Feeding strategies

In many cases, problems cannot be overcome by biological means. This is especially true for those related to inhibition by substrate or product. There may, however, be technical solutions to these problems. Nowadays, complicated feed strategies with different substrates can be achieved through the use of flow injection analysis, on-line sensors, mass flow meters and sophisticated computer control. Such control coupled to a fed-batch mode of operation (Figure 2.5) can often eleviate problems caused by substrate inhibition. For some processes, continuous product removal can avoid the problems associated with product inhibition the various options include ... 

Models may be used in training and education. Many important aspects of reactor operation can be simulated by the use of simple models. These include process start-up and shut down, feeding strategies, measurement dynamics, heat effects and control. Such effects are easily demonstrated by computer, as shown in the accompanying simulation examples, but are often difficult and expensive to demonstrate in practice. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

Depending on the type of substrate combination to be used, different cultivation processes and feeding strategies are required. 

Nielsen J H, Lund-Nielsen T and Skibsted L (2004), Higher antioxidant content in organic milk than in conventional milk due to feeding strategy , Newsletter from Danish Research Centre for Organic Farming, September, No. 3. 

A semi-continuous reactor is used to carry out the following parallel reaction, where P is valuable product and Q is unwanted waste. The problem is to optimise the feed strategy to the reactor such that the maximum favourable reaction selectivity is obtained, for similar systems but of differing kinetic rate characteristics. 

For optimal performance, the feeding strategy for the chromatographic reactor should be carefully designed. In addition, the following criteria should be fulfilled [132] ... 

Based on these devices, different biomass estimation experiments were performed based on the culture fluorescence monitoring and feeding strategy studies were developed as well as bioreactor characterizations via mixing time experiments. During the next years smaller fluorescence probes were developed which could be interfaced with bioreactors via standard electrode ports. These open end detector systems measured the fluorescence fight in the backward di-... 

Suspension systems can be operated in different modes batch, fed-batch, chemostat, and perfusion (Fig. 1). These operation modes differ basically in the way nutrient supply and metabolite removal are accomplished, which in turn determines cell concentration, product titer and volumetric productivity that can be achieved [8]. The intrinsic limitation of batch processes, where cells are exposed to a constantly changing environment, limits full expression of growth and metabolic potentials. This aspect is partially overcome in fed-batch cultures, where a special feeding strategy prolonges the culture and allows an increase in cell concentration to be achieved. In perfusion and chemostat processes nutrients are continuously fed to the bioreactor, while the same amount of spent medium is withdrawn. However, in perfusion cultures the cells are retained within the bioreactor, as opposed to continuous-flow culture (chemostat), which washes cells out with the withdrawn medium [9]. 

Scalability of the systems is a must and the use of low MOI strategies is obligatory if the goal is the industrial application. Complex feeding strategies must be avoided since they impose high risks, and costs, to the overall process. 

Box 7.2 The flat rate feeding strategy as applied in dairy production systems in Denmark... 

Roughage quality is a very important factor when using the flat rate feeding strategy. 

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