Using a Wetland Bioreactor to Remediate Ground Water Contaminated with Nitrate (mg/L) and Perchlorate (μg/L)

Wetland plants and their rhizospheric microorganisms were used to remove perchlorate from nitrate-contaminated ground water. A wetland bioreactor was constructed with the wetland plants Typha spp., Scirpus spp., and Cyperus spp. These plants provided a habitat and a food source for the indigenous denitrifying microorganisms presumed responsible for the perchlorate and nitrate removal. Ground water contaminated with nitrate (68 mg/L) was collected from a well and injected with concentrations of potassium perchlorate similar to those found in several local wells (50 and 100 μg/L). The water flowed continuously through the wetland bioreactor with hydraulic retention times (HRT) ranging from 0.5 to 400 h. Because microbial denitrification depends, in part, on the nature and amount of carbon available to the microorganisms, four carbon sources (dried leaf matter, dried algae, milk replacement starter, and sodium acetic acid) were evaluated. Analyses for perchlorate This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-18. concentration in ground water were performed using negative electrospray mass spectrometry/mass spectrometry. Of the carbon sources tested, sodium acetic acid was the most efficient at accelerating the nitrate and perchlorate removal rates. The HRT required to remove perchlorate (100 μg/L) to below the detection limit, without carbon source amendment, was 4 d. With the addition of sodium acetic acid (0.26 g/L) the required HRT decreased to 0.5 d. These results suggest that denitrifying microorganisms, supported in a wetland bioreactor amended with a carbon source, remove perchlorate from nitrate contaminated ground water.