FOG (Fat, Oil & Grease)


For the past couple of decades, yellow grease, or used fryeroil, has been the goto source for biodiesel production. Each gallon of yellowgrease produces almost the same volume of biodiesel. Though the biodiesel yield is much lower for brown grease(50 percent), pioneering organisations are discovering uses for all types ofgrease trap waste.

In a study conducted at North Carolina State University, researchers found that methane production increased by 317 percent when FOGs were introduced at a rate of 20 percent of volume. However, an increase in the amount of FOG per volume didn’t fare well — at 40 percent of volume, methane production decreased.

Sustainable energy pioneers are finding that grease trap waste, if properly processed, can be used in a number of other ways.

- Argent Energy, supplying high grade, sustainable diesel from wastes

- Anaerobic Co-Digestion of Grease Trap Waste enhances the biogas production

- Interesterification of grease trap waste lipidsusing methyl acetate under supercritical conditions


Einstein said, “Energy cannot be created or destroyed, it can only be changed from one form to another.” Wouldn’t it make sense, then, to harness the energy from what started out as our primary energy source — food —in the first place?

Saying that grease trap waste is an abundant resource would be a vast understatement. A 1998 study by the National Renewable EnergyLaboratory of 30 U.S. metropolitan areas found that about 13 pounds of trap grease are generated per person per year. Research shows that that number has actually increased over the past 20 years, but by using that data as a starting point, with the current population of 313.9 million people, food service establishments produce well over 4 billion pounds of trap grease per year.

That’s 4 billion pounds of grease trap waste that’s carted to landfills, to wastewater treatment facilities and sprayed over fields — none of those are necessarily sustainable solutions. In some instances, water treatment facilities are even refusing the water waste brought in from pump trucks because community and industrial growth has greatly diminished capacity.

Until recently, companies weren’t exactly chomping at the bit to take a swing at using grease trap waste for energy production. For starters, it stinks. It also contains a large percentage of free fatty acids(more on those later), has significant solids contamination (food and inorganic material), is mixed in with water when pumped, and the grease is solid at room temperature. But, with proper processing, all those issues can be rectified and the product not only is a sustainable energy source, but also a solution to a waste management problem.

Turning grease trap waste into alternative energy isn’t just good for the environment — it’s good for the haulers as well. When compared to dumping all the waste at the landfill, disposal costs are much cheaper. In turn, this cuts down on the amount of illegal dumping. 


When grease trap waste is first pumped from a food service establishment’s tank, it’s not yet in a useable state due to the large amount of water, up to 90 percent. The remaining 10 percent is split pretty evenly between food particles and grease.

Dewatering the waste isn’t an easy task. Though technologies vary, the liquid part of the grease trap waste is removed through filtration, evaporation or another separation process. Many waste treatment plants use large-scale equipment to separate the solids from the liquid, but smaller set-ups are available for pumping businesses. 

The separated water is returned to a municipality’s water treatment system, while the grease can be repurposed.

Super-capacity grease traps, like Thermaco’s Trapzilla, can significantly reduce the dewatering burden because they trap more grease and less water. For example, Trapzilla traps upwards of 90 percent of its total volume—this translates into more than 630 pounds of fats, oil and grease. As a comparison, traditional concrete traps need to be emptied when they hit 25percent capacity. 

Once the grease is dewatered, there are several energy-producing possibilities.


Dewatered FOGs can be used as a substitute for coal or wood in power plants. One pound of compressed, dewatered FOG material actually has more heat energy than a pound of wood. FOGs have between 7,000 and 10,000 BTUs(British Thermal Units), whereas a block of wood has about 6,500 BTUs. Though dewatered grease is more effective than wood, coal maintains the BTU lead at about 12,000 BTUs.

Dewatered FOGs have also been used successfully when combined with wood chips with wood fuel systems at gasification or combustion facilities. Coined the “FOG cake,” the 50/50 ratio works well.


It takes about 7.5 pounds of trap grease to make one gallon of biodiesel. Using the grease trap statistics above, the U.S. could potentially produce between 500-600 million gallons of biodiesel each year from grease trap waste. That’s a small, but not inconsequential, portion of the 40billion gallons of diesel consumed in the United States each year.


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