A system for a fast-rate preparation just before use of organic peroxyacids, in a hydroalcoholic environment, by mixing at temperatures lower than 40.degree. C., preferably lower than 25.degree. C., a first reactant and a second reactant, kept separate from each other during storage, to obtain an activated solution, the first reactant is in the solid or liquid state at a temperature from 5 to 45.degree. C. and includes at least one acyl donating group, and the second reactant is in the solid state, at least in the temperature range from 5.degree. C. and 40.degree. C., and comprises a peroxide anion source in a concentration such as to provide at least 10-fold molar excess of peroxide with respect to the stoichiometric amount of the acyl-donor, a biocidal agent including at least one C.sub.1 C.sub.18 linear or branched aliphatic and/or aromatic alcohol, and a stabilizing buffer component suitable for keeping the second reactant at a desired pH value.