Efficacy and limitations of the A2O process in simultaneous removal of surfactants and nutrients from municipal wastewater

This study evaluated the efficacy of the Anaerobic-Anoxic-Oxic (A2O) process for the simultaneous removal of organic pollutants, specifically surfactants (detergents), and nutrients (nitrogen and phosphorus) from municipal wastewater. Sampling was conducted over a 12-month period from September 23, 2023 to September 22, 2024, at a monthly frequency. During each sampling event, grab samples were collected from multiple points within the treatment train: the raw influent wastewater, the influent and effluent streams of the anaerobic, anoxic, and aerobic tanks, and the final effluent from the secondary clarifier. The anionic surfactants (as methylene blue active substances, MBAS), ammonium-nitrogen (NH₄⁺-N), nitrate-nitrogen (NO₃⁻-N), nitrite-nitrogen (NO₂⁻-N), and total phosphorus (TP)—were quantified in accordance with Standard Methods for the Examination of Water and Wastewater. The mean final effluent concentrations were 0.22 ± 0.05 mg/L for linear alkylbenzene sulfonate (LAS), 13.18 ± 3.7 mg/L for nitrate (as NO₃-N), and 4.46 ± 0.18 mg/L for phosphorus (as P). Process performance data indicated that the oxic tank was the primary site for LAS and phosphorus removal, while the anoxic tank facilitated the most significant nitrate reduction. While the Anaerobic-Anoxic-Oxic (A2O) process proficiently removes surfactants and phosphorus via microbial metabolism, its performance in nitrate elimination is constrained. Inadequate denitrification in the anoxic stage, frequently due to a limited biodegradable carbon source or improper redox conditions, indicates a need for process optimization.