Strategies to improve aerobic granular sludge stability and nitrogen removal based on feeding mode and substrate.

A systemic strategy was proposed to improve aerobic granular sludge (AGS) stability and nitrogen (N) removal efficiency by optimizing feeding mode and substrate aiming at complicated wastewater characteristics. Key functional groups at the genus level identified by high-throughput sequencing were evaluated as well. The results showed that anaerobic feeding mode and acetate promoted the compact AGS formation with excellent total nitrogen (TN) removal efficiency (averaging 91.7% ± 4.1%) at various dissolved oxygen conditions. While the aerobic feeding mode led to a loose AGS structure with a vulnerable anaerobic core and poor TN removal efficiency (averaging 58.8% ± 7.4%). Simultaneous nitrification and denitrification process played the dominant role in N removal in compact AGS over the alternating nitrification and denitrification process. High-concentration glucose undermined feast-famine condition with filamentous bacteria growth out of granule and decreased TN removal efficiency to 67.3% ± 15.2%. Lower food to microorganism ratio may result in a lower N removal rate attributed to the sharply increased biomass concentration fed by glucose. Ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, denitrifying bacteria, and denitrifying phosphorus accumulation organisms enriched during AGS granulation also contributed to the efficient N removal. The proposed strategy provided insights into the relationship between various factors and stable AGS formation, and systemic operation methods for various complicated wastewater treatment.