The treatment unit includes an evaporation device including a gas circulation pipe, and a material with a large specific surface filling an evaporation section of the circulation pipe； a device for circulating the gas through the circulation pipe； a liquid impregnating the material with a large specific surface, the liquid containing at least one product or a mixture of volatile biocide and/or phytoprotective products, with a boiling temperature between 130 and 280° C., the material with a large specific surface having a liquid retention capacity greater than 50 L/m3 of material with a large specific surface at 20° C.； a recharging device, arranged to re-impregnate the material with a large specific surface with liquid or to replace the spent material with a large specific surface with a new material with a large specific surface impregnated with liquid.
