BIOCHEMICAL ENGINEERING FUNDAMENTALS

J.E. BAILEY and a very broad range of applications. The funda­ University of Houston mentals comprise those particular topics which Houston, Texas 77004 profoundly influence the behavior of man-made or and natural microbial or enzyme reactors. Such D. F. OLLIS biological examples include the dependence of Princeton University enzyme (and thus microbial) activity on substrate Princeton, New Jersey 08540 concentration, pH, temp, rature, and ionic strength, the existence of a small number of im­ MICROBIAL AND ENZYMATIC activities portant metabolic paths among the multitude of have been an intimate part of man's history. microbial species, the cellular control mechanisms Microbes probably account for greater than ninety for complex internal reaction networks, and percent of all animal mass; their biochemical molecular devices for biological information action contributes significantly to chemical storage and transmittal. Useful topics chosen processes found in agriculture, diseases, digestion, from chemical and engineering sciences are the antibiotic production, food manufacture and energetics of isothermal, coupled reactions; processing, spoilage, sanitation, waste disposal, mixing; transfer of heat and molecular solutes; and marine and soil ecology. Consequently, it is · ideally and imperfectly mixed chemical reactors; remarkable that the study of biochemical processes and filtration. is not an established component of chemical The general character of these fundamentals engineering education. is subsequently stressed by applications to class One factor which seems to contribute to the examples and a wide variety of homework neglect of biochemical engineering courses in problems. These latter exercises include analyses many departments presently is the tendency in of spectrophotometry, desugaring of egg white, current texts and monographs to concentrate on silver recovery from photographic film, exotoxin a particular class of applications such as fer­ production, enzyme electrodes, home winemaking, mentations, enzyme utilization or wastewater chlorination disinfection, detergent biodegrada­ tion, steam reaeration, anaerobic digester heat balances, production of optically pure amino acids, and soil nitrification. When confronted with A second resistance in some of the previous many pages of descriptive text efforts in biochemical engineering education arises on biochemistry and microbiology, . .. from the assumption of significant d priori back­ overcoming student apprehension is perhaps the greatest challenge ground in the biological sciences. Many ChE in teaching the course. students have not studied biochemistry and microbiology, yet a working familiarity with both fields is necessary in biochemical engineering. Consequently, about thirty percent of our course treatment. While each such topic is important, it is devoted to a rapid survey of those elements of appears that only a course aimed at all aspects microbiology and biochemistry essential to under­ of biochemical engineering applications is likely standing biochemical reactors. It is assumed at to provide a sufficiently broad learning base to the outset that the student is unfamiliar with both justify incorporation into most ChE curricula. topics. We have minimized this problem in our course During the presentation of this material, an by stressing underlying common fundamentals attempt is made to relate life sciences funda-

162 CHEMICAL ENGINEERING EDUCATION mentals to their process implications. For interactions and associated applications. example, following discussion of molecular With this parallel approach, the molecular• genetics, viruses, mutation, and genetic manipula­ cellular• population paradigm is maintained tion, we investigate recent applications of micro­ throughout the lectures in fundamentals and ap­ bial genetics in developing especially productive plications, description and analysis. microorganisms for several fermentation pro­ cesses. Searches for explanations of the improved TEACHING THE COURSE characteristics of the mutated microbes quickly COURSE HAS BEEN taught in both a leads to consideration of metabolic control systems THE single quarter and a single semester format. and membrane transport, areas which have also In order to allow coverage of all elements of the been examined earlier in the course. outline during this period, an extensive set of Obviously there is an alternative to our ap­ notes has been developed so that many topics can proach: require the students to take regular be presented in the form of outside reading assign­ courses in the biological sciences before entering ments. Besides their use in the courses at Houston and Princeton, all or portions of these notes have been used in biochemical engineering courses at Many ChE students have not the University of California at Berkeley, Iowa studied biochemistry and microbiology ... State University, the University of Maryland, and Consequently, about thirty percent of our course the University of Virginia. A textbook derived is devoted to a rapid survey of from these notes is now in press. those elements of microbiology We have noted that engineering students may essential to understanding biochemical reactors. become a bit disoriented when confronted with many pages of descriptive text on biochemistry and microbiology, each introducing one or more new terms in an expanding cascade of new the biochemical engineering course. In what are vocabulary. Overcoming this student apprehen­ already crowded curricula, imposition of such pre­ sion is perhaps the greatest challenge in teaching requisites greatly limits the students' opportunity the course, and we have used a variety of to study biochemical engineering, and only those strategies in concert to ameliorate the problem. students actively engaged in research in the area First, divertissements from the onslaught of are likely to elect such a sequence. On the other new biological concepts and terminology are pro­ hand, by presenting biological fundamentals vided in both local and longer scales in the lec­ integrated with engineering analyses, design tures and notes. The best example of the latter principles, and applications in a single course, the case is the location of topics III and IV in the subject is easily accessible to any graduate course outline. In addition to the reasons given student, and indeed to any interested upper level earlier, the presence of these topics in the midst undergraduate. Following this course, those of biological basics provides the engineering students concentrating in biochemical engineering student a respite in the relatively familiar terri­ can and should broaden their base in the life tory of kinetics, transport-reaction interaction, sciences through additional, more advanced and commercial processes. Moreover, these topics courses taught in biochemistry, microbiology, bio­ show the student that the biochemistry from physics, and other related departments. topic II is indeed necessary and useful, and thus The course is summarized in Table 1. The motivation is instilled for digging into energetics, material progresses from atomic to macroscopic metabolism, and genetics in topics V and VI. dimensions; i.e., from molecular through cellular Also, practical implications of basic concepts to microbial population dynamics. Applications are briefly indicated during the fundamentals and the associated engineering design and analysis discussions. One example of this approach has principles are presented as soon as the necessary already been mentioned; another is the discussion background life science material has been covered. of the influence of iron ion on •the citric acid Thus, enzyme isolation and applications are con­ fermentationjn conjunction with the presentation sidered before discussion of cell metabolism, and · of the tricarboxylic acid cycle. At this point pre­ pure culture fermentations are examined before vious consideration of enzyme cofactor effects can delving into the complexities of multiple species also be recalled and put into a commercial process

