Abstract: The invention relates to 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 comprises 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 backflow pH from the original pH value to a first pH value between the sedimentation step and the biological treatment step, and adding a coagulant and/or an oxidant to the backflow after the adjustment of the backflow pH to the first pH value and before backflow's entry to the biological treatment step.

Abstract: A method for removing humic substances comprising lignin, other lignin type compounds and their disintegration products from an aqueous alkaline waste water from a bleaching of chemical pulp, which method comprises —obtaining an aqueous alkaline waste water comprising humic substances such as dissolved lignin, and —adding a high cationic starch having a charge density value of at least 1.8 meq/g dry matter of starch derivates determined at pH 7-7.5 to the alkaline waste water to precipitate humic substances.

Abstract: A method for removing humic substances comprising lignin, other lignin type compounds and their disintegration products from an aqueous alkaline waste water from a bleaching of chemical pulp, which method comprises—obtaining an aqueous alkaline waste water comprising humic substances such as dissolved lignin, and—adding a high cationic starch having a charge density value of at least 1.8 meq/g dry matter of starch derivates determined at pH 7-7.5 to the alkaline waste water to precipitate humic substances.

Abstract: Method for detecting transparent exopolymer particles in a water sample. The method comprises step of obtaining a water sample and introducing a fluorochromatic reagent to the water sample. The fluorochromatic reagent is specific to vicinal hydroxide groups of transparent exopolymer particles, whereby the fluorescence signal of the reagent changes when it comes into contact with transparent exopolymer particles, i.e. TEP. Finally the fluorescence signal from the water sample is detected and the TEP level of the sample is determined.