Efficient sludge reduction and phosphorus recovery in innovative coupled sequencing batch and worm reactor Process: Performance, mass balance and metagenomic mechanisms.

The efficient release and phosphorus recovery (PR) are core to enhancing the sustainable operation of municipal wastewater treatment systems. To address this issue, this study constructed an innovative coupled sequencing batch reactor (SBR)-worm reactor (WR)-PR process. By leveraging the synergistic regulation between worm predation and microbial activity, the process achieved the dual objectives of sludge reduction and the efficient release and targeted recovery of phosphorus from the solid phase to the liquid phase. By subjecting only approximately 6% of the influent flow to chemical phosphorus recovery, an efficient recovery of 45% of the influent total phosphorus (TP) was achieved. During 160 days of continuous operation, the coupled process exhibited excellent stability in pollutant removal, with removal rates of chemical oxygen demand (COD), total nitrogen (TN), and TP reaching 95%, 71%, and 97%, respectively. Sludge reduction of 49% was achieved through worm predation, with direct worm predation contributing 69%. Sludge characteristics were significantly improved, with the sludge volume index (SVI) decreasing by 46% and dewaterability increasing by 20%. Extracellular polymeric substance (EPS) analysis revealed that side‑stream predation reduced total EPS content, increased the protein/polysaccharide (PN/PS) ratio. Metagenomic analysis confirmed that side-stream biological predation significantly enriched key functional microbial groups and intensified the expression of genes related to phosphorus transport and metabolism. This work elucidates the microbial synergistic mechanisms within the coupled process, providing a novel pathway for the simultaneous achievement of efficient sludge reduction and PR in municipal wastewater treatment.