Free- floating plants have most of their photosynthetic parts above the surface of the water and their root below it. Typical plant species that have been used in the large scale applications are water hyacinth and duckweed species (Lemna, Spirodela, and Wolffiela). Free floating plants can be used as raw sewage as well as for primary or secondary treated effluents. The use of temperate climates of reed beds with water hyacinth, one of the most productive plants in the world, is limited, because hyacinth needs high temperature for its growth. The major disadvantage of duckweed compared to water hyacinth is their shallow root system and sensitivity towards wind, however, major advantage is their lower sensitivity towards colder climates [2].
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