Two-stage partial nitritation/Anammox (PN/A) for mainstream wastewater treatment: Achieving high nitrogen removal at
Xiaodan Gu1, Feng Wang1, Yongwei Ding2
1School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou, 215009, China; National and Local Joint Engineering Laboratory of Municipal Sewage Resource Utilization Technology, Suzhou, 215009, China.
Abstract:
Under low temperature and low ammonia nitrogen conditions, the partial nitritation/Anammox (PN/A) process faces challenges such as unstable partial nitritation and insufficient nitrogen removal. Here, a novel two-stage PN/A reactor was developed to investigate nitrite-oxidizing bacteria (NOB) inhibition and nitrogen removal performance in mainstream wastewater treatment. This investigation was conducted with multi-strategy regulation under a high influent ammonia nitrogen loading rate (ANLR) of 0.8-1.3 kg N/(m3·d). The results indicated that when the water temperature was 26-30 °C, combining low DO levels of 0.2 mg/L with a SRT of 25 days achieved an ammonia nitrogen conversion efficiency (ACE) of 65.8 ± 2.1 % and nitrite accumulation efficiency (NiAE) of 80.4 ± 1.8 %. However, when the water temperature dropped below 20 °C, relying solely on low DO levels (0.35-0.40 mg/L) and a shorter SRT (15 days) was ineffective due to the proliferation of NOB. After combining the low-nitrite strategy to selectively inhibit NOB activity, the ACE and NiAE reached approximately 47.4 ± 8.3 % and 79.5 ± 4.6 %, respectively. Finally, in the two-stage PN/A system, the integrated process achieved a nitrogen removal efficiency of 92.8 ± 1.9 % and a nitrogen removal rate of 0.99 ± 0.03 kg/(m3·d) below 20 °C. Microbial community analysis revealed that Bacillus and Nitrosomonas were the dominant functional microorganisms in the PN zone, which confirmed the synergistic nitrogen removal by the denitrification and Anammox pathway. This study offers critical insights for advancing the practical application of the PN/A process in treating mainstream wastewater under high-ANLR and low-temperature conditions.
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