New analysis from UK researchers could provide sustainable bioenergy for the future

New analysis from the Department of Engineering Science, Department of Plant Sciences, Tropical Power, Imperial College London and the Royal Botanic Gardens at Kew, say that CAM species like Opuntia ficus-indica (prickly pear) and Euphorbia tirucalli could make a huge contribution to providing sustainable bioenergy for the future.

Traditional biofuels such as bioethanol are made from food crops like corn and sugarcane that require prime agricultural land – a commodity in relatively short supply. Competition between food and fuel crops means that large scale bioethanol production is therefore controversial.

Department of Engineering Science DPhil student, Mike Mason, who led tMike Masonhe research said: “Plants that perform photosynthesis using crassulacean acid metabolism (CAM) may enable bioenergy production without disrupting food supplies. CAM plants are adapted to grow on arid and semi-arid land, where low or unpredictable rainfall makes conventional agriculture difficult. Semi-arid land is estimated to take up 12–18% of the world’s land area and while some of this is already used for farming, much of it is relatively unproductive grazing land. CAM plants can flourish here by conserving water more effectively than traditional crops – they capture carbon dioxide from the air at night and convert it to malate, which fuels photosynthesis during the day. By avoiding the need for gas exchange during the day, they reduce evaporative losses through their leaves and so require much less water per unit of biomass than other plants”.

Mike Mason added: “Electricity production from biogas is incredibly flexible, you can bring it up or down as demand goes up and down. The problem is that there isn’t much resource to turn into biogas and it’s horribly expensive. But CAM plants, which can be grown cheaply on marginal land, have the potential to change this”.

Euphorbia tirucalli growing as a test plot in Northern Kenya (photo courtesy of Tessy George and Live Energies GmbH)
Euphorbia tirucalli growing as a test plot in Northern Kenya (photo courtesy of Tessy George and Live Energies GmbH)
Research analysis reveals that it would take between 4% and 12% of available semi-arid land to generate 5PWh of electricity per year, equivalent to that generated globally from natural gas. The products of anaerobic digestion, nutrient rich wastewater and solid digestate, can be re-used for irrigation or as fertilisers. The wastewater could also be used for highly productive forms of aquaculture – potentially increasing food production from land growing biofuels instead of decreasing it.

Professor Ian Thompson from the Department said: “The potential of CAM plants as a feedstock is enormous, largely been overlooked and could revolutionise our thinking in terms of sustainable energy”.

Although a very few of the perhaps 15,000 species of CAM plants, such as pineapple and agave, are currently cultivated on a large scale, they are not currently employed for biogas production and little research has been done on their energy potential. Mike Mason said: “We are with CAM plants where we were with cereal crop development 10,000 years ago. There is no doubt that plant science and breeding improves crops, so with increasing research interest and sustainable electricity in ever greater demand, that situation might change quickly, and even greater yields and lower costs may be possible”.

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