Revealing the effect of biofilm formation in partial nitritation-anammox systems: Start-up, performance stability, and recovery.

Successful application of partial nitritation-anammox (PNA) processes is currently and primarily associated with biofilm systems. Biofilm characteristics significantly influence start-up, performance stability, and recovery. Here, two PNA systems with and without carriers were implemented simultaneously for treating wastewater containing 50 mg-NH/L. The performance characteristics of these two PNA systems were compared. Stable nitrogen removal efficiencies of 76.3 ± 2.8% and 72.9 ± 1.6% were obtained for suspended sludge and biofilm systems, respectively. The slow process of biofilm colonization resulted in a long start-up time in the biofilm system. Biofilm enrichment and protection conferred stable performance when exposed to aeration shock. The suspended sludge system displayed good elasticity during performance recovery after shock compared to the slow recovery in the biofilm system. Moreover, suitable control of dissolved oxygen could improve the activity and abundance of the functional microbes. This study provides new insights into the operation and control of PNA systems for treating mainstream wastewater.