Bioethanol, a biologically produced alcohol, is the most common biofuel globally and is produced by the fermentation of sugars found in various feedstocks such as corn, sugar cane, and sugar beets. With some engine alterations, it can be used directly as a gasoline substitute in vehicles. According to Francisco Boshell, a technology analyst and author of a 2017 International Renewable Energy Agency report, with ‘the right selection of the right raw material about 12 per cent of transport fuel could come from renewable sources by 2030.’
While Bioethanol offers a promising substitute, the transition may not be as smooth as some are hoping for. Crucially, Boshell explains that ‘the right materials might include forest waste such as sawdust, fast-growing trees, agricultural residue, algae, and high-energy crops, such as grasses grown on degraded parcels of land around the world.’
One of the main barriers to the widespread use of biofuels is the water-energy-food-environment nexus. This means the escalation of biofuel consumption could come at the expense of food crops, water, and fertile pastureland. A 2016 study found that, contentiously, ‘bioethanol is mostly produced with domestic crops’ and ‘altogether, biofuels rely on about 2-3 per cent of the global water and land used for agriculture, which could feed about 30 per cent of the malnourished population.’
Energy experts have subsequently been trying to develop ways of maximising the potential benefits of biofuels, without sacrificing the availability of other valuable resources. Recent research led by an international team found that the agave plant, a high-sugar succulent native to arid and semi-arid regions of the Americas, and the base ingredient of Tequila, could offer a solution.
The study, published in the Journal of Cleaner Production, states that: ‘Agave could be a promising bioenergy feedstock given its potentially high productivities, ability to thrive in semiarid regions, high water-use efficiency and low requirements for nitrogen fertilisers.’ When compared to other sources of bioethanol such as sugarcane and corn, it promises some significant environmental advantages and is now being grown as a fuel source on the Atherton Tablelands in Far North Queensland, Australia.
Associate professor Daniel Tan explains that because it can be grown in unfavourable conditions and is not a major food crop, agave causes minimum pressure on food production and water resources. ‘It can grow in semi-arid areas without irrigation; and it does not compete with food crops or put demands on limited water and fertiliser supplies. Agave is heat and drought tolerant and can survive Australia’s hot summers,’ he says.
Lead author Dr Xiaoyu Yan who led the lifecycle assessment, says: ‘The results suggest that bioethanol derived from agave is superior to that from corn and sugarcane in terms of water consumption and quality, greenhouse gas emissions, as well as ethanol output.’
The study found that sugarcane yields 9,900 litres of fuel per hectare each year (more than agave). However, agave outperforms sugarcane on a range of measures, including freshwater eutrophication, marine ecotoxicity, and water consumption. Agave uses 69 per cent less water than sugarcane and 46 per cent less water than corn for the same yield. For US corn ethanol, the yield was lower than agave, at 3,800 litres a hectare a year.
This is promising for Australia; the driest inhabited continent in the world with the largest proportion of semi-arid land. There are hopes that agave can thrive in its vast, unfarmed regions and in addition to fuel, help meet the current demand for hand sanitizer, which requires a high alcohol content.
There may be some way to go, however, as Tan states: ‘The economic analysis suggests that a first generation of bioethanol production from agave is currently not commercially viable without government support, given recent the collapse in the world oil price. However, this may change with the emerging demand for new ethanol-based healthcare products, such as hand sanitizers.’