The aim of this study is to isolate denitrifying bacteria utilizing ɛ-caprolactam as the substrate, from a polyacrylonitrile fibre manufactured wastewater treatment system. The aim is also to compare the performance of PAN (polyacrylonitrile) mixed bacteria cultures acclimated to ɛ-caprolactam and isolated pure strain for treating different initial e-caprolactam concentrations from synthetic wastewater under anoxic conditions. The result showed that the PAN mixed bacteria cultures acclimated to e-caprolactam could utilize 1538.5 mg/l of ɛ-caprolactam as a substrate for denitrification. Sufficient time and about 2200 mg/l of nitrate were necessary for the complete ɛ-caprolactam removal. Paracoccus thiophilus was isolated from the polyacrylonitrile fibre manufactured wastewater treatment system and it could utilize 1722.5 mg/l of ɛ-caprolactam as a substrate for denitrification. About 3500 mg/l of nitrate was necessary for the complete removal of ɛ-caprolactam. When the initial ɛ-caprolactam concentration was below 784.3 mg/l, the removal efficiency of ɛ-caprolactam by Paracoccus thiophilus was better than that for the PAN mixed bacteria cultures. The growth of Paracoccus thiophilus was better. However, when the initial ɛ-caprolactam concentration was as high as 1445.8 mg/l, both the ɛ-caprolactam removal efficiency by Paracoccus thiophilus and Paracoccus thiophilus specific growth rate were similar to the PAN mixed bacteria cultures.

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