Hot or cooled (below 40 degrees C) post-condensation wastewaters were pretreated by flotation under scale-up conditions (stand capacity 1.0 m(3)/h). The treatment was carried by using either a common flocculent and dispersed air or by an author's proprietary method based on an addn. of H2O2. The efficiency of the treatment of hot post-condensation wastewater was similar for both methods, while for the cooled wastewater the author's method was more effective. For the cooled wastewater, the Et2O ext. and total suspended solids were removed in above 98%. The COD and BOD were by 10-20 and 5-15%, resp. higher as well as more repeatable when the H2O2-assisted method was implemented than the dispersed air flotation technique was used.