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15 May 2023 | Story Leonie Bolleurs | Photo Supplied
Spineless Cactus
Axel Tarrisse (far left), a PhD student in the Department of Sustainable Food Systems, working on the biogas and fodder potential of spineless cactus in Africa. Pictured with him are Prof Maryna de Wit, his supervisor and Associate Professor in the UFS Department of Sustainable Food Systems and Development, and Dr Herman Fouché from the Agricultural Research Council.

The spineless cactus is a unique perennial plant that is able to yield close to 40 tons of dry matter per hectare per year with a rainfall of 500 mm per annum. “This equates eight tons of biomethane or 11 000 litres of diesel-equivalent energy per hectare,” says Axel Tarrisse, a PhD student in the Department of Sustainable Food Systems and Development at the University of the Free State (UFS), who is working on the biogas and fodder potential of spineless cactus in Africa.

Tarrisse believes biogas, produced from the spineless cactus, has the potential to complement the supply of South Africa’s existing industrial energy companies to produce sustainable jet fuel and diesel and a variety of other products with the gas-to-liquid process they use.

Developing biogas

He says with rainfall, key nutrients, carbon dioxide, and solar energy it is possible to produce biomass from cactus.

“First, we harvest the cactus and macerate it prior to going into an anaerobic digester where it is heated to 38°C, the same as a cow’s body temperature. Inside the digester, naturally occurring bacteria, similar to those found in their stomachs, break down the cactus, resulting in the production of biogas. This biogas is composed of both methane and carbon dioxide,” he explains.

According to him, biogas generated through this process can be used in a number of ways. This includes running generators to produce electricity or burning it to generate heat. It will also serve as a feedstock to replace coal and natural gas used by companies such as PetroSA and Sasol in their production of synthetic renewable fuels.

“The methane can also be separated from the carbon dioxide and compressed into bottles, creating compressed biomethane. This can be used as a replacement for liquid petroleum gas (LPG), as well as petrol and diesel in vehicles, such as bakkies, tractors, buses, and delivery trucks.”

The carbon dioxide produced in the process can, for example, be used to replace the fossil-based carbon dioxide typically used in the production of carbonated beverages. Additionally, it can be applied to extend the shelf life of packaged foods, serve as a water softener, and even be applied to a variety of industrial applications.

Commercialisation 

Biogas/biomethane is already produced in Mexico on a commercial scale. In Northeast Brazil, farmers have planted 600 000 hectares of spineless cactus, also known as Palma Forrageira, but the machinery needed to harvest it only became commercially available this year.

Back home in South Africa, just 30 km outside of Bloemfontein, Barren Energy farm is at Stage 1 with 140 hectares of high-density cactus planted to provide the initial feedstock for anaerobic digestion. With 600 hectares, they will be able to produce five million litres of diesel-equivalent methane.

Tarrisse says, “With the right methodology and management system, producing biogas from the spineless cactus will be adopted relatively quickly on a commercial scale.”

He believes that the lack of investment in cultivating the spineless cactus as a crop for fodder in South Africa may be due to a few factors. “It is easier to stick to what is known, such as irrigating lucerne and maize and managing these crops with existing planters, pest management solutions, and harvesting machinery than to develop local machinery and management solutions for a perfectly adapted crop,” he says. 

Compelling reasons

According to Tarrisse, there are several compelling reasons to consider the spineless cactus as a source of biogas in South Africa.

Firstly, he explains, “Only the cactus pads, harvested from high-density plantations (20 000 plants per hectares), are used for biogas production.”

“Secondly, the spineless cactus can yield large volumes of biomass from marginal semi-arid land where conditions are unsuitable for conventional crop cultivation. This makes it an ideal option for the 65% of South African land that receives less than 500 mm of rainfall annually.”

Thirdly, he says, “The plant contains 30 to 50% of easily digestible sugars, which degrades easily in an anaerobic digester. This simple, low-tech process can provide a substantial amount of baseload energy with relatively limited capital expenditure, which is particularly important in developing countries such as South Africa where capital is difficult to raise.”

