A dissolved air flottation unit to treat effluent from the food industry (pastries) no longer reduces COD effectively.
Despite a thorough cleaning of the equipment and pipes, the expected bubbling is not apparent at its surface. A pressure pump sends the effluent at 8 bars to a compressor (which produces outlet pressure of only 3 bars max.) before returning to the dissolved air flottation unit.
Do you have any possible explanations for this malfunction?