Robustness of the synergistic partial-denitrification, anammox, and fermentation process for treating domestic and nitrate wastewaters under fluctuating C/N ratios.

The synergistic partial-denitrification, anammox, and fermentation (SPDAF) process presents a promising solution to treat domestic and nitrate wastewaters. However, its capability to handle fluctuating C/N ratios (the ratios of COD to total inorganic nitrogen) in practical applications remains uncertain. In this study, the SPDAF process was operated for 236 days with C/N ratios of 0.7–3.5, and a high and stable efficiency of nitrogen removal (84.9 ± 7.8%) was achieved. The denitrification and anammox contributions were 6.1 ± 7.1% and 93.9 ± 7.1%, respectively. Batch tests highlighted the pivotal role of in situ fermentation at low biodegradable chemical oxygen demand (BCOD)/NO 3 − ratios. As the BCOD/NO 3 − ratios increased from 0 to 6, the NH 4 + and NO 3 − removal rates increased, while the anammox contribution decreased from 100% to 80.1% but remained the primary pathway of nitrogen removal. The cooperation and balanced growth of denitrifying bacteria, anammox bacteria, and fermentation bacteria contributed to the system's robustness under fluctuating C/N ratios. [Display omitted] • The SPDAF process had a robustness under fluctuant C/N ratios of 0.7–3.5. • The SPDAF process obtained a stable and high nitrogen removal efficiency (84.9 ± 7.8%). • The anammox contribution (93.9 ± 7.1%) always kept at the lead in the nitrogen removal. • Fermentation played a key role in the full utilization of the complex organics. • Main functional bacteria cooperated and supported the robustness of SPDAF process. [ABSTRACT FROM AUTHOR]