The National Renderers Association defines yellow grease as no more than 15 percent free fatty acids (FFA) and no more than 2 percent moisture, insolubles and unsaponifiables (MIU). The historical reference on FOG, Bailey’s Industrial Oil and Fat Products, defines brown grease as having an FFA level between 15 and 50 percent.
But what is brown grease? Edible Brown grease historically came from agricultural spoils, carcass, and meat cut waste. While innedible Brown Grease generally comes from the recoverable oils from the grease trap and dissolved air flotation skimmings. It should be noted that within this paper we are defining “edible vs inedible” by the United States feed standard. Definitions may vary in other jurisdictions.
Traditionally brown grease was a term for “abused” but still livestock-edible fats and oils, whose acid value, oxidative stability, and other quality parameters exceeded the standard for the original product.
For example, a rendering facility might sell edible tallow at <4% FFA as edible tallow, while another branch of the company that renders carcass and hide sells their tallow as brown grease due to its significantly deteriorated quality.
Brown grease vs trap brown grease
Today, the terms brown grease and trap brown grease are often used interchangeably (albeit incorrectly). Trap brown grease is a subset of the category brown grease. It’s only become considered a worthwhile product recently, as the price of grease has increased. When grease values are lower, the 2-3% of grease found in grease trap waste is not worth the money it takes to recover and is generally disposed of by other means. Note, it is NOT legal to feed trap brown grease to livestock in the US and many other countries.
Trap brown grease is non-edible because it can be contaminated with heavy metals, bacteria and viruses from septic backflow and/or restaurant origin. Consequently Trap Brown Grease is considered to be unfit for animal and human consumption in many countries.
Should you pay to dispose of brown grease or make biodiesel?
Brown grease that comes from a grease trap has long been considered a waste product. When a trap is cleaned, the solids, wastewater and brown grease all have to be disposed of. Restaurants pay grease trappers to clean their traps/interceptors and take care of that disposal. However, the oil layer of trap grease contains high FFA oil and in the past decade researchers have developed processes to turn high FFA oil into bio and renewable diesel.
Still, because trap brown grease returns a relatively low percentage of oil (~2%) and the cost to process it into biodiesel fuel is high, historically, there has been little interest in trap brown grease as a feedstock for biodiesel. But now, with oil and fat prices at all time highs more and more fuel producers are considering it as a viable input source. While the market value for Trap Brown Grease is not always high (only a fraction of yellow grease), the good news is that there is a profitable and growing market!
The upside in trap brown grease recovery is not limited to the grease revenue. By removing the grease before further processing the waste water the amount of coagulant and flocculant required downstream is reduced, as is the total amount of solid waste requiring disposal. The savings and revenue is multi-faceted.
The financial argument for processing trap brown grease
A waste product that is costly to dispose of, instead, becomes a desirable feedstock for biofuel manufacturing. The revenues generated from the sale of the trap brown grease create a reasonably fast ROI for high volume pumpers while simultaneously improving the quality of waste left to be disposed of. This can mean lower tipping fees at disposal, and/or lower polymer use amongst other benefits.
Do you operate a grease trap waste processing facility? Contact us. We would be happy to help you set up a grease recovery process, and to assist you in attaining fair value for your work.