the method of this invention is suitable for controlling microbiological populations in programs for bleaching all manner of cellulose pulps including pulp made from recycled paper pulps from sulfite or sulfate cooking mechanical pulp thermomechanical pulp and chemothermomechanical pulp the method is especially suitable for controlling microbiological populations responsible for degrading hydrogen peroxide during the bleaching process in de inking plants as used herein u201c controlling u201d encompasses both reducing microbiological populations and inhibiting the growth of microbiological populations the aqueous biocide solution of this invention typically comprises about 5 to about 60 percent by weight of one or more organic peracids about 5 to about 60 percent by weight of the corresponding organic carboxylic acids and about 10 to about 20 percent by weight hydrogen peroxide the aqueous biocides solution may also contain stabilizers to prolong the storage stability of the peracid representative stabilizers include ethyleneaminopolymethylenephosphonic acids hydroxyethylidene diphosphonic acid or salts thereof and heterocyclic carboxylic acids such as dipicolinic acid quinolinic acid and the like u201c organic peracid u201d means a compound of formula rc o ooh where r is straight or branched c 1 c 6 alkyl or phenyl representative organic peracids include peracetic acid perpropionic acid perbenzoic acid and the like in a preferred aspect of this invention the organic peracid is peracetic acid.