Integrating anaerobic treatment with partial nitritation (PN)/anammox is a promising technology to achieve energy-efficient wastewater treatment, while partial nitritation of the mainstream anaerobic effluent (Aneff) was rarely reported. A PN reactor fed with low-strength Aneff was employed in this study to investigate the performance and technology bottleneck of this process. When operated at low dissolved oxygen (DO) concentration (0.30-0.43 mg/L), gene coding hydroxylamine oxidation (hao) was severely suppressed by bio-refractory organics, which results in a decreased ammonia-oxidizing bacteria activity and nitrite accumulation rate. The ammonium conversion and nitrite accumulation were recovered by increasing the DO concentration to a moderate-high level (1.10 ± 0.20 mg/L) and achieved long-term stable operation. At this condition, hao showed a dramatic increase while gene encoding nitrite oxidoreductase was appropriately suppressed; the effluent NO2-/NH4+ ratio reached 1.17, and a low NO3-/NOx- ratio of 0.38 was achieved simultaneously. The findings in this study revealed the adverse effects of Aneff on PN and supported a practical operating strategy for efficient PN of Aneff.
Keywords: Ammonia-oxidizing bacteria; Anaerobic effluent; Dissolved oxygen; Nitrite-oxidizing bacteria; Partial nitritation.
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