Pilot-scale study on a sludge-biofilm symbiotic system for enhancing partial nitrification-anammox in nitrogen removal from high-ammonia nitrogen industrial wastewater
The single-phase partial nitrification and anammox (SPN/A) process has seen limited widespread application due to its slow startup and difficulties in enriching anaerobic ammonium-oxidizing bacteria (AnAOB). This study utilized high-ammonia nitrogen wastewater to initiate and enhance the SPN/A process in a pilot-scale integrated fixed-film activated sludge (IFAS) reactor. By establishing an IFAS-SPN/A coupled system based on the symbiotic relationship between biofilm and sludge, rapid startup and efficient AnAOB enrichment were achieved. An innovative sludge inoculation strategy was employed: first, conventional nitrifying sludge was inoculated to initiate shortcut nitrification and allow ammonia-oxidizing bacteria (AOB) to colonize blank carriers; subsequently, anammox sludge was inoculated to promote efficient AnAOB enrichment on the AOB biofilm. The influent was low-temperature shift condensation water from a synthetic ammonia workshop, with an average ammonium nitrogen concentration of 2300 mg/L and COD ranging from 50 to 200 mg/L. The 180-day experiment comprised three stages: shortcut nitrification startup, SPN/A startup, and load intensification. The system successfully started up SPN/A within 120 days, achieving total nitrogen removal efficiency and removal load of (90.21±2.18)% and (0.31±0.07) kg/(m³·d), respectively, through synergistic biofilm and suspended microorganisms. During load intensification, AnAOB relative abundances in biofilm and flocs reached 18.8% and 35.3%, respectively, and removal load increased to (0.64±0.11) kg/(m³·d). Stable influent quality is a prerequisite for efficient and stable nitrogen removal; a surge in influent ammonium concentration caused nitrite accumulation imbalance and deteriorated performance. Adding an equalization tank before the aeration tank mitigates water quality fluctuations, and a 'dilution-reconstruction' strategy for low-ammonia wastewater facilitates rapid recovery after performance deterioration.