MASS-TRANSFER EFFECTS ON MICROBIAL UPTAKE OF NAPHTHALENE FROM COMPLEXNAPLS

The bioavailability of naphthalene present as a component of a complex nonaqueous phase liquid (NAPL) comprised by nine aromatic compounds w as investigated. Specifically, the effects of naphthalene mass transfe r from the NAPL to the aqueous phase on rates of its microbial degrada tion were examined. The investigations were conducted using a pure cul ture, ATCC 17484, and a mixed culture of naphthalene-degrading bacteri a, the former having been implicated previously in the direct uptake o f sorbed naphthalene. The studies were conducted in mass-transfer-limi ted, segregated-phase reactors (SPRs) in which both the NAPL and aqueo us phases were internally well-mixed. A 30-day active biodegradation p eriod was preceded and followed by a 5-7-day period devoid of bioactiv ity, during which time the rates and extents of mass transfer of compo nents from the NAPL to the aqueous phase were quantified. The NAPL-pha se naphthalene mass depletion profiles during biodegradation were comp ared to those predicted by assuming maximum mass depletion under mass- transfer-limited conditions using both pre- and post-biodegradation di ssolution rate and equilibrium parameters. The observed mass depletion rates were high during the initial stages of biodegradation but decre ased significantly in later stages. Throughout biodegradation, even in the initial rapid stage, mass depletion rates never exceeded maximum predicted rates based on pre-biodegradation mass transfer parameters. Reduced depletion rates in the later stages appear to relate to mass t ransfer hindrance caused by formation of biofilms at the NAPL-water in terface. (C) 1998 John Wiley & Sons, Inc.