Terrestrial Storage of Biomass (Biomass Burial): a Natural, Carbon-efficient, and Low-cost Method for Removing CO2 From Air

Abstract

Terrestrial Storage of Biomass (TSB) is a Negative Emission Technology (NET) that can remove CO2 already in the atmosphere. TSB is compared to other NET’s and shown to be a natural, carbon-efficient, and low-cost option. Nature does the work of CO2 removal by growing biomass via photosynthesis. The key to permanent sequestration is to bury biomass in underground pits designed to minimize decomposition. The chemistry of biomass formation and decomposition is reviewed to provide hints on how decomposition can be minimized. Based on the chemistry, several best practices of TSB pit design are provided. While decomposition can be minimized, some decomposition is expected. By analogy to municipal landfills, any decomposition that does occur will take place in several distinct sequential chemistry phases. The last phase is an anaerobic decomposition phase which produces a biogas having a CH4:CO2 ratio of about 1:1. Methane formation has been raised as a concern since it has a greenhouse gas potential about 25 times that of CO2. This concern is shown here to be unfounded due to a great mismatch between the time constants for methane formation and its removal from the air by ozone oxidation. Methane has a very short lifetime in air of only about 12 years. For municipal landfills, the rate of methane formation is known to undergo an exponential decline at its onset. This leads to an asymptotic fraction decomposed that is substantially less than one before the landfill goes dormant. Landfills can take decades to reach dormancy. Methane formation is spread over that timeframe. For wood slash from the logging industry, the initial targeted feedstock for TSB, methane formation may last hundreds to thousands of years. Woody biomass is inherently slower to decompose than most substrates in municipal waste due to the cross-linking and dense packing of cellulose which means attack can only occur at the surface. A model was developed that couples the slow and exponential decay of the rate of methane formation with fast removal by oxidation upon entering the atmosphere. The model shows that methane remaining in the air will peak at a very small fraction of buried biomass carbon within about 10 years and then rapidly decline towards zero. The implication is that no additional equipment needs to be added to TSB projects to collect and burn the methane.

Keywords: Carbon dioxide, methane, sequestration, terrestrial, storage, biomass, burial, bioethanol, olivine, enhanced weathering