A Novel Continuous-Flow Self-Circulating Upflow Granular Sludge Bed Process for Treating Real Domestic Wastewater
Aerobic granular sludge (AGS) is an economical and efficient technology, yet its application has been largely confined to sequencing batch reactors (SBRs). This study introduces a novel continuous-flow self-circulating upflow granular sludge bed (Zier) process with separate aeration for treating real domestic wastewater. By regulating operational parameters, the nitrogen removal performance and granular sludge stability were investigated. Under hydraulic retention time of 10 h, self-circulation times of 29–58, and upflow velocity of 11–18 m·h−1, effluent NH4+-N and TN averaged (5±3.4) mg·L−1 and (10±2.8) mg·L−1, respectively, with COD at (30±6.2) mg·L−1. The process maintained sludge stability: mixed liquor suspended solids increased from 5,080 to 6,650 mg·L−1, mean particle size was 209.6 μm, and sludge volume index (SVI) remained at 50–60 mL·g−1. Extracellular polymeric substances (EPS) increased from 26.05 to 68.27 mg·g−1, with proteins (PN) rising from 21.26 to 59.44 mg·g−1 and polysaccharides (PS) from 4.79 to 8.82 mg·g−1, elevating the PN/PS ratio from 4.4 to 6.7. These results confirm that the Zier process preserves granular structure and function in continuous flow. The process demonstrates robust nitrogen removal and offers a novel approach for continuous-flow AGS applications in real wastewater treatment.