Continuous Fermentation Process

The concept of continuous fermentation processes is closely linked to the chemostat, where one nutrient is growth limiting and used to determine the growth rate.

From: Biopharmaceutical Processing , 2018

DEVELOPMENT OF A HIGHLY EFFICIENT PROCESS WITH HIGH CELL DENSITY FOR THE LONG-TIME CONTINUOUS PRODUCTION OF ETHANOL FROM INDUSTRIAL SUBSTRATE

Y.L. YANG , ... C.Y. CHOI , in Biomass for Energy and the Environment, 1996

CONCLUSIONS

The continuous fermentation process using the moving filter was developed to solve many problems caused by solid particles and to overcome the problems of conventional processes using flocculent yeast such as tower fermentor and a process with settler. Steps of continuous fermentation processes were made up of batch culture, SBR operation and continuous culture. In SBR operation, the timing for changing media was determined by using pH upshift as a good indicator of substrate starvation. When the solid particles were removed by a simple solid/liquid separator, the stable and long-time continuous operation with high cell density was possible. So the novel process with high productivity was developed for the production of fuel ethanol. The moving filter reactor with flocculent yeast was simple, easy to operate and easy to scale-up because of simple cofiguration and low mass transter resistance of the screen filter relative to microfiltration membrane.

The results show that this newly developed process with moving filter reactor has a great potential in the economic production of ethanol and other metabolites in a continuous fermentation system with high cell density at high productivity for a long period of time using industrial substrate.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080428499500227

Sustainability of Products, Processes and Supply Chains

Hangzhou Wang , ... Jinsong Zhao , in Computer Aided Chemical Engineering, 2015

6.7.1 Conditions of Oscillatory Phenomena

The oscillation phenomenon has been widely reported in continuous fermentation processes by Z. mobilis. Presumably, sustained oscillations naturally arise from product inhibition. In previous research, oscillatory phenomena have been ascribed to Hopf singularities and their bifurcations. By considering the effects of these oscillations on product yield, we have improved the biochemical process design over previous works. We also simulated the oscillatory dynamics of the fermentation system. Here we emphasize that the Hopf singularity is a trigger point that automatically generates oscillations for any combination of variables lying on that point. The detailed characteristics of the oscillation are determined for the initial values of the process. In this chapter, we related the amplitude/period of the oscillation to the operating conditions; specifically, we altered the dilution rate of the feedstock and observed the changes in the amplitude and period, maintaining the other variables at their Hopf singularity values. We found that oscillatory phenomena respond to slight changes in the feedstock dilution rate. It should be noted that we varied the feedstock dilution rate because this parameter is easily manipulated.

We conclude that whereas oscillation is triggered by a Hopf singularity, the dynamic behavior (amplitude and period of the oscillations) is determined by small deviations of the initial values from the Hopf singularity. This indicates that during the design process, the operating point must avoid not only the Hopf singularity (which triggers oscillations) but also regions close to the Hopf singularity, conditional on the effects of those oscillations (i.e, oscillations exerting small effects are permitted).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444634726000069

DEVELOPMENT OF A CONTINUOUS FERMENTATION PROCESS FOR FUEL ALCOHOL PRODUCTION

A.J. Payne , G.E. Guidoboni , in Energy: Money, Materials and Engineering, 1982

Fermenter System

A decision was taken by ALCON to develop a truly continuous fermentation process. The main advantages which a continuous fermentation process can offer include, a substantial reduction in capital cost through better productivity, ease of operational control through the existence of steady-state conditions in a basically simple plant and an improvement in yield resulting mainly from the precision with which optimum operating conditions can be maintained for long periods without difficulty. The continuous stirred tank reactor (CSTR) in which a single agitated vessel operates at steady-state with continuous feed of substrate and continuous extraction of product, was selected for development as the fermentation vessel. The productivity (rate of alcohol production per unit volume) however is severely limited in a basic CSTR system because of the need to avoid wash-out of the yeast from the system if the flow rate into the fermenter exceeds the rate at which the yeast in the fermenter can grow.

The performance of the CSTR is dramatically improved if yeast can be retained in the system, either directly within the fermenter vessel itself or by removing the yeast from the fermenter product stream and recycling the yeast back to the fermenter. With yeast retention in the system it is possible to exercise control over yeast concentration and yeast growth and by manipulation of these variables to optimise fermentation performance for high productivity and optimum yield of sugar to alcohol.

