METHOD FOR TREATING AQUEOUS FEED BY DISSOLVED GAS FLOTATION

The invention relates to a method for treating aqueous feed by dissolved gas flotation， especially by dissolved air flotation (DAF)， the aqueous feed originating from an industrial processing of fibrous material of cellulosic origin， such as manufacture of pulp， paper， board， recycled fibre pulp or the like， wherein the aqueous feed comprises an aqueous phase and solid particulate material suspended in the aqueous phase. The method comprises bringing a flocculant in contact with the aqueous feed and flocculating suspended solid particulate material into flocs through interaction of flocculant and suspended solid particulate material and contacting formed flocs with gas bubbles and inducing their flotation in a flotation basin. The flocculant， which is used for flocculating suspended solid particulate material， comprises a polymer composition having a charge density of at the most 1.7 meq/g dry， preferably at the most 1.5 meq/g dry， more preferably at the most 1.1 meq/g dry， and the polymer composition comprises a cationic synthetic first polymer， which has a charge density at least 1.0 meq/g dry at pH 2.8， and at least one second polymer， which is a polymer obtained by polymerisation of (meth)acrylamide， the second polymer being polymerised in presence of the cationic first polymer， wherein the first polymer has a higher charge density than the second polymer. The invention relates to a method for treating aqueous feed by dissolved gas flotation， especially by dissolved air flotation (DAF)， the aqueous feed originating from an industrial processing of fibrous material of cellulosic origin， such as manufacture of pulp， paper， board， recycled fibre pulp or the like， wherein the aqueous feed comprises an aqueous phase and solid particulate material suspended in the aqueous phase. The method comprises bringing a flocculant in contact with the aqueous feed and flocculating suspended solid particulate material into flocs through interaction of flocculant and suspended solid particulate material and contacting formed flocs with gas bubbles and inducing their flotation in a flotation basin. The flocculant， which is used for flocculating suspended solid particulate material， comprises a polymer composition having a charge density of at the most 1.7 meq/g dry， preferably at the most 1.5 meq/g dry， more preferably at the most 1.1 meq/g dry， and the polymer composition comprises a cationic synthetic first polymer， which has a charge density at least 1.0 meq/g dry at pH 2.8， and at least one second polymer， which is a polymer obtained by polymerisation of (meth)acrylamide， the second polymer being polymerised in presence of the cationic first polymer， wherein the first polymer has a higher charge density than the second polymer.