Production of high-starch duckweed and its conversion to bioethanol

Growing high-starch duckweed for its conversion to bioethanol was investigated as a novel technology to supplement maize-based ethanol production. Under the fall (autumn) climate conditions of North Carolina, the biomass accumulation rate of Spirodela polyrrhiza grown in a pilot-scale culture pond using diluted pig effluent was 12.4 g dry weight m−2 day−1. Through simple transfer of duckweed plants into well water for 10 days, the duckweed starch content increased by 64.9%, resulting in a high annual starch yield of 9.42 × 103 kg ha−1. After enzymatic hydrolysis and yeast fermentation of high-starch duckweed biomass in a 14-l fermentor, 94.7% of the theoretical starch conversion was achieved. The ethanol yield of duckweed reached 6.42 × 103 l ha−1, about 50% higher than that of maize-based ethanol production, which makes duckweed a competitive starch source for fuel ethanol production.

► Spirodela polyrrhiza grew rapidly in pig effluent under field conditions.
► Duckweed pond was efficient in removing nutrients from pig effluent.
► Duckweed biomass was readily hydrolysed and fermented to ethanol.
► Ethanol yield of duckweed was substantially higher than that of corn.
► This pilot-scale study provides important information and experience for future work.