Pig Manure Converted to Crude Oil

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"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."

For more energy-related news, scroll down.

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