Insights into the Implementation of Partial Denitrification-Anammox in Actual Municipal Wastewater: A Comparison of Two Strategies.

Efficient and sustainable nitrogen removal is vital for wastewater treatment, and the partial denitrification-anammox (PDA) process shows promise for achieving high performance. The responses of anammox to PDA implementation with different strategies (gradual and abrupt bioprocess integration) were evaluated. Anammox (AnAOB) enrichment was initially achieved under synthetic medium conditions with a nitrogen removal efficiency (NRE) of 85.5%, which increased to 94.3% after the introduction of real wastewater, demonstrating system robustness and adaptability. The gradual PDA implementation strategy involved controlled nitrate supplementation and progressive adjustment of nitrate-nitrite availability, promoting cooperative interactions between AnAOB and denitrifying bacteria (DNB), resulting in 75.4 ± 5.0%, with heterotrophic denitrification contributing up to 57.4% of NRE. In contrast, abrupt PDA implementation relied on direct high-nitrate exposure, leading to distinct nitrogen conversion pathways, with an anammox reaction contribution of 58.1 ± 2.8%, although with low ammonium removal of 33.1 ± 0.8%. The availability of refractory organic compounds from the anaerobically pretreated municipal wastewater was identified as the limiting factor for higher substrate production (nitrite) levels for AnAOB during partial denitrification. A pronounced shift in microbial diversity was observed, with a notable increase in the abundance of partial denitrifiers from the