Enhanced Biodegradation Kinetic of Phenanthrene by <i>Rhodococcus zopfii</i> with Natural Biofilm

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have been detected in municipal and industrial wastewater, and are widely known as a toxic and carcinogen contaminant to human health. Currently, PAHs are treated by suspended growth bacteria in the municipal and industrial wastewater, but this method is not effective due to the washed-out effect of the bacteria from the aeration treatment. Therefore, this study investigates the attached bacteria on biofilm surface to enhance the biodegradation of PAHs. Phenanthrene (phe) and Rhodococcus zopfii (R. zopfii) were selected as the target contaminant and bacteria due to their presence and an abundancy in the wastewater. Surface characterization study of the natural biofilm was conducted using Fourier transform infrared spectroscopy (FTIR) and environmental scanning electron microscope (ESEM). Chemical functional groups present on the surface of the natural biofilm were hydroxyl (O-H), carbonyls (C═O), and alcohol (C─ O). These chemical functional groups provide sources of carbon for R. zopfii. Pore sizes of the natural biofilm were in the range of 1.97 to 20.60 μm, and they provide shelter for R. zopfii to grow and enhanced biodegradation rate of phe. The biodegradation kinetics of phe by R. zopfii with the natural biofilm (kwith biofilm: 0.26 mg/L/day) was increased 1.52&nbsp;times compared with without the natural biofilm (kwithout biofilm: 0.17 mg/L/day) within 7&nbsp;days. The biodegradation of the phe by the R. zopfii with the natural biofilm was significantly affected by difference of pH conditions (pH 7–9). The greatest biodegradation kinetic rate of phe was observed at pH 7 (kwithbiofilm: 0.441 mg/L/day) compared with other pH conditions. Phe was significantly transformed to catechol, coumarin, and phthalic acid via dihydroxylation reaction. This study provides new knowledge on the role of the natural biofilm as a shelter for R. zopfii to grow and enhance biodegradation kinetic of phe by R. zopfii in the wastewater treatment system.