity was further induced in the presence of glucose. The mixotrophic culture was scaled up in a 15 L airlift photobioreactor equipped with an inner and an outer light source. A modified Monod model incorporating the specific growth rate and the average light intensity in the reactor was developed to describe cell growth appropriately. The understanding of mixotrophic growth and relevant physiological features of Anabaena sp. PCC 7120 would be meaningful for cultivation and exploitation of this important cyanobacterial strain.

Modeling of Fusarium redolens Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production

Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20-50 g l(-1) glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l(-1)) than in the batch culture (194 mg l(-1)). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures.

Experimental study on pressurized activated sludge process for high concentration pesticide wastewater

Abstract Pressurized biochemical process derived from traditional activated sludge processes is an innovative technology for wastewater treatment. The main advantage of the pressurized process is that the oxygen transfer barrier can be overcome by increasing the dissolved oxygen level. In this study, high concentration pesticide wastewater was treated by pressurized activated sludge process. It was found that the removal of chemical oxygen demand (COD) increased steadily with the increase of operating pressure, aeration time, and sludge concentration. When the operation pressure was 0.30 MPa and the aeration time was 6 hr, 85.0%-92.5% COD, corresponding to an effluent COD of 230-370 mg/L, was removed from an influent COD of 2500-5000 mg/L. The obtained outlet COD concentration was lower than 350-450 mg/L for the identical process operated under the atmospheric pressure. In addition, pressurized biochemical process could produce a higher COD volumetric loading rate at 5.8-7.6 kg COD/(m 3·day), compared with 2.0-2.8 kg COD/(m 3·day) using the same equipment at the atmospheric pressure. The COD concentration followed a modified Monod model with V max 2.31 day −1 and K S 487 mg/L.

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

ABSTRACT 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 (μmax) 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, μmax 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.