Anaerobic degradation of polycyclic aromatic hydrocarbons in sludge

Abstract

Sludge samples were collected from municipal and petrochemical active sludge to assess the potential for biotreating polycyclic aromatic hydrocarbons (PAHs) in contaminated sludge. Our results show that the order of degradation rates for PAHs in municipal sludge under anaerobic conditions was: phenanthrene > pyrene > anthracene > fluorene > acenaphthene. In petrochemical sludge the order was acenaphthene > fluorene > phenanthrene > anthracene > pyrene. PAH degradation was slower in municipal sludge than in petrochemical sludge. No significant differences were found in PAH degradation rates within a pH range of 6.0–8.0, but a delay was noted at pH 9.0 in both sludge types. Various anaerobic conditions revealed a high-to-low order of biodegradation rates of sulfate-reducing conditions > methanogenic conditions > nitrate-reducing in both sludge types. It was also found that when the five PAHs were mixed in petrochemical sludge, all of their individual degradation rates were enhanced; however, in municipal sludge, acenaphthene, anthracene and fluorine degradation rates were enhanced, but phenanthrene and pyrene degradation rates were delayed.