ESEL Paper Review_20130122

 

By Hong Guo

Mail: hongguo@gist.ac.kr

Phone: (+82) (0)10 82276568

1, Title and Author

Title: Recent progress in the numerical modeling of wastewater sedimentation tanks

Journal: Process Safety and Environmental Protection

Authors:

T.Matko1 , N. Fawcett 2, A. Sharp 1 , T.Stephenson 3

1 BHR Group, Cranfield, Bedfordshire, UK

2 Yorkshire Water Services, Bradford, West Yorkshire, UK

3 School of Water Science, Canfield University, Cranfield, Bedfordshire, UK

2. Summary of Paper

This paper briefly reviewed the traditional design methods and the more sophisticated computational modeling technique, which are widely applied to the optimization of the tank. The authors compared the advantages and disadvantaged of the empirical and CFD models to show the how do they apply to the design of the sedimentation tanks.

2. Results

2.1 Empirical design method

? The considered hydraulic characteristic: Reciculating flow, Jet flow, Turbulent boundary layers, Stratification, Flow impingement, Flow dispersion, Turbulent parameters, Wind shear

? The clarifier was divided in to four different zones (inlet, settling, thickening and separation), to estimate sludge volumes and predicted sludge volumes close to measured.

? Another study assumed plug flow fluid dynamics for each unit process in an activated sludge plant and calculated its flow and mass balances.

? Solid mass flux model is also applied to the activated sludge clarifiers. (Two exponential terms for suspended solids concnetrations per volume fraction)

2.2. CFD models

? Constant eddy-viscosity models or zero equation models have been unable to model accurately the recirculating flows in sedimentation tanks.

? model could be used for calculating the distribution of turbulence in sedimentation tanks and local regions of mixing cause a reduction in the solids removal. However, the main limitation is that model is the assumption of the isotropic eddy viscosity

? The clarifier efficiency was found to be dependent on the inlet densimetric Froude number, as before, and the return activated sludge flow, rather than the Reynolds number of the influent

3. Contribution:

The author reviewed the whole studies for the sedimentation tank design and modeling. And the most helpful thing is that the paper discusses that the most important factors and useless for the CFD models. It could be helpful for the future sedimentation works.