Explain the mechanisms and applications of aerobic granular sludge technology.

Aerobic granular sludge (AGS) represents a paradigm shift in biological wastewater treatment. Granule formation: Self-immobilization of bacteria into dense, spherical aggregates (0.5-3 mm) through selection pressure. Sequential batch reactor (SBR) operation with short settling time selects for fast-settling granules over flocs. Feast-famine regime and slow-growing organisms (PAO, nitrifiers) in anaerobic/aerobic phases promote EPS production and granule stability. Structure and function: Outer aerobic layer - nitrification, aerobic COD removal. Anoxic core - denitrification using nitrate from outer layer. Anaerobic periods - phosphate release, VFA storage. Simultaneous N and P removal in single reactor without recycles. Benefits: 75% smaller footprint; excellent settling (SVI <50 mL/g); energy reduction; reduced sludge production. Applications: Nereda technology commercialized by Royal HaskoningDHV; 80+ full-scale plants; municipal and industrial wastewater. Design considerations: start-up period (3-6 months), shear forces, substrate composition, selective pressures. Extension to continuous flow systems under development.