Enhanced nitrogen removal through supernatant-assisted recovery in an ANAMMOX reactor after biomass loss

The ANAMMOX process offers energy-efficient nitrogen removal but remains vulnerable to biomass loss due to the slow growth of ANAMMOX bacteria. This study evaluated the potential for performance recovery after biomass washout by supplementing with supernatant from a stable ANAMMOX reactor. A 5L reactor experienced intentional Mixed Liquor Suspended Solid(MLVSS) loss and was operated under reduced nitrogen loading. Recovery was initiated by adding 4 L of filtered supernatant. Reactor performance improved rapidly, with MLVSS increasing from 340 mg/L to 590 mg/L and Nitrogen Removal Rate(NRR) from 0.076 to 0.1832 kg-N/m^3/day within 8 days. Sponge-type carrier media also showed biomass accumulation. The results suggest that the supernatant contained components that stimulated ANAMMOX activity, enabling fast recovery. Supernatant supplementation may offer a practical strategy for restoring ANAMMOX performance after biomass loss.