Dear Muhammad,

Because the sludge age in your reactor is infinite, the inert COD from cells may be increasing day by day. Because even biological sludge has a part that can not be biodegradable. So, as time goes on, these non-biodegradable residues are increasing in the reactor. I think you should consider sludge waste. Don't change OLR. Reduce sludge age a little bit in two or tree days check the MLVSS/MLSS ratio. May be you will need more sludge waste.

Thank you so much for your help. I will surly try this way. 

Hi Muhammad 

By the way, since you are using synthetic wastewater, precipitation of some inorganics may be possible and may be these inorganics are play a part of MLSS. So, when you filter sludge for determine MLSS, inorganics be yield of decreasing MLVSS/MLSS ratio.

Please think about it.

I had this consideration in my mind as well. Thank you so much for pointing out this too. I think this can also be one of main reason