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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

Research into surrogate milk important to wildlife conservation
2017-05-08

Description: Prof Garry Osthoff  Tags: Prof Garry Osthoff

Prof Gary Osthoff from the UFS Department of
Microbial, Biochemical and Food Biotechnology,
will soon work on a milk formula for elephants.
Photo: Supplied

Research is being done at the University of the Free State (UFS) to analyse and synthetically imitate the unique milk of various wildlife species. This research is not only of scientific value, but also serves the conservation of South Africa’s wildlife species. At the forefront of this research is Prof Garry Osthoff from the Department of Microbial, Biochemical and Food Biotechnology.

Orphaned rhino calf pulled through with surrogate milk

“There is still a lot of research to be done. Naturally the research is of scientific importance, but with surrogate milk having the same composition as the mother’s milk of a specific species, orphaned calves or cubs of that species could be pulled through during a difficult time of weaning. Bearing in mind that exotic animals fetch thousands and even millions of rands at auctions, it goes without saying a game farmer will do everything possible to provide only the best nourishment to such an orphaned animal. In such a case, synthetically-manufactured milk would be the right choice,” says Prof Osthoff.

The fruits of his research were recently demonstrated in Germany when a rhino calf was left orphaned in the Leipzig Zoo. Prof Osthoff’s article: “Milk composition of a free-ranging white rhinoceros during late lactation” was used as a directive for applying surrogate milk for horse foals (which is already commercially available), since the composition of horse and rhino milk largely corresponds. The surrogate milk was used with great success and the rhino calf is flourishing. He mentions that such an orphan is often given the wrong nourishment with the best intentions, resulting in the starvation of the animal despite the amount of cow’s milk it devours.

With surrogate milk having the same
composition as the mother’s milk of a
specific species, orphaned calves or
cubs of that species could be pulled
through during the difficult time
of weaning.

Milk formula for baby elephants in the pipeline
With baby elephants left orphaned due to the increase in elephant poaching for their ivory, several attempts have been made to create a milk formula in order to feed these elephants. To date, many elephants have died in captivity from side effects such as diarrhoea as a result of the surrogate formula which they were fed.

Prof Osthoff recently received a consignment of frozen milk which he, together with researchers from Zimbabwe, will use to work on a milk formula for elephants. They are studying the milk in a full lactation period of two years. During lactation, the composition of the milk changes to such an extent that a single surrogate formula will not be sufficient. Four different formulas should probably be designed.

Prof Osthoff says that of the different species he has researched, elephants are the most interesting and deviate most from the known species.

Although his research to develop surrogate milk is adding much value to the wildlife industry, and although he finds this part of his work very exciting, his research focus is on food science and nutrition. “What is currently authentic in milk research is the study of the fat globules with content, the structure and composition of the casein micelle, and the prebiotic sugars. The knowledge which is gained helps to improve the processing, development of new food products, and development of food products for health purposes,” says Prof Osthoff.

 

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