Ammonia (NH 3) emissions during drying of untreated and dewatered biogas digestate in a hybrid waste‐heat/solar dryer.

Digestate from the biogas digestion process contains high amounts of water and nitrogen, which can lead to over-fertilization problems in regions with intensive livestock farming due to a surplus of ammonium, which contributes to the global warming effects. The best option to reduce thewater content aswell as to concentrate the nitrogen is to dry digestate; however, volatile nitrogen present in the digestate has the tendency to be emitted. Therefore, the objective of this study was to investigate the emissions of untreated and dewatered digestate during the drying process and to determine the nitrogen loss of the drying product by calculating the loss over time by the emissions and compare it with initial and final ammonium content made by chemical analysis. The drying procedure was performed in a hybrid waste-heat/solar dryer.Ammoniaratewas measured continuously during drying by Fourier transform infrared spectroscopy. Untreated digestate showed higher cumulative emissions of ammonia (25.9 gNH3 kgDM −1) than dewatered material (7.75 gNH3 kgDM −1) due to lower water content and shorter drying time. Emissions fromthe filtratemay still be an issue, which should be addressed in future studies.