Feed Substrate Concentration Research Articles

Cascade enzymatic synthesis of a statin side chain precursor - the role of reaction engineering in process optimization.

Statins are an important class of drugs used to lower blood cholesterol levels and are often used to combat cardiovascular disease. In view of the importance of safe and reliable supply and production of statins in modern medicine and the global need for sustainable processes, various biocatalytic strategies for their synthesis have been investigated. In this work, a novel biocatalytic route to a statin side chain precursor was investigated in a one-pot cascade reaction starting from the protected alcohol N-(3-hydroxypropyl)-2-phenylacetamide, which is oxidized to the corresponding aldehyde in the first reaction step, and then reacts with two equivalents of acetaldehyde to form the final product N-(2-((2S,4S,6S)-4,6-dihydroxytetrahydro-2H-pyran-2-yl)ethyl)-2-phenylacetamide (phenylacetamide-lactol). To study this complex reaction, an enzyme reaction engineering approach was used, i.e. the kinetics of all reactions occurring in the cascade (including side reactions) were determined. The obtained kinetic model together with the simulations gave an insight into the system and indicated the best reactor mode for the studied reaction, which was fed-batch with acetaldehyde feed to minimize its negative effect on the enzyme activity during the reaction. The mathematical model of the process was developed and used to simulate different scenarios and to find the reaction conditions (enzyme and coenzyme concentration, substrate feed concentration and flow rate) at which the highest yield of phenylacetamide-lactol (75%) can be obtained. In the end, our goal was to show that this novel cascade route is an interesting alternative for the synthesis of the statin side chain precursor and that is why we also calculated an initial estimate of the potential value addition.

Investigating the efficiency of a two-stage anaerobic-aerobic process for the treatment of confectionery industry wastewaters with simultaneous production of biohydrogen and polyhydroxyalkanoates.

The scope of the current study was to investigate the efficiency of a two-stage anaerobic-aerobic process for the simultaneous treatment and valorization of selective wastewater streams from a confectionary industry. The specific wastewater (confectionary industry wastewater, CIW) was a mixture of the rinsing eluting during washing of the cauldrons in which jellies and syrups were produced, and contained mainly readily fermentable sugars, being thus of high organic load. The first stage of the process was the dark fermentation (DF) of the CIW in continuous, attached-biomass systems, in which the effect on hydrogen yields and distribution of metabolites were studied for different packing materials (ceramic or plastic), hydraulic retention times, HRTs (12 h–30 h) and feed substrate concentration (20 g COD/L- 50 g COD/L). In the second stage, the effectiveness of the aerobic treatment of the DF effluents was evaluated in terms of the reduction of the organic load and the production of polyhydroxyalkanoates (PHAs) through an enriched mixed microbial culture (MMC). The MMC was developed in a continuous draw and fill system, in which the accumulation potential of PHAs was studied. It was shown that the hydrogen production rates decreased for increasing substrate concentration and HRTs, with a maximum of 12.70 ± 0.35 m3 H2/m3 initial CIW achieved for the lowest HRT and feed concentration and using ceramic beads as packing material. Butyrate, acetate and lactate were the main metabolites generated in all cases, in different ratios. The distribution of metabolites during DF was shown to highly affect the efficiency of the second process in terms of both the reduction of organic load and the PHAs yields. The highest removal of organic load achieved after 48 h of aerobic treatment was 84.0 ± 0.9 %, whereas the maximum PHAs yield was 21.46 ± 0.13 kg PHAs/m3 initial CIW.

