Carbon Sequestration via Biomineralization: Processes, Applications and Future Directions

Abstract

Carbon dioxide (CO2) emissions from anthropogenic and natural sources contribute to greenhouse gas emissions causing climate change and variability. In recent years, microbially-induced biomineralization of CO2 to precipitate calcium carbonate has been widely explored as a potential strategy to sequester carbon. Several microorganisms occurring in marine, lacustrine and terrestrial ecosystems, including cyanobacteria have capacity to sequester carbon dioxide via biomineralization. Similarly, a number of plant species sequester carbon dioxide through biomineralization. The objectives of this chapter are: (1) to summarize the processes and mechanisms of microbially- and plant-mediated biomineralization, (2) highlight potential applications of biomineralization in CO2 sequestration, and (3) highlight key knowledge gaps and future research directions. Microbially-mediated calcium carbonate precipitation occurs via three main mechanisms: (1) microbially-controlled, (2) microbially-induced, and (3) biologically-influenced biomineralization. Several metabolic processes control biomineralization, including: (1) urea hydrolysis, (2) activity of carbonic anhydrase, (3) microbial reduction of Fe(III), (4) photosynthesis by cyanobacteria fixes CO2, and (5) sulphate reduction. Microbial mats and extracellular polymeric substances (EPS) also play a critical role in microbially-mediated biomineralization. Plant species such as the oxalogenic iroko tree (Milicia excelsa) common in coastal tropical Africa, and several acacia species in Australia have been reported to sequester carbon dioxide via the oxalate-carbonate pathway. Calcium carbonate has a longer residence time in the order of millennia, thus is a more stable carbon pool than organic carbon in soils and live biomass. Accordingly, calcium carbonate formed via biomineralization serves a dual function: (1) in carbon capture and storage systems, microbially mediated biomineralization is used as a benign sealant to avoid escape of CO2 directly injected into deep geological systems, and (2) both microbially-and plant-mediated biomineralization sequester CO2, thus reducing its concentration in the atmosphere. For example, an 80 year-old iroko tree is estimated to sequester 500 kg of carbon in its trunk, and approximately 1000 kg of carbon in the surrounding soil, giving a total of 1500 kg of carbon. Microbially-mediated biomineralization is also used in construction materials, cementation and stabilization of porous materials, sub-surface barriers, aquacultural ponds, industrial filler materials, hydraulic control and environmental remediation. Although not designed to store carbon, these applications also constitute a stable carbon pool, thus contribute to carbon sequestration. However, large scale commercialization of the technology remain low, while the economics, and long-term behaviour of biominerals remain poorly understood.