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

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.

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).

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).

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.