Rates of nutrient uptake and growth of the water hyacinth [ Eichhornia crassipes (mart.) Solms

Abstract

The nutrient uptake and growth of an aquatic macrophyte, water hyacinth [ Eichhornia crassipes (Mart.) Solms], were investigated in a static system and a continuous flow system of a nutrient solution. It was found that the specific growth rate was dependent on the air temperature, plant density and N content. The N uptake rate was correlated with the N concentration by the Michaelis-Menten-type equation, in which the maximum uptake rate of N was expressed as a function of the temperature and plant density. While the P uptake rate was influenced by not only the P concentration, temperature and plant density, but also by variations of the P content of the plant. The results of the simulation study using the proposed rate equations suggested that the efficiencies of the N and P removals from the secondary sewage effluent, by means of a water hyacinth cultivation, were exceedingly influenced by the surface base retention time of the water ( R h ), and did not depend on the plant density either after harvesting or the harvesting period itself under the usual culture conditions, and it was suitable that R h was 40 day m −1 in a temperate climate, such as Japan's, in order to obtain a high removal efficiency of 70%.