Step-by-step Simulation of Gas-lift Anaerobic Digester of Municipal Wastewater Sludge

Document Type : Research Paper


1 Ph.D Student of Mechanization, Department of Biosystems Engineering, Faculty of Agricultural Department, University of Tabriz, Tabriz, East Azarbaijan, Iran.

2 Faculty Member of Department of Biosystems Engineering, Faculty of Agricultural Department, University of Tabriz, Tabriz, East Azarbaijan, Iran.

3 Faculty Member of Department of Mechanics of Biosystems Engineering, Faculty of Agricultural Engineering and Rural Department, Agricultural Sciences and Natural Resources University of Khuzestan, Iran.


The purpose of this study was to present a strategy for designing and simulating an anaerobic digester for the digestion of raw municipal sewage sludge, based on the flow patterns within the digester, and to investigate the sediment deposition conditions in this anaerobic digester. For this purpose, the simulations were performed based on a step-by-step strategy. First, the inlet gas velocity to the digester was determined, then in the next steps, the draft tube and the conical hanging baffle were added to the digester design, respectively, and simulations were performed with them and determined their characteristics. Simulations were performed for a pilot-scale cylindrical digester. A transparent cylindrical digester was built based on the computational fluid dynamics (CFD) simulations results. Sludge analysis was performed, and determine the sludge sedimentation velocity using the image processing process, so the sludge particle size and each percentage of them based on the total solids (TS) of sludge was performed. According to the results, only in a small area of the floor attached to the digester wall, the velocity of the fluid is less than the sedimentation velocity of the largest particles in the sludge (4.71 × 10-5 m / s) so there was a sedimentation possibility of a small amount of these particles in this area, which confirmed the success of digester design based on step-by-step simulation and flow patterns for mixing in a gas-lift anaerobic digester and showed a step-by-step simulation strategy is suitable and can be used to simulate gas-lift anaerobic digesters successfully.


