Whether Fermentation Is Best to Be Run as a Batch, Fed Batch or Continuous - Assignment Example

FERMENTATION: CULTURE SYSTEMS By Location Question: Discuss the factors you would consider in deciding whether fermentation is best to be run as a batch, fed batch or continuous. Provide example for each case Fermentation is a process employed in the production of gases, volatile liquids, extracellular and intracellular molecules that exhibit solubility, and insoluble solids. Experts in the fermentation process have defined certain goals that a successful Bioprocessing must achieve. Some of the most critical aspects that it should register are lowered costs, time reduction, waste reduction, compliance with regulatory conditions, and markedly high profits. Economic viability is an essential consideration prior to setting up the bioreactor. Some factors that determine the appropriate choice of reactor include the expected yield, product concentration, the reliability rates, conversion of the substrates, and the effect of impurities (Balasubramanian 2007, p. 89.) Factor to consider when deciding the appropriate culture 1. Economic Viability Since the three types of cultures described are alternative Bioprocessing techniques commonly used in large industrial fermentation, choosing the best system is of critical significance. Evidently, the economic viability is of critical consideration when making this choice. As highlighted above, the closed batch system proves to be cheaper in setting up when compared to the continuous culture. As mentioned, continuous culture requires a unique bioreactor that allows both an inflow and an outflow (Heritage, Evans, & Killington 2006, p.32). The level of required manpower is an additional consideration. The closed batch system requires a remarkable level of expertise to operate successfully. In cases where minimal labour is available, the automated continuous culture is the best option. Striking a balance between the cost of the bioreactor and the automation of the bioprocesssing is a decision that the strategic planners of any company that relies on fermentation face the compulsion to make. 2. Productivity Moreover, the productivity of the chosen system is of critical consideration. Evidently, the need for an industry to register high yields of the required product cannot receive any underestimation. Therefore, despite the low costs presented by batch cultures, the lengthy downtime, and the lack of consistency in the product formation poses a challenge. In addition, the challenges posed by the product and substrate inhibition in the batch systems the productivity rate (Ghosal & Srivastava 2009, p. 54). Many industries rely on feeding the batch in a bid to overcome some of the challenges posed by the closed system. This explains why many industries rely on either the batch or the fed batch systems. 3. Number and Types of Impurities Evidently, the fermentation process presents a major challenge of a range of impurities. The three culture systems described above have different level of impurities. For the industry, purity of the product is essential since eliminating impurities requires additional processes and costs. Therefore, it is imperative for ay industry to choose the culture system that yields a manageable quantity of impurities. 4. Reliability and Operability For any industry manufacturing fermentation products, reliability and operability is an essential aspect. Therefore, reliability is a pertinent factor determines the desirable culture system. For many industries, the batch system offers an easier task because of the ease of setting it up. For others, the automated operation of continuous cultures makes them desirable. 5. Yields The yields emanating from any bioprocessing plant determine its success. Each setup is targeted to yield a certain product. For economic stability, the culture system chosen should register high yields. Therefore, a culture system that offers the assurance of high yields is often desirable, although this must be balanced with other factors. 6. Degree of Substrate Conversion For any effective bioprocessing, all the substrates must be converted to the desired product for increased yield. In cases where substrates eventually are wasted, it becomes a loss. Therefore, the degree of substrate conversion is an additional factor considered in the choice of the preferred culture system. Moreover, different strains convert substrates at varying rates depending on the conditions of the fermenter. Batch Culture This is one of the most preferred Bioprocessing in many industries. Batch culture represents a closed system, a technique that involves loading the bioreactor with the appropriate substrate and nutrients. After loading of the sterilization, and inoculation with the strain of microorganism followed (Boudreau & McMillan 2007, p. 76). The closed bioreactor is allowed time for completion. The final step comprises of product removal. Moreover, the closed bioreactor presents the need for salient control of the pH, aeration, gases produced and foam. In essence, batch cultures only exhibit closure only in reference to the substrate because of the salient control of the above factors (Yang 2007, p. 34). Batch culture presents certain challenges because of its closed nature. Batch systems do not register a constant growth rate. In the initial phases, when the microorganism exhibits a high growth rate, product formation is minimal. When the depletion of the nutrients approaches, product formation increases. The lack of constancy of product formation in such bioreactors has proved to be one of the most critical concerns of experts. The fermentation process exhibits four stages namely lag phase, log phase, stationary phase and death phase. During the lag phase, limited growth is exhibited since the microorganism is yet to adapt to the bioreactor conditions. The log phase is defined by an increase in cell weight, while the log phase registers a fast multiplication of cells accompanied by a high yield of primary metabolites. After adapting to the conditions, the microorganism, then exhibits an enhanced growth rate during the exponential phase, until the entry of the stationary phase. The stationary phase is defined by an increasing concentration of products that exhibit toxicity, a factor that decreases the growth rate (Dunford 2012, p. 65). Notably, after during the stationary phase, depletion of nutrients makes is impossible for the bioreactor to sustain the growth of the microorganisms. After the depletion of the nutrients, the microorganism enters the death phase. Advantages and disadvantages of Batch Culture The adoption of batch culture is prompted by the fact that it proves viable for the secondary metabolite production. Moreover, batch systems exhibit flexibility because of the possibility of producing several products of interest. The closed nature of the system presents a lower probability of breaking down. Setting up a batch system is cheaper. However, batch cultures exhibit certain disadvantages that make it hard for application (Doran 2011, p. 90). Moreover, the stationary and death phase often exhibits long periods of downtimes, limiting the production rate. This serves as a critical disadvantage because of relatively low output. The lengthy downtimes increase the rate of costs in terms of charging. However, in some cases, the downtime suffices as effective time for maintenance. The analysis has revealed that batch systems pose high requirements of labour, as they need constant monitoring, and pose challenges in establishing control. Fed Batch Culture Fed batch culture denotes a closed system that offers the possibility of adding some nutrients as the Bioprocessing runs. Therefore, fed batch systems have an inflow, but lack an outflow. The establishment of the fed batch culture requires sufficient understanding of the microorganism physiology and metabolic pathways (Flickinger 2013, p. 43). Moreover, there is a salient need for prior determination of the rate at which the addition of the nutrients occurs. The addition of the nutrients serves to minimize the occurrence of catabolite repression and inhibition caused by the substrate. Fed batch cultures present the possibility of higher densities in the bioreactor. This is because additions of the nutrients lengthen the working period. Moreover, feeding the batch at specified intervals allows industries to establish a form of control on the level of product inhibition. The addition of the critical nutrients only prevents the formation of unwanted toxic products. A fed-batch also presents an opportunity for replacing the water subject to loss through evaporation. In cases where batch systems are utilized for the production of bioremediation products, then feeding it serves to increase the efficiency of the system. Since the alteration from the batch system only adding nutrients at different rates, fed batch cultures hardly require a new apparatus or bioreactor (McNeil, Harvey, & Wiley InterScience 2008, p.90). Despite the advantages highlighted above, successful operation of fed-batch cultures requires a prior analysis of the metabolic pathways of the strain used. Moreover, understanding its physiology and other requirements is critical in the determination of the nutrients that require addition. Evidently, feeding batch cultures requires expertise and extreme care in the minimization of the any chances of contamination. The feeding cycles introduce a risk for mutation of the strain. Such setbacks need to be addressed for effective feeding of batch systems. Continuous Culture Continuous cultures require specified bioreactors that allow removal of the medium and its replacement with fresh medium. The removal and replacement of the medium are defined to take place at the same rate. This serves to ensure that the volume in the bioreactor registers a constant volume throughout the working period. In some setups of the continuous cultures, a chemostat state exists, which is defined by limiting one of the nutrient concentrations in the inflow. However, a steady state is achievable in other continuous culture set-ups. The washout rate in the outflow system requires determination, and is denoted as the critical dilutions rate. Evidently, the inflow serves to introduce a fresh medium into the bioreactor, replacing the biomass extracted into the collecting vessel until a steady state exists (Krumbein, Paterson, & Zavarzin 2003, p. 87). Advantages and Disadvantages of Continuous Cultures Evidently, a continuous culture offers a new realm of automation of the Bioprocessing system. Such automation serves to reduce the labour costs. This translates to minimal expertise and work force. Moreover, the constancy in the working volume ensures high productivity rates throughout the process without registering any downtimes as is evident in the batch systems. Experts have highlighted that continuous cultures are setups that ensure a constant monitoring of any eventualities, maximizing productivity. Despite these evident benefits, continuous cultures are subject to contamination because of the challenges of maintaining sterility during the inflow and the outflow. Experts have also highlighted that the production of secondary metabolites is unachievable with continuous cultures (Hu & Biener 2006, p. 78). Notably, the inflow of the substrate leads to a measure of wastage. Moreover, only few recovery systems for continuous cultures exist. Research reveals that continuous cultures lack the ability to meet the demands in the market. However, experts have highlighted that continuous culture proves effective for the production of single cell proteins (Lim, & Shin 2013, p. 98). Conclusion As highlighted above, fermentation technology has advanced in the modern era, in a bid to enhance the productivity level of many Bioprocessing plants. The three common culture systems are batch, fed batch and continuous cultures. The three systems present a diverse range of benefits and setbacks, compelling certain critical aspects to be considered in the choice of the most appropriate. Many industries have adopted the batch and fed batch systems that register lower set-up costs. Bibliography Balasubramanian, D 2007, Concepts in biotechnology, Hyderabad: Universities Press. Boudreau, A, & McMillan, GK 2007, New directions in bioprocess modeling and control: Maximizing process analytical technology benefits, Research Triangle Park, NC: ISA. Doran, PM 2013, Bioprocess engineering principles, Amsterdam: Elsevier/Academic Press. Dunford, NT 2012, Food and industrial bioproducts and bioprocessing, Chichester, West Sussex, UK: Wiley-Blackwell. Flickinger, MC 2013, Upstream Industrial Biotechnology, 2 Volume Set, Hoboken: Wiley. Ghosal, S, & Srivastava, AK 2009, Fundamentals of bioanalytical techniques and instrumentation, New Delhi: PHI Learning. Heritage, J, Evans, E, & Killington, RA 2006, Introductory microbiology, Cambridge [England: Cambridge University Press. Hu, W.-S, & Biener, R 2006, Cell culture engineering, Berlin: Springer. Krumbein, W, Paterson, D, & Zavarzin, GA 2003, Fossil and recent biofilms: A natural history of life on earth, Dordrecht [u.a.: Kluwer Acad. Publ. Lim, H, & Shin, HS 2013, Fed-batch cultures: Principles and applications of semi-batch bioreactors. McNeil, B, Harvey, LM., & Wiley InterScience (Online service) , 2008, Practical fermentation technology, Chichester, England: Wiley. Yang, S.-T 2007, Bioprocessing for value-added products from renewable resources: New technologies and applications. Amsterdam: Elsevier. Read More