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

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 microbially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was identified as the optimal solid-phase carbon source with superior DOC bioavailability, achieving a 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 (cellulase, hexosaminidase) 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, which promoted NO3− reduction. This research provides the theoretical basis for the in situ resource utilization of BPs for advanced wastewater denitrification.