Reactivation performance of aerobic granules under different storage strategies

Aerobic granules storage process is complicated and the affective mechanism is not very clear, which is influenced by storage temperature, storage substrate and storage time. The effects of storage temperature (-25 °C, 4 °C and room temperature) and storage substrate (distilled water and 400 mg/L glucose solution) on long-term storage and subsequently reactivation performance of aerobic granules were investigated in this study. The results showed that storage temperature had huge impact on the morphology and physical properties and storage substrate had relatively small influence on granules. Granules reactivation was a re-stability process of granules structure, physical properties and microbial communities. Storage at 4 °C was more suitable for maintenance of structural integrity and granules long-term stability storage. Granules stored at -25 °C achieved excellent settling ability after reactivation and PN/PS ratio was basically unchanged, which demonstrated that storage at -25°Cwas more suitable for the maintenance of the internal microstructure. Aerobic granules under different storage conditions could be reactivated after 10 days operation and the microbial activity (SOUR) could be fully restored. Furthermore granules stored at 4 °C obtained the best recovery performance, and granules at room temperature presented the worst restoration performance. In conclusion, no matter what the storage temperature or the storage substrate is, aerobic granules after long-term storage (8 months) could be restored within 10 days and stored granules could be successfully used as bioseed for reactor fast startup.