Attachment performance between micro particles and different sized aerobic granular sludge: from outside to inside

The aerobic granular sludge (AGS) is an emerging technology widely spread, since most organic matters in actual domestic sewage were particulate matters, this study aims to determine whether the attachment between micro particles and different sized AGS was influenced by granule surface area. The attachment of micro particles by different sized AGS (2.0–5.0 mm) were investigated. Furthermore, to simulate the attachment by broken fragments of AGS, complete 4.0–5.0 mm AGS were cut into 2,4, and 8 pieces, and the attachment performance between the broken pieces and similar sized complete AGS were compared. Fourier transform infrared (FTIR) and fluorescence staining were applied to analyze the chemical bonds and amyloid-glucan like structure of AGS from outside to inside. The results showed the 3.1–4.0 mm AGS had the best surface area attachment of micro particles, followed by the 2.5–3.1 mm AGS. The attachment performance of micro particles was not determined by specific surface area, but was closely related to the surface roughness caused by the amyloid-glucan like structure. The distribution density of amyloid-glucan like structure decreased from outside to inside, and if an granule was broken into pieces during aeration, micro particles were preferential to be attached by the outer layer of the broken pieces from the initial granule. The micro particles attachment showed little relationship with the hydrophilicity of AGS surface, either the outer layer or the inner layer. This study highlighted the crucial role of AGS outer layer in micro particle attachment, particularly the broken pieces from the original AGS outer layer, which facilitate to attach micro particles and contribute to form new granules.