TY - JOUR
T1 - Yield stress and rheological characteristics of activated sludge in an airlift membrane bioreactor
AU - Yang, Fei
AU - Bick, Amos
AU - Shandalov, Semion
AU - Brenner, Asher
AU - Oron, Gideon
N1 - Funding Information:
The work was supported by The Beracha Foundation, The Stephen and Nancy Grand Water Research Institute, The Technion, Haifa Israel, The Palestinian–Jordanian–Israeli Project (PJIP) (1996), on Membrane Technology for Secondary Effluent Polishing: From Raw Sewage to Valuable Waters and Other By-Products, The Levin Family Foundation, Dayton, Ohio, USA, on Membrane Use for Wastewater Reclamation, and by Research Authority of Jerusalem College of Technology (JCT), Israel. The work was also partially supported by The IWRM (Integrated Water Resource Management)-SMART (Sustainable Management of Available Water Resources with Innovative Technologies) project on development, modeling and providing tools for optimal water use in arid regions, which is supported by The Federal Ministry of Education and Re-search, Germany and The Ministry of Science and Technology (MOST) of the State of Israel. The authors thank Dr. Mark Karpasas from the National Institute for Biotechnology Negev (NIBV), Ben-Gurion University of the Negev for his assistance in the rheological tests. The authors are indebted to the anonymous referees for their contributive comments.
PY - 2009/5/15
Y1 - 2009/5/15
N2 - The viscosity of activated sludge plays a major role on oxygen transfer and mass transport and consequently influences the hydrodynamic regime and the system performance of a membrane bioreactor (MBR). Yield stress is an important concept in rheology related to the mixing and power requirements in a stirred tank. This study examined the rheological characteristics of activated sludge sampled in a pilot airlift MBR system for domestic wastewater treatment under ambient desert conditions, using a rotational rheometer (AR 2000, TA Instruments, USA) equipped with cone-plate geometry. Both static and dynamic yield stresses were observed at the transition point of 25 s-1 of shear rate for an MLSS concentration range of 2.74-10.2 g/L. The static yield stress is a phenomenon that has not yet been evaluated for activated sludge. The mechanisms of the co-existence of both static and dynamic yield stresses and their engineering significance are discussed. In addition, a mathematical model to describe the rheological properties of the sludge is proposed. The relationships between viscosity, MLSS, temperature and shear rate were obtained statistically. The activation energy for the viscosity of the sludge in the airlift sMBR was found to be 9.217 kJ mol-1, and could be the cause of rapid fluctuation of transmembrane pressure with temperature variations.
AB - The viscosity of activated sludge plays a major role on oxygen transfer and mass transport and consequently influences the hydrodynamic regime and the system performance of a membrane bioreactor (MBR). Yield stress is an important concept in rheology related to the mixing and power requirements in a stirred tank. This study examined the rheological characteristics of activated sludge sampled in a pilot airlift MBR system for domestic wastewater treatment under ambient desert conditions, using a rotational rheometer (AR 2000, TA Instruments, USA) equipped with cone-plate geometry. Both static and dynamic yield stresses were observed at the transition point of 25 s-1 of shear rate for an MLSS concentration range of 2.74-10.2 g/L. The static yield stress is a phenomenon that has not yet been evaluated for activated sludge. The mechanisms of the co-existence of both static and dynamic yield stresses and their engineering significance are discussed. In addition, a mathematical model to describe the rheological properties of the sludge is proposed. The relationships between viscosity, MLSS, temperature and shear rate were obtained statistically. The activation energy for the viscosity of the sludge in the airlift sMBR was found to be 9.217 kJ mol-1, and could be the cause of rapid fluctuation of transmembrane pressure with temperature variations.
KW - Activation energy
KW - Airlift membrane bioreactor
KW - Rheology
KW - Static and dynamic yield stress
UR - http://www.scopus.com/inward/record.url?scp=64049089011&partnerID=8YFLogxK
U2 - 10.1016/j.memsci.2009.02.022
DO - 10.1016/j.memsci.2009.02.022
M3 - Article
AN - SCOPUS:64049089011
SN - 0376-7388
VL - 334
SP - 83
EP - 90
JO - Journal of Membrane Science
JF - Journal of Membrane Science
IS - 1-2
ER -
