Biodegradable Plastics as Carbon Sources: DOC Release and Temperature-Driven Microbial Succession

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Abstract
The accumulation of biodegradable plastics (BPs) in wastewater treatment plants (WWTPs) presents a novel environmental concern, while carbon deficiency concurrently limits advanced biological denitrification. Herein, this research explored the fate of BPs and their viability as solid-phase carbon donors for denitrification. Six prevalent BPs were selected, results showed that dissolved organic carbon (DOC) release from BPs varies considerably with the synthesis type, microbially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as the optimal solid-phase carbon source with superior DOC bioavailability, achieving the denitrification rate of 0.72 mg/(g·h). Light irradiation and pH variations accelerated DOC release via surface micro-cleavage, predominantly yielding highly active aliphatic oligomers without disrupting the primary polymeric backbone. Furthermore, macromolecular depolymerization genes (acsABCDE, cdhCDE) and nitrous oxide reductase genes (nosZ, nosD) were strongly temperature-dependent, which induced the directional enrichment of the core denitrifying genus Thauera, and upregulated expression at 25 °C that promoted NO₃⁻ reduction. This research provided the theoretical basis for the in-situ resource utilization of BPs for advanced wastewater denitrification.
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