A New Process for Continuous Production of Succinic Acid

A new efficient integrated membrane bioreactor-monopolar electrodialysis process was developed for succinate production at high yield (1.35 mol/mol), high titer (83 g/L) and high volumetric productivity (10.4 g/L.h) . The combination of these three parameters shows that this system could be economically viable for the development of a biological route to succinic acid production.

The World's First Bio-based Succinic Acid Plant has been launched

According to BioBasedNews.com, A succinic acid plant from BioAmber with an annual production capacity of 2,000 metric tons has started construction in Pomacle Francein and expect to begin production in the fall of 2009.

A collection of research papers on biobased succinic acid production

Modeling of batch fermentation kinetics for succinic acid production by Mannheimia succiniciproducens (2008). Kinetic models are proposed for the batch production of succinic acid from glucose by Mannheimia succiniciproducens MBEL55E. The models include terms accounting for both substrate and product inhibitions. Experimental data collected from a series of batch fermentations with different initial glucose concentrations were used to estimate parameters and also to validate the models proposed. The optimal values of the parameters were approximated by minimizing the discrepancy between the model predictions and corresponding experimental data. The growth of M. succiniciproducens could be expressed by a modified Monod model incorporating inhibitions of glucose and organic acids accumulated in the culture broth. The Luedeking–Piret model was able to describe the formation of organic acids as the fermentation proceeded, in which succinic, acetic, and formic acids followed a mixed-growth-associated pattern. However, unexpectedly, lactic acid fermentation by M. succiniciproducens was nearly nongrowth-associated. In all cases, the model simulation matched well with the experimental observations, which made it possible to elucidate the fermentation characteristics of M. succiniciproducens during efficient succinic acid production from glucose. These models thus can be employed for the development and optimization of biobased succinic acid production processes.

Succinic Acid Production by Continuous Fermentation Process Using Mannheimia succiniciproducens LPK7 (2008). To achieve a higher succinic acid productivity and evaluate the industrial applicability, this study used Mannheimia succiniciproducens LPK7 (knock-out: ldhA, pflB, pta-ackA), which was recently designed to enhance the productivity of succinic acid and reduce by-product secretion. Anaerobic continuous fermentation of Mannheimia succiniciproducens LPK7 was carried out at different glucose feed concentrations and dilution rates. After extensive fermentation experiments, a succinic acid yield and productivity of 0.38 mol/mol and 1.77 g/l/h, respectively, were achieved with glucose feed concentration of 18.0 g/l and 0.2 h-1 dilution rate. A similar amount of succinic acid production was also produced in batch culture experiments. Therefore, these optimal conditions can be industrially applied for the continuous production of succinic acid. To examine the quantitative balance of the metabolism, a flux distribution analysis was also performed using the metabolic network model of glycolysis and the pentose phosphate pathway.

From genome sequence to integrated bioprocess for succinic acid production by Mannheimia succiniciproducens (2008). Mannheimia succiniciproducens is a capnophilic gram-negative bacterium isolated from bovine rumen.Wild-type M. succiniciproducens can produce succinic acid as a major fermentation product with acetic, formic, and lactic acids as byproducts during the anaerobic cultivation using several different carbon sources. Succinic acid is an important C4 building block chemical for many applications. Here, we review the progress made with M. succiniciproducens for efficient succinic acid production; the approaches taken towards the development of an integrated process for succinic acid production are described, which include strain isolation and characterization, complete genome sequencing and annotation, development
of genetic tools for metabolic engineering, strain development by systems approach of integrating omics and in silico metabolic analysis, and development of fermentation and recovery processes. We also describe our current effort on further improving the performance of M. succiniciproducens and optimizing the mid- and downstream processes. Finally, we finish this mini-review by discussing the issues that need to be addressed to make this process of fermentative succinic acid production employing M. succiniciproducens to reach the industrial-scale process.

