A hindered settling velocity model related to the fractal dimension and activated sludge flocs characteristics: Application to a sludge with a previous fragmentation and flocculation process

• Published in: Separation and purification technology Vol. 300; p. 121812
• Main Authors: Asensi, E., Alemany, E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2022
• Subjects: Activated sludge; Fractal dimension; Hindered settling; Secondary settling tank; Settling velocity model; Activated sludge; Settling velocity model; Hindered settling; Fractal dimension; Secondary settling tank
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2022.121812

[Display omitted] •A new hindered settling velocity model for activated sludge is proposed.•This model is related to fractal dimension and other flocs characteristics.•It describes the settling velocity after a fragmentation-flocculation process.•The model reproduces the abrupt decrease of final hindered settling velocity.•The fractal dimension explains the structure of flocs formed from primary flocs. The modelling of the activated sludge hindered settling velocity as a function of the flocs characteristics and the incorporation of these models to the secondary settling tanks simulation is a hardly studied subject. Commonly used empirical models cannot describe the changes in the settling velocity caused by changes in the flocs characteristics. In this paper, a model for the hindered settling velocity as a function of the fractal dimension and other flocs characteristics is proposed. The model was used to describe the settling velocity after a flocculation process originated by activated sludge fragmentation. The model reproduces the observed abrupt decrease of hindered settling velocity in a small range of suspended solids concentration. It also enables to relate the flocs characteristics and the settling velocity to the fragmentation and sludge aggregation mechanisms.