Steering carbon and nitrogen toward biopolymer recovery in synthetic municipal wastewater using an intertidal wetland sediment-seeded biofilm-based reactor.

Recovering value-added biopolymers from municipal wastewater offers a promising route to improve the sustainability of wastewater treatment. In this study, two moving bed biofilm reactors (MBBRs) seeded with intertidal wetland sediment (IWS) (Riws) and conventional activated sludge (AS) (Ras) were operated in parallel for synthetic municipal wastewater treatment and biopolymer recovery. A higher total nitrogen (TN) removal efficiency was achieved in the Riws than in the Ras (92.4 ± 0.5% and 80.1 ± 3.8%, respectively). Moreover, Riws achieved a higher alginate-like exopolymers (ALE) yield than Ras, reaching 374.3 ± 10.5 mg/g VSS compared with 242.6 ± 8.4 mg/g VSS. The recovered ALE from Riws also contained more protein (890.0 ± 11.7 mg/g ALE) and showed a higher alginate-equivalent response (598.6 ± 32.5 mg/g ALE). Estimated COD and nitrogen partitioning further showed that ALE-associated COD accounted for 17.5% of influent COD in Riws and 6.9% in Ras, while ALE protein-associated N represented 19.1% and 5.9% of influent TN, respectively. Moreover, metagenomic analysis showed that the mature Riws biofilm had higher abundances of genes associated with nitrogen assimilation and denitrification, together with genes involved in ALE biosynthesis, and extracellular-polymer regulation through quorum sensing and c-di-GMP-related pathways. These functional differences were consistent with the greater retention of wastewater carbon and protein-associated nitrogen in recoverable ALE in Riws. These results demonstrate that inoculum selection can effectively regulate microbial assembly and redirect wastewater carbon and nitrogen toward extracellular biopolymer synthesis and recovery, providing a feasible strategy for wastewater valorization.