Prospects for a bio-based succinate industry. Bio-based succinate is receiving increasing attention as a potential intermediary feedstock for replacing a large petrochemical-based bulk chemical market. The prospective economical and environmental benefits of a bio-based succinate industry have motivated research and development of succinate-producing organisms. Bio-based succinate is still faced with the challenge of becoming cost competitive against petrochemical-based alternatives. High succinate concentrations must be produced at high rates, with little or no byproducts to most efficiently use substrates and to simplify purification procedures. Herein are described the current prospects for a bio-based succinate industry, with emphasis on specific bacteria that show the greatest promise for industrial succinate production. The succinate-producing characteristics and the metabolic pathway used by each bacterial species are described, and the advantages and disadvantages of each bacterial system are discussed.

Succinic acid production using metabolically engineered Escherichia coli (2007). Thesis.

Simultaneous fermentation and crystallization in succinic acid (2006). MS Thesis.

Production of Succinic Acid by E.coli from Mixtures of Glucose and Fructose (2005), a thesis by Andreas Lennartsson evaluated whether AFP184 can utilize fructose, both alone and in mixtures with glucose, as a carbon source for the production of succinic acid. The results showed that the Escherichia coli strain AFP184 can utilize fructose both alone and in mixtures with glucose. A succinic acid concentration of 52 g/L was reached with a mixture of fructose and glucose. The corresponding mass yield was 0.71 gram succinic acid per gram anaerobically consumed sugar. It was also shown that a high initial concentration of glucose (100 g/L) did not yield high levels of acetate during fermentations with Escherichia coli strain AFP184.

Fermentative Production of Succinic Acid from Glucose and Corn Steep Liquor by Anaerobiospirillum succiniciproducens (2005), a research by by Lee et al found that A. succiniciproducens was able to grow in a minimal medium containing glucose when supplemented with corn steep liquor (CSL) as the sole complex nitrogen source. The concentration of CSL had a significant effect on the glucose consumption by A. succiniciproducens. When 10-15 g/L of CSL was supplemented, cells were grown to an OD660 of 3.5 and produced 17.8 g/L succinic acid with 20 g/L glucose. These results are similar to those obtained by supplementing yeast extract and polypeptone, thereby suggesting that succinic acid can be produced more economically using glucose and CSL.

In Silico Metabolic Pathway Analysis and Design: Succinic Acid Production by Metabolically Engineered Escherichia coli as an Example (2002). In this study, Lee et al have constructed in silico metabolic pathway network of Escherichia coli consisting of 301 reactions and 294 metabolites. Metabolic ux analyses were carried out to estimate ux distributions to achieve the maximum in silico yield of succinic acid in E. coli. The maximum in silico yield of succinic acid was only 83% of its theoretical yield. The lower in silico yield of succinic acid was found to be due to the insufficient reducing power, which could be increased to its theoretical yield by supplying more reducing power. Furthermore, the optimal metabolic pathways for the production of succinic acid could be proposed based on the results of metabolic flux analyses. In the case of succinic acid production, it was found that pyruvate carboxylation pathway should be used rather than phosphoenolpyruvate carboxylation pathway for its optimal production in E. coli. Then, the in silico optimal succinic acid pathway was compared with conventional succinic acid pathway through minimum set of wet experiments.The results of wet experiments indicate that the pathway predicted by in silico analysis is more efficient than conventional pathway.

Kinetic study for the extraction of succinic acid with TOA in Fermentation broth; effects of pH, salt and contaminated acid. Reactive extraction can be used for the recovery of carboxylic acids from fermentation broth. Through the formation of complex with extractants at the two-phase interface, the carboxylic acids are partitioned into organic solvents. However, the recovery of carboxylic acids is interrupted by the conditions of fermentation broth. In this study, the effects of conditions of fermentation broth on the extraction kinetics were investigated using a microporous membrane-based stirred cell for the extraction of succinic acid with tri-n-octylamine. The interfacial concentrations of species in various systems were correlated and thus the effects of pH, salts and contaminated acid on the intrinsic reaction kinetics were discovered. The reaction rate constants were determined from the forward reaction rate equation reported in our previous work. It was found that the extraction rates were steeply decreased at pH values larger than 3 due to the dissociation of carboxylic group. Competitive extraction of salts, and contaminated acid, which was pyruvic acid, had negative influence on the extraction process of succinic acid and thus the extraction rates were decreased. The interfacial concentrations of succinic acid and TOA in fermentation broth had no difference with those in artificial single acid systems. Therefore, the decrease of extraction rates can be explained by the change of ionic strength in fermentation broth.

