Mass transfer studies in batch fermentation: Mixing characteristics

Studies have been undertaken to investigate the mass transfer parameters due to mixing effects during fermentation using Candida utilis in a 2·0-dm³ batch fermentor. Mechanical agitation and mixing via air flow have been studied and each varied independently of the other. Oxygen transfer rates were found to increase up to a limiting value when both air flow rate and agitation were increased. Aerobic fermentation is characterised by the specific oxygen rate which increased with agitation and air flow rate. It was found, however, that agitation and aeration had no effect on the carbon dioxide production rate but the mass transfer coefficient increased markedly with increasing agitation. Values for all the mass transfer terms were determined. The mass transfer coefficient, k_La, has been correlated with the impeller agitation speed, N, as follows: k_La=1·079×10^-3N^1·96.