Article

Downstream separation and purification of bio-based alpha-ketoglutaric acid from post-fermentation broth using a multi-stage membrane process

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Abstract

In this study, a multi-stage membrane process, assisted by vacuum evaporation and crystallization, for recovery of bio-based alpha-ketoglutaric acid from the actual post-fermentation broth was designed and investigated. In the first part of this study, pre-treatment of crude fermentation broth (centrifugation-ultrafiltration-nanofiltration) was carried out to remove biomass, proteins, sugars, part of inorganic ions and color compounds. The commercial ceramic UF membrane (15 kDa) and nanofiltration ceramic membrane (200 Da or 450 Da) were applied. Electrodialysis with a bipolar membrane was proposed for separation of ionic compounds and simultaneous electro-acidification to the acid form. During bipolar membrane electrodialysis carried out under acidic conditions, it was possible to remove close to 90 % of alpha-ketoglutaric acid. Moreover, the migration of other acids present in the fermentation broth (lactic and acetic) was significantly limited. The calculated specific energy consumption was low and equal to 0.6 kW h/kg. The final purification using crystallization assisted vacuum evaporation allowed obtaining alpha-ketoglutaric acid in solid form. Analysis of the final product showed that the proposed method of alpha-ketoglutaric acid recovery gives the acid of high purity equal to 94.8 %. Furthermore, the presented results have practical relevance and may in future be the basis for the development of separation technologies of alpha-ketoglutaric acid from the fermentation broth on industrial scale.

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Lactic acid is produced industrially from bacterial fermentation of carbohydrates (e.g., sugar, starch) followed by separation processes such as precipitation, distillation, and reactive extraction. However, these conventional separation processes are energy-intensive. In this study, we report an integrated membrane separation process consisting of ultrafiltration (UF) and nanofiltration (NF) for lactic acid recovery from fermentation broth, combined with ion exchange (IEX) and vacuum-assisted evaporation. Most organic and inorganic components in lactic acid fermentation broth, including microbes, glucose and inorganic salt ions, were successfully removed by UF and NF processes. Membrane fouling in the UF process became severe due to the high concentration of microbes and organic compounds. The effects of various UF membranes on the extent membrane fouling were also studied to enhance separation efficiency. The separation of lactic acid continued using NF membranes, considering both size exclusion and Donnan exclusion effects. Finally, IEX and vacuum evaporation (VE) processes were also used to eliminate residual salt ions and to increase lactic acid purity. The hybrid membrane-separation process produced lactic acid with high purity (> 99.5 %).
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The purpose of this research work was to prepare nanosized formulation of alpha ketoglutarate as dry powder inhaler for cyanide poisoning. Nanosizing can be approached by solid phase and liquid phase method. The different conditions encountered in both these approaches can greatly affect the particle characteristics. In this study milling and precipitation technique were compared to study their effect on α-KG particles characteristics. Differences in choice of stabilizers were observed between the two processing techniques. Sonication processes followed by HPH produced small sized particles in which Pluronic F68 was employed as stabilizing agent. Precipitation approach produced ultrafine drug particles by utilizing combination of stabilizers (PVA + PEG 400). Amongst the two sonication processes, probe sonication process produced well stabilized small sized particles. The designed particles showed 43.13±2.36% lung deposition when compared with ultrasonication and precipitation technique that showed 31.69% and 21.67% respirable fraction. The MMAD of the designed particles was found suitable for deep alveolar deposition. Clinical studies (Phase-I trial) showed whole lung deposition of 52.51% for DPI. The P/C ratio was found to be 1.02 suggesting uniform distribution of particles in different lung compartments.
Article
Environmentally friendly process of production of alpha-ketoglutaric acid (AKG) from model water solutions by bipolar membrane electrodialysis (EDBM) was carried out. Two-chamber EDBM stack with the anion exchange membrane-bipolar membrane (AM-BM) configuration was used to transport AKG ions through AM from the diluate to concentrate chamber and convert them to AKG acidic form. The influence of initial pH of diluate solution, initial concentration of AKG salts in the diluate and concentrate chambers and current efficiency was evaluated by considering such factors as voltage drop, alpha-ketoglutaric acid concentration, current efficiency and energy consumption for 1 kg of AKG production. Under optimum conditions the process EDBM allows achievement of a high concentration of AKG, high current efficiency and low energy consumption, equal to 4.83 g/L, 71.8%, 3.72 kWh/kg, respectively, while the corresponding results obtained after 180 min EDBM process without optimization were 1.6 g/L, 24% and 15.26 kWh/kg, respectively. In addition, the obtained results indicate that bipolar membrane electrodialysis may be used for the production of AKG from actual post fermentation broth in the future.