Optimization of Fermentation Conditions for Biocatalytic Conversion of Decanoic Acid to Trans-2-Decenoic Acid

Trans-2-decenoic acid has a wide range of applications, including those in medicine, food, and health care. Therefore, the industrial production of trans-2-decenoic acid is particularly important. However, few studies have focused on medium-chain unsaturated fatty acids. Therefore, we aimed to optimize the fermentation process of decanoic acid biocatalysis to synthesize trans-2-decenoic acid using an engineered Escherichia coli constructed in the laboratory. Early-stage culture and the effect of the seed liquid culture time, culture temperature, inoculum amount, induction temperature, dissolution effects of the substrate solvent, metal ions, and substrate loading on the titer of trans-2-decenoic acid were evaluated. Based on a single-factor experimental optimization, a Box–Behnken design (BBD) was used for response surface testing using the substrate feeding concentration, inducer concentration, and MnCl2 concentration as response variables and trans-2-decenoic acid production as the response value. The optimal fermentation process was as follows: Seed culture time of 20 h, culture temperature of 37 °C, inoculation amount of 1%, induction temperature of 30 °C, substrate flow of 0.15 g/L, inducer concentration of 5.60 g/L, and MnCl2 concentration of 0.10 mM. Under these conditions, the average production of trans-2-decenoic acid was 1.982 ± 0.110 g/L, which was 1.042 g/L higher than that obtained in the basic LB medium. Compared with that of the previous period, the titer of the trans-2-decenoic acid studied increased by 1.501 ± 0.110 g/L, providing a basis for further research on the fermentation process of the biocatalytic decanoic acid synthesis of trans-2-decenoic acid.

Membrane biorreactor, reverse osmosis and UV/H2O2 process integration for ethinylestradiol removal: A cost-benefit analysis

The presence of 17α-ethinylestradiol (EE2) in water bodies and its potential risks to human health and the environment have been frequently described in the literature, in addition to its limited removal in conventional wastewater treatment plants. Many studies have evaluated this removal by advanced processes, including photodegradation and membrane separation. A significant number of studies also assess the economic analysis of these technologies. However, few works articulate both perspectives: the specificity involved in estrogen removal and economic analysis. Given this gap, this work evaluates the synergies involved in the integration of reverse osmosis (RO) and advanced oxidative processes by UV/H2O2 (AOP) in the post-treatment of membrane bioreactor (MBR) effluents. To this end, the integrated plant possibilities were represented through a superstructure that integrated EE2 removal and cost models of each process. The use of a Hook and Jeeves optimizer considering these processes standard operating conditions made it possible to determine the percentage of stream division for each equipment and even the absence of any of these in an integrated plant with lower cost and EE2 concentration output below the recommended limit by the European Union (0.035 ng.L−1). For EE2 feed content up to 3 ng.L−1, the lowest cost configuration is to route 20% of the MBR effluent to the AOP, 30% to the RO, and the remainder to a final mixer. For concentrations above 15 ng.L−1, the sufficient and lowest cost configuration is the MBR-RO-AOP series. Intermediate values have a more advantageous integrated process configuration with the parallel and series configurations combined, with a stream distribution dependent on the feed concentration. Moreover, a parameter sensitivity analysis was performed, clarifying paths for design improvements and acting as a systematic guide for future work in this area. This analysis highlights that EE2 removal is more sensitive to temperature (1.04%), feed substrate concentration (−1.18%), solid retention time in the MBR (0.32%), and irradiance in AOP (−0.46%). Investment costs also proved to be decisive in the composition of the total cost, enhancing the relevance of the maturation process of these technologies in light of simple changes in operating parameters.

Optimum Design of N Continuous Stirred-Tank Bioreactors in Series for Fermentation Processes Based on Simultaneous Substrate and Product Inhibition

Optimization of the continuous fermentation process is important for increasing efficiency and decreasing cost, especially for complicated biochemical processes described by substrate and product inhibition. The optimum design (minimum volume) of CSTRs in series assuming substrate and product inhibition was determined in this study. The effect of operating parameters on the optimum design was investigated. The optimum substrate concentration in the feed to the first reactor was determined for N reactors in series. The nonlinear, constrained optimization problem was solved using the MATLAB function “fmincon”. It was found that the optimum design is more beneficial at high substrate conversion and at a medium level of feed substrate concentration. The best number of reactors is two to three for optimum arrangements and two for equal-size arrangements. The presence of biomass in the feed to the first reactor reduces the reactor volume, while the presence of product in the feed slightly increases the required total volume. The percentage reduction in the total volume using the optimum design compared to equal-volume design (R%) was determined as a function of substrate conversion and substrate concentration in the feed to the first reactor. The obtained R% values agree with experimental data available in the literature for ethanol fermentation.

