Continuous process for ethanol production by bacterial fermentation

DETAILED DESCRIPTION The accompanying FIGURE will provide a background for the following discussion in which the method and apparatus for carrying out this invention are described in detail.
Referring to the FIGURE, nutrient medium 1 in reservoir 2 is fed by a pump 3 to a fermenter 4 containing a fermentation medium 5.
The medium is maintained at a constant volume in the fermenter by means of an overflow weir 6 that empties into a container 7.
Carbon dioxide formed during the fermentation is vented at 8.
The fermenter 4 is provided with an agitator 9 for mixing the fermenter contents.
A pH probe 10 is immersed in the fermentation medium 5 and is connected to a pH controller 11 for regulating the amount of pH regulating agent 12 in reservoir 13 added by a pump 14 to the fermentation medium 5.
The temperature of the fermentation medium is monitored by temperature probe 15.
The fermentation medium is heated or cooled as required through a coil 16 and regulated by the temperature controller 17.
The fermentation medium is formulated so that all but a single essential nutrient are available in excess of the amount required to synthesize a desired cell concentration.
The single growth-limiting nutrient controls the size of the steady-state cell population.
Conventional expressions are used throughout this description when the kinetics of the fermentation process are discussed.
The abbreviations identified in the following list have been used in order to facilitate the discussion.
Units of measure have been included where appropriate.
S.
sub.
r =Substrate concentration in the feed stream to the fermenter; g/liter, i.
e.
g/L.
S.
sub.
o =Substrate concentration in the effluent from the fermenter; g/L.
V=Volume of fermentation medium in the fermenter; L.
X=Concentration of biomass in the fermentation medium (dry basis); g/L.
[P]=Concentration of ethanol in the fermentation medium; g/L.
u=Specific growth rate (mass); hr.
sup.
-1.
D=Dilution rate; hr.
sup.
-1.
N*=Amount of a given nutrient; g.
q.
sub.
s =Specific rate of substrate uptake; g substrate/g biomass-hr