Effect of Changes in Biomass Concentration and Light Cycle on Chlorella Vulgaris Microalgae in Nitrate and Phosphate Removal from Municipal Wastewater

Abstract

Introduction and purpose: Municipal wastewater effluents contain high amounts of nitrate and phosphate nutrients. Microalgae have been considered as a bioreactor to absorb nutrients in wastewater due to their environmental friendliness and ability to produce valuable products. In the present study, the effects of light-dark cycles and microalgae biomass concentrations on the nitrate and phosphate removal from municipal wastewater were investigated. Methods: In this study, Chlorella vulgaris (green microalgae) was first cultured in a membrane photobioreactor with a light intensity of 300 μmol photons in three light cycles (12 h light-12 h dark, 16 h light-8 h dark, and 24 h light and 0-h dark). Afterward, the best light cycle in municipal wastewater effluent was investigated at constant concentrations of microalgae (0.5 g L-1, 1 g L-1, and 1.5 g L-1). Results: According to the results, the highest growth rate (2.3 g L-1) and the highest amount of nitrate and phosphate removal (87% and 86%) were obtained in the 24-0 light cycle. Following that, the concentration of 1 g L-1 of microalgae in the 24-0 light cycle was recorded as the highest amount of nitrate and phosphate removal from municipal wastewater (91% and 87%, respectively). Conclusion: The results indicated that light-dark cycles and initial concentrations of microalgal inoculation could have an undeniable effect on the growth of microalgae. Moreover, it could have a significant impact on the removal of nitrate and phosphate from municipal wastewater through microalgae cultivation. This removal percentage increased with the optimization of light conditions and biomass concentration.

Keywords

• biomass concentration
• light cycle
• microalgae
• municipal wastewater effluent
• nitrate and phosphate