Anaerobic biodegradation of naphthalene, phenanthrene, and biphenyl by a denitrifying enrichment culture

In previous results [Rockne and Strand (1998) Environ. Sci. Technol. 32, 29 62-3967], anaerobic biodegradation of the polycyclic aromatic hydrocarbons, naphthalene, phenanthrene, and biphenyl in a fluidized bed reactor (FBR) e nrichment was demonstrated. In this paper, re-feeding and mineralization ex periments with sub-cultures of the nitrate-reducing enrichment are describe d. The sub cultures continued to remove the PAHs after three feedings. PAH biodegradation ceased when nitrate was depleted and resumed when the enrich ment was fed nitrate, demonstrating that PAH biodegradation was dependent u pon nitrate reduction. Tests with radiolabeled PAH confirmed that PAH was m ineralized, although the extent of mineralization differed greatly with dif ferent PAHs. Only partial mineralization (17% of initial carbon) was observ ed when the culture was fed naphthalene, whereas nearly complete mineraliza tion (96%) was observed with phenanthrene. PAH carbon was incorporated into cell mass and mineralized after complete biodegradation of the PAHs, with 78-102% recoveries of radiolabel for naphthalene and phenanthrene. respecti vely. PAH carbon incorporation into biomass also varied considerably. Minor assimilation of biphenyl or phenanthrene was observed in the culture, wher eas extensive assimilation of naphthalene carbon (57%) was observed when th e culture was challenged with naphthalene. PAH degradation was approximatel y stoichiometric with the amount of nitrate consumed. Headspace analysis sh owed production of N2O suggesting the enrichment coupled the biodegradation of PAH to denitrification. (C) 2000 Published by Elsevier Science Ltd.