Duckweed: The All-In-One Environment Saver?

If you have ever been driving with your windows down on a summer afternoon and smelled a paper mill, fresh cow pasture, or rotting fragment of road-kill, then you can surely appreciate the situation for the people living near swine farms in eastern North Carolina. The smell of swine feces, an infinitely worse stench than you can imagine, has the known ability to permeate not only the surrounding air for miles, but a person’s clothes, hair, house, and food.

Researchers at North Carolina State University (NCSU), specifically Dr. Anne-Marie Stomp in the department of forestry, Dr. Jay Cheng in the department of biological and agricultural engineering, and Dr. Mike Yablonski, a post-doctoral researcher, are stepping in to meet the challenge of the odiferous lagoons and are posing solutions to even more pressing problems in the process.

Finding the solution to the stinky lagoon problem, past researchers looked in the most unlikely of places…in an unattractive, tangled mass of root and leaf-like structures collectively known as “duckweed”. While past researchers studied duckweed for applications ranging from consumption to very recently ethanol production, the researchers at NCSU are the first to bridge the gap between thought and actually making ethanol production from duckweed viable. Before the method on how to make ethanol is described, it is important to see if duckweed can handle the differences found in the various lagoons across NC.

Stomp and Cheng, in their paper written in the year 2000 for the initial problem of nutrient removal from swine lagoons, partly focused on finding the combination of duckweed species (three species were chosen to experiment with from past work) and lagoon effluent concentration that maximized the ability to produce duckweed biomass, the primary precursor to ethanol. In order to find the best lagoon effluent concentration to generate biomass and best variety of duckweed to handle a desired concentration, the researchers allowed the three varieties of duckweed to grow on varying effluent concentrations (20, 25, 33, 50, and 67%) for 12 days in greenhouse conditions simulating typical summer weather. The testing conditions were special to this study because the effluent was taken from the NC State University Field Laboratory and could not represent all of the varying types of swine effluent in eastern NC, but the conclusions of the study prove a very important point.

After sampling the duckweeds intermittently for 12 days and measuring the wet weight, dry weight, and percent dry weight, the researchers were able to determine a trend and prove that any swine lagoon could be optimized for either duckweed biomass production or cleaning of the swine wastewater. The researchers even venture to say that the lagoons (and duckweed species) should be optimized before biomass production is ever attempted.

Due to these findings about ten years ago, the researchers continued the work and studied how duckweed grew in swine feces and ways in which they could convert it to ethanol. The culmination of their work will come to fruition with the completion of a pilot plant for harvesting aimed at the steady production of duckweed, which will provide the biomass necessary for ethanol conversion. The process the researchers will use to convert the biomass to ethanol mimics the same process for converting corn biomass to ethanol, of which the process is very well understood. The ultimate deciding factor, though, will remain in the economic analysis, of which the researchers are completing at this point in time.

While at first glance appearing to be an ugly aquatic weed, duckweed has given hope to a remedy for the stinky swine lagoon problem and a possible source of ethanol production. Maybe natures most exciting solutions to man-made problems do come in the smallest and most unnoticeable packages.

By Steven Burgess

Peer-reviewed research can be found at:

Bergmann, B. A. et al "Nutrient Removal from Swine Lagoon Effluent by Duckweed." American Society of Agricultural Engineers 43.2 (2000): 263-269. Print.

Cheng, Jay J., and Anne-M Stomp "Growing Duckweed to Recover Nutrients from Wastewaters and for Fuel Ethanol and Animal Feed." Clean Soil Air Water 37.1 (2009): 17-26. Print.