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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

Historians must place African history on world stage – Dr Zeleza
2017-05-30

 Description: Historians must place African history on world stage Tags: Historians must place African history on world stage

From the left: Panellists Rev Henry Jackson,
Prof Irikidzayi Manase and Arno Van Niekerk at a book
launch and panel discussion on Africa Day hosted by the
UFS Sasol Library.
Photo: Mamosa Makaya

“African historians must take seriously the challenge of placing African history in world history, and in the history of our species, Homo sapiens.”

With these words, Dr Paul Tiyambe Zeleza, Vice Chancellor of the United States International University-Africa in Nairobi, Kenya, stressed the continent’s challenge.

According to him the contest should continue to recover and reconstruct Africa’s long history. Liberating African knowledges can be done by: “Provincialising Europe that has monopolised universality, universalising Africa beyond its Eurocentric provincialisation, and engaging histories of other continents on their own terms.”

University celebrates Africa Month in various ways  
Dr Zeleza delivered the ninth Africa Day Memorial Lecture, titled The Decolonisation of African Knowledges, at the University of the Free State (UFS). The lecture, hosted by the Centre for Africa Studies (CAS), took place on 24 May 2017 in the Equitas Auditorium on the Bloemfontein Campus and was one of the ways in which the UFS celebrated Africa Month.

Scholars should immerse themselves in these thoughts

Dr Zeleza focused on two issues, which he said were interconnected. They were the unfinished project of decolonising African knowledges and the continent's positioning in global knowledge production.

He said Africa’s scholars and students should “immerse themselves in the rich traditions of African social thought going back millennia”. According to him the continent’s research profile still remains weak in global terms.

“It is imperative that the various key stakeholders in African higher education from governments to the general public to parents, and to students, faculty, staff, and administrators in the academic institutions themselves, raise the value proposition of African higher education for 21st century African societies, economies, and polities.”

“Colonialism is associated with injustice
and inequality, but what happens when
our liberators become our oppressors?”

Library celebrates with panel discussion and book launch
The UFS Sasol Library celebrated Africa Day by presenting a book launch and panel discussion on 25 May 2017, on the pertinent and current political theme of land redistribution with a comparative basis of land invasions in Zimbabwe.

Prof Irikidzayi Manase discussed his book White Narratives: The Depiction of Post-2000 Land Invasions in Zimbabwe, accompanied by Rev Henry Jackson who wrote Another Farm in Africa. A perspective of the economic implications of land redistribution in South Africa was discussed by panellist Arno Van Niekerk: Senior Lecturer of Economics at the UFS Faculty of Economic and Management Sciences.

Inequality still an African problem
The content of the books are a stark reminder of the burning issues of inequality and loss of identity of those who lost their farms in Zimbabwe, a collection of memoirs by white farmers and their families. Rev Jackson gave a religious perspective on reconciliation, forgiveness and the question of land ownership, saying that healing of injustice begins with forgiveness of past transgressions.

Van Niekerk highlighted that while land issues were important, “social cohesion is affected by the economic decisions that will be made”. In closing, Prof Manase called for serious consideration of what the future may hold. “Colonialism is associated with injustice and inequality, but what happens when our liberators become our oppressors?” 

The panel discussion was attended by staff and students of the university, and was lit up by robust discussions on possible historical and future solutions to the question of land, decolonisation and political power struggles in Southern Africa and lessons to be learned from Zimbabwe.

UFS celebrates Africa Month (24 May 2017)

 

 

 

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