Within a plume, the redox processes are the main driver of pollutants’ behavior and fate. In fact, when fuel-derived organic compounds, such as BTEX and MTBE, are released in groundwater, they degrade by direct mineralization or fermentation. The oxidation of the primary substrate and/or the fermentation by-products, such as H2 and Acetate, (electron donors) obviously triggers the reduction of redox-sensitive compounds (electron acceptors) naturally present and/or anthropogenically released in the aquifer, well known as Terminal Electron Accepting Process (TEAP). The TEAP is catalyzed by different microbial species, each one utilizing the available substrate and a corresponding electron acceptor. Thus, if in the same polluted site, in addition to endogenous electron acceptors (i.e. Nitrate, Mn(III/IV) hydr-oxides, Fe(III) hydr-oxides, Sulfate, etc.), chlorinated ethenes (i.e. PCE, TCE, DCEs, VC) are present, reductive dichlorination process could likely be inhibited, because of the competition among the corresponding microbial species. In order to deepen these issues, the modeling of reactive transport has been applied, simulating the degradation processes and interaction among several compounds along the main flow path (1-D model) in a coastal aquifer, where 10-15 meters thick sandy and silty sandy deposits aquifer overlay an clayey aquiclude. Here, several foundry wastes burials (high content of Mn and As-rich Fe hydr-oxides), an oil spill from a fuel station tanks and a residual chlorinated solvents residual phase were revealed. For kinetically controlled processes (i.e. fuel-derived organic compounds degradation and reductive dechlorination), different equations have been used and compared: the first-order equation, the Michaelis-Menten equation, and the Monod equation. The simulation has been performed by means of the software Phreeqc and the results validated using chemical analyses made on groundwater samples collected in a 43 well monitoring network. The first results show a persistence of reductive dechlorination by-products (i.e. DCEs and VC) in groundwater, near the largest foundry wastes burial. In fact, the correspondence between the high concentration of DCEs and VC and the high concentration of Mn, Fe and As in groundwater suggests a strong competition for the substrate.
Reactive transport modeling for the evaluation of field scale substrate competition in a complex contaminated site
Di Curzio D.
;Rusi S.
2017-01-01
Abstract
Within a plume, the redox processes are the main driver of pollutants’ behavior and fate. In fact, when fuel-derived organic compounds, such as BTEX and MTBE, are released in groundwater, they degrade by direct mineralization or fermentation. The oxidation of the primary substrate and/or the fermentation by-products, such as H2 and Acetate, (electron donors) obviously triggers the reduction of redox-sensitive compounds (electron acceptors) naturally present and/or anthropogenically released in the aquifer, well known as Terminal Electron Accepting Process (TEAP). The TEAP is catalyzed by different microbial species, each one utilizing the available substrate and a corresponding electron acceptor. Thus, if in the same polluted site, in addition to endogenous electron acceptors (i.e. Nitrate, Mn(III/IV) hydr-oxides, Fe(III) hydr-oxides, Sulfate, etc.), chlorinated ethenes (i.e. PCE, TCE, DCEs, VC) are present, reductive dichlorination process could likely be inhibited, because of the competition among the corresponding microbial species. In order to deepen these issues, the modeling of reactive transport has been applied, simulating the degradation processes and interaction among several compounds along the main flow path (1-D model) in a coastal aquifer, where 10-15 meters thick sandy and silty sandy deposits aquifer overlay an clayey aquiclude. Here, several foundry wastes burials (high content of Mn and As-rich Fe hydr-oxides), an oil spill from a fuel station tanks and a residual chlorinated solvents residual phase were revealed. For kinetically controlled processes (i.e. fuel-derived organic compounds degradation and reductive dechlorination), different equations have been used and compared: the first-order equation, the Michaelis-Menten equation, and the Monod equation. The simulation has been performed by means of the software Phreeqc and the results validated using chemical analyses made on groundwater samples collected in a 43 well monitoring network. The first results show a persistence of reductive dechlorination by-products (i.e. DCEs and VC) in groundwater, near the largest foundry wastes burial. In fact, the correspondence between the high concentration of DCEs and VC and the high concentration of Mn, Fe and As in groundwater suggests a strong competition for the substrate.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
