Feed Substrate Concentration Research Articles

Evaluation of deep eutectic solvents as co‐solvent for steroids 1‐en‐dehydrogenation biotransformation by Arthrobacter simplex

AbstractBACKGROUNDAs a low‐cost alternative to the traditional ionic liquids (ILs), deep eutectic solvents (DESs) have currently attracted increasing attention for their various applications including biocatalysis. This study aimed at analyzing the effect of DESs on Δ1, 2‐dehydrogeneration of cortisone acetate(CA) to prednisone acetate (PA) by Arthrobacter simplex.RESULTSOf the three DESs examined, ChCl:U was successfully employed as co‐solvent to improve the bioconversion efficiency. For substrate feeding concentration of 5 g L−1, substrate conversion reached 93% by immobilized A. simplex cells (4 gDW L−1) with ChCl:U content of 6%, which is more efficient than conversions without DESs. Importantly, it has been shown that DESs and the immobilized cells can be easily recovered and then reused for five batches of bioconversion with a final conversion above 80%.CONCLUSIONOur results show the potential use of DESs‐based systems in industrial steroid biodehydrogenation by A. simplex, and provide an environmentally benign means of steroid biotransformation. © 2015 Society of Chemical Industry

Improving the stability of glutamate fermentation by Corynebacterium glutamicum via supplementing sorbitol or glycerol

Corynebacterium glutamicum is widely used in glutamate fermentation. The fermentation feature of the strain varies sometimes. These variations may lead to the reduction in the ability of the strain to resist environmental changes and to synthesize glutamate, resulting in abnormal glutamate fermentations. In the abnormal glutamate fermentations, glutamate accumulation stopped after glucose feeding and the final glutamate concentration was at a lower level (50 to 60 g/L). The r NAD +/r NADH ratio was lower than that in normal batch which was reflected by lower oxidation-reduction potential (ORP) value. The abnormal fermentation performance was improved when glucose was co-fed with sorbitol/glycerol at a weight ratio of 5:1 or adding 10 to 15 g/L of sorbitol/glycerol in the initial medium. Under these conditions, glutamate synthesis continued after substrate(s) feeding and final glutamate concentration was restored to normal levels (≥72 g/L). r NAD +/rNADH ratio, ORP, and pyruvate dehydrogenase (PDH), isocitrate dehydrogenase (ICDH), and cytochrome c oxidase (CcO) activities were maintained at higher levels. Sorbitol and glycerol were not used as carbon sources for the fermentation. They were considered as effective protective agents to increase cells' resistance ability against environmental changes and maintain key enzymes activities.

On the estimation problem of a class of continuous bioreactors with unknown input

The estimation problem of substrate–biomass reactors with isotonic or nonisotonic growth is addressed. The unmeasured reactor and time-varying feed substrate concentrations must be estimated from the dilution rate input and biomass measurements. First, the solvability conditions (nonlinear-global observability or detectability) are characterized, finding that: (i) the conditions depend on particular motions and growth mechanisms, and (ii) with isotonic (or nonisotonic) growth, the unknown input–state pair is observable in the classical (or nonstandard) single-valued (S) [or bivalued (B)] sense. Then, a robustly convergent S (or B)-observer is designed accordingly. The S-observer yields the estimate of the only unmeasured input–state trajectory pair associated with the measured input–output signal. The B-observer yields the estimates of the two possible unmeasured input–state trajectory pairs associated with the measured input–output signal, each one satisfying the reactor mass balances. The developments and findings are illustrated with representative (Monod and Haldane) examples through analytic assessment and numerical simulation.

Correction to Effect of the Feed Substrate Concentration on the Dynamic Performance of the Bioethanol Fermentation Process Using Zymomonas mobiliz

Correction to Effect of the Feed Substrate Concentration on the Dynamic Performance of the Bioethanol Fermentation Process Using <i>Zymomonas mobiliz</i>

Potentialities of a membrane reactor with laccase grafted membranes for the enzymatic degradation of phenolic compounds in water.

