A method of reducing undesirable microorganism concentration in an aqueous fluid stream employed in a sugar production process or a sugar-based fermentation production process includes (a) generating ClO2 gas, (b) dissolving the ClO2 gas to form a ClO2 solution, and (c) introducing an aqueous ClO2 solution into the aqueous fluid stream. Another method includes introducing ClO2 having an efficiency as ClO2 of at least about 90% into the aqueous fluid stream. An apparatus for reducing undesirable microorganism concentration comprises a ClO2 generator fluidly connected to a batch tank, fluidly connected to a sugar production vessel or sugar-based fermentation vessel.
