Enhanced Natural Attenuation zum In-situ-Bioabbau von Heterocyclischen Kohlenwasserstoffen im Grundwasser - erste Pilotanwendung an einem Feldstandort
During the KORA research project "Enhanced Natural Attenuation (ENA) for the in-situ biodegradation of heterocyclic hydrocarbons in groundwater" a hydraulic remediation technology - the groundwater circulation well (GCW) - was upgraded and successfully used for a homogeneous and effective mixing of hydrogen peroxide in the contaminated groundwater. On a technical scale and during the field application an aerobic biological degradation of the persistent PAH (Acenaphthen) and NSO-HET was initiated. Degradation rate between 55 - 80% of the initial contaminant mass flux were achieved. During the large scale experiments in the completely hydraulic controlled model aquifer "Large Fume" an aerobic degradation rate of over 85% was determined. These high degradation rates were initiated by the addition of hydrogen peroxide causing high oxygen contents in the groundwater. In the close vicinity of the GCW oxygen contents in the groundwater between 10 - 20 mg/L resulted from the mixing process and a nearly instant decomposition of hydrogen peroxide into water and oxygen. The positive effects for the groundwater quality by the addition of hydrogen peroxide were verified in the pilot application on the KORA-test site (Testfeld Süd in Stuttgart).
The GCW is based on common well drilling techniques. The installation method of the system is stat-of-the-art and could be used for good permeable aquifers. Problems during operation may result from high iron contents in the groundwater in combination with oxidants mixing (oxygen, hydrogen peroxide). As a simple and reliable technical solution the usage of "satellite wells" in the zone of the circulation flow has proved to be cost effective and to stabilize the operation and the control of the hydraulic system. The use of a monitoring well for the installation of a GCW was innovative. By this method existing wells can be used for the system. Monitoring wells are mostly existent on contaminated sites and located in the plume. Furthermore it was demonstrated that in contrast to earlier applications of GCW no large diameters of a GCW are necessary to control a groundwater circulation flow. So the investment costs are minor and the flexibility of the system is improved.
The developed numerical method for the simulation of the GCW offers the opportunity of the hydraulic design and dimensioning of an infiltration system with commercially available simulation software. Thus offers the opportunity for hydraulic engineers and consultants to consider nearly every geological and hydraulic situation at an early stage of the remediation design for contaminant plumes.
Based on the pilot application the estimated costs of ENA using hydrogen peroxide in order to treat about 80% of the contaminant mass flux of the plume at the pilot site are lower than the costs for standard hydraulic remediation techniques (pump & treat). ENA is comparable to the costs of passive systems (reactive barrier).
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Federal Ministry of Education and Research (BMBF)
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