Partitioning of Brominated Flame Retardants in Wastewater Treatment: Model Calibration and Loading Projections

Data from an intensive inter-stage sampling project at an advanced wastewater treatment plant, which characterized congeners of the flame retardants polybrominated diphenyl ethers (PBDEs), were used to calibrate a fate model of the treatment plant. Flow and solids balances were first established, followed by predicting of the fate of the different congeners through the treatment plant. A biodegradation rate coefficient value of 1E-05 L/mg VSS-h was used for all congeners in the absence of any published values. Sensitivity analysis was used to assess the effect of varying the magnitude of the biodegradation rate coefficient on the fate of different representative congeners. Most of the PBDEs (approximately 90%) are predicted to partition to the wastewater residual solids, with most of the remaining mass discharged in the treated effluent. Biodegradation may account for a small mass of the lower brominated congeners. Air emissions were predicted be very small. Estimates of the mass of PBDEs discharged nationally by U.S. POTWs were calculated based on flows reported in the 2004 EPA Needs Survey.