One of the stages of raw material preparation for plywood producing is hydrothermal treatment of birch wood. Wastewater of hydrothermal basins are characterized by the high degree of contamination, because they contain hemicelluloses, lignin and wood extractive substances (HLES). The combination of physico-chemical methods, especially methods of coagulation and ozonation is an effective way to clean wastewater from HLES. To validate the viability decision of the application of coagulation and ozonation method was necessary to conduct comprehensive studies on the efficacy of HLES removal in the presence of aluminium salts and to determine effectiveness of ozonation stage. birch wood. Wastewater of hydrothermal basins are characterized by the high degree of contamination, because they contain hemicelluloses, lignin and wood extractive substances (HLES). The combination of physico-chemical methods, especially methods of coagulation and ozonation is an effective way to clean wastewater from HLES. To validate the viability decision of the application of coagulation and ozonation method was necessary to conduct comprehensive studies on the efficacy of HLES removal in the presence of aluminium salts and to determine effectiveness of ozonation stage.