Carbon footprint of industrial-beet sugars stored as raw thick juice for use as a fermentation feedstock

Abstract

Raw thick juice is a concentrated beet extract that enables fermentable sugar storage and could help extend campaigns and reduce capital investments for industrial-beet processing into biobased chemicals including ethanol fuel. The aim of this work was to determine the carbon footprints of fermentable sugars stored as raw thick juice and of ethanol produced from raw thick juice. This enabled comparisons with carbon footprints of fermentable sugars obtained through conventional processing of sugar beets and corn grain, and of combusted gasoline. The carbon footprint of fermentable sugars in raw thick juice was assessed from cradle to gate since raw thick juice can be used as a feedstock for various industrial fermentations, including that for ethanol production. The carbon footprint of ethanol produced from raw thick juice was assessed from cradle to grave and it included juice fermentation and ethanol purification. Ethanol production was modeled assuming either that all fermentable sugars are stored as raw thick juice before fermentation, or that only half of the sugars are stored as raw thick juice before fermentation and the other half directly fermented after extraction. Analyses were also conducted to understand the importance of beet sugar content and of frozen beet pile storage on the carbon footprints. Fermentable sugars stored as raw thick juice have a carbon footprint that is 29% and 52% lower than those of fermentable sugars from conventional processing of sugar beets and corn grain, respectively. Raw juice concentration is the processing step with the largest effect on the overall carbon footprint, representing 26% of the total. Beet ethanol produced under the assumed scenarios could enable a reduction in greenhouse-gas emissions of up to 57% compared to gasoline, qualifying as an advanced biofuel in the U.S. under the Energy Independence and Security Act of 2007.