Going Beyond Carbon Redirection: Integrating Operational Conditions to Maximize Carbon and Phosphorus Removal in the A-Stage Process

This study explores the use of the alternating activated adsorption (AAA) system to achieve a balance between sustaining high COD redirection toward recovery streams and high effluent quality, in terms of COD and phosphorus removal. It investigates a novel integrative operational approach that includes hydraulic retention time (HRT), solid retention time (SRT), dissolved oxygen (DO) concentration, and effluent recirculation. Results indicated that integrating long HRT (4 h) with limited DO concentration (below 0.5 mgO₂/L) effectively controlled COD oxidation while allowing for high COD redirection. Effluent recirculation further improved solid capture and COD redirection, while short SRT limited the associated oxidation through hydrolysis. Notably, this resulted in achieving COD redirection and removal above 50 and 80%, respectively. Meanwhile, such conditions achieved biophosphorus removal efficiencies as high as 55–60%, which surpasses other A-stage systems. To achieve higher phosphorus removal, enhanced biological phosphorus removal (EBPR) should be induced under conditions that slightly diminish the COD redirection and, to a lesser extent, the COD removal efficiency. Significantly, this research suggests a novel approach to designing and operating the A-stage process, particularly AAA, acknowledging its holistic role in fostering sustainable and energy-efficient wastewater treatment.