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Effect of Aliphatic Nonaqueous Phase Liquids on Naphthalene Biodegradation in Multiphase Systems

Dep. of Chemistry, Washington State Univ., Tri-Cities, 100 Sprout Road, Richland, WA 99352;

R. S. Achin

Dep. of Nat. Resour. Sci., Univ. of Rhode Island, Kingston, RI 02881,

R. W. Traxler

Dep. of Food Sci. and Nutr., Univ. of Rhode Island, Kingston, RI 02881.

^* Corresponding author (apg{at}beta.tricity.wsu.edu).

ABSTRACT

Biodegradation of naphthalene by a Coryneform bacterium was examined in multiphase aqueous slurry systems containing a nonaqueous phase liquid (NAPL). The evolution of ¹⁴CO₂ provided an index of biodegradation under aerobic conditions. The effect of NAPL hydrophobicity was evaluated by considering a homologous series of n-alkanes (C6–C16). Experiments were conducted in NAPL-water and soil-NAPL-water systems where the inoculum was pre-incubated with a sandy aquifer material. Relative to aqueous systems, conversion to CO₂ increased in the presence of decane, dodecane, and hexadecane. Biodegradation was apparent, but decreased in the presence of octane, and was negligible in the presence of hexane. Thus biodegradation was sustained in multiphase systems where log K_ow of the NAPL was >5, and was inhibited in systems where the log K_ow of the NAPL was <4. Naphthalene partitioning between water and each of the NAPLs was similar, indicating that the observed differences in biodegradation among the homologous series were not due to differences in naphthalene distribution. Naphthalene sorption to the sandy aquifer material was minimal and the aquifer material did not significantly modify biodegradation. Mineralization rates were reduced in multiphase systems when compared with aqueous systems; CO₂ production curves were described with a first-order kinetic model. Reduced mineralization rates in soil-NAPL-water systems can be explained by the lower aqueous phase concentration. This was not the case in the NAPL-water system, suggesting a direct effect of the NAPL on the bacteria.