Effect of exogenous CO₂on algae growth and wastewater treatment under simulated natural light/dark cycle using municipal wastewater as feedstock

This study investigated the effect of exogenous CO₂ on algae biomass accumulation and wastewater nutrient removal under different light intensities and a simulated natural light/dark cycle for algae strain Chlorella kessleri, using highly concentrated municipal wastewater (centrate) as feedstock. The results showed that Chlorella kessleri could easily adapt to centrate wastewater in batch reactors under simulated natural light/dark cycles with CO₂ injections under all tested light intensities. Both CO ₂ concentration and light intensity had a significant effect on algae growth and nutrient removal from wastewater. The study confirmed that there was an optimum CO₂ level for algae growth, which was 2.5% for this investigation. When the light intensity reached a certain lower limit, the effect of CO₂ supplementation became minimum because the photoautotrophic efficiency was significantly reduced. It is also found that the application of continuous or fed-batch cultivation system was preferred over batch cultivation process due to the fact that the nutrients was depleted and the algae biomass concentration decreased on Day 8.