Bioremediation Fueling the rapid growth of duckweeds requires substantial amounts of nutrients.  Thus duckweeds have evolved the ability to rapidly remove minerals necessary for their growth from the water on which they float.  When present, duckweeds also can remove many organic nutrients.  These mineral and organic nutrients are converted into the substance of the plants, that is, their biomass.  Research has shown that duckweeds are especially adept at removal of phosphates and nitrogen, particularly ammonia. The treatment of sewage and wastewater from agricultural operations requires the removal of great amounts of nitrogen and phosphate.  These wastes are a growing problem around the world because of population growth and the trend of modern farming operations to concentrate livestock in small areas. The duckweed biomass that results from water treatment operations must itself be removed from the water.  This can be done by skimming it off.  Duckweed grown on sewage or animal wastes normally does not contain toxic pollutants and can be fed to fish or to livestock, or spread on farmland as a fertilizer.  If the duckweed is to be fed to animals, a retention period in clean water will be necessary to ensure that the biomass is free of water-borne pathogens. The links on this page illustrate both potential and proven duckweed applications.

Above:  swine in North Carolina, Below:  a duckweed treatment lagoon inside a plastic greenhouse.  Photos courtesy of Paul Skillikorn.

• A diagram:  Biological processes in duckweed-based wastewater treatment. [ .bmp file ] drawn after M.D. Smith and Moelyowati, I. (2001) "Duckweed based wastewater treatment (DWWT):  design guidelines for hot climates."  Water Sci. & tech. 43(11): 291-299.

• Nature's pollution fighter:  Duckweed aids wastewater treatment systems, Gary D. Robertson, The Associated Press, a link from Canoe, Canada's largest web site, published Monday, March 27, 2000.

• Duckweed Wastewater Treatment and Reuse for Fodder in Palestine (West Bank),  Nader Al Khateeb, Water and Environmental Development Organization (WEDO), Bethlehem.  See also this [ link ].
  

• USDA Research: Finding better processes to convert renewable materials into value-added bioproducts.  USDA Northern Regional Research Center, Peoria, Illinois.  CRIS Report, FY1999.
• "The purpose of this research is to improve the technologies for the conversion of renewable agricultural biomass into value-added products (e.g., fuel ethanol, lactate, and enzymes). Such conversions are currently possible but are cost prohibitive if using plant biomass other than starch."

• US EPA Report:  Design Manual Constructed Wetlands and Aquatic Plant Systems for Municipal Wastewater Treatment, US EPA Office of Research and Development, Center for Environmental Research Information, Cincinnati, OH 45268, September 1988, 1058 kB

• Duckweed and waste water treatment: importance of macrophyte, algae and bacteria, a slide show by Jan Vermaat & Sabine Koerner, Department of Environmental Science and Water Resources, University of Delft, Netherlands, and

Treatment of domestic sewage, from the postdoctoral research project of Sabine Körner, now at IGB-Berlin, Germany.
'The relative importance of duckweed, bacteria and microalgae for the treatment of domestic sewage in duckweed-covered systems' Laboratory scale experiments on duckweed-covered domestic sewage were carried out to determine whether removal of organic material is faster in the presence of duckweed...  ...Removal of COD was significantly faster in the presence of duckweed.  ...approximately ¾ of the total N-and P-loss could be attributed to the duckweed mat."

Publications on duckweed growth in wastewater from this group:
Vermaat, Jan & Hanif, Khalid (1998) Performance of common duckweed species (Lemnaceae) and the water fern (Azolla filiculoides) on different types of waste water.  Water Res.  32(9):2569-2576.
Körner, S., Vermaat, J.E. & Lyatuu, G.B. (1998) The influence of Lemna gibba L. on the degradation of organic material in duckweed-covered domestic wastewater.   Water Res. 32: 3092-3098. (Summary)
Körner, S. and Vermaat, J.E. (1998) The relative importance of Lemna gibba L., bacteria and micro-algae for the treatment of domestic sewage in duckweed-covered systems.   Water Res. 32: 3651-3661. (Summary)
Körner, S.; Das, S.K.; Vermaat, J.E. and Veenstra, S. (in prep.) Ammonia toxicity to the duckweed Lemna gibba used for the treatment of wastewater.  

• Alternative Wastewater Treatment Method for Swine Production:  Students of Jay Cheng at North Carolina State University have studied a reactor and harvesting systems for growing and removing duckweed, a small aquatic plant, from swine wastewater.

