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The spineless cactus, a promising source of sustainable energy

15 May 2023 | Story Leonie Bolleurs | Photo Supplied

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

Questions about racial integration in residences answered

2007-07-31

Answers to frequently asked questions about the racial integration of student residences at the UFS

1. Why does the UFS want to change the current situation in the student residences?

There are many reasons why a new approach to placement in the student residences is necessary. However, the main reason is of an educational nature. As a university, the UFS should create an environment in its residences where students can learn to appreciate and respect the rich diversity that is on offer at the university. A university accommodates students from many different backgrounds in terms of race, language, religion, economic status, culture and other aspects. If a student can learn to appreciate the value in this rich diversity at university, he or she will also be able to appreciate the value of this diversity in the workplace and broader society.

The current situation of predominantly white and predominantly black residences has not been able to cultivate such an appreciation for diversity and respect for one another as human beings, and will not equip students with the knowledge and skills required to manage diversity.

Besides this, there are many other areas of life in the residences that need attention. For one, we need to urgently establish a human rights culture in the residences so that the rights of all students can be respected. We need to address the abuse of alcohol, provide disabled students with their rightful place, and last but not least, really entrench a culture of learning in student residences.

Let us make the residences places we can be proud of – places of learning, of diversity, of respect; places of growth and development. This is the ideal we should all strive to achieve.

2. Why does the management want to force us to integrate?

It is a false argument to debate the issue in terms of “force”. Any decision by a University, or any other organisation, regarding matters of policy, rules and regulations implies a restriction on the choice of an individual and an obligation to comply. What we should focus on is whether this decision of the Council is in the best interests of our students.

The management of the university believes that it has a responsibility to give students the best education possible, not only in terms of what you learn in the lecture rooms, but especially in the residences as well. The residences can be very powerful places of learning about matters of great importance, both academic and non-academic.

The parallel-medium language policy separates students into largely white/Afrikaans and black/English classes. Efforts are being made to bridge this divide in the classroom, but we can also try to eliminate it in the residences.

The university is committed to building a new culture for the entire institution that is based on values and principles – such as an academic culture, non-racialism, respect for human rights and diversity – among staff and students.

In the context of student residences, the application of these values and principles still allows substantial room for the voluntary exercising of choice by individuals as well as by Residence Committees, notably with regard to the placement of students (they can still place 50 percent of first-year students), as well as the determination of the future character and traditions of a diverse residence.

Furthermore, students can still choose their residences (subject to availability of places), can choose a roommate, and so forth.

3. What about freedom of association?

The rights we enjoy in a democracy must be balanced against other rights, as well as the laws of the country. This means that the right to freedom of association must be balanced against laws that make it illegal to discriminate against other people on the basis of race, language or religion, for instance.

Freedom of association pertains to the right of individuals to form voluntary organisations such as clubs or private boarding houses, or their right to join or not join existing organisations. You exercise that right when you decide to become a student of the UFS, and again when you choose to live in one of its residences.

However, once you have decided to join an organisation voluntarily, you cannot subsequently demand that that organisation should provide a “club” or residence to your liking where, for instance, you only associate with your choice of co-members. You must accept the policies of that organisation.

In any case, how would that right of yours be balanced against the right of another individual who wishes to associate with a different set of co-members? (For instance – what about the freedom of a student to associate with students NOT from his own background, but indeed from another language, cultural, racial or economic background?)

The constitutional right to freedom of association can, in any case, not be used to exclude or discriminate on the basis of race or religion (Section 18 of the Bill of Rights).

Besides, the new policy guidelines will still make provision for freedom of association. This right can be exercised freely within a diverse residence with regard to friendships, joint academic work, socialising, sport, etc.

4. Will residences not lose their traditions?

The University appreciates that there are many valuable elements of tradition in residences. However, we must bear in mind that the traditions and character of student residences have evolved and changed over time, and they will continue to evolve and to change. In addition, we do not need to accept all aspects of residence life purely on the basis of tradition, including the unacceptably high level of alcohol abuse and unsavoury, humiliating and discriminatory orientation practices. The new approach to integrated residences provides the opportunity to retain the positive aspects of the current traditions and character, but also to develop new traditions and give residences a new character.

We can now establish a tradition and a character for each residence that are reconcilable with the values of the University as a place of scholarship and are aligned with the human rights approach of our country’s Constitution, the laws of our country and the strengths and diversity of the students in a particular residence.

5. Have students been involved in this process? Is there a role for them to play after the decision has been taken by the Council of the UFS?

In the first semester of 2007, during two rounds of consultations, the primes, SRC and student organisations were consulted about the proposed new placement policy to increase diversity in residences. Some residences also made written submissions on the matter (such as Madelief, Soetdoring, Wag-'n-bietjie, Vergeet-my-nie, Emily Hobhouse). Other residences requested and were granted more time, but did not make any submissions in the end (such as Reitz and Armentum).

Management also had several meetings with the above-mentioned structures to hear first-hand from students their concerns and solutions regarding possible challenges presented by integration in residences.

During these interactions, several excellent ideas and proposals were put forward by students. These views had a definite impact on the eventual proposal that was taken to the University Council, in particular regarding the minimum level of diversity (30%) in junior residences and the fact that residences still want to have a say in the placement of students, rather than the placement decision being left in the hands of Management alone (hence the 50% placement portion of residences). Management values the effort that was put into the process by the primes and residence committees, and thanks them for their contributions.

However, it should be stressed that consultation should not be understood as a process of negotiation, nor does it imply that consensus must be reached. What it means is that Management must take a considered decision after hearing the views of stakeholders.

Management would like students to continue to provide input and ideas regarding the implementation details of the policy guidelines. Task teams have been established and students will be informed about how they can interact with the task teams on an ongoing basis.

6. But integration in the residences was tried in the past (in the late 1990s), and then it failed. Why will it work now?

Yes, the University of the Free State did integrate its residences as far back as 1993, and for a few years it worked. The UFS did it at that time and is now doing so again, because it is the right thing to do. Yet it is important to understand why the previous attempt at racial integration in residences was not successful.

Firstly, both black and white students were much polarised because of the apartheid past. Secondly, there was insufficient management support for students in the residences, the student leaders generally as well as residence heads, in terms of dealing with diversity and related issues. Thirdly, the institutional culture of the UFS and the residences in particular was not addressed as part of broader transformation and integration in residences, whereas it is now being addressed.

In addition, the current decision to integrate residences has the benefit of being implemented after several more years of integration in schooling, sport, workplaces and other aspects of life.

This decision is also based on Management’s commitment to give all the possible support it can to this process.

This is a very important initiative that the UFS is undertaking. Management, in co-operation with students, must ensure that it succeeds. Integrated residences that produce high-quality graduates equipped to deal with the challenges of the workplace and our society is a worthwhile ideal we should all strive to achieve.

If you would like to make a proposal regarding the implementation and practical aspects of the new policy, please send it to the following email address: rector@ufs.ac.za

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