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Summary
The Danish National Environmental Research Institute (NERI) have
carried out a series of measurements of dioxin in bio-ash from straw
fired stoves, smaller straw- or wood-chip fired district heating plants
and smaller wood chip fired stoves. The study has been conducted in
2002 in connection with the Danish Dioxin Monitoring Program 2001-
2003, sponsored by the Danish Environmental Protection Agency
(DEPA).
The purpose of the investigation has been to add important data for
the mass flow analysis for dioxin, sources and emissions. A total of
twentythree samples has been analysed, comprising ash from seven
smaller strawfired stoves on farms, two strawfired and two chipfired
district heating plants, twelve chipfired stoves and a one small
woodfired stove. The strawfired stoves are geographical located in
the region of Århus, whereas the other locations are distributed over
the country; two of the chipstoves are located in Sweden.
The results of the study show that the average dioxin content in the
ash from strawfired farm stoves is 3.7 ng/kg I-TEQ, varying from
0.02 to 12 ng/kg I-TEQ. This variation is surprisingly large and can
hardly be ascribed to differences in the straw or the stoves, which are
very similar. The annual production in Denmark of ash from such
stoves is estimated to 1 million tons, corresponding to a national
emission of 3.7 g I-TEQ per year. According to the Danish EPA none
of the participating farmers in this study have spread out bio-ash
from strawfired stoves on their fields.
The ash from the smaller district heating plants contains considerably
less dioxin with an average of 0.6 ng/kg I-TEQ, varying from 0.03 to
1.4 ng/kg I-TEQ. The average content in ash from the wood chipfired
stoves is 18 ng/kg I-TEQ, which is considerably higher than the
strawfired stoves, and they display significantly higher variation, the
values ranging from 0.02 to 74 ng/kg I-TEQ. The single ash sample
from the small wood stove contains very little dioxin, 0.03 ng/kg ITEQ.
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