Anoxic degradation of nitrogenous heterocyclic compounds by activated sludge and their active sites

The potential for degradation of five nitrogenous heterocyclic compounds (NHCs), i.e., imidazole, pyridine, indole, quinoline, and carbazole, was investigated under anoxic conditions with acclimated activated sludge. Results showed that NHCs with initial concentration of 50 mg/L could be completely degraded within 60 hr. The degradation of five NHCs was dependent upon the chemical structures with the following sequence: imidazole > pyridine > indole > quinoline > carbazole in terms of their degradation rates. Quantitative structure–biodegradability relationship studies of the five NHCs showed that the anoxic degradation rates were correlated well with highest occupied molecular orbital. Additionally, the active sites of NHCs identified by calculation were confirmed by analysis of intermediates using gas chromatography and mass spectrometry.

Graphical abstractCorrelation between pseudo first-order rate constant and EHOMO.Figure optionsDownload full-size imageDownload as PowerPoint slide