Integrated passive sampling and fugacity model to characterize fate and removal of organophosphate flame retardants in an anaerobic-anoxic-oxic municipal wastewater treatment system.

It is crucial to deeply understand the fate and removal mechanism of various organophosphate flame retardants (PFRs) in specified wastewater treatment processes. However, concentration fluctuation and matrix effect in wastewater challenge quantification of PFR flux for both field observation and model validation. We present measured seasonal distribution profiles of time-weighted average (TWA) concentrations by in situ hydrophobic and polar passive samplers and modeled mass transport and transformation by means of fugacity for 11 PFRs with varied structures in an anaerobic-anoxic-oxic (A-A-O) municipal wastewater treatment system, and provided a systematic approach to characterize fate and removal mechanism of PFRs in major compartments via various treatment processes. We find evidence that PFRs have a unique structural-dependent fate and removal in the A-A-O system. Hydrophilic chlorinated-PFRs present persistent in all major compartments and dominate in effluents with significant variations; alkyl-PFRs are majorly reduced by biodegradation; whereas hydrophobic aryl-PFRs have the highest removal percentage, contributed by both sorption on solids and biotransformation. Sensitive analysis shows the most influential operation parameters on removal efficiency varied among the PFRs with different properties. We also conclude passive sampling can be effectively applied to estimate TWA wastewater concentrations and to validate fugacity model prediction.