Large volumes of ammoniacal nitrogen enter the municipal sewage through wastewater from households and commercial enterprises. Protein compounds from microorganisms that are contained in the sewage decompose into ammoniacal nitrogen. Another important source of ammoniacal nitrogen in sewage is urea. This is introduced in great quantities into the sewage through human and animal feces. For example, urea is developed in the human metabolism through the decomposition of proteins. Large quantities of nitrogen fertilizer are used in agriculture. Normally only part of the nitrogen fertilizer is absorbed by the plants. Some of the excess nitrogen is washed away by the rain. When rainwater or surface water enters the sewage system, this can lead to considerable contamination of washed-out ammoniacal nitrogen.
The volatile residual ammonia found in sewage sludge changes from liquid to gas during the drying process due to the impact of the hot gas. The admixture of sulfuric acid, which is integrated into the dryer by the process control unit, binds the ammonia completely. Crystalline ammonium sulfate is produced with the molecular formula (NH4)2SO4. The procedure means that the ammonia present in the exhaust gas is no longer detectable. The integrated exhaust gas treatment in the dryer completely replaces the stripping process or comparable exhaust gas treatment, achieving a significantly higher degree of cleaning.