Aerobic granular sludge for high-strength textile wastewater: Advancing sustainable solutions through enhanced pollutant removal

• Aerobic granular sludge was developed from real textile wastewater sludge, showing compact granules and active pollutant removal mechanisms. • Stable aerobic granules with diameters of 1–3 mm formed under high hydrodynamic shear and short settling times. • The system achieved more than 70% removal of color and organic pollutants from high-strength textile effluent. • Removal of suspended solids exceeded 95% with settling times below three minutes. • Granular sludge retained high treatment performance after 60 days of idle storage. This study investigates the application of aerobic granular sludge (AGS) for treating real textile wastewater (RTWW) from a knit dyeing industry. The RTWW exhibited high pollutant loads, with an average color of 3300 Pt-Co at 455 nm, COD of 1000 mg/L, and TSS of 120 mg/L. An AGS reactor was developed using activated sludge (MLSS: 4600 mg/L) and operated in a sequencing batch reactor (SBR) mode over 58 cycles. Flocculant sludge was converted to AGS under selection pressures, including hydrodynamic shear forces (2.4–3.6 cm/s) and short settling times (3–5 min). Mature granules (1–3 mm) were confirmed via scanning electron microscopy (SEM), showing distinct morphology compared to flocculant sludge. AGS performance was assessed during the granulation phase, reactivation after a two-month idle period, and during anaerobic–aerobic (An–Ae) SBR operation. The system achieved over 70% removal of both color and COD and over 95% removal of TSS, even after the idle period. Fourier-transform infrared spectroscopy (FTIR) indicated functional group changes associated with pollutant degradation, further supporting AGS's treatment capabilities. These results demonstrate that the AGS is a core biological unit within a train, reporting the incremental benefit and energy/footprint trade-offs for sustainable wastewater management in the textile industry.