Stability and Performance Analysis of Bioethanol Production with Delay and Growth Inhibition in a Continuous Bioreactor with Recycle

This paper proposes and analyzes a mathematical model for the production of bioethanol in a continuous bioreactor with recycling. The kinetics correspond to the use of Saccharomyces bayanus for the fermentation of sugars found in wastewater from soft drinks. The proposed model considers product growth latency, which was experimentally found in batch studies of ethanol production. Furthermore, the inhibition effect of ethanol is expressed by a modified version of the classical Andrew’s model for substrate inhibition. The proposed model consists of only three ordinary differential equations containing a minimal number of operating parameters, which include the bioreactor residence time, glucose feed concentration, recycle ratio and the fraction of biomass removed from the reactor by the flow. The positivity and the boundedness of solutions of the model were confirmed under reasonable restrictions of parameters. The stability analysis showed that there is a value of residence time at which an exchange of stability occurs between the trivial washout and non-washout solutions. This critical value depends only on the substrate feed concentration, biomass death rate, recycle ratio and purge fraction. Dynamic simulations of the model were carried out for substrate concentration in the range of 100–250 g/L, commonly used for the production of ethanol. An inverse response due to the inhibition effects of ethanol was observed in the time evolution of substrate and biomass concentrations. Parametric studies showed that ethanol concentration increases with the recycle ratio, with the inverse of residence time and with the inverse of purge fraction. The effect of ethanol latency has, on the other hand, a substantial effect on ethanol concentration. Despite its unstructured nature and the fact that some parameters such as temperature and acidity were not taken into consideration, the proposed model managed to provide useful results on the bioreactor-settler stability and the effect of key parameters on its dynamic behavior, which could pave the way for future optimization studies.

Robust Multi-Objective Singular Optimal Control Ofpenicillin Fermentation Process

The determination of optimal feeding profile of fed-batch fermentation requires the solution of a singular optimal control problem. The complexity in obtaining the solution to this singular problem is due to the nonlinear dynamics of the system model, the presence of control variables in linear form and the existence of constraints in both the state and control variables. Traditionally, during the optimization process, uncertainties associated with design variables, control parameters and mathematical model are not considered. In this contribution, a systematic methodology to evaluate uncertainties during the resolution of a singular optimal control problem is proposed. This approach consists of the Multi-objective Optimization Differential Evolution algorithm associated with Effective Mean Concept. The proposed methodology is applied to determine the feed substrate concentration in fed-batch penicillin fermentation process. The robust multi- objective singular optimal control problem consists of maximizing the productivity and minimizing the operation total time.

Dynamical Analysis of Chemostat Model Incorporated with Substrate Inhibition and Variable Yield Coefficient

This paper analyses a chemostat model for microbial production by considering substrate inhibition and variable yield coefficient. The Andrews growth model is considered to describe the inhibitory effect of high substrate concentration towards the microbial growth. The dependency of product yield towards the substrate concentration also incorporated in the chemostat model. The stability and bifurcation analyses of the chemostat model are presented to investigate the dynamical behaviour of microbial in the chemostat and to identify the parameter region that generates oscillations in the chemostat. The steady state solutions and their stability are determined as a function of residence time. When the feed substrate concentration is adjusted to be more than 6.1 g/L, there exist a parameter range of residence time that improves the microbial production in the chemostat.

