Fat, oil and grease wastewater and dishwashers: Uncovering the link to FOG deposition

Abstract

Fats, oils, and grease (FOG) in wastewater generated by commercial food establishments can cause severe environmental damage if not adequately treated. Grease interceptors (GIs) are an effective solution to limit FOG disposal into the sewer, but their efficiency greatly depends on the wastewater's characteristics. This laboratory study examined the physical and chemical properties of synthetic FOG wastewater from handwashing sinks and dishwashers using cooked animal fats and oils, some food solids and the same amount of detergent to explore the impact of dishwashers on key FOG components that contribute to FOG depositions. Results showed that dishwasher-generated wastewater had a significant influence on fatty acid (FA) transformations, particularly in producing very long chain saturated FAs. Relative proportions of FAs revealed a considerable proportion of very long chain FAs, such as palmitoleic (C16:1), linoleic (C18:2), α-linolenic (C18:3), arachidic (C20:0), paullinic (C20:1), behenic (C22:0), erucic (C22:1), lignoceric (C24:0) and nervonic (C24:1), among which most were not highlighted in the real field FOG wastewater. These FAs may play a significant role in FOG solidification if not sufficiently removed before disposal to sewer. The study also found that dishwashers were able to break down FOG particles, creating smaller particles (75 % being ≤68.8 μm and 50 % being ≤7 μm), while handwashing sinks produced larger particles (50 % being ≤118 μm and 10 % being ≤7 μm and). Samples containing cooked animal fats were more likely to be fragmented into smaller sizes than cooking oils due to the impact of the dishwasher. Confocal microscopy analysis results were consistent with the particle sizes measured by laser diffraction. These distinct properties could serve as criteria for updating GI designs, limiting the amount of FOG and FAs disposed of in the sewer system and controlling solidification and blockages, which pose significant threats to the environment.