Monitoring Rheology as a Tool for Measuring the Effective Shear - PowerPoint PPT Presentation

“ Monitoring Rheology as a Tool for Measuring the Effective Shear Rate in the Bubble Columns .” Presenter: Veena Bobade V.Bobade 1 , J.C. Baudez 2 , Geoffrey Evans 3 , N. Eshtiaghi 1 1 ‐ RMIT University, Australia 2 LIST, Luxemburg. 3 The University of Newcastle, Australia.

Industrial Importance and Applications of Aeration Industrial Applications Importance of Aeration Aerated Chocolate Increases the taste and Mouth feel Aerated Food Provides new texture, reduces caloric density and increases satiety. Aerated Gels Aeration decreases the hardness and increases the structural strength of gels. Aerated Pharmaceutical Aeration makes its lighter and increases the foam & Cosmetic products texture and improves the quality of product. Aerated Sludge Improves mixing in the reactor and increases the efficiency of the process ( 75% of the energy is consumed by the Aeration) 2

Common Problems encounter in Gas Mixing in Non-Newtonian fluids • Maintain homogeneous condition • Reduction in oxygen transfer efficiency • Increased cost of treatment 3

Objective • To predict the effective shear rate within the bubble column. • To understand the relationship between changes in physicochemical properties of municipal waste activated sludge and with the stress induced by gas injection. 4

Impact of gas injection on viscosity of 3% WAS sludge 10000 Gas injection and time of injection has no without gas impact on viscosity 1000 with 3 LPM @20 mins Viscosity, (Pa.s) 100 with 3 LPM @40 mins 10 1 0,1 0,0001 0,001 0,01 0,1 1 10 100 shear rate, (1/s) 5

Impact of gas injection on solid like behaviour of 4.2%WAS at 2 gas flow rate Time sweep Creep test 10 Gas injection Gas injection impacts Storage Modulus G‘ and Loss Modulus G" , (Pa) decreases the on sludge floc elasticity of the structure sludge . 1 100 Strain, (%) 0,1 G' at no gas injection G" at no gas injection At no gas injection G' at 0.5 LPM of gas injection G" at 0.5 LPM of gas injection At 0.5 LPM of gas injection G' at 1.5 LPM of gas injection G" at 1.5 LPM of gas injection At 1.5 LPM of gas injection 10 0,01 5 50 500 0,01 1 100 Step time, (s) Time, (s ) 6

Simulating the solid behaviour of aerated 4.2% WAS with a unaerated sludge 10 Creep test with 0.5 LPM of gas at 0.89 Pa with 1 Pa stress for un ‐ aereated sludge sample 1 Strain, (%) 10 0,1 1 Strain,(%) 0,1 0,01 with 1.5 LPM of gas at 0.89 Pa. 0,01 with1.2 Pa stress for un ‐ aereated sludge sample 0,001 0,001 0,01 0,1 1 10 100 Step time, (s) 0,001 0,001 0,01 0,1 1 10 100 Step time, (s) 7

Time sweep 1000 Storage modulus (G') & Loss Modulus (G"), G' at 0.5 LPM, and 0.08% Strain G" at 0.5 LPM, and 0.08% Strain G" without gas injection at 0.2% Strain G" without gas injection at 0.2% strain 100 Pa. 10 Storage Modulus (G') & Loss 100 Modulus (G"), Pa. 1 10 5 50 500 Time, (s) G' at 1.5 LPM, and 0.08% strain G" at 1.5 LPM, and 0.08 % Strain G' without gas injection at 0.3% strain G" without gas injection at 0.3% strain 0,1 3 30 300 Time, (S) 8