This paper describes the degradation of phenolic compounds by laccases from Trametes versicolor in an enzymatic membrane reactor (EMR). The enzymatic membranes were prepared by grafting laccase on a gelatine layer previously deposited onto α-alumina tubular membranes. The 2,6-dimethoxyphenol (DMP) was selected from among the three different phenolic compounds tested (guaiacol, 4-chlorophenol and DMP) to study the performance of the EMR in dead end configuration. At the lowest feed substrate concentration tested (100 mg·L−1), consumption increased with flux (up to 7.9 × 103 mg·h−1·m−2 at 128 L·h−1·m−2), whereas at the highest substrate concentration (500 mg·L−1), it was shown that the reaction was limited by the oxygen content.

Effect of the Feed Substrate Concentration on the Dynamic Performance of the Bioethanol Fermentation Process Using Zymomonas mobiliz

In this work, a structured verified nonlinear mathematical model for a single continuous fermenter of bioethanol production using Zymomonas mobiliz is developed to investigate the effect of the feed substrate concentration, which is taken as the main bifurcation parameter for performing a bifurcation analysis. The chaotic, oscillatory, and steady-state behaviors of the fermentation system are investigated. It is found that the system is dominated by oscillatory behavior in the medium gravity (MG) region (80.76 < Cso < 213.6), while it is dominated by stable steady state outside this range; however, at high Cso and low dilution rate, the chaotic behavior dominates the system. It is found that the fermentation system accomplishes the maximum averages of substrate conversion and bioethanol yield in the range of 80.76 < Cso < 97 g/L. These results are in agreement with the experimental results in the literature.

Enhancement of microbial hydroxylation of 13-ethyl-gon-4-ene-3,17-dione by Metarhizium anisopliae using nano-liposome technique

The introduction of 11α-hydroxy to 13-ethyl-gon-4-ene-3,17-dione (GD) by microbial transformation is a key step in the synthesis of oral contraceptive desogestrel, while low substrate solubility and uptake into cells are tough problems influencing biotransformation efficiency greatly. Nano-liposome technique was used in the hydroxylation of GD by Metarhizium anisopliae. The substrate GD was processed to be GD-loaded nano-liposomes (GNLs) with high stability and encapsulation efficiency, and then applied in microbial hydroxylation by M. anisopliae. The results proved that the yield of the main product 11α-hydroxy-13-ethyl-gon-4-ene-3,17-dione (HGD) tripled compared to regular solvent dimethylformamide dispersion method at 2g/l of substrate feeding concentration, and the HGD conversion rate showed no obvious reduction when the substrate feeding concentration increased from 2 to 6g/l, which indicated the improvement of GNL addition method on biotransformation. Furthermore, the main byproduct changed from 6β-hydroxy derivative of GD (with similar polarity to HGD) to 6β,11α-dihydroxy derivative, which benefits the following purification of HGD from fermentation broth. These advantages suggest a great potential for the application of nano-liposome technique in microbial steroid transformation.

Structured Mathematical Modeling, Bifurcation, and Simulation for the Bioethanol Fermentation Process Using Zymomonas mobilis

A structured nonlinear dynamic model for a single continuous fermentor of ethanol production using Zymomonas mobiliz is built and validated to investigate the effect of dilution rate. A detailed bifurcation analysis is performed at different feed substrate concentrations. It is found that oscillatory behavior dominates the system for both feed substrate concentrations at 140 and 200 g/L; however, the high periodicity in the form of a period-doubling cascade appeared at the higher value of feed substrate concentrations. The model gives reasonable results compared with experiments.

Studies on generalized kinetic model and Pareto optimization of a product-driven self-cycling bioprocess

The aim of this study is the optimization of a product-driven self-cycling bioprocess and presentation of a way to determine the best possible decision variables out of a set of alternatives based on the designed model. Initially, a product-driven generalized kinetic model, which allows a flexible choice of the most appropriate kinetics is designed and analysed. The optimization problem is given as the bi-objective one, where maximization of biomass productivity and minimization of unproductive loss of substrate are the objective functions. Then, the Pareto fronts are calculated for exemplary kinetics. It is found that in the designed bioprocess, a decrease of emptying/refilling fraction and an increase of substrate feeding concentration cause an increase of the biomass productivity. An increase of emptying/refilling fraction and a decrease of substrate feeding concentration cause a decrease of unproductive loss of substrate. The preferred solutions are calculated using the minimum distance from an ideal solution method, while giving proposals of their modifications derived from a decision maker's reactions to the generated solutions.

