Abstract
Water quality purification using water hyacinth, Eichhornia Crassipes (Mart.) Solms, has attracted from the point of view of energy cost on wastewater treatment systems. Water hyacinth, however, is originally a subtropical flora. Therefore it is necessary to investigate the applicability on temperate climate as Japan. The purpose of this study is to investigate the characteristics of nitrogen uptake and growth of water hyacinth on the temperate climate conditions. Rates of nitrogen uptake and growth were measured in cultures of water hyacinth growing outdoors in continuously flowing nutrient solutions. Either NH4Cl or NaNO3 was added as the resource of nitrogen in nutrient solutions. Maximum growth rate coastant kmax was expressed as an exponential function of air temperature, kmax=a [eb (T-10)-1.0](1/hr). This model is a nonlinear function, because experimental results were analyzed using a nonlinear parameter estimation program that employs the method of Gauss-Newton least-squares. As the results a=0.00623 and b=0.0326 were obtained. An empirical model of nitrogen uptake rate of water hyacinth was simulated by the Michaelis-Menten equation with Vmax, the maximum specific rate of nitrogen uptake. The total nitrogen uptake rate was caliculated by a mass balance equation with nitrogen in each culture. Half-saturation constants were estimated to be 0.650 mg-N/1 in the case of NH4Cl as nitrogen resource and 0.893 mg-N/l for NaN03. On the other hand, the yield coefficent of water hyacinth was 0.0279mg-DW/mg-N when NH4Cl, was used as the nitrogen resource.
