title: A new settling velocity model to describe secondary sedimentation.
abstract: Secondary settling tanks (SSTs) are the most hydraulically sensitive unit operations in biological wastewater treatment plants. The maximum permissible inflow to the plant depends on the efficiency of SSTs in separating and thickening the activated sludge. The flow conditions and solids distribution in SSTs can be predicted using computational fluid dynamics (CFD) tools. Despite extensive studies on the compression settling behaviour of activated sludge and the development of advanced settling velocity models for use in SST simulations, these models are not often used, due to the challenges associated with their calibration. In this study, we developed a new settling velocity model, including hindered, transient and compression settling, and showed that it can be calibrated to data from a simple, novel settling column experimental set-up using the Bayesian optimization method DREAM(ZS). In addition, correlations between the Herschel-Bulkley rheological model parameters and sludge concentration were identified with data from batch rheological experiments. A 2-D axisymmetric CFD model of a circular SST containing the new settling velocity and rheological model was validated with full-scale measurements. Finally, it was shown that the representation of compression settling in the CFD model can significantly influence the prediction of sludge distribution in the SSTs under dry- and wet-weather flow conditions.
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 113, 2800 Kgs. Lyngby, Denmark. Electronic address: elhr@env.dtu.dk.
authors.forename: Elham
authors.initials: E
authors.lastname: Ramin
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 113, 2800 Kgs. Lyngby, Denmark. Electronic address: dosaw@env.dtu.dk.
authors.forename: Dorottya S
authors.initials: DS
authors.lastname: Wágner
authors.affiliation: DHI Water & Environment (S) Pte Ltd, Singapore 63714, Singapore. Electronic address: lay@dhigroup.com.
authors.forename: Lars
authors.initials: L
authors.lastname: Yde
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 113, 2800 Kgs. Lyngby, Denmark. Electronic address: pjbi@env.dtu.dk.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Binning
authors.affiliation: Department of Civil Engineering, Aalborg University, Sohngaardsholmsvej 57, 9000 Aalborg, Denmark. Electronic address: mr@civil.aau.dk.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Rasmussen
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 113, 2800 Kgs. Lyngby, Denmark. Electronic address: psmi@env.dtu.dk.
authors.forename: Peter Steen
authors.initials: PS
authors.lastname: Mikkelsen
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 113, 2800 Kgs. Lyngby, Denmark. Electronic address: beep@env.dtu.dk.
authors.forename: Benedek Gy
authors.initials: BG
authors.lastname: Plósz
mesh_terms: D000465:Algorithms; D001499:Bayes Theorem; D002138:Calibration; D003198:Computer Simulation; D057446:Hydrodynamics; D008390:Markov Chains; D009010:Monte Carlo Method; D012212:Rheology; D012722:Sewage / Q000737:chemistry*; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D012722:Sewage; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Activated sludge; Calibration; Compression; Computational fluid dynamics; Monte Carlo Markov Chain; Rheology