October 14, 2011

Duckweed Wastewater Treatment Plant near Kunming, China

Chengdu Institute of Biology in China has constructed a duckweed treatment system out of a retired wastewater treatment plant. The facility treats raw municipal wastewater along with algae-polluted water from the adjacent, and beautiful (though green), Lake Dianchi.

Video 1: View of Lake Dianchi near Kunming, Yunan (China). Algae in lake predominantly microsystis cyanobacteria.

Location of the Lake Dianchi Duckweed Wastewater Treatment Facility:

The facility keeps track of influent and effluent water quality through 13 different treatment scheme. Each treatment scheme consists of a unique duckweed specie or combination of species; since, it has been found that different species are particularly adept at nutrient removal, ethanol production, biomass production, etc.

Video 2: Explanation of the duckweed treatment system near Kunming (China)

Figure: Dr. Zhao Hai (fifth from left with camera around his neck) and a part of his research group--these are the folks that makes it all happen, with the help of duckweed.

Figure: Treatment process flow chart. Preliminary bar screen, then pass through four serpentine anaerobic zones (black liquid), pre-treatment cells (for high concentration wastewater and/or Lake Dianchi algae removal), B and then C cells 13 series of four cells with different combinations of duckweed species.

Figure: Headworks for screening and possibly some grit removal.

Figure: Qualitative difference between influent (left) and effluent (right).

Figure: Quantitative difference between effluent (left) and influent (right).
Qin = approximately 25-110 m^3/d
NTU = 82 (in) 6.8 (out)
NH4-N = 24 (in) <0.05 (out)
NO2-N = 0.05 (in) 0.02 (out)
NO3-N = 1.8 (in) <1.0 (out)
PO4-P = 3.74 (in) 0.25 (out)
COD = 79 (in) <10 (out)

Figure: Division between two species: Spirodela polyrhiza and Landoltia

Figure: The popular duckweed species--Spirodela polyrhiza.

Figure: Duckweed species--Landoltia punctata (distinguished by Lemna by having characteristic purple color underneath frond where Lemna is green underneath).

Figure: Landoltia duckweed species with green color on top of frond (same as Lemna).

Figure: Landoltia duckweed species with purple underside of frond (distinguished from Lemna which has green underside).

Figure: Duckweed species--Lemna aequinoctialis

Figure: Duckweed species--Wolffia globosa

Figure: Polyculture of Wolffia, Spirodela, and Lemna.

Figure: Four cells making up a treatment series using Water Hyacinth (all other cells contain duckweed only).

Figure: I'm very grateful to Zhao Hai and his colleagues for giving us a tour of their facility. By the way, green duckweed on top of the cells is much more attractive than brown activated sludge--an advantage for duckweed systems.


  1. Dear Jon,

    I salut you on your blog effort. You are one of the few people who are blogging about duckweed on the professional level. I'm planning on start my own research in collaboration with a top-notch university. Further more, im also planning on creating the first duckweed social network. If your interested in further discussion please contact me on : yassin@belakhdar.com.

    greenfully yours,
    Yassin Shaar

  2. Jon,

    I will be visiting Kunming this April 2012. Can you tell me how to get in touch with Zhao Hai and possibly arrange a tour of this facility? And the address of the treatment plant?

    My name is Brian and I am a water environment professional in the USA. Visiting wastewater treatment plants is a professional hobby of mine.

    Thank you,

  3. Jon,

    My email is tangodip@hotmail.com

    Thank you,

  4. This is cool stuff, Jon. Congrats on finishing your thesis defense!

  5. Jon, your site is great. Looking for you and others interested in duckweed to join the ILA (International Lemna Association) when you get the chance either via our website: www.InternationalLemnaAssociation.org or our LinkedIn group by the same name. I am scaling up to two acres of ponds this spring for animal feedstock here in KY. Looking forward to seeing a blanket of healthy, high-protein green. Best wishes, Tamra

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