|Flora, Joseph R.|
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2011
Publication Date: 6/14/2011
Citation: Berge, N.D., Ro, K.S., Mao, J., Flora, J.V., Chappell, M.A., Bae, S. 2011. Hydrothermal carbonization of municipal waste streams. Environmental Science and Technology. 45:5696-5703. Interpretive Summary: Hydrothermal carbonization is an aqueous thermal conversion process that converts organic wastes into value-added char called hydrochar. Because of diverse chemical functional characteristics of hydrochar, it has several beneficial end-use applications such as; adsorbent for removing harmful pollutants, a soil amendment to build up soil quality, and feedstock for carbon fuel cells. The objective of this study was to evaluate the environmental implications associated with the carbonization of municipal waste streams such as paper, food, municipal solid wastes, and anaerobic digestion sludge. This study shows that 49-75% of the initially present carbon was retained within the hydrochar, while 20-37% and 2-11% of the carbon was transferred to the liquid- and gas-phases, respectively. Carbon dioxide is the major gaseous product while many different chemicals were formed in the liquid phase. High degree of aromaticity in hydrochar will provide biostability when applied as a soil amendment. Because of very high buffer capacity of the anaerobic digestion sludge, its carbonization was not completed as with other waste streams. Process energy calculation suggests that the carbonization reaction is exothermic; i.e., the process gives off heat and reduces heating requirement.
Technical 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), 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.