It is clear that the use of biomass residual biochar as fertiliser and carbon sink is one of the most effective methods to mitigate greenhouse gas emissions of CH4, CO2, N2O and NH3. The project describes a new method where biochar is added in the composting process to produce fertilizer in a sustainable way. The manure so produced can then be used in agriculture and then reduce greenhouse gas emissions. The project will, through experiments, determine the optimal conditions for composting by varying the amount of biochar and particle size, biomass type and pyrolysis temperature, etc. The composting trials will be conducted in a 6-liter bioreactor at Mid Sweden University. The results from the optimization in bioreactor will be scaled up to the 1.5 m3 pilot bioreactor for composting borrowed for the project. A life cycle assessment (LCA) will be used to carefully evaluate each parameter that can affect greenhouse gas emissions in the process chain.