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In contrast to BAC media from the Bendigo WTP and the Kyneton WTP, iron was shown to be the major phase in biogenic deposits on Antarctic BAC and ammonium exchanged zeolite media, with no detectable manganese (Table 3, Figure 7). Figure 7(a) illustrates a biogenic mineral fragment on Antarctic BAC media. Elemental analysis of this structure clearly shows the sorption of lead and phosphorus transported in the soil water to the BAC media surface. The presence of phosphorus is likely attributed to dissolution of the calcium phosphate coating of Zeopro™ within the PRB (Mumford et al. 2013). Similarly, in the presence of ammonium exchanged zeolite, biofilm structures were shown to sorb chromium and nickel from solution (Figure 7(b)). The similarity in manganese concentrations between the control and PRB samples (Table 3) is reflected in the absence of manganese by EDS analysis (Figure 7(b)). These data show that iron biogenic minerals offer the potential for the removal of a wide range of aqueous pollutants at sites contaminated with metals and hydrocarbons. The potential for iron biogenic mineral formation also has important implications for the application and performance of zero-valent iron for groundwater metal remediation within PRBs (e.g. Statham et al. 2015).
Figure 7

Energy dispersive X-ray microanalysis of biogenic mineral formation on Antarctic BAC media (a) and ammonium exchanged zeolite (b) within laboratory flow cells. Images show that iron is the most abundant mineral within these deposits. The white arrows (b) indicate clusters of biogenic minerals together with EPS on the ammonium exchanged zeolite surface. The images indicate the location of the sample analysed and the inset shows the spectra of the minerals observed.

Figure 7

Energy dispersive X-ray microanalysis of biogenic mineral formation on Antarctic BAC media (a) and ammonium exchanged zeolite (b) within laboratory flow cells. Images show that iron is the most abundant mineral within these deposits. The white arrows (b) indicate clusters of biogenic minerals together with EPS on the ammonium exchanged zeolite surface. The images indicate the location of the sample analysed and the inset shows the spectra of the minerals observed.

Table 3

Iron and manganese concentrations on PRB media from Old Casey Station, east Antarctica, and on ammonium exchanged zeolite within laboratory flow cells replicating field conditions (n = 3). Error range represents ± one standard deviation

PRB compositionIron (mg/kg)Manganese (mg/kg)
Control 1:2 (v/v) aactivated carbon and ZeoproTM 171 ± 6.3 115 ± 6.0 
PRB 1:2 (v/v) aactivated carbon and ZeoproTM, 30–40 cm depth 391 ± 2.1 131 ± 1.9 
Control 1:2 (v/v) aactivated carbon and Zeolite 184 ± 11 85 ± 5.9 
PRB 1:2 (v/v) aactivated carbon and Zeolite, 30–40 cm depth 304 ± 16 100 ± 2.0 
Laboratory flow cells: control ammonium exchanged zeolite 225 ± 2.3 81 ± 2.1 
Laboratory flow cells: ammonium exchanged zeolite at 432 bed volumes passing 256 ± 3.5 80 ± 1.1 
PRB compositionIron (mg/kg)Manganese (mg/kg)
Control 1:2 (v/v) aactivated carbon and ZeoproTM 171 ± 6.3 115 ± 6.0 
PRB 1:2 (v/v) aactivated carbon and ZeoproTM, 30–40 cm depth 391 ± 2.1 131 ± 1.9 
Control 1:2 (v/v) aactivated carbon and Zeolite 184 ± 11 85 ± 5.9 
PRB 1:2 (v/v) aactivated carbon and Zeolite, 30–40 cm depth 304 ± 16 100 ± 2.0 
Laboratory flow cells: control ammonium exchanged zeolite 225 ± 2.3 81 ± 2.1 
Laboratory flow cells: ammonium exchanged zeolite at 432 bed volumes passing 256 ± 3.5 80 ± 1.1 

aRefers to GC1200 granular activated carbon. ZeoproTM is a commercial nutrient-amended zeolite to promote the biodegradation of petroleum hydrocarbons within PRBs (Freidman et al. 2016). Soil used within laboratory flow cells was collected within close proximity to the PRB at Old Casey Station. Control refers to unused PRB material mixtures employed as blanks.

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