Up to 12 percent of the world’s human-caused greenhouse gas emissions could be sustainably offset by producing biochar from plants and other organic material, according to a new study published in the journal Nature Communications.
"This study demonstrates that biochar can help tackle our climate concerns in a major and sustainable way," says Visiting Professor Stephen Joseph, a biochar pioneer in the UNSW School of Materials Science and Engineering and one of the authors of the study.
"The beauty of the technology is that it is a win-win solution: it can be used to produce energy but at the same time reduce carbon dioxide emission in the atmosphere."
Biochar is made by thermally decomposing agricultural and urban residues such as green waste, chicken manure, rice husks, corn cobs and peanut shells at relatively low temperature in a process called pyrolysis. Many biochars are stable for over 100 years and some biochars even thousands of years, keeping greenhouse gases like carbon dioxide out of the air longer. Normally, such material would break down (compost) and release its carbon into the atmosphere within a decade or two.
The pyrolysis process also produces some bio-based gas and oil that can produce energy offsetting emissions from the burning of fossil fuels.
Biochar can improve soil health and fertility by increasing microbial activity, increasing porosity of the soil, reducing acidity, reducing leaching of nutrients, increasing plant nutrient uptake and by boosting their ability to hold water. It can also reduce nitrous oxide and methane emissions from the soil into which it is tilled, the study notes.
A team led by Dr Jim Amonette, a soil chemist at the US Department of Energy’s Pacific Northwest National Laboratory, calculated the world’s sources of biomass that aren’t already being used by humans as food, such as corn leaves and stalks, rice husks, livestock manure and yard trimmings. They then calculated the carbon content of that biomass and how much of each source could realistically be used for biochar production.
With this information, they developed a mathematical model that could account for three possible scenarios. In one, the maximum possible amount of biochar was made by using all sustainably available biomass. Another scenario involved a minimal amount of biomass being converted into biochar, while the third offered a middle course. The maximum scenario required significant changes to the way the entire planet manages biomass, while the minimal scenario limited biochar production to using biomass residues and wastes that are readily available with few changes to current practices.
The team found that if all available biomass was used to make biochar it could offset up to the equivalent of 1.8 petagrams – or 1.8 billion tonnes - of carbon emissions annually and a total of 130 billion tonnes throughout in the first 100 years.
The estimated annual maximum offset is 12 percent of the 15.4 billion tonnes of greenhouse gas emissions that human activity adds to the atmosphere each year. Researchers also calculated that the minimal scenario could sequester just under 1 billion tonnes annually and 65 billion tonnes during the same period.
* The UNSW School of Materials Science and Engineering has an active group in biochar research. Professor Mark Hoffman, Head of School, strongly supports biochar research for its significant potential national benefits, reflected by the amount of non-government research funding it is attracting. UNSW has a three-year Australian Research Council Linkage Grant with Biomass Energy Services Technology Pty Ltd to advance scientific understanding of biochar (see earlier report here).