Study On Feed-batch Technics For Acetic Acid Fermentation

As a digestive seasoning, vinegar has some diet-cure functions such as antibacterial, sterilization, increasing appetite and anti-tire. Moreover, acetic acid is an important organic acid. Nowadays, there are numerous vinegar companies with behindhand producing processes in China. The processes are difficult to be controlled steadily. The peroxidation of acetic acid is apt to take place in later phase of the fermentation, and a great deal of heat is emitted, which decrease the product quality and economy benefits.In order to prevent the peroxidation, the process was controlled by the self-designed fermentation distributed control system, and the alcohol level was automatically measured online by an auto-instrument. The control system was made up of touch-screen computer and intelligent controller, required to measure the concentration of alcohol and dissolved oxygen and to control temperature, pH, agitating speed and liquid level on line. With serial communication, local instrument was connected by sensors and transducers.The acetic acid fed-batch fermentation was performed in the 15L self- inspiriting fermenter. In this fermenter, the gas is uniformly distributed, the air-transfer to the liquid is fast and the fermentation period is short. In the 35th hour, the acetic acid concentration was reached to 27.2g/L, and the average acetic acid producing rate was 1.35 g/L·h, while the alcohol-acid transform ratio was 81.38%. Afterwards, the acetic acid concentration began to decrease. Peroxidation appeared so as to oxidize acetic acid into CO2 and H2O.Ten experiments of two factors at five different levels were designed based on the principle of central composite design. The total concentration of fermentation broth(X1) and the discharging volume (X2) were considered as independent variable, while the average acetic acid producing rate(Y1)and the alcohol-acid transform ratio (Y2)were considered as responded value. Acetic acid fed-batch fermentation was carried through and alcohol concentration was monitored continuously in the above mentioned distributed control system. The optimal experiment conditions were obtained with response surface analysis, the discharging volume was 27% and total concentration of fermentation broth was 6.2. The prediction of average acetic acid producing rate was 2.32 g/L·h, and the prediction of alcohol-acid transform ratio was...