Article
The separation and concentration of succinic acid from 3-component model solutions and actual post-fermentation broth after pre-treatment processes were studied in a 10-chamber large-scale EDBM setup. The influence of current density and initial concentration of succinates in the diluate chamber was evaluated by considering such factors as: i) final succinic acid concentration, ii) current efficiency and iii) energy consumption for 1 kg of succinic acid production. According to the results, the highest acid concentration in the concentrate chamber and the highest current efficiency of 75.4% after 180 min of the process were obtained when the current density and the initial concentration of succinic acid salt in the diluate chamber were equal to 120 A/m² and 200 g/L, respectively. The results have proved that it is possible to use the EDBM process as one of the steps of separation and concentration of succinic acid from the actual post-fermentation broth after biotechnological conversion of glycerol. Moreover, it should be stressed that the application of EDBM process allows the concentration of succinic acid and additionally the conversion from salts to the acidic form.
Article
Despite its superb separation performance, ultrafiltration (UF) still faces challenges in treating the Microcystis aeruginosa-laden water of lakes or reservoirs, due to membrane fouling and poor rejection of soluble organics. In this work, to better understand the mechanisms of membrane fouling, cell breakage and organic rejection and their mutual influence, a comparative UF experiment was conducted under a variety of transmembrane pressures (TMPs, 50–250 kPa) with lab-cultured Microcystis aeruginosa. Membrane fouling was characterized with respect to flux decline and fouling reversibility, and cell breakage during UF filtration was evaluated using a flow cytometer. Moreover, the rejection of extracellular organic matter (EOM) by UF was investigated with respect to the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and microcystin-LR (MCLR). The results indicated that the accumulation of Microcystis cells and EOM on the membrane surface caused serious reversible fouling that substantially aggravated with the increasing TMP and was successively governed by pore blocking and cake filtration. The cell breakage during filtration was less than 5% and mainly occurred in the cake layer due to hydraulic shear, but the breakage did not substantially vary with increasing TMP. EOM removal by UF ranged from 40% to 70% (in terms of DOC removal), and the removal performance increased with the reversible resistance, implying a trade-off between organic removal and permeability. Regarding soluble and small organics such as MCLR, a higher degree of removal was also found at higher TMP, despite of some variations over the duration of the filtration tests, and the cake layer retention proved to be the principle removal mechanism, especially during steady filtration stages.
Article
The process of recovering citric acid from fermented liquid by bipolar membrane electrodialysis (BMED) was studied. Two bipolar membranes and one cation exchange membrane were stacked to form a two-compartment BMED stack configuration. The effects of the current density, initial concentration of sodium citrate, and structure of the acid compartment (AC) and base compartment (BC) on the performance of the BMED process were investigated. Filling mixed-bed ion exchange resins in BC could decrease the compartment resistance and led to a pure base solution for reuse. The highest acid recovery of 97.1% was achieved with 3.3% initial sodium citrate under a current density of 40 mA cm⁻¹. Additionally, a decrease of voltage across AC by filling cation exchange resins restricted the migration of H⁺ ions from AC to BC. A higher initial concentration of sodium citrate has an adverse effect on the recovery of citric acid. BC with a bipolar membrane (BPM) exhibited lower energy consumption and a higher recovery rate of citric acid. BMED appears to be a promising technology for recovering citric acid from fermented liquid.
