Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2008
Publication Date: January 7, 2009
Citation: Hunter, W.J., Shaner, D.L. 2009. Soybean Oil Based Biobarriers Remove Atrazine from Contaminated Water: Laboratory Studies. Journal of Contaminant Hydrology. 103-29-37. Interpretive Summary: Biobarriers are a promising new technology for removing a number of contaminants form groundwater. Research has shown that nitrate, perchlorate, chlorate, chlorinated solvents (i.e. trichloroethylene or TCE) and metals may be removed from contaminated water by biobarriers containing innocuous vegetable oil. The barrier is positioned downstream or below of the contaminant plume and contaminants are degraded as the movement of water carries the contaminant into the barrier. Biobarriers may be created by digging a trench and backfilling the trench with a mixture of sand, gravel and vegetable oil. The sand and gravel allow for the movement of water while the vegetable oil provides a carbon substrate that stimulates microbial activity. Microbial activity in deeper soils and aquifers is usually limited by the availability of carbon. The vegetable oil provides the carbon stimulating microorganisms to degrade contaminants that serve as microbial electron acceptors. Also, since vegetable oils are liquids, biobarriers containing vegetable oils can be formed by injecting the oil into the aquifer. In this investigation, laboratory columns containing biobarriers made by coating sand with soybean oil were used to remove atrazine from flowing water. The process required the presence of atrazine degrading microorganisms and was inhibited when poisoned when mercury was added to the influent water. Mercury poisoning shows the biological processes rather than abiotic processes were a major part of the degradation process. In addition, nitrate nitrogen (5 ppm-N) reduced the efficiency of degradation. The results of the study show that biobarriers containing soybean oil can be used as a remediation process to remove atrazine from groundwater provided that the groundwater does not contain large amounts of nitrogen.
Technical Abstract: In the US almost 35 million kg of atrazine are used annually. This usage coupled with its mobility and recalcitrant nature in deeper soils and aquifers makes atrazine a frequent groundwater contaminant. We formed biobarriers in sand filled columns by coating the sand with soybean oil, inoculated the barriers with a consortium of atrazine degrading microorganisms, and evaluated the ability of the barriers to remove atrazine from a simulated groundwater containing 1 mg L-1 atrazine. The soybean oil provided a carbon rich and nitrogen poor substrate to the microbial consortium. Biobarriers based on this methodology were effective at removing atrazine. Levels of atrazine in the biobarrier effluents declined with time and by the 24th week of the study no detectable atrazine was present (limit of detection < 0.005 mg L-1). Larger amounts of atrazine were also removed by the biobarriers; when biobarriers were fed 16.3 mg L-1 atrazine 97% of it was degraded. Nitrate, 5 mg L-1 N, reduced the efficiency of the barriers by almost 60%. Poisoning of the biobarriers with mercury chloride resulted in an immediate and large increase in the amount of atrazine in the barrier effluents confirming that biological activity and not abiotic factors were responsible for the degradation of atrazine. The presence of hydroxyatrazine in the barrier effluents indicated that dehalogenation was one of the pathways of atrazine degradation. Permeable barriers might be formed in situ by the injection of innocuous vegetable oil emulsions into an aquifer or sandy soil and used to remove atrazine from a contaminated groundwater or to protect groundwater from an atrazine spill.