Research led by the U.D. Department of Agriculture (USDA) scientists is looking at how to encourage algae in to producing oil from waste papayas and other unmarketable crops or byproducts such as glycerol. The lead scientist for the project is Lisa Keith, a plant pathologist with USDA’s Agricultural Research Service (ARS). The experiments are taking place in Hilo Hawaii and utilizing Chlorella protothecoides algae. They are part of larger efforts to reduce Hawaii’s need for imported oil and energy through zero-waste systems.

Keith’s research uses specialized vats called “bioreactors,” which allow for the growth of 150 liters’ worth (approximately 40 gallons) of algae. Her team selected “UTEX 249,” a top-performing strain of C. protothecoides that can store as much as 60 percent its cellular weight in lipids when grown—in the absence of sunlight—on a diet of 35 percent papaya juice.

In addition to sugar, papaya juice contains carbon, a critical but costly component of current algal-based methods of producing oil for conversion into biodiesel. The zero-waste system only uses unmarketable papayas, which account for one-third of Hawaii’s $11-million crop and represent a substantial revenue loss for growers there.

Keith has been awarded a $1.6 million grant for the project from the Hawaii Department of Agriculture’s Agribusiness Development Corporation.