Biogas production from bioplastics: Pretreatment strength assessment through repeated batch tests under mesophilic and thermophilic conditions

초록

Pretreatment of bioplastics (BPs) is known to be an essential step to overcome the incomplete degradation and slow reaction rates in anaerobic digestion. While pretreatment can enhance solubilization, its actual benefit to methane potential yield (MPY) remains unclear, increased solubility does not always warrant enhanced CH4 production. This study aimed to minimize the required pretreatment strength for BPs by employing a novel approach using repeated biochemical methane potential (BMP) tests under both mesophilic and thermophilic conditions, enabling assessment of microbial adaptation. Polyhydroxybutyrate (PHB) and polylactic acid (PLA) were pretreated with varying alkaline dosages (50-300 g OH-/kg BP) at 100 degrees C for 3 h, and the MPY were compared over three consecutive batch tests. Pretreatment resulted in a gradual solubilization increase from around 10 %-60 %. PHB consistently showed high MPY (->90 %) regardless of pretreatment, indicating that pretreatment is unnecessary. In contrast, PLA required pretreatment (up to 200 g OH-/kg BP) to improve CH4 production in the first batch test. However, subsequent batches showed a significant performance increase even without pretreatment achieving 65 % MPY from untreated PLA, the highest ever reported, indicating that a significant fraction of CH4 can be attained from the solid part of PLA by natural adaptation. Thermophilic conditions further enhanced natural adaptation, with >85 % (based on 1 g COD = 350 mL CH4) MPY achieved for pretreated PLA. In addition, depending on the substrate and temperature regime, notable changes in dominant bacterial and archaeal species were observed.

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