The commercial flame retardant is an emerging contaminant (EC) commonly found in soils and sediments. A coupled UVphotolysis-biodegradation process was used to decompose decabromodiphenyl ether (BDE-209) in clay slurries. A novel bioslurry bioreactor (NBB) was employed in which BDE-209 degradation was maximized by the simultaneous application of LED UVA irradiation and biodegradation by a mixed bacterial culture. The rate of BDE-209 degradation decreased in the order: coupled UV photolysis-biodegradation (1.31 × 10-2 day-1) > UV photolysis alone (1.10 × 10-2 day-1) > biodegradation alone (1.00 × 10-2 day-1). Degradation intermediates detected included hydroxylated polybrominated diphenylethers, partially debrominated PBDE congeners and polybrominated dibenzofuran. The UV-resistant bacterial strains isolated that could utilize BDE-209 as a sole carbon source included Stenotrophomonas sp., Pseudomonas sp., and Microbacterium sp. These strains encoded important functional genes such as dioxygenase and reductive dehalogenases. Continuous UV irradiation during the NBB process affected various biochemical oxidative reactions during PBDEs biodegradation. Simultaneous photolysis and biodegradation in the NBB system described reduces operational time, energy, expense, and maintenance-demands required for the remediation of BDE-209 when compared to sequential UV-biodegradation process or to biodegradation alone. Keywords Coupled UV photolysis-biodegradation. Decabromodiphenyl ether. Novel bioslurry bioreactor. UV-resistant bacterial strains. Polybrominated dibenzofuran Highlights • A time, energy, and cost-saving technique using a coupled UV photolysis-biodegradation process for degrading BDE-209 in a novel bioslurry bioreactor. • Identification of isolated UV-resistant bacterial strains that potentially are able to utilize PBDEs as sole carbon source and the analysis of related functional genes. • The prediction of a possible pathway for BDE-209 degradation by coupled photolysis-biodegradation.