There are two considerations ...

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There are two considerations that work against the notion of using lamella plates or tubes in activated sludge secondary clarifiers.  The primary concern is that bacteria and biofilms will  grow on the lamella surfaces, both impeding flow (plugging)  but also creating the potential for anaerobic activity in the attached biofilm that can release methane and H2S.  The methane bubbles may attach to the solids which would tend to float, causing a deterioration in effluent turbidity.  H2S is a concern primarily for odors.

Another concern is that the high concentration of mixed liquor suspended solids from the aeration zone may exceed the maximum concentration that lamella plates could handle.  Perhaps the best candidate for addressing this issue is a configuration similar to what is used in the Suez Superpulsator for water treatment, i.e. deep, widely spaced, lamella plates.  Lamella tube settlers for polishing on top of lamella plates below for bulk solids separation may be the best approach, if the biological growth problem can be solved.

The biological growth problem possibly could be solved by impregnating the lamella surfaces with "quorum sensing" disruption chemicals that interfere with biofilm formation, thus preventing biogrowth on the surface.  Such chemicals are used in surgical instruments and its been a topic in water and wastewater discussions for at least 15 years.

 

2 Comments

I tend to agree with this comment, biofilm development attaching to the lamella plates in biological treatment processes, and particularly those with high sludge yield, tend to get clogged with biomass growth or high sludge accumulation

accurate and regular desludging therefore becomes critical, 

seems to be less of a problem on RBC installations where sludge production is less, therefore less solids load

 

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Joseph,

 

I think this is the best explanation given as to why a Lamella style clarifier is not utilized in biological treatment units. I have personally seen a lamella clarifier clog with debris and biological growth on an INFLUENT water stream that did not dose bleach into the raw river water it was treating. The spaces between the plates and tubes are perfect environments for bacteria to attach and grow even without mixed liquor flowing through them. You add that to the mix and the plates will plug so rapidly that I do not know if you will ever get proper flow through them

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