Long-term storage and subsequent reactivation of aerobic granules

This study investigated a seven month storage and the subsequent reactivation of aerobic granules. The granule size and structure integrity were remained during storage, whereas some cavities and pleats appeared on the surface and further deteriorated the settleability. Along with the reactivation, the physical characteristics and microbial activities of aerobic granules were gradually improved. Activities of heterotrophs and nitrifiers can be fully recovered within 16 days and 11 days, respectively. Nitrifiers decayed slower during storage and reinstated rapider during reactivation than heterotrophs. In fresh aerobic granules, the dominated ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were Nitrosomonas and Nitrospira, respectively. During storage, the initially dominated populations decayed rapider than the initially less dominated ones. Extracellular polymeric substances (EPS) significantly decreased within the first month, and then gradually accumulated during the last six months storage. Accumulation of EPS was an effective strategy for maintaining structural integrity of aerobic granules during long-term storage.