Isolation and characterization of succinic-acid producing Mannheimia sp. from bovine rumen. A novel succinic acid-producing bacterium was isolated from bovine rumen. The bacterium is a non-motile, non-spore-forming, mesophilic and capnophilic gram-negative rod or coccobacillus. Phylogenetic analysis based on the 16S rRNA sequence and physiological analysis indicated that the strain belongs to the recently reclassified genus Mannheimia as a novel species, and has been named Mannheimia succiniciproducens MBEL55E. Under 100% CO2 conditions, it grows well in the pH range of 6.0–7.5 and produces succinic acid, acetic acid and formic acid at a constant ratio of 2:1:1. When M. succiniciproducens MBEL55E was cultured anaerobically in medium containing 20 g l–1 glucose as carbon source, 13.5 g l–1 of succinic acid was produced.

Succinic Acid Adsorption from Fermentation Broth and Regeneration (2004). More than 25 sorbents were tested for uptake of succinic acid from aqueous solutions. The best resins were then tested for successive loading and regeneration using hot water. The key desired properties for an ideal sorbent are high capacity, complete stable regenerability, and specificity for the product. The best resins have a stable capacity of about 0.06 g of succinic acid/g of resin at moderate concentrations (1–5 g/L) of succinic acid. Several sorbents were tested more exhaustively for uptake of succinic acid and for successive loading and regeneration using hot water. One resin, XUS 40285, has a good stable isotherm capacity, prefers succinate over glucose, and has good capacities at both acidic and neutral pH. Succinic acid was removed from simulated media containing salts, succinic acid, acetic acid, and sugar using a packed column of sorbent resin, XUS 40285. The fermentation byproduct, acetate, was completely separated from succinate. A simple hot water regeneration successfully concentrated succinate from 10 g/L (inlet) to 40–110 g/L in the effluent. If successful, this would lower separation costs by reducing the need for chemicals for the initial purification step. Despite promising initial results of good capacity (0.06 g of succinic/g of sorbent), 70% recovery using hot water, and a recovered concentration of >100 g/L, this regeneration was not stable over 10 cycles in the column. Alternative regeneration schemes using acid and base were examined. Two (XUS 40285 and XFS-40422) showed both good stable capacities for succinic acid over 10 cycles and >95% recovery in a batch operation using a modified extraction procedure combining acid and hot water washes. These resins showed comparable results with actual broth.

Effective purification of succinic acid from fermentation broth produced by Mannheimia succiniciproducens (2006). The present study deals with the development of purification and separation processes required to produce the highly purified succinic acid from the fermentation broth produced by recombinant microorganism, Mannheimia succiniciproducens. The newly developed process consists of the pretreatment process such as reactive extraction and vacuum distillation step and the crystallization process for the highly purified succinic acid production. By-produced acids were effectively removed by the reactive extraction as a primary separation. In addition, the crystallization was applied without adding any salts to produce highly purified succinic acid. The purified succinic acid, with 99.8% purity and 73.1% yield rate was obtained through this newly developed purification process.

Improved Succinic Acid Production in the Anaerobic Culture of an Escherichia coli pflB ldhA Double Mutant as a Result of Enhanced Anaplerotic Activities in the Preceding Aerobic Culture (2007). Escherichia coli NZN111 is a pflB ldhA double mutant which loses its ability to ferment glucose anaerobically due to redox imbalance. In this study, two-stage culture of NZN111 was carried out for succinic acid production. It was found that when NZN111 was aerobically cultured on acetate, it regained the ability to ferment glucose with succinic acid as the major product in subsequent anaerobic culture. In two-stage culture carried out in flasks, succinic acid was produced at a level of 11.26 g/liter from 13.4 g/liter of glucose with a succinic acid yield of 1.28 mol/mol glucose and a productivity of 1.13 g/liter _ h in the anaerobic stage. Analyses of key enzyme activities revealed that the activities of isocitrate lyase, malate dehydrogenase, malic enzyme, and phosphoenolpyruvate (PEP) carboxykinase were greatly enhanced while those of pyruvate kinase and PEP carboxylase were reduced in the acetate-grown cells. The two-stage culture was also performed in a 5-liter fermentor without separating the acetate-grown NZN111 cells from spent medium. The overall yield and concentration of succinic acid reached 1.13 mol/mol glucose and 28.2 g/liter, respectively, but the productivity of succinic acid in the anaerobic stage dropped to 0.7 g/liter _ h due to cell autolysis and reduced anaplerotic activities. The results indicate the great potential to take advantage of cellular regulation mechanisms for improvement of succinic acid production by a metabolically engineered E. coli strain.

