- Duckweed is the
smallest flowering plant. It floats on the water surface in a bright
green layer. Duckweed has no stems and no leaves. Some may have tiny
roots. It is basically a green sphere, sometimes called fronds but
having nothing in common with leaves or fronds. Some comprise a pair
of "fronds" with tiny roots.
- Duckweed does not
flower frequently, and usually reproduces by budding on the margin or
base of the "fronds". Each "frond" can only do
this a limited number of times before dying of old age, whereupon they
turn yellow as they lose their chlorophyll. In temperate climates,
Duckweed survives the winter by producing buds that sink to the bottom
of the pond. Duckweed disperse by water or are transported by water
birds. The plants are also small enough to be carried along with
weather like tornadoes.
systems are one of the options that have been widely applied for
combined handling of wastewater with the nutrients used for poultry
and aquacultural projects. The pollutant removal efficiency of
duckweed-based pond systems varies widely depending on retention time,
water depth, initial nutrient concentration, duckweed density, used
genera type, and harvesting regimes.
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.
Duckweed floats and require little structural fibres (5-15%), it has
more nutrition by weight compared to other vascular plants: protein
(15-25% in natural conditions, 15-45% when cultured under ideal
conditions), fat, nitrogen, and phosphorus. It also contains higher
amounts of essential amino acids than most plants. In fact, it most
closely resembles animal proteins. It also contains large
concentrations of trace minerals that make Duckweed good supplements
for animal feed.
absorbing nutrients, Duckweed also has potential as a natural water
purifier, converting waste water and sewage into pure water and edible
Duckweed with little resulting sludge. The only drawbacks are that a
large surface area is required; and Duckweed cannot handle toxic
wastes and heavy metals. But Duckweed can become a serious weed in
nutrient rich, shallow ponds.
use of duckweed as envisaged appears to have only limited application
in the rural areas of developing countries because it largely exports
the nutrients to a central site where sewage works are installed and
the cost of transporting nutrients back to the farm where they can be
an asset would be extremely high.
Bangladesh the Grameen bank has sponsored a highly successful
small-scale loan system which encourages the development of small
scale farming practices. Taking Bangladesh as an example, the
organised production of duckweed could provide in sufficient
quantities to replace at a minimum 50% of the protein meals required
by the small poultry producer if a simple and economic system of
collection/sun drying and marketing could be put in place.
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