Fate and Effects of Polyethylene Terephthalate (PET) Microplastics During Anaerobic Digestion of Disintegrated Sludge

2021-12-24
Hatinoğlu, Makbule Dilara
Modern wastewater treatment plants effectively remove microplastics (MPs) from wastewater but unfortunately concentrate them in sludge. Anaerobic digesters were recently reported to be affected by MPs. Despite their resilience to natural degradation, polyethylene terephthalate (PET) plastics have inherent weaknesses to alkali and thermal conditions and become more susceptible to biodegradation if exposed to them. Sludge disintegration practices aiming to increase the biogas production by disrupting sludge’s floc structure show great similarity with the stress factors mentioned. Thus, this study aimed to integrate disintegration with anaerobic digesters and investigate the fate and effects of PET MPs during these processes. With this purpose, waste activated sludge samples spiked with different doses of PET (0,1,3,6 mg/g TS) in sizes of 250-500 μm were disintegrated by 0.5 M alkali for two days and thermally hydrolyzed at 127°C for 120 min. 60 days of biochemical methane potential reactor operation concluded that MPs dose significantly affected the methane yield positively in non-disintegrated reactors. Integrating disintegration prior to digestion, on the other hand, increased the yield by 22.0% and made the impact of MPs on digester efficiency no longer observable. PET also experienced changes in their physical (surface morphology/mass) and chemical (crystallinity/carbonyl index) properties depending on whether they were exposed to disintegration before digestion. Moreover, for the first time in literature, a method was developed for the analysis of MPs in sludge based on chemical oxygen demand removal as the indicator of organic matter removal. The method provides over 80% MPs recovery efficiency, meeting the recommendations in the literature.

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Citation Formats
M. D. Hatinoğlu, “Fate and Effects of Polyethylene Terephthalate (PET) Microplastics During Anaerobic Digestion of Disintegrated Sludge,” M.S. - Master of Science, Middle East Technical University, 2021.