Bioprocess operational steps

Expanded-bed adsorption (ERA) has gained popularity in bioprocessing since its commercial introduction in the 1990s because of its ability to handle a crude feedstock that contains cells or other particulates. ERA ehminates the need for a dedicated clarification step by combining sohd-hquid separation and adsorption into a single-unit operation [Hjorth et al., in Subramanian (ed.), op. cit., vol. 1, pp. 199-226 Mattiasson et al., in Ahuja (ed.), op. cit., pp. 417-451]. A... 

Another advantage to the incorporation of bioprocessing aids into the Step I procedure is that the clarified extract can be used directly for subsequent purification steps even without the use of a Step II system to dewater or concentrate the process stream. These factors are especidly relevant when HPLC systems arc used in Step IB for the chromatographic procedures. Nucleic acids, pigmented organics and especially cellular debris can very quickly foul an HPLC column. This is an even more important consideration for large scale protein purification schemes where the volumes of material and costs of the operation are greatly increased (3). 

The following steps are used to operate a bioprocess plant. 

When planning an industrial-scale bioprocess, the main requirement is to scale up each of the process steps. As the principles of the unit operations used in these downstream processes have been outlined in previous chapters, at this point we discuss only examples of practical applications and scaling-up methods of two unit operations that are frequently used in downstream processes (i) cell separation by filtration and microfiltration and (ii) chromatography for fine purification of the target products. 

In the downstream processing of bioprocesses, fixed-bed adsorbers are used extensively both for the recovery of a target and for the removal of contaminants. Moreover, their performance can be estimated from the breakthrough curve, as stated in Chapter 11. The break time tg is given by Equation 11.13, and the extent of the adsorption capacity of the fixed bed utilized at the break point and loss of adsorbate can be calculated from the break time and the adsorption equilibrium. Affinity chromatography, as weii as some ion-exchange chromatography, are operated as specific adsorption and desorption steps, and the overall performance is affected by the column capacity available at the break point and the total operation time. 

Bioprocessing addresses the phases, developments, and process unit operations required to take a technology from the conceptual or bench-scale stages of development to the pilot, demonstration, and commercial development stages. These critical steps in technology development o ften stand between the invention and the ultimate goal of commercial success. 

The integration of two unit operations lies at the heart of process engineering. More often in bioprocesses it is the integration of product formation with the following recovery steps that is critical.5 In the specific case of biocatalytic processes the product recovery is also critical, but in this chapter the focus will be on the integration of the surrounding chemical steps with the biocatalysis. 

Figure 1.4. Flow chart sheet of the strategy of bioprocess kinetic analysis for different process situations stationary/instationary, homogeneous/heterogeneous, differential/ integral, and true dynamic/balanced (frozen) reactor operation, rds, rate-determining step qss, quasi-steady-state, (From Moser, A. 1983.)...

Transient reactor operation plays an increasingly important role in bioprocessing and has to some extent already been considered (classification, see Fig. 3.31 fed-batch culture, see Fig. 3.37 situation, see Fig. 4.4 guidelines to solution, see Sect. 4.2 and Fig. 4.5 structured cell model concept, see Fig. 4.7 application, see Chap. 6). Both balanced and frozen conditions have also been considered in Fig. 3.34. A biosystem is in balanced condition when the mechanism is fully adapted, as in a quasi-steady-state (if x ). All different equations can be reduced to algebraic equations. A biosystem is in frozen condition of the initial state (if x x ) and the mechanism may be neglected due to the fact that the slowest step is rate determining ( rds concept ). By this procedure, equations are reduced to parameters so that the number of equations is reduced (e.g., the case of dropwise addition of substrate). This is the case of steady state CSTR. 

Perhaps the first decision to be made in process development is the difficult decision of whether the enzymes to be used should be used in an integrated format. Such a question does not arise with conventional single biocatalytic steps but is highly important in multienzyme processes. One of the key criteria here is whether the enzymes can be operated together without compromise to any of the individual enzyme s activity or stability. An interaction matrix (see Section 10.6) can be used to assist such decision making. In cases where the cost of one or more of the enzyme(s) is not critical, it will be possible to combine in a one-pot operation. In other cases, where the cost of an individual enzyme becomes critical, then it may be necessary to separate the catalysts, such that each can operate under optimal conditions. Likewise, selection of the biocatalyst format (immobilized enzyme, whole cell, cell-free extract, soluble enzyme, or combinations thereof) in combination with the basic reactor type (packed bed, stirred tank, or combinations thereof) and biocatalyst recovery (mesh, microfiltration, ultrafiltration, or combinations thereof) will determine the structure of the process flowsheet and therefore is an early consideration in the development of any bioprocess. The criterion for selection of the final type of biocatalyst and reactor combination is primarily economic and may best be evaluated by the four metrics in common use to assess the economic feasibility of biocatalytic processes [29] ... 

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