Researching Brown Grease as a New Opportunity

By Robert Wallace and John Pierson
Georgia Tech Research Institute

Identifying new opportunities for rendered animal products has typically addressed finding new markets for fats and proteins, although these efforts are increasingly focused on addressing sustainable processes associated with inedible products (e.g., animal feeds). However, in recent months animal feed prices have been extremely volatile. Greater demand in Asia, interest as biofuels and other uses, and processing costs due to energy, labor, and transportation have caused spikes in the cost of corn and soybeans, and less acreage devoted to the planting of cotton and other crops has resulted in higher costs of these crops.

Some commodity prices have mitigated recently following the fluctuating price of petroleum, but this underscores the volatility of these markets. Price volatility may not disappear in the foreseeable future due to global demand, but additional, diverse sources of animal feed may dampen these waves of price instability relative to their quantity and availability. Thus, the challenge for finding sustainable, new opportunities for rendered animal products is tied to increasing animal feed components without impacting current supplies of corn, soybeans, cotton seed, and other oil seed plants. With that said, this article will focus on brown grease, a mix of partially oxidized lipids – i.e., waste vegetable oil, animal fat, grease – recovered from post-rendering processes during wastewater pretreatment.

Inedible fat and protein feedstocks primarily include sources such as farmed animals, aquaculture, and post-consumer materials. Chemical and physical properties, palatability, digestibility, growth, and physiological effects are a few of many considerations for determining component value. Animal fats, vegetable oils, fatty acids, and other similar materials are routinely recovered at rendering facilities, but some materials like brown grease and solids from centrifuges and separators are generally not used in any higher value applications because of the impurities they contain such as water, solids, protein, and free fatty acids (FFAs). These materials are not problematic on their own, but cause increased rancidity and other issues when in an otherwise stabilized fat.

One cannot magically convert brown grease with 20 percent water, 40 percent FFAs, and large quantities of pigments to virgin vegetable oil, but the quality and stability of certain fractions of the brown grease may be increased to a point usable in an animal feed product. The quality and constituents cover a very large range depending on initial feedstock, age, temperature, recovery method, etc. In aggregate, undesirable materials include oxidative components such as gums or hydrated unsaponifiables that are removed by degumming, color bodies treated by bleaching, and FFAs and volatiles removed by refining processes also called deodorization or deacidification.

Maximizing neutral oil yield is a primary objective, although treatment process selection depends on the desired extracted oil quality. Refined plant oils and animal fats result from established physical and chemical treatment processes designed to remove undesirable materials. Due to the variety of components in brown grease, it is amenable to fractionation by centrifuge.

There are a number of ways to deal with these impurities, which vary in complexity and expense. Steam has increasingly been used versus chemical treatment to remove gums and oxidative components while minimizing soapstock formation. However, neutral oil removal as vapor can occur with high temperature steam distillation used during vegetable oil refining to also remove volatiles. Proteins are removed by clarification and filtration, most often with diatomaceous earth or bleaching clay followed by steam to remove FFAs. Dewaxing can also be used to improve flow properties, although waxes and fatty acids have value for energy and digestibility. Interest in enzymatic approaches as well as more exotic technologies such as supercritical oxidation is growing, but cost considerations continue to limit viability.

As a potential animal feed ingredient, brown greases recovered from post-rendering processes should be analyzed for lipid refinement. The choice and order of refining processes may vary based on the desired use of the extracted oil. Removing water should be a primary concern as it contributes to hydrolysis of triglycerides, which yields FFAs and begins polymerization. This may be accomplished by degumming, neutralization, or vacuum distillation.

Degumming for phospholipid and bound water removal may be considered depending on the wastewater treatment techniques used, although phospholipids tend not to be a significant contaminant. Often used as a degumming process, steam treatment does provide rapid heat transfer, which also allows the wax crystals present to melt and recrystallize in a form more amenable to centrifugation, but other degradation may occur due to polymerization as lipids lose stability and darken, develop bitterness, and form pigments.

Chemical neutralization (caustic addition) of FFAs will result in significant soapstocks and additional water; therefore, alternatives should be considered if possible, including non-aqueous generally regarded as safe (GRAS) solvents that can move water and even some amount of FFAs, aldehydes, ketones, and other undesirable chemicals to another fraction. Bleaching is typically considered for pigment removal, and studies have shown that dewaxing may also improve neutral oil transparency, brightness, and palatability.

In conclusion, the choice of refinement methods and the order in which they are performed is dependent on the initial feedstock and the desired use. Significant improvements in feed oil quality may be achieved with equipment currently in-house at most rendering facilities with chemical addition and possible additional storage to allow for recrystallization of the wax particles. For example, dewaxing can improve cold-flow properties of neutral oil allowing for non-heated storage with the added benefits of improved optical qualities, palatability, and digestibility. Non-aqueous, GRAS solvents can move FFAs from one fraction to another resulting in a more stable oil. Bleaching should be considered on a case-by-case basis as it reduces pro-oxidants, peroxides, and can help with FFAs.

There are still a number of research opportunities with respect to degraded fats, such as chemical choice to select different FFA removals and rates, conversion of FFAs to monoglyceride or even diglyceride, separating and concentrating odor components from both fat and wastewater, and dealing with dissolved air flotation skimmings, just to name a few.

Tech Topics – August 2010 RENDER | back