Achkari- Begdouri, A. & Goodrich, P. R. (1992). Rheological properties of dairy cattle manure. Journal of Bioresource Technology, 40, 149-156.
ANSYS-Fluent Inc. (2008). Fluent 12.0. ANSYS-Fluent Inc, Lebanon, N.H.
Baudez, J. C., Markis, F., Eshtiaghi, N. & Slatter, P. (2011). The rheological behavior of anaerobic digested sludge. Journal of Water Researches, 45 (17), 5675-5680.
Bergamo, U., Viccione, G., Coppola, S., Landi, A., Meda, A. & Gualtieri, C. (2020). Analysis of anaerobic digester mixing: comparison of long shafted paddle mixing vs gas mixing. Water Science & Technology, 81 (7), 1406-1419.
Borole, A. P., Klasson, K. T., Ridenour, W., Holland, J., Karim, K. & Al-Dahhan, M. H. (2006). Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste. Journal of Applied Biochemistry and Biotechnology, 131 (1–3), 887–896.
Brade, C. E. & Noone, G. P. (1981). Anaerobic digestion- need it be expensive. Journal of Water Pollution Control, 80, 70–76.
Bridgeman, J. (2012). Computational fluid dynamics modelling of sewage sludge mixing in an anaerobic digester. Journal of Advances in Engineering Software, 44, 54-62.
Casey, T. J. (1986) Requirements and methods for mixing in anaerobic digesters. Anaerobic Digestion of Sewage Sludge and Organic Agricultural Wastes. Elsevier Applied Science Publishers. 90–103.
Celik, I. B., Ghia, U., Roache, P. J., Freitas, C. J., Coleman, H. & Raad, P. E. (2008). Procedure for estimation and reporting of uncertainty due to discretization in CFD applications. Journal of Fluids Engineering, 130, 078001.
Chen, J., Chen, A., Shaw, J., Yeh, Ch. & Chen, Sh. (2019). CFD Simulation of Two-Phase Flows in Anaerobic Digester. In: 3rd International Conference on Fluid Mechanics and Industrial Applications. Journal of Physics: Conference Series 1300 012048.
Dapelo, D., Alberini, F. & Bridgeman, J. (2015). Euler-Lagrange CFD modelling of unconfined gas mixing in anaerobic digestion. Journal of Water Researches, 85, 497–511.
Dutton, F. B. (1961). Dalton's law of partial pressures. Journal of Chemical Education, 38, A545.
Jegede, A. O., Gualtieri, C., Zeeman, G. & Bruning, H. (2020). Three phase simulation of the hydraulic characteristics of an optimized Chinese dome digester using COMSOL multiphysics. Renewable Energy.
Hoffmann, R. A., Garcia, ML., Veskivar, M., Karim, K., Al-Dahhan, MH. & Angenent, LT. (2008). Effect of shear on performance and microbial ecology of continuously stirred anaerobic digesters treating animal manure. Biotechnology Bioengineering, 100, 38–48.
Karim, Kh., Varma, R., Vesvikar, M. & Al-Dahhan, M. H. (2004). Flow pattern visualization of a simulated digester. Journal of Water Researches, 38, 3659–3670.
Karim, Kh., Klasson, k. T., Hoffmann, R., Drescher, S. R., DePaoli, D. W. & Al-Dahhan, M. H. (2005). Anaerobic digestion of animal waste: Effect of mixing. Journal of Bioresource Technology, 96, 1607–1612.
Karim, K., Thoma, G. J. & Al-Dahhan, M. H. (2007). Gas-lift digester configuration effects on mixing effectiveness. Water Researches, 41, 3051-3060.
Kojima, H., Saawai, J., Uchino, H. & Ichige, T. (1999). Liquid circulation and critical gas velocity in slurry bubble column with short size draft tube. Journal of Chemical Engineering Science, 54, 5181–5187.
 Kontandt, H. G. & Roediger, A. G. (1977). Engineering operation and economics of methane gas production. In: Schlegel, H.G., Barnea, J. (Eds.), Microbial Energy Conversion. Pergamon Press, Oxford. 379–392.
Lee, S. R., Cho, N. K. & Maeng, W. J. (1995). Using the pressure of biogas created during anaerobic digestion as the source of mixing power. Journal of Fermentation and Bioengineering, 80 (4), 415–417.
Lestinsky, P., Vayrynen, P., Vecer, M. & Wichterle, K. (2012). Hydrodynamics of airlift reactor with internal circulation loop: experiment vs. CFD simulation. Procedia Engineering, 42, 892-907.
Lin, C.C. & Chien, K.S. (2008). Mass-transfer performance of rotating packed beds equipped with blade packings in VOCs absorption into water. Journal of Separation and Purification Technology, 63, 138–144.
Mahmoodi-Eshkaftaki, M. & Ebrahimi, R. (2019). Assess a new strategy and develop a new mixer to improve anaerobic microbial activities and clean biogas production. Journal of Cleaner Production, 206, 797-807.
McFarland, M. J. (2001) Biosolids Engineering. New York: McGraw-Hill.
Merchuk, J. C. & Gluz, M. (1999) Bioreactors, Gas-lift Reactors. Encyclopedia of Bioprocess Technology: Fermentation, Biocatalysis, and Bioseparation. New York: John Wiley. pp. 320-353.
Meynell, P. J. (1976) Methane: Planning a Digester. London: Prism Press. 55–57.
Morgan, P. F. & Neuspiel, P. J. (1958) Environmental control of anaerobic digestion with gas diffusion. In: J. McCabe & W. W. Eckenfelder (Eds.), Biological Treatment for Sewage and Industrial Wastes (vol. 2). New York: Reinhold.
Pironti, F. F., Medina, V. R., Calvo, R. & Saeza, A. E. (1995). Effect of draft tube position on the hydrodynamics of a draft tube slurry bubble column. Chemical Engineering Journal, 60 (1–3), 155–160.
Reinhold, G. & Markl, H. (1997). Model-based scale-up and performance of the Biogas Tower Reactor for anaerobic waste-water treatment. Journal of Water Research, 31 (8), 2057–2065.
Sawyer, C. N. & Grumbling, A. M. (1960) Fundamental consideration in high-rate digestion. Inc. Sewage Engineering Division. ASCE, 86–92.
Suslov, D. Y.  & Temnikov, D.O. (2021). Define of effective process working combine mixing system. In: Innovations and Technologies in Construction (BUILDINTECH BIT 2021).  Journal of Physics: Conference Series 1926 012003.
Teitel, M., Ziskind, G., Liran, O., Dubovsky, V. & Letan, R. (2008). Effect of wind direction on greenhouse ventilation rate, airflow patterns and temperature distributions. Biosystems Engineering, 101, 351–369.
Terashima, M., Goel, R., Komatsu, K., Yasui, H., Takahashi, H. & Li, Y. Y. (2009). CFD simulation of mixing in anaerobic digesters. Bioresource Technology, 100, 2228–2233.
Vesvikar, M. S. & Al-Dahhan, M. (2016). Hydrodynamics investigation of laboratory-scale Internal Gas-lift loop anaerobic digester using non-invasive CAPRT technique. Biomass and Bioenergy, 84, 98-106.
‌Wu, B. & Chen, S. (2008). CFD simulation of non-Newtonian fluid flow in anaerobic digesters. Journal of Biotechnology Bioengineering, 99, 700-711.
Wu, B. (2010). CFD simulation of gas and non-Newtonian fluid two-phase flow in anaerobic digesters. Journal of Water Researches, 44, 3861-3874.
Wu, B. (2014). CFD simulation of gas mixing in anaerobic digesters. Journal of Computers and Electronics in Agriculture, 109, 278–286.
Yang, J., Yang, Y., Ji, X., Chen, Y., Guo, J., & Fang, F. (2015). Three-Dimensional Modeling of Hydrodynamics and Biokinetics in EGSB Reactor. Journal of Chemistry.
Zhang, R. H., Yin, Y., Sung, S. & Dague, R. R. (1997). Anaerobic treatment of swine waste by the anaerobic sequencing batch reactor. Transactions of the ASAE, 40, 761–767.