Biofuel from Zanzibar jungle

 By Robin Wylie

African researchers found that tubers from two kinds of tropical plant, could provide a new source of bioethanol. The two plants found to be useful are the Zanzibar Yam and the plant Pyrenacantha kaurabassana, a flowering tree found in many tropical regions, which previous research suggested may contain anti-HIV compounds. Importantly, as these tubers are inedible, this would overcome the common problem of “competing uses” in bioethanol production, potentially making the process cheaper.

Two tropical shrubs found in the African rainforest could provide a previously untapped source of renewable energy, according to new research from Tanzania.

The plants, Dioscorea sansibarensis (commonly called the Zanzibar Yam) and Pyrenacantha kaurabassana (which doesn’t seem to have an English name!), are widespread in the wetland forests of sub-Saharan Africa. They’re both inedible. But researchers from Dar es Salaam, Tanzania’s largest city, have found that these unassuming shrubs could have a different use, as a source of renewable biofuel.

In a paper published this month, scientists showed for the first time that the tubers of D. sansibarensisand P. kaurabassana can be used to produce bioethanol — an alcoholic hydrocarbon that is made by the fermentation of organic matter.

Before this discovery, the Zanzibar Yam had received scant scientific attention, though in parts of Africa it has long been thought to possess magical powers. P. kaurabassana, on the other hand, had already shown promise as a treatment for HIV. Neither one, however, had been considered as a candidate for biofuel production.

Bioethanol – which is chemically identical to the ethanol found in most alcoholic drinks – is the world’s most popular biofuel. It is most commonly used in motor engines, where it can completely or partially replace standard petroleum. Fuels containing bioethanol (such as ENI’s “E85″ fuel, a mixture of 85% bioethanol and 15% petrol) offer numerous advantages over regular fuel. According to the United Nations Conference of Trade and Development’s “The State of the Biofuels Market” report, not only are these fuels less toxic, but they can also have a lower carbon footprint. While burning bioethanol does release CO2, because the plants used to produce it absorb CO2, the effect is partially offset.

Many of the crops used to produce bioethanol, most notably sugarcane and corn, are also vital foodstuffs. Competition with agriculture drives up the price of bioethanol, and is one of the main barriers to its expansion as a fuel source. Seen in this light, the discovery in Tanzania looks especially important. The Zanzibar Yam and P. kaurabassana are not used at all in agriculture, so could potentially be exploited for bioethanol without stepping on any farmer’s toes. What’s more, since the shrubs already grow abundantly in the wild, production costs for any derived fuel would be massively reduced.

“These tubers are readily available in the tropical forest … they can just be collected and used for bioethanol production without the cost of growing them,” Anselm Moshi, lead author of the study, told EniDay.

In recent years, the African biofuel industry has been booming. In 2011 (the latest year for which data are available), the continent exported over 100 million liters (26 million gallons) of biofuel – compared to just 20 million liters (5.2 gallons) in 2007, most of which was derived from sugarcane and Jatropha, a flowering plant whose oil-rich seeds can be used to produce “biodiesel” (which ENI also produces at its “Green Refinery”). The discovery of two new sources of renewable energy growing wild in its forests bodes well for Africa’s biofuel future.

This Infographic by showing the share of population without electricity access and the major energy infrastructures in Africa

Energy in Africa today (source: Iea 2014)
about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.