Tiny Super-Plant Can Clean Up Hog Farms and Be Used For Ethanol Production

Researchers at North Carolina State University have found that a tiny aquatic plant can be used to clean up animal waste at industrial hog farms and potentially be part of the answer for the global energy crisis. Their research shows that growing duckweed on hog wastewater can produce five to six times more starch per acre than corn, according to researcher Dr. Jay Cheng. This means that ethanol production using duckweed could be "faster and cheaper than from corn," says fellow researcher Dr. Anne-Marie Stomp.

"We can kill two birds - biofuel production and wastewater treatment - with one stone - duckweed," Cheng says. Starch from duckweed can be readily converted into ethanol using the same facilities currently used for corn, Cheng adds.

Corn is currently the primary crop used for ethanol production in the United States.  However, its use has come under fire in recent years because of concerns about the amount of energy used to grow corn and commodity price disruptions resulting from competition for corn between ethanol manufacturers and the food and feed industries. Duckweed presents an attractive, non-food alternative that has the potential to produce significantly more ethanol feedstock per acre than corn; exploit existing corn-based ethanol production processes for faster scale-up; and turn pollutants into a fuel production system. The duckweed system consists of shallow ponds that can be built on land unsuitable for conventional crops, and is so efficient it generates water clean enough for re-use. The technology can utilize any nutrient-rich wastewater, from livestock production to municipal wastewater.

Large-scale hog farms manage their animal waste by storing it in large "lagoons" for biological treatment. Duckweed utilizes the nutrients in the wastewater for growth, thus capturing these nutrients and preventing their release into the environment. In other words, Cheng says, "Duckweed could be an environmentally friendly, economically viable feedstock for ethanol."

"There's a bias in agriculture that all the crops that could be discovered have been discovered," Stomp says, "but duckweed could be the first of the new, 21st century crops. In the spirit of George Washington Carver, who turned peanuts into a major crop, Jay and I are on a mission to turn duckweed into a new industrial crop, providing an innovative approach to alternative fuel production."

Cheng, a professor of biological and agricultural engineering, co-authored the research with Stomp, associate professor of forestry, and post-doctoral research associate, Mike Yablonski. The research, which is funded by the North Carolina Biofuels Center, was presented March 21 at the annual conference of the Institute of Biological Engineering in Santa Carla, Calif.

Cheng and Stomp are currently establishing a pilot-scale project to further investigate the best way to establish a large-scale system for growing duckweed on animal wastewater, and then harvesting and drying the duckweed.

 

Authors: Jay J. Cheng, Anne-M. Stomp and Mike Yablonski, North Carolina State University

Presented: March 21, 2009, at the 14th Annual Institute of Biological Engineering Conference in Santa Carla, Calif.

Abstract: Recently there has been a great drive to significantly expand fuel ethanol production in the United States to reduce our dependency on foreign oil. Currently corn is a primary crop for fuel ethanol production in the US. However, it is clear that tremendously increasing ethanol production from corn would not be practical because the ethanol industry would then compete for limited resource of corn against the food and feed industries. Thus, additional sources of fermentable carbohydrates are needed to meet the expanding fuel ethanol demand. Our research focuses on exploring a new feedstock for ethanol production - duckweed. Duckweed or Lemnaceae is an aquatic plant that has a great potential for fuel ethanol production. Duckweed proliferates through clonal, vegetative budding of new fronds and accumulates biomass faster than field crops, almost 28 times faster than corn. Duckweed can be grown on wastewaters for nutrient management and biomass production. Our current research focuses on development of a system to use animal wastewater to produce high-starch duckweed that is then converted to ethanol using existing starch-based conversion technologies. Duckweed starch content is highly variable, ranging from 3-75% of dry weight depending on species and individual stains. A number of parameters including nutrient profiles and concentration play a major role in starch accumulation.  In our laboratory study, a North Carolina strain of duckweed, Spirodela polyrrhiza, could be grown on anaerobically treated swine wastewater with a starch content of 45.8% (dry weight). Enzymatic hydrolysis of the high-starch duckweed biomass with amylases yielded a hydrolysate with a reducing sugar content corresponding to 50.9% of the original dry duckweed biomass. Fermentation of this solution using yeast gave an ethanol yield of 25.8% of the dry duckweed biomass. These results indicate that duckweed biomass can produce appreciable quantity of starch that can be readily fermented into ethanol. Duckweed has a great potential for the development of an environmentally friendly, economically viable ethanol production technology. A pilot-scale duckweed system with approximately 600m² water surface is being established on a commercial farm to investigate the scale-up factors on growing duckweed on animal wastewater, duckweed harvesting and drying, and economic analysis. Progress of the pilot system will be presented at the meeting.