Nutrient Removal in Algal-Bacterial Consortia Treating Secondary Effluent During Light-Dark Cycles

The scope of this study was to evaluate different environmental factors that affect the ability of algal-bacteria consortia to remove nutrients. The dark-cycle nitrogen removal process was investigated, providing valuable insights for improving wastewater treatment systems. The behavior of the consortia was examined under various illumination regimes (continuous 24-h light and a 12:12 h light-dark cycle) and varying aeration conditions (0 to 12 h and 0 to 24 h of air supply). Continuous light exposure combined with continuous aeration resulted in the highest nitrate and phosphorus removal. The results indicated that light duration had a greater effect on nutrient removal than air supply. When light and aeration were stopped after 12 hours, the zero‑order removal rate constants during the dark period decreased by 36% for nitrates and 55% for phosphorus compared with the 24‑hour light and aeration condition. Nitrate removal occurred more rapidly than phosphorus removal in the light and slightly faster in the dark. Although nutrient removal during the dark phase decreased approximately 58% for nitrates and 45% for phosphorus relative to the light phase, it did not cease entirely, even when the culture was refed without additional aeration. These findings demonstrate that algal-bacteria consortia can efficiently remove nitrates and phosphorus from wastewater, even in the absence of light, offering important information for the design and optimization of outdoor algal-based wastewater treatment systems.