Bacterial-algae biofilm formation deciphering phenolic wastewater degradation code: Revealing microbial community succession and tripartite synergistic networks

Phenolic compound treatment in phenol wastewater is challenging due to their toxicity and resistance. This study constructed a bacterial-algal biofilm reactor to treat simulated wastewater containing phenolic compounds, focusing on microbial succession and inter-kingdom synergy under phenol-induced stress and hydraulic retention time (HRT) shocks. After the initial biofilm formation, increasing influent phenol concentration (25 to 50 mg/L) at a 6-day HRT led to complete phenol degradation and approximately 95% COD removal. However, NH₃-N conversion decreased to about 16% under short HRT shock, limiting nitrogen removal. High-throughput sequencing revealed: (1) Microbial diversity peaked mid-operation, while short HRT led to biofilm detachment and reduced diversity; (2) Under increasing phenol load, the community evolved into a stable tripartite structure, marked by key taxa abundance thresholds (e.g., Sphingobium > 22%, Fusarium > 66%) linked to optimal degradation. Core functional microbiota included Sphingobium for phenol ring-opening, Zoogloea for biofilm stability, Fusarium for phenol hydroxylation and ring cleavage via laccase and cytochrome P450, and Chlorophyta for photosynthetic oxygen and fixed carbon supply. The tripartite network of bacteria, fungi, and algae drives efficient phenol mineralization, with algae sustaining the consortium through photosynthesis and providing carbon for fungal metabolism. However, the system's nitrogen removal capacity remains limited.