Rapid and stable transition of magnetite-assisted mycelial pellets to aerobic granular sludge under hypersaline environment

To accelerate aerobic granular sludge (AGS) startup in hypersaline wastewater, magnetite-assisted mycelial pellets (MMPs) cultivated by salt-tolerant fungus Cladosporium tenuissimum NCSL-XY8 were used as inoculum, and single aerobic mode and anaerobic/aerobic mode were respectively utilized to investigate the stability of transition/filling process and long-term operation process. The results showed that granules met AGS standards immediately (Day 0) and remained strict criteria (D 50 > 300 μm, SVI 30 /SVI 5 > 0.9, and SVI 30 < 50 mL/g) throughout 95 days cultivation under anaerobic/aerobic mode. Cross-sections with Prussian blue/Nuclear fast red staining and scanning electron microscopy (SEM) further confirmed hollow MMPs transitioned into dense AGS within 4 days, whereas aerobic mode generated unstable structures. Near-complete total organic carbon (TOC) removal (>97 %) in hypersaline wastewater was achieved within 10 days, 21 days faster than aerobic mode. The inoculated fungus played key roles in transition process, as well as the yeast ( Cutaneotrichosporon and Apiotrichum ) and bacteria ( Vibrio , Glutamicibacter , and Acinetobacter ). Overall, this study proposed a simple method to obtain the extremely rapid & stable development of salt-tolerant AGS with elevated operational stability by realizing MMPs-AGS transition/filling process. • A novel technology enabled rapid SAGS cultivation with high operational stability. • Prussian blue/Nuclear fast red method was used to stain magnetite and biomass. • MMPs stably filled/transitioned into solid AGS in 4 days. • Granules met size/settleability criteria throughout 95 days cultivation via A/O mode. • High TOC removal (>97 %) was achieved in hypersaline wastewater within 10 days.