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Size-dependent effects of polystyrene microplastics on anaerobic digestion performance of food waste: Focusing on oxidative stress, microbial community, key metabolic functions

Journal of Hazardous Materials 2022 65 citations

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Researchers investigated how polystyrene microplastics of different sizes affect anaerobic digestion of food waste and found that smaller particles caused greater inhibition of methane production, with reductions up to 33%. The study suggests that small microplastics induce more oxidative stress in microbial communities and suppress key enzymes involved in methane-producing metabolic pathways.

Polymers

Polystyrene (PS) microplastics (MPs) are widely existed in food waste (FW) due to the usage of plastic food-packaging. However, the effects and mechanisms of PS MPs with different sizes on anaerobic digestion (AD) performance of FW have not been comprehensively studied yet. Herein, the impacts of different PS MPs sizes (1 mm, 100 µm and 1 µm) with 20, 200 particles/g-TS were investigated. Results showed that 20 particles/g-TS PS MPs decreased cumulative methane production by 1.46-18.11 %, while the higher levels (200 particles/g-TS) significantly inhibited by 9.14-33.08 % (p < 0.05) compared with control group. The inhibiting effects were enhanced as particle size smaller. Physicochemical analysis indicated that MPs prolonged organic matter hydrolysis, weakened the volatile fatty acids metabolism and inhibited methanogenesis-related microorganisms (Synergistetes, Proteiniphilum and Methanosarcina). Small-sized MPs could induce more reactive oxygen species causing cell toxicity and suppressed key enzymes (α-glucoside, protease, acetate kinases and F) activities, thereby restraining methane production. The analyses of acetyl-CoA synthase and methyl-coenzyme M reductase functional genes illustrated that small-sized MPs negatively affected acetoclastic methanogenesis pathways. Overall, these results provide new insights into the size-dependent effects on AD performance induced by PS MPs.

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