In order to be able to operate a dust separator with or without a lower closure element (44), the closure element (44) is part of a separate closure unit (40) which is mounted under the dust separator if required. For this purpose, the dust separator, the closure unit (40) and optionally further components, such as a delivery flow generator, are kept available in a kit so as to be able to assemble the treatment unit as required. The dust separator can be operated in batches by means of the closure element (44).