Rheology Results for Sludge & Polymer

Brought to you by Albert Chang and Sheena Vince Cruz

Introduction

n  King Country Waste Water South Treatment Plant is using more polymer than they want to and still not getting the separation efficiency desired.

n  It has been speculated that given the high viscosity of the fluids, significant mixing is required to cause proper flocculation

n  Maxing out on the presently installed Sharpe Mixer is still not producing the desired mixing results.

n  Understanding flow and mixing properties of these unusual low index fluids will help solve the problem

Objectives

n  The overall class objective is to model the flow and mixing of the polymer and sludge under various situations

n  Experimentally determine fluid behavior of the two fluids and various mixtures thereof

Experimental Set Up

n  Two cups of digested sludge and polymer (Ciba Zetag 8819) samples were obtained on site

n  Transported to Sharpe Mixer Labs for Viscosity testing with a Brookfield DVII+ viscometer

n  Different spindles were used for various viscosity ranges

Expectations and Analysis

bθκη =

Curve fits can quantify the behavior of this fluid which is known to have power law properties. Power law fluids are governed by the following equations:

& θη loglog ba +=

Viscosity of Digested Sludge

Digested Sludge Behavior

y = -0.749x + 3.3461R2 = 0.9818

2

2.5

3

3.5

4

4.5

-1.5 -1 -0.5 0 0.5 1 1.5

Log (Shear Rate)

Lo

g (

Vis

co

sit

y)

Viscosity Vs. Shear Rate

y = 2218.6x-0.749

R2 = 0.9818

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

0 2 4 6 8 10 12 14

Shear Rate

Vis

cosi

ty

Viscosity of Polymer

Viscosity vs. Shear Rate

y = 2043.1x -0.7412

R2 = 0.9968

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 5 10 15 20 25

Shear Rate

Vis

co

sit

y

Polymer Behavior

y = -0.6808x + 3.2745R2 = 0.9795

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

4.2

-1.5 -1 -0.5 0 0.5 1 1.5

Log (Sheer Rate)

Lo

g (

Vis

cosi

ty)

Mixture of Sludge and Polymer n  Recipe: 46 ml of polymer

per 235 ml sludge n  Vigorous mixing produces

flocculation and coagulation

n  Unable to measure viscosity of anything that’s not continuous because water forms a liquid bearing around coagulated solids

Observations

n  Produced jello-like chunks in relatively clear liquid water

n  Prolonged mixing produces chunks of smaller sizes and ultimately over-mixing reduces mixture back into a continuous fluid

Viscosity of Over-mixed Sludge

Combined Overmixed Behavior

y = -0.994x + 3.2054R2 = 0.9814

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-1 -0.5 0 0.5 1 1.5

Log Shear Rate

Log

Vis

cosi

ty

50% polymer strength

50% Polymer Over-Mixed

y = -0.8278x + 3.5775R2 = 0.9991

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-1.5 -1 -0.5 0 0.5 1 1.5

Log Shear Rate

Log

Visc

osity

75% polymer strength

75% Polymer Solution Over-Mixed

y = -0.806x + 3.3675R2 = 0.9952

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-1.5 -1 -0.5 0 0.5 1 1.5

Log Shear Rate

Log

Vis

cosi

ty

Conclusions

n  All solutions are strongly non-Newtonian, shear thinning, power law fluids

n  Both the polymer and the sludge have very low power indexes (table)

n  Viscosity data is crucial to FEMLAB modeling of flow and mixing situations

Solution Power law index Polymer 0.319 Sludge 0.251

Over-Mixed 0.055