Initial Glycerol Concentration Research Articles

Elucidation of synergism in Ce-Zr/SBA-15 mesoporous catalysts and the effects on the activity in selective glycerol to lactic acid reaction

The continued conversion of glycerol to value-added chemicals is essential in ensuring the sustainable development of the biodiesel industry. Selective catalytic oxidation of glycerol to lactic acid provides an alternative approach to valorizing glycerol. A mesoporous SBA-15 supported mixed-metallic oxide catalyst is deemed essential to selectively produce lactic acid in this mixed parallel and multi-step reaction. SBA-15-supported bimetallic Ce and Zr oxides were proved to be highly efficient catalysts for the selective glycerol oxidation into lactic acid in base-free media. The synergism between Ce and Zr in the bimetallic oxide compounds could enhance the creation of oxygen vacancies in the catalyst via the reduction of Ce4+ to Ce3+. The 2:1CeZr/SBA-15 catalyst exhibited prominent catalytic activity in selectively oxidizing glycerol to lactic acid, with a glycerol conversion of 91.8% and a lactic acid yield of 35.1%. This work achieved superior catalytic performance compared to previously conducted studies, primarily due to the significantly higher initial glycerol concentration employed in this study. To ascertain the intrinsic active sites of the catalyst, the physicochemical properties of the catalyst were thoroughly examined using BET, FTIR, XRD, FESEM, TEM, CO2-TPD, O2-TPD, and H2-TPR analysis. This work concluded that the synergistic interaction of the active sites, which led to the formation of active oxygen species, facilitated primary dehydrogenation of the terminal -OH bond in glycerol. Hence, in this work, a plausible glycerol conversion mechanism over the 2:1CeZr/SBA-15 catalyst was also proposed.

Bio-hydrogen production from crude glycerol: Optimisation through response surface methodology and artificial neural network approach

Crude glycerol (CG) is the main by-product of biodiesel production from the transesterification of vegetable or animal oils. The CG's high energy content makes it an effective carbon source for bio-hydrogen production. However, the purity of CG derived from the transesterification process may vary due to impurities such as methanol, soap, salt, etc., which influence the hydrogen production yield. The present study investigated the impacts of initial glycerol, methanol, and soap concentration of CG on the hydrogen production by dark fermentation, and the effect of various factors was evaluated and optimised with the response surface methodology (RSM) and artificial neural network (ANN) approach to maximise the yield of hydrogen production. Both the results of these approaches showed good fitting. The correlation coefficient between actual and predicted values from RSM and ANN models is closer to ∼1, and the lower error shows the applicability of these models. A maximum of 17.67 mmol/L of hydrogen production was obtained via RSM with optimum methanol, soap and glycerol concentrations of 2.75 g/L, 6.07 g/L, and 20.45 g/L, respectively. Besides, the 3-D response surface graphs illustrated the suppressive impact of increased initial concentration of methanol and soap, along with higher initial concentrations of glycerol, on hydrogen production. Further, the outcome of the controlled experiment shows that the presence of impurities (methanol and soap) in glycerol reduces the cumulative hydrogen production by 5 %–17 % compared to the control for over five days.

Aqueous-phase Reforming of Glycerol using Cu-Ni Bimetal Catalyst Supported over Coconut Shell Activated Carbon