Article
Anaerobic fermentation of organic waste streams by mixed culture generates a mixture of short chain carboxylic acids. To avoid inhibitory effects of the acids or their consumption in internal conversion reactions in the mixed culture environment, in-situ recovery of acids can be beneficial. In this study, electrodialysis with bipolar membranes (EDBM) was applied to a mixed culture fermentation on organic waste streams using a novel EDBM stack with “direct contact” operation mode. We could demonstrate simultaneous recovery of carboxylates from the fermenter by the EDBM stack while in-situ generation and transport of hydroxyl ions to the fermenter allowed direct pH control. Experiments showed productivity increase after EDBM coupling to the fermenter, and complete elimination of external base consumption. It was also observed that EDBM was able to drive the mixed culture fermentation towards acetate and propionate type of carboxylates.
Article
In this study, mucilage, a residue from coffee production, was investigated as substrate in fermentative L(+)-lactic acid production. Mucilage was provided as liquid suspension consisting glucose, galactose, fructose, xylose and sucrose as free sugars (up to 60 g L-1), and used directly as medium in Bacillus coagulans batch fermentations carried out at 2 and 50 L scales. Using mucilage and 5 g L-1 yeast extract as additional nitrogen source, more than 40 g L-1 lactic acid was obtained. Productivity and yield were 4-5 g L-1 hour-1 and 0.70-0.77 g lactic acid per g of free sugars, respectively, irrespective the scale. Similar yield was found when no yeast extract was supplied, the productivity, however, was 1.5 g L-1 hour-1. Down-stream processing of culture broth, including filtration, electrodialysis, ion exchange chromatography and distillation, resulted in a pure lactic acid formulation containing 930 g L-1 L(+)-lactic acid. Optical purity was 99.8 %.
Article
The utilisation of acid whey by the dairy industry is limited by the high concentrations of lactate in the solution. In the present study, three commercially available nanofiltration membranes: HL, XN45 and DK were used in to evaluate the separation of lactose and lactate as a function of pH. Raw acid whey was used after microfiltration, while two laboratory prepared solutions comprising lactic acid and lactose; and sodium lactate and lactose were also tested for comparison. The rejection of lactic acid was found to increase with the degree of acid dissociation. About 50% of the lactate could be removed at pH ∼3 due to the lower degree of dissociation. For all pH values tested, over 90% of the lactose was retained. The molecular weight cutoff and permeability of the membranes had little influence on the separation performance.
Article
Organic acids, which are chemically synthesized, are also natural intermediates in the metabolic pathways of microorganisms, among which the tricarboxylic acid (TCA) cycle is the most crucial route existing in almost all living organisms. Organic acids in the TCA cycle include citric acid, α-ketoglutaric acid, succinic acid, fumaric acid, l-malic acid, and oxaloacetate, which are building-block chemicals with wide applications and huge markets. In this review, we summarize the synthesis pathways of these organic acids and review recent advances in metabolic engineering strategies that enhance organic acids production. We also propose further improvements for the production of organic acids with systems and synthetic biology-guided metabolic engineering strategies. Copyright © 2015. Published by Elsevier Inc.
Article
Malic acid is a valuable organic acid and important acidulant in food and pharmaceutical industries and can be produced using electrodialysis with bipolar membrane (EDBM). The aim of this study was to investigate the possibility of malic acid production using a system integrating EDBM and biochemical process, i.e., the microbial electrodialysis and chemical-production cell (MEDCC). With an applied voltage of 1.0 V, the MEDCC successfully conversed 0.3 M malate into 0.23 M malic acid, which was about four times as that produced in the EDBM (0.06 M). The maximum current density in the MEDCC was five times higher than that in the EDBM (10 vs. 1.9 A/m2). The specific electric consumption for the malic acid production in the MEDCC was 0.34 kWh/kg, which was only 10–30% of that in the reported EDBMs. In the MEDCC, the energy from the anode biodegradation provided about 50% of the total energy demand (0.68 kWh/kg) during the malic acid production. Our results show that the MEDCC should be a promising method for organic acid production with advantages of lower electrical consumption and diverse substrates utilized by exoelectrogens.
