Best Practice Guide on Metals Removal From Drinking Water By Treatment

Contents

About this Best Practice Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxvii Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxix

Chapter 1 Drinking water quality standards and regulations . . . . . . . . . . . . . . . . . . . . . . . . .

Asher Brenner and Eddo J. Hoekstra

1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.2 Drinking Water Quality Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.3 Drinking Water Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.4 Bacteriological and Microbial Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.5 Chemical, Physical and Radiological Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.6 Trends for the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 3 3 4 5 7

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Best Practice Guide on Metals Removal from Drinking Water by Treatment

Chapter 2 Guide to the selection of water treatment processes for removal of metals. . . .

Zsuzsanna Bufa-Do˝ rr, Mátyás Borsányi and Ali Tor 2.1 2.2

9

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Technologies for Remove Metals from Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.1 Coagulation/filtration technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.2 Adsorption technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.3 Co-removal of arsenic, iron and manganase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.4 Ion exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.5 Membrane processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.6 Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.3 Point of Use/Point of Entry (POU/POE) Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 9 11 12 14 14 15 16 16 17

Chapter 3 Oxidation for metal removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Larry Russel, Todd Russell and Brian Croll

19

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overview of Iron and Manganase Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal via Aeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal via Chlorination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal via Chlorine Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal via Ozone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Iron Removal with Potassium Permanganate (KMnO4) . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Filtration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal via Aeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal via Chlorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal via Chlorine Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal via Ozone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manganese Removal via Potassium Permanganate (KMnO4) . . . . . . . . . . . . . . . . . . . . .

Removal of Iron and Manganase Using Microbiologically Active Filters (Biological Iron and Manganase Removal) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 20 20 21 22 22 22 23 23 24 24 25 25 26 26 26 27

Chapter 4 Coagulation, flocculation and chemical precipitation . . . . . . . . . . . . . . . . . . . . .

Mehmet Emin Aydın, Zdravka Lazarova, Ali Tor and Senar Ozcan

29

4.1 4.2 4.3 4.4

29 29 30 31

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description of Technologies Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Coagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Coagulation Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Contents

vii

4.5 Flocculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.6 Flocculation Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.7 Chemical Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 33 34 35

Chapter 5 Sedimentation and flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ali Tor, Senar Ozcan and Mehmet Emin Aydın

37

5.1 Description of Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2 Design Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.3 Advantages and Disadvantages of Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.4 Description of Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.5 Advantages and Disadvantages of Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37 38 41 41 43 43

Chapter 6 Removal of metals from drinking water by filtration . . . . . . . . . . . . . . . . . . . . . .

Lary Russell and Todd Russell

45

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.2 Filtration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.3 The Autocatalytic Reaction of Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.4 Filter Hydraulics and Backwashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.5 Coal and Sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.6 Greensands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.7 Pilot Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

45 45 46 46 47 47 48 49

Chapter 7 Electrochemical treatment methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ona Gyliene˙

51

7.1 Theoretical Background of the Electrochemical Processes . . . . . . . . . . . . . . . . . . . . . . . .

7.2 Electrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.3 Electrodialysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.4 Electrocoagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51 51 53 55 58

Chapter 8 Adsorption processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Magdalena Zabochnicka-Swiatek, Ona Gyliene, Karin Cederkvist and Peter E. Holm 8.1 8.2

61

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Factors Influencing Sorption Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

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8.3 8.4

Adsorption Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Applications of Adsorbent Materials for Metals Removal from Water . . . . . . . . . . . . . . . .

8.4.1 Zeolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.4.2 Activated carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.4.3 Biosorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.4.4 Iron oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.5 Advantages and Disadvantages of Adsortpion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

62 63 63 64 65 66 67 68

Chapter 9 Ion exchange processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Magdalena Zabochnicka

71

9.1 9.2 9.3

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Factors Influencing Ion Exchange Selectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Applications of Ion Exchange Materials for Metals Removal from Water . . . . . . . . . . . .

9.3.1 Zeolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9.3.2 Organic and inorganic ion exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9.4 Ion Exchange Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

71 71 72 72 74 75 76

Chapter 10 Membrane processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Asher Brenner and Zdravka Lazarova

77

10.1 10.2 10.3

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description of Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Implementation of Technology for the Removal of Heavy Metals and Related Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10.4 Advantages and Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10.5 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10.6 Future Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 11 Arsenic removal processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zdravka Lazarova, Sabrina Sorlini, Frausta Prandini and D. Staniloae 11.1 11.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Available Technologies and Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.1 Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.2 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.3 Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.4 Ion exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.5 Membrane filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.2.6 Novel removal methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

77 78 78 79 80 81 81

83 83 84 84 84 85 86 86 87

Contents

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11.3 Consideration on Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.4 Treatment Process and Residuals Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.5 Examples of Real Scale Treatment Plants for the Arsenic Removal in Europe . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

89 89 90 92

Chapter 12 Hybrid processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zdravka Lazarova

95

12.1 12.2

Description of Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Implementation of Technology for the Removal of Heavy Metals and Related Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12.3 Advantages and Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12.4 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12.5 Future Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

95 96 98 98 99 100

About this Best Practice Guide

This Guide is one of a series produced by the International Water Association’s Specialist Group on Metals and Related Substances in Drinking Water. It is a state-of-the-art compilation of the range of scientific, engineering, regulatory and operational issues concerned with the removal of metals from drinking water by treatment. It will be of interest to water utility practitioners, health agencies and policy makers.

The Specialist Group is supported by members from 26 European countries, Canada and the United States. It is an active research network and has regularly convened international conferences and seminars. It has close working links with the World Health Organization, the European Commission’s Joint Research Centre, Health Canada and the US Environmental Protection Agency. The Specialist Group developed out of COST Action 637 (www.cost.esf.org) and the funding received from COST from December 2006 to November 2010 is duly acknowledged. The Specialist Group web-site is now part of the IWA Water Wiki accessible via www.iwahq.org.

The Guide is supported by a two-day training course. Information about training courses and the Specialist Group in general is available from www.iwahq.org Dr. Colin Hayes Chairman IWA Specialist Group on Metals and Related Substances in Drinking Water (METEAU)

Preface

The EU drinking water directive sets a range of standards for metals and related substances in drinking water, many of which are concerned with health protection. A number of these standards are very stringent and require compliance to be assessed at the point of use. Because of the difficulties associated with monitoring, historic practices in many countries have concentrated on the quality of water within the distribution network. As a result, the magnitude of problems with some metals and related substances in drinking water is not fully appreciated in all European countries, and the extent and nature of corrective actions differ widely. Standards for metals in drinking water are variously set by many other countries and often derive from WHO Guidelines; standards vary slightly according to local circumstances.

This Best Practice Guide on Metals Removal from Drinking Water describes drinking water standards and regulations, and explains the impact of a range of water treatment processes on metal levels in drinking water. Its objectives are to provide a basis for assessing the extent of problems and to identify appropriate water treatment options. It provides a reasoned guide to the selection of key water treatment processes. Each chapter focuses on a specific water treatment process and has been written by experts in that particular process.

This Guide provides practice-based knowledge for water engineers and scientists in large and small water utilities, regulatory agencies, health agencies and local municipalities (from cities through to small rural communities). The Guide should also be able to support University level teaching in degree schemes that relate to water management.

