Fate and effect of Polyamide-6 microplastics in mesophilic and thermophilic anaerobic digestion

• Published in: Environmental pollution (1987) Vol. 361; p. 124855
• Main Authors: Şimşek, İrem, Sanin, F. Dilek
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.11.2024
• Subjects: Carbonyl index; Crystallinity; Mesophilic digestion; Microplastic; Polyamide-6; Thermophilic digestion; Thermophilic digestion; Polyamide-6; Crystallinity; Microplastic; Mesophilic digestion; Carbonyl index
• ISSN: 0269-7491; 1873-6424; 1873-6424
• DOI: 10.1016/j.envpol.2024.124855

Research has demonstrated that depending on the type and concentration, microplastics affect anaerobic digestion (AD). Owing to the high abundance of polyamide-6 (PA6) in wastewater treatment plants and limited understanding of its behavior, this study investigates PA6 microplastics' effect in AD. Biochemical methane potential experiments were performed under mesophilic (35 °C) and thermophilic (55 °C) conditions using PA6 at concentrations from 0 to 200 particles/g total solids (TS). Under both conditions, methane production increased in the highest (200 particles/g TS) PA6-dosed reactors, with thermophilic conditions having a statistically significant effect. Methane yield increased from 403.1 ± 5.3 mL/g VS to 436.6 ± 9.2 mL/g VS under thermophilic and from 332.1 ± 1.5 to 340.6 ± 6.6 mL/g VS under mesophilic conditions for the 200 particles/g TS dose, corresponding to increases of 8.3% and 2.6% respectively. PA6 crystallinity decreased from 32.8% to 27.1% and 26.8%, corresponding to decreases of 17.4% in mesophilic and 18.2% in thermophilic reactors compared to pristine control. Similarly, crystallinity decreased in PA6 microplastics collected from abiotic reactors, with thermophilic conditions showing a greater effect. The carbonyl index (CI) values were similar between biotic and abiotic reactors, but PA6 from all reactors had significantly higher CI than pristine PA6, suggesting abiotic factors also affect carbonyl bonds. Additionally, an increase in average PA6 mass was observed for mesophilic and thermophilic conditions by 22.0 % and 23.0 %, respectively. The study shows that temperature and other abiotic factors, like sludge chemistry, significantly influence the fate and effect of PA6 microplastics in digesters. Including abiotic reactors seems crucial for a full understanding of the impact of microbial and non-microbial factors in microplastic studies in the AD process. Studying the effects of microplastics on AD is only one part of the picture, whereas simultaneously examining their fate in digestion is necessary for a complete understanding. [Display omitted] •Fate and impact of PA6 particles in mesophilic and thermophilic digestion studied.•In mesophilic digestion, PA6 did not affect the performance or CH4 production.•In thermophilic digestion, CH4 yield increased with PA6, independent of the dose.•Both digestions decreased crystallinity and increased CI compared to pristine PA6.•Abiotic controls showed PA6 particle changed owing to abiotic conditions.