A co-firing process is described using coal and processed biomass to reduce adverse by-products in a coal combusting apparatus. The coal feedstock is selected from coal, a coal substitute processed biomass, or an aggregate blend of coal and processed biomass. The biomass feedstock comprises processed biomass pellets. The total energy density is predetermined and can be similar to the coal component or higher than the coal component. The intracellular salt in the processed biomass is at least 60 wt % less for the processed organic-carbon-containing feedstock used to make the processed biomass pellets than that of the starting un-processed processed organic-carbon-containing feedstock.