Fate of perchlorate-contaminated water in upflow wetlands

The potential of natural wetland systems to treat perchlorate-contaminated water was investigated in vertical upflow wetland columns planted with and without Bulrush (Scirpus sp.). In the absence of nitrate (NO3−–N <1 mg/L), wetland columns were capable of removing ClO4− to levels below the detection limit (<4 μg/L) for a series of influent ClO4− (4, 8, 16, and 32 mg/L). At an influent ClO4− concentration of 32 mg/L, ClO4− breakthrough was observed with the increase in nitrate concentration. ClO4− and NO3− degradation rate constants (Kpc and ) were also determined using a 1-D transport model with dispersion. Kpc declined with the increase of influent ClO4− and NO3− –N concentration (6.49–0.42 day−1 for unplanted columns, and 7.80–0.21 day−1 for planted columns, respectively). followed similar trends but was relatively higher than Kpc. Plant uptake was directly linked with ClO4− concentration in the rhizosphere, and the stem bio-concentration factor (BCF) was estimated to be 57. A mass balance indicated plant uptake accounted for 0–14.3% of initial ClO4− input. Microbial degradation played a more important role than plant uptake and transformation in ClO4− degradation in this wetland system. This study suggests that constructed wetlands may be a promising technology to treat perchlorate-contaminated waters.