Considerations Regarding FOG Determinations (Oil And Grease)

By Dr. J.H. Wakefield

It is incumbent upon us that we understand what FOG (fats, oils, and grease) levels are before and after treatment with DO₂E Digesters (and Aerators, too).  Legislation has been enacted to define precise manners of these determinations in a variety of wastewater-related streams. These may be found in the Federal Register (U.S. EPA methods); the publication Standard Methods for Wastewater Analysis (aka Standard Methods); and the publication of the American Society for Testing and Materials (ASTM Standards). Let us now examine these methods and decide which one (or ones) is (are) applicable to our situation(s).

As a general understanding is required, we may find commonality in all of these methods as all of them require a dissolved (or emulsified) oil or grease to be extracted from an aqueous phase (water) by means of intimate contact with an extracting solvent. Note: Molecules are polar, non-polar, or ionic. Non-polar molecules have a symmetrical charge distribution over the entire molecule; polar molecules have oppositely charged parts of the molecule which result in positively and negatively charged areas on the molecule; ionic compounds dissolve almost totally in water into separate parts (positive and negative ions).