Analysis of the performance and criteria for rational design of a sequencing batch reactor for xenobiotic removal

Substrate toxicity can impose operability challenges in the biological treatment of xenobiotic compounds. These can arise from transients in the feed to conventional continuous processes, as well as in more challenging systems, sequencing batch reactors (SBRs), whose operation is always inherently dynamic. Via the use of the classic Haldane model for microbial toxicity, and unsteady-state material balance equations for SBR operation, we have analysed the behaviour of an SBR reactor operating over multiple cycles and have shown that both high performance and low performance can be obtained depending on the feed substrate concentration and the selected SBR exchange ratio. That is, both the intrinsic microbial kinetics as well as the selection of process operating conditions can lead either to high performance (high removal efficiency) or low performance (low removal efficiency) operation. Using this approach, we have also discussed the performance for the SBR treatment of 2 “real” substrates possessing widely different kinetic parameters, showing the impact of these parameters, as well as process operating conditions, on the operability of SBR biotreatment systems handling xenobiotic compounds. This could be of significant value to practitioners wishing to select high performance operating regimes for the treatment of a specific xenobiotic compound. To our knowledge, this is the first systematic study of the impact of substrate toxicity on SBR operability, and is also a first step in modeling the impact of substrate detoxification, via the use of discontinuous Two-Phase Partitioning Bioreactors, on the dynamic performance of xenobiotic biotreatment processes.

Comparison of activity behaviors of particle based and monolithic immobilized enzyme reactors operated in semi-micro-liquid chromatography system

The activity behaviors of particle based and monolithic immobilized enzyme reactors (IMERs) developed for proteomics applications in semi-micro-liquid chromatography were comparatively investigated. For monolithic IMER, the plain monolith was synthesized by in situ thermal copolymerization of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDM) in fused silica capillary. For particle based IMER, monodisperse-porous poly(GMA-co-EDM) beads 6.8μm in size were synthesized by staged-shape template polymerization and used as support in a stainless steel microbore column. α-Chymotrypsin (CT) was covalently attached onto the particle based and monolithic supports via amination and glutaraldehyde coupling stages. In the case of monolithic IMER, higher final substrate conversions were achieved particularly with high substrate feed rates with respect to particle based IMER probably due to the convective diffusion in the macropores of continuous monolithic block. The final substrate conversion increased with increasing substrate feed concentration for monolithic IMER while a decrease was observed for particle based IMER. Hence monolithic IMER was superior when high substrate feed concentration was used with sufficiently high substrate feed flow rates.

Nitrile hydratase of Rhodococcus erythropolis: characterization of the enzyme and the use of whole cells for biotransformation of nitriles

The intracellular cobalt-type nitrile hydratase was purified from the bacterium Rhodococcuserythropolis. The pure enzyme consisted of two subunits of 29 and 30 kDa. The molecular weight of the native enzyme was estimated to be 65 kDa. At 25 °C the enzyme had a half-life of 25 h. The Michaelis–Menten constants Km and vmax for the enzyme were 0.624 mM and 5.12 μmol/min/mg, respectively, using 3-cyanopyridine as the substrate. The enzyme-containing freely-suspended bacterial cells and the cells immobilized within alginate beads were evaluated for converting the various nitriles to amides. In a packed bed reactor, alginate beads (2 % alginate; 3 mm bead diameter) containing 200 mg/mL of cells, achieved a conversion of >90 % for benzonitrile and 4-cyanopyridine in 38 h (25 °C, pH 7.0) at a feed substrate concentration of 100 mM. The beads could be reused for up to six reaction cycles.