Genome-Based Metabolic Engineering of Mannheimia succiniciproducens for Succinic Acid Production (2006). Succinic acid is a four-carbon dicarboxylic acid produced as one of the fermentation products of anaerobic metabolism. Based on the complete genome sequence of a capnophilic succinic acid-producing rumen bacterium, Mannheimia succiniciproducens, gene knockout studies were carried out to understand its anaerobic fermentative metabolism and consequently to develop a metabolically engineered strain capable of producing succinic acid without by-product formation. Among three different CO2-fixing metabolic reactions catalyzed by phosphoenolpyruvate (PEP) carboxykinase, PEP carboxylase, and malic enzyme, PEP carboxykinase was the most important for the anaerobic growth of M. succiniciproducens and succinic acid production. Oxaloacetate formed by carboxylation of PEP was found to be converted to succinic acid by three sequential reactions catalyzed by malate dehydrogenase, fumarase, and fumarate reductase. Major metabolic pathways leading to by-product formation were successfully removed by disrupting the ldhA, pflB, pta, and ackA genes. This metabolically engineered LPK7 strain was able to produce 13.4 g/liter of succinic acid from 20 g/liter glucose with little or no formation of acetic, formic, and lactic acids, resulting in a succinic acid yield of 0.97 mol succinic acid per mol glucose. Fed-batch culture of M. succiniciproducens LPK7 with intermittent glucose feeding allowed the production of 52.4 g/liter of succinic acid, with a succinic acid yield of 1.16 mol succinic acid per mol glucose and a succinic acid productivity of 1.8 g/liter/h, which should be useful for industrial production of succinic acid.

Metabolic Engineering of Escherichia coli for Enhanced Production of Succinic Acid, Based on Genome Comparison and In Silico Gene Knockout Simulation (2005). Comparative analysis of the genomes of mixed-acid-fermenting Escherichia coli and succinic acid-overproducing Mannheimia succiniciproducens was carried out to identify candidate genes to be manipulated for overproducing succinic acid in E. coli. This resulted in the identification of five genes or operons, including ptsG, pykF, sdhA, mqo, and aceBA, which may drive metabolic fluxes away from succinic acid formation in the central metabolic pathway of E. coli. However, combinatorial disruption of these rationally selected genes did not allow enhanced succinic acid production in E. coli. Therefore, in silico metabolic analysis based on linear programming was carried out to evaluate the correlation between the maximum biomass and succinic acid production for various combinatorial knockout strains. This in silico analysis predicted that disrupting the genes for three pyruvate forming enzymes, ptsG, pykF, and pykA, allows enhanced succinic acid production. Indeed, this triple mutation increased the succinic acid production by more than sevenfold and the ratio of succinic acid to fermentation products by ninefold. It could be concluded that reducing the metabolic flux to pyruvate is crucial to achieve efficient succinic acid production in E. coli. These results suggest that the comparative genome analysis combined with in silico metabolic analysis can be an efficient way of developing strategies for strain improvement.

Succinic acid production and purification (US patent, 1999). A highly efficient process for the production and recovery of pure succinic acid from a succinate salt that involves minimal use of additional reagents, and produces virtually no waste by-products, and permits internal recycle of the base and acid values, is provided. The method involves the formation of diammonium succinate, either by using an ammonium ion based material to maintain neutral8 pH in the fermenter or by substituting the ammonium cation for the cation of the succinate salt created in the fermenter. The diammonium succinate can then be reacted with a sulfate ion, such as by combining the diammonium succinate with ammonium bisulfate and/or sulfuric acid at sufficiently low pH to yield succinic acid and ammonium sulfate. The ammonium sulfate is advantageously cracked thermally into ammonia and ammonium bisulfate. The succinic acid can be purified with a methanol dissolution step. Various filtration, reflux and reutilization steps can also be employed.

