What is the best approach to restart a FOG pretreatment unit?
The facility in question has a dissolved air flotation system (FeCl3 and polymer injection) with a hydrolysis tank (single agitator), two reactors, a biomass tank and, at the end, a gravity belt. When there are malfunctions, the reactors go septic and there is no flocculation whatsoever on the gravity belt. The facility also process activated sludge from a WWTP, which can be added to the biomass or upstream of the reactors. Usually, collected municipal sludge helps restart the unit.
When treating fats, oils and grease, acidification is done in the hydrolysis tank. To avoid sepsis and/or fermentation, you can inject caustic soda or lime at a pH level between 7.5 and 8.5, thereby avoiding disruption of the aerobic digestion of fats. This should improve performance on the gravity belts in terms of flocculation.
Thank you very much for your help.
Lime is preferable as caustic soda mixed with fat = soap production.
Adding the sludge from the aeration basin acts as a buffer.