A productivity signal feedback controller for continuous bioreactors

The control of continuous stirred bioreactors using productivity signal feedback consists of using the direct relation between the optimal static dilution rate and the optimal static productivity. This strategy drives the bioprocess to its optimal productivity point, irrespective of the feeding substrate concentration, and specific growth rate or substrate concentration estimates. While the algorithm covers a wide class of bioprocesses, explicit relations are given for the Monod and Haldane cases.

Simple Kinetic Model of Cellulase Production by Trichoderma Reesei for Productivity or Yield Maximization

A simple kinetic model of cellulase production by Trichoderma reesei on lactose was developed and parameters identified using bibliographic and personal data. Assuming a mean representation of industrial hyperproducer strains, this model was used to simulate and compare several cultivation strategies regarding three criteria: in addition to usual productivity and yield calculation, oxygen demand was studied and used as a constraint for protocol design.Results showed that none of the protocols maximizes both productivity and yield, requiring to find a compromise for these parameters. Moreover, substrate concentration in the feed was the main criterion for the choice of the protocol, while oxygen demand and biomass concentration were the main issues to reach high productivities. The model will be useful for an economic study of cultivation strategies.

Synthesis of a monolithic, micro-immobilised enzyme reactor via click-chemistry

An immobilised enzyme reactor (IMER) in the form of capillary monolith was developed for a micro-liquid chromatography system. The plain monolith was obtained by in situ thermal copolymerisation of glycidyl methacrylate and ethylene dimethacrylate in a fused silica capillary (200 × 0.53 mm ID) by using n-propanol/1,4-butanediol as porogen. The enzyme, α-chymotrypsin (CT), was covalently attached onto the monolith via triazole ring formation by click-chemistry. For this purpose, the monolithic support was treated with sodium azide and reacted with the alkyne carrying enzyme derivative. CT was covalently linked to the monolith by triazole-ring formation. The activity behaviour of monolithic IMER was investigated in a micro-liquid chromatography system by using benzoyl-L-tyrosine ethyl ester (BTEE) as synthetic substrate. The effects of mobile-phase flow rate and substrate feed concentration on the final BTEE conversion were investigated under steady-state conditions. In the case of monolithic IMER, the final substrate conversion increased with increasing feed flow rate and increasing substrate feed concentration. Unusual behaviour was explained by the presence of convective diffusion in the macropores of monolith. The results indicated that the monolithic-capillary IMER proposed for micro-liquid chromatography had significant advantages with respect to particle-based conventional high-performance liquid chromatography-IMERs.

Simulation and Optimization of a Continuous Biochemical Reactor

The present work focused on the dynamic and optimization of a continuous biochemical reactor using the glucose as a substrate. Simulated model provides the development of the process and reducing the risk of experimental runs. The selected process variables are; dilution rate (D), feed substrate concentration (Si), pH and temperature (T). The effect of D was observed at Si below 20 g/L. pH and T are affecting within Si of 60 g/L. Si is the effective process variable on the dynamic characteristics of the reactor. Reasonable agreement has found when compared the simulated results with that obtained by the previous work .Optimization technique guides the decision maker to select the best operating conditions. Stochastic genetic algorithm has found suitable for the nonlinear reactor. Optimal results indicate that the maximum biomass concentration (X) is 80.57 g/L at Si of 197.56 g/L and low D of 0.1(1/hr). Si was the sensitive variable for changing of the objective X.

Effect of hydraulic retention time on up-flow anaerobic stage reactor performance at constant loading in the presence of antibiotic tylosin

The present investigation was aimed at determining the impact of the macrolide antibiotic Tylosin in reduced HRT at constant organic loading rate (OLR) by varying feed substrate concentration in an up-flow anaerobic stage reactor (UASR). The antibiotic concentration was maintained at 200 mg.L-1, at constant OLR of 1.88 kg COD.m-3.d-1, by varying feed substrate concentration to the UASR and the HRT was decreased gradually from 4 to 1 d. Throughout the operation period, brewery wastewater was used as simple feed substrate to elevate the concentration of easily biodegradable carbon in comparison with the concentrations of more recalcitrant Tylosin substrate. The reactor alkalinity was controlled in all the stages of UASR by adding 1000 - 2000 mg.L-1 CaCO3. Results showed the total COD removal efficiency at 4 d HRT was around 92%, after which point there was a slight decrease at 3 and 2 d HRT (average 82%), and this was reduced further (average 77%) at a HRT of 1 d. The UASR showed stable operation with effluent volatile fatty acid (VFA) less than 300 mg.L-1 throughout the experimental period (HRT 4 - 1 d). Moreover, the average methane yield (CH4.kg CODr-1) showed a relatively constant profile and was largely unaffected by HRT in all the stages of UASR. These results show that bacteria were readily adapted to wastewater containing Tylosin at lower HRTs and did not affect the reactor performance substantially.

