The Effects of Solids Retention Time in Full-Scale Activated Sludge Basins on Trace Organic Contaminant Concentrations

Although pharmaceuticals and personal care products (PPCPs) and endocrine disrupting compounds (EDCs) are largely unregulated, water resource recovery facilities are increasingly using advanced chemical/physical treatment technologies (e.g., advanced oxidation and reverse osmosis) to remove or destroy these trace organic contaminants (TOrCs). This can both reduce potential adverse human health effects in reuse applications and mitigate environmental effects on aquatic ecosystems. Unfortunately, advanced treatment technologies are typically energy intensive and costly to implement, operate, and maintain. The goal of this study was to determine whether optimization of solids retention time (SRT) provided sufficient benefits to warrant such operational strategies for TOrC mitigation. Specifically, SRTs of 5.5, 6, and 15 days were evaluated to determine the effects on several standard wastewater parameters (e.g., nitrite, nitrate, and ammonia concentrations) and the degradation of TOrCs. The experimental SRTs were operated simultaneously in parallel, full-scale activated sludge basins. The results indicate that it can be beneficial to implement biological process optimization strategies using existing infrastructure while reducing reliance on advanced treatment technologies. This study also identified potential operational issues that might arise in activated sludge systems operating at extended SRTs.