The rapid start-up of AGS by inoculating seed granular sludge in treatment of industrial park wastewater: performance evaluation and structural characterization†

Abstract

Seed granular sludge (SGS) inoculation serves as an effective strategy for accelerating the start-up efficiency of aerobic granular sludge (AGS); however, its performance in treating practical wastewater deserves further investigation. Herein, this study established a cost-effective technological pathway for preparing SGS from dewatered sludge and applied it in treatment of wastewater from industrial parks. The preparation cost of SGS was preliminarily estimated to be 194.66 CNY per ton and the validation results demonstrated that SGS inoculation successfully skipped over the granulation stage and was maintained for 80 days operation. The sludge volume index (SVI₃₀) of matured AGS reached 28.36 ± 6.6 mL g⁻¹, with average removal efficiencies of 94.86 ± 2.53% for chemical oxygen demand (COD), 97.58 ± 3.99% for NH₄⁺-N, 51.16 ± 10.88% for total nitrogen (TN), and 71.24 ± 16.85% for total phosphorus (TP). In terms of the particle structure, the Fe proportion in inoculated AGS is 12.0-fold higher compared to naturally formed AGS, confirming that Fe and its complexes construct the granular skeletal framework. Furthermore, metagenomic analysis revealed significant enrichment of nitrogen-metabolizing microbial consortia (Myxococcota, Actinobacteriota, and Nitrospirota) in inoculation systems, along with marked upregulation of denitrification functional genes including nirK, nar, nap, and norBC. The results of this study can provide a reference for SGS production and application in treatment of practical wastewater with complex components.