Article
Lactic acid, mainly produced by fermentation, has been widely used in the food, chemical, and pharmaceutical fields. Because of the high downstream processing costs in traditional technology, the cost-effective production of high-purity lactic acid has remained a challenge for decades. This study provides an integrated membrane process to recover lactic acid from sodium salt fermentation broth that consists of ceramic membrane filtration, nanofiltration (NF), and bipolar membrane electrodialysis (BMED). In the ceramic membrane process, the flux changed with the membrane pore size in the order of 50 nm > 200 nm > 500 nm > 20 nm. At an operating pressure of 0.1 MPa, the flux of the membrane with a pore size of 50 nm reached a maximum of 192 L·m–2·h–1, and the removal rate of cells was up to 99.3%. In the subsequent NF step, the flux increased linearly with the operating pressure from 0.5 to 2.0 MPa, whereas the rejection rates of Mg2+, Ca2+, and Na+ increased with increasing TMP, and a flux of 5.0 L·m–2·h–1 was obtained at the operating pressure of 2.0 MPa, with 87.7% of Ca2+, 95.0% of Mg2+, and 98.9% of protein being retained. The BMED process was developed for the conversion of 95.0% NaL into NaOH and HL, and the energy consumption was 1.05 kWh·kg–1 under a current density of 400 A·m–2. Our results indicate that the proposed integrated membrane process is technically feasible for lactic acid production from fermentation broth.
Article
The effect of successive limiting current density (LCD) determination procedures on electrodialysis with ultrafiltration membrane (EDUF) system was studied in order to evaluate their impact on ion-exchange (IEM) and ultrafiltration membranes (UFM) integrity by measuring in situ the membrane potential difference. In the first protocol, two successive LCD determination procedures were carried-out by increasing the voltage by 2 V from 0 to 40 V, spaced by a rest period of 60 min. In the second protocol, the LCD determination procedures were performed every 20 min during 60 min. For both protocols, voltage-current curves were plotted for IEM and UFM and Ilim values were determined. Results showed that only anion-exchange membrane (AEM) showed a typical sigmoidal curve for both protocols. Moreover, it was demonstrated that a rest time period of 60 min between two successive LCD determination procedures had no impact on system current density and membrane potential difference while four successive LCD determinations spaced by a constant rest period of 20 min allowed delaying the appearance of Ilim and over-limiting current region. A mathematical approach was also proposed allowing for the first time the calculation of the different parameters typical of water splitting phenomenon from a voltage-current curve.
Article
Experimental investigations were carried out on cross-flow nanofiltration of microfiltrate fermentation broth of lactic acid during membrane-integrated fermentative production of monomer grade lactic acid. Three types of composite polyamide nanofiltration membranes (NF2, NF3 and NF20) manufactured by Sepro Co. (USA) were used in nanofiltration. Lactic acid fermentation broth produced by fermentation of sugar cane juice by Lactobacillus plantarum in a membrane-integrated hybrid reactor system was filtered by NF membranes after preliminary filtration through microfiltration membranes for cell separation and recycle. Effects of cross flow rate, transmembrane pressure and pH on flux and rejection of both acid and unconverted sugars for recycle were analyzed. NF3 membrane was successful in retaining 94% unconverted sugars while allowing 32% lactic acid to permeate at a flux of 113 L m−2 h−1 at pH 5.5, temperature 37 °C, transmembrane pressure of 13 bar and cross-flow velocity 2.48 m s−1. The study shows that integration of a properly selected nanofiltration membrane with a cell-recycle fermentation unit and lactate conversion unit can yield l (+) lactic acid with an optical purity of 85.6% through an economically attractive route by recovering and recycling of unconverted sugars. The nanofiltration combine with bipolar electrodialysis in downstream purification can replace the multiple purification steps by two steps while yielding a monomer grade lactic acid from a mixture of unconverted sugars and lactic acid.
Article
An experimental study was carried out to achieve a continuous integrated operation of fermentation and electrodialysis with bipolar membranes (EDBM). There need three steps to accomplish this experiment: (1) individual continuous fermentation; (2) individual continuous EDBM; (3) integrated operation of fermentation and EDBM under continuous condition. The results indicate that the maximum feed rate (fermenter can afford) is 0.24L/h, which is also equal to the feed rate of the subsequent individual continuous EDBM. During continuous EDBM, the recovery ratio of lactate from the fermentation broth can reach 69.5% under a current density of 40mA/cm(2). The net end concentration and total molar quantity for lactic acid can reach 1.46mol/L and 2.18mol, and for OH(-) are 1.32mol/L and 1.70mol, respectively. The integration can be achieved only under an initial alkali concentration of no less than 1mol/L and a current density of no less than 30mA/cm(2).
