Dynamics of Nitrogen Cycling in Lemna Wastewater Treatment Systems

Wastewater, formerly called sewage, must be treated before being released into the environment to prevent the spread of disease. Normally sewage is treated in special treatment plants that use bacteria, fungi and protozoa to decompose the organic matter present in wastewater into simpler, less toxic compounds. This decomposition takes place in both aerobic and anaerobic environments.   The objective of all wastewater treatment plants is to decompose the organic matter contained in wastewater and to destroy any pathogens present, thereby preventing the spread of disease. Recycling wastewater nutrients or producing useful products from this waste material is not normally a priority in conventional wastewater treatment.

The Lemna Technologies of St. Paul, Minnesota has patented a new form of wastewater treatment. This technology combines conventional wastewater treatment lagoons with a pond covered by duckweed. This floating mat of duckweed effectively reduces the growth of phytoplankton (algae) and submerged aquatic plants by competing for nutrients dissolved in the wastewater and creating shade, which also prevents the growth of these plants. Furthermore this duckweed can be harvested and used as food for ducks and fish. This technology has the potential for recycling nutrients and producing useful products as well. Widespread use of this and similar technologies can kill 2 birds with one stone: treat wastewater and produce high protein feed materials. This technology should be particularly useful for developing countries. My interest in this technology was sparked by the abundance of life I found growing in and among the floating layer of duckweed. I was also excited by the potential duckweed has for wastewater treatment, an urgent concern all over the world.


Location Date Plants Animals
Broussard Sept. 8, 1995 Floating Duckweed Midge Larvae
Lemna obscura (Chironomid larvae)
(dominant plant) Oligochaetes
Wolffia globosa Nais elinguis 
(watermeal) Ostracods
Limnobium spongia
Sunset March 13, 1997 Wolffia columbiana Oligochaetes
Lemna obscura Aelosoma sp.
Scenedesmus sp. Rotifers

Microbes found in both Sunset and St. Martinville treatment ponds:

Protozoa – Paramecium, Stentor, Colpidium, and Spirostomum

Bacteria – Gram negative rods

4 Responsesto “Dynamics of Nitrogen Cycling in Lemna Wastewater Treatment Systems”

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  3. Alexander Fordyce says:

    Dr. Landesman,

    I’ve recently completed a small study on the effects of different concentrations of SIS medium on the growth of Lemna minor as part of the 3rd year of my BSc Biology degree and have a couple of questions:

    Can I ask your permission to quote and reference your website?
    What is the best way to go about structuring this reference?
    Are there any other sources you could point me towards with regards to previous studies done on growth factors of this species?

    Thank you in advance for any help you can give me.

    P.S. any comments from other users are welcome and appreciated.


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