Storage and reactivation of aerobic granular sludge: A review

Aerobic Granular Sludge (AGS) is a biological wastewater treatment process. This technology offers both low land use and cost efficiency. However, the long start-up time is one of the main problems the AGS is facing; to overcome this challenge, several methods have been proposed. Storing and then reactivating AGS is one of the methods proposed. It considerably reduces the start-up time due to skipping most of the granulation procedures. This method collects mature AGS from a running AGS bioreactor, stores it in different forms and environments (depending on the techniques used), and then reactivate the stored AGS when needed. This review summarizes the previously-proposed granules storage techniques such as soaking in different mediums, freezing, and drying. Additionally, the storing techniques are analysed discussing their advantages and disadvantages. The review result indicated that the AGS storage and reactivation method is successful in shortening the lengthy start-up period of the AGS technology. Moreover, storing AGS in dried form using a combination of air drying and dehydration solutions showed a high potential for recovering the removal performance after reactivation. The stored-then-reactivated AGS not only shortens the lengthy start-up period, but it may also lead to an AGS stocking business with further investigation.