Other important operational characteristics of the CSTR include the fact that the composition of the fermenter contents is uniform and virtually identical to that of the outflowing product. The concentration of the alcohol is at its maximum value and that of the sugar substrate is at a minimum. Whilst conventionally high alcohol and low sugar concentration are deleterious to fermentation performance, in the ALCON CSTR system the effects of alcohol inhibition are offset by increasing the yeast concentration and the sugar substrate limitation does not take effect until the concentration has fallen to a very low threshold.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080287744500373

Pervaporation membrane reactors

A. Amelio , ... P. Luis , in Membrane Technologies for Biorefining, 2016

14.3.3.3 Process development

To overcome low cell density in traditional ABE fermentation, continuous fermentation processes with suspended cell, cell recycling, and immobilized cell fermentation have been applied successfully. This approach helped maintain high productivities for a long period without cell degeneration. The immobilization strategy has been claimed to improve the stability and solvent tolerance of microorganisms, reduce reactor volumes, give greater productivity, and enhance the flexibility of the reactor design (such as fixed bed, trickle bed, and fluidized bed) for continuous operation (Ezeji et al., 2004a,b). However, demerits of the immobilized system are mass transfer limitation of the substrate and activity loss because of immobilization. There are various reports on different techniques of immobilization, such as adsorption, entrapment, and covalent bond formation, and carriers ranging from synthetic to biodegradable polymers and fibers (Dolejš et al., 2014b; Ranjan and Moholkar, 2012). Cultures of C. acetobutylicum were immobilized over calcium alginate beads, bone char (Qureshi and Maddox, 1988), corn stalks (Zhang et al., 2009), sugarcane bagasse (Wu et al., 2015), lignocellulosic materials (Survase et al., 2012), bricks (Yen and Li, 2011; Yen et al., 2011), polyurethane foam, nylon scrubber, polyacrylamide, activated carbon, corncob, coke, kaolinite, montmorillonite, ceramic rings, and silica gel (Efremenko et al., 2011; Ranjan and Moholkar, 2012). Moreover, Liu et al. (2013a) immobilized C. acetobutylicum as a biofilm on a fibrous matrix, with increased butanol tolerance and ABE productivity of the cells. Huang et al. (2004) used a fibrous-bed bioreactor to produce high cell density by feeding glucose and butyrate as a cosubstrate, with greatly improved butanol yield compared with conventional ABE fermentation. Aragão Börner et al. (2014) presented a new cell immobilization technique: Cells ofC. acetobutylicum DSM 792 formed a macroporous aggregate through cryogelation with concomitant cross-linking together with activated polyethyleneimine and poly(vinyl alcohol) (PVA).

Ultrafiltration- or microfiltration-membrane cell recycle reactors have been investigated for many years as another option for improving reactor productivity, even though the need for an expensive membrane plant or membrane fouling impedes the commercial development of cell recycling technology (Afschar et al., 1985; Jin et al., 2011; Pierrot et al., 1986; Tashiro et al., 2005).

Multistage continuous fermentation has also been investigated to improve butanol productivity (Bankar et al., 2012; Jin et al., 2011).

Process integration is a further strategy to enhance the economics of biobutanol production (Köhler et al., 2015). Ezeji et al. (2004a,b) claimed that in the integrated fed-batch fermentation and product recovery system, solvent productivities were improved to 400% of the control batch fermentation. A simultaneous saccharification, fermentation, and vacuum recovery process was developed for ABE fermentation, with a lower cost of biobutanol production (Qureshi et al., 2014c). Qureshi and Maddox (2005) reduced process stream and processing costs by coupling ABE fermentation with pertraction for removal. Other studies reported continuous ABE production with direct product removal to eliminate product inhibition and increase the productivity of butanol formation (Bankar et al., 2012; Chen et al., 2014; Eckert and Schügerl, 1987; Ezeji et al., 2003, 2007b,c, 2013; Grobben et al., 1993; Izák et al., 2008; Li et al., 2014b; Liu et al., 2013, 2014a; Maddox et al., 1995; Mariano et al., 2012; Qureshi et al., 2014a; Wu et al., 2012, 2015; Yen and Wang, 2013).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780081004517000141

Material Balances

Pauline M. Doran , in Bioprocess Engineering Principles (Second Edition), 2013

Acetobacter aceti bacteria convert ethanol to acetic acid under aerobic conditions. A continuous fermentation process for vinegar production is proposed using nongrowing A. aceti cells immobilised on the surface of gelatin beads. Air is pumped into the fermenter at a rate of 200   gmol   h−1. The production target is 2   kg   h−1 acetic acid and the maximum acetic acid concentration tolerated by the cells is 12%.

(a)

What minimum amount of ethanol is required?

(b)

What minimum amount of water must be used to dilute the ethanol to avoid acid inhibition?

(c)

What is the composition of the fermenter off-gas?