The increasing generation of glycerol as a waste from biodiesel production calls for its various consumptions, especially in producing industrial chemicals. However, the focus of popular studies in this process is on using noble metals as the catalyst. It should be shifted to a low cost and abundant element to ensure sustainability. Therefore, this study uses activated carbon from coconut shells to support a bimetal catalyst copper-nickel in converting glycerol into value-added products. The catalyst was synthesized via the wet impregnation method and was characterized using scanning electron microscopy-energy dispersive X-ray spectroscopy, Fourier-Transform infra-red spectroscopy, and a surface area analyser. It was revealed that the BET surface area (582 m2/g) is smaller than the pristine carbon because of the exposure to high temperature during calcination. The average pore size (1.7 nm) is also smaller than the coconut shell carbon due to the same effect. The surface functional groups mainly consist of carboxylic acids that is known to contribute to the hydrogenolysis of glycerol. At 20 wt% initial glycerol concentration, 20 bar and 200 °C, acetic acid, propylene oxide, carbon monoxide and acetaldehyde were detected as the products. A possible mechanism was proposed considering the aqueous-phase reforming of glycerol and the dehydration process. The optimum operating conditions in this case are 20 wt% initial glycerol concentration, 25 bar and 200 °C. More studies are needed to evaluate the reactions involved in aqueous-phase reforming of glycerol using the Cu-Ni doped on coconut shell activated carbon. In conclusion, glycerol can be converted to valuable chemicals under mild conditions by using the cost-effective catalyst.

Studies of polyol production by the yeast Yarrowia lipolytica growing on crude glycerol under stressful conditions

Crude glycerol, the principal by-product of biodiesel production process, was employed as substrate by three wild-type Yarrowia lipolytica strains (ACA-YC 5030, LMBF 20 and NRRL Y-323). Stressful conditions (low pH value = 2.0 ± 0.3, low incubation temperature T = 20 ± 1 °C, non-aseptic conditions) were employed. Interesting production of yeast biomass and polyols (viz. erythritol, mannitol and arabitol) was noted at pH = 2.0 ± 0.3 and T = 20 ± 1 °C. Strains failed to produce significant quantities of cellular lipid, while variable quantities of intra-cellular polysaccharides were produced. Fermentations under previously pasteurized media supported significant biomass and polyols production for most of the tested strains, while only one strain (NRRL Y-323), managed to produce polyols at media that were not previously thermally treated at all. The production of mannitol was favored at low initial glycerol (Glol0) concentrations, whereas higher Glol0 quantities favored the biosynthesis of erythritol. For the strain NRRL Y-323, highly aerated / agitated bioreactor trials showed different physiological profiles as compared to the respective flask experiments. Finally, in flask experiments with the strain NRRL Y-323 at high Glol0 amounts (≈140 g/L) at low medium pH (=2.0 ± 0.3), a significant production of polyols (=84.2 g/L) with the corresponding remarkable conversion yield on glycerol consumed = 62 % w/w was achieved. Practical applicationRenewable and biodegradable fuels, such as biodiesel, are safer and environmentally friendlier than the conventional petroleum diesel. Glycerol is a cost-effective substrate obtained as the main side-product from biodiesel production process and is currently being employed in the realm of Industrial Microbiology and Biotechnology to produce metabolic products with added value. Current research focuses on using glycerol as a starting substrate for biotechnological conversions aiming at producing, amongst other compounds, polyols, microbial biomass, citric acid, etc. from selected strains of the Generally Recognized Αs Safe (GRAS) yeast Yarrowia lipolytica. In the current investigation therefore, we examined the capacity of new wild-type non-extensively studied strains of this yeast to grow and assimilate this inexpensive substrate. Specifically, we have performed the acclimatization of the mentioned strains to stressful environments (i.e., low pH, low incubation temperature, non-aseptic conditions, etc.) and remarkable quantities of the added-value compounds (polyols, yeast mass, citric acid) were produced.

Sugar Alcohol Sweetener Production by Yarrowia lipolytica Grown in Media Containing Glycerol.

Most of the world's annual production of mannitol is by chemical means, but, due to increasing demand for natural sweeteners, alternative production methods are being sought. The aim of the study was to screen Yarrowia lipolytica yeast strains and select culture conditions for the efficient and selective biosynthesis of mannitol from glycerol. From 21 strains examined in the shake-flask culture for mannitol biosynthesis from glycerol (100 g/L), three strains were selected-S2, S3, and S4-and further evaluated in batch bioreactor cultures with technical and raw glycerol (150 g/L). The best production parameters were observed for strain S3, which additionally was found to be the most resistant to NaCl concentration. Next, strain S3 was examined in batch culture with regard to the initial glycerol concentration (from 50 to 250 g/L). It was found that the substrate concentrations of 50 and 75 g/L resulted in the highest mannitol selectivity, about 70%. The fed-batch culture system proposed in this paper (performed in two variants in which glycerol was dosed in four portions of about 50 or 75 g/L) resulted in increased mannitol production, up to 78.5 g/L.

