Mass transfer effects on microbial uptake of naphthalene from complex NAPLs (vol 60, pg 750, 1998)

The bioavailability of naphthalene present as a component of a complex nona queous phase liquid (NAPL) comprised by nine aromatic compounds was investi gated. Specifically, the effects of naphthalene mass transfer from the NAPL to the aqueous phase on rates of its microbial degradation were examined. The investigations were conducted using a pure culture, ATCC 17484, and a m ixed culture of naphthalene-degrading bacteria, the former having been impl icated previously in the direct uptake of sorbed naphthalene. The studies w ere conducted in mass-transfer-limited, segregated-phase reactors (SPRs) in which both the NAPL and aqueous phases were internally well-mixed. A 30-da y active biodegradation period was preceded and followed by a 5-7-day perio d devoid of bioactivity, during which time the rates and extents of mass tr ansfer of components from the NAPL to the aqueous phase were quantified. Th e NAPL-phase naphthalene mass depletion profiles during biodegradation were compared to those predicted by assuming maximum mass depletion under mass- transfer-limited conditions using both pre- and post-biodegradation dissolu tion rate and equilibrium parameters. The observed mass depletion rates wer e high during the initial stages of biodegradation but decreased significan tly in later stages. Throughout biodegradation, even in the initial rapid s tage, 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 transfer hindrance caused by formati on of biofilms at the NAPL-water interface. (C) 1998 John Wiley & Sons, Inc .