Table 1.
The design of the four-stage column experimenta
| Experimental Stage | Purpose | Amendments | # PVs |
|---|---|---|---|
| I: pre-equilibration | Mimic “landfill conditions” | 1 mM lactate and 100 μg L−1 As(III) | ~38b |
| II: mineral formation | Induce the formation of Fe minerals | 1 mM lactate, 100 μg L−1 As(III), 1 mg L−1 bromide, 10 mM nitrate and 4 mM Fe(II) | ~38 |
| Intermission: clean residual nitrate—Fe(II) amendment | 1 mM lactate | ~4 | |
| III: enhanced reduction | Further stimulate reduction | 10 mM lactate | ~45 |
| IV: reactive filter | Return to “landfill conditions” | 1 mM lactate and 100 μg L−1 As(III) | ~120 |
a
Three replicate Dover columns were sacrificed at the end of Stages II, III and IV, respectively. Sand column was sacrificed at the end of Stage V. More details, such as how the influents were prepared, are in SI Table S1.
b
We attempted to switch the experimental stage from Stage I to II at about PVs = 30, but switched back to Stage I after about 0.2 PV of injection (2 h) because precipitation was noticed in the Fe(II) influent. We therefore continued with Stage I for another 8 PVs (i.e., about 38 PVs in total) before successfully switching to Stage II.