2005-11-01. Evaluering af nul-valent jern til ... - NorthPestClean

Abstract
At groyne 42 located on Harboøre Tange there is an old depot, which from 1953-62 was used to
deposit residuals from the production of pesticides at Cheminova A/S.
At present time it has been planned to bung up the polluted area with sheet piling. In this connection
it is of interest to find a suitable method to remediate the area. A permeable reactive barrier
with zero-valent iron has on several occasions proven to be a suitable method to remediate
groundwater polluted with organically substances. Tests with zero-valent iron have earlier on
shown a promising potential for the method’s applicability against the pollution on the location.
Therefore the method’s ability to remediate the polluted location has been examined further
through the performance of column experiments with the polluted groundwater from the site.
Through chemical analyses it has been observed that 20 of the 23 measured xenobiotic compounds
can be degraded to the limit of detection. For the most toxic compounds the degradation
occurred rapidly at the first contact between the compound and the zero-valent iron. This was the
case throughout the entire experiment. The development of a front through the reactive zone was
observed for the less toxic compounds. As a result of this more and more compounds will break
through the reactive zone with time. Part of the removal of the less toxic compounds could be
described by sorption, but not above one third of the removal. The removal is therefore mostly a
result of degradation.
Toxicity studies with the crustacean Daphnia magna showed that the toxicity of the polluted
groundwater could be completely reduced to non-toxic conditions, corresponding to a toxicity
reduction of at least 1250 times. As the less toxic compounds break through the reactive zone,
the reduction in toxicity declines. It is estimated that the toxicity reduction will be around 100
times when all the less toxic compounds has broken through the reactive zone. If the toxicity is
to be eliminated completely, the toxicity of the water leaving the reactive zone will have to be
reduced around 10 times more. This reduction can occur as a result of natural attenuation. The
environmental impact of the pollution has been seen to be reduces significantly.
Through the chemical and toxicological examinations the method shows very promising abilities
in connection with remediation of the polluted location. A problem with the method can occur as
a result of the high content of ions in the aquifer. This can cause precipitation of minerals in the
reactive iron zone, which will shorten the lifetime of the reactive barrier. It is therefore recommended
that a small scale field demonstration is performed, where especially the more long term
changes in the efficiency of the reactive barrier are examined.
Zero-valent iron can also be injected into the polluted source area in the form of particles. Therefore
batch tests with two types of iron particles (nano and micro) and heavily polluted sediment
from boring V29 at the location has been performed.
It was observed that the iron particles resulted in a complete transformation of high concentrations
of methyl- and ethyl parathion into methyl- and ethyl-amino-parathion. This transformation
resulted in a toxicity reduction of 40-60 times. Hereby the method shows potential as a way to
treat the hotspots at the location. This could be done in combination with the reactive barrier.
Before the suitability of the iron particles as a remediation method can be properly evaluated
more examinations must be performed. These examinations should reflect the conditions in the
aquifer in a more realistic manner.