Nutrient removal by water lettuce (Pisitia stratiotes)

Abstract

The nutrient uptake and growth rates of the water lettuce [Pisitia stratiotes] were investigated in a batch culture system and a continuous flow system. As the water hyacinth [Eichhornia crassipes] is well known and widely researched as an aquatic macrophyte, water hyacinths were used as a control in a batch culture system. It was found that the specific growth rate of water lettuce was slightly higher in dry season, and in rainy season the growth rate of water hyacinths decreased almost 70%, but the rate of water lettuce decreased only 45%. From this result, water lettuce is thought to be grow up enough even under low solar radiation. The nitrogen, phosphorus and ash contents of biomass were about 1.5 times higher in water hyacinths than in water lettuce (N:2.15% & 1.65%, P:1.67% & 1.03%, ash 19.6% & 19.9% respectively). As the biomass of water lettuce is not so big and heavy (wet weight of water lettuce was under 100g and the width and height of the plant was under 20cm), removal of surplus biomass from water bodies is easy. It was made clear that water lettuce is very effective for removing nutrient from water bodies.