Pig waste: from the lagoon to the highway

Pig farmer scooping hog waste

Pig farmer scooping manure

No, I’m not reporting on a spill from a manure lagoon. A young college professor has found a way to make asphalt adhesive from pig waste. It’s not only a greener blacktop, not only less expensive than petroleum adhesives, but at low temperatures (pothole weather) it’s actually more durable.

As a graduate student at the University of Illinois, Ellie Fini looked for more sustainable ways to improve the sealant used to repair cracks in the roadway. She has continued that research since joining the faculty at North Carolina A&T University in Greensboro in 2008.

Asphalt comprises 95% crushed rock and 5% petroleum-based adhesive. Petroleum refiners can make more money from synthetic fuels than from asphalt adhesive, so they limit how much adhesive they make.

To be more sustainable, alternatives to petroleum cannot use raw materials that can be used as food. It also cannot use materials that require a lot of water. Fini began looking at pig waste in 2009 and discovered that it produces an excellent adhesive.

Here are just some of the benefits of hog waste for this application:

  • It has high water content and no nutritional value for humans.
  • It is an abundant, infinitely renewable resource. In limited quantities it is a great fertilizer, but the hogs produce much more than can be safely applied to cropland.
  • Therefore, disposal is a huge problem for farmers. Common practice is to push it into lagoons, which occasionally spill their contents.
  • Farmers are happy to have someone collect it. No money need change hands in the process.
  • Once Fini’s process removes the carbon from it the leftovers (nitrogen potassium, and phosphorus) still make great fertilizer.

Bioadhesive Alliance and PiGrid

Pigs rest in hoop house

Pigs rest in hoop house (Hog heaven!)

Along with a faculty colleague and a student who plans to continue graduate studies at NCA&T, Fini has formed a company, managed by the university’s Office of Technology Transfer, called Bioadhesive Alliance. The company’s product is called PiGrid (pronounced pie-grid, which sort of rhymes with hybrid).

So far, Fini can only make 250 mg at a time, but already she’s receiving calls both from farmers who want to unload their manure and from asphalt producers and road builders who want to be first in line to receive product once the manufacturing is scaled up. She hopes to have a 75-gallon reactor up and running by summer 2014.

PiGrid is  glue, and Bioadhesive Alliance is considering licensing manufacturing to other adhesive companies somewhere down the line. Bioadhesive Alliance should eventually be able to make 88 million gallons of adhesive per year, enough to supply 40% of the American demand for asphalt. Licensees will be able to make even more.

Currently, petroleum refiners charge $2 a gallon for asphalt adhesive. Bioadhesive Alliance expects to sell it for 50¢ a gallon. Demand for asphalt is worldwide, so the potential both for profits and reduced need for petroleum is huge.

If it turns out that asphalt adhesive can absorb only half of the manure pigs produce, there will still be no need for farmers to pile the rest in lagoons. Numerous pilot waste to energy projects are already underway. I earlier wrote about one that turns hog waste into electricity. That one would be even better for the environment if it captured and used the methane.

Meanwhile, Ellie Fini has not morphed into some kind of corporate tycoon. She is still actively engaged in engineering research. What uses will she find for chicken droppings?

Since I live in Greensboro, this article is based on notes I took on two articles last spring in the local paper. I have a hard time finding anything in particular on its website, but here is an informative video I found while searching in vain for the articles on Google.


Photo credits:
Pig farmer scooping manure.Some rights reserved by Wisconsin Department of Natural Resources.
Pigs rest in hoop house. Some rights reserved by friendsoffamilyfarmers. Photographer’s caption: Deep bedded hoop houses provide pigs the opportunity to exhibit natural behaviors and interact with other pigs. Straw is used for bedding, which provides nice bedding and serves to reduce odors and eliminate a need for manure pits or manure lagoons.


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