Preparation of ACE-inhibitory peptides from milk protein in continuous enzyme membrane reactor with gradient dilution feeding substrate

In this study, a novel method of gradient dilution feeding substrate (GDFS) was established to improve the yield of angiotensin-converting enzyme (ACE) inhibitory peptides from milk protein. The hydrolysis process stability, enzymatic efficiency and kinetics of the method were studied and compared with traditional feeding modes, viz., adding water after feeding substrate or constant concentration feeding substrate. Results showed that the GDFS mode achieved the highest membrane flux and lowest fluctuation of protein concentration in the reactor. Moreover, the GDFS maximized protein conversion rate, yield of peptides, and ACE-inhibitory activity, with their values of 67.58 %, 138.51 g/(g*Neutrase), and 0.74 mg/mL (IC50), respectively. In further study, the kinetic model of GDFS mode was successfully established with KM of 69.481 g/L and Vmax of 0.752 g·L−1 min−1. Based on the optimum condition of the kinetic model, the practical longest runtime was 720 min. Obtained results suggested that GDFS mode could be used as an alternative method in the preparation of high-yield bioactive peptides.

Analysis of open-loop and [formula omitted] controlled closed-loop behavior of the Cholette’s bioreactor under different operating conditions

The scope of this paper is the analysis of open-loop and L2/D controlled closed-loop behavior of the Cholette’s bioreactor under different operating conditions. The open-loop behavior is studied by means of the steady-state multiplicity areas formed by substrate feed concentration and substrate concentration in the output using the nonlinear model of the bioreactor. The stability of each steady-state inside areas is determined by a polynomial representation. The nonlinear dynamic and steady-state multiplicity areas of the Cholette’s bioreactor are shown to depend on the operating conditions and concentration required. The closed-loop behavior is studied by the tuning of a set of Pareto-optimal L2/D linear controllers at a stable operating point. Numerical simulations and phase portraits are used to evaluate the control system. This paper could be a guide for theoretical and practical applications in the fields of biotechnology and automatic control.

Extremum seeking control for a mass structured cell population balance model in a bioreactor

This paper is concerned with the design of an adaptive extremum seeking control scheme for a mass structured cell population balance model in a bioreactor. The feed substrate concentration is considered as the manipulated input to drive system states to the desired setpoints that maximize the value of an objective function of the cell density. We assume limited knowledge on the objective function and we use the substrate concentration measurements to estimate this function. We use the Lyapunov’s stability theorem and a persistency of excitation condition to show that the proposed adaptive extremum seeking control achieves the exponential convergence to the desired set points. Numerical simulation has been performed to illustrate the performance of the proposed approach.

Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

A biophotoreactor with a transparent glass flat panel with polymethyl methacrylate (PMMA) grid columnar for enhanced biofilm growth with Rhodopseudomonas palustris GCA009 was developed and tested at 590 nm incident light. Continuous photofermentative hydrogen production from glucose was tested using this novel reactor. At light intensity of 210 W/m2, feed substrate concentration of 56.0 mmol/L, and crossflow velocity of 1.68 × 10−6 m/s, a maximum hydrogen production rate of 32.6 mmol/L-d (3.56 mmol/m2-h), hydrogen yield of 1.15 mol H2/mol glucose and light conversion efficiency of 5.34% can be achieved. Since the revised grid columnar effectively enlarged the surface area of reactor and enhanced cell attachment, the present reactor design led to higher hydrogen production rates than literature works.

Impact of Wastewater Concentration and Feed Frequency on Ammonia Inhibition in Microbial Fuel Cells

Excessive amount of ammonia slows down exoelectrogenic bacteria activities in microbial fuel cells (MFCs). The aim of this study is to analyze the impact of wastewater concentration and feed frequency on the ability of exoelectrogenic bacteria to withstand against ammonia inhibition in MFCs, in particular, for total ammonium nitrogen (TAN) concentration ranging from 29 mgN to 2000 mgN. MFCs were constructed to measure electric current and power density and tested in wastewater of selected TAN concentration samples. The MFCs frequently feed (2-days intervals) with full strength wastewater achieved a maximum power density between 0.8 mW and 1.2 mW. The MFC less frequently feed (6-days feed intervals) with full strength wastewater and also the MFC frequently feed (2-days feed intervals) with low strength wastewater exhibited a relatively lower electricity generation. Increasing the concentration of total ammonium nitrogen resulted in a gradual decrease of chemical oxygen demand (COD) removal efficiency. Experimental results demonstrated that the frequency of feed and higher substrate concentration increase exoelectrogenic bacteria activities in generating electric current in MFCs.

