Rapid cultivation and stability of autotrophic nitrifying granular sludge

Autotrophic nitrifying granular sludge (ANGS) was cultivated by gradually decreasing the influent organics and adding exogenous nitrifying bacteria. Under the strategy, ANGS was domesticated within 36 days. Stability of the seed heterotrophic granules decreased significantly during conversion of organic wastewater to inorganic ammonia wastewater. Obvious granular breakage was observed during these days. However, the granular debris still had good settlement performance. With microbes gradually acclimated to the new environment, the debris provided a large number of carriers for the attached growth of the exogenous nitrifying bacteria, and they replaced the heterotrophic bacteria and became the dominant species. The domesticated ANGS showed good nitrification performance during the 37th to the 183rd day (ammonia nitrogen load between 0.28 and 0.29 kg/m³ · d). The removal rate of ammonia nitrogen was usually more than 95%, and nitrite accumulation rate was always larger than 50%. However, nitrification ability was gradually lost with the increase of the ammonia nitrogen load (0.3-0.64 kg/m³ · d) from the 184th day, and it almost approached the influent ammonia nitrogen at the 269th day. Interestingly, good structure stability of the ANGS was maintained during long-term operation, and the ANGS became smoother and denser at the end of the experiment.