Chemical composition of the title fractions and rate of biochemical oxidation of the individual components was studied. O₂ demand for the oxidation and time of microbe adaptation increased withincreasing carbon number of monocarbonic acids present in the condensate. THe studies on dynamic, of biooxidation of some phenolic acids showed that the presence of methoxyl group in the molecule and, all the more, that of aliphatic chain with a double bond, retards the biooxidation process. Considering the prolonged nature of utilization of monocarbonic acids C₄-C₇ and tar components, biochemical sewage treatment is recommended done by the extension of the aeration time and local adsorption, by the means of which methoxyl phenols and oligomers based on them should be removed.