Effects of rising biogas bubbles on the hydrodynamic shear conditions around anaerobic granule

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 273; pp. 111 - 119
• Main Authors: Wu, Jing, Zhang, Jinbai, Poncin, Souhila, Li, Huai Z., Jiang, Jiankai, Rehman, Zohaib Ur
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2015; Elsevier
• Subjects: Anaerobic reactor; Biogas bubbles; Chemical and Process Engineering; Engineering Sciences; Environmental Engineering; Environmental Sciences; Granular sludge; Hydrodynamic conditions; PIV; Shear rate; Biogas bubbles; Hydrodynamic conditions; PIV; Granular sludge; Anaerobic reactor; Shear rate
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2015.03.057

[Display omitted] •In situ biogas production in a reactor was studied using a high-speed camera and PIV.•Shear rate exerted on granules in typical motions was studied at first time.•56.8–96.6% shear rate exerted on a granule stems from the generated biogas bubbles.•Shear rate exerted on granule linearly correlates with specific bubble population.•The study could facilitate understanding hydrodynamic conditions around sludge. Anaerobic reactor is one of gas–liquid–solid three-phase bio-reactors and has attracted high attentions worldwide due to biogas, a renewable energy. As is well-known, hydrodynamic conditions play crucial roles in the performance of the three-phase reactors. But the knowledge about the hydrodynamic conditions around sludge (microbial aggregates) is limited. The hydrodynamic shear force exerted on sludge derives from the liquid flow and rising biogas bubbles nearby. The in situ investigation in a two-dimensional micro anaerobic reactor shows that 56.8–96.6% shear rate exerted on one piece of granular sludge (major axis of 2mm and minor axis of 1.5mm) in typical motions stems from the rising bubbles when biogas production rate is greater than 0.1m3kgVSS−1d−1 and the superficial liquid velocity of reactor was fixed at 6.48mh−1 in this study. Furthermore it linearly correlates with specific bubble population with R2 of superior to 0.95. The specific bubble population plays more important roles in the shear rate on granules than the bubble diameter. Liquid flow is also important for the shear rate exerted on moving sludge in term of the relative velocity between sludge and liquid flow rather than the superficial liquid velocity. Thus the shear rate derived from liquid flow would be significantly lower than that part originated from bubbles. A high-speed digital camera and a particle image velocimetry (PIV) system were used to in situ quantify the bubbles and their behavior in reactor. This study could facilitate understanding and improving the hydrodynamic conditions in three-phase bio-reactors.