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Fuel from papaya

<p>HOLLYN JOHNSON/Tribune-Herald</p><p>Culled papayas are seen here at U.S. Pacific Basin Agricultural Research Center on Wednesday afternoon.</p>


Tribune-Herald staff writer

By the time a fresh crop of papayas is ready to be harvested, plenty of a farmer’s time, money, and general green-thumbery has been invested into them.

But despite such attention, almost 35 percent of those papayas will end up going to waste, says Lisa Keith, a research plant pathologist with the U.S. Pacific Basin Agricultural Research Center.

“And even that number could be low, because it only counts the fruit that is rejected at the packing houses. It doesn’t take into account the ones left in the field,” she said.

Be it due to insect damage, physical imperfections, or over-ripeness, papayas that don’t meet standards allowing them to be marketed to consumers end up being a drain on farmers’ bottom lines. But now, a pilot project of the Hilo office of the U.S. Department of Agriculture’s Pacific Basin Agricultural Research Center aims to develop a method for recycling those wasted papayas, turning them into biofuel and high-protein animal feed.

It’s a process that could potentially work for a variety of other feedstocks besides papayas, said Keith, who is the lead scientist on the project. The technology, which utilizes special strains of algae and fungi to break down plant matter, could work with crops like sweet potatoes, sugar cane, mango, and even the albizia — an invasive tree spreading rapidly through Puna, where it poses a danger to pedestrians and homeowners because it can grow to great heights in a short period of time but is very weak and prone to toppling over.

“We chose papaya because there is so much of it here on the island,” Keith said. “And because it really is one of the crops with the highest amount (of fruit culled due to imperfections). Because so much is rejected, I think the market really has the potential to increase. But it could work on any number of other feedstocks.”

Part of what makes the whole project so innovative is the fact that feedstocks can be a remarkably expensive part of the process of developing biofuel, said James Nakatani, executive director of Hawaii’s Agribusiness Development Corporation.

“This Hawaii-based technological development is a major breakthrough that focuses on key components hampering the sustainability efforts of other microorganism based biofuel projects. These obstacles include the high cost of feedstock. Approximately 70 percent of the cost for production is consumed in this area. Using unmarketable plant and other waste material drastically reduces this cost driver.”

For the last year, Keith has worked in her lab with the support of a technician and a student scientist to perfect a small-scale process for converting culled papayas into energy. The papayas are juiced, using a device similar to a grape press used to make wine, and that juice is added to flasks with water and a specially evolved, “heterotrophic” strain of algae, provided by partner company BioTork Hawaii LLC. Instead of sunlight providing the algae with energy through photosynthesis, the algae derives its energy from the sugars in the papaya.

After a period of 14 days in the heterotrophic environment of the flasks — during which time the solution is continually shaken to introduce oxygen to fuel the chemical reaction — the algae is added to test tubes filled with metal beads and shaken. The mechanical action of the beads breaks open the cell walls of the algae and releases the energy-filled oils stored within, Keith said. That oil, after a refining process, could theoretically be used to fuel things like traditional combustion engines.

“When we started, we were getting approximately 10 percent lipids, or oil. Now, we’re up to about 50 percent,” she said.

That yield could theoretically climb to as high as 70 percent by the time all the kinks in the process are worked out, but there is still much work to be done.

In addition to making biofuel from the papaya juices, any remaining plant matter, such as rind and pulp, could later be converted into feed for cattle, creating a zero-waste system that helps farmers recapture lost revenue from fruit they can’t sell for consumption.

As a result of the project’s success, on Saturday, before making his appearance in the Merrie Monarch Royal Parade, Gov. Neil Abercrombie presented PBARC with a $200,000 check from the state Department of Agriculture that will pay for a large bioreactor. The device is capable of performing the same job as the flasks in Keith’s first phase of the experiment, but on a much grander scale.

PBARC and partner company BioTork have so far invested more than $1 million into the project. Keith said that the new bioreactor could take a long time to go through the purchasing process, but once it is ready to go, she expects the next phase of refining the process for a larger scale to take about a year. Then, it could move to a commercial phase, with the state’s Agribusiness Development Corporation becoming a venture partner to globally export the rapid conversion technology in association with PBARC and BioTork.

“This patented evolutionary technology is unique to the marketplace and places Hawaii in a leading position in the area of biofuel and feed research,” Abercrombie said at the weekend press conference. “With this technology, farmers can turn agricultural waste into an additional revenue stream, and local production of biofuel can lower dependence on Hawaii’s import of fossil fuels.

“Aside from the benefit of producing biofuel, this technology has the ability to create another revenue stream for papaya and other tropical agriculture farmers. Local high protein feed production — another byproduct of this process — can greatly benefit cattle, hog, chicken and aquaculture farms through competitive market pricing.”

Email Colin M. Stewart at


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