Hydrothermal Carbonization of Municipal Waste Streams

TLDR

Hydrothermal carbonization converts municipal waste into sterilized hydrochar, yet it has mainly been studied on simple feedstocks, leaving its application to complex waste streams largely unexplored. The study aims to assess the environmental impacts, material properties, and energy balance of hydrothermal carbonization of representative municipal waste streams. Batch experiments were conducted to carbonize municipal waste streams, measuring carbon retention, product composition, and energy changes to characterize the process. Batch results show 49–75 % of carbon remains in char, 20–37 % in liquid, 2–11 % in gas, with hydrochar exhibiting high aromaticity from dehydration and decarboxylation, and the process is exothermic.

Abstract

Hydrothermal carbonization (HTC) is a novel thermal conversion process that can be used to convert municipal waste streams into sterilized, value-added hydrochar. HTC has been mostly applied and studied on a limited number of feedstocks, ranging from pure substances to slightly more complex biomass such as wood, with an emphasis on nanostructure generation. There has been little work exploring the carbonization of complex waste streams or of utilizing HTC as a sustainable waste management technique. The objectives of this study were to evaluate the environmental implications associated with the carbonization of representative municipal waste streams (including gas and liquid products), to evaluate the physical, chemical, and thermal properties of the produced hydrochar, and to determine carbonization energetics associated with each waste stream. Results from batch carbonization experiments indicate 49–75% of the initially present carbon is retained within the char, while 20–37% and 2–11% of the carbon is transferred to the liquid- and gas-phases, respectively. The composition of the produced hydrochar suggests both dehydration and decarboxylation occur during carbonization, resulting in structures with high aromaticities. Process energetics suggest feedstock carbonization is exothermic.