TWO STAGE (PHASE) FERMENTATION

PICTURE TAKEN FROM WWW. BIO. IC,AC.UK)

The use of two stage or two phase fermentation usually involves the the use of a two tank system or two fermentors in sequence and physically connected. These two tanks are usually in a series with the process starting in tank A and flowing and continued into tank B.

The two stage or two phase fermentation system is usually applied in a mixed fermentation system involving at least two groups pf microorganisms. The separation into two groups of microorganisms into two tanks are not really exclisive whereby tank A contain a particular species and tank B contain another species. The physical separation of the tanks into two dominant groups of microorganisms are really more physiological than physical. The two tanks still usually contain similar types of microorganisms but the conditions applied differently to each tank resulted in the enrichment of certain groups of microorganisms in each tank

For example, the first tank might be fukky aerobic or have shorter retention time or exposed to rapid sugars. The second tank might be anaeobic or might have a different composion of substrate and even longer retention time

We could view the two stage or two phase fermentation more as a 'plug flow' fermentation system too as the flow is one way! passing through the two tanks

The two stage or two phase fermentation system allows the optimization and finer control of the fermentation process


While admittedly the optimization of a two stage or two phase fermentation system depends on the two reactors providing two separate optimal conditions, the important point is that the flow of the mixed liquor or fermentation broth from one reactor to the other should be a smooth flow. This is made possible by adjusting the hydraulic retention time of the second reactor. Usually the second reactor is larger to accomodate the longer retention time. Of course there are various reactor configurations that can accomodate the flow