Fats, Oils, and Grease
The Science
Metabolic Pathways of FOG Removal w/ In-Pipe Technology
Fats and oils are esters of fatty acids and glycerol that are either solid (fats) or liquid at room temperature (oils) while grease is a general term to describe a soft or melted animal fat or a lubricant (Campbell, 1999). Collectively, they are referred to as fats, oils, and grease (FOG).
Large amounts of FOG are disposed of into wastewater on a continuous basis particularly where there are high numbers of restaurants or food processing facilities. When FOG enters the wastewater, it tends to congeal within the pipe, at lift stations, and in the headworks, which creates flow problems and odors. This occurs due to FOG’s hydrophobicity and therefore poor solubility in water. However, some microbes are highly efficient at degrading FOG by using two main mechanisms: (1) biosurfactant production and (2) extracellular enzyme production.
After the FOG is more bioavailable from biosurfactants, two types of extracellular enzymes can be used to degrade the FOG: lipases and esterases. Lipases are produced to break down the long-chain triglycerides that are insoluble in water while esterases degrade short chain carboxylic acids (Jaeger et al. 1994; Sayali et al. 2013). Bacterial lipases and esterases are highly diverse in their activity levels with some having broad substrate specificity and others being highly substrate specific. For example, the Bacillus subtilis lipase attacks fatty acids with chain lengths of 8 carbons found in the 1, 3-positions of a triglyceride while the Staphylococcus aureus lipase has a broad range of substrate degradation capabilities (Thomson, 1999). Activity levels can also vary based on environmental conditions such as pH, temperature, and salinity. For example, Bacillus licheniformis lipase activity is optimal at pH 10.5 with significantly reduced activity levels are neutral pH (Nthangeni et al. 2001).
After the FOG has been made more bioavailable with biosurfactants and degraded by enzymes, the resulting by-products of this metabolism are free fatty acids and glycerol. These exogenous fatty acids are used by all known bacteria (Yao and Rock 2017). First, the fatty acids are transported into the cell, then oxidized to acetyl-CoA via a pathway called β-oxidation (Jimenez-Diaz et al. 2017). β-oxidation of fatty acids, in combination with the tricarboxylic acid cycle and respiratory chain, provides more energy per carbon atom than any other energy source (Zubay, 1996).
Our proprietary blend of bacteria is specialized for FOG metabolism. These selected bacteria produce high levels of biosurfactants and extracellular enzymes (e.g., esterases and lipases). Although these organisms require an aerobic environment to grow, there is sufficient oxygen in the wastewater to support their metabolism of FOG and they can survive oxygen deprivation. Another added benefit of these microorganisms are their tolerance to a wide-range of environmental conditions, including toxic compounds commonly found in wastewater collection systems, making them well-adapted to metabolize FOG in a collection system.