Could Papayas Help Hawaii Become Energy Independent?

Papayas are big business in Hawaii. In 2016, the islands produced nearly 20 million pounds of the tropical melon, valued at an estimated $10 million. The Hawaiian papaya is also highly controversial. After the papaya ringspot virus decimated the island’s crop three decades ago, much of the fruit grown there today has been genetically modified to be resistant.  For Hawaiian farmers, selling the papayas can be difficult. Countries are often reticent to import genetically modified crops. Farmers also face an uphill battle because of the high cost of imported fertilizers. But even more problematic is waste. Approximately a third of the Hawaiian papaya crop is discarded because it’s bruised or misshapen. Farmers throw out these otherwise saleable crops when margins are already thin. Lisa Keith, a plant pathologist with the USDA in Hilo, Hawaii, may have a solution. Keith and her team of researchers have been gathering leftover papayas from local packing houses and turning them into a fuel that’s used to produce biodiesel. It’s a surprisingly simple process that includes adding algae to large tanks that contain a sterile pureed papaya solution, where a process called heterotrophic growth takes place—in the absence of sunlight, algae feed on the sugar in the papaya. When the algae becomes starved of nitrogen after depleting the nutrients in the puree, it stimulates lipid production, which causes the lipid cells to balloon up with oil in just under two weeks’ time. These oils can be used for biodiesel production after the glycerol present in the cells is extracted.