Fermentation and purification process for succinic acid (US Patent, 1992). A process for economically producing highly purified succinic acid comprises growing a succinate-producing microorganism on a low cost carbohydrate substrate; simultaneously neutralizing the fermentation broth and precipitating the succinate as calcium succinate by adding a calcium ion source to form calcium succinate; isolating the calcium succinate; slurrying the calcium succinate in water and treating it with sulfuric acid to form calcium sulfate and succinic acid; and then treating the succinic acid with first a strongly acidic ion exchanger and then a weakly basic ion exchanger to remove impurities and obtain a highly purified succinic acid product. In a preferred embodiment, the calcium succinate is isolated from the fermentation broth by filtration; the filtrate is heated to precipitate additional calcium succinate; and, the spent filtrate which contains nutrients is recycled to the fermentor.

Batch and continuous cultures of Mannheimia succiniciproducens MBEL55E for the production of succinic acid from whey and corn steep liquor (2003). Mannheimia succiniciproducens MBEL55E isolated from bovine rumen is able to produce a large amount of succinic acid in a medium containing glucose, peptone, and yeast extract. In order to reduce the cost of the medium, whey and corn steep liquor (CSL) were used as substrates for the production of succinic acid by M. succiniciproducens MBEL55E. Anaerobic batch cultures of M. succiniciproducens MBEL55E in a whey-based medium containing CSL resulted in the production of succinic acid with a yield of 71% and productivity of 1.18 g/l/h, which are similar to those obtained in a whey-based medium containing yeast extract (72% and 1.21 g/l/h). Anaerobic continuous culture of M. succiniciproducens MBEL55E in a wheybased medium containing CSL resulted in a succinic acid yield of 69% and a succinic acid productivity as high as 3.90 g/l/h. These results show that succinic acid can be produced efficiently and economically by M. succiniciproducens MBEL55E from whey and CSL.

Influence of C02-HC03- Levels and pH on Growth,Succinate Production, and Enzyme Activities of Anaerobiospirillum succiniciproducens (1992). Growth and succinate versus lactate production from glucose by Anaerobiospirillum succiniciproducens was regulated by the level of available carbon dioxide and culture pH. At pH 7.2, the generation time was almost doubled and extensive amounts of lactate were formed in comparison with growth at pH 6.2. The succinate yield and the yield of ATP per mole of glucose were significantly enhanced under excess-CO2-HCO3 growth conditions and suggest that there exists a threshold level of CO2 for enhanced succinate production in A. succiniciproducens. Glucose was metabolized via the Embden-Meyerhof-Parnas route, and phosphoenolpyruvate carboxykinase levels increased while lactate dehydrogenase and alcohol dehydrogenase levels decreased under excess-CO2-HC03- growth conditions. Kinetic analysis of succinate and lactate formation in continuous culture indicated that the growth rate-linked production rate coefficient (K) cells was much higher for succinate (7.2 versus 1.0 g/g of cells per h) while the non-growth-rate-related formation rate coefficient (K') was higher for lactate (1.1 versus 0.3 g/g of cells per h). The data indicate that A. succiniciproducens, unlike other succinate-producing anaerobes which also form propionate, can grow rapidly and form high final yields of succinate at pH 6.2 and with excess CO2-HCO3 as a consequence of regulating electron sink metabolism.

Downstream processing of biobased succinic acid (5)

Approach V: Sorption-Based SA Purification
(Davison et al. Appl. Biochem. Biotech, Vol. 113-116,653 (2004))

Key points for the process
–Key desirable properties for an ideal sorbent
--High capacity: >0.06 g SA/ g resin at moderate concentrations (1-5 g/l)
--Complete low-cost stable regenerability: 70% recovery using hot water and >95% using a modified extraction combining acid and hot washes
--Specificity for the product: a recovered concentration> 100 g/L

What about the feasibility for commercialization?

