Biomass composting with gaseous carbon dioxide capture

Abstract

Biomass carbon removal and storage (BiCRS) technologies must scale rapidly to mitigate climate change via the removal of carbon dioxide (CO₂) from the atmosphere. BiCRS technologies passively concentrate atmospheric CO₂ and thus greatly reduce energy demands for atmospheric carbon removal, relative to direct air capture (DAC) technologies. Composting with gaseous CO₂ capture is an overlooked BiCRS technology with significant potential for atmospheric carbon removal. For the first time, we demonstrate the capture of high purity gaseous CO₂ from biomass composting. Biomass is composted in simple, closed reactors with automated cycling of air or oxy-fuel to generate gaseous streams with CO₂ concentrations varying between 18 and 95%, which are significantly higher than the CO₂ concentration of air (∼0.04%); the minimum thermodynamic energy needed for CO₂ capture from composting is 72–98% lower than that for the capture of CO₂ directly from the air. Genomic data indicate microbial diversity decreases with the use of oxy-fuel relative to air. Globally, the composting of food waste could capture 0.3–1.0 billion tonnes of biogenic CO₂ per year, and the inclusion of other biomass feedstocks could increase the total capture rate to more than 3.5 billion tonnes per year.