An aeration energy model for an immersed membrane bioreactor B. Verrecht a , S. Judd a, *, G. Guglielmi b , C. Brepols c , J.W. Mulder d a School of Water Sciences, Cranfield University, SIMS, Building 39, Cranfield, Bedfordshire MK43 0AL, UK b Trento University, Trento, Italy c Erftverband, Germany d Water Authority of Hollandse Delta, The Netherlands article info Article history: Received 14 May 2008 Received in revised form 1 September 2008 Accepted 6 September 2008 Published online 1 October 2008 Keywords: Immersed membrane bioreactor Aeration energy Aeration intensity Flat sheet Hollow fibre Empirical model abstract A simple model for evaluating energy demand arising from aeration of an MBR is pre- sented based on a combination of empirical data for the membrane aeration and bio- kinetic modelling for the biological aeration. The model assumes that aeration of the membrane provides a proportion of the dissolved oxygen demanded for the biotreatment. The model also assumes, based on literature information sources, a linear relationship between membrane permeability and membrane aeration up to a threshold value, beyond which permeability is unchanged with membrane aeration. The model was benchmarked against two full-scale plant to obtain the most appropriate and conserva- tive value of the slope of the flux:aeration curve and the blower efficiency. Benchmarking in this way produced a match to within 20% of all key process plant operational parameters. The model demonstrated that significant reductions in aeration energy could be obtained through operation at lower flux and reducing the membrane aeration requirement accordingly, so-called ‘‘proportional aeration’’ at lower flows. Similarly, increasing oxygen transfer from membrane aeration would also be expected to decrease energy demand. A sensitivity analysis of some of the key parameters revealed that, of the key operating parameters, loading, SOTE and MLSS concentration remain the most critical in determining energy demand. It is suggested that a key parameter representing membrane aeration in MBRs is the mean in-module air upflow velocity U, since this gives a reasonable representation of the shear applied through membrane aeration. U was found to vary between 0.04 and 0.1 m/s across a number of modern large pilot and full- scale plant. An analysis reveals that significant reductions in energy demand are attained through operating at lower MLSS levels and membrane fluxes. Evidence provided from recent controlled pilot trials implies that halving the flux can reduce the aeration is suggested whereby the number of membrane tanks on line and/or the membrane aeration intensity is adjusted according to the flow, and thus flux, so as to reduce the overall aeration energy demand. Crown Copyright ª 2008 Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: þ44 1234 754 842. E-mail address: s.j.judd@cranfield.ac.uk (S. Judd). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter Crown Copyright ª 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2008.09.013 water research 42 (2008) 4761–4770