The use of a bleach activator compound which is an ester of a carboxylic acid to generate peroxy acids in relatively dilute aqueous acidic environments is described. The product is used in situ as an oxidising agent, for instance for use as a bleach, biocide or disinfectant. Preferred processes use aqueous hydrogen peroxide with preferably at a concentration of less than 20 % w/v the sodium salts of nonanoyloxybenzene sulphonate. The pH is preferably less than 6.5.