Transport, Fate And Remediation Of Perchloroethylene In Groundwater

Advection, dispersion, adsorption and degradation are important factors affecting the transport and fate of chlorinated organics in groundwater. Batch tests, column tests and mathematical methods were applied to investigate the environmental behaviors of perchloroethylene (PCE) in groundwater. The researches aimed at the adsorption characteristics of PCE to sandy materials, the best remediation technique for the groundwater contaminated by PCE, the transport and transformation of PCE in groundwater and the mathematical model to describe the transport, fate and remediation of PCE in groundwater.The batch non-equilibrium adsorption tests of PCE to sandy materials with organic carbon percent (f_oc) ranging from 0.080% to 0.540% show that the apparent equilibrium can be reached in 2 hours. Pore filling and capillary condensation probably play an important role in sorption kinetics for the media with f_oc 0.080～0.090% while the uptake by organic matter plays an important role in sorption kinetics for the media with relatively high f_oc 0.220～0.540%.The adsorption isotherm of PCE to media with f_oc 0.080～0.090% fit the amended dual-mode model developed from Linear and Langmuir isotherm model while the adsorption isotherm of PCE to media with f_oc 0.220～0.540% fit Linear model. The corresponding retardation factor (R) was defined to describe the retardation transport of PCE in aquifer similar to media with f_oc 0.080～0.090%. In given adsorption system, the retardation factor decreases gradually while the solute concentration increases.The degradation tests of PCE was carried out in five groups of degradation systems, that is, zero-valent iron alone, zero-valent zinc alone, anaerobic microbial community alone, the combination of zero-valent iron and anaerobic microbial community (FeMB), the combination of zero-valent zinc and anaerobic microbial community. The results show that within 25 days, the FeMB degradation system had the highest removal efficiency of PCE (99.9%), and about 44% of PCE was degraded to the non-chlorinated hydrocarbons, for example, ethylene, acetylene and ethane, it suggests that the FeMB remediation technique can dechlorinate more PCE and the reaction intermediates to less-chlorinated organics or non-chlorinated hydrocarbons. The results also showed that the degradation of PCE and its intermediates fit the pseudo-first-order kinetic reaction model. The major pathways of PCE degradation in FeMB degradation system are different from others. PCE was mainly via hydrogenolysis degraded to trichloroethylene (TCE), then TCE via hydrogenolysis to 1,1-dichloroethylene (1,1-DCE) and then 1,1-DCE viaα-elimination to ethylene. The integrated technique combining the iron and the microbial community showed better degradation efficiency than the others; it may be viewed as an environmentally desirable remediation.The advection-dispersion transport model coupling amended dual-mode adsorption model and pseudo-first-order kinetic reaction model was developed to simulate the transport process of PCE in modeling column for the FeMB remediation, the simulated transport process accorded with the observed very well. The model can be used to describe the environmental behaviors and forecast the fate of PCE in groundwater.