Attachment and adhesion force between biogas bubbles and anaerobic granular sludge in the up-flow anaerobic sludge...

The performance of the up-flow anaerobic sludge blanket (UASB) is significantly governed by the hydrodynamics of the reactor. Though the influence of hydrodynamics on mass transfer, granular size distribution, and biogas production was well studied, the interaction between biogas bubbles and anaerobic granular sludge (AGS) is poorly understood. This study used the impinging-jet technique and bubble probe atomic force microscope (AFM) to investigate the attachment and adhesion force between biogas bubbles (CH₄ and CO₂) and AGS. The fluxes of normalized CH₄ or CO₂ bubble-attachment on two kinds of AGS were directly affected by gas velocity and decreased with an increase in the Reynolds number ranged from 40 to 140. The bubble-attachment had a positive linear relationship with the contact angles, ratio of exopolymeric protein and polysaccharide, and hydrophilic functional groups of AGS. A bubble probe AFM was used to explore the adhesion force between a single bubble and AGS. The results indicated that the adhesion force between the bubbles and the two kinds of AGS also decreased with increasing approach velocity. Overall, these results contribute to a new insight into the understanding of interaction between biogas bubbles and AGS in UASB reactors.