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.