By With fuel prices skyrocketing, pushing the cost living high in South Africa, the latest discovery by 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; that the spineless cactus is a promising source of fuel is very much welcomed.
According to Tarrisse, 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. He says that equates to eight tons of biomethane or 11 000 litres of diesel-equivalent energy per hectare.
Tarrisse is convicted that the energy industry can benefit from the unique plant, as it has the potential to supply the industry and produce sustainable jet-fuel and diesel and a variety of other products with the gas-to-liquid process they use.
For the cactus to be able to produce biomass, Tarrisse says it needs rainfall, key nutrients, carbon dioxide, and solar energy. Explaining the processes in producing fuel from the plant, Tarrisse said:
“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 Tarrisse, 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.” He said.
The PhD student says 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.
As one can imagine, the discovery has commercial potential which can be referenced to Mexico, as they are one of the biggest markets producing biogas/biomethane, Europe is the largest by far. According to Tarrisse; 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.
He says 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.
“With the right methodology and management system, producing biogas from the spineless cactus will be adopted relatively quickly on a commercial scale. 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 said.
Tarrisse said 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, 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,” explained Tarrisse.
The venture of producing biogas comes with the potential of creating job opportunities. “This farming can create one million direct job opportunities from only 3% of South Africa’s land area, approximately 4 million hectares,” he explained.
