ANAEROBIC DEGRADATION OF PHTHALIC-ACID ESTERS DURING DIGESTION OF MUNICIPAL SOLID-WASTE UNDER LANDFILLING CONDITIONS

Anaerobic microorganisms in municipal solid waste samples from laborat ory-scale landfill reactors and a pilot-plant biogas digestor were inv estigated with the aim of assessing their ability to transform four co mmercially used phthalic acid esters (PAEs) and phthalic acid (PA). Th e PAEs studied were diethyl phthalate (DEP), butylbenzyl phthalate (BB P), dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP). No biological transformation of DEHP could be detected in any of the exp eriments. Together with waste samples from the simulated landfilling c onditions, the PAFs (except DEHP) were hydrolytically transformed to t heir corresponding monoesters. These accumulated as end products, and in most cases they were not further degraded. During incubation with w aste from the biogas digestor, the PAEs (except DEHP) were completely degraded to methane and carbon dioxide. The influence of the landfill development phase on the transformations was investigated utilizing PA and DEP as model substances. We found that during both the intense an d stable methanogenic (but not the acidogenic) phases, the microoganis ms in the samples had the potential to transform PA. A shorter lag pha se was observed for the PA transformation in the samples from the stab le methanogenic phase as compared with earlier phases. This indicates an increased capacity to degrade PA during the aging phases of the mun icipal solid waste in landfills. No enhancement of the DEP transformat ion could be observed as conditions in the methanogenic landfill model changed over a year's time. The results indicate that microorganisms developing in a methanogenic landfill environment have a substantially lower potential to degrade PAEs compared with those developing in a b iogas reactor.