Effect of temperature and CO₂ concentration on biological nutrient removal from tertiary municipal wastewater using microalgae Chlorella prototheocoides

This study investigates the potential of phototrophic microalgae, specifically Chlorella protothecoides, for biological wastewater treatment, with a focus on the effects of air temperature and CO₂ concentration on nutrient removal from tertiary municipal wastewater. Utilizing both the Monod and Arrhenius kinetic models, the research examines how temperature and nutrient availability influence microalgal growth and nutrient removal. The study finds that optimal biomass productivity occurs at 25 °C, with growth slowing at higher temperatures (30 °C, 40 °C, and 45 °C). The Monod and Arrhenius models, which showed strong agreement with experimental data, revealed that temperature significantly impacted growth kinetics, with the Arrhenius model accurately predicting growth rates at lower temperatures. Activation energies for growth and cell death were determined as 5.4 kJ mol⁻¹ and 88.4 kJ mol⁻¹, respectively. The study also demonstrated that optimal nitrogen and phosphorus removal occurred at 25°C-30 °C, with 100 % total nitrogen (TN) removal and 85 % total phosphorus (TP) removal achieved at 30 °C. Additionally, CO₂ concentration influenced biomass productivity, with peak productivity and nutrient removal at 6 % CO₂, highlighting the importance of CO₂ levels in optimizing growth and nutrient elimination. These findings provide valuable insights into optimizing conditions for microalgae-based wastewater treatment, particularly in seasonal cultivation strategies, and contribute to improving biodiesel production and nutrient removal efficiency.