Ancillary tank (2) has a connected circulation circuit, preferably equipped with a primary pump (4) and Venturi tube (3) with two conical diffusers (6,7) for passage of liquid, while ozone input (9) from ozone generator (1) is connected to the Venturi tube (3) nozzle (8). The ancillary tank (2) has in its lower part a discharge outlet (11), preferably with closure (12), after which a washing chamber (14) connected via secondary pump (15) and interconnected with the upper part of the ancillary tank (2) through interconnecting tube (16) can be located. Using the method according to the invention, the liquid is ozonized by circulation from and to the ancillary tank (2) through the Venturi tube (3) into which ozone is fed. Ozonized liquid is then preferably injected with jets (19) into a sealed washing space filled with residual gaseous ozone fed from the upper part of the ancillary tank (2). Circulation of liquid accompanied with ozonization is performed cyclically or continuously, processes in the washing space are performed cyclically.
