I want to ask what is the allowable depth of Blanket Zone in the in the secondary sedimentation tank in Activated Sludge WWTP?
please can you help me in any design criteria?
Thank you in advance
Please refer to Wastewater Engineering:Treatment, Disposal&Reuse by Metcalf & Eddy Chapter 9. There you can handle more than one solved example and Tables for the standard specifications but approximately the side water depth should not exceed 3 m.
I agree with @Nabeel Hameed. The sludge settling depth is determined by type of polluted wastewater and size of WWTP.
To say truth, as far as I know the sludge settling depth is determined by
- the sludge properties (i.e., specific gravity, affinity for water, composition of the biomass population);
- the operational rule of the settling tank (mainly the excess sludge wasting rate).
I believe that the original wastewater has no more than an indirect effect.
The classical textbook by by Metcalf & Eddy is certainly a "must" to study and peruse for most wastewater and sludge treatments.
It is odd that it is just so-so about anaerobic sludge stabilization ...
3 m side water depth (SWD) shall indeed be the minimum considering that at least the upper 0.8 m would be needed for clarification.
The final SWD shall be determined from the minimum MLSS required in the upstream bioreactors, from the maximum solid flux and from the worst case (highest) sludge volume index (SVI) with corresponding modeling and simulations: steady state (scenario based) + hydrodynamic incl. peak loads from sudden stop of the RAS pumps (e.g. caused by power failure).
In practice we arrive in most cases at about 4 m SWD for medium-large clarifiers.
It can depend on the mechanism for sludge removal. For flights, a couple of feet is adequate. For vacuum pickup, I would suggest one-foot of accumulated sludge
Dear NH.
Points given by @NH..to be folllowed
@ SN has mentioned the proerties of sludge in simple terms.
Now comes the question as to why you need it , specifics, Is it for maintenance then prevailent practical experience is to be followed..
Well wishes.
Prof Ajit Seshadri. Vels University. Chennai. INDIA..
Whatever you decide you need to remember that this is part of the sludge inventory and will contribute to the treatment effectiveness of the overall process. Include the sludge mass in your calculation for sludge age and f/m.
There are some important factors affecting the depth of sludge in ASP
1. The capacity of treatment plant is the major factor. The capacity is directly proportional to the rate of sludge generation.
2. The main aim for design a settling zone for the sludge is the type of settling occurs. The depth should be such that so it leads to the hindered settling. Also SVI for the particular case should be determined accordingly the depth can be decide.
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