A method for the removal of biofilm, flocculent bulked sludge or bulkedbiologically activesludge from an aqueous system involves adding one or more chlorinatedhydantoins, such asdichloro- or monochlorodialkylhydantoin, to the aqueous system. Alternatively,the chlorinatedhydantoin may be formed in situ by adding a chlorine source and an alkylatedhydantoinseparately to the aqueous system. This is particularly advantageous because ofthe outstandingphotostability of the chlorinated hydantoin solutions even when exposed tosunlight.
