Animal Feed Ingredient
Glycerin is commonly used as an animal feed. Researchers at Iowa State University (ISU) and the USDA found that pigs fed a 20% glycerin diet showed equal growth performance between the glycerin-supplemented diet and a more conventional corn/soy meal diet. Another study at ISU, using poultry fed a 5%, 10% and 15% glycerin diet found the energy was used with high efficiency by 48 laying hens with no adverse effects (McElroy 2007). A study conducted on cattle fed 5%, 10% and 20% glycerin at the university of Missouri-Columbia found for maximum results, feed efficiency on a 10% diet inclusion of glycerin produced a 12% improvement in feed efficiency and equal weight gains to a diet with no glycerin. The study also showed that at a 10% addition of crude glycerin to feed for cattle, the average daily weight gain was 635 grams compared to 590 grams without the glycerin (Fienman 2007).
Digester Feed Material
Glycerin is also a great additive to any biodigestor feedstock that contains ample nitrogen but lacks energy content. Glycerin acts as a carbon source and as a significant energy source. An addition of 5% by weight of glycerin to cow manure increases the methane production by nearly 10%. Creating a synergistic co-fermentation effect that produces more methane combined than either feedstock alone can produce (Robra et al 2010; Astals et al. 2011). With pig manure this co-fermentation effect is even greater. With a 20% addition of glycerin to 80% pig manure researchers found a 125% increase in methane production (Astals et al. 2011).
According to Torrijos et al. (2008) glycerin has a high potential for methanisation because of its high methane potential (465 ml CH4/g VS) and high metabolization rates (0.42 g VS/g VSS.d). It is so efficient as a feedstock for microbial methanisation that in multiple studies all the glycerin was was completely digested to biogas with no residual remaining.
Gas Scrubbing Material
Crude glycerin is readily available, inexpensive, and non-toxic (WHO Geneva 1976). It has been found to remove most of the contaminants in raw biogas in other applications. Glycerin is an extremely polar compound and it has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. Research has shown that glycerin scrubbing solutions have a high absorbability of CO2. Limitations have been identified in selecting CO2 over N2 in tests (Chen H., Majurmdar S., Sirkar K.K. 2001); however, when cleaning raw biogas this selectivity is not a concern because both these contaminants need to be removed to produce renewable natural gas (RNG) that meets advanced transportation fuel standards and specifications. Other research has shown glycerin to dissolve H2S (CAS No. 7783-06-4), as well hold siloxances, trace contaminants in raw biogas, in suspension making them available for removal (Santamaria, F.G. 2003).