N-Dynamics During Composting — Overview and Experimental Results

Abstract

The theor. of the processes most important for N dynamics during composting are described, focusing on ammonification, nitrification, denitrification, immobilization and N released via leachate and waste gases. Expts. were carried out in a lab. composting unit with 100-​L bioreactors to evaluate their importance in composting. The composting parameters, such as water content, aeration, pH and temp. were evaluated with respect on their effect to the processes of N dynamics. Ammonification was lower during curing than during intensive rotting. Three patterns could be detected; ammonia​/ammonium formation during curing is significant, formation was negligible or immobilization is significantly higher than ammonia formation. Ammonification reaches higher rates for non-​lignocellulosic substrates compared to lignocelluloses, independent of the N content of the input material. Nitrification and denitrification occurred only during curing. Nitrification was limited at >30°, pH >8 and moistened substrate. Immobilization effects are assumed for the whole composting process and could be detected for the curing phase. They have not necessarily been catalyzed by microorganisms. Chem.-​phys. processes may also be the reason. Releases take place via leachate (only if the process is insufficiently aerated) and via exhaust air. Ammonia releases via off gas were high for non-​lignocellulosics and low​/not detectable for lignocelluloses.