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Growing High-Starch Duckweed for the Production of Fuel Ethanol

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2011 Louisville, Kentucky, August 7-10, 2011  1110811.(doi:10.13031/2013.37320)
Authors:   Jiele Xu, Jay J Cheng, Anne M Stomp
Keywords:   Ethanol, Nutrients, Spirodela polyrrhiza, Starch, Swine wastewater

Corn-based ethanol production has raised much concern over its impact on food/feed supply. It is necessary, therefore, to explore novel starch sources to supplement corn starch to make the development of ethanol industry more sustainable. Duckweed is a small floating aquatic plant within the family Lemnaceae, which has been studied extensively to remove nutrients from wastewaters due to its rapid proliferation and excellent nutrient uptake ability. Duckweed is also considered as a potential starch source. Depending on the duckweed species and the growing conditions applied, starch contents ranging from 3-75% dry weight have been reported. Studies also show that starch accumulation in duckweed plant can be triggered at specific growing conditions especially nutrient starvation. To investigate the promise of growing high-starch duckweed for fuel ethanol production, in this study, the duckweed Spirodela polyrrhiza was grown using swine wastewater in a pilot-scale duckweed culture pond. The harvested duckweed was transferred to well water for starch accumulation. Enzymatic hydrolysis and yeast fermentation of the high-starch duckweed biomass were carried out to evaluate the effectiveness of ethanol production. The results show that Spirodela polyrrhiza grew well in swine wastewater in summer months and simple transfer of duckweed plants into well water for 10 days caused increases of total biomass by 81.4% and starch content by 64.9%, which resulted in a starch yield of 9.42 x103 kg ha-1. After enzymatic hydrolysis and yeast fermentation of high-starch duckweed biomass, 94.7% of the theoretical starch conversion was achieved.

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