Biodegradation of Various Aromatic Compounds by Enriched Bacterial Cultures: Part B--Nitrogen-, Sulfur-, and Oxygen-Containing Heterocyclic Aromatic Compounds.

Present study focused on the biodegradation of various heterocyclic nitrogen, sulfur, and oxygen (NSO) compounds using naphthalene-enriched culture. Target compounds in the study were pyridine, quinoline, benzothiophene, and benzofuran. Screening studies were carried out using different microbial consortia enriched with specific polycyclic aromatic hydrocarbon (PAH) and NSO compounds. Among different microbial consortia, naphthalene-enriched culture was the most efficient consortium based on high substrate degradation rate. Substrate degradation rate with naphthalene-enriched culture followed the order pyridine > quinoline > benzofuran > benzothiophene. Benzothiophene and benzofuran were found to be highly recalcitrant pollutants. Benzothiophene could not be biodegraded when concentration was above 50 mg/l. It was observed that 2-(1H)-quinolinone, benzothiophene-2-one, and benzofuran-2,3-dione were formed as metabolic intermediates during biodegradation of quinoline, benzothiophene, and benzofuran, respectively. Quinoline-N and pyridine-N were transformed into free ammonium ions during the biodegradation process. Biodegradation pathways for various NSO compounds are proposed. Monod inhibition model was able to simulate single substrate biodegradation kinetics satisfactorily. Benzothiophene and benzofuran biodegradation kinetics, in presence of acetone, was simulated using a generalized multi-substrate model.