Recovery of aerobic granular sludge in a sequencing batch reactor by inoculating stored granules with different storage methods

The recovery of aerobic granular sludge (AGS) with different storage time and storage methods was investigated. After storage, the AGS showed different morphological characteristics: AGS stored at wet room temperature for two years was loose and disintegrated; AGS stored at wet room temperature for one year showed no obvious disintegration, but the anaerobic core was clearly observed; the color, morphology and sedimentation performance of the nitrifying granular sludge stored in agar for five months did not change a lot. After re-aeration, MLSS (4.85~10.51 g/L), MLVSS/MLSS (0.6~0.75), EPS (15.05~38.36 mg/g MLSS), average particle size (0.61~1.12 mm) and granulation rate (80.92%~97.60%) increased rapidly, and the removal rates of COD and ammonia nitrogen also increased to more than 90% in 19 days and 15 days, respectively. During the recovery process, granular sludge experienced a process of firstly breakage and then re-granulation. According to physicochemical characteristics of AGS during the recovery process, the mixed granules were successfully recovered within 21 days. Inoculating part of stored nitrifying granular sludge effectively increased the enrichment rate of nitrifying bacteria, which provided a new idea for the rapid enrichment of nitrifying bacteria in AGS in application.