Mass transfer and biodegradation of polycyclic aromatic hydrocarbons from non-aqueous phase liquids.

摘要

Organic liquids such as crude oils, creosotes and coal tar often remain in contact with groundwater or surface waters for long periods of time before or during any attempted remediation. Potentially toxic solutes such as polycyclic aromatic hydrocarbons (PAHs) are continuously released from pollutant oil phases described above to the water phase. The research was aimed at understanding how physicochemical as well as biological phenomena affect dissolution and biodegradation of PAH compounds from pollutant oil phases. These phenomena were investigated for a simple two-component non-aqueous phase liquid (NAPL) and for creosote, a multi component NAPL.; Mass transfer experiments of naphthalene from a synthesized two-component NAPL were conducted to assess the extent of variation of mass transfer rate coefficients between column and completely mixed flow-through (CMFT) systems. The differences in the hydrodynamics between column and CMFT systems, employed in this study, resulted in a difference in the mass transfer rate coefficients of a factor of 3. Several reported empirical correlations for the estimation of mass transfer coefficients in batch and column systems were verified. Good agreement between Sherwood numbers, a dimensionless quantity reflecting the magnitude of the mass transfer coefficient, predicted by the reported correlations and those calculated from mass transfer coefficients obtained from the experiments was obtained in all cases.; The biodegradation kinetic coefficients mumax and Ks for the biodegradation of naphthalene from a two-component NAPL, coated onto uniformly sized nonporous particles, were evaluated in completely mixed batch reactor (CMBR) systems and in flow-through column systems. The values obtained for mumax and Ks from column systems were very close to those obtained from CMBR systems. This suggests that both coefficients estimated from CMBR or column systems can be applied for modeling studies. The development of biofilms at the NAPL-water interface reduced mass transfer rates of naphthalene by 70% in column systems and 60% in CMBR systems.; Viscous interfacial films develop at the creosote-water interface when creosote is aged in water for a period of time. The mass transfer rate coefficient of naphthalene from creosote to water was reduced by 30% over a one-week aging period. Minor additional reductions were observed with further aging. Hindered diffusion through the bulk creosote phase and changes in composition of creosote as a result of extended dissolution did not account for the observed reductions.