Ten-Thousand-Ton Scale Engineering Practice of Retrofitting a UASB Reactor into an Aerobic Granular Sludge Process

• • Rapid start-up: AGS system reached 75% of design capacity (20,000 m3/d) by day 10 and 90% by day 26, with a maximum hydraulic load of 25,001 m3/d, demonstrating operational resilience and reduced commissioning time. • • Enhanced granulation: Sludge average particle size increased to 2.6 times the inoculum by day 44 and 3.2 times by day 110, with granules (>200 μm) comprising 17.3% and 33.4% of the sludge, respectively, indicating robust granule formation. • • High pollutant removal: Average removal efficiencies of 83.2% for COD, 97.0% for NH4+-N, 75.9% for TN, and 94.4% for SS were achieved over 4 months, even under low BOD5/TN ratios (<4), highlighting effective nitrogen removal. • • Cost and footprint reduction: Compared to conventional A/O process, AGS reduced electricity consumption by 77.3%, chemical usage by 25.4%, sludge production by 30.4%, and footprint by 65.6%, offering significant economic and land-saving benefits.