Your high COD values are ...
Published by Gerd Teunissen, technical director at INTERAGUA, Lda.
Your high COD values are probably related to the O&G and TSS concentrations. You might want to try a small DAF unit to remove most of both parameters and reduce your peak loads considerably. Storing wastewater is not a good option because if you want to treat with aeration and activated sludge, you need to feed the biomass regularly (preferably daily), so a small SBR would do the job.