Downstream processing of biobased succinic acid (4)

Approach IV: Reactive Extraction-Based SA Purification: Extraction and Crystallization (Huh, et al. Process Bio. 41(2006)1461-1465

Key points for the process

• TOA has high extractability and used for selective removal of contaminated organic acids and salts from dilute fermentation broth
  --Only extract the undissociated form of carboxylic acids
  -- Need multistage extraction using different degrees of dissociation of each acid with pH


• Vacuum distillation
  --Concentrate the pretreated broth and remove volatile organic acids such as acetic acid, formic acid etc.


• Crystallization
  --The crystal of SA is formed more than other organic acids in saturated fermentation broth (after vacuum distillation) and low solubility

Any comments for this method? Advantages and disadvantages? Cost or simplexity?

Downstream processing of biobased succinic acid (3)

Approach III: Ammonium-Based SA Purification: Extraction and Crystallization
(Huh, et al. Process Bio. 41(2006)1461-1465

•Key points for the process
–SA crystallizer: Succinate ion is protonated by ammonium bisulfate to form ammonium sulfate and SA. SA crystallizes due to its low solubility at pH 1.5-1.8 (optimal yield generated)
–Methanol purification: SA is advantageously dissolved in methanol but sulfates relatively insoluble in methanol
–Thermal craker: Ammonium sulfate cracks to produce ammonium and ammonium bisulfate, which can be reused.

•Advantages
–Minimal use of additional reagents
–Produce virtually no waste by-products
–Permit internal recycle of the base and acid

It is recommended!

Biobased succinic acid players

According to Huw Kidwell, the current worldwide use of succinic acid is around 20,000 to 30,000 tonnes per year and this is on the increase by around 10 per cent a year, which attracts industrial interests in biobased sugar platform succinic acid production. This is a big cake and who will be the first to have the market share?

1. BioAmber

Bioamber, a joint venture by ARD and DNP develop a commercially viable technology for the production of succinic acid by fermentation of various renewable feedstocks. It will use carbon dioxide from the ethanol plant for its fermentation process, according to the company. The plant will have an annual capacity of 5,000 metric tons, producing succinic acid, ethanol and biodiesel.

2. MBI International

MBI, established in 1981 by the Michigan High Technology Task Force, has a history of developing biobased chemicals and agricultural feedstocks into chemicals derived from fermentation processes. In 1996, the company patented the unique bacterium it isolated for production of succinic acid from sugars. MBI is actively seeking commercial partnerships for its biobased succinic acid platform.

3. BioEnergy International LLC

BioEnergy International, LLC is a privately-held, science and technology company in the development and commercialization of next generation biorefineries for the production of high-value bio-based chemicals (such as succinic acid) and fuels from renewable feedstock through the use of its proprietary biocatalyst technology.

4. DSM and ROQUETTE Joined Forces

Royal DSM N.V., and ROQUETTE have joined forces to implement and commercialize the fermentative production of biorenewable succinic acid, which – amongst other applications - opens the possibility to produce bio-based performance materials. By the end of 2009 a demonstration plant in Lestrem (France) will be operational.

Downstream processing of biobased succinic acid (2)

Approach II: A Combination of Electrodialysis and Water Splitting
(Glassner et al. US Patent, 5,143,834)

1. Key points for the process
–Use conventional electrodialysis to recover and concentrate the succinate salt from a whole broth containing cells and impurities
–A water-splitting electrodialysis to convert the succinate salt to succinic acid and base
–Treatment with ion-exchangers to remove charged impurities from succinic acid

2. Advantages
–Allow cell-containing whole broth to be sent directly to electrodialysis without pretreatment such as filtration and centrifuge
–Preferential recovery of desired succinate salt over acetate through the membranes

3.Disadvantages
–High cost associated with electrodialysis such as membrane costs and electrical energy costs

Downstream processing of biobased succinic acid (1)

Unlike ethanol, which you can just distill away from other components, you cannot do that with succinic acid! Downstream processing is key steps to commercialize biobased succinic acid production. The broth of succinic acid (SA) fermentation has a lower SA concentration (~60 g/L) with the side products such as acetic acid, meleic acid, formic and lactic acid etc. It is a major factor involved in industrial scale production using fermentation due to the cost (60%) involved in downstream processing to concentrate and purify the products.

