Table 1.
Parameters and results associated with column experiments
| no.a | Column description | Steady-state pH | Fitted rate constants k (min−1) | Removal efficiency b | ||
|---|---|---|---|---|---|---|
|
| ||||||
| Pd vicinity | Effluent | At electrodes | Between anode and Cathode 2 | |||
| C1 | 3 mM Na2SO4 + 0.5 mM CaSO4 | 2.5–3.0 | 7.5–8.0 | – | – | – |
| C2c | 3 mM Na2SO4 + 0.5 mM CaSO4 | 3.5–4.0 | 6.5–7.5 | – | – | – |
| C3 | 3 mM Na2SO4 + 2 mM NaHCO3 | 3.5–4.5 | 7.5–8.5 | – | – | – |
| C4 | 3 mM Na2SO4 + 5 mM NaHCO3 | 3.5–5.0 | 8.0–8.5 | – | – | – |
| C5 | 5.3 mg/L TCE, no Pd/Al2O3 | – | – | 0.090 d 0.045 e |
– | 31% |
| C6 | 5.3 mg/L TCE, no Pd/Al2O3, 10 mg/L Fe(II) | – | – | 0.090 d 0.045 e |
0.007 | 36% |
| C7 | 5.3 mg/L TCE, 2 g Pd/Al2O3 | 3.0–3.5 | 6.5–7.0 | 0.090 d 0.045 e |
0.018 | 44% |
| C8 | 5.3 mg/L TCE, 2 g Pd/Al2O3, 5 mg/L Fe(II) | 2.5–4.0 | 6.5–7.5 | 0.090 d 0.045 e |
0.042 | 59% |
| C9 | 5.3 mg/L TCE, 2 g Pd/Al2O3, 10 mg/L Fe(II) | 2.7–4.0 | 6.5–7.5 | 0.090 d 0.045 e |
0.069 | 68% |
| C10 | 5.3 mg/L TCE, 2 g Pd/Al2O3, 5 mg/L Fe(II), 1 mM sulfite | 2.5–4.5 | 6.5–7.5 | 0.090 d 0.045 e |
0.072 | 71% |
| C11 | 5.3 mg/L TCE, 2 g Pd/Al2O3, 5 mg/L Fe(II), 31.3 μM sulfide | 2.5–4.5 | 6.5–7.5 | 0.090 d 0.045 e |
0.042 | 57% |
| C12 f | 5.3 mg/L TCE, 2 g Pd/Al2O3, 5 mg/L Fe(II), 31.3 μM sulfide | 2.5–4.5 | 6.5–7.5 | 0.090 d 0.045 e |
0.020–0.041 g | 46% |
a
For C5–C11, 3 mM Na2SO4 and 0.5 mM CaSO4 were dissolved in groundwater as background electrolytes.
b
Removal efficiency refers to total fitted removal percentages of TCE in columns under steady state.
c
Two electrodes were used.
d
Reaction rate at Cathode 1.
e
Reaction rate at Cathode 2.
f
A much longer period of 10 d was lasted.
g
Time-dependent rate constants in the region between Anode and Cathode 2.