the invention comprises the recognition that the concentration of carbon dioxide in the gas mixture bubbling out of a fermentation broth can be increased to very high levels , indeed to such levels that further processing is often not necessary to produce commercial grade carbon dioxide , if the concentration of the oxygen in the oxidant fluid provided to the fermentation broth is at a defined high level and if the flowrate of the oxidant fluid provided to the fermentation broth is limited so that the total amount of oxygen provided to the fermentation broth is not more than a defined upper limit . the invention will be described in greater detail with reference to the drawings . referring now to fig1 fermentation vessel 1 contains fermentation broth 20 . typically fermentation broth 20 comprises an aqueous mixture of carbohydrates such as sugars and microorganisms such as yeast for fermentation to produce ethanol . however this invention is not limited to ethanol fermentation . any fermentation or microbial process wherein oxygen is used to sustain the growth of a microorganism and / or microbial or biochemical activity and wherein carbon dioxide is produced as a byproduct may be carried out in the practice of this invention . oxidant fluid 21 is provided to the fermentation broth through piping 5 . the oxidant fluid has an oxygen concentration of at least 40 mole percent , preferably at least 80 mole percent , most preferably at least 90 mole percent . the oxidant fluid may , if desired , be commercially pure oxygen having an oxygen concentration of 99 . 5 mole percent or more . in the embodiment illustrated in fig1 the oxidant fluid is provided to the fermentation broth while the fermentation broth is housed within vessel 1 . the oxidant fluid passes from piping 5 through one or more fine bubble diffusers 4 and , as small bubbles , out into fermentation broth 20 . preferably substantially all of the oxygen provided to the fermentation broth with the oxidant fluid is dissolved in the fermentation broth . oxygen from the oxidant fluid is used by the microorganisms or other oxygen consuming entity within broth 20 to carry out microbial growth and fermentation of various carbonaceous materials , e . g . carbohydrates , within broth 20 to produce carbon dioxide and , for example , ethanol . in the embodiment illustrated in fig1 the oxidant fluid distribution is facilitated by stirring or mixing broth 20 by means of agitator 3 driven by motor 2 . the oxidant fluid is provided to the fermentation broth at a flowrate such that the total amount of oxygen provided to the fermentation broth is not more than 5 weight percent of the total amount of carbon dioxide produced and bubbled out of the fermentation broth . if the amount of oxygen provided into the fermentation broth were to exceed this defined upper limit , the viability and the optimal population of the culture in the fermentation broth would be compromised by depleting the carbonaceous substrate for yeast growth thus reducing the carbon dioxide yield in any subsequent fermentation stages which have no oxygen injection . typically the oxygen provided to the fermentation broth is within the range of 0 . 05 to 5 weight percent of the total carbon dioxide produced , preferably within the range of from 0 . 1 to 4 weight percent of the total carbon dioxide produced , more preferably within the range of from 0 . 2 to 3 weight percent of the total carbon dioxide produced , and most preferably within the range of from 0 . 4 to 2 weight percent of the total carbon dioxide produced in all fermentation stages . typically the flowrate of the oxygen into the fermentation broth for an ethanol fermentation process using yeast is within the range of from 0 . 0003 to 0 . 0015 vvm where vvm means the volume of gas per volume of fermentation fluid or fermentation broth in the vessel per minute . the carbon dioxide and other gases within broth 20 bubble out of broth 20 and form a gas mixture 22 having a carbon dioxide concentration of at least 97 . 5 mole percent . depending upon the process conditions , the carbon dioxide concentration of gas mixture 22 could exceed 98 . 5 mole percent and even exceed 99 . 5 mole percent . the oxygen concentration of the gas mixture 22 is generally not more than 1 . 0 mole percent , and typically is less than 0 . 