Enhancing anaerobic methane production in the co-presence of PLA, TPS, and PBAT mixed under hydrogen-rich conditions

Abstract

Methane (CH₄) production was compared during mesophilic anaerobic digestion (AD) under H₂/CO₂ purged versus N₂ purged, investigating the biodecomposition of polylactic acid (PLA), thermoplastic starch (TPS), and polybutylene adipate terephthalate (PBAT) as the co-presence of PLA/TPS (LS), TPS/PBAT (SB), PLA/PBAT (LB), and PLA/TPS/PBAT (LSB). Therein, 427.37 and 339.22 mL CH₄/g volatile solid (VS) were produced endogenously under H₂/CO₂ and N₂ purged, respectively. CH₄ production from LS and SB was further increased from 170 to 193 mL CH₄/g VS compared to the respective control samples. The degradation of LB and LSB resulted in significantly higher CH₄ production under H₂/CO₂ (157.49 and 229.21 mL CH₄/g VS) than under N₂ (106.88 and 119.63 mL CH₄/g VS, respectively). Metagenome sequencing revealed that H₂/CO₂ purged led syntrophs of hydrogenotrophic methanogens (e.g., Firmicutes) overcoming higher strengths of fatty acids and utilizing H₂ to produce more CH₄. Subsequently, PLA and PBAT exhibited breakdowns in the polymer chains and molecular weight along with increased crystallinity. This was confirmed through Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). This study highlights the critical roles of co-digestion with H₂ and bioplastics in increasing CH₄ production in the AD system.