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Anaerobic dehalogenation of cfc gases in landfill environment. Batch studies

This project is the final thesis for master degree in Environamental Engeneering, ‘’Università degli studi di Padova’’, Italy. The work has been carried out in the department ‘’Miljo & Ressources’’ (Environment & Resources), in DTU (Danske Techniske Universitet) in Denmark. The period of studies has lasted from the beginning of September 2005 to the end of March 2006. Prof. R. Cossu and his collaborator Ing. R. Raga gave me the possibility to work in a partner university as DTU, under the supervision of Prof. P. Kjeldsen and Prof. C. Sheutz. This experience started with an introduction to chemical and chromatography laboratories. The majority of the time of this project has been spent in the laboratory, as many problems for obtaining acceptable and satisfactory results rose up during the experimental period. An important technical supervision has been given by various technicians of the laboratories of E&R and PHd students. Special thanks have to be given to Jens Sharuup Sorensen, to Karina…, to Hector Garcia and to Anders M. Fredenslund, who followed and advised me during all the lab work. A very big help was given to me by Hans Mosbaek with technical and theoretical advices, as the first part of this project was strictly related to analytical chemistry and very specific knowledge about laboratory techniques. Special thanks have to be given to all E&R department, for the warm and kind environment I found and for the availability of facilities and structures in which I could work very comfortably. The international environment in which I lived in the department E&R proves the capacity of meet and integrate different ways of working and thinking. P. Kjeldsen and Ch. Sheutz supervised me in planning the work, in finding new ways to carry out the experiments, in evaluating the results and in writing the report.

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19 1. INTRODUCTION Blowing agents (BA) for insulation foam in home appliances as refrigerators and freezers have been usually halocarbons having very high global warming or ozone depletion potentials. After their cycle of life, which lasts normally 10 – 15 years, in many countries most of the appliances are shredded and disposed into landfills. For the next decade it is expected that only in the U.S. 8 millions of fridges per year will be disposed off (3). This means that 4000 tons of CFC-11 (Trichloro- Fluoro-Methane, the most used BA in the last 20 years, also called FREON-11) will be released in the atmosphere, assuming that 500 g of CFC-11 per fridge is lost (3). There is the interest in data about the fate of the BAs, because many environmental assessments of household refrigerators don’t take into account the degradation processes taking place in landfills, which could play a not negligible role in attenuating the polluting potential of BAs’’ (1, 2, 3). Peter Kjeldsen, Charlotte Sheutz and co-workers carried out studies about the release of the gases from the shredded foams, in order to know the release rates and the factors influencing them (3). The other side of this research has been a data collection about degradation processes affecting BAs in landfill environment. The potential of anaerobic (methanogenic) bacteria to degrade blowing agents under landfill condition was tested in several batch and column studies focusing on both degradation rates and mass balance (2). The degradation rates of some BAs were found to be correlated with the number of chlorine atoms attached to the carbon. The products of the degradation of CFC-11 are HCFC-21, HCFC-31 and HFC-41. ‘’A complete degradation of CFC-11 to HFC-41 would lead to emission of a compound from landfills with zero ozone depletion potential and very low global warming potential’’ (2). However, considering just the gaseous products, more than 70% of the stoichiometric amount was missing (2). The hypothesis of defluorination, i.e. the rupture of the carbon-fluoride bond, as last step in the CFCs degradation, has been done. This hypothesis can be proved thanks to a recovery of free fluoride in the matrix where degradation occurs. Furthermore, an accurate recovery of fluoride in simulated landfill conditions (batch or column studies) could lead to a more exhaustive mass balance of the CFCs degradation process. ‘’The integrated evaluation of the fate of halocarbons contained in foam waste disposed in a landfill, carried out by P. Kjeldsen and co-workers, extended a

Tesi di Laurea

Facoltà: Ingegneria

Autore: Andrea Schievano Contatta »

Composta da 144 pagine.

 

Questa tesi ha raggiunto 290 click dal 13/10/2006.

 

Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.