Ammonia and methane emissions during drying of dewatered biogas digestate in a two-belt conveyor dryer.

Aim of the present study was to identify type and amount of emissions during the drying of biogas digestate in a two-belt conveyor dryer at different temperature settings and to investigate the effect on its nutrient content. Furthermore, the possibility of recovering nitrogen from the exhaust air was investigated. Emissions of CH, CO and NH were measured by Fourier transform infrared spectroscopy. Biogas is mainly composed of CH and CO, hence gas release from the digestate during drying was expected to increase the concentration of these components. Although CO concentration was elevated above the background concentration, CH did not exceed the background concentration. Maximum NH concentration of 183.3mg·m was detected during drying. A NH concentration of 10.8mg·m was measured in the exhaust air of the ammonia scrubber, which is equal to a NH reduction rate of 94%.