97/01434 Biodegradation of naphthalene from coal tar: An assessment of the potential for slurry treatment at MGP sites

Abstract

The rates and extents of microbial degradation of naphthalene from coal tar has been evaluated in gently mixed batch reactors. Substantial depletion of naphthalene from coal tar by microbial degradation under optimal conditions was observed. The rate of degradation of naphthalene, the principal constituent in coal tar, was found to be significantly influenced by the rate of external surface mass transfer from the coal tar. Results show that the rate of mass transfer may control the overall rate of biotransformation in mixed systems where coal tar is present as a globule (k{sub l}a {approx_equal} 2/day). Mass transfer does not limit biodegradation in slurry systems when coal tar is distributed among a large number of small microporous silica particles, for which k{sub l}a is several thousand per day. The microbial degradation process is dependent on relationships between the NAPL composition and equilibrium aqueous naphthalene concentration, the naphthalene mass transfer rate between the NAPL and aqueous phases, and the intrinsic rates of microbial degradation of naphthalene. These relationships have been investigated and quantitative criteria to assess whether mass transfer or biokinetic limitations control the overall rate of biotransformation of PAH compounds are identified. These results with gently-mixed batch reactors under optimal conditionsmore » for microbial degradation provide an indication of the maximum potential rates of microbial degradation of naphthalene from coal tar.« less