Better Fuel Through Pig Manure

Better Fuel Through Pig Manure
By Brandon Keim June 12, 2008 | 4:41:34 PMCategories: Animals, Energy, Environment

Gasoline made from pig manure might not smell nice, but sometimes you've just got to pinch your nose and bear it.

In a study published today in the journal Fuel, researchers from the National Institute of Standards and Technology provided the most detailed analysis yet of pig manure-based biofuel. It's not quite ready for the road, they found, but researchers now know what to fix.

Even more importantly, said NIST fuel expert and study co-author Tom Bruno, the methods used in the study could transform fuel analysis.

"The real significance of what we have done is not so much contributing to the development of this particular fuel source, but rather the development of a measurement technique that can be applied to all manner of fuels, including those derived from bio or renewable feed stocks," Bruno said.

Bruno's samples came from an experimental pig manure processing plant designed two years ago by Yuanhui Zhang and Les Christianson at the University of Illinois at Urbana-Champaign. By heating and pressurizing manure, they turned it into crude oil.


Boasting a manure-to-fuel efficiency of 70 percent, the researchers predicted that a single pig's production-cycle excretions could yield 21 gallons of crude oil and a neat per-pig profit of $10.

Multiply that by the 100 million pigs slaughtered each year in the U.S., and it's a billion-dollar industry. And while the amount of oil produced would be relatively small in comparison to total U.S. fuel consumption, every drop counts -- and it could help rehabilitate the 110 million tons of waste produced each year on U.S. hog farms. Much of that waste ends up in rivers, and has fed the expansion of a New Jersey-sized dead zone in the Gulf of Mexico.

That, however, remains hypothetical. The NIST analysis showed that so-called pig manure crude is still quite crude. It's about 15% water by volume, reducing its energy efficiency, and suffused with sulfur, heavy metals and nutritional supplements -- all of which could end up back in the air.

Pig crude, said Bruno, is at present "less 'clean' than petroleum-derived fuel. Of course that will change if the process is tweaked."

Such tweaks require further fine-grained analysis of the fuel -- and though NIST isn't actually involved in its production, other researchers could use their methodology, which improved upon the so-called distillation curve traditionally used to measure fuel composition and performance.

As with regular distillation curves, Bruno's team observed the fuel's change during heating. But they did so by heating the sample in precise gradations, broke down the energy and pollutant content of fuel burned at each stage of heating, and bombarded leftover char with neurons to detect the heavy metals inside.

That process gives an unusually clear picture of the fuel, and can be used to analyze other biofuels.

"Could that have a carbon emission impact, either in revising current estimates or improving fuel use?" I asked.

"You betcha," he said