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Formation and degradation of PCDD/F in waste incineration ashes
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The disposal of combustible wastes by incineration is a controversial issue that is strongly debated by both scientists and environmental activists due to the resulting emissions of noxious compounds, including (inter alia) polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), heavy metals and acid gases like sulfur dioxide. Currently available air pollution control devices are capable of effectively cleaning flue gases, and PCDD/F emissions to air from modern municipal solid waste (MSW) incinerators are low. However, the PCDD and PCDF end up in ash fractions that, in Sweden, are usually deposited in landfills.

The European Union has recently set a maximum permitted total concentration of 15 µg TEQ/kg for PCDD/F species in waste. Fly ash from municipal solid waste (MSW) incineration containing PCDD/Fs at concentrations above this limit will have to be remediated to avoid disposing of them in landfills; an expensive and environmentally unfriendly option. Therefore, effective, reliable and cost-effective methods for degrading PCDD/F in fly ash are required, and a better understanding of the behavior of PCDDs and PCDFs during thermal treatment will be needed to develop them.

In the studies this thesis is based upon both the formation and degradation of PCDDs and PCDFs in ashes from MSW incineration were studied.

The main findings of the investigations regarding PCCD/F formation were:

- The concentrations of PCDD and PCDF in fly ash increased with reductions in the temperature in the post-combustion zone.

- The homologue profile in the ash changed when the temperature in the post-combustion zone changed.

- The final amounts of PCDD and PCDF present were affected by their rates of both formation and degradation, and the mechanisms involved differ between PCDDs and PCDFs.

The main findings from the degradation studies were:

- The chemical composition of ash has a major impact on the degradation potential of PCDD and PCDF.

- The presence of oxygen during thermal treatment can enhance the degradation of PCDD and PCDF.

- Thermal treatment is a viable option for degrading PCDD and PCDF in ashes from MSW.

- Shifts in chlorination degree occur during thermal treatment.

- Rapid heat transfer into the ash is a key factor for ensuring fast degradation of PCDD and PCDF.

- Degradation of other chlorinated organic compounds, e.g. PCB and HCB, also occurs during thermal treatment of ash.

- Reductions in levels of PCDD and PCDF were not solely due to their desorption to the gas phase.

- Differences between the behavior of 2378-substituted congeners of PCDD and PCDF and the other congeners during thermal treatment were observed.

- Differences in isomer patterns of both PCDD and PCDF were observed between the ash and gas phases after thermal treatment at both 300 and 500 oC.

Overall, the results show that the formation and degradation mechanisms of PCDDs differ substantially from those of PCDFs. Thus these groups of compounds should be separately considered in attempts to identify ways to reduce their concentrations.

Place, publisher, year, edition, pages
Umeå: Kemi , 2007. , 59 p.
Keyword [en]
MSW, fly ash, remediation, ash, PCDD, PCDF, formation, degradation, destruction, dechlorination, thermal treatment
National Category
Environmental Sciences
Identifiers
URN: urn:nbn:se:umu:diva-1395ISBN: 978-91-7264-411-3 (print)OAI: oai:DiVA.org:umu-1395DiVA: diva2:140875
Public defence
2007-11-09, N320, Naturvetarhuset, Umeå Universitet, Umeå, 13:00
Opponent
Supervisors
Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2011-03-10Bibliographically approved
List of papers
1. Distribution of mono- to octa-chlorinated PCDD/F in fly ashes from a municipal solid waste incinerator
Open this publication in new window or tab >>Distribution of mono- to octa-chlorinated PCDD/F in fly ashes from a municipal solid waste incinerator
2004 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 42, no 4, 1245-1250 p.Article in journal (Refereed) Published
Abstract [en]

