Autotrophic and mixotrophic growth of microalgae Micractinium pusillum Fres. isolated from wastewater stabilization pond: influence of light and temperature
In the wastewater stabilization pond, the growth of the microalgae depends on several factors such as temperature, light and nutriments. In addition to these factors, the presence of the organic matter has great influence on the development in such system. In the aim to study the dynamic of the microalgae in the wastewater stabilization pond of Ouarzazate city (south of Morocco) and possibly its modelling, the determination of the growth parameters (μmax, Iopt and b) has been carried out according to the model of PEETERS and EILERS (1978). Indeed, Micractinium pusillum, a Chlorococcal green algae developing in the experimental wastewater stabilization pond of Ouarzazate city has been isolated and cultured under controlled conditions of light and temperature on synthetic medium (DAUTA, 1982) enriched in nitrogen and phosphorus. In autotrophic conditions, application of the PEETERS and EILERS model to the growth of Micractinium pusillum, resulted in the determination of the parameters: μmax (0,58 day-1), Iopt (182 μE·m-z·s-1) and b (0,1) using the maximal growth temperature of 35°C. In mixotrophic conditions under the same temperature, these parameters were respectively 0,85 day-1, 150 μE·m-z ·s-1 and 1. According to the trophic mode, the growth of Micractinium pusillum revealed a variation of the parameters μmax, Iopt and b. The mixotrophic growth, probable behaviour in the wastewater stabilization pond, has induced particularly the elevation of the growth rate and the coefficient b. Also, this study showed that light intensity has varied effects on the growth of microalgae in the two trophic modes.