There are techniques needed for pure SA production and efficient recovery process. SA fermentation usually proceeds best at an approximately neutral pH (6.0-7.0), but acid products will eventually lower the pH,therefore,the pH of the broth needs to be rained and maintained by addition of base; The added basic compounds generally react with the acid to form salts rather than the desired free acid product itself. The traditional succinic acid recovery method is based on precipitation and crystallization technology, acidification by ion-exchange resins and crystallization process:
–Removal of insoluble materials such as dead cells

–Concentrate the fermentation broth
–Acidification
–Crystallization and filtration
–Purification of the acidified product by ion-exchange resins

Approach I: Ca-Based SA Separation: Precipitation and Washing
(Datta et al. US Patent, 5, 168,055)

• Key process-related problems
–Separation of dilute product streams and the related cost of recovery
–Elimination of the salt waste from current purification process
–The reduction of inhibition to the product of the fermentation itself
–Separation of other acidic by-products such acetic acid, formic acid, lactic acid, citric acid,etc.

•Product related problems
- one mole of product ends up one mole of gypsum, which is a by-product with little value
- Odor and color contamination

- Comsumption of CaO, CaOH, and H2SO4, which are not regenerated within the process

A review: Production of succinic acid by bacterial fermentation

A review paper titled "Production of succinic acid by bacterial fermentation" was published in "Enzyme and Microbial Technology 39 (2006) 352–361" .This paper reviews processes for fermentative succinic acid production, especially focusing on the use of several promising succinic acid producers including Actinobacillus succinogenes, Anaerobiospirillum succiniciproducens, Mannheimia succiniciproducens and recombinant Escherichia coli.

Integrated biorefinery for SA and bioethanol production

Since SA fermentation needs CO2 input and biothanol fermentation produce CO2 as a main product, a integrated biorefinery has been suggested for the biorefinery, i.e. Integrating the succinate and the ethanol fermentations would decrease carbon lost as waste CO2 and produce three commercial products; ethanol, SA and diethyl succinate as shown below:

Succinic acid production

Traditionally, SA can be synthesized through chemical process from maleic anhydride through n-butane using petroleum as starting material; the high raw material cost of maleic anhydride limits the use of succinic acid for a wide range of applications. Recently efforts have been focusing on produce SA via fungal or bacterial fermentations through the TCA reactions because the increased market expected to come from the synthesis of biodegradable polymers; polybutylene succinate (PBS) and polyamides (Nylon®x,4) and various green solvents.

During biochemical pathways for SA synthesis, bacteria used mainly utilize the phosphoenolpyruvate (PEP) carboxylation reaction and the reductive arm of the TCA cycle. It requires CO2 input; Formation of by-products such as acetic, formic and lactic acid can be a major problem, but will be solved by improving the microbs and the fermentation conditions. Theoretically, redox balance gives 1.714 mol succinate per mol glucose or 1.12 g succinate each gram glucose.

The manufactering cost is mainly affected by succinic acid yield, productivity, raw material cost and utilization, and product recovery method. The technological efforts still need to reduce the cost of both aerobic and anaerobic fermentations – nutrients and carbon feedstocks; improve the robustness of fermentations, increase the productivity of organisms – a minimum of 2.5 g/(L. h) is needed for the process to be economically competitive; and ferment both 5 and 6 carbon sugars.

Where are we for succinic acid commercialization?

"The Quest to Commercialize Biobased Succinic Acid" written by By Jessica Ebert from Biomass Magazine.

Succinic Acid

Succinic acid (SA), also known as amber acid or butanedioic acid, is a dicarboxylic acid having the molecular formula of C4H6O4. After its first purification of succinic acid from amber by Georgius Agricola in 1546, it has been produced by microbial fermentation for the use in agricultural, food and pharmaceutical industries, i.e. one of the fermentation end-products of anaerobic metabolism (Fig.1).

Fig. 1. Biochemical Pathways for SA synthesis

Currently, most of commercially available succinic acid is produced by chemical process, in which liquefied petroleum gas or petroleum oil is used as a starting material.

Succinic acid can be used as a precursor of many industrially important chemicals and considered by US-DOE as one of twelve top chemical building blocks that can be manufactured from biomass (Fig. 2.).

Fig. 2.