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.
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."
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,
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
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
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)
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 ]
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
Lemna Solves Algae Problems in Ashland Chemical
"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
Ms Platt identified the following deficiencies for
duckweed water purification:
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.
Duckweed purification ponds must be large, flat, and
shallow; so they can't be used in mountains or cities.
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?
researchshows 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
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
"...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
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
"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)."
"The Mirzapur Shobuj Shona
project, inaugurated in 1989 was the first flow-through
wastewater treatment system in the world to cover capital
and O&M costs while also making a healthy profit on
operation of the system itself."
The video and books listed below demonstrate the overall design
and productivity of the Prism project.
This book describes the Prism 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."
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 ].
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):
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
this system. Also see research by NASA.
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
"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