Anaerobic Pre-treatment of Pharmaceutical Wastewater using Packed Bed Reactor

Effluents from manufacturing operations in the pharmaceutical industry, such as antibiotic formulation, usually contain recalcitrant compounds. An approach towards appropriate technology for the treatment of pharmaceutical wastewaters has become imperative due to strict water quality legislation for environmental protection. Typically, pharmaceutical wastewater is characterized by high chemical oxygen demand (COD) concentration, and some pharmaceutical wastewaters can have COD as high as 80,000 mg.L-1. Due to high organic content, anaerobic technology is a promising alternative for pharmaceutical wastewater treatment. Consequently, in the present study, an anaerobic packed bed reactor was employed to treat highly polluted pharmaceutical wastewater. The effect of organic loading rate (OLR) was assessed by adjusting feed substrate concentration and hydraulic retention time (HRT). The reactor performance was characterized in terms of chemical oxygen demand (COD) removal, volatile fatty acid (VFA), gas production, methane yield and pH. At an average reactor OLR of 1.58 kg COD.m-3.d-1 (HRT 5.6 d), the average soluble COD reduction was 73%. However, when the OLR was increased to 2.21 and 4.66 kg COD.m-3.d-1 the COD removal efficiency decreased gradually until 60 - 70% soluble COD removal was observed. Further increase of the OLR resulted in only around 53% soluble COD removal (average) was observed at an OLR of 5.71 kg COD.m-3.d-1, signifying as OLR was increased; the increasing load of complex pharmaceutical wastewater may have affected the methanogens.

On the choice of the optimal periodic operation for a continuous fermentation process

In this contribution we investigate the impact of the forcing waveform on the productivity of a continuous bioreactor governed by an unstructured, nonlinear kinetic model. The (periodic) forcing is applied on the substrate concentration in the feed. To this end, some alternative waveforms commonly encountered in practice are evaluated and their performance is compared. An analytical/numerical approach is used. The preliminary analytical step is based on the π-criterion that gives useful information for small amplitudes. The extension to larger amplitudes, when significant improvements are expected, is then performed through a continuation-optimization procedure. It is found that the choice of the specific waveform has an impact on the performance of the process and there is no unique best forcing for any process condition, but its choice depends on the operating parameters and the forcing amplitude and frequency values. Further, the influence of the waveform functions on the wash-out conditions are extensively examined. The analysis shows that all the waveforms examined in this work may lead to significant enlargement of the nontrivial regime with respect to a steady state operation. In particular, square-wave forcing leads in practice to the extinction of the wash-out conditions for any feed substrate concentration and for a well defined choice of the forcing parameters.

On the improvement of performance of bioreactors through periodic forcing

Abstract The paper investigates the periodic operation of a continuous bioreactor described by an unstructured model for which the yield coefficient is linearly dependant on the substrate. The model was studied by a number of authors who showed its ability to predict oscillatory behavior for some range of dilution rates. The paper investigates the different dynamic behaviors predicted by the model when the substrate feed concentration is periodically varied. It is shown that when a region of stable limit cycle is forced with a relatively high forcing frequency, the behavior of the process alternates between periodic and complex chaotic behavior via a number of mechanisms of transition, including period doubling and intermittency. It is shown that the time-average performance of the bioreactor can be substantially improved by an appropriate selection of the forcing amplitude. The effect of the position of the center of forcing on the nature of the emerging patterns are also studied.