1. Numerical modelling of non-Newtonianfluid in a rotational cross-flow MBRT. R. Bentzen1, N. Ratkovich1, S. Madsen2, J. C.Jensen2, S. N. Bak2 & M.R. Rasmussen1 1Department of Civil Engineering, Aalborg University Denmark2Grundfos BioBooster Denmark6th IWA Specialist Conference on Membrane Technology for Water & Wastewater Treatment October 5, 2011, Aachen - Germany No. 1 of 17

2. OutlineIntroduction & Objectives Fouling Rotational Cross-Flow MBRBackground Non-Newtonian behavior (viscosity) Wall shear stress in rotating systemsMethodology Experimental measurements & CFD modelResults & discussion Wall shear stressConclusionsNo. 2 of 17 3. IntroductionMembrane fouling Fouling is the main bottleneck of the widespread of MBR systems. Decrease permeate flux Increase trans-membrane pressureControl/reduction of fouling Process hydrodynamics can decrease and/or control fouling by increasing liquid cross-flow velocity. Increase permeate flux Surface shear stress scouring effect Increase mass transfer (cake layer bulk region) No. 3 of 17 4. Rotational cross-flow (RCF) MBR (GrundfosBioBooster) It operates between 20 40 lmh pressurize system (~5 bar) up to 5 times higher sludge concentration than in conventional MBR systems (TSS up to 50 g l-1). Rotating impellers betweenfiltrationmembranediscsprevent fouling. Impellers ensures low viscosityin the reactor biomass due tothe non-Newtonian behaviourof activated sludge (AS). energy consumption andflux. No. 4 of 17 5. Background (I) No. 5 of 17 6. Background (II)No. 6 of 17 7. Methodology (I)Tangential velocity measurements RCF MBR operates between 50 to 350 rpm Experimental tangential velocity measured at 59, 119 and 177 rpmwith water Measured with Laser Doppler Anemometry (LDA) LDA is an optical technique to measure velocity field in transparentmedia and cannot be used with activated sludge. No. 7 of 17 8. Methodology (II)CFD modelStar CCM+ v6.04Single phaseRigid body motionTurbulent model k- SST (water) - validation Laminar (AS)Enhanced wall treatment (y+ < 1)No. 8 of 17 9. Results (I)Reynolds number for waterReynolds number for ASNo. 9 of 17 10. Results (II)Tangential velocity measurements for water A good agreement between the experimental measurements and theCFD simulation results, with an error up to 8 %. No. 10 of 17 11. Results (III)Shear stress (for water) 50 rpm150 rpm250 rpm350 rpm No. 11 of 17 12. Results (IV)Disk type kShear stress for water Infinite smooth0.313 disks Shear stress at the membraneSmooth disks0.450 Theoretical solution: Disk with vanes 0.650 0.840 k: velocity coefficient which depends on disk geometry (vanes)Grundfos (140.795 vanes) 2000 rpm *Torras et al, 2009 No. 12 of 17 13. Results (V)Area-weighted average shear stress at the membrane No. 13 of 17 14. Results (VI) 250 rpmShear stress for AS 30 g/l 40 g/l 50 g/lNo. 14 of 17 15. Results (VII)250 rpmNo. 15 of 17 16. Results (VIII) Area-weighted average shear stress(Pa)AS AS AS Water (rpm) (30 g l-1) (40 g l-1) (50 g l-1)50 1.8 13.5 22.6 34.3 150 8.2 19.9 29.0 40.7 25013.8 25.5 34.6 46.3 35019.2 30.9 40.0 51.7 No. 16 of 17 17. Conclusions A proper validation of the CFD model was made in terms oftangential velocity measurements using a LDA system with water. RCF MBR operates with AS and LDA measurements cannot bemade. CFD model was modified to account for the viscosity of AS. Local shear stress at any place of the membrane surface and area-weighted average shear stress was determined. An empirical relationship was made, to determine the area-weighted average shear stress in function of the angular velocity (inrpm) and the TSS. No. 17 of 17 18. Thank you for your attention No. 18 of 17 19. Consultancy services on CFD for MBR CFD has become a frontline tool for virtual simulations (conceptual design& performance prediction) CFD not only gives qualitative data very exact quantitative predictions. CFD tools and techniques are extensively validated with experimental andanalytical results allowing more robust models for R&D. Software expertise: CAD: Rhino Meshing: GAMBIT, ICEM, Star CCM+ Solver:Star CCM+, CFX, Fluent Domain expertise CAD repair for meshing Moving mesh Turbulence modelling Multiphase modellingNo. 19 of 17