Ferrogenic aquifer

Figure 14.11 Reduction of NACs in ferrogenic aquifer solid columns. Concentrations of 4-chloronitro-benzene (4-C1-NB, ) and of its transformation product 4-chloro-aniline (4-Cl-An, o) vary with position (and time) in the column. Also indicated is the excellent mass balance (a). Adapted from Heijman et al. (1995).

NACs in a laboratory column system containing aquifer material from the banks of a river-groundwater infiltration site (Fig. 14.11). The columns were run under ferrogenic conditions. Note that zero-order kinetics suggests that the reactive sites were always saturated such as encountered in enzyme kinetics at saturation (Box 12.2). In this system, all model compounds as well as other NACs including again TNT, ADNTs, and DANTs (data not shown, see Hofstetter et al., 1999) reacted at virtually the same rate. However, when present in mixtures, the compounds showed competition for the reactive sites. A competition quotient, Qc (competition with the reference compound 4-C1-NB present at about equal concentrations) was determined for all model compounds ... 

Table 4. Model NACs compound names, one-electron reduction potentials ( EJO, carbon-normalized second-order rate constants (Icnom) for the reaction with Hyde County NOM, second-order rate constants for the reaction with an iron porphyrin (kpep), and apparent zero-order rate constants for reduction in an aquifer column under ferrogenic conditions (k bs)...

Figure 11. General reaction scheme proposed by Heijman et al. (25) for the reduction of NACs in aquifer columns under ferrogenic conditions.

Figure 14. Comparison of the relative reduction rates (krei, the rates are relative to 4-Cl) of the mono-substituted nitrobenzenes listed in Table 4 in three different systems (a) in aqueous solutions containing hydrogen sulfide and natural organic matter data from (11) (b) in aqueous solutions containing cysteine and a water soluble iron porphyrin data from (64) (c) in aquifer columns under ferrogenic conditions data from (25) The relative rates, expressed as log k gi, are plotted against the normalized one-electron reduction potentials, [El, (ArN02)/0.059 V], of the compounds.

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