Phototrophic Bioremediation of Municipal Tertiary Wastewater Coupling with Lipid Biosynthesis Using Scenedesmus dimorphus: Effect of Nitrogen to Phosphorous Ratio with/without CO2 Supplementation

Abstract

Scenedesmus dimorphus was utilized for the tertiary treatment of municipal wastewater in an effort to remove nutrients from secondary treated wastewater. In addition to the concurrent generation of biomass containing lipids for biofuel production. The effect of nitrogen to phosphorous (N:P) ratios (1:1 to 8:1) in culture media without carbon dioxide (CO2) supplementation (air supply alone, Case 1) and with CO2 supplementation (2% CO2 in air, Case 2) was investigated through a series of systematic parametric batch experiments. Case 2 produces greater biomass at all N:P ratios than Case 1. In Case 1, the highest biomass output for a N:P ratio of 8:1 is 567 mg/L at pH 8.4. In Case 2, however, the maximum biomass yield is 733 mg/L when the N:P ratio is 2:1 and the pH is 7.23. Scenedesmus dimorphus is capable of absorbing nitrogen and phosphorous from wastewater in a CO2 environment and at the optimal N:P ratio. In Case 1, total nitrogen removal ranges from 28% to 100% and in Case 2, total nitrogen removal ranges from 60% to 100%, depending on the N:P ratio. For an initial concentration of 13 mg/L, the total phosphorous removal ranges from 37% to 57%, depending on the N:P ratio in both cases. Case 2 yields a maximum lipid content of 29% of the biomass dry weight when the N:P ratio is 1:1. These results suggest the viability of removing nutrients from secondary treated wastewater utilizing microalgae Scenedesmus dimorphus and lipid biosynthesis in the generated biomass.