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Pig Manure Converted to Crude Oil

Stefan Lovgren
for National Geographic News
July 2, 2004
 
Crude oil and gasoline prices are near an all-time high. But don't despair. One scientist has found an alternative source of energy: pig manure.

Yuanhui Zhang, an agricultural engineering professor at the University of Illinois in Urbana-Champaign, has succeeded in turning small batches of hog waste into oil.



The process, called thermochemical conversion, uses heat and pressure to break down carbohydrate materials and turn waste into liquid. The project is still in its infancy.

For now, each half-gallon (two-liter) batch of manure converts to only about 9 ounces (0.26 liter) of oil.

But Zhang believes the conversion process could eventually solve the problem of pollution and odor at modern hog farms, where farmers pay big money to get rid of the waste. And, he says, pig oil could also offer an alternative to petroleum oil.

"If 50 percent of U.S. swine farms adopted this technology, we could see a [U.S.] 1.5-billion-dollar reduction in crude oil imports every year," Zhang said. "And swine producers could see a 10 percent increase in their income—about $10 to $15 per hog."

Oil Crisis

During the oil crisis in the 1970s, U.S. researchers attempted to turn wood sludge and coal into oil. But it proved too costly. When oil prices later fell, the whole idea of turning waste into fuel became less attractive.

"The science is not new, but it has failed because of economics," Zhang said. "If you can buy crude oil at [U.S.] $20 a barrel, why bother with pig oil? It's too expensive."

But with crude oil prices now hovering around U.S. $40 a barrel, pig oil once again seems like an attractive fuel alternative.

Zhang's research team developed a small-scale thermochemical conversion reactor that applies heat and pressure to swine manure. The process breaks the manure's long hydrocarbon chains down into shorter ones. Methane, carbon dioxide, water, and oil are produced as by-products.

"The process we have developed is quite different from most conventional thermochemical conversion processes," said Zhang. "There is no need for the addition of a catalyst, and our process does not require predrying of the manure."

Each conversion takes about 15 minutes, and the process has a strong energy return. "For every one portion of energy in, you get three portions of energy out," Zhang said.

Negative Cost

The researchers converted as much as 70 percent of swine manure volatile solids into oil. About 20 percent of the manure is considered solid; the rest is largely water. Some 90 percent of that solid manure is volatile, or organic. Those volatile solids are the part of the manure that can be converted to oil.

The manure excreted by one pig during its life span on an average hog farm could produce up to 21 gallons (80 liters) of crude oil. A swine farm producing 10,000 market hogs per year could produce 5,000 barrels, or 210,000 gallons (795,000 liters), of crude oil per year.

Simply getting rid of manure is a big business. "It's a negative-cost material to us," Zhang said. "People are willing to pay for you to use it."

Manure has advantages over raw materials, like wood sludge, because the pig has already done most of the work. "It's a very nice material that is easy to process, because it's already been biologically processed by the pigs," Zhang said.

The process could also work with manure from chickens or cows, though it would have to modified. Human waste, which is similar to that of pigs, would, in theory, work well in Zhang's system with little or no modification.

After the conversion, the researchers took the crude oil and further processed it, obtaining refined oil that Zhang says has a heating value similar to that of diesel fuel.

Environmental Benefits

As a renewable energy, pig oil has great environmental benefits. Minerals are preserved in the treatment system, odor is reduced, and the biological oxygen demand of manure is reduced by 70 percent.

"Biological oxygen demand" refers to the fact that, as manure breaks down, the process sucks oxygen from its environment. When manure leeches into a water supply, say due to runoff, it harms aquatic life by decreasing the oxygen available to fish, water plants, and other organisms.

Also, unlike petroleum oil, pig oil uses no additives.

"For me, it's primarily an environmental thing," Zhang said. "We have to look to renewable or alternative energy. We know that eventually we can't keep digging up petroleum oil."

The next step for Zhang's research team is to develop the batch process into what he calls a continuous-mode process at a pilot plant.

"Then, the heat generated from the process can be recycled more efficiently, reducing the operating costs," Zhang said. "Reactor volume can be reduced for the same capacity, which reduces the investment costs. And automated controls can be adapted more readily, which reduces the labor costs."

So should oil companies be worried about Zhang?

"Maybe," he said. "I have no support from the oil companies, that's for sure."

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