A method and composition for suppressing or inhibiting the decomposing action of enzymes on hydrogen peroxide, e.g. peroxidase and catalase, during bleaching of cellulose fibres with hydrogen peroxide, especially in connection with the production of recycled paper, in such a way that microorganisms are not markedly affected, and discharges that are dangerous to the environment are minimized. The composition contains hydroxylamine, thiocyanate salts, formic acid, ascorbic acid or nitrites.

A collector that is intended to be used at deinking of waste paper according to the flotation process. The collector includes a polyester obtained through reaction between polyalkylene glycol, di and/or tricarboxylic acid and/or anhydrides thereof as well as a saturated fatty acid with 12-18 carbon atoms. The polyester shows a molecular weight between 3000-10000.