Investigating the effect of changing the decay coefficient in an activated sludge model


  • S. S. Alsaeed
  • M. I. Nelson
  • M. Edwards
  • A. H. Msmali



The activated sludge process (ASP) is widely used to treat both domestic and industrial wastewaters. The main disadvantage of the ASP is the expense of disposing of excess sludge, which can account for between fifty to sixty percent of the operating costs of a treatment plant. We examine a model for the ASP in which the biochemical processes are represented by a simplified version of the well known activated sludge model No. 1. A promising method to decrease sludge production is to increase sludge biodegradability. A variety of experimental methods exist to do this, such as enzyme treatment, ozonation, heat treatment, and ultrasound. We investigate the effect of increasing the decay coefficient upon two important process variables: the chemical oxygen demand and the total suspended solids.


  • R. T. Alqahtani, M. I. Nelson, and A. L. Worthy. Sludge disintegration. Appl. Math. Model. 40.17–18 (2016), pp. 7830–7843. doi: 10.1016/j.apm.2016.03.040
  • A. E. Billing and P. L. Dold. Modelling techniques for biological reaction systems; 2. Modelling of the steady state case. Water SA 14.4 (1988), pp. 193–206.
  • European Council. Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment. Official J. E.U. L135 (1991), pp. 40–52.
  • X. Hao, Q. Wang, Y. Cao, and M. C. M. van Loosdrecht. Evaluating sludge minimization caused by predation and viral infection based on the extended activated sludge model No. 2d. Water Res. 45.16 (2011), pp. 5130–5140. doi: 10.1016/j.watres.2011.07.013
  • M. Henze, C. P. L. Grady Jr, W. Gujer, G. V. R. Marais, and T. Matsuo. A general model for single-sludge wastewater treatment systems. Water Res. 21.5 (1987), pp. 505–515. doi: 10.1016/0043-1354(87)90058-3
  • S. G. Lu, T. Imai, M. Ukita, M. Sekine, T. Higuchi, and M. Fukagawa. A model for membrane bioreactor process based on the concept of formation and degradation of soluble microbial products. Water Res. 35.8 (2001), pp. 2038–2048. doi: 10.1016/S0043-1354(00)00461-9
  • M. I. Nelson, E. Balakrishnan, H. S. Sidhu, and X. D. Chen. A fundamental analysis of continuous flow bioreactor models and membrane reactor models to process industrial wastewaters. Chem. Eng. J. 140.1-3 (2008), pp. 521–528. doi: 10.1016/j.cej.2007.11.035
  • M. I. Nelson, H. S. Sidhu, S. Watt, and F. I. Hai. Performance analysis of the activated sludge model (number 1). Food Bioprod. Process. 116 (2019), pp. 41–53. doi: 10.1016/j.fbp.2019.03.014
  • Y. Wei, R. T. Van Houten, A. R. Borger, D. H. Eikelboom, and Y. Fan. Minimization of excess sludge production for biological wastewater treatment. Water Res. 37.18 (2003), pp. 4453–4467. doi: 10.1016/S0043-1354(03)00441-X
  • S.-H. Yoon and S. Lee. Critical operational parameters for zero sludge production in biological wastewater treatment processes combined with sludge disintegration. Water Res. 39 (2005), pp. 3738–3754. doi: 10.1016/j.watres.2005.06.015





Proceedings Engineering Mathematics and Applications Conference