The invention relates to products, containing a solid biocide and a composite material (11) for the absorption of contaminants and the release of active ingredients as a composite preparation for the simultaneous, separate or programmed sequential application on sterilisation and long-term conservation of a liquid (6) for purification. According to the invention, the activity of the solid biocide can be maintained by additionally treating the liquid (6) with the composite material (11), which absorbs (5.1, 5.2) from which the liquid and/or contaminants simultaneously releases active ingredients (13.1, 13.2) for sterilising and/or reducing the contaminants (5.1, 5.2) in the liquid (6). The products and the method are particularly suitable for sterilising and long-term conservation of water/oil emulsions which are contaminated by sulphur-containing compounds.