Theory and Design of Fermentation Processes

Davide Dionisi

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000469547
• Edition: 1
• Topic: Medizin
• Subtopic: Biotechnologie in der Medizin

This book covers the kinetics and design of fermentation processes, defined in the broader sense as any industrial processes that use living microorganisms or cells, both under aerobic and anaerobic conditions. It starts with a concise introduction to microbes and their metabolism, followed by rate equations, stoichiometry, derivation and use of mass balances for the design processes. It covers oxygen transfer and mass balances, heat transfer and design and scale-up/scale-down of fermentation processes. It further includes industrially relevant process examples, over 100 solved examples, questions and problems, and solutions of differential equations and systems of equations in Excel.

Features

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• Uses chemical engineering principles for the study of fermentation processes

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• Provides detailed coverage of stoichiometry and kinetics of fermentation processes

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• Discusses pertinent oxygen transfer theory and its applications

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• Concisely covers microorganism biochemistry and metabolism

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• Includes solved examples and problems with solutions

This book is designed as a textbook for undergraduate students in chemical engineering; however, it is also suitable for postgraduate students and for process engineers interested in these topics.

1Introduction to Fermentation Processes

DOI: 10.1201/9781003217275-1

This chapter introduces the main concepts on fermentation processes used in this book. Humans have been using fermentation processes for thousands of years. There's evidence of the use of fermented alcoholic beverages in Neolithic China, and the fermentation of milk to make yogurt was probably discovered even before then. Nowadays, industrial fermentation processes are carried out at very large scales, for example, bioethanol is produced from starchy or sugary feedstocks using yeasts at rates of millions of cubic metres per year. Commercial-scale fermentation processes need, therefore, to be designed and optimised taking into consideration their kinetics and stoichiometry, mass and energy balances and mass and heat transfer, which are the main focus of this book.

1.1 Fermentation Processes and Microorganisms

In this book, we will use the term “fermentation” in the broadest sense to indicate any reactions that involve the growth of living microorganisms. In a stricter sense, the term fermentation is often used to indicate anaerobic reactions which produce a compound of interest in the liquid phase (e.g. alcoholic fermentation), but in this book we will refer to both aerobic and anaerobic processes.

Microorganisms (Figure 1.1) are unicellular (mostly) or multicellular organisms, in the order of micrometres in size, which grow (duplicate) on a carbon source and mineral nutrients.

FIGURE 1.1 Examples of microorganisms. Top left: Aspergillus niger conidia (van Leeuwen et al., 2013, Creative Commons license). Bar is 10 μm. Top right: Lactobacillus acidophilus (Bob Blaylock, CC BY-SA, https:/​/​creativecommons.org/​licenses/​by-sa/​3.0, https:/​/​commons.wikimedia.org/​wiki/​File:20101212_200110_LactobacillusAcidophilus.webp). Numbered ticks are 11 μm apart. Bottom left: Methanosarcina mazei (https:/​/​bacdive.dsmz.de/​strain/​7096, Copyright Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH). Bottom right: Saccharomyces cerevisiae, SEM image (Mogana Das Murtey and Patchamuthu Ramasamy, CC BY-SA 3.0, https:/​/​commons.wikimedia.org/​w/​index.php?curid=52254246).

FIGURE 1.1 Long Description

Examples of microorganisms as seen under microscope.

For engineering purposes, in general terms the metabolism of any microorganisms can be schematised in a simple way (Figure 1.2). The microorganisms live in water and absorb from the external environment the carbon source (often called the “substrate”) and the mineral elements that they need to grow (increase in number). The growth of microorganisms occurs by duplication. When they grow, microorganisms generate products that are released into the environment. Depending on the type of microorganisms and the environmental conditions, different products can be generated by the microorganisms, e.g. carbon dioxide (which is produced in most cases), organic acids, methane and many others. In this book, we will generally use “substrate” to express the carbon source and we will use the terms “microorganisms” and “biomass” with the same meaning. In addition to microorganisms, the theories and models presented in this book can be applied to cultures of animal cells, e.g. mammalian or stem cells, which are used in medical applications.

FIGURE 1.2 Conceptual scheme of microbial metabolism.

FIGURE 1.2 Long Description

Conceptual scheme of microbial metabolism, showing the use of substrate and nutrients for the growth and generation of products.

Fermentation processes are carried out for two main reasons:

• We are interested in the fermentation products, which are of industrial relevance, for example, ethanol, antibiotics, enzymes. In medical applications, viral vaccines and therapeutic proteins are among the products of the fermentation of mammalian cells.
• We want to remove polluting organic substances from the water phase. This is what happens in biological wastewater treatment processes.

When they are used to produce some products, fermentation processes are alternative to processes which use chemical synthesis. Some products can be produced by both fermentation and chemical processes and the process chosen to be used at industrial scale depends on the cost and availability of the feedstocks. For example, lactic acid (Figure 1.3) can be produced by fermentation of carbohydrates by microorganisms of Lactobacillus or other species or by chemical synthesis from acetaldehyde, which is derived from coal or petroleum. Glutamic acid is another example of a substance which can be produced by either fermentation or chemical synthesis, the fermentation process being currently the preferred one in the industry. Generally, fermentation processes have the advantage over chemical synthesis processes, of requiring fewer reaction stages. When fermentation processes are available to produce a certain chemical, microorganisms may be able to convert the feedstock into the desired chemical in just one stage. On the other hand, chemical synthesis may require many reaction stages to obtain the same chemical. Another advantage of fermentation processes is that they are able to work with wet feedstocks (many organic materials are present in nature with a large fraction of moisture) and in some cases with mixed feedstocks as organic waste, while chemical processes usually require purified feedstocks. On the other hand, advantages of chemical processes are the faster reaction rates and often the easier separation of the products, due to the absence of water and the consequent higher concentration of the products.

FIGURE 1.3 Process scheme for lactic acid production using chemical synthesis (top) and fermentation processes (bottom).

FIGURE 1.3 Long Description

Comparison of process flow sheets for the production of lactic acid using chemical synthesis and fermentation.

Fermentation products are also very important in medical applications, for example, production of antibiotics and vaccines (examples of these processes are given in Chapter 6).

1.2 Classification of Microorganisms

Microorganisms can be classified in many ways. From the phylogenetic point of view, microorganisms can be classified into one of the three domains: Bacteria, Archaea and Eukarya. Bacteria and Archaea are unicellular microorganisms without a membrane-bound nucleus (prokaryotes). They have a length typically in the range 0.5–5.0 micrometres and can be of various shapes, e.g. spherical or rod-shaped. Bacteria typically reproduce by binary fission. Microorganisms in the Eukarya domain are characterised by having a membrane-bound nucleus and membrane-bound organelles. Eukarya microorganisms are much larger than Bacteria or Archaea. Most of the Eukarya microorganisms, used in fermentation processes, belong to the groups of yeasts and moulds. Yeast reproduces by budding. In budding, a small cell is formed from a parent cell. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud continues to grow until it separates from the parent cell, forming a new cell. Moulds grow as multicellular filaments called hyphae and reproduce by generating a large number of small spores.

Microorganisms are named according to their species, which is a binary combination of the name of the genus followed by a single specific epithet which indicates some properties or characteristics of the microorganisms, e.g. Saccharomyces cerevisiae. Table 1.1 reports some examples of microorganisms used in industrial fermentations.

TABLE 1.1 Examples of Microorganisms and Fermentation Products

Microorganism	Classification	Carbon Source	Product	Industry
Penicillium spp.	Mould	Sucrose, lactose, glucose, and others	Penicillin	Pharmaceutical
Saccharomyces cerevisiae	Yeast	Glucose and others	Ethanol	Energy, chemical
Bacillus subtilis	Bacterium	Proteins and carbohydrates	Proteases	Food, detergents
Candida antarctica	Yeast	Lipids, glucose, lactose	Lipases	Detergents
Lactobacillus delbruekii	Bacterium	Lactose	Lactic acid	Food, plastics
Various	Various	Sugars, molasses	Amino acids	Food, pharmaceutical, chemical

1.3 Structure and Components of Microbial Cells

The main distinction in the structure of microorganisms’ cells is between prokaryotic and eukaryotic cells (Figure 1.4). Prokaryotic cells (Bacteria and Archaea) do not have a nucleus or internal compartmentalised organelles, which are instead present in eukaryotic cells (Eukarya).

FIGURE 1.4 Differences between eukaryotic and prokaryotic cells. (Adapted from N. Gleitchmann, 2020, https:/​/​www.technologynetworks.com/​cell-science/​artic...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright Page
• Dedication Page
• Contents
• Preface
• About the Author
• Chapter 1 Introduction to Fermentation Processes
• Chapter 2 Kinetics and Stoichiometry
• Chapter 3 Mass Balances and Design for Batch, Continuous and Fed-Batch Reactors
• Chapter 4 Oxygen Transfer
• Chapter 5 Heat Generation and Heat Balances
• Chapter 6 Design Summary and Examples of Industrial Fermentation Processes
• Appendix A: Numerical Solutions of Differential Equations in Excel
• Appendix B: Numerical Solutions of Systems of Equations in Excel
• Appendix C: Answers and Solutions
• Bibliography
• Index