We have estimated the concentration and distribution of the mono to octa-chlorinated congeners of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) in fly ashes at various sampling points in a large-scale municipal solid waste incinerator at Umeå, Sweden, as they cooled from 700 to 170 °C. Differences between the ashes were observed, the PCDD homologue profile was found to vary with temperature. The total amount of PCDD and PCDF increased as the temperature decreased in the postcombustion zone. The increase was due to both adsorption to the fly ash and formation of PCDD and PCDF. Mono- to trichlorinated PCDD predominated at high temperatures, whereas hepta- and octachlorinated PCDD predominated at temperatures below 400 °C. PCDF predominated over PCDD in the whole temperature range. However, the changes in homologue profile for PCDF were minor. The isomer distribution within the homologue groups was not changed as the temperature decreased in the postcombustion zone.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2004
Keyword
dibenzo P dioxins, de novo synthesis, MSW incineration, isomer patterns, thermal formation, mass-balance, combustion, PCDD/PCDF, phenols, precursors
National Category
Environmental Sciences Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-2645 (URN)10.1021/es0717919 (DOI)000253250800047 ()
Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2017-12-14Bibliographically approved
2. Thermal degradation of PCDD/F in municipal solid waste ashes in sealed glass ampules
Open this publication in new window or tab >>Thermal degradation of PCDD/F in municipal solid waste ashes in sealed glass ampules
2005 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 39, no 10, 3872-3877 p.Article in journal (Refereed) Published
Abstract [en]

Due to their high concentrations of toxic organic compounds such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), metals, and water-soluble salts, fly ashes are classified as hazardous waste in the European Union and are required to be deposited in controlled landfills. We have shown here that the tetra- to octachlorinated PCDD/F in fly ash can be degraded by thermal treatment. The temperature needed for total degradation of PCDD/F depends on the composition of the fly ash. Its concentrations of unburned carbon and alkaline compounds were found to be important in this respect. Experimental design was used to investigate the effects of varying the temperature, residence time, and atmosphere on the degradation of PCDD/F in three different types of fly ash. The results showed that the three ashes clearly showed different degradation potentials for PCDD/F during thermal treatment. The concentrations of unburned carbon, alkaline species such as CaO and Na2O, and metals such as copper and iron strongly influenced the degradation of PCDD/F. However, the different combinations of pH and amounts of native PCDD/F, unburned carbon, metals (Cu, Fe, Sn and Na), and sulfur in the ashes made it difficult or even impossible to conclude that any single parameter was responsible for the degradation of PCDD/F in these thermal treatment experiments. The decreases observed in all of the experiments are due to dechlorination and/or destruction of PCDD/F: depending on the temperature and ash composition, either of these processes may be the more important.

Place, publisher, year, edition, pages
Washington: American Chemical Society, 2005
Identifiers
urn:nbn:se:umu:diva-2646 (URN)10.1021/es0485513 (DOI)
Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2017-12-14Bibliographically approved
3. Thermal degradation of PCDD/F, PCB and HCB in municipal solid waste ash.
Open this publication in new window or tab >>Thermal degradation of PCDD/F, PCB and HCB in municipal solid waste ash.
2007 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 67, no 3, 474-481 p.Article in journal (Refereed) Published
Abstract [en]

A thermal degradation procedure for reducing the concentrations of mono- to octa-chlorinated PCDD/Fs, PCBs and hexa-chlorobenzenes (HCB) in filter ash from incinerated municipal solid waste (MSW) is described. Thermal treatment of filter ash samples at 500 °C for 60 min in a closed system providing low oxygen conditions resulted in 97% and 99% reductions in the total and I-TEQ concentrations of PCDD/Fs, to 6.8 μg kg−1 ash and <0.05 μg I-TEQ kg−1 ash, respectively. Increasing the thermal treatment time to 480 min, at the same temperature, yielded 99% reductions in both total and I-TEQ concentrations of the mono- to octa-chlorinated PCDD/Fs. Similar effects were observed for HCB and PCBs. The data from this study indicate that PCDD/Fs and other toxic organic compounds in ash from incinerated MSW, can be effectively degraded by this procedure, which combines relatively low-temperatures, short treatment times, and low oxygen conditions.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2007
Keyword
PCDD/F, PCB, HCB, Thermal degradation, MSW, Fly ash
Identifiers
urn:nbn:se:umu:diva-10112 (URN)10.1016/j.chemosphere.2006.09.057 (DOI)17109915 (PubMedID)
Available from: 2007-03-02 Created: 2007-03-02 Last updated: 2017-12-14Bibliographically approved
4. Fate of PCDD and PCDF during thermal treatment of waste incineration ash
Open this publication in new window or tab >>Fate of PCDD and PCDF during thermal treatment of waste incineration ash
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2648 (URN)
Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2010-01-13Bibliographically approved

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