Article
We report the design of several elastomers based on the thermal polycondensation of α-ketoglutaric acid and one of three triols: glycerol, 1,2,4-butanetriol, or 1,2,6-hexanetriol. By varying the curing temperature and the duration of the curing process, a wide range of mechanical properties was achieved. The values of the Young’s modulus (0.1−657.4 MPa), ultimate stress (0.2−30.8 MPa), and ultimate strain (22−583%) encompass the mechanical properties of many biological materials, increasing the probability of success for the use of poly(triol α-ketoglutarate) as a biomaterial. Furthermore, the poly(triol α-ketoglutarate) series hydrolytically degraded in as fast as 2 days and as long as 28 days in phosphate-buffered saline solutions. For postpolymerization modifications, the repeat units contain ketones, which are capable of reacting with a variety of oxyamine-terminated molecules to generate stable oxime linkages. Finally, the versatility and utility of these elastomers were demonstrated by creating micropatterned structures and films for biospecific cell scaffold supports.
Article
Succinic acid is a valuable four-carbon platform chemical with wide applications in many fields. One step recovery of the desired product succinic acid crystal from the fermentation broths was studied for the first time. In a fed batch fermentation by Actinobacillus succinogenes BE-1, the final concentrations of succinic acid, formic acid, lactic acid and acetic acid in the bioreactor reached 97.8g/L, 23.5g/L, 5.1g/L and 17.4g/L, respectively. These organic acids have different proportions of dissociated and undissociated forms at different pH values, and the solubility of these forms of acid is different substantially. When the pH value of the fermentation broth was controlled less than 2.0, crystallization of succinic acid could be carried out at 4°C easily, while major acid by-products such as lactic acid, acetic acid and formic acids were miscible in solution. By this one step recovery method, succinic acid yield was 70%, and the purity was 90%. In comparison, for traditional calcium precipitation coupled ion-exchange adsorption, the yield and purity were 52% and 92%, respectively. Crystallization could be regarded as not only the final purification step but also the first recovery step for the downstream separation process. In this study, succinic acid can be feasibly purified from fermentation broths selectively, which could be integrated with other separation method to optimize the downstream process.
Article
Surfactin biosurfactant was produced by fermentation method with culture of Bacillus subtilis ATCC 21332. Downstream processing for surfactin recovery by ammonium sulfate salting-out, ultrafiltration (UF), nanofiltration (NF), and their hybrid process was studied. Experiments were performed at different initial concentrations of surfactin (210–3620mg/L), the concentrations of added ammonium sulfate (0–46%, w/v) and micelle-destabilizing solvent ethanol (0–44%, v/v), and membrane molecular-weight cut-off (MWCO, 1–300kDa) were investigated. When 23% (w/v) ammonium sulfate and 33% (v/v) ethanol were added to the broths, it was shown that surfactin micelles could be efficiently destroyed and other protein macromolecules could be removed. On the other hand, the UF membrane with MWCO less than 100kDa was found to be suitable for the retention of surfactin micelles, and the NF membrane with a MWCO less than 1kDa was found to be suitable for the retention of surfactin monomers. Finally, the hybrid salting-out and membrane filtration (UF or NF) process was proposed and tested. Comparisons among these single and hybrid processes demonstrated that the hybrid process not only enhanced the recovery yield but also improved the purity of surfactin.
Article
Flux decline during dead-end ultrafiltration (UF) of the fermentation broths of Bacillus subtilis ATCC (American Type Culture Collection) 21332 culture was studied, in which polyethersulfone membrane with a molecular weight cut-off of 100 kDa was used. Prior to UF, the broth was treated by centrifugation at 10,000 × g. All experiments were performed at a feed pH of 7, a feed surfactin concentration of 0.56 g L−1, and a stirring speed of 300 rpm but at different applied pressures (ΔP, 86–430 kPa). The resistance-in-series model was used to analyze flux behavior, which involves the resistances of membrane itself and the cake as well as those due to adsorption and solute concentration polarization. It was shown that the resistance due to solute concentration polarization dominated the flux decline under the conditions studied. The resistances due to cake formation and solute adsorption were comparable, and their sum contributed below 3% of the overall resistance.