A group of tiny aquatic plants commonly known as uckweeds(Lemma spp.) are a promising commercial aquaculture crop. Species of duckweed are hardy and fast growing and have the same protein quality of soybean. They appear to be a complete nutritional package for such fish as carp and tilapia. In addition, duckweed-based wastewater treatment systems can provide effective and inexpensive solutions to wastewater problems for towns and villages with limited resources. Duckweed wastewater treatment systems, which are essentially lagoon systems, remove, by bio-accumulation, as much as 99 per cent of the nutrients and dissolved solids contained in wastewater. Duckweed systems distinguish themselves from other efficient wastewater treatment mechanisms in that they also produce a valuable, protein-rich biomass as a by-product while reducing the continual influx of harmful substances (nitrogen, phosphorous) into receiving bodies of water (rivers, lakes or seas).

In collaboration with the United Nations Capital Development Fund (UNCDF) and the Government of Bangladesh, the Bangladeshi NGO, PRISM, undertook a project to establish a viable and replicable integrated system of small-scale intensive fish-farming and duckweed production. The output from duckweed ponds was to serve the feeding needs of the fish ponds. The project duckweed production was based on the technology developed at the Mirzapur Centre, one of two extension services centres established by the project. The project targetted landless or marginal farmers in order to provide them with a new source of income.

Although a recent mid-term evaluation of the project indicates the project is not meeting all expectations, the duckweed technology remains one of the more positive aspects of the project. Although not an original objective of the project, the construction of improved our flash typelatrines, connected to the duckweed ponds to treat human waste, proved very popular with local families. Households were highly appreciative of non-tangible benefits of this technology, i.e., no smell, and reduced flies and mosquito populations due to the complete coverage of water surfaces by duckweed.

Within the project areas there was evidence of a high level of interest in duckweed technology, with individuals approaching project staff for information. Naturally-occurring duckweed, previously available free from non-project ponds, is now recognised as a resource, and a market in the supply and trade of fresh duckweed is developing. The failure of the duckweed production to provide all the feed necessary for the fish ponds as originally planned was attributed to poor project planning. An evaluation of the project concluded that duckweed had the potential to become a complete feeding source.

Sources: Sultana and Roy 1996; Skillicorn, Spira and Journey 1993.

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