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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.

Full report in PDF format (431 KB)
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Helle Thomsen

01.11.2007


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