5 mole percent . this very low oxygen concentration not only speaks to the efficiency of the process of this invention but also reduces or eliminates the fire hazards potential which is present with many conventional carbon dioxide production processes wherein volatile flammable organic compounds are present . gas mixture 22 is withdrawn from vessel 1 in piping 6 , mixed with gas produced in later fermentation stages , and this total carbon dioxide produced is recovered as product carbon dioxide which may be used commercially as is or may undergo one or more further purification steps such as low temperature distillation or solvent absorption . the fermentation of the carbonaceous materials is exothermic . the exothermic nature of fermentation can lead to such a heat buildup within the fermentation broth that the microbial growth rate and fermentation rate within the fermentation broth may decline . in order to avoid this decline in production , a fermentation broth cooling recirculation loop is employed . referring back now to fig1 fermentation broth is withdrawn from vessel 1 in stream 23 , passed through valve 24 and as stream 25 to recirculation pump 7 . resulting pumped stream 26 is passed through heat exchanger 8 wherein it is cooled by indirect heat exchange with cooling fluid 30 such as water . resulting cooled fermentation broth 9 is returned back into fermentation vessel 1 through main recirculation stream 27 and / or bypass recirculation stream 28 and bypass valve 29 . [ 0024 ] fig2 illustrates another embodiment of the invention wherein the oxidant fluid is provided to the fermentation broth as it is passing through the recirculation loop . the numerals in fig2 are the same as those for fig1 for the common elements and these common elements will not be described again in detail . referring now to fig2 cooled recirculation stream 27 is passed into receptacle 31 which houses fine bubble generation device 10 . device 10 could , for example , be a sintered metal fine bubble sparger / diffuser , a ceramic fine bubble diffuser , a membrane type bubble diffuser , a sonic - nozzle , a gas / liquid mixing nozzle , a venturi - type gas liquid mixing nozzle , an orifice plate or a gas / liquid flow restriction device . oxidant fluid is passed in stream 32 into device 10 and is bubbled out into the fermentation broth within receptacle 31 . the resulting oxygen - containing fermentation broth is withdrawn from receptacle 31 in stream 33 . if desired , some or all of stream 33 may pass through gas / liquid contact loop 11 which serves to increase gas / liquid contact time and thus enhance the dissolution of the oxidant fluid into the fermentation broth . the remainder of stream 33 , if any , is passed through valve 34 and then is mixed with the fluid , if any , from loop 11 to form stream 35 which is provided to diffuser 12 and out from diffuser 12 into the fermentation broth housed in vessel 1 where the bulk of the microbial growth and fermentation take place in the same manner as was previously described . diffuser 12 can be any effective gas / liquid dispersing nozzle such as , for example , a liquid circulation eductor . the high concentration of oxygen within the oxidant fluid in the practice of this invention serves to reduce the amount of inerts and residual oxygen passed into the fermentation vessel which will ultimately find their way into the carbon dioxide gas mixture product , thus serving to attain and maintain the carbon dioxide concentration at a beneficially high level . in addition , this high oxygen concentration serves to reduce the energy required to operate the fermentation plant , and , in addition , will reduce odor emissions from certain types of fermentation plants . the following example is provided for illustrative purposes and is not intended to be limiting . using an arrangement similar to that illustrated in fig1 oxidant fluid , having an oxygen concentration of 99 . 5 mole percent was provided into the fermentation broth at a flowrate of typically from 0 . 0003 to 0 . 0015 vvm . the yeast species in the fermentation broth was saccharomyces cerevisiae and the carbonaceous substrate within the fermentation broth was hydrolyzed saccharides from starchy material at a concentration of 17 to 20 weight percent . the fermentation temperature was 35 ° c . and the fermentation time was from 40 to 60 hours . the gas mixture bubbling out from the fermentation had a carbon dioxide concentration of 99 . 5 mole percent and passed out of the fermentation broth at a flowrate of from 100 to 160 m 3 / minute where m 3 is measured at ntp conditions of 70 ° f . and 14 . 7 psia . the amount of oxygen provided and dissolved into the fermentation broth was from about 0 . 5 to 1 weight percent of the total amount of carbon dioxide produced in and bubbled out of the fermentation broth . although the invention has been described in detail with reference to certain preferred embodiments , those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims .