Biodegradation of chlorobenzenes was assessed at an anoxic aquifer by combining hydrogeochemistry and stable isotope analyses. In situ microcosm analysis evidenced microbial assimilation of chlorobenzene (MCB) derived carbon and laboratory investigations asserted mineralization of MCB at low rates. Sequential dehalogenation of chlorinated benzenes may affect the isotope signature of single chlorobenzene species due to simultaneous depletion and enrichment of 13C, which complicates the evaluation of degradation. Therefore, the compound-specific isotope analysis was interpreted based on an isotope balance. The enrichment of the cumulative isotope composition of all chlorobenzenes indicated in situ biodegradation. Additionally, the relationship between hydrogeochemistry and degradation activity was investigated by principal component analysis underlining variable hydrogeochemical conditions associated with degradation activity at the plume scale. Although the complexity of the field site did not allow straightforward assessment of natural attenuation processes, the application of an integrative approach appeared relevant to characterize the in situ biodegradation potential. 相似文献
An emplaced source of coal tar creosote within the sandy Borden research aquifer has documented the long-term (5140 days) natural attenuation for this complex mixture. Plumes of dissolved chemicals were produced by the essentially horizontal groundwater flowing at about 9 cm/day. Eleven chemicals have been extensively sampled seven times using a monitoring network of approximately 280, 14-point multilevel samplers. A model of source dissolution using Raoult's Law adequately predicted the dissolution of 9 of 11 compounds. Mass transformation has limited the extent of the plumes as groundwater has flowed more than 500 m, yet the plumes are no longer than 50 m. Phenol and xylenes have been removed and naphthalene has attenuated from its maximum extent on day 1357. Some compound plumes have reached an apparent steady state and the plumes of other compounds (dibenzofuran and phenanthrene) are expected to continue to expand due to an increasing mass flux and limited degradation potential. Biotransformation is the major process controlling natural attenuation at the site. The greatest organic mass lost is associated with the high solubility compounds. However, the majority of the mass loss for most compounds has occurred in the source zone. Oxygen is the main electron acceptor, yet the amount of organics lost cannot be accounted for by aerobic mineralization or partial mineralization alone. The complex evolution of these plumes has been well documented but understanding the controlling biotransformation processes is still elusive. This study has shown that anticipating bioattenuation patterns should only be considered at the broadest scale. Generally, the greatest mass loss is associated with those compounds that have a high solubility and low partitioning coefficients. 相似文献
We study numerically the dynamics of particles of dispersed phase in a turbulent gas flow in planar shock waves (SWs) sliding along a solid surface with a depression of trapezoid shape. The ascent of particles from the cavity walls has been computed in the approximation of a rarefied gas–particle mixture. A considerable influence of the passing SW strength and the initial location of particles on the characteristics of particles’ ascent, the non-monotonicity of the dependence of the particle-ascent height on the initial longitudinal coordinate, and the SW Mach number, and a possibility of the formation of particles’ accumulation and removal zones on the depression bottom are shown. 相似文献
This paper is devoted to the numerical and experimental investigation of hydrogen self-ignition as a result of the formation of a primary shock wave in front of a cold expanding hydrogen gas jet. Temperature increase, as a result of this shock wave, leads to the ignition of the hydrogen–air mixture formed on the contact surface. The required condition for hydrogen self-ignition is to maintain the high temperature in the area for a time long enough for hydrogen and air to mix and inflammation to take place.
Calculations of the self-ignition of a hydrogen jet are based on a physicochemical model involving the gas-dynamic transport of a viscous gas, the kinetics of hydrogen oxidation, the multi-component diffusion, and the heat exchange. We found that the reservoir pressure range, when a shock wave formed in the air during depressurization, has sufficient intensity to produce self-ignition of the hydrogen–air mixture formed at the front of a jet of compressed hydrogen. We present an analysis of the initial conditions (the hydrogen pressure inside the vessel, the temperature of the compressed hydrogen and the surrounding air, and the diameter of the hole through which the jet was emitted), which leads to combustion. 相似文献