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Researchers Tap Papaya-Loving Algae to Make “Home-Grown” Biodiesel for Hawaii

Posted by Jan Suszkiw, Public Affairs Specialist, Agricultural Research Service in Research and Science
Aug 01, 2017
Papayas
Discarded papayas are being examined as part of a zero-waste system to producing algal oils for biodiesel. (ARS photo by Peggy Greb).

Think algae is just slimy green pond scum? Well, think again!

Thanks to advances in science and technology, these microscopic plant-like organisms are now star players in biologically-based approaches to producing fuel for transportation and other energy needs.

In Hilo, Hawaii, Agricultural Research Service (ARS) Plant Pathologist Lisa Keith is leading an effort to produce biodiesel using a type of green algae known as Auxenochlorella protothecoides (formerly Chlorella protothecoides).

Oh, and she’s also using the pulp of discarded papayas, namely, those deemed too blemished, malformed, or damaged to be sold for market.

So how, you may ask, does one go from green algae to papaya to biofuel? 

That’s where the science and technology part comes in—along with support from the state government of Hawaii, which hopes to ease the state’s reliance on imports of petroleum-based oil.

The system devised by Keith and her colleagues calls for growing the algae in giant vats, called “bioreactors.” There, hidden from sunlight, the algae are fed what might be likened to a papaya smoothie.

“While nearly all algae are capable of using energy from light to produce organic molecules from carbon dioxide and water, some algae, including Auxenochlorella protothecoides, can also absorb organic molecules such as sugars from sources such as papaya juice,” explains Keith. She is with ARS’s Daniel K. Inouye U.S. Pacific Basin Agricultural Research Center in Hilo.

In the process, these industrious algae end up storing 60 percent of their cellular weight in lipids. These lipids (or oils), in turn, provide material for making biodiesel.

The algae are like the gift that keeps on giving.

Keith’s team thinks their remains from the oil-extraction process, called “algal meal,” can offer Hawaiian farmers a low-cost source of feed for fish or livestock, cutting importation costs.  The algae’s fondness for papaya also could offer a way for growers to recoup some of the losses on about one-third of Hawaii’s $11-million papaya crop discarded because of defects.

It’s all part of what Keith and colleagues call a “zero-waste” system.

“The goal is to make agriculture more profitable and to address food- and energy-security issues in Hawaii,” she says.

Category/Topic: Research and Science

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Comments

Ahmed Rifat
Aug 03, 2017

There are many health benefits to consuming fruits and vegetables, and papaya is no different. However, there are benefits related specifically to papaya, and some are quite surprising.

zenaida q. tolentino
Aug 03, 2017

I want to know HOW MUCH WOULD BE THE COST PER GALLON OF BIODIESEL USING YOUR TECHNOLOGY. BECAUSE COST IS THE MAIN CONSIDERATION IN THE COMMERCIAL PRODUCTION. THANKS AND BEST REGARDS.

Ben Weaver
Aug 16, 2017

@zenaida q. tolentino - thank you for your comment. We have not calculated the cost per gallon of biodiesel using the zero waste technology. It is currently on our to-do list. It is hard to get an estimate when upstream and downstream processing have been very hands-on and not fully functional with the equipment necessary to complete the process. The main energy inputs as it stands now are for sterilization/cultivation. However, feedstock and land costs have been brought to a minimum.

We have been able to convert the estimated yield calculation to gallons. Our highest yield was 21 g oil/kg papaya, using 35% papaya culture medium. With ~10 million pounds of waste papaya available on Hawaii Island per year, the zero waste/papaya system could produce close to 25,000 gal biodiesel with ~60 metric tons of meal left for feed ingredients.

Brad Reeves
Aug 25, 2017

Why can't this waste be used as food? Have you looked into drying it?