Calculating stress imposed by gas injection via two different tests creep test Gas Flow rate applied stress for aerated applied stress for stress imposed by the gas (pa) (LPM) sludge (pa) un-aerated (Pa) 0.5 0.89 1 1-0.89 = 0.11 1.5 0.89 1.2 1.2-0.89 = 0.31 Time sweep test Gas Flow rate applied strain for applied strain for un- strain imposed Equivalent stress (LPM) aerated sludge (%) aerated sludge (%) by the gas (%) imposed by the gas (Pa) = [(%strain)/100] x G* 0.5 0.08 0.2 0.2-0.08= 0.12 (0.12/100)*144 = 0.17 1.5 0.08 0.3 0.3 – 0.08= 0.22 (0.22/100)*144 = 0.31 Proved that gas injection imposes extra shear on sludge and changes its rheological behaviour 9

0 1 Challenges / Limitations occurred 0.5 LPM 2.5% 1LPM 6.7%

Shear Stress induced by different gas flow rates at different concentration of WAS Stress imposed, (N/m 2 ) Gas flow Gas velocity rate (m/s) (L/min) A simple model based on sludge 3.00% 4.00% 5.00% 5.50% concentration and gas velocity is developed to predict the stress 1 0.00182 4.4564 2.67855 2.42791 1.04614 induced by gas injection 3 0.00545 7.7987 5.3571 3.884656 3.13842 5 0.00909 10.0269 7.1428 4.85582 4.18456 7 0.0145 14.4833 10.7142 9.71164 5.2307 P < 0.05 & R Square = 0.89 1 1

Shear rate within bubble column 40 35 30 ( shear rate induced by the 25 Shear rate, (1/s) 20 15 10 5 0 6 8 10 12 14 16 18 20 Shear stress ,(Pa) 1 2

Effective shear rate formula used in the literature Reference Equation used � � eff = 5,000 ug (Nishikawa, Kato et al. 1977) � (Henzler 1980) � eff = 1500 ug � (Babaei, Bonakdarpour et al. � eff = 50 ug 2015, Babaei, Bonakdarpour et al. 2015) � � eff = 2800 ug (Schumpe and Deckwer 1987) 1 3

Impact of gas injection on different physical properties of sludge A.Zeta Potential B.Soluble COD C.Total Suspended Solids 1 4

Gas Flow rate, (L/min ) 0 Gas velocity (m/s) sCOD (mg/l) 0 1 2 3 4 5 6 7 8 55 3% 4% 5% 5.50% 50 3%Ts 4%TS 5% TS 5.5%TS -5 Zeta Potential,(mV) Suspended solids, (mg/l) 45 3% ss 40 0 4860 5250 5390 5830 4% ss -10 35 5% ss 0.00182 5340 6030 5750 6190 30 5.5% ss 25 -15 0.00546 6060 6480 5900 6350 20 15 0.0091 7260 6540 6600 6590 -20 0 0,002 0,004 0,006 0,008 0,01 0,012 0,014 Gas velocity, (m/s) 0.01274 7410 7230 7070 7470 -25 C = Fitting parameter = 2.12, (m 2 /N) a = Fitting parameter = 2.01, (m 2 /N) b = Fitting parameter = 2.75, (m 2 /N) 1 1 5 5

Conclusion 1 6

1. Gas injection has negligible impact on viscosity of sludge 2. Gas injection imposes extra shear on sludge was proved 3. Developed a simple equation based on total solids and gas velocity to understand the stress imposed whish is proportional to the shear rate in the bubble column. 4. Stress imposed by gas injection showed a linear relation to percentage change in physical properties of sludge and indicated that rheology can monitor the changes in sludge physical properties 1 7

Publications A. Journal Paper 1. "Impact of gas injection on the apparent viscosity and viscoelastic property of waste activated sewage sludge." Water Research 114: 296-307 (2017). 2. “Influence of gas injection on viscous and viscoelastic properties of Xanthan gum.” . Water Research 134: 86-91 (2018) 2. “Relationship between changes in physicochemical properties of municipal waste activated sludge and its rheology during gas injection”. (Manuscript under review with Water Research ) 1 8

Acknowledgement I wish to acknowledge • Mount Martha treatment plant for providing sludge to carry out research work. • School of Graduate Research (SGR) of RMIT University for providing scholarship to carry out the research. 1 9

Thank you for your attention 20