Animal bone chars as sorbents and providers of ammonium nitrogen from biogas digestates

Biochars are well-known for their high sorption capacity of cationic substances. Whereas the pyrolysis of vegetation-based feedstock produces biochar with high carbon concentrations (70-90 %), these chars contain only very small fractions of plant-relevant macronutrients with good bioavailability. The usage of animal bones as pyrolysis feedstock, however, produces phosphorus-rich biochars (10-15 % P) that are low in carbon (10-20 % C). The deficiency in nitrogen of these bone chars can be compensated for by sorbing nitrogen prior to use them as soil improvers.