Abstract:

Multicomponent plume in groundwater which blends chlorinated solvents with petroleum hydrocarbons has recently attracted great attention because of its wellknown carcinogenicity in humans and exceptional difficulty to be remedied simultaneously. This paper presents some column experiments which were conducted to evaluate the effects of benzene, toluene on reductive dechlorination of perchloroethene (PCE) by granular iron. The results showed that the kinetics of PCE (at the initial concentration of 2 mg/L more or less) reduction accorded with pseudo firstorder even in the presence of benzene or toluene (at about 2 mg/L, respectively). The presence of benzene increased PCE degradation by 135％ averagely; nevertheless, in the existence of toluene, PCE reduction rates averagely decreased by 138％. These data suggested that benzene would be a potential promoter, but toluene suppressed the removal of PCE. Furthermore, the dechlorinated daughter products in the presence/absence of benzene or toluene were identical. Trichloroethylene (TCE), cis1, 2dichloroethene (cis1, 2DCE), 1, 1dichloroethene (1, 1DCE) and vinyl chloride (VC) except for trans1, 2dichloroethene (trans1, 2DCE), were observed as the chlorinated intermediates, and cis1, 2DCE was the majority. Otherwise, ethyne, ethylene and ethane were observed as the major nonchlorinated end products. The accumulation of chlorinated intermediates was consistent with the removal ratios of PCE. In addition, the investigated changing of groundwater chemistry showed a noticeable disappearance of calcium (II), bicarbonate and sulfate. However, in the presence of benzene or toluene, there were slight variations in these changes. The results indicated that the effects of such copollutants should be considered in designing the sequential permeable reactive barriers (PRBs) combined iron walls with biotreated zones for groundwater remediation.

Key words:

granular iron; benzene; toluene; perchloroethylene (PCE); permeable reactive barrier (PRB); groundwater remediation; kinetics