A carrier-assisted strategy for accelerating aerobic granulation under low superficial gas velocity: Critical contributions of sediment biochar and camellia shell biochar carriers.

Long granulation time and instability limited the practical application of aerobic granular sludge (AGS) technology. This study presents a strategy for enhancing AGS formation by adding granular biochar carriers (camellia shell biochar and dredged sediment biochar) in two low-energy sequencing batch reactors (SBRs). Three SBRs were established, labeled R1 (no carriers added), R2 (dredged sediment biochar), R3 (camellia shell biochar added). The results indicated that the maturation period were reduced by 35 days in R3 and 14 days with R2 compared to the control (R1). Moreover, R3 exhibited better performance, with a 1.5-fold larger mature particle size (565 μm) and higher extracellular polymeric substances (EPS) content. The accumulation of polysaccharide-dominated EPS which were mainly composed of humic-like substances in carriers-amended reactors played a vital role in stabilizing particles. Under low superficial gas velocity (SGV,0.64 cm/s), the hierarchical porosity and rough surface of both biochar carriers facilitated microbial adhesion while maintaining stable treatment efficiency. Microbial community analysis indicated enhanced diversity and evenness in carriers-added reactors, with Proteobacteria becoming the dominant phylum (80.22 % in R3). Notably, high specific surface area and nutrient-rich composition of camellia shell biochar fostered a syntrophic environment for denitrifies and EPS-producing bacteria, while the inorganic components of sediment biochar improved granule density in short term. This work highlights the roles of two waste-derived biochar carriers as the structural nucleus and metabolic regulator, offering a cost-effective solution for rapid AGS cultivation in energy-efficient reactors.