Nutrient Removal Mechanisms of Algal-Bacteria Consortia in Secondarily Treated Wastewater

Abstract This study aimed to evaluate how the different environmental conditions affect the nutrient removal mechanism of algal-bacteria consortia. For the first time, the dark cycle nutrient removal mechanism was investigated offering an essential reference for enhancing wastewater treatment systems. Algal-bacteria consortia behavior was studied under different air supply (0 to 12 and 0 to 24 h) and illumination (24 h light and 12:12 h light: dark) periods. The highest nitrate and phosphorus removal was obtained with continuous light irradiation and air supply. The results demonstrated that illumination duration was a more important factor than air supply. So, when the light and air ceased on the 12-hour, the removal rate zero-order constants during darkness decreased by 36 and 55% for nitrates and phosphorus, respectively, compared to the 24-hour illumination and aeration culture. Nitrates appeared to be eliminated quite faster than phosphorus in the light, and slightly faster in the dark period. Refeeding of the culture during the dark period, without additional air, did not prevent nutrient removal, which was lower by about 58 and 45% for nitrates and phosphorus, respectively, compared to the removal in the light period. Algal-bacteria cultures can effectively remove nitrates and phosphorus from wastewater even during the dark period, providing valuable data for designing algal-based outdoor wastewater treatment systems.