Comparison of anaerobic digestion of starch- and petro-based bioplastic under hydrogen-rich conditions.

To identify an economically viable waste management system for bioplastics, thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) were anaerobically digested under hydrogen (H ₂ )/carbon dioxide (CO ₂ ) and nitrogen (N ₂ ) gas-purged conditions to compare methane (CH ₄ ) production and biodegradation. Regardless of the type of bioplastics, CH ₄ production was consistently higher with H ₂ /CO ₂ than with N ₂ . The highest amount of CH ₄ was produced at 307.74 mL CH ₄ /g volatile solids when TPS digested with H ₂ /CO ₂ . A stepwise increased in CH ₄ yield was observed, with a nominal initial increment followed by accelerated methanogenesis conversion as H ₂ was depleted. This may be attributed to a substantial shift in the microbial structure from hydrogenotrophic methanogen (Methanobacteriales and Methanomicrobiales) to heterotrophs (Spirochaetia). In contrast, no significant change was observed with PBAT, regardless of the type of purged gas. TPS was broken down into numerous derivatives, including volatile fatty acids. TPS produced more byproducts with H ₂ /CO ₂ (i.e., 430) than with N ₂ (i.e., 320). In contrast, differential scanning calorimetry analysis on PBAT revealed an increase in crystallinity from 10.20 % to 12.31 % and 11.36 % in the H ₂ /CO ₂ - and N ₂ -purged conditions, respectively, after 65 days of testing. PBAT surface modifications were characterized via Fourier transform infrared spectroscopy and scanning electron microscopy. The results suggest that the addition of H ₂ /CO ₂ can enhance the CH ₄ yield and increase the breakdown rate of TPS more than that of PBAT. This study provides novel insights into the CH ₄ production potential of two bioplastics with different biodegradabilities in H ₂ /CO ₂ -mediated anaerobic digestion systems.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Chang Gyun Kim reports financial support was provided by Korea Environmental Industry and Technology Institute. Chang Gyun Kim reports administrative support was provided by Inha University.].
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