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780122208515000046

28th European Symposium on Computer Aided Process Engineering

Robert Spann , ... Gürkan Sin , in Computer Aided Chemical Engineering, 2018

Abstract

A mechanistic process model describing a lactic acid bacteria (LAB) fermentation was applied to develop a continuous fermentation process. Producing LAB for the dairy industry in a continuous cultivation, which would allow harvesting the cells during the cultivation, would reduce production costs compared to traditional batch processes. To this end, a validated mechanistic model of a Streptococcus thermophilus fermentation was used for a model-based continuous process evaluation. The fermentation model consists of biological and chemical mechanisms including a description of the growth rate as a function of pH and inhibition effects of metabolites. The optimal dilution rate and substrate concentration in the feed were estimated in order to maximize the cell yield (biomass concentration) and to minimize the waste of substrate during the continuous fermentation in a 50   m3 bioreactor for two scenarios: downstream capabilities are i) flexible, and ii) fixed. The biomass concentration is restricted by the growth-inhibiting lactic acid concentration, which is produced by the growing bacteria. Furthermore, the substrate, which is supplied by the feed, should be consumed completely in the fermentation and not wasted in the bioreactor effluent owing to raw material costs. The resulting non-linear optimization problem was formulated and solved in MATLAB®. A Monte Carlo simulation showed the robustness of the results, where a biomass concentration of 5   g L-1 could be achieved in the continuous fermentation with a substrate wastage of less than 3 % in the bioreactor effluent. The productivity of the continuous process was similar to a traditional batch process, but frequent cleaning and sterilization are no longer necessary in a continuous process resulting in a shorter unproductive downtime of the bioreactors. This promising potential of a continuous process for LAB cultivations encourages pilot-scale studies for a comprehensive techno-economic evaluation.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444642356502795

Combined Gasification-Fermentation Process in Waste Biorefinery

Konstantinos Chandolias , ... Mohammad J. Taherzadeh , in Waste Biorefinery, 2018

3.6.2 Ethanol

Ethanol is currently the most desirable product from biomass-derived syngas fermentation [95]. The highest ethanol production that has been achieved by the wild-type Clostridium ljungdahlii is 48 g/L in a continuous fermentation process with cell recirculation [90]. According to another study on Clostridium ljungdahlii, ethanol and acetate were produced at syngas pressures between 0.8 and 1.8   atm [52]. According to the authors, the ethanol production was promoted by the H2 and CO2 of the syngas, and the highest ratio of ethanol/acetate obtained was 0.54   g ethanol/g acetate. Moreover, the kinetics of growth dependence on CO was presented by Andrew equation, and the inhibition constant was obtained at 2   mmol CO per liter of medium. In another work on continuous fermentation of syngas by Alkalibaculum bacchi strain CP15, ethanol, n-propanol, and n-butanol were concurrently produced with maximum concentrations of 8, 6, and 1   g/L, respectively [64].

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444639929000057

PHYSICAL REMOVAL OF MICROFLORAS | Filtration

A.S. Sant'Ana , in Encyclopedia of Food Microbiology (Second Edition), 2014

Continuous High-Cell-Density Bioreactors

Most biological conversion processes are conducted in batch mode. The advantages of such technologies are numerous, particularly simplicity and the low cost of the technology and materials. Nevertheless, there are disadvantages in comparison with continuous fermentation processes: low productivity (long periods for start-up and shutdown), batch-to-batch variations in quality, and high upstream and downstream processing costs. Researchers and manufacturers looking for an efficient continuous process with high volumetric productivity and simplified downstream processing technology therefore developed the concept illustrated in Figure 4 for the continuous production of propionic acid. A continuous stirred tank reactor is coupled to a microfiltration unit in a closed-loop configuration, including a recirculation pump, to achieve the flow velocity required by the filtration process. The total volume of the system is kept constant by adjusting the incoming new medium flow rate to the permeate flow rate. The membrane is chosen to allow a complete retention of the cells in the loop and to obtain a cell-free permeate, which contains the desired biosynthesized molecules (which must be able to pass through the pores of the membrane). The downstream processing is simplified by the sterile nature of the effluent, allowing most separation methods to be used afterward (electrophoresis, chromatography, etc.). One of the major advantages of this system is the increase of the cell biomass inside the loop. In such bioreactors, cell densities as high as 100   g   l−1 (dry weight) can be obtained for bacteria and can reach more than 330   g   l−1 for yeasts. With such cell concentrations, the volumetric productivities increase drastically: Propionic acid productivity is more than 430 times higher than in the classical batch process.

Figure 4. Membrane bioreactor for propionic acid production. UF, ultrafiltration.

