Key Takeaways & Executive Findings
- •• • 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.
Abstract
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.
1. Introduction
The single-phase partial nitrification and anammox (SPN/A) process offers a sustainable alternative for nitrogen removal from high-ammonia industrial wastewater, yet its commercial deployment has been hindered by slow startup and the difficulty of enriching anaerobic ammonium-oxidizing bacteria (AnAOB). Conventional nitrification-denitrification systems require substantial organic carbon and energy, whereas anammox-based processes reduce aeration and sludge production. However, the long doubling time of AnAOB (approximately 10-14 days) and their sensitivity to environmental conditions have limited the practical application of SPN/A, particularly in industrial settings with fluctuating wastewater characteristics.
This study addresses these bottlenecks by employing an integrated fixed-film activated sludge (IFAS) reactor that combines biofilm and suspended biomass, creating a symbiotic environment that accelerates AnAOB enrichment. The innovative two-step inoculation strategy—first establishing ammonia-oxidizing bacteria (AOB) on carriers, then introducing anammox sludge—promotes rapid biofilm colonization and functional microbial stratification. Using real wastewater from a synthetic ammonia plant with an average NH4+-N of 2300 mg/L, the pilot-scale system achieved stable SPN/A startup within 120 days and reached a nitrogen removal load of 0.64 kg/(m³·d) after intensification. These results demonstrate a viable path to overcome the startup and enrichment barriers, offering a practical solution for high-ammonia industrial wastewater treatment.
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SUN Haofei, LI Jialin, SUN Zhaoqiang, ZHANG Liang (2026). Pilot-scale study on a sludge-biofilm symbiotic system for enhancing partial nitrification-anammox in nitrogen removal from high-ammonia nitrogen industrial wastewater. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605002
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Frequently Asked Questions
What are the critical operational parameters for achieving rapid startup of SPN/A in an IFAS reactor treating high-ammonia wastewater?
The study achieved startup within 120 days by using a two-step inoculation strategy: first inoculating conventional nitrifying sludge to establish AOB on carriers, then inoculating anammox sludge. Key parameters included maintaining influent NH4+-N around 2300 mg/L and COD between 50-200 mg/L. The system reached a TN removal efficiency of (90.21±2.18)% and a removal load of (0.31±0.07) kg/(m³·d) during the startup phase.
How does the system respond to sudden increases in influent ammonia concentration, and what mitigation strategies are recommended?
A surge in influent ammonium nitrogen concentration caused NO2--N accumulation imbalance and deteriorated nitrogen removal performance. To mitigate this, the study recommends installing an equalization tank before the aeration tank to buffer water quality fluctuations. Additionally, a 'dilution-reconstruction' strategy using low-ammonia wastewater was effective for rapid recovery after performance deterioration.
What are the relative abundances of AnAOB in the biofilm and flocs, and how do they contribute to the overall nitrogen removal?
During the load intensification stage, AnAOB relative abundances were 18.8% in the biofilm and 35.3% in the flocs. This dual enrichment allowed the system to achieve a removal load of (0.64±0.11) kg/(m³·d), demonstrating that both phases contribute significantly to nitrogen removal, with flocs playing a previously overlooked role.
What is the practical significance of the nitrogen removal load achieved in this pilot-scale study compared to conventional processes?
The achieved removal load of 0.64 kg/(m³·d) is substantially higher than typical nitrification-denitrification systems (often below 0.1 kg/(m³·d) for high-strength wastewater) and comparable to other anammox-based processes. This higher volumetric load translates to smaller reactor footprints and lower capital costs, making the IFAS-SPN/A process economically attractive for industrial applications.
What are the main challenges for scaling up this IFAS-SPN/A process to full-scale industrial wastewater treatment?
Key challenges include maintaining stable influent quality, as fluctuations can disrupt the delicate balance between AOB and AnAOB. The study emphasizes the need for robust equalization and control strategies. Additionally, the long-term stability of AnAOB enrichment and biofilm integrity under varying load conditions must be validated. The successful pilot-scale results provide a foundation, but full-scale implementation will require careful process control and monitoring.
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