Evolution of elemental nitrogen involved in the carbonization mechanism and product features from wet biowaste

Hydrothermal carbonization (HTC) represents elegant thermochemical conversion technology suitable for energy and resource recovery from wet biowaste, while the elemental nitrogen is bound to affect the HTC process and the properties of the products. In this review, the nitrogen fate during HTC of typical N-containing-biowaste were presented. The relationship between critical factors involved in HTC like N/O, N/C, N/H, solid ratio, initial N in feedstock, hydrothermal temperature and residence time and N content in hydrochar were systematic analyzed. The distribution and conversion of N species along with hydrothermal severity in hydrochar and liquid phase was discussed. Additionally, the chemical forms of nitrogen in hydrochar were elaborated coupled with the role of N element during hydrochar formation mechanism and the morphology features. Finally, the future challenges of nitrogen in biowaste involved in HTC about the formation and regulation mechanism of hydrochar were given, and perspectives of more accurate regulation of the physicochemical characteristics of hydrochar from biowaste based on the N evolution is expected.

Automated summary

This review focuses on the nitrogen fate during the hydrothermal carbonization (HTC) of N-containing biowaste. The impact of critical factors such as N/O, N/C, N/H, solid ratio, initial N in feedstock, hydrothermal temperature, and residence time on the nitrogen content in hydrochar is analyzed. The distribution and conversion of nitrogen species in both hydrochar and liquid phase are discussed. Furthermore, the chemical forms of nitrogen in hydrochar and its role in the hydrochar formation mechanism are elaborated. Challenges and perspectives for the formation and regulation of nitrogen in biowaste during HTC are also presented.