Bioseparation Engineering,Chapter 1 Introduction,1.1 Downstream processing in biotechnology,The producing process of a biotechnological product is termed bioprocess, that can be divided into two processes as follows Upstream processing：strain development and bioreaction （enzyme catalyze reaction, microbial fermentation, plant/mammalian cell culture, etc） Downstream processing：the isolation and purification of biotechnological products The complexity of downstream processing is determined by the required purity of the product, in turn determined by its application.,The downstream processing scheme normally can be divided into the following stages,Broth,Solid-liquid separation,Extracellular product,Intracellular product,Cell disruption,Removal of cell debris,Primary isolation,purification,formulation,Final product,1.2 Demands on the downstream processing,Strictly monitor the DSP steps for keeping the activity of the product; Rapidly remove those impurities can affecting the stability of the final product; Generally it is necessary to apply special efficient methods to the purification of the product; Since many products are applied to food, pharmaceutical, and cosmetics, those substances harmful to mankind health must be removed; Since the product concentration is low in the culture broth, it is necessary to concentrate the broth for removing large amounts of water. Because those of unit operations are costly, the cost of DSP is increased observably.,1.3 Separation mechanism and unit operation,According to different separation principles the unit operations can be sorted into two groups： Mechanical separation Object：unhomogeneous phase system Mechanism：separation based on the difference of substances size and density Unit operation：filtration, settling, centrifugation, etc. Mass transfer separation Object：homogeneous phase system Transport/velocity separation Mechanism：separation based on the migration velocity difference of solutes drove by bearing a applied force Unit operation：ultrafiltration, reverse osmosis, electrophoresis, etc. Diffusion/equilibrium separation Mechanism：separation based on the difference of distribution of substances between the two phases Unit operation：extraction, crystallization, adsorption, ion exchange, etc.,1.4 Estimation for separation efficiency,There are three criteria on assessing the efficiency of a downstream processing, i.e. concentration degree, isolation-purification degree, and recovery rate Concentration degree Generally can be represented as concentrated factor,Isolation-purification degree Can be represented by separation factor/coefficient,Recovery rate,Chapter 2 Solid-liquid separation and cell disruption,2.1 Cell separation,2.1.1 Settling,Stokes settling velocity of global particle,Where d is particle diameter, s and L are the density of particle and liquid, separately, is resistance coefficient, Re is Reynolds number, and L is the viscosity of liquid.,The volume of the cells is so small that its settling velocity is very slow. For accelerating settling process agglomeration of individual cells into large flocs is done by the addition of flocculating agents such as polycations, or inorganic salts.,2.1.2 Centrifugation,Centrifugation velocity,Where r is centrifugal radius, is rotary angular speed, N is revolution of centrifuge, and S is sedimentation coefficient.,Centrifugation Differential centrifugation It is an unit operation commonly used in the biochemical industry. According to the characteristics of the broth, the aim of isolation, and the extent of separation requested, different components can be separated from the broth separately by selecting proper operational parameters in practice. Zonal centrifugation Rate-zonal density gradient sedimentation Isopycnic density gradient sedimentation Besides sucrose, CsCl and NaBr can be used for achieving the density gradient, and applied to the separation of nucleic acid and lipoprotein, respectively.,Centrifuges The tubular bowl rotor centrifuge is commonly applied on a laboratory scale, and the types of tubular bowl and disc stack are commonly used on an industrial scale.,The processing capacity of the tubular bowl centrifuge is described by,Where L is the length of the tube, r2 is the inside radius of the tube, and is usually called the area of centrifugal sedimentation, a function of the structure of the centrifuge and the operating conditions.,2.1.3 Filtration,Definition：a technology, apply filter media to retain the particle while allowing the passage of the liquid through the filter, is used to achieve solid-liquid separation.,The flow through the filter,Where Q is the volume of the filtrate, A is the area of the filter, p is the pressure difference, L is the viscosity of the filtrate, Rm and Rc are the resistance of the filter medium and the cake, is the average specific resistance of the cake, and W is the weight of the d