The impact on stripping observed using those alternative gases (Fig. 4a) could be well explained by their CO2 content. The final stripping degrees after 4 h (Fig. 4b) were 45% and 16% for flue gas and biogas, respectively, whereas 86% ammonia-nitrogen removal was achieved through air stripping. The pH increase (Fig. 4c) during the beginning of a stripping run was lowered at higher CO2 concentration in the gas stream leveling to 8.8 (air), 8.3 (flue gas) and 8.0 (biogas stripping).