R. Dupont et C. Dahl, A ONE-DIMENSIONAL MODEL FOR A SECONDARY SETTLING-TANK INCLUDING DENSITY-CURRENT AND SHORT-CIRCUITING, Water science and technology, 31(2), 1995, pp. 215-224
Citations number
15
Categorie Soggetti
Water Resources","Environmental Sciences","Engineering, Civil
This paper presents a dynamic one-dimensional flux model for the secon
dary settling tank which is suitable for use with the latest innovatio
ns in models for activated sludge tanks, and which takes into account
observed effects of density current and short-circuiting. The componen
ts of the influent to the settling tank are divided into three fractio
ns. Soluble components, non-settleable particulate components (primary
particles), and settleable particulate components. (macroflocs). Solu
ble components and primary particles are considered to follow the hydr
aulic flow in the settling tank. The transport of macroflocs in the se
ttling tank is modelled according to the traditional flux theory on a
layer model of the settling tank extended with a model for density cur
rent and short-circuiting. For modelling of the density current in the
inlet region of the settler a dynamic inlet height is introduced. The
short-circuiting is modelled by the introduction of a factor which ac
counts for the dilution in the suspended solids concentration at the b
ottom of the settling tank down to the concentration in the return slu
dge flow. Settling velocities of the macroflocs for both free and hind
ered sedimentation are measured and a new model for the settling veloc
ity is proposed. The model is validated with data from the wastewater
treatment plant Lynetten, Copenhagen, Denmark. It was found that the s
uspended sludge concentration profile and the suspended sludge concent
ration in the return sludge were predicted well with the model.