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Injection of nanosized iron oxides into aquifers

Julian Bosch1, Andreas Fritzsche2
1 Institut für Grundwasserökologie, Helmholtz Zentrum München
2 FSU Jena, LS Hydrogeologie

O 12.6 in Grundwasserqualität

29.05.2014, 15:00-15:20, H19, NW II

Microbial Fe(III) reduction is an important biogeochemical process in suboxic aquifers. It is coupled to the oxidation of organic matter (OM), e.g. organic contaminants, resulting in their degradation. However, the low bioavailability of aged, immobile Fe oxides in aquifers limits the rate and extent of microbial Fe(III) reduction and thus the rate and extent of OM oxidation, i.e. the degradation of organic contaminants. Compared to their intensively aggregated and crystalline counterparts, colloidal Fe oxide aggregates exhibit an enhanced reactivity and availability. This suggests their promising application for an extensive remediation of BTEX- and PAH-contaminated aquifers. However, an economically reasonable remediation of whole aquifers requires the buildup of a sufficiently sized zone enriched with colloidal Fe oxides, i.e. the reactive zone, with the lowest possible number of injection wells. In turn, this requires Fe oxides with a high, but finite mobility within the aquifer. We developed industrially producible suspensions of Fe oxide aggregates. These were stabilized at dH ~500 nm unless they were in contact with strong electrolyte solutions, i.e. the groundwater from a tar oil-contaminated aquifer below a former smoulder facility, which served as test site for our field-scale studies. In contact with groundwater, colloid aggregation occurred rendering them immobile within the aquifer. This prevented the advective discharge of the injected Fe oxides from the reactive zone. Approximately 23 m3 of Fe oxide suspension were injected at a rate of ~1.8 m3 h-1. This produced a homogeneous reactive zone of ~5 m in diameter and ~4 m in height. Pore clogging was not critical. Thus, the suspension was introduced gravitationally to the aquifer, except for the final injection stage, where an extra pressure up to 30 kPa had to be applied. We detected a direct and immediate response of the pressure heads in ambient wells, which were 30 - 200 m distant from the injection well. This increase was higher than the previous daily variations but was remarkably lower than the variations on a monthly and annual basis. This in particular applies when considering single events like the extreme rainfalls in late spring 2013. Consequently, the injection of such Fe oxide suspensions is not considered to artificially damage the pore architecture in the aquifer, which would cause severe subsequent complications. If the injected Fe oxide colloids perform comparably to the lab-scale observations in terms of BTEX degradation and toxicity, we consider this remediation technique as sustainable, cost-efficient way for oxidative contaminant degradation in sub-/anoxic porous media with a low risk of post-injection complications.



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Letzte Änderung 09.04.2014