 B.A. Bergmann, J. Cheng, J. Classen, A.-M. Stomp, In vitro selection of duckweed geographical
 isolates for potential use in swine lagoon effluent renovation, (2000) Bioresource Technology 73 (1)
 pp. 13-20 


Cheng, J, Landesman, L, Bergmann, BA, Classen, JJ, Howard, WJ, Yamamoto, YT (2002)  Nutrient Removal from Swine Lagoon Liquid by Lemna minor 8627.  Trans. Amer. Soc. Agric. Eng. 45(4):1003-1010. [ link to download site ]


Lyerly, Courtney Neil, Swine Wastewater Treatment in an Integrated System of Anaerobic Digestion and Duckweed Nutrient Removal: Pilot Study, M.S. Thesis, North Carolina State University, Biological and Agricultural Engineering, Raleigh, NC, 2004, 104 pp. [ link to download site ]

Smith, Ryan Andrew. Harvesting Duckweed By Skimming, M.S. Thesis, North Carolina State University, Biological and Agricultural Engineering, Raleigh, NC, 2003, 153 pp. [ link to download site ]

• Duckweed - The Super Plant, "Babalouie's Duckweed Application Page" - by Louis Landesman, now at Texas State University-San Marcos, San Marcos, TX.
"Duckweed may be the most promising plant for the twenty-first century for the following reasons:
• Duckweed produces more protein per square meter than soybeans  UTA.
• Duckweed is easier to harvest than algae or other aquatic plants.
• Duckweed can be used to feed fish, poultry and cattle (PRISM, INC) .
• Duckweed can purify and concentrate nutrients from wastewater (sewage effluent).
• Duckweed provides food for wildlife, especially waterfowl (Wetlands)."
Dr. Landesman has worked closely with Jay Cheng and his group (see previous link) on using duckweed to recover nutrients from swine wastewater."   Publication:

Landesman L, Parker N C, Fedler C B and Konikoff M (2005) Modeling duckweed growth in wastewater treatment systems. Livestock Research for Rural Development. Vol. 17, Art. #61. Retrieved October 30, 2005, from http://www.cipav.org.co/lrrd/lrrd17/6/land17061.htm

• Case Study:  Lemna Wastewater Treatment Process Ogema Sanitary District, Wisconsin. by Ernesto R. Lopez and Charles Pycha, Environmental Engineers, Technical Support Section, Water Compliance Branch, U.S. EPA, Chicago, IL  60604.
  
 
• Wastewater Facility Using Duckweed Plants In Process Gets EPA Award (3/19/97)

In this lagoon, Lemnaceae plants (duckweed) were introduced to create a floating blanket of vegetation that prevents sunlight from reaching the water. Allen Atkins, supervisor of public works for the town, explained that this "helps with the control of algae in our lagoon, and also helps remove other nutrients from the wastewater."
 
•  Lemna Solves Algae Problems in Ashland Chemical Polishing Ponds

"One in five industrial plants uses lagoons for some part of its wastewater treatment process. These lagoons are often troubled with excessive algae growth which can cause compliance problems.  Lemna Systems, widely used to solve this problem in municipal lagoons, can also be used for the same purpose in industrial polishing ponds. One such application was done for Ashland Chemical's methanol production facility in Plaquemine, Louisiana."  (A Lemna Technologies application.)
 
• Duckweed is a Low-Cost Water Purifier, Anne E. Platt, Worldwatch Institute.

Ms Platt identified the following deficiencies for duckweed water purification:
1. Duckweed can't process heavy metals, pesticides, or toxic substances; so if the duckweed is to be used as food, it must be tested first.
2. Duckweed purification ponds must be large, flat, and shallow; so they can't be used in mountains or cities.
3. On a per person basis, duckweed purification takes up more room that conventional plants; it takes two square meters of duckweed per person to do the purifying.
Can these deficiencies be overcome by creative thinking or new technology?
• Recent research shows that duckweeds actively remove and metabolize certain pesticides and industrial wastes.
• New designs for duckweed purification plants take up less space. [ link to patent ]

• Phytoremediation Web Page,  Biological remediation of environmental problems using plants.  Links to:  conferences, research sponsors, books, and more phytoremediation links.
  
 
• Uptake of Heavy Metals.

Zayed, A. Phytoaccumulation of trace elements by wetland plants. I. Duckweed. (1998) Journal of Environmental Quality 27 (3):715-721.
"...under experimental conditions, duckweed [Lemna minor L.] proved to be a good accumulator of Cd, Se, and Cu, a moderate accumulator of Cr, and a poor accumulator of Ni and Pb."  "The toxicity effect of each trace element on plant growth was, in descending order of damage, Cu > Se > Pb > Cd > Ni > Cr. We conclude that duckweed shows promise for the removal of Cd, Se, and Cu from contaminated wastewater since it accumulates high concentrations of these elements. Further, the growth rates and harvest potential make duckweed a good species for phytoremediation activities."

