Using N-Limiting Growth Conditions to Remove Atrazine from Groundwater: Laboratory Studies.

Authors: Hunter, William; Shaner, Dale

Submitted to: In Situ and on Site Bioremediation Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2009
Publication Date: 5/1/2009
Citation: Hunter, W.J., Shaner, D.L. 2009. Using N-Limiting Growth Conditions to Remove Atrazine from Groundwater: Laboratory Studies. In Situ and on Site Bioremediation Symposium Proceedings, the 10th International Symposium. Poster Abstracts.

Interpretive Summary:

Technical Abstract: Typically, respiratory redox reactions are the driving mechanism behind in situ bioremediations that use a carbon substrate. This is because electron (e-) donor availability generally restricts subsurface microbial activity. Thus, microbial growth and respiration can be greatly stimulated by the addition of compounds that function as respiratory e- donors. This increased respiration will usually drive the system anaerobic. Under these conditions groundwater contaminants that can serve as microbial respiratory e- acceptors (i.e. nitrate, perchlorate, trichloroethylene, etc.) are often reduced to less harmful compounds. In contrast, for this study, the microbial degradation of atrazine made use of atrazine’s potential to function as a microbial nitrogen source. The environment that was established within the biobarrier was one where it was the supply of nitrogen that limited microbial activity. Other growth requirements, including the e- donor and e- acceptor, were available in excess. In addition, the biobarriers were bioaugmented with an inoculum containing atrazine degrading microorganisms. For this study two reactors placed in series were used. The first was a biobarrier formed in a sand filled column by coating the sand with soybean oil as the columns were packed. The porous matrix allowed water to flow freely through the biobarriers while the oil provided a carbon rich and nitrogen poor substrate to the microbial inoculum. The second was an air injection reactor at the effluent end of the biobarrier. A simulated groundwater containing 1 mg/L atrazine and 5 mg/L nitrate-N was pumped through the columns for 22 weeks. At intervals effluents from the biobarriers were collected and analyzed for atrazine and nitrate. The results showed that the first reactor, the biobarrier, was effective at removing nitrate and the second reactor, the aerobic reactor, was effective at removing atrazine. Atrazine levels in the effluents of the 1st reactor, the anaerobic reactor, remained high throughout the study but declined with time in the 2nd reactor, the aerobic reactor, and by the 21th week of the study no detectable atrazine was present in biobarrier effluents (limit of detection < 0.005 mg/L). Such barriers, when inoculated with atrazine degrading bacteria, might be used in situ to remove atrazine from aquifers that are contaminated with both nitrate and atrazine.