figues de barbarie

Biofuels… from Prickly Pears

(Fr: Biocarburants produits de figues de barbarie)

Biofuels are a great idea, but making them mostly from corn is a bad idea. Corn is a water-intensive crop, and dedicating hundred of thousands of acres to growing fuel instead of food isn’t the smartest use of resources for a planet that is low on both fresh water and food.There’re a lot of start-ups nowadays which are specialized more and more in clean energy, biomass waste, wind power from photovoltaics etc. We wrote last year about how biofuels from coffee grounds could help to power London or  even how to produce fuel from whisky residues.

The knowledge that most of people have about the prickly pears is limited. People see the prickly pears just as an an exotic fruit with a special flavor that requires some skill to clean in order to not cause any injury. On the contrary, some  UK researchers considered prickly pear the perfect biofuel source because cacti don’t require much water. But why is that? Turns out the secret is crassulacean acid metabolism (CAM).

Prickly pear is a term used to refer to several species of cactus belonging primarily to the genus Opuntia. In general, these species present an exceptional ability to produce biomass in soil and climate conditions unfavorable for most plant species, in part due to their high water use efficiency. Given the current increase demand for renewable energy and the future prospect of more limited water resources, the potential use of prickly pear cladodes for biofuel production deserves to be investigated.

The idea came to Nopalimex’s Rogelio Sosa about a decade ago when he was looking for ways to lower the energy bills for his company, which manufactures corn and cactus chips.

Nopalimex has built the world’s first cactus-powered plant in Mexico. The company is utilizing a digester to make biogas from prickly pear cacti. In addition to powering Nopalimex’s operations, the digester’s 8-ton daily production will fuel the town of  Zitacuaro’s vehicle fleet in central Michoacan state, Noticias MVS reported.

According to a study ($) ,the estimated potential of ethanol production for prickly pear (1490–1875 L ha−1 yr−1) was low when compared to traditional biomass sources (sugarcane and sugar beet, for example). However, it appears that prickly pear stands out as a biomass with potential for high production rates of methane (3717 m3 ha−1 yr−1), being comparable to traditional energy crops. Further studies are needed to assess more consistently both the sustainability of biomass production as the potential for ethanol, and biogas production, specially for newly released varieties of prickly pear.

How does one go about turning prickly pear into biogas? You harvest the fin-like pads, which just happen to have the percentage of fibrous material that is the sweet spot for anaerobic digestion. This is the process by which microorganisms break down organic material in the absence of oxygen. Prickly pear pads are ideal because they degrade quickly—five to ten times faster than manure. This means the time needed to convert the plant material to usable gas is . . . I don’t know, because Google wouldn’t tell me. But it’s shorter than for many other plants.

The only sticking point is the fact that biogas is mostly methane. Methane is a greenhouse gas. When it is burned it also emits carbon dioxide. However, biogas advocates like to remind people that this is still better than burning fossil fuels because the cactus absorbed carbon from the air while it was growing. Thus, it emits the same amount of carbon that it has recently absorbed, making it carbon neutral.

It is worth noting that the water quantities that have been absorbed for the development of the prickly pear after its  digestion and biogas production, it is  secreted, thus generated, and moist or solid fertilizer are produced in their turn whichcan contribute to the development of food crops which it would not have obtained under normal conditions .

One owner of a prickly pear biogas facility in Chile, Rodrigo Wayland Morales, told Renewable Energy World he sees vast potential for the crop. He has cactus biogas projects in various stages of completion in Mexico, India, Chile, Brazil, Ecuador and Colombia.

Sources: Renewable Energy World, Science Direct, Ecowatch.com, Climatechange.news, researchgate.net

  • Read: 

Agricultural Production of Prickly Pear Cactus for Biomass in the Intermountain West

 

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