A one-dimensional model for a secondary settling tank including density current and short-circuiting

1995 ◽  
Vol 31 (2) ◽  
Keyword(s):  
Settling Tank ◽  
Density Current ◽  
Dimensional Model ◽  
One Dimensional ◽  
Secondary Settling

A one-dimensional model for a secondary settling tank including density current and short-circuiting

1995 ◽  
Vol 31 (2) ◽  
pp. 215-224 ◽  
Author(s):  
René Dupont ◽  
Claus Dahl
Keyword(s):  
Settling Tank ◽  
Treatment Plant ◽  
Density Current ◽  
One Dimensional ◽  
Solids Concentration ◽  
Primary Particles ◽  
Flux Model ◽  
Secondary Settling ◽  
Soluble Components ◽  
Sludge Concentration

This paper presents a dynamic one-dimensional flux model for the secondary settling tank which is suitable for use with the latest innovations in models for activated sludge tanks, and which takes into account observed effects of density current and short-circuiting. The components of the influent to the settling tank are divided into three fractions. Soluble components, non-settleable particulate components (primary particles), and settleable particulate components. (macroflocs). Soluble components and primary particles are considered to follow the hydraulic flow in the settling tank. The transport of macroflocs in the settling tank is modelled according to the traditional flux theory on a layer model of the settling tank extended with a model for density current 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 accounts for the dilution in the suspended solids concentration at the bottom of the settling tank down to the concentration in the return sludge flow. Settling velocities of the macroflocs for both free and hindered sedimentation are measured, and a new model for the settling velocity is proposed. The model is validated with data from the wastewater treatment plant Lynetten, Copenhagen, Denmark. It was found that the suspended sludge concentration profile and the suspended sludge concentration in the return sludge were predicted well with the model.

Effect of Activated Sludge Processes on Secondary Settling Tank Efficiencies

1988 ◽  
Vol 20 (4-5) ◽  
pp. 153-163 ◽  
Author(s):  
Z. Koníček ◽  
J. Burdych
Keyword(s):  
Settling Tank ◽  
Standard Test ◽  
Density Current ◽  
Secondary Settling ◽  
Final Settlement ◽  
Activated Sludge Processes ◽  
Harmful Effects ◽  
Current Zone ◽  
Better Than ◽  
Number Of Particles

Some calculations and experimental work on the turbulence in aeration tanks using different aeration systems and its effect on floc cohesion are presented. Vigorous aeration causes floc dispersion and it can be quantified in standard test conditions using velocity gradient calculations and comparing these with the numbers of particles in the supernatant liquor after 30 minutes settlement of the sludge. Tests on final settlement tanks indicated that the density current is of prime importance and that the harmful effects of this can be overcome by installing deep inlets and arranging to have the outlet weir inset and as near to the inlet as possible. Mixing calculations also indicated that circular tanks are more efficient than rectangular and that if the latter were used transverse flow is better than longitudinal flow. A test on a full scale plant indicated that flocculation occurred in the density current zone of the final tank so that the number of particles in the supernatant decreased to an extent similar to that produced by mild agitation.

Dynamic one-dimensional modeling of secondary settling tanks and system robustness evaluation

2014 ◽  
Vol 69 (11) ◽  
pp. 2339-2349 ◽  
Author(s):  
Ben Li ◽  
M. K. Stenstrom
Keyword(s):  
Numerical Methods ◽  
Numerical Technique ◽  
Settling Tank ◽  
Operating Conditions ◽  
Parabolic Partial Differential Equation ◽  
Engineering Practice ◽  
Time To Failure ◽  
One Dimensional ◽  
Secondary Settling ◽  
The Yrd

One-dimensional secondary settling tank models are widely used in current engineering practice for design and optimization, and usually can be expressed as a nonlinear hyperbolic or nonlinear strongly degenerate parabolic partial differential equation (PDE). Reliable numerical methods are needed to produce approximate solutions that converge to the exact analytical solutions. In this study, we introduced a reliable numerical technique, the Yee–Roe–Davis (YRD) method as the governing PDE solver, and compared its reliability with the prevalent Stenstrom–Vitasovic–Takács (SVT) method by assessing their simulation results at various operating conditions. The YRD method also produced a similar solution to the previously developed Method G and Enquist–Osher method. The YRD and SVT methods were also used for a time-to-failure evaluation, and the results show that the choice of numerical method can greatly impact the solution. Reliable numerical methods, such as the YRD method, are strongly recommended.

Modelling Techniques in Applied Glaciology: Numerical Modelling of Avalanches

1983 ◽  
Vol 4 ◽  
pp. 297-297
Author(s):  
G. Brugnot
Keyword(s):  
Finite Difference Method ◽  
Transverse Velocity ◽  
Longitudinal Velocity ◽  
Momentum Conservation ◽  
Dimensional Model ◽  
One Dimensional ◽  
Modelling Techniques ◽  
Reference Grid ◽  
The One ◽  
Near Future

We consider the paper by Brugnot and Pochat (1981), which describes a one-dimensional model applied to a snow avalanche. The main advance made here is the introduction of the second dimension in the runout zone. Indeed, in the channelled course, we still use the one-dimensional model, but, when the avalanche spreads before stopping, we apply a (x, y) grid on the ground and six equations have to be solved: (1) for the avalanche body, one equation for continuity and two equations for momentum conservation, and (2) at the front, one equation for continuity and two equations for momentum conservation. We suppose the front to be a mobile jump, with longitudinal velocity varying more rapidly than transverse velocity.We solve these equations by a finite difference method. This involves many topological problems, due to the actual position of the front, which is defined by its intersection with the reference grid (SI, YJ). In the near future our two directions of research will be testing the code on actual avalanches and improving it by trying to make it cheaper without impairing its accuracy.

An equation for the empirical design of anoxic zones used to eliminate rising sludges at nitrifying activated sludge plants

1996 ◽  
Vol 33 (3) ◽  
pp. 185-194 ◽  
Author(s):  
M. Sarioglu ◽  
N. Horan
Keyword(s):  
Activated Sludge ◽  
Empirical Equation ◽  
Nitrate Nitrogen ◽  
Critical Concentration ◽  
Settling Tank ◽  
Limited Information ◽  
Batch Experiments ◽  
Anoxic Zone ◽  
Secondary Settling ◽  
Anoxic Zones

Anoxic zones are designed for the removal of nitrogen in nitrifying activated sludge plants. This can be carried out either to achieve a nitrogen discharge consent or to eliminate the problem of rising sludges. The rising sludge problem is mostly encountered in medium and small size plants in warm conditions and there is limited information as to the appropriate design of anoxic zones to protect against rising sludges in the secondary sedimentation tanks. Therefore a series of batch experiments were undertaken in order to establish the critical concentration of nitrate-nitrogen which causes rising sludge in the secondary settling tank and the effect of environmental factors such as temperature (15°C to 30°C) and residual carbon source (100 to 600 mg/1 COD) were examined. Based on the results of these experiments an empirical equation was presented which can be used to size an anoxic zone to eliminate rising sludges. The application of this equation at full-scale plants is discussed.

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