Environmental Performance of Hydrothermal Carbonization of Four Wet Biomass Waste Streams at Industry-Relevant Scales

TLDR

Biowaste water content and hydrochar composition are key factors influencing the environmental performance of hydrothermal carbonization. The study evaluates hydrothermal carbonization of green waste, food waste, organic municipal solid waste, and digestate as a potential biowaste treatment technology. Life cycle assessment is employed to quantify the environmental impacts of the HTC process. Hydrochar from green waste ranks best in two of fifteen impact categories, including climate change, owing to low transport and efficient pumping, while hydrochar from organic MSW ranks best in six categories but poses significant human health and ecosystem risks from toxic ash; overall, HTC’s environmental performance is comparable to existing options, with the greatest optimization potential arising from heat and electricity use at larger plant sizes, though it is largely influenced by the local waste management system it replaces.

Abstract

Hydrothermal carbonization (HTC) of green waste, food waste, organic fraction of municipal solid waste (MSW), and digestate is assessed using life cycle assessment as a potential technology to treat biowaste. Water content of the biowaste and composition of the resulting hydrochar are important parameters influencing environmental performance. Hydrochar produced from green waste performs best and second best in respectively 2 and 10 out of 15 impact categories, including climate change, mainly due to low transportation needs of the biowaste and optimized pumping efficiency for the feedstock. By contrast, hydrochar produced from the organic fraction of MSW performs best in 6 impact categories, but has high potential impacts on human health and ecosystems caused by emissions of toxic elements through ash disposal. The greatest potential for environmental optimization for the HTC technology is in the use of heat and electricity with increasing plant size, but its overall environmental performance is largely influenced in a given geographic location by the incumbent waste management system that it replaces. Impact scores are within the range of existing alternative treatment options, suggesting that despite being relatively immature technology, and depending on the geographic location of the plant, HTC may be an attractive treatment option for biowaste.