Such membrane bioreactors could be used with one or several stages with the same or different microorganisms in each bioreactor. The concept of membrane bioreactors also is used widely with enzymes. The membrane is chosen to retain the enzyme (and very often, the macromolecular substrates such as proteins or starch) in the loop, while the products pass through the membrane (in most of the cases, ultrafiltration membranes). Many such processes with microorganisms or enzymes have been developed on an industrial scale worldwide since the 1980s for the production of ethanol, sparkling wine, organic acids, and peptides.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847300002524

An Overview of Existing Individual Unit Operations

Solmaz Aslanzadeh , ... Mohammad J. Taherzadeh , in Biorefineries, 2014

1.5.2 Fermentation Modes of Operation

The production of n-butanol has been investigated in batch, fed-batch, continuous, and continuous flash fermentation systems. The presence of inhibitors in hydrolyzates of cellulosic substrates (barley straw, corn stover, and switch grass hydrolyzate) was noticed in a number of studies on n-butanol production via batch fermentation. However, these inhibitors could be effectively eliminated through treatment of the hydrolyzates [144,145]. Batch and fed-batch fermentation processes were inadequate due to several factors, including time consumed in the sterilization of bioreactors, reinoculation, solvent inhibition, and low productivity. Using continuous fermentation processes compensated for these limitations.

The most common approaches for continuous fermentation have involved using free cells, immobilized cells, and cell recycling [146,147 ]. The immobilized cell continuous fermentation process is more advantageous than the free cell continuous fermentation process. For instance, cell immobilization permits longer cell survival time due to the absence of mechanical agitation in the solventogenesis phase with no regular cell regeneration. This process was applied in a fibrous bed bioreactor with C. acetobutylicum cells, using corn as substrate. The results revealed a significantly enhanced n-butanol yield (20% higher than the yields from conventional continuous fermentation techniques). Additionally, a shorter acidogenesis phase was reported, with butyric acid used as a co-substrate in the feed stream in order to increase the duration of solventogenesis phase [148]. Qureshi et al. [146] scaled up a continuous immobilized cell reactor using Clostridium beijerinckii and achieved a yield close to the yield from laboratory-scale reactor. However, excessive cell growth caused blockage problems. In order to tackle the problem, the nutrient supply was limited to reduce the cell growth. This approach failed because of the inactivation (spore forming) of a large number of cells. Research is still needed in order to scale up continuous immobilized cell bioreactors for the production of n-butanol in an economical manner.

In an attempt to improve free cell continuous fermentation, an altered version called the "cell recycling and bleeding process" was tested using high cell density of Clostridium saccharoperbutylacetonicum. In this method, membrane filtration was used to recycle the cells into the bioreactor in order to enhance the concentration of cells, leading to higher n-butanol yield. In contrast, an optimized dilution rate facilitated cell bleeding (i.e., elimination of excess cell concentration) from the bioreactor, upholding the optimum density of fermentation broth [149]. In order to prevail over the low efficiency of synthesizing n-butanol, a flash fermentation technology was proposed that consisted of three interconnected units, the fermentor, the cell retention system, and the vacuum flash vessel for continuous recovery of butanol from the broth. This process can also be of help in reducing the distillation costs, while resulting in less wastewater output, thus helping the environment [150].

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444594983000014

SINGLE CELL PROTEIN | Mycelial Fungi

P.S. Nigam , A. Singh , in Encyclopedia of Food Microbiology (Second Edition), 2014

Commercial Production of Mycelial Protein

Pekilo Process

Pekilo is a fungal protein product produced by fermentation of carbohydrates derived from spent sulfite liquor, molasses, whey, waste fruits, and wood or agricultural hydrolysates. It has a good amino acid composition and is rich in vitamins. Extensive animal feeding test programs showed that Pekilo protein is a good protein source in the diet of pigs, calves, broilers, chickens, and laying hens. Pekilo protein is produced by a continuous fermentation process. The organism, Paecilomyces variotii, a filamentous fungus, gives a good fibrous structure to the final product. The first plant was installed at the Jamsankoski pulp mill in central Finland in 1973. As an animal feed component, Pekilo protein is comparable to fodder yeast, which is also produced by fermenting spent sulfite liquor.

Mycoprotein Production

In the UK Rank-Hovis-McDougall, in conjunction with Imperial Chemical Industries (ICI) (in 1993, ICI demerged into Zeneca and became the new ICI) commercially marketed another fungal protein, mycoprotein (Quorn), derived from the growth of a Fusarium fungus on simple food-grade carbohydrates. Unlike almost all other forms of SCP, mycoprotein is produced for human consumption.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847300003116