Mathematical analysis of bioethanol production through continuous reactor with a settling unit

Bioethanol generated from biomass and bioenergy crops has been promulgated as one of the most feasible alternatives to fossil fuel, as it is considered to be clean, green and of course renewable. In this paper, we develop a nonlinear chemostat model for bioethanol production. The growth rate is given by a modified Andrew expression with inhibition by ethanol, which is often used to model the growth of biomass. Then the uniqueness, invariance and dissipation of solutions of the model are established. Steady state solutions of the model and their stability are also determined as a function of the residence time. We also investigate the effects of the model parameters on a physically valid region.Finally, we compare the performance of a reactor, using a recycling process, against that of without recycling process. With a substrate feed concentration of 100 g/L, there is a critical value of the residence time which identifies a turning point in the reactor performance for the removal of substrate.

Biohydrogen fermentation of galactose at various substrate concentrations in an immobilized system and its microbial correspondence

The effects of substrate concentration on fermentative hydrogen production from galactose at a fixed hydraulic retention time of 12h were investigated in an immobilized continuously stirred tank reactor. Peak hydrogen production rate and hydrogen yield of 9.57L/L-d and 1.10mol/mol galactoseadded, respectively, were obtained at a feed substrate concentration of 30g/L and an organic loading rate of 60L/L-d. Quantitative polymerase chain reaction analysis showed that the variations in the performance resulted primarily from metabolic alterations within the metabolism of the established microbial community rather than modifications in the population. The results obtained showed that optimal substrate concentration is essential for the efficient, continuous production of hydrogen from galactose.

Effect of the variation of the operating parameters in the production of methane from lignocellulosic waste

Anaerobic digestion has been widely used in recent years for the treatment of agro-industrial or municipal wastes as carbon source to obtain alternative energy sources such as methane (CH4). Great efforts are currently being made to understand this phenomenon, generally as a first approximation in batch experiments, but due to the growing need to produce more environmentally friendly fuels, it is imperative to study the process as a continuous production. Starting from a three-state model and its parametric characterization in batch experiments, this paper analyzes the effect of the variation of two parameters of the mathematical model from continuous balances: the dilution rate (D) and the substrate feeding concentration (Si). The increase in the concentration of substrate in the inflow allows a greater production of methane, while small values allow reaching the trivial solution in the system. The choice of the dilution rate can be solved as an optimization problem since the production reaches a maximum at values close to 4 d_1.

Modeling and simulation of continuous extractive fermentation with CO2 stripping for bioethanol production

The major bottleneck in industrial alcoholic fermentation is inhibition by the product, which limits the ethanol yield and productivity. An efficient way of overcoming this problem is to use gas stripping to remove the ethanol during the process. In this work, the production of ethanol from sugarcane using extractive continuous fermentation with CO2 stripping was modeled and simulated. The ethanol stripping performance was first evaluated experimentally, varying the specific CO2 flow rate (ϕCO2), the solution temperature (Tsol), and the initial ethanol concentration (CE0). The parameters ϕCO2 and Tsol showed positive influences on the stripping kinetics. The proposed CO2 stripping model considered the removal of ethanol and water, as well as changes in the solution volume, and was able to accurately describe the process. Modeling and simulation of the continuous fermentation were performed considering different conditions of feed substrate concentration and cell recycling. The results indicated that ethanol inhibition could be alleviated by CO2 stripping. In addition, the combined use of stripping and cell recycling enabled the use of feed musts containing up to 400gL−1 of sucrose, with high substrate conversion, ethanol productivity of 10.79gL−1h−1, and total ethanol amount produced of 174.80gL−1 (22.2°GL), which is about twice the value achieved in an industrial process without ethanol removal by CO2 stripping. This strategy is very promising, compared to traditional processes used in Brazilian distilleries, and has the potential to reduce the global process costs, since it decreases the energy consumed for product recovery and allows the use of smaller fermenters.

