A so called “carbon sink” is any kind of reservoir, that takes CO2 temporally or permanently out of the air. Lowering the CO2 amount in the air lowers the greenhouse effect and is a key challenge to stop the global crisis of climate change.
Biomass has adsorbed CO2 via photosynthesis. By regular composting of biomass waste (or burning it for energy supply), the CO2 gets released to the air again. The RE-DIRECT approach offers an actual carbon sink by producing carbon products from biomass waste so that CO2 does not get released again at least for a longer time period.