Evaluation of the toxicity of char residues produced in the co-pyrolysis of different wastes

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Abstract

The high amounts of solid waste produced in industrial installations and in urban centers is a complex problem of today's society. The traditional strategies for solid waste transformation and disposal include landfilling or incineration. Other approaches are being exploited namely waste selective collection and recycling or the energetic valorization of solid wastes through pyrolysis. In the pyrolytic process, the wastes are converted into a gaseous and liquid phase that can be used in energy production or as feedstock in chemistry industries. A solid residue (char) is also produced in a proportion that depends on the pyrolysis conditions. Even when the operating conditions are optimized in order to minimize the solid fraction, a reasonable amount of chars are obtained. These chars are mainly composed of a carbon-rich matrix that contains the mineral matter initially present in the wastes as well as components of the liquid fraction. Therefore, these solid residues have a toxicity potential due to the presence of heavy metals or organic compounds that must be assessed in order to define their safe reutilization or disposal. In the present study, the chars produced in the co-pyrolysis of plastics, pine biomass and tyres were characterized through chemical and ecotoxicological tests. A fraction of the solid chars was treated by extraction with dichloromethane. Different volatility groups of compounds present in the extracted and non extracted char were evaluated. A selected group of heavy metals was determined in both chars. Chars were subjected to the leaching test ISO/TS 21268 - 2 and the resulting eluates were further characterized by determining a group of inorganic and organic parameters. An ecotoxicological characterization was performed by using the bio-indicator Vibrio fischeri. The chemical and ecotoxicological results were compared and analysed according to the Council Decision 2003/33/CE and the Criteria on the Evaluation Methods of Waste Ecotoxicity (CEMWE). The results of the chemical characterization indicate that the extraction of the char residues with an appropriate organic solvent allows the efficient elimination of the volatile organic contaminants thus decreasing the potential toxicity of these chars. The semi-volatile and non-volatile fractions were not, apparently, affected by this pre-treatment. Regarding the release of heavy metals from extracted and non-extracted chars during the leaching tests, a strong contamination with Zn was found in both eluates, which contribute to a classification of the corresponding chars as hazardous and ecotoxic materials. Also the results of the ecotoxicological characterization of the eluates led to a classification of these chars as ecotoxic materials.
Original languageEnglish
Title of host publicationTurning Waste into Ideas. ISWA/APESB 2009 World Congress. Book of Abstracts
EditorsJosé M. P. Vieira, Paulo J. Ramísio, Ana I. E. Silveira
Place of PublicationLisbon
PublisherInternational Solid Waste Association (ISWA)
Number of pages8
ISBN (Print)978-989-96421-1-9
Publication statusPublished - Oct 2009
EventInternational Solid Waste Association (ISWA)/Associação Portuguesa de Engenharia Sanitária e Ambiental (APESB) 2009 World Congress - Centro Cultural de Belém, Lisbon, Portugal
Duration: 12 Oct 200915 Oct 2009

Conference

ConferenceInternational Solid Waste Association (ISWA)/Associação Portuguesa de Engenharia Sanitária e Ambiental (APESB) 2009 World Congress
CountryPortugal
CityLisbon
Period12/10/0915/10/09

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