G.N.H. Rahmani, S.P.K. Sternberg, Bioremoval of lead from water using Lemna minor, Bioresource
 Technology 70 (3) (1999) pp. 225-230.
 

• Aprovechamiento de Plantas Acuaticas para el Tratamiento de Aguas Residuales, "Advantages of Aquatic Plants for the Processing of Aqueous Residues," Eugenia Olguín, Elizabeth Hernández, Patricia Coutiño y Rosalía González, from Tecnologías ambientales para el desarrollo sustentable, ISBN 968-7213-63-9.

"Las macrofitas acuáticas han sido consideradas por varios autores como una plaga debido a su rápido crecimiento, ya que en ocasiones llegan a invadir lagunas y generan varios problemas (Arrivallaga y Arredondo, 1978). Sin embargo, si las plantas acuáticas se manejan adecuadamente, su poder de proliferación , su capacidad de absorción de nutrientes y bioacumulación de otros compuestos del agua, las convierten en una herramienta útil en el tratamiento de aguas residuale (Boyd, 1970)."

Aquaculture

• Duckweed as a Primary Feedstock for Aquaculture. - A technical article with literature references by John W. Cross.

• Integrated Tilapia & Duckweed Farming System.  "The fish and the waters of the tilapia growout ponds provide the nutrients upon which the duckweed will thrive. In turn, the duckweed removes unwanted nutrients and waste products from the system, converting the nutrients into plant biomass. This plant biomass, in turn, becomes a high protein food for the tilapias. While all this is going on, water within the integrated system is conserved and purified. The entire system is a natural and sustainable approach to aquaculture."

• Duckweed Aquaculture, Paul Skillicorn, William Spira & William Journey. A New Aquatic Farming System for Developing Countries. (1993) The World Bank, 76 pp.  Available from The World Bank Group, World Development Sources in printed copy.

This book describes an experimental program in Mirzapur, Bangladesh, where duckweed cultivation was established and fresh duckweed fed to carp and tilapia.  "Duckweed-fed fish production does not depend on mechanical aeration and appears to be significantly more productive and easier to manage than traditional pond fish culture processes."

United Nations Capital Development Fund evaluation of the Bangladesh project.  For color photos see the home page of the Bangladesh Livestock Research Institute (BLRI).  


• Shobuj Shona Evaluation,  Bangladesh, (1993) Enterprise, Asset Accumulation and Income Generation in Bangladesh: A New Model for Women in Development, Rebecca Torres, University of California, Davis  (428k)

For other World Bank publications related to duckweed applications in the developing world [ link ].

• Duckweed as a feed supplement for livestock.  - Links to on-line papers.

 
• Nutritional value.  - Tables of nutrients and links to sources.

 
• Other recent references (feed for tilapia, crayfish)

Fasakin, EA, Balogun, AM and Fasuru, BE. (1999) Use of duckweed, Spirodela polyrrhiza L. Schleiden, as a protein feedstuff in practical diets for tilapia, Oreochromis niloticus L. Aquaculture Research 30(5): 313.
Fletcher, A., Warburton, K. (1997) Consumption of fresh and decomposed duckweed Spirodela sp. by Redclaw crayfish, Cherax quadricarinatus (von Martens) Aquaculture Research 28(5): 379.

• Duckweed in Space:  Aquatic food production modules in bioregenerative life support systems.  The smallest duckweed, Wolffia, is being tested as part of an aquatic food production system for spaceflight at Ruhr-Universitaet Bochum in Germany.  Read about the design of this system.  Also see research by NASA.

• Duckweed Aquaculture - Potentials, Possibilities and Limitations for Combined Wastewater Treatment and Animal Feed Production in Developing countries, [pdf, 990 k] by Sascha Iqbal, SANDEC Report No. 6/99. Price: CHF 25.-
  (scroll down to Agricultural and Aquacultural Aspects of Waste Reuse)
  

"SANDEC is the Department of Water and Sanitation in Developing Countries at the Swiss Federal Institute for Environmental Science and Technology (EAWAG) in Duebendorf, Switzerland.  ...Its mandate is to assist in developing appropriate and sustainable water and sanitation concepts and technologies adapted to the different physical and socio-economic conditions prevailing in developing countries"

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Revised:  October 30, 2005