Minimizing the use of chemicals to control scaling in SWRO : improved predicition of the scaling potential of calcium carbonate

186 Pages·2011·4.587 MB·English

by  T K A Waly

MINIMIZING THE
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M USE OF CHEMICALS
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SCALING IN SWRO
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This thesis aimed to improve the accuracy of calcium carbonate scaling prediction, A
and subsequently prevent overdosing the chemicals employed to control scaling in L POTENTIAL
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seawater reverse osmosis (SWRO) systems. The scaling potential was estimated T OF CALCIUM
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employing theoretical calculations and experimental data. Furthermore, the kinetics of
C CARBONATE
precipitation were investigated employing induction time measurements at different O
levels of super saturation. N
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The outcome of this study showed that the degree of supersaturation of SWRO O
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concentrate was lower than commonly expected. An important reason was that the S
calculated pH value of seawater reverse osmosis concentrate was systematically higher C
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than that measured in full scale plants. In addition, kinetic studies indicated that vaterite L
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precipitated instead of calcite. Consequently, the supersaturation is significantly lower N
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than expected when calcite is assumed to be the precipitating phase. I
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These findings suggest that reducing or even eliminating acid/antiscalant to prevent W
calcium carbonate scaling may be possible in sea water reverse osmosis plants. R
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This hypothesis is supported by the fact that a limited number of sea water reverse
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osmosis plants no longer apply acid or antiscalant to control calcium carbonate scaling. T
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Moreover, a sea water reverse osmosis pilot plant in the Netherlands has been in
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operation for more than 6 months without acid or antiscalant, with no signs of scaling. E
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W tarek kamal abdalla waly
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MINIMIZING THE USE OF CHEMICALS TO CONTROL
SCALING IN SWRO:
IMPROVED PREDICTION OF THE SCALING POTENTIAL OF
CALCIUM CARBONATE
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MINIMIZING THE USE OF CHEMICALS TO
CONTROL SCALING IN SWRO:
IMPROVED PREDICTION OF THE SCALING
POTENTIAL OF CALCIUM CARBONATE

DISSERTATION

Submitted in fulfillment of the requirements of
the Board for Doctorates of Delft University of Technology
and of
the Academic Board of the UNESCO-IHE Institute for Water Education
for the Degree of DOCTOR
to be defended in public
on Wednesday, April 27, 2011 at 12:30 hours
in Delft, the Netherlands

by

Tarek Kamal Abdalla Waly
born in Cairo , Egypt

Master of Science in Sanitary Engineering
UNESCO-IHE Institute for Water Education, The Netherlands
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Acknowledgments

I would like to express my gratitude to my supervision team Prof. Gary Amy, PhD,
Prof. Geert-Jan Witkamp, PhD, MSc, Prof. Jan Schippers, PhD, MSc and Prof. Maria
Kennedy, PhD for their shepherding roles and critical comments - all of which have
helped sharpen this study.

I gratefully acknowledge the financial support of the Middle East Desalination
Research Centre (MEDRC), Oman and the support of Dr. Venkat Reddy and Dr.
Noreddine Ghaffour.

My deep gratitude to Rinnert Schurer, MSc and Evides NV for allowing us to
conduct the pilot testing at their pilot plant in Zeeland, The Netherlands.

I also acknowledge, with thanks, the two Msc. students namely Saleh Saleh and
Ruben Munoz Toro for their valuable contributions. To the UNESCO-IHE laboratory
staff, namely Fred Kruis, Don van Galen and Peter Heering and Lyzette Robbemont
- thanks for your friendliness and support.

My sincere thanks to the department of municipal water and infrastructure staff
members for their help, support and friendly advice during the full length of my
PhD study, and in particular to Jan Herman Koster, MSc and our hard working
secretary Tanny van der Klis.

Thanks to my colleagues Saeed Bagoth, Sergio Salinas Rodriguez, Loreen Villacorte,
Assiyeh Tabatabai, Sabine Lattemann, Victor Yangali, Chang-Won Ha, Sung Kyu
(Andrew) Maeng for their direct and indirect help during my time at UNESCO-IHE.

To my family whom supported me and sacrificed with all what they can to make
this step achievable.

Above all, my heartfelt thanks to Allah for his support and accepting my prayers.
This study was funded by the
MIDDLE EAST DESALINATION
RESEARCH CENTER
P.O BOX 21

AL Khwair, P.C. 133

Muscat
Sultanate of Oman

Tel: [phone]
Fax: [phone]

Website: www.medrc.org
Content vii

Contents

Content ............................................................................................................... νii
Summary ................................................................................................................ xi
Samenvatting ............................................................................................................ xv

Chapter 1 ......................................................................... 1

1.1 Background ................................................................................................ 2
1.2 Problem definition ..................................................................................... 5
1.3 The Overall Aim of the research ................................................................ 6
1.4 Research objectives ................................................................................... 6
1.5 References ................................................................................................. 7

Chapter 2 ....................................................................... 11

2.1 Abstract ................................................................................................... 12
2.2 Background .............................................................................................. 13
Introduction ............................................................................................. 13
Induction time ......................................................................................... 13
Measurement tools ................................................................................. 15
Effect of exchange CO on induction time ............................................... 16
2
2.3 Materials .................................................................................................. 18
Inductively coupled plasma ..................................................................... 18
Conductivity meter .................................................................................. 19
pH meter .................................................................................................. 19
Reactors ................................................................................................... 20
Synthetic seawater concentrate preparation .......................................... 21
2.4 Methods .................................................................................................. 23
Measurement of calcium with ICP .......................................................... 23
Salinity and accuracy of direct measurement of calcium in solution ...... 23
Measurement of calcium carbonate retained on membrane filters ....... 24
Effect of salinity, stability and accuracy of conductivity and pH
measurment ............................................................................................ 25
Effect of mixing on the induction time .................................................... 27
2.5 Results ..................................................................................................... 26
Effect of salinity on the ICP measurements and accuracy ....................... 28
Accuracy of measurement of calcium carbonate retained on membrane
filters ....................................................................................................... 30
The effect of salinity on the conductivity and the pH measurments ...... 31
The effect of carbon dioxide exchange in an open system ..................... 33
2.6 Conclusions .............................................................................................. 34
2.7 List of Symbols ......................................................................................... 35
2.8 References ............................................................................................... 36
viii Content

Chapter 3 .................................................................................................. 41

3.1 Abstract ................................................................................................... 42
3.2 Background .............................................................................................. 42
3.3 Materials .................................................................................................. 45
Synthetic seawater concentrate preparation .......................................... 46
3.4 Methods .................................................................................................. 47
The effect of particles in synthetic seawater on the induction time ....... 47
The effect of particle addition ................................................................. 48
Mixing effect ............................................................................................ 49
3.5 Results and discussion ............................................................................. 49
The effect of particles in synthetic seawater on the induction time ....... 49
The effect of particle addition ................................................................. 51
The effect of mixing speed on the induction time ................................... 52
The nucleation mechanism ...................................................................... 53
3.6 Conclusions .............................................................................................. 55
3.7 List of symbols ......................................................................................... 56
3.8 References ............................................................................................... 57

Chapter 4 .................................................................................................. 59

4.1 Abstract ................................................................................................... 60
4.2 Background .............................................................................................. 60
Introduction ............................................................................................. 60
Solubility of salts ...................................................................................... 61
Common methods used to determine the precipitation potential of
CaCO : ...................................................................................................... 62
3
Stiff & Davis Stability Index (S&DSI) ......................................................... 62
Saturation Index (SI) ................................................................................ 63
Saturation Ratio (Sa) ................................................................................ 64
Mechanism of nucleation ........................................................................ 64
Homogenous nucleation .......................................................................... 65
Heterogeneous nucleation in a solution .................................................. 66
Induction time ......................................................................................... 66
CaCO phases ........................................................................................... 68
3
The formation of hydrated CaCO forms ................................................. 69
3
4.3 Materials .................................................................................................. 71
pH meter .................................................................................................. 71
Reactors ................................................................................................... 71
Synthetic seawater concentrate preparation .......................................... 72
4.4 Methods .................................................................................................. 73
Induction time measurements ................................................................ 73
Solutions concentrations ......................................................................... 73
Calculation of SI using PhreeqC ............................................................... 74
4.5 Results ..................................................................................................... 74
The solubility product used by the S&DSI ................................................ 77
Homogenous and heterogeneous nucleation ......................................... 79
Content ix

4.6 Conclusions .............................................................................................. 85
4.7 List of symbols ......................................................................................... 86
4.8 References ............................................................................................... 88

Chapter 5 .................................................................................................. 93

5.1 Abstract ................................................................................................... 94
5.2 Introduction ............................................................................................. 95
5.3 Background .............................................................................................. 95
Saturation indices .................................................................................... 95
Calculation of pH in SWRO concentrates ................................................. 97
Effect of salinity on dissociation constants .............................................. 98
Effect of salinity on the ion activity ......................................................... 99
5.4 Materials and Methods ......................................................................... 100
Pilot plant .............................................................................................. 101
Concentrate pH in SWRO systems ......................................................... 102
5.5 Results and Discussion ........................................................................... 106
pH calculations using equilibrium equations ......................................... 106
pH calculations using manufacturers software ..................................... 109
pH prediction using Phreeqc evapouration model ................................ 110
Field seawater concentrate measurements .......................................... 112
5.6 Conclusions ............................................................................................ 113
5.6 List of Symbols ....................................................................................... 114
5.7 References ............................................................................................. 115

Chapter 6 ................................................................................................ 119

6.1 Abstract ................................................................................................. 120
6.2 Background ............................................................................................ 120
Introduction ........................................................................................... 120
Calcium carbonate phases ..................................................................... 121
The role of inorganic ions ...................................................................... 123
Solubility of salts ................................................................................... 125
Common methods used to determine the precipitation potential of
CaCO : .................................................................................................... 125
3
Saturation indices (SI and Sa) ............................................................... 126
Mechanism of nucleation ...................................................................... 126
Induction time ....................................................................................... 128
6.3 Materials ................................................................................................ 129
pH meter ................................................................................................ 129
Reactors ................................................................................................. 129
Synthetic seawater concentrate preparation ........................................ 130
6.4 Methods ................................................................................................ 132
Induction time measurements .............................................................. 132
Determination of co-precipitation ......................................................... 132
Determination of the final crystal phase of calcium carbonate ............ 132
6.5 Results and discussion ........................................................................... 134