The Riga city drinking water treatment plant sludge are disposed in Olekte river more than 10 years, causing river pollution with aluminium hydroxide and other pollutants containing these sludge. In this paper are defined following aims to solve the Olekte river pollution problem: (1) evaluate WTP “Daugava” filter wash water and sludge from settling tanks treatment quality; (2) investigate sedimentation properties of sludge from settling tanks; (3) propose alternative tretment possibilities for WTP “Daugava” filter wash water and for sludge from settling tanks.