In the quest to mitigate climate change, scientists are exploring innovative carbon dioxide removal (CDR) techniques that not only capture carbon but also contribute to soil restoration. A recent study published in the journal “Frontiers in Climate” (translated from German) sheds light on the promising combination of enhanced rock weathering (ERW) and pyrogenic carbon capture and storage (PyCCS), also known as biochar carbon removal. The research, led by Maria-Elena Vorrath from the Institute for Geology at the University of Hamburg, offers insights into how these technologies can be synergistically applied to create more effective carbon sinks.
The study, titled “Pyrogenic carbon and carbonating minerals for carbon capture and storage (PyMiCCS) part II: organic and inorganic carbon dioxide removal in an Oxisol,” investigated the co-application of rock powder and biochar, as well as the production of rock-enhanced (RE) biochar through co-pyrolysis of rock powder with biomass. The experiment involved incubating these materials in a clay-rich, nutrient-poor Oxisol under different carbon dioxide levels and simulated rainfall conditions.
“Our goal was to quantify the carbon sink development of these combined approaches and understand their long-term potential,” Vorrath explained. The results were promising, showing strong initial fluxes of total alkalinity, dissolved inorganic carbon, dissolved organic carbon, and major cations, which decreased over time. Notably, elevated CO2 levels had minimal impact on the release of dissolved organic carbon but doubled the total alkalinity flux from enhanced rock weathering.
One of the key findings was the impact of waterlogging on water fluxes in soil columns without biochar, which reduced the amount of leached cations from rock and biochar. This highlights the importance of biochar in improving soil structure and water retention. “Biochar increases water-holding capacity, prevents waterlogging of soils, and likely improves the retention of organic carbon in soils,” Vorrath noted.
The study defined the carbon sink to include all dissolved inorganic carbon of geogenic and biogenic origin, as well as pyrogenic carbon from biochar. Biogenic cations were not considered as contributing to additional CO2 sequestration. For a soil application equivalent to 12 tonnes per hectare, the total net carbon sink ranged from -0.1 to 30.9 tonnes of CO2 per hectare after 27 weeks under 1.2% CO2. A 20-year forecast suggests net carbon sinks between 0.5 and 28.7 tonnes of CO2 per hectare, driven by increased contributions from weathering, alongside a carbon sink loss due to biochar mineralization.
While biochar alone generally produces a larger carbon sink, the co-application with rock powder fosters soil remineralization and provides a higher permanence of the carbon sink. This research could have significant implications for the energy sector, particularly in the development of carbon capture and storage technologies. The combination of ERW and PyCCS offers a dual benefit: not only does it enhance carbon sequestration, but it also improves soil health and fertility.
As the world seeks sustainable solutions to combat climate change, the findings from this study provide a glimpse into the future of carbon removal technologies. The synergistic application of enhanced rock weathering and biochar carbon removal could pave the way for more effective and sustainable soil restoration and carbon sequestration strategies. Vorrath’s research underscores the potential of these combined approaches to contribute to a more resilient and carbon-negative future.