Kinetic Study of Liquid-Phase Glycerol Hydrodeoxygenation into 1,2-Propanediol over CuPd/TiO2-Na.

Hydrodeoxygenation (HDO) kinetics of glycerol into 1,2-propanediol (1,2-PDO) in the liquid phase is studied on Cu-Pd/TiO2 catalysts. At a stirring speed higher than 480 rpm and an average diameter of the catalyst particles smaller than 89.5 μm, no mass transfer resistance artifacts are observed. The increasing temperature and H2 concentration promote the glycerol conversion and the selectivity to 1,2-PDO and disfavor the selectivity to acetol. Based on the experimental data, empirical kinetic pseudo-homogeneous expressions are proposed for glycerol disappearance, 1,2-PDO formation, and acetol formation in the catalytic system. Dependence of the disappearance rate of glycerol is closer to 1 with respect to glycerol and nonmeaningful with respect to H2. The formation rate of 1,2-PDO is not highly dependent on the initial concentration of glycerol or H2, and the formation rate of acetol is directly dependent on glycerol and inversely dependent on H2, since it accelerates acetol conversion to 1,2-PDO. The activation energies for glycerol disappearance (77.8 kJ/mol), 1,2-PDO formation (51.2 kJ/mol), and acetol formation (84.6 kJ/mol) evidenced the selective formation of 1,2-PDO in this catalytic system.

Yeast Lipid Produced through Glycerol Conversions and Its Use for Enzymatic Synthesis of Amino Acid-Based Biosurfactants

The aim of the present work was to obtain microbial lipids (single-cell oils and SCOs) from oleaginous yeast cultivated on biodiesel-derived glycerol and subsequently proceed to the enzymatic synthesis of high-value biosurfactant-type molecules in an aqueous medium, with SCOs implicated as acyl donors (ADs). Indeed, the initial screening of five non-conventional oleaginous yeasts revealed that the most important lipid producer was the microorganism Cryptococcus curvatus ATCC 20509. SCO production was optimised according to the nature of the nitrogen source and the initial concentration of glycerol (Glyc0) employed in the medium. Lipids up to 50% w/w in dry cell weight (DCW) (SCOmax = 6.1 g/L) occurred at Glyc0 ≈ 70 g/L (C/N ≈ 80 moles/moles). Thereafter, lipids were recovered and were subsequently used as ADs in the N-acylation reaction catalysed by aminoacylases produced from Streptomyces ambofaciens ATCC 23877 under aqueous conditions, while Candida antarctica lipase B (CALB) was used as a reference enzyme. Aminoacylases revealed excellent activity towards the synthesis of acyl-lysine only when free fatty acids (FAs) were used as the AD, and the rare regioselectivity in the α-amino group, which has a great impact on the preservation of the functional side chains of any amino acids or peptides. Aminoacylases presented higher α-oleoyl-lysine productivity and final titer (8.3 g/L) with hydrolysed SCO than with hydrolysed vegetable oil. The substrate specificity of both enzymes towards the three main FAs found in SCO was studied, and a new parameter was defined, viz., Specificity factor (Sf), which expresses the relative substrate specificity of an enzyme towards a FA present in a FA mixture. The Sf value of aminoacylases was the highest with palmitic acid in all cases tested, ranging from 2.0 to 3.0, while that of CALB was with linoleic acid (0.9-1.5). To the best of our knowledge, this is the first time that a microbial oil has been successfully used as AD for biosurfactant synthesis. This bio-refinery approach illustrates the concept of a state-of-the-art combination of enzyme and microbial technology to produce high-value biosurfactants through environmentally friendly and economically sound processes.

