Denitrification with ɛ-caprolactam by acclimated mixed culture and by pure culture of bacteria isolated from polyacrylonitrile fibre manufactured wastewater treatment system

Abstract

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.