US 12,421,145 B2
Method for treating wastewater
Sakari Halttunen, Espoo (FI); and Miia Niemelä, Helsinki (FI)
Assigned to Kemira Oyj, Helsinki (FI)
Appl. No. 17/779,465
Filed by Kemira Oyj, Helsinki (FI)
PCT Filed Nov. 24, 2020, PCT No. PCT/FI2020/050791
§ 371(c)(1), (2) Date May 24, 2022,
PCT Pub. No. WO2021/105558, PCT Pub. Date Jun. 3, 2021.
Claims priority of application No. 20196011 (FI), filed on Nov. 25, 2019.
Prior Publication US 2022/0402790 A1, Dec. 22, 2022
Int. Cl. C02F 1/52 (2023.01); C02F 1/56 (2023.01); C02F 1/66 (2023.01); C02F 1/72 (2023.01); C02F 3/12 (2023.01); C02F 103/28 (2006.01)
CPC C02F 3/1215 (2013.01) [C02F 1/5236 (2013.01); C02F 1/56 (2013.01); C02F 1/66 (2013.01); C02F 1/72 (2013.01); C02F 2103/28 (2013.01); C02F 2209/08 (2013.01); C02F 2301/046 (2013.01); C02F 2305/026 (2013.01)] 14 Claims
OG exemplary drawing
 
1. A method for treating wastewater in an activated sludge process, which comprises a biological treatment step followed by a sedimentation step for separation of sludge and treated effluent water, the method comprising
directing a part of the treated effluent water as a backflow from the sedimentation step to the biological treatment step, the backflow having an original pH value;
adjusting the original pH value of the backflow to a first pH value in a range of 3-6.0, between the sedimentation step and the biological treatment step, and
adding a coagulant and/or an oxidant to the backflow after adjusting the original pH value of the backflow to the first pH value and before backflow's entry to the biological treatment step.