Authors

Prof. Dr. Asher Brenner, Unit of Environmental Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel Dr. Eddo, J. Hoekstra’ Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra I-21027, Italy Dr. Zsuzsanna Bufa-Dörr, National Institute of Environmental Health, Water Safety Department, Hungary Prof. Dr. Matyas Borsanyi, National Institute of Environmental Health, Water Safety Department, Hungary Dr. Larry Russell, Reed International Ltd. Berkeley, CA 94704, USA Prof. Dr. Mehmet Emin Aydin, Dept. of Environmental Engineering, Selcuk University, Konya, 42031, Turkey Prof. Dr. Zdravka Lazarova, AIT Austrian Institute of Technology GmbH, Dept. Health & Environm., 3430 Tulln, Austria Dr. Ali Tor, Dept. of Environmental Engineering, Konya University, Konya, Turkey Dr. Senar Ozcan, Dept. of Environmental Engineering, Konya University, Konya, Turkey Dr. Ona Gyliene, Institute of Chemistry of the Centre for Physical Sciences and Technology, A. Goštauto 9, 2600 Vilnius, Lithuania Dr. Magdelena Zabochnicka-Swiatek, Czestochowa University of Technology, Institute of Environmental Engineering, Brzeznicka 60A, 42-200 Czestochowa, Poland Prof. Dr. Peter E. Holm, Department of Basic Sciences and Environment, University of Copenhagen, Denmark Dr. Karin Cederkvist, Department of Basic Sciences and Environment, University of Copenhagen, Denmark Dr. Sabrina Sorlini, Ricercatrice di Ingegneria Sanitaria Ambientale, DICATA – Facoltà di Ingegneria – Università degli Studi di Brescia via Branze 43 – 25123 Brescia, Italy Dr. Frausta Prandini, Ricercatrice di Ingegneria Sanitaria Ambientale, DICATA – Facoltà di Ingegneria – Università degli Studi di Brescia via Branze 43 – 25123 Brescia, Italy Dr. D Staniloae, National Research-Development Institute for Industrial Ecology, ECOIND 90-92 Panduri 050663 Bucharest Romania

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Best Practice Guide on Metals Removal from Drinking Water by Treatment

Todd Russell, Dept. of Civil and Environmental Engineering, Stanford University, Stanford California 94305, USA Dr. Brian Croll, Consultant (UK) Dr. Colin Hayes, Swansea University (UK) Dr. Tom Hall, Principal Consultant – Water Supply (UK) Dr. Lisa Barrott, MWH (UK) Professor Mustafa Ersoz, Selcuk University (TR)

Foreword

Metals in drinking water can arise from a number of sources. They may occur naturally in source waters because of geological conditions, or result from man-made contamination, for example from mining wastes. They may originate from chemicals used in water treatment, particularly the iron and aluminium based coagulants. The most common cause of lead and copper in drinking water is their use in plumbing systems. Some metals, such as arsenic and lead, have obvious toxicity implications for consumers, and need to be removed effectively to protect public health. Other metals, such as copper or zinc, can impart unpleasant taste to the water at elevated levels, and some, such as iron or manganese, can impair the appearance of the water.

Overall, there is a need to maintain effective water treatment to remove metals from water or prevent contamination during or after treatment. A wide range of water treatment processes are available, and process selection, design and operation for metals removal can pose a challenge to water engineers. This Guide reviews the treatment processes that can be used for metals removal. It covers not only the conventional treatments that have been used for many years, such as coagulation, clarification and filtration, but also membrane processes, adsorption and electrochemical treatment. It therefore provides a comprehensive source of information on treatment for both current and future implementation, to help ensure effective removal of metals from drinking water.

Dr. Tom Hall Principal Consultant – Water Supply WRc (UK)

Executive Summary

This Best Practice Guide on Metals Removal from Drinking Water by Treatment describes drinking water standards and regulations for metals, and explains the impact of a range of water treatment processes on metal levels in drinking water. Among water pollutants, heavy metals are considered to cause particular concern because of their cumulative toxic characteristics even at low concentrations. Future drinking water quality standards may probably be gradually changed due to the cumulative knowledge gathered regarding the effect of various substances on human health. Another issue that will affect future trends is the advance of analytical instruments capable of identifying compounds in the nano-gram per liter range, and of other sophisticated sensors for toxicity testing.

Different raw water quality characteristics and operating practices, technical, economical, environmental, geological differences between the countries mean that no single technology is most efficient for metal removal. In choosing a treatment technology attention should be paid to the practicality, efficiency, chemical interferences, public health aspects and possible future improvements.

The process of metal removal includes disposal of waste solids (e.g. spent filter material, coagulant sludge) and residual fluids likely to contain high levels