Lipid production by Rhodosporidium toruloides from biodiesel-derived glycerol in shake flasks and bioreactor: Impact of initial C/N molar ratio and added onion-peel extract

Rhodosporidium toruloides NRRL Y-27012 grown in glycerol, produced yeast biomass and secondary metabolites as lipids (L) and intra-cellular polysaccharides (IPS) in trials under nitrogen limitation (initial C/N molar ratios ≈ 50, ≈ 100, ≈ 160 and ≈ 240). The initial glycerol (Glol0) concentration for all experiments was ≈ 90 g/L. The yeast demonstrated significant dry cell weight (DCW) production irrespective of the C/N ratio employed, ranging between 19 and 29 g/L. The optimum C/N ratio medium was that of 100 moles/moles, where a DCWmax = 24.5 g/L containing c. 50% w/w of lipids was recorded. Endopolysaccharides presented indeed impressive values (≥ 50% w/w) even at the very early growth steps, while IPS/DCW values decreased as the fermentation proceeded, with simultaneous increase of L/DCW values. Experiments were also conducted in media with a hydroglycerolic extract of onion peels (at 40 mL/L), while a blank experiment (no extract) was also realized. The trial with the added extract was performed under both aseptic (previous sterilization) and non-aseptic (previous thermal treatment at T = 100 °C; 5 min) conditions. The aseptic experiment with the added extract resulted in a relative decrease in lipid production in relation to the control (L=8.6 g/L in the control vs L = 6.2 g/L with the extract). Under non-aseptic conditions, lipid production was slightly lower (L = 5.2 g/L). Finally, the optimum trial in shake flasks was scaled-up in a batch bioreactor, and higher glycerol assimilation rate, and biomass and lipid production occurred compared to the flask trial (final DCW and lipid values ≈27 g/L and 13.5 g/L respectively). Cellular lipids, rich in palmitic and oleic acid, were mainly composed of neutral fractions. Phospholipids were more saturated than the neutral lipids.

Photo-Oxidation of Glycerol Catalyzed by Cu/TiO2

In the present study, glycerol was oxidized by photocatalysis to glyceraldehyde, formaldehyde, and formic acid. Copper-doped TiO2 was synthesized by the evaporation-induced self-assembly approach and it was used as catalyst during the glycerol photo-oxidation reactions. The prepared mesoporous material exhibited high specific surface area (242 m2/g) and band gap energy reduction of 2.55 eV compared to pure titania (3.2 eV) by the synthesis method due to the presence of copper cations (Cu2+ identified by XPS). The catalyst showed only anatase crystalline phase with nanocrystals around 8 nm and irregular agglomerates below 100 μm. The selectivity and formation rate of the products were favored towards formaldehyde and glyceraldehyde. The variables studied were catalyst amount, reaction temperature, and initial glycerol concentration. The response surface analysis was used to evaluate the effect of the variables on the product’s concentration. The optimized conditions were 0.4 g/L catalyst, 0.1 mol/L glycerol, and temperature 313.15 K. The response values under optimal conditions were 3.23, 8.17, and 1.15 mM for glyceraldehyde, formaldehyde, and formic acid, respectively. A higher selectivity towards formaldehyde was observed when visible light was used as the radiation source. This study is useful to evaluate the best reaction conditions towards value-added products during the oxidation of glycerol by photocatalysis using Cu/TiO2.

