There are few studies on the application of organic materials as carrier (nuclei) in aerobic granular sludge (AGS) system. Therefore, we evaluated the feasibility of sodium alginate (SA) as nuclei (SAN) to enhance the aerobic granulation process. Firstly, SAN at different dosages were mixed with activated sludge in lab-scale sequencing batch reactors and the system was in operation for 15 days. Batch experiments showed the addition of SAN was beneficial to accelerated aerobic granulation and enhanced biomass retention, while overdosing was unfavorable. The optimal dosage was determined to be 0.04-0.08 mg/ MLSS. In the optimal dosage SAN addition group (P2-R1), AGS with an average size of 1.9 mm was achieved successfully in P2-R1 after around 10 days, while there were no particles in the absence of SAN (P2-BK). It was further found that extracellular polymeric substances (EPS) in P2-R1 enhanced during granulation, especially extracellular protein (PN). On pollutant removal efficiency, P2-R1 presented notably higher removal rates of COD, ammonia nitrogen, total nitrogen, and total phosphorus than those of P2-BK without SAN.<br/>Through the SEM images of SAN and particles, we further summarize the potential granulation mechanism under this innovative rapid method. According to SEM images, a transparent and viscous gel-forming film was observed on the surface of the granular, which may be due to EPS production by SAN at the first. In addition, plenty of cocci, bacilli, and filamentous cells were attached to the surface and interior of SAN. During granulation, filamentous bacteria can serve as skeletons to bridge and trap free cells. However, when filamentous bacteria predominated in granules, excessive filaments might lead to the disruption of structural integrity. Accordingly, some filaments were observed on the surface of mature granules at the aging phase, which constantly cracked into fragments.

Adding aodium alginate as a nucleus can shorten granulation of aerobic sludge

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