Computational fluid dynamics investigation of shallow circular secondary settling tanks: Inlet geometry and performance indicators

• Published in: Chemical engineering research & design 2016-08, Vol.112, p.122-131
• Main Author: Patziger, M.
• Format: Article
• Language: English
• Subjects: Activated sludge system; CFD modeling; Density current; Inlet geometry; Secondary settling tank; Wastewater treatment
• ISSN: 0263-8762
• DOI: 10.1016/j.cherd.2016.06.018

[Display omitted] •The hydrodynamic investigation of an old shallow circular SST is presented in the paper.•A CFD model was developed, calibrated and validated against full-scale measurements.•A direct dependence was found between the inlet height and performance indicators.•An optimized inlet facility considerably decreases the kinetic energy and the size of large scale flow structures.•This results in enormously improved performance indicators even of shallow SSTs. The paper presents the results of a long-term research program on the improvement of existing shallow circular secondary settling tanks (SSTs) based on the computational fluid dynamics (CFD) investigation of their inner hydrodynamic processes. The results provide insight into the flow and concentration pattern within such SSTs and highlight some important details that largely determine their performance. As a novel detail of the research of SSTs, a direct dependence was found between the inlet height and the length of the radial density jet induced by the entering water–sludge suspension. A hydrodynamically optimized (low positioned) inlet facility decreases the kinetic energy and the length of the density jet, as a result of which it vanishes before hitting outer boundary of the SST. This results in an enhanced performance indicators even of such shallow SSTs, under both dry weather and peak load conditions as well.