The answer to your question ...

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The answer to your question will be dependent on your inlet TSS concentration and VSS/TSS ratio of the influent. If there is low VSS/TSS ratio meaning higher inert solids present in the influent then certainly your MLVSS/MLSS ratio in the aeration tank would not be as optimal as 0.65-0.75 which We consider as a standard rule to design Extended Aeration Tank . It will be on lower side but highly dependent on your inlet TSS concentration and its composition for inert solids or iTSS. If that is low then there might not be an issue. 

you need to understand that when you dont put a primary clarifier then from process point of view, the MLVSS/MLSS ratio would not be as optimum as you think on paper because inert solids will be accumulated in the MLSS decreasing your volumetric biomass (read here MLVSS) fraction for the same level of MLSS. 

 

I mean if you operate one plant with MLSS levels of 3000 ppm and if that plant is with Primary Clarifier then MLVSS/MLSS ratio would be naturally higher due to removal of both inert solids and lot of TSS at Primary stage. While without Primary Clarifier, everything will be going to your Aeration Tank and thus inert solids will contribute to

your MLSS and thus reduce MLVSS/MLSS ratio. That means your MCRT would be lower for same MLSS without a Primary clarifier. 

 

Hope that helps from process point of view.