2008 Awards

Growing Duckweed on Swine Wastewater for Ethanol Production - N.C. State University

Funding recipient:  North Carolina State University, Raleigh, N.C.

Award amount:  $199,733

For a number of years, researchers at North Carolina State University have used Duckweed, the world’s smallest flowering plant, to effectively clean swine wastewater lagoons. This fast-growing plant contains properties that make it a potential feedstock for North Carolina-based ethanol production. The Biofuels Center of North Carolina is sponsoring research into cost-effective growing, harvesting, drying, and pre-production techniques to make Duckweed an agriculturally and economically sustainable crop for ethanol production.

Week-old duckweed.

Biomass production, processing costs and scale-up potential are critical factors in commercialization of plant biomass for ethanol production. Previous research at N.C. State University has investigated the use of hog wastewater for production of Duckweed biomass that could be used as a feedstock for ethanol production. Researchers demonstrated ethanol production from Duckweed biomass using existing corn-based methods. These achievements provided proof-of-concept that Duckweed biomass could be used to produce ethanol for fuel.

In the Biofuels Center-funded research, a scaled-up, pilot version of the system was built on an operational hog farm in Johnston County to design and test protocols for cropping, harvesting, and drying of Duckweed biomass, to produce ethanol from this biomass, and to conduct the first economic analysis of ethanol production from Duckweed biomass.

The goal of the cropping, harvesting and drying studies is to identify low-cost, scaled-up protocols that would be easily integrated into hog farm operations and determine the cost to produce dry duckweed biomass. The objectives of the ethanol study are to determine:

  • if the dry Duckweed is a good fermentation feedstock;
  • the yield of ethanol from Duckweed biomass;
  • and the cost to produce ethanol from Duckweed biomass.

Results indicate that hog wastewater will serve as an excellent source of nutrients to support fast growth of Duckweed biomass at yields of minimally 6 tons dry weight/acre over North Carolina’s 30-week growing period. Simple pumping and sieving methods can be used for harvesting using readily available materials and equipment. Air drying is sufficient for reducing the moisture content of fresh Duckweed to less than 15%. At this moisture content the organic constituents of the biomass are stable. This cropping and drying system produces Duckweed biomass with a protein content of 35-40% of dry weight and approximately 10% starch. A further growth step was investigated to determine if a method could be developed to induce the plants to accumulate higher starch levels sufficient for economical commercial ethanol production. Results indicate that several factors impact starch accumulation and that accumulation remains variable. In spite of that variability, starch accumulation of at least 25% of dry weight can be readily achieved.  At this level, starch yields would be 1.5 tons starch/acre.

An interview with researcher, Anne Stomp can be heard in the MEDIA section of the website. Additional information will be available upon completion of the project.

North Carolina counties benefiting from this project: Johnston and Wake

For additional information about the impact of Biofuels Center funding and a brief explanation of award recipient reporting requirements, click HERE: