During the processing of biomass as well as during waste water treatment, residual materials with a high water content are produced. They must therefore be dried prior to thermal utilization. Classical drying processes often use fossil raw materials to generate the necessary energy. With sour gas-based drying based on carbon dioxide-air mixtures, an alternative is presented that considers CO2 as a valuable raw material (second life) and uses it in the process for drying sewage sludge and fermentation residues. Especially in the drying of fermentation residues, significant differences in dry substance content (DS) were measured, which in individual cases amounted to up to 35 % DS with the same drying time. This is expressed, among other things, in a higher carbon content of 0.42 wt % (wf) in the dry material, accompanied by a heating and calorific value that is more than 1 MJ kg(-1) higher.