FALL 1976 163 A. The Enzyme-Substrate Complex and Enzyme Action Jay Bailey, Professor of Chemical Engineering at the University B. Simple Enzyme Kinetics with One and Two of Houston, concentrates his teaching and research activities in bio­ Substrates (Michaelis-Menten kinetics; chemical engineering, chemical reactor analysis, and process dynamics. two-substrate reactions and cofactor activa­ A Ph.D. graduate of Rice University, Dr. Bailey received a Camille tion) and Henry Dreyfus Teacher-Scholar Grant in 1974 . He plays guitar C. Determination of Elementary Step Rate and 5-string banjo, now struggles with piano, and also enjoys Constants (pre-steady-state, relaxation photography. kinetics) D. Other Patterns of Substrate Concentration David F. Ollis, Associate Professor of Chemical Engineering Dependence (activation; inhibition; multiple at the Princeton University, received his B.Sc. at Caltech., M.E. at substrates) Northwestern and Ph.D ('69) at Stanford. He was a process research E. Modulation and Regulation of Enzymic engineer at Texaco. He was a post-doctoral fellow at CNRS, Nancy, Activity France in 1969 and on sabbatical at CNRS in Lyons, France in 1975. F. Other Influences on Enzyme Activity (pH, His research interest include heterogenious and homogeneous catalysis temperature, mechanical forces) and biochemical engineering. G. Enzyme Reactions in Heterogeneous Sys­ tems (insoluble substrates; immobilized enzymes) IV. ISOLATION AND UTILIZATION OF ENZYMES perspective. Worked examples interspersed in the A. Production of Crude Enzyme Extracts course serve a similar function of breaking up the B. Enzyme Purification (chromatography; new biological material. Finally, homework dialysis; solid phase syntheses) exercises on all topics have been prepared, and C. Enzyme Immobilization these are regularly assigned (a collection of D. Application of Hydrolytic Enzymes (esterases, carbohydrases, proteases) problems is available from the authors upon re­ E. ·Other Enzyme Applications (medical, new quest). Combined with frequent quizzes, these pro­ technology) vide the engineering student with regular oppor­ F. Immobilized Enzyme Technology (industrial tunities to attempt quantitative analyses. Besides processes; medical and analytical applica­ their obvious important pedagogical role, these tions; utilization and regeneration of co­ factors) exercises also alleviate the "culture shock" ( !) of G. The Scale of Enzyme Technology facing many new biological terms and con­ cepts. • V. METABOLIC PATHWAYS AND ENERGETICS OF THE CELL A. The Concept of Energy Coupling: ATP and NAD B. Anaerobic Metabolism: Fermentation (gly­ TABLE 1: COURSE OUTLINE colysis; other pathways) C. Respiration and Aerobic Metabolism (TCA Biochemical Engineering Fundamentals cycle; respiratory chain; partial oxidation; I. A LITTLE MICROBIOLOGY regulation) A. Biophysics and the Cell Doctrine D. Photosynthesis: Tapping the Ultimate Source B. The Structure of Cells (procaryotic cells; (Calvin Cycle; chloroplasts) eucaryotic cells, cell fractionation) E. Biosynthesis (ATP utilization; small mole­ (Example: Analysis of particle motion in cules; macromolecules) a centrifuge) F . Transport Across Cell Membranes (passive, C. Important Classes of Microbes· (bacteria; facilitated, active transport) (Example: yeasts; molds, algae and protozoa) Transport of nitric acid through a liquid membrane) II. CHEMICALS OF LIFE A. Lipids (fatty acids; fat-soluble vitamins; VI. CELLULAR GENETICS AND CONTROL steroids) Example: Modification of bio­ SYSTEMS membrane permeability A. Molecular Genetics (DNA translation; B. Sugars and Polysaccharides replication; mutation; induction; repres­ C. From Nucleotides to RNA and DNA (co­ sion) enzymes; RNA, DNA) B. Growth and Reproduction of a Single Cell D. Amino Acids into Proteins (polypeptides; (synchonous culture; E. coli cell cycle; protein structure; biological regulation) eucaryotic cell cycle) E. The Hierarchy of Cellular Organization C. Alteration of Cellular DNA (viruses, phage; transformation, conjugation; composite III. THE KINETICS OF ENZYME-CATALYZED DNA) REACTIONS D. Commercial Applications of Microbial

