Newsletter and Technical Publications
of Alternative Technologies for Freshwater Augumentation
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2.4 Wastewater Treatment Using Duckweed
This is a relatively new technology in which small-scale wastewater
treatment can be achieved using duckweed (Lemna spp. or Spirodela sp.).
Duckweed is a self growing plant abundant in the tropical countries. It is
commonly used as a fertilizer in paddy fields, but has recently been used
in the treatment of wastewater in Bangladesh. In Mirzapur, Bangladesh,
this technology has been implemented at the village level as part of a
UNDP project examining the potential of duckweed-based wastewater
treatment and fish production.
Operation and Maintenance
Use of this technology is simple, being based upon a modification of
conventional maturation lagoon technology (see Wastewater Treatment Using
Lagoons below). Maintenance consists of removal of excess biomass to
encourage continued growth of the duckweed community, and thereby removal
of nutrients from the wastewater, and maintenance of the containment
structure of the pond.
Level of Involvement
This technology can be implemented at either the individual farm or
No data are available, but costs are estimated to be low.
Effectiveness of the Technology
Since 1989, PRISM, Bangladesh, has developed farming systems using
duckweed-based technology and tested their potential for wastewater
treatment and fish food. The results have been promising and, together
with similar activities in Lima, Peru, have succeeded in generating
interest among multilateral as well as bilateral donors in further
examining the potential of this technology.
This technology is suitable in tropical climates.
This technology is inexpensive to construct and operate, and easy to
implement. Duckweed is a prolific plant, especially in nitrogen-rich
environments, and can be easily used as mulch or a natural soil organic
If the flows through the oxidation pond are not properly controlled,
there is a possibility that the duckweed will flow out with the effluent.
Treatment capacity may also be lost during high floods, if the area is not
No problems relating to the use of this technology are known to occur.
Further Development of the Technology
More research through pilot projects is needed in order to refine the
sizing of the ponds used and to determine the correct innocculum of plant
material to achieve a predetermined effluent quality.
Gert van Sanden, EMTAG, INUWS, The World Bank, 1818 H
Street NW, Washington DC.
Jan van der Laan, DGIS, Royal Netherlands Embassy, New
Erik S. Jensen, Danida, Royal Danish Embassy, Road 51,
Gulshan, Dhaka, Bangladesh, Tel. 880 2 881799, Fax 880 2 883638.
Mohammed Ikramullah, PRISM, Bangladesh, House 67, Road
5A, Dhanmondi, Dhaka, Bangladesh, Tel./Fax 880 2 861-170.
Paneer Selwam and Arun Mudgal,
UNDP-World Bank Regional Water and Sanitation Group, 53, Lodi Estate, Post
Office Box 416, New Delhi 110 003, India, Tel. 91-11 469 0488/9, Fax 91-11