What is your SV₃₀? What is your sludge age? What is the soluble COD? Is this a new start-up? What is the effluent BOD?

My reason for asking these questions is that I'm trying to determine if this is a start-up problem, an operational problem, or a design problem. If the settling is a problem, then the soluble COD should be much lower than the total COD. BOD may indicate how much of the COD is biologically treatable. A new start-up may involve sludge age problems and sludge age may identify WAS problems. SV₃₀ results may indicate sludge age, settling, and/or start-up problems. If the design was based on the original load parameters; then it could very well be an operational problem. The other design factors that may impact operation could be the the decanting and WAS design which may cause some problems.

grrun

Based on the limited information provided it seems that yummy very well be overloading the system with each batch of 400 m3. If the 80 m3 is achieving the emission limit then 400 m3 does seem like a bit too much.
Why don't you carry out some bench tests using various loading rates equivalent to the 80 m3 batch and upwards. Then check the "treated" effluent quality in the different scenarios.
You would also be advised to check nutrient levels in the incoming wastewater as well.
However I do think that you are probably overloading the system with the 400 m3 batch.

Thanks a lot for your advise and comment .
I forgot
MLSS is  3500ppm
SST 800
but with this parameters  F/m >1
I want know this F/m is possible ?or we have design problem.

I agree with Tom - you have a big design problem! Based on your figures a load of 80m3 would give an F/M of 0.2 - 0.3 which is more realistic.

I won't argue with the previous poster's conclusions. MEG is very biodegradable and you haven't responded with DO concentrations during the cycles. If the DO during filling goes to zero, you need to provide additional DO to maintain the MLSS. Your TSSs also impact the higher COD and are an indication that settling is not satisfactory. The 80 m³ discharge may also be the result of poor settling and/or inadequate oxidation.

What is the sludge age of your MLSSs and what is the SV₃₀? I'm just trying to tie up some of the unknowns of your problem.

grrun

What else is in the waste?  What are the oil and grease and suspended solids concentrations of the influent?  How much variability in the influent is there?