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The remarkable power of the prickly pear
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The benefit of using nopal plant matter for creating biofuel is that it is grown for other uses, helping to make efficient use of land and resources (Credit: Getty Images)
A stalwart of the Mexican landscape is finding a second life powering up buildings in the desert, and it is proving to be an unusually sustainable biofuel.
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The landscape could be one straight from a postcard of a Mexican desert. With strong sun almost directly overhead, a green field of cacti cover the dusty surroundings of Camémbaro, a farming community in the state of Michoacan. Nopal, as this type of oval-leafed plant is known all over the country, does not only grow in these lands. Also known as the prickly pear, it can be found all over the Mesoamerican region and it is so emblematic that it has a prime spot on Mexico’s national flag. It is regularly consumed as salad or in healthy shakes, or in less virtuous tortillas and nacho chips. The inedible waste products are normally discarded but in this town, after the cactus had given all it can as a food, people saw the potential of turning this waste into a new fuel source.

In 2009, local businessman Rogelio Sosa Lopez had already succeeded in the corn-made tortilla industry and partnered with Miguel Angel Ake to found Nopalimex, a company that grows cacti as a cheaper alternative to corn. They found that nopal crops produce between 300 and 400 tonnes of biomass per hectare in less fertile lands, and up to 800-1,000 tonnes in richer soils. Nopal also requires minimum water consumption and its waste, if properly processed, can be turned into biofuel.

“We are sowing nopal for three reasons. The first one is social – it creates jobs and prevents emigration. Secondly, from an economic perspective, it reduces the cost of industrial processing of nopal-based products. Lastly and most importantly, there is an environmental reason,” says Ake. The hope is that biofuel from nopal can be a viable alternative to fossil fuels in the region.

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Ake started to explore biofuels more than 40 years ago, but he began to experiment with cacti in 2007. Now, his company is producing enough fuel for the buildings that process all parts of the nopal plant in a sustainable way. But he plans to go further. He has already signed a commitment with the local government of Zitacuaro, in the state of Michoacan, to provide official vehicles, from police cars to ambulances, with cactus-based fuel.

“With the amount of nopal we have in Mexico, and a productivity of over 100 tonnes of gas per acre, we believe that this could eventually replace the traditional use of gas and fuel of non-renewable sources,” he says.

The process is relatively simple. First, the cacti are cut and processed to extract flour, which is used to make tortilla chips. The remaining inedible scraps of the plant are mixed with cow dung in a bio-processor, a fermentation tank that heats the wasted cactus pulp. Then the fuel is distilled from the remaining liquid and collected via tubes and into a tank.

Nopal is used in a number of traditional Mexican dishes, but a lot of the inedible plant matter is thrown away (Credit: Getty Images)

Nopal is used in a number of traditional Mexican dishes, but a lot of the inedible plant matter is thrown away (Credit: Getty Images)

Making use of agricultural waste is likely to play an increasing role in the production of fuels, says Teresa Domenech Aparisi, researcher and lecturer in industrial ecology and the circular economy for UCL’s Institute for Sustainable Resources. “We have to increase biofuels without increasing water consumption,” she says. “The future should look especially at agricultural and industrial waste.” This cactus-based method of fuel production is a very good example, she says, because any type of agricultural product often generates a huge amount of waste after harvest.

When it comes to nopal cacti, they are very useful to produce fuels, because they are a high source of sugars, which is really important to produce biofuel – Juan Francisco Perez

One of the appeals of this process is that it gets around a major pitfall in the conventional production of biofuels. Crops such as corn, sugar cane, soybean and palm oil, which make up 97% of biofuels worldwide, are often grown in large monocultures. This takes up land that could otherwise be used to produce food, destroys habitats and leads to less balanced ecosystems. It also leads to intense pressure on water resources, and has been linked to drought.

The appeal of Ake’s cactus system is that it makes use of waste from another industry, rather than growing a crop specifically for fuel. “You have the product but also the by-product, which can be a source of energy,” Domenech Aparisi says.

Round trip

The shift towards cactus biofuel is part of an effort to move away from the idea of “waste” as something useless that you must dispose of. “Currently we have a very linear system, so you extract products from nature, you transform them and in a very short period of time, sometimes a bit longer, they end up in waste,” says Domenech Aparisi. “In a circular economy you try to maintain the resources, materials and products in the system for as long as possible, and then you have waste to regenerate those resources and recover them for the system.”

Another good example of how biofuels could work in a circular economy is coffee. Nearly 500,000 tonnes of coffee grounds are thrown away every year in the UK. In Scotland, two entrepreneurs are using the remaining coffee grounds to extract oil as a sustainable alternative to palm oil. Elsewhere in the UK, the clean technology company Bio-bean is collecting coffee waste and turning it into fuel.

Since 2017, researchers at the University of Coventry have been studying how different innovative approaches to coffee could help us move towards sustainable societies. In one project, they found that from a circular economy perspective, roasted coffee grounds can be reused as the basis of some composts and are a good basis to grow mushrooms on. However, their findings also showed that there is still little waste management across the industry.

If biofuel industries are to become truly circular, there are still some significant obstacles. “One of the problems is the infrastructure to collect and then actually extract energy from biomass,” says Domenech Aparisi. This includes both at an individual and industrial-waste level. “Scaling this up doesn’t happen because in many places people aren’t considerate about waste. So how do you actually define the structure and the governance around this to make it happen?”

Green gold

Back in Mexico, Juan Francisco Perez has been researching how to produce biofuels from different plants for over a decade. He now leads projects at the national research centre, Cinvestav, looking into different types of food waste for energy production.

It is precisely because nopal is used in cooking that makes it a particularly sustainable biofuel (Credit: Getty Images)

It is precisely because nopal is used in cooking that makes it a particularly sustainable biofuel (Credit: Getty Images)

“When it comes to nopal cacti, they are very useful to produce fuels, because they are a high source of sugars, which is really important to produce biofuel and bio-methane gas. It is also very convenient because in Mexico we have many lands that are arid semi-desert, so it is impossible to have other kinds of crops,” says Perez. “Nopal uses very little water.”

Nopal’s multiple properties has led Ake to describe this type of cactus as “green gold”. So far, Nopalimex is running on the energy they produce from biogas. “We are already producing between seven and eight tonnes of tortillas with nopal and nopal-produced energy every day, but researchers and farmers are still developing different uses for this cactus, for example as an alternative to plastic wraps, fabrics and resins,” says Ake.

Yet they are not stopping there. Ake says that researchers are looking into using avocado waste in the state of Michoacan and Sargasso as potential sources of biofuels.

Although they all share optimism that biofuels can play a role in replacing fossil fuels, Domenech Aparisi considers that expectations should be more realistic. “They won’t fully replace them, we will have renewable technologies, and biomasses will have a percentage within those technologies to replace fossil fuel,” she says. “We are already in a transition to low-carbon economies but biofuels will not be the only solution. It will have to be combined with other forms of energy generation from renewable resources.”

This is particularly important because waste-based biofuels are among the most sustainable kind of fuel there is, says Danay Carrillo, a biofuels researcher at the Monterrey Technologic Institute in Mexico. “For biofuels to be sustainable it is very important to give them at least a first use for human consumption, instead of growing organic materials only for fuel production, which would only increase water consumption and land use,” says Carrillo.

So we shouldn’t be surprised to find more and more waste products gaining a second life as a fuel source, be they cactus trimmings or coffee grounds. In fact, if we are going to make biofuels a core part of the energy mix, we need them to. With the aid of such strategies, Carillo estimates that in as soon as a decade organic-waste biofuels could all but replace non-renewable energies in Mexico.

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