Fate of phthalic acid esters during digestion of municipal solid waste under landfill conditions

Sammanfattning: The objective of this thesis has been to investigate whether anaerobic microorganisms developing in acidogenic and methanogenic landfill environments have the potential to degrade phthalic acid esters (PAEs) and what kinds of intermediates may be formed, assuming PAE degradation. PAEs form a group of compounds widely used in huge amounts worldwide, mainly as plasticiser in PVC-plastics. PAEs are presently entering Swedish landfills, mostly via PVC-plastics deposited as refuse, but also via other products. At landfills they are subjected to an anaerobic environment and may be stored for several decades and centuries under such conditions. Diluted and homogenised municipal solid waste (MSW) samples from different landfill environments were used as inocula in an assay developed for the purpose to determine the potential of microbial PAE degradation. The results showed that the microorganisms present in the MSW-samples were able to transform almost all PAEs investigated. However, the degradation of PAEs may give rise to compounds which are more chemically inert than the parental compounds. As an example bis(2-ethylhexyl) phthalate (DEHP) was observed to be degraded to mono(2-ethylhexyl) phthalate during 300 days of incubation. Monoesters of PAEs were observed in leachate from methanogenic landfill lysimeters in concentrations up to 12 mg per litre during MSW degradation. Ten fold amounts of PVC-plastic were also added to landfill lysimeters to investigate whether PAEs or degradation intermediates could be detected in the lysimeter leachate above the indigenous concentrations of PAEs. This was shown not to be the case for methanogenic conditions. However, the PVC-plastics subjected to methanogenic conditions were shown to be leached of PAEs, which did not occur for samples under acidogenic conditions. The results imply that microbial degradation enhanced the loss of PAEs from the PVC-plastics incubated under methanogenic conditions