Ten Years After: The Status of Polybrominated Diphenyl Ethers (PBDE) in Canadian Biosolids and Their Fate Through Solids Treatment Processes

Occurrence of persistent organic pollutants such as polybrominated diphenyl ether (PBDE) flame retardants in biosolids are a concern as these contaminants may be transported into the environment during land application. This study monitored the concentration of 21 PBDE congeners in raw sludge and biosolids collected from nine sludge treatment facilities across Canada that employed 4 different solids treatment processes. The overall ΣPBDE-Br concentration varied between 0.25 to 1.5 μg-Br/g dry weight. Deca-BDE (BDE-209) was the predominantly occurring congener and its concentration constituted 40-65% of the overall ΣPBDE-Br concentration in both raw sludge and biosolids samples. Tri-, hepta-, and octa- BDE made up less than 1% of the overall ΣPBDE-Br in the raw sludge and biosolids samples. Contaminant mass balances were assembled around the treatment systems and the overall fate of the PBDEs was found to depend upon the treatment technology. While there was no significant change in mass flow during pelletization, ΣPBDE-Br mass flow was reduced by approximately 30% during alkaline stabilization. The removal of PBDE was not consistent in aerobic or anaerobic digestion treatment systems.