Pilot-scale study on a sludge-biofilm symbiotic system for enhancing partial nitrification-anammox in nitrogen removal from high-ammonia nitrogen industrial wastewater

• • The IFAS-SPN/A system achieved successful startup within 120 days, reaching a total nitrogen removal efficiency of (90.21±2.18)% and a removal load of (0.31±0.07) kg/(m³·d) under an influent NH4+-N concentration of 2300 mg/L, demonstrating rapid process initiation for high-strength industrial wastewater. • • Through a two-step inoculation strategy (nitrifying sludge first, then anammox sludge), AnAOB relative abundance reached 18.8% in biofilm and 35.3% in flocs during load intensification, enabling a doubling of nitrogen removal load to (0.64±0.11) kg/(m³·d) – critical for cost-effective full-scale implementation. • • A surge in influent ammonium nitrogen concentration was identified as the primary cause of NO2--N accumulation imbalance and system performance deterioration, emphasizing the need for robust equalization (e.g., an equalization tank) to maintain stable operation. • • The 'dilution-reconstruction' strategy, involving low-ammonia wastewater, proved effective for rapid recovery of system performance after deterioration, offering a practical operational protocol for managing transient upsets in industrial applications.