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 <1mg/L), wetland columns were capable of removing ClO4- to levels below the detection limit (<4 microg/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 KNO3- -N) 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). KNO3- -N 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.