Analysis of leaching additives from plastics and investigation of change in plastic properties during sludge pretreatment prior to anaerobic digestion

Date

2024-1

Author

Cemalgil, Nermin

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Microplastics (MPs) are small in size and have a high specific surface area, which makes them easily transported into soil, air, and water. Unfortunately, a large amount of MPs that end up in wastewater treatment plants are accumulated in sludge. Anaerobic digestion (AD) of sludge is known to be affected by MPs. Sludge disintegrations are applied before AD to enhance digestion efficiency by increasing biogas production and disrupting the complex structure of sludge. This study aimed to investigate the effects of different disintegration methods on polyethylene terephthalate (PET), polypropylene (PP) and polycarbonate (PC) MPs. Sludge samples spiked with MPs with 10 mg/g total solid (TS) dose were exposed to 0.5 M alkali for two days, thermally treated at 127°C for two hours and enzymatically disintegrated by pancreatin enzyme with 150 mg/g and 200 mg/g TS doses at 38°C for 24 hours, separately. Alkali-thermal and thermal-enzyme combined disintegrations were also applied. Phthalates and bisphenol-A (BPA) leaching after disintegrations were quantified using GC-MS following solid-phase extraction. Phthalates, mostly, did not leach upon disintegration. BPA concentration, on the other hand, drastically increased 4000 times in PC-containing sludge after alkalithermal combined disintegration. The carbonyl index decreased in PET and PC-MPs after both combined treatments, whereas that of PP-MPs was found to be negligible. The crystallinity of PET decreased by 10% after alkali-thermal disintegration and that of PP increased by 7% and 3% after alkali-thermal and thermal-enzyme treatments, respectively. For the first time, this study demonstrated the effects of sludge disintegrations on PP-MPs and PC-MPs.

Subject Keywords

Microplastics, Anaerobic digestion, Sludge disintegrations, Plastic additives

URI

https://hdl.handle.net/11511/108778

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Graduate School of Natural and Applied Sciences, Thesis