Competitive metabolism of polycyclic aromatic hydrocarbon (PAH) mixtures in porous media biofilms

Complex mixtures of polycyclic aromatic hydrocarbons and other organic compounds are usually present in contaminated sites. This may influence biodegradation patterns and changes in biofilm growth and development. Biodegradation studies of naphthalene, phenanthrene and pyrene were conducted in sole-substrate systems and in binary and tertiary mixtures to examine substrate interactions on biofilms in porous media systems. It was shown that phenanthrene and pyrene could not be degraded as sole carbon sources in the system, but binary systems of the 3- and 4-ring PAHs with acetate and naphthalene supplements stimulated their degradation, with up to 87.9% and 70.1% removal efficiencies respectively. However, in the tertiary systems the presence of phenanthrene inhibited pyrene degradation. Adsorption of PAHs to sand media was determined to be negligible. Biofilm growth, development and changes in composition were analyzed over time; these showed increases in both firmly and loosely attached viable biomass, as well as extracellular polymeric substance production that formed a complex matrix. Heterogeneous surface films and a variety of biological aggregate structures and growth patterns were observed by confocal microscopy.