Process Measurement and Control
In a fermentation process, aeration, pH, feed rate, dissolved oxygen, temperature, and foaming level must be measured and controlled. Parameters automatically measured during fermentation generally include fermenter temperature, volume and temperature of cooling water, volume of air supplied into the fermenter, concentrations of O2 and CO2 in the exhaust gas, pressure within the tank, feed volume, agitation rate, agitation energy, pH, dissolved oxygen, and degree of foaming. Sampled broth is analyzed mainly for optical density, sugar concentration, amino acids, and organic acids. Fermentation temperature, pH, aeration, feed volume, and foaming level are automatically controlled. In continuous fermentation, equipment capable of controlling the volume of both discharged and the liquid surface is provided.
Amino acids are typically recovered and purified either by chromatographic methods or by concentration-direct crystallization methods. Although most amino acids may be isolated and purified using an ion exchange resin, this tends to increase the cost of waste-liquor treatment because of the large volume of diluted waste liquor. On the other hand, with the concentration-direct crystallization method, the discharged mother liquors have a high biological oxygen demand and contain a large amount of plant-growth-promoting factors and may thus be used as fertilizer. This makes the cost of waste-liquor treatment less burdensome; however, this method cannot be applied to all amino acids because the chemical composition of fermentation broth strongly affects the purification steps.
In recent years, treatment of fermentation waste liquor has become more and more important in the planning process. When chromatographic purification is employed, the low concentration and large volume of waste liquor is burdensome, and the cost of treatment by the active sludge method is high, exerting much influence on the cost of the final product. In this respect, the direct crystallization method is advantageous, though it may not be applicable to many products due to characteristics peculiar to those products. It is necessary to construct a process that takes waste treatment into consideration as soon as the raw materials have been selected.
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