Catalytic Hydrogenation of Dimethyl-Nitrobenzene to Dimethyl-Aniline in a Three-Phase Reactor: Reaction Kinetics and Operation Condition

The catalytic transfer hydrogenation of dimethyl-nitrobenzene (DN) to Dimethyl-aniline (DA) was studied in the temperature range 343–403<i>°K</i>, pressure range of 4–10 bar H₂ and ethanol as solvent using Ni on alumina-silicate as catalyst above agitation speed 800 rpm. The substrate feed concentration was varied in the range from 0.124 to 0.745 kmol/m³ while catalyst loading was in the range 4–12% (w/w) of dimethyl-nitrobenzene. Dimethyl-aniline was the only reaction product, generated through the hydrogenation of the Nitro group of dimethyl-nitrobenzene. The effects of hydrogen partial pressure, catalyst loading, dimethyl-nitrobenzene concentration and temperature on the reaction conversion have been reported. Near first-order dependence on dimethyl-nitrobenzene concentration and hydrogen pressure were observed for the initial rate of dimethyl-nitrobenzene hydrogenation over the Ni catalyst. Furthermore, an increase in the catalytic activity as the reaction temperature, pressure and weight of catalysts was observed. Conventional Arrhenius behavior was exhibited by catalyst, Ni showed activation energies of 808 J/mol.

Predictive Modeling of Biogas Production from Anaerobic Digestion of Mixed Kitchen Waste at Mesophilic Temperature

Growth of population is directly influencing the municipal solid waste generation rate. Although, kitchen waste is disposed of mostly in developing countries and its potential of biogas production is not explored well. Anaerobic digestion provides opportunity of twofold benefits i.e. pollution abutment for environmental protection and biogas generation for sharing energy load. Present study was intended to understand the biogas production process at mesophilic temperature (37°C). The organic waste from kitchen was used to make up substrate, which was anaerobically digested in an experimental continues stirred tank reactor (CSTR). Inhibition phase was detected when the graph was plotted for first 60 days and about 28th day it was inhabited. Biogas production from recovered condition was subjected to statistical analysis. Simple regression yielded a good predictive model that gave a correlation of 0.995 despite of including the inhibition phase in complete analysis. An acceptable agreement between observed and modeled biogas production (BGP) rates has vetted sanctity of regression based predictive model. Such models can also be used to keep check on digestion process for optimization of biogas yield and deciding the substrate feeding rate and concentration on time scale.

Biological synthesis of coumarins in Escherichia coli.

BackgroundCoumarins are a major group of plant secondary metabolites that serves as defense compounds against pathogens. Although coumarins can be obtained from diverse plant sources, the use of microorganisms to synthesize them could be an alternative way to supply building blocks for the synthesis of diverse coumarin derivatives.ResultsConstructs harboring two genes, F6′H (encoding feruloyl CoA 6′ hydroxylase) and 4CL (encoding 4-coumarate CoA:ligase), were manipulated to increase the productivity of coumarins. Escherichia coli expressing the two genes was cultured in medium supplemented with hydroxycinnamic acids (HCs) including p-coumaric acid, caffeic acid, and ferulic acid, resulting in the synthesis of the corresponding coumarins, umbelliferone, esculetin, and scopoletin. Cell concentration and initial substrate feeding concentration were optimized. In addition, umbelliferone, and esculetin were synthesized from glucose by using a ybgC deletion mutant and co-expressing tyrosine ammonia lyase and other genes involved in the tyrosine biosynthesis pathway.ConclusionsTo produce coumarin derivatives (umbelliferone, scopoletin, and esculetin) in E. coli, several constructs containing F6′H and 4CL were made, and their ability to synthesize coumarin derivatives was tested. The solubility of F6′H was critical for the final yield. After optimization, 82.9 mg/L of umbelliferone, 79.5 mg/L of scopoletin, and 52.3 mg/L of esculetin were biosynthesized from the corresponding HCs, respectively in E. coli. Umbelliferone and esculetin were also synthesized from glucose using engineered E. coli strains. The final yields of umbelliferone and esculetin were 66.1 and 61.4 mg/L, respectively.