Title: Water treatment waste: comparison between sedimentation and flotation for sludge thickening at a Brazilian water treatment plant

Authors: Keila Fernanda Soares Hedlund; Manoel Maraschin; Ivo André Homrich Schneider; Beatriz Stoll Moraes; Ezequiel Somavilla; Elvis Carissimi

Addresses: Department of Sanitation and Environmental Engineering, Federal University of Santa Maria (UFSM), Av. Roraima 1000, CT Lab, Santa Maria, RS 97105-900, Brazil ' Department of Sanitation and Environmental Engineering, Federal University of Santa Maria (UFSM), Av. Roraima 1000, CT Lab, Santa Maria, RS 97105-900, Brazil ' Laboratory of Mineral and Environmental Engineering, Federal University of Rio Grande do Sul (UFRGS), Brazil ' Laboratory of Mineral and Environmental Engineering, Federal University of Rio Grande do Sul (UFRGS), Brazil ' Department of Sanitation and Environmental Engineering, Federal University of Santa Maria (UFSM), Brazil ' Department of Sanitation and Environmental Engineering, Federal University of Santa Maria (UFSM), Brazil

Abstract: Water treatment plants (WTPs) are essential for the production of potable water. However, they produce large amounts of waste that must be treated and disposed of properly. Thickening is the prior step and most important phase for sludge disposal or even reuse. This study evaluated the thickening of the sludge of a WTP by sedimentation and dissolved air flotation (DAF), using anionic, non-ionic, and cationic polymers, with dosages ranging from 0 to 5.5 mg polymer/g TSS. The parameters evaluated after thickening were: turbidity of the clarified water; concentration of solids and filtration resistance, of thickened the sludge. DAF thickening resulted in lesser turbidity in the clarified water (23.3 NTU) when compared to sedimentation (46.3 NTU). The highest solids concentration was found in the sludge thickened by sedimentation (7.10%). Sedimentation thickening resulted in sludge with a smaller filtration resistance (9.0E + 12 m.kg^-1) than flotation (10.9E + 12 m.kg^-1). In comparison with thickening, sedimentation proved to be a more promising alternative, showing better results regarding solids concentration and filtration resistance, thus being a good treatment alternative to avoid undue disposal of this residue.

Keywords: sulphate sludge; flotation thickening; sedimentation thickening; sludge treatment; polymers; sludge disposal.

DOI: 10.1504/IJEWM.2022.124690

International Journal of Environment and Waste Management, 2022 Vol.29 No.4, pp.477 - 493

Received: 28 Aug 2019
Accepted: 08 Jun 2020
Published online: 08 Aug 2022 *

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