Optimization of the phytoremediation conditions of wastewater in post-treatment by Eichhornia crassipes and Pistia stratiotes : kinetic model for pollutants removal

This study aims at determining the optimal conditions for pollutants removal in wastewater using Eichhornia crassipes (E. crassipes) and Pistia stratiotes (P. stratiotes) as appropriate aquatic plants for a post-treatment by phytoremediation. From factors such as residence time, plant density and initial PO43− concentration, four responses, i.e. the removal efficiency of PO43−, NO3−, NH4+ and the chemical oxygen demand (COD) were followed, using complete factorial design. After validation of the regression models by the statistical analyses, optimal conditions were obtained by using the global desirability function. Global desirabilities of 0.96 and 0.97 were respectively obtained for E. crassipes and P. stratiotes, for a residence time of 30 days, a plant density of 60 feet/m2 and an initial PO43− concentration of 10 mg/L. Using E. crassipes, this corresponds to the elimination of 94.2% of PO43−; 93.3% of NO3−; 95.0% of NH4+ and 63.6% of COD. In the case of P. stratiotes, 93.9% of PO43−; 83.4% of NO3−, 99.5% of NH4+ and 84.4% of COD were removed. Finally, under the used conditions, E. crassipes are able to better eliminate phosphorus and nitrates, while P. stratiotes are very effective in removing NH4+ and COD.