Abstract: A method for producing carbon dioxide at a flow rate is disclosed. The method comprises several steps including the provision of an oxidant fluid to a fermentation broth, use of oxygen from the oxidant fluid to promote fermentation and microbial growth in a fermenter while producing carbon dioxide within the broth, passing a fermentation broth stream out from the fermenter, and then through a heat exchanger, and then back into the fermenter via a recirculation loop, bubbling carbon dioxide out therefrom the broth creating a gas mixture containing a carbon dioxide concentration of 97.5 mole percent and recovering the gas mixture as product carbon dioxide. The oxidant fluid is provided to the fermentation broth at a flow rate such that the amount of oxygen provided to the fermentation broth is not more than 5 weight percent of the total amount of carbon dioxide being produced. The oxidant fluid contains an oxygen concentration of at least 40 mole percent.

Abstract: A method for producing carbon dioxide in a high concentration suitable for direct usage or more facile further purification wherein microbial growth and fermentation of one or more carbonaceous materials are carried out with the use of defined high concentration oxidant fluid which is provided to a fermentation broth to provide oxygen in a defined limited amount.

Abstract: Concentrated black liquor formed in a kraft pulp mill process is treated to effect exothermal oxidation of black liquor solids, so as to heat the concentrated black liquor and consume a proportion of the black liquor solids. Such procedure eliminates the need to use steam to preheat black liquor and decreases the overall heating value of the concentrated black liquor, allowing an increased black liquor recovery boiler capacity to be achieved.