The Non-solventogenic Clostridium beijerinckii Br21 Produces 1,3-Propanediol From Glycerol With Butyrate as the Main By-Product

Ever-increasing biofuel production has raised the supply of glycerol, an abundant waste from ethanolic fermentation and transesterification, for biodiesel production. Glycerol can be a starting material for sustainable production of 1,3-propanediol (1,3 PD), a valued polymer subunit. Here, we compare how Clostridium pasteurianum DSMZ 525, a well-known 1,3-PD-producer, and the non-solventogenic Clostridium beijerinckii Br21 perform during glycerol fermentation. Fermentative assays in 80-, 390-, or 1,100-mM glycerol revealed higher 1,3-PD productivity by DSMZ 525 compared to Br21. The highest 1,3-PD productivities by DSMZ 525 and Br21 were obtained in 390 mM glycerol: 3.01 and 1.70 mM h−1, respectively. Glycerol uptake by the microorganisms differed significantly: C. beijerinckii Br21 consumed 41.1, 22.3, and 16.3%, while C. pasteurianum consumed 93, 44.5, and 14% of the initial glycerol concentration in 80, 390, and 1,100 mM glycerol, respectively. In 1,100 mM glycerol, C. beijerinckii Br21 growth was delayed. Besides 1,3-PD, we detected butyrate and acetate during glycerol fermentation by both strains. However, at 80 mM glycerol, C. beijerinckii Br21 formed only butyrate as the by-product, which could help downstream processing of the 1,3-PD fermentation broth. Therefore, C. beijerinckii Br21, an unexplored biocatalyst so far, can be used to convert glycerol to 1,3-PD and can be applied in biofuel biorefineries.

EFFECTS OF SALTS IN BIODIESEL DERIVED CRUDE GLYCEROL ON VANCOMYCIN PRODUCTION FROM AMYCOLATOPSIS ORIENTALIS ATCC® 19795™

Bioconversion of crude glycerol (CG), the primary byproduct in biodiesel generation, is currently of great interest due to its promising potential in producing chemicals of high commercial interest. The efficient use of CG is still limited primarily due to the presence of impurities that may vary in composition based on the parent feedstock, biodiesel generation process, and any recovery/ purification conducted. In this study, laboratory scale fermentation of vancomycin using Amycolatopsis orientalis ATCC® 19795™ was analyzed based on the presence of salts as an impurity in biodiesel derived CG. Results showed that CG as the sole carbon source inhibited the cell growth, but the vancomycin production was approximately the same (158±2 mg L-1) as that of refined glycerol (RG)-based media at varying initial glycerol concentrations studied (5 g L-1 to 40 g L-1). NaCl as an impurity in biodiesel derived CG reduced both the growth yield coefficient (YX/S) and vancomycin formation at high concentrations. Among other salts tested are NaNO3 and KCl. NaNO3 (0.8 g L-1) supplemented media generated a higher YX/S (1.1 g biomass (g glycerol consumed)-1) and a similar vancomycin concentration (193 mg L-1) compared to the media with added NaCl (YX/S of 0.4 g biomass (g glycerol consumed)-1 and a vancomycin concentration of (190 mg L-1)). Relatively, both the YX/S (0.55 g biomass (g glycerol consumed)-1) and vancomycin concentration (135 mg L-1) was reduced in KCl (0.7 g L-1) supplemented media. The results suggest the potential of using CG (with salts i.e., NaCl as impurities) as an excellent low-cost alternative for RG in fermentation of vancomycin using Amycolatopsis orientalis ATCC® 19795™.

Influence of Operating Conditions on Reuterin Production Using Resting Cells of Limosilactobacillus reuteri DPC16

Limosilactobacillus reuteri strains can secrete a potentially valuable chemical and broad-spectrum antimicrobial substance named reuterin (3-hydroxypropionaldehyde, 3-HPA). L. reuteri DPC16 is a novel and patented probiotic strain that is used commercially because of its proven ability to kill various foodborne pathogens. A two-step process has been developed for reuterin production from glycerol using L. reuteri DPC16. Cells were grown, followed by harvesting, and then were incubated with glycerol for reuterin production. Parameters investigated during the glycerol conversion included the initial glycerol concentration, the biomass concentration, pH, culture age at harvesting, conversion time, and temperature. The highest reuterin yield was obtained using 21 g/L 24 h old cells, to convert glycerol solution (300 mmol/L) in 1 h at 30 °C and pH 6.2. The most efficient transformation of glycerol to reuterin was achieved in approximately 20 h of growth of cells at 25 °C and pH 6.8. Using the regression equation of this study, the maximum concentration of reuterin can be obtained using 25 g/L 20 h old DPC6 cells to ferment 350 mmol/L glycerol (initial concentration) for 2 h at 25 °C and pH 6.8 The ranking of effects on reuterin production for the six single factors was glycerol concentration > pH > conversion time > biomass concentration > temperature > culture age.

Continuous Culture of Auxenochlorella protothecoides on Biodiesel Derived Glycerol under Mixotrophic and Heterotrophic Conditions: Growth Parameters and Biochemical Composition.

As crude glycerol comprises a potential substrate for microalga fermentation and value added products’ biosynthesis, Auxenochlorella protothecoides was grown on it under heterotrophic and mixotrophic conditions and its growth kinetics were evaluated in a continuous system under steady state conditions. Increasing initial glycerol concentration (from 30 to 50 g/L) in the heterotrophic culture led to reduced biomass yield (Yx/S) and productivity (Px), but favored lipid accumulation. Under heterotrophic conditions, the microalga was found to grow better (biomass up to 7.888 g/L) and faster (higher growth rates), the system functioned more effectively (higher Px) and crude glycerol was exploited more efficiently. Heterotrophy also favored proteins synthesis (up to 53%), lipids (up to 9.8%), and carbohydrates (up to 44.6%) accumulation. However, different trophic modes had no significant impact on the consistency of proteins and lipids. Oleic acid was the most abundant fatty acid detected (55–61.2% of the total lipids). The algal biomass contained many essential and non-essential amino acids, especially arginine, glutamic acid, lysine, aspartic acid, leucine, and alanine. In all the experimental trials, the protein contents in the microalgal biomass increased with the increasing dilution rate (D), with a concomitant decrease in the lipids and carbohydrates fractions.

Sustainable arabitol production by a newly isolated Debaryomyces prosopidis strain cultivated on biodiesel-derived glycerol

The purpose of this research was the bioconversion of biodiesel-derived glycerol to arabitol through the adoption of sustainable bioprocessing. Arabitol production by Debaryomyces prosopidis FMCC Y69 was significantly affected by initial glycerol concentrations. The highest arabitol concentration of 45.5 g/L was achieved in the case of 120 g/L initial glycerol combined with the highest yield (0.379 g arabitol/g initial glycerol). The yeast strain showed a non-typical oleaginous behavior with low accumulation of lipids (up to 20.9% w/w) despite nitrogen-limited condition that prevailed in the fermentation media. Endopolysaccharides (IPs) were considerably high with a yield on the produced dry cell weight (YIPs/X) (=40.9% w/w) when 85 g/L of glycerol was utilized as the starting material. The fermentation efficiency was further improved when the optimal carbon to nitrogen (C/N) ratio was applied. More specifically, arabitol production was maximized (reaching 56.5 g/L) at a C/N ratio of 158 moles/moles while yield and productivity were also enhanced with respective values of 0.48 g arabitol/g consumed glycerol and 0.112 g/L.h. The increase in C/N ratios led to a decrease in cell dry weight (DCW) concentrations, which is rationally associated with decreased nitrogen availability in the growth medium. YIPs/X values were remarkably high (23.1–26.1% w/w) at the end of each fermentation with the highest concentration in absolute values of 7.3 g/L achieved at the lowest C/N ratio employed (i.e., 79 moles/moles). This study demonstrated the efficient arabitol production along with other value-added metabolites, such as IPs and cellular lipids, implementing biotechnology and renewable resources and thus contributing to the development of circular economy technologies.

Bioconversions of Biodiesel-Derived Glycerol into Sugar Alcohols by Newly Isolated Wild-Type Yarrowia lipolytica Strains

The utilization of crude glycerol, generated as a by-product from the biodiesel production process, for the production of high value-added products represents an opportunity to overcome the negative impact of low glycerol prices in the biodiesel industry. In this study, the biochemical behavior of Yarrowia lipolytica strains FMCC Y-74 and FMCC Y-75 was investigated using glycerol as a carbon source. Initially, the effect of pH value (3.0–7.0) was examined to produce polyols, intracellular lipids, and polysaccharides. At low pH values (initial pH 3.0–5.0), significant mannitol production was recorded. The highest mannitol production (19.64 g L−1) was obtained by Y. lipolytica FMCC Y-74 at pH = 3.0. At pH values ranging between 5.0 and 6.0, intracellular polysaccharides synthesis was favored, while polyols production was suppressed. Subsequently, the effect of crude glycerol and its concentration on polyols production was studied. Y. lipolytica FMCC Y-74 showed high tolerance to impurities of crude glycerol. Initial substrate concentrations influence polyols production and distribution with a metabolic shift toward erythritol production being observed when the initial glycerol concentration (Gly0) increased. The highest total polyols production (=56.64 g L−1) was obtained at Gly0 adjusted to ≈120 g L−1. The highest polyols conversion yield (0.59 g g−1) and productivity (4.36 g L−1 d−1) were reached at Gly0 = 80 g L−1. In fed-batch intermittent fermentation with glycerol concentration remaining ≤60 g L−1, the metabolism was shifted toward mannitol biosynthesis, which was the main polyol produced in significant quantities (=36.84 g L−1) with a corresponding conversion yield of 0.51 g g−1.

Optimization and feedback control system of dilution rate for 1,3-propanediol in two-stage fermentation: A theoretical study.

In utilizing glycerol to produce 1,3-propanediol by microbial fermentation, the problems of low utilization rate and poor production performance need to be addressed. Based on the analysis of a mathematical model for 1,3-propanediol production from glycerol by Klebsiella pneumoniae, this study theoretically investigated the effects of the dilution rate and the initial glycerol concentration in a two-stage fermentation process and the feasibility of applying the feedback control methods. First, the optimal operation conditions of initial glycerol concentration and dilution rate were obtained. Through the use of feedback control theory, a control strategy for dilution rate was designed and optimized to shorten the settling time (time required for fermentation to reach stability) from 60.92 to 36.68 h for the first reactor, and from 53.66 to 22.68 h for the second reactor. In addition, the yield of 1,3-propanediol in both two reactors reached up to 0.5g·g-1 . The simulation results indicated that the feedback control strategy for dilution rate increased the product concentration, reduced the residual glycerol in the fermentation broth, and greatly improved the performance of the fermentation. A feeding strategy of automatic control for dilution rate has been established and will be applied as an effective guiding scheme in automatic continuous fermentations for production of 1,3-propanediol.

Photocatalytic production of hydrogen and methane from glycerol reforming over Pt/TiO2–Nb2O5

In this study, platinized mixed oxides (TiO2–Nb2O5) were tested on photocatalytic hydrogen production from a glycerol solution under UV light. Different samples with different Ti:Nb ratios were prepared by using a simple method that simultaneously combined a physical mixture and a platinum photochemical reduction. This method led to improved physicochemical properties such as low band gap, better Pt nanoparticle distribution on the surface, and the formation of different Pt species. Niobia content was also found to be an important factor in determining the overall efficiency of the Pt–TiO2–Nb2O5 photocatalyst in the glycerol reforming reaction. The photocatalytic results showed that Pt on TiO2–Nb2O5 enhanced hydrogen production from the aqueous glycerol solution at a 5 wt% initial glycerol concentration. The influence of different operating conditions such as the catalyst dosage and initial glycerol concentration was also evaluated. The results indicated that the best hydrogen and methane production was equal to 6657 μmol/L and 194 μmol/L, respectively after 4 h of UV radiation using Pt/Ti:Nb (1:2) sample and with 3 g/L of catalyst dosage. Moreover, the role of water in photocatalytic hydrogen production was studied through photocatalytic activity tests in the presence of D2O. The obtained results confirmed the role of water molecules on the photocatalytic production of hydrogen in an aqueous glycerol solution.

