Variations and modelling of oxygen demand in amino acid production

The L-lysine fermentation by Brevibacteria lactofermentum was investigated in this study. The objective was to improve the process performance by manipulating cellular environment conditions. The main factor under consideration was dissolved oxygen concentration (DOC) in the broth. To implement effective process control, a process model was developed based on combined kinetic study and material balances. The process dynamics at the dissolved oxygen tensions (DOTs) of 2%, 5%, 10%, and 20% was analysed. The results showed that inhibition of high oxygen level could occur during the very early growth phase and depressive effect of low oxygen availability was confined to the rest of the process, suggesting that different fermentation stages required different DOTs. Batch experiments were conducted with 3% DOT for the first 24 h, 10% for 24-48 h, and 5% for the rest of the fermentation, and the results were compared with those under 20% DOT throughout. The final L-lysine concentration reached 51.4 g/l compared with 45 g/l; the overall yield increased from 0.300g/g to 0.343g/g; and the productivity was improved from 0.616 g/l/h to 0.633 g/l/h. Also importantly, the low DOT settings required much less energy for agitation and aeration