Biological Remediation of Groundwater Containing both Nitrate and Atrazine

Authors: Hunter, William; Shaner, Dale

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2009
Publication Date: 1/1/2010
Citation: Hunter, W.J., Shaner, D.L. 2010. Biological Remediation of Groundwater Containing both Nitrate and Atrazine. Current Microbiology. 60: 42-46.

Interpretive Summary: Microbial based in-situ biobarriers have become an established technique for cleansing contaminants from aquifers and saturated soils and research has shown that (per)chlorate, nitrate, chlorinated solvents and heavy metals can be removed with this technology. The driving mechanism involved in these past remediations has involved microbial respiratory oxidation and reduction reactions. The contaminants were removed directly or indirectly as a result of microbial respiratory reactions. Recently, we demonstrated that atrazine can be removed via microbial biobarriers but that the mechanism involved was not associated with redox reactions or respiration. Rather atrazine was being degraded as a microbial nitrogen source and the microbial communities need for nitrogen was the driving mechanism involved. Thus, the presence of alternative nitrogen sources interfered with this remediation approach. This study addressed this problem and showed that by using two reactors in sequence atrazine can be removed from water that also contained large amounts of nitrate-N. This is important as these two contaminants often occur together. For the study a denitrifying biobarrier was used to remove nitrate and a downstream aerobic reactor was used to remove atrazine. This two reactor system removed 99.9% of the atrazine during the study with the first reactor, a denitrifying biobarrier, removing ~98% of the nitrate and ~30% of the atrazine while the second, an aerobic reactor, removed ~70% of the atrazine. A mercury poisoning study blocked the degradation of atrazine indicating that biological processes were involved. An in-situ denitrifying biobarrier coupled with a downstream air injection system or other oxygenation process might be used to remove both nitrate and atrazine from contaminated groundwater or to protect groundwater from an atrazine spill.

Technical Abstract: Due to its high usage, mobility and recalcitrant nature, atrazine is a common groundwater contaminant. Moreover, groundwaters that are contaminated with atrazine often contain nitrate as well. Nitrate interferes with the biological degradation of atrazine and makes it more difficult to use in-situ biological methods to remediate atrazine contaminated groundwater. To solve this problem we used two reactors in sequence as models of in-situ biobarriers; the first was a vegetable-oil based denitrifying biobarrier and the second an aerobic reactor that oxygenated the denitrifying reactor’s effluent. The reactors were inoculated with an atrazine degrading microbial consortium and supplied with water containing 5 mg L-1 nitrate and 3 mg L-1 atrazine. Our hypothesis was that the denitrifying barrier would remove nitrate from the flowing water and that the downstream reaction would remove atrazine. Our hypothesis proved correct, the two reactor system removed 99.9% of the atrazine during the final 30 weeks of the study. The denitrifying barrier removed ~98% of the nitrate and ~30% of the atrazine while the aerobic reactor removed ~70% of the initial atrazine. The system continued to work when the amount of nitrate in the influent water was increased to 50 mg L-1. A mercury poisoning study blocked the degradation of atrazine indicating that biological processes were involved. An in-situ denitrifying barrier coupled with an air injection system or other oxygenation process might be used to remove both nitrate and atrazine from contaminated groundwater or to protect groundwater from an atrazine spill.