Method for treating aqueous feed by dissolved gas flotation

A method for treating an aqueous feed by dissolved gas flotation, the aqueous feed originating from an industrial processing of fibrous material of cellulosic origin, wherein the aqueous feed comprises an aqueous phase and a solid particulate material suspended in the aqueous phase, wherein the method comprises:

• bringing a flocculant in contact with the aqueous feed and flocculating the suspended solid particulate material into flocs through interaction of the flocculant and the suspended solid particulate material,
• contacting formed flocs with gas bubbles and inducing their flotation in a flotation basin,
• wherein
• the flocculant, which is used for flocculating the suspended solid particulate material, comprises a polymer composition having a charge density of at the most 1.7 meq/g dry, and the polymer composition comprises:
• comprising:
• a cationic synthetic first polymer, which has a charge density of at least 1.0 meq/g dry at pH 2.8,
• at least one cationic second polymer, which is a polymer obtained by polymerization of (meth)acrylamide and at least one cationic second monomer in presence of the cationic first polymer, an amount of the second monomer being 0.2-19 weight-%, calculated from total dry polymeric material weight of the polymer composition, and
• wherein the cationic synthetic first polymer has a higher charge density than the at least one second cationic polymer.