Wastewater nutrients removal by Chlorella vulgaris: Optimization through acclimation

The unicellular green alga, Chlorella vulgaris, was acclimated in wastewater for a period of 14 days before employed in treating primary settled wastewater. The acclimated cells had significantly higher cellular chlorophyll content than the unacclimated ones. The rate of chlorophyll synthesis in the acclimated cells was double that of the unacclimated cells during the initial 3 days in the course of wastewater treatment. This indicated that the acclimated cells were physiologically mole active and took up more nutrients from the wastewater for their growth and metabolism, resulting in a nutrient removal efficiency of 86% inorganic N and 70% inorganic P for a retention time of 2 days. Such rates were much higher than those obtained in the unacclimated system with similar algal density, where removal rates for total inorganic N and P were 54% and 50%, respectively. Acclimation proved to be a valuable means to improve efficiency of wastewater nutrient removal by the microalgal species which were not indigenous in sewage.