Methods for oxidizing a liquid with an oxidization gas in a closed volume reactor. A feed liquid which contains compounds to be oxidized is fed into the closed volume reactor, and a feed gas containing oxygen is fed into the reactor so as to form a gas overhead above the feed liquid. The overhead is later purged at a specific rate so as to ensure a predetermined oxygen partial pressure is maintained in the gas overhead. The value of this partial pressure corresponds to a predetermined, desired rate of oxidation of the compounds contained in the feed liquid.