Comparison of the Performance of Internal and External Loop Air-lift Reactors for Water Treatment by Activated Sludge

Subject Areas : Environment Pullotion (water and wastewater)

Mohammad Ali Salehi ¹ , Nasrin Hakimghiasi ²

1 - استادیار مهندسی شیمی، گروه مهندسی شیمی، دانشکده فنی مهندسی، دانشگاه گیلان، رشت، ایران *(مسوول مکاتبات)
2 - MSc of chemical engineering/ Guilan University

Received: 2016-12-03 Accepted : 2017-10-25 Published : 2019-11-22

Keywords: superficial gas velocity, Gas holdup, Airlift reactor, Mass Transfer,

Abstract :

Background and Objective: In This study the impacts of operating conditions such as aeration rate, the downcomer-to-riser cross-sectional area ratio (Ad/Ar), and liquid phase properties on the hydrodynamics and volumetric mass transfer coefficient in three-phase airlift reactors was investigated. Method: Experiments were conducted in external loop air-lift reactor with downcomer to riser cross-sectional area ratio (AD/AR=0.14) and internal air-lift reactors with downcomer to riser cross-sectional area ratios 0.36 and 1. Air and Water were used as gas and liquid phases, respectively and activated sludge is used as the solid phase. Findings: The liquid circulation velocity, gas holdup and mass transfer coefficient increased with an increase in the superficial gas velocity, decrease the sludge concentration and decrease downcomer to riser cross-sectional area ratio. The maximum amount of gas hold up, 0.178 in external air-lift reactor with 1%(w/w) activated sludge in superficial gas velocity 0.24(m/s) was observed. A model to predict the effect of activated sludge concentration, the superficial gas velocity and the downcomer-to-riser cross-sectional area ratio on the mass transfer activated sludge airlift reactors provided which with the experimental results are in good agreement. Discussion and Conclusion: The evaluation of internal and external reactors performance at different concentration and superficial gas velocity show that the air-lift reactor with external loop has better performance in comparison with internal airlift reactors.

References:

1. Chisti, M., & Moo-Young, M., 1987, Airlift reactors: characteristics, applications and design considerations. Chemical Engineering Communication,. 60: p. 195-242.


2. Bentifraouine, C., Xuereb, C., and Riba, J. P., 1997, An experimental study of the hydrodynamic characteristics of external loop airlift contactors. Journal of Chemical Technology and Biotechnology, 69: p. 345-349.


3. Malfait, J., Wilcox, D., Mercer, D., and Barker, L., 1981, Cultivation of a filamentous mold in a glass pilot‐scale airlift fermentor. Biotechnology and Bioengineering, 23: p. 863-877.


4. Schlüter, S., Steiff, A., and Weinspach, P.M., 1995, Heat transfer in two-and three-phase bubble column reactors with internals. Chemical Engineering and Processing: Process Intensification, 34: p. 157-172.


5. Merchuk, J. C., and Gluz, M., 1996, Airlift Reactors, in the encyclopedia of bioprocess technology, 38-54.


6. Jin, J. V. L. B., Doelle, H., and Yu., Q., 1999, The influence of geometry on hydrodynamic and mass transfer characteristics in an external airlift reactor for the cultivation of filamentous fungi. World Journal of Microbiology and Biotechnology, 15(1): p. 73–79.


7. Nikakhtari, H., and Hill, G. A., 2005, Hydrodynamic and oxygen mass transfer in an external loop airlift bioreactor with a packed bed. Biochemical Engineering Journal, 27: p. 138-145.


8. Yang, F., Bick, A., Shandalov, S., Brenner, A., and Oron, G., 2009, Yield stress and rheological characteristics of activated sludge in an airlift membrane bioreactor. Journal of Membrane Science, 334: p. 83-90. Persian


9. Al Taweel, A., Idhbeaa, A., and Ghanem, A., 2013, Effect of electrolytes on interphase mass transfer in microbubble-sparged airlift reactors. Chemical Engineering Science, 100: p. 474-485.


10. Jin, B., Yin, P., and Lant, P., 2006, Hydrodynamics and mass transfer coefficient in three-phase air-lift reactors containing activated sludge. Chemical Engineering and Processing: Process Intensification, 45: p. 608-617.


11. Kilonzo, P. M., Margaritis, A., Bergougnou, M., Yu, J., and Ye, Q., 2007, Effects of geometrical design on hydrodynamic and mass transfer characteristics of a rectangular-column airlift bioreactor. Biochemical Engineering Journal, 34: p. 279-288.


12. Krichnavaruk, S., and Pavasant, P., 2002, Analysis of gas–liquid mass transfer in an airlift contactor with perforated plates. Chemical Engineering Journal, 89: p. 203-211.


13. Lu, W. J., Hwang, S. J., and Chang, C. M., 1995, Liquid velocity and gas holdup in three-phase internal loop airlift reactors with low-density particles. Chemical Engineering Science, 50: p. 1301-1310.


14. Benyahia, F., and Jones, L., 1997, Scale effects on hydrodynamic and mass transfer characteristics of external loop airlift reactors. Journal Chemical Technology and Biotechnology, 69: p. 301-308.


15. Pittoors, E., Guo, Y., and Van Hulle, S. W., 2014, Oxygen transfer model development based on activatedsludge and clean water in diffused aerated cylindrical tanks. Journal of Chemical Engineering, 243: p. 51-59.


16. Yang, F., Bick, A., Shandalov, S., Brenner, A., and Oron, G., 2009, Yield stress and rheological characteristics of activated sludge in an airlift membrane bioreactor. Journal of Membrane Science, 334: p. 83-90.


17. Petersen, E. E., and Margaritis, A., 2001, Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems. Critical Reviews in Biotechnology, 21: p. 233-294.


18. Siegel, M. H. H., Herskowitz, M., and Merchuk, M., 1989, Hydrodynamics and mass transfer in a three-phase air lift reactor. Advances in Biotechnology Process. p. 337-351.