Evaluation of hydrothermal carbonization of biomass residues for bioenergy: A life-cycle based comparison against incumbent technologies

Hydrothermal carbonization of biowaste with energy recovery was evaluated as a biowaste treatment technology using attributional life cycle assessment carried out in line with ISO 14044. Results show that important differences were observed for individual impact categories. Hydrothermal carbonization outperformed all other incumbent technologies in three impact categories and performed on par with anaerobic digestion and composting in the climate change category, where impact scores across three different wet biowaste streams ranged from -0.014 to -0.032 kg CO2 equivalents per kg of wet biowaste treated. However, it performed the worst in those environmental impacts which address resource depletion, including mineral, fossil and renewable resource depletion. This stresses the need to include all impact categories when evaluating environmental performance of biowaste treatment technologies. Differences in the ranking between different midpoint categories corroborate earlier studies suggesting that the general waste hierarchy might not necessarily apply to hydrothermal carbonization of biowaste.