In an earlier post, I compared a number of methods, including using biochar and olivine as soil supplements, biomass burial in sea or on land, BECCS (BioEnergy with Carbon Capture and Storage/Sequestration), etc.
Pyrolyzing biomass and then adding the resulting biochar to soil can remove CO2 from the atmosphere and can avoid many emissions that would otherwise occur.
By contrast, both composting or burying biomass will each result in more emissions, since the biomass will decompose and that will add CO2 and CH4 to the atmosphere. When biomass is buried, it may take a bit longer before it will decompose, but decomposition will eventually occur, and such emissions will be more and it will typically occur earlier than in the case of biochar, which can remain in the soil for hundreds if not thousands of years.
As temperatures keep rising, there's increased risk of flooding (causing more CH4 emissions) and of wildfires (which besides emissions of CO2 and CH4 also come with soot and CO emissions). This growing risk makes biochar an increasingly attractive method.
Turning biowaste into biochar through pyrolysis and then adding the biochar to soil can prevent wildfires in two ways: firstly, because the biomass is removed from the land, this biowaste can no longer fuel wildfires; and secondly because the biochar increases the soil's capability to retain moisture and helps soil become more fertile, thue result is more and healthier vegetation growth (and thus CO2 capture) while the extra moisture in the soil gives additional protection against wildfires.
Biochar is also beneficial in regard to flooding. Firstly, the biochar makes that the soil can absorb more water. Secondly, the healthier vegetation that results from biochar will be deeper rooted and can better withstand flooding in general and this will in turn also prevent erosion.
Soil becomes more fertile when adding biochar to soil, which makes that application of pesticides and chemical fertilizers can be reduced and avoided. Nitrogen fertilizers are responsible for dead zones in lakes, seas and oceans, and for N2O emissions. Adding a combination of biochar and olivine sand to soil can make the soil become more fertile (without adding chemical fertilizers), enabling both the olivine and the healthier vegetation to take more CO2 out of the atmosphere. It can be economic to add both biochar and olivine sand to soil simultaneously, which can reduce the overall cost of adding soil supplements and keeping vegetation healthy in general.
Heating up biomass through pyrolysis can turn half the carbon that's contained into biomass into biochar, while turning the other half into bio-oil and syngas. As said, this will avoid emissions of greenhouse gases that would oterwise occur when the biomass was left to decompose or get burned in wildfires. The energy needed to heat up the biowaste can come from the biomass itself, but it can also come from clean power sources such as wind turbines.
The other half of the carbon that goes into bio-oil and syngas can be burned for energy, but it can also be turned into hydrogen, carbon, oxygen, etc. The hydrogen can then be used as clean energy, while the carbon can be used in construction or to produce carbon fiber, graphite, etc.
In conclusion, adding biochar to soil can remove CO2 from the atmosphere and can avoid many emissions that would otherwise occur, all with little or no emissions, at least for a very long time. This makes biochar an excellent method to reduce levels of carbon dioxide in the atmosphere and to avoid greenhouse gas emissions.
Biochar is discussed in more detail at the Biochar group.
[ Earlier posted at the Geoengineering group and added at the Biomass page ]