The Biocatalytic Production of 3-Hydroxypropionaldehyde and Evaluation of Its Stability

3-Hydroxypropionaldehyde (3-HPA, reuterin) is a broad-spectrum natural antimicrobial agent used in the food industry and other fields. The low yield from the industrial production of 3-HPA using Lactobacillus reuteri and the spontaneous conversion of 3-HPA to acrolein have limited its more widespread use. We isolated L. reuteri BR201 as a biocatalyst for 3-HPA production and confirmed the effect of each factor in the two-step procedure for 3-HPA bioconversion. After initial cultivation for 8 h (late exponential phase), this isolate produced 378 mM of 3-HPA in 1 h at a concentration of OD600 nm 100, 30 °C, and an initial glycerol concentration of 500 mM. This is the highest reported biocatalytic yield of 3-HPA from a glycerol aqueous solution without additives. We confirmed that 4 mM of 3-HPA had antimicrobial activity against five pathogens. The degradation of 3-HPA to acrolein was greater at high temperatures, and there was little degradation when 3-HPA was maintained at 4 °C for 4 weeks. Our results may be useful for future applications of 3-HPA.

Kinetic modelling of 2,3-butanediol production by Raoultella terrigena CECT 4519 resting cells: Effect of fluid dynamics conditions and initial glycerol concentration

Biodiesel-derived glycerol was biologically converted to 2,3-butanediol, an organic compound with multiple industrial applications. Recent studies showed that Raoultella terrigena CECT 4519 is an effective biocatalyst for the bioprocess under conventional growing conditions. In the present work, a novel biocatalyst composed by R. terrigena resting cells was evaluated for the first time. Fluid dynamic conditions has been optimized to maximize 2,3-butanediol production in terms of titre, yield, and selectivity. Regarding the effect of initial glycerol concentration in batch runs, no substrate inhibition was detected in the studied conditions (concentrations between 45 and 250 g/L were used). Employing pure glycerol as carbon source, 82.0 g/L 2,3-butanediol titre was achieved, whereas 76.5 g/L were reached using raw glycerol. These numbers involve an achieved yield respect to maximal theoretic yield of 79% and 77%, respectively. A successful kinetic modelling of the bioprocess was developed and it is able to describe both the evolution of concentrations of relevant components with time and the rates calculated at experimental time values. Estimated specific 2,3-butanediol production rate was 0.034 g2,3-BDO/gX·h, while the estimated empirical pseudo-stoichiometric coefficient glycerol/2,3-butanediol was 2.52 gGly/g2,3-BDO. The obtained results showed that R. terrigena resting cells is a promising biocatalyst, which provides new opportunities for developing and scaling-up glycerol biorefineries.

Development of a fermentation strategy to enhance the catalytic efficiency of recombinant Escherichia coli for l-2-aminobutyric acid production.

Microbial fermentation for enzyme production and then whole-cell catalysis for l-2-aminobutyric acid (l-ABA) production have huge potential for industrial application, but the catalytic capacities of cells are directly related to the fermentation process. Using a 50L fermenter, the effects of initial glycerol concentration in the medium and rotating speed on cell catalytic capacity were investigated. Fermentation cells showed the best catalytic activity when the initial glycerol concentration was 12g/L and the rotating speed was 250rpm. Furthermore, we studied the difference between glycerol and glycerol mixtures as fed-batch media in pH-stat fed-batch fermentation. Results showed that glycerol had better catalytic activity than the glycerol mixture, and the effect of fed-batch fermentation was better than batch fermentation. Meanwhile, the enzyme activities of leucine dehydrogenase and formate dehydrogenase reached 129.87 U/g DCW and 437.02 U/g DCW, respectively, and the intracellular NAD(H) concentration reached 14.94μmol/g DCW. Using the optimized fermentation parameters, amplified fermentation was then carried out in a 5000L fermenter to demonstrate the industrial production of l-ABA by Escherichia coli BL21.