164 CHEMICAL ENGINEERING EDUCATION Genetics and Mutant Populations (Implica­ modeling and optimization for production tions for medium formulation; auxotrophic of a-Galactosidase by a Monascus sp. mutants) mold) VII. KINETICS OF SUBSTRATE UTILIZATION, X. BIOLOGICAL REACTORS, SUBSTRATES, AND PRODUCT YIELD, AND BIOMASS PRODUC PRODUCTS I: SINGLE SPECIES APPLICA­ TION IN CELL CULTURES TIONS A. Growth Cycle Phases for Batch Cultivation A. Fermentation Technology (medium formula­ (lag phase; exponential growth, the Monod tion; aseptic practice; cell harvesting, equation; stationary and death phase) product recovery) B. Mathematical Modeling of Batch Growth (re­ B. Product Manufacture by Fermentation (brew­ action networks; structured, unstructured ing and wine making; oxidative transfor­ models; mold growth) mations; organic, amino acids; complex C. Product Synthesis Kinetics (fermentation molecules: gibberelins, vitamins, anti­ classifications; Shs segregated model) biotics; undesirable products) (Example: D. Overall Kinetics in Cases of Reaction-Mass Reaction rates in microbial films; tempera­ Transport lnteration (lumped, distributed ture programming for optimal pencillin models for cells, floes, mold pellets) production) E. Thermal Death Kinetics of Cells and Spores C. Reactors for Biomass Production (food; food processing; agricultural applications; im­ VIII. TRANSPORT PHENOMENA IN MICROBIAL munology, tissue culture, and "Vaccine" SYSTEMS production) (Examples: A batch growth A. Gas-Liquid Mass Transfer in Microbial Sys­ model for liquid hydrocarbon fermenta­ tems (basic concepts; metabolic oxygen tions; production of a low-intermediate utilization rates) (Example: Effectiveness molecular weight product; cell growth and factor of a microbial monolayer) virus propagation kinetics in tissue culture) B. Determination of Oxygen Transfer Rates (gas-liquid reactions; dissolved oxygen XI. ANALYSIS OF MULTIPLE, INTERACTING measurements) (Examples: Warburg MICROBIAL POPULATIONS respirometer; electrochemical determina­ A. Neutralism, Mutalism, Commensalism, and tion of k za) Ammensalism C. Mass Transfer for Freely Rising or Falling B. Mathematical Preliminaries (Example: Two­ Bodies Species dynamics near a steady state) D. Mass Transfer Across Free Surfaces C. Competition: Survival of the Fittest E. Forced Convective Mass Transfer (key D. Predation and Parasitism (Lotka-Volterra dimensionless groups; mass transfer co­ model; other one predator-one prey models) efficient correlations) (Example: Model discrimination and de­ F. Surface Area Correlations for Mechanically velopment via stability analysis) Agitated Vessels E. Effects of the Number of Species and their G. Other Factors Affective kza (diffusivities; Web of Interactions (trophic levels, food ionic strength; surface active agents) chains, food webs; mass action models; H. Non-Newtonian Fluids (models; suspensions; qualitative stability; randomly constructed power consumption mass transfer) food webs) (Examples: An application of I. Scaling of Mass Transfer Equipment the mass action theory; qualitative stability J. Particulate Mass Transfer: Filtration (single of a simple food web) fiber efficiencies; mass transfer coefficients) F. Spatial Patterns K. Heat Transfer (microbial heat generation; heat transfer correlations) XII. BIOLOGICAL REACTORS, SUBSTRATES, AND PRODUCTS II: MIXED MICROBIAL POPULA­ IX. BIOLOGICAL REACTOR DESIGN AND TIONS IN APPLICATIONS AND NATURAL ANALYSIS SYSTEMS A. The Ideal Continuous Flow Stirred Tank Re­ A. Uses of Well-Defined Mixed Populations actor (Monod's chemostat; incomplete (Example: Enhanced growth of methane­ m1xmg, films, recycle effects; enzyme utilizing Pseudomonas sp. due to mutalistic catalyzed reactions) (Example: Agitated interactions in a chemostat CSTR design for a liquid hydrocarbon fer­ B. Spoilage and Product Manufacture by Spon­ mentation) taneous Mixed Cultures B. Residence Time Distributions (measure­ C. Microbial Participation in the Natural Cycles ments; applications) of Matter and Energy C. Tubular and Tower Reactors (ideal plug flow D. Biological Wastewater Treatment (waste­ tubular reactor; tower reactors; tanks-in­ water characteristics; activated sludge series and dispersion models) process; trickling biological filters; an­ D. Sterilization Reactors (bath; continuous) aerobic digestion) (Example: Simulation E. Relationships Between Batch and Continuous studies· of control strategies for anaerobic Biological Reactors (Example: Reactor digesters)

FALL 1976 165