“On top of that, anaerobic digestion only extracts carbon, oxygen, and hydrogen molecules from the cactus, while most of the macro- and micronutrients, water, and some fibres remain in the digestate. This nutrient-rich cactus digestate can then be spread on the cactus fields, reducing the need for fertiliser once the plantation has been fertilised in the first two years of implementation.”

Societal impact

Besides the benefits of producing biogas from the cactus plant, there is also the opportunity of job creation. “This farming can create one million direct job opportunities from only 3% of South Africa’s land area, approximately 4 million hectares,” says Tarrisse.

He is of the opinion that if production was at scale, as opposed to the current small orchard-style farming of cactus, there would be substantial biomass available to sustain not only biomethane, but also to support various bio-industries, such as protein production through cactus fermentation, biomaterials as a substitute for wood-based cellulose, organic acids, and bioplastics. “Consequently, cactus provides a climate-resilient, drought-resistant, and perennial feedstock for food, feed, fibre, and fuel in semi-arid Southern Africa,” he says.

Tarrisse states that this initiative also has the potential to significantly reduce migration from rural to urban areas, therefore addressing issues related to the growth of urbanisation, such as the provision of infrastructure and crime.

News Archive

Researcher in mathematics ranks among world’s top peer reviewers
2016-10-07

Description: Abdon Peer Review Tags: Abdon Peer Review

Prof Abdon Atangana, from the UFS Institute
for Groundwater Studies.
Photo: Johan Roux

Thirty-year-old Prof Abdon Atangana has received the prestigious Sentinels of Science Award 2016. This award honours the highest achievers in peer review across the world’s journals. The elite contributors to scholarly peer review and editorial pursuits internationally are also honoured with this award. Recipients have demonstrated an outstanding, expert commitment to protecting the integrity and accuracy of published research in their field.

Prof Atangana, who ranks number one in the mathematics discipline with a merit of 324, is a professor at the Institute for Groundwater Studies at the University of the Free State (UFS).

He is editor of 17 international journals, editor-in-chief of two international journals and also reviewer of more than 200 international accredited journals. He has been lead and guest editor of some special issues. He is also editor of 19 journals of applied mathematics and mathematics and has presented and participated in more than 20 international conferences.

Prof Atangana’s research interests are methods and applications of partial and ordinary differential equations, fractional differential equations, perturbations methods, asymptotic methods, iterative methods, and groundwater modelling.

“Editors in more than 100 journals
trust my opinion to assess
whether a submitted paper
can be published or not.”

Peer review requires a respected expert in a given field

According to the professor, reviewers play a central role in scholarly publishing. “In the academic field, peer review is the process of subjecting an author’s scholarly work, research, or ideas to the scrutiny of others who are experts in the same field, before a paper describing this work is published in a journal or as a book. The peer review process helps the publisher to decide whether the work should be accepted, considered acceptable with revisions, or rejected.

“Peer review requires a respected expert in a given field, who is qualified and able to perform the review in a given timeframe. Due to the impact of my research papers in the field of mathematics and applied mathematics, and also my international recognition in the field of applied mathematics, many editors in more than 100 journals of applied mathematics trust my opinion to assess whether a submitted paper in a given journal of mathematics and applied mathematics can be published or not. Only this year I was able to review more than 100 papers from different journals of applied mathematics, applied physics, mathematics, engineering and hydrology,” he said.

A successful peer reviewer displays passion for the development of science

Key to his success as peer reviewer is his passion for the development of science, his ability to write fair reports about a given manuscript, as well as his knowledge on what has been done and what are the challenges in a given field to be able to give a report that will help the advancement of science.

Currently he is developing new mathematics tools that will be used to accurately model statistical problems as well as physical problems with many layers.

“To be the number one peer reviewer in the world in mathematics is a product of love, patience and determination to enhance science,” Prof Atangana said.

His advice to young researchers is to put their trust in God and to work hard. “Not necessarily for money but for love because the future of Africa is in the hands of young Africans,” he said.

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