Removal and transformation of TCPP in activated sludge collected from a full-scale industrial WWTP: A comparative study under anoxic and aerobic conditions

The persistence of tris(1-chloro-2-propyl) phosphate (TCPP) in aquatic environments makes it essential to clarify its behavior and fate in wastewater treatment plants (WWTPs). This study systematically investigated the removal mechanisms, degradation pathways, and toxicity evolution of TCPP under anoxic and aerobic conditions in WWTP-derived activated sludge. Results showed that aerobic sludge exhibited higher removal efficiency (67.3%) than anoxic sludge (58.5%), which was confirmed in laboratory tests. While adsorption mediated the initial rapid removal, biodegradation was the dominant long-term removal mechanism, contributing up to 69.7% (anoxic) and 92.4% (aerobic) to overall elimination. Furthermore, characterization of dissolved organic matter showed stronger soluble microbial product-like fluorescence and altered protein-like signals under aerobic conditions, consistent with the higher TCPP biodegradation observed in the aerobic system. Three transformation products were tentatively identified, which elucidate two distinct degradation pathways: hydrolysis (O-dealkylation) under both conditions and a ketonization pathway exclusively in the aerobic process. Toxicity prediction revealed that all TPs were substantially less toxic than TCPP, suggesting that activated sludge-mediated biodegradation is an effective detoxification process. These findings offer critical insights for optimizing wastewater treatment strategies to mitigate the environmental risks of persistent organic pollutants.