a green process and system are disclosed for utilizing a biomass filter aid in the filtration of a bio - oil . the process comprises filtering a bio - oil containing residual solids from a conversion reaction in the presence of the biomass filter aid to produce a filtered bio - oil . the biomass filter aid facilitates efficient removal of residual solids from the bio - oil . the spent biomass filter aid containing the residual solids may be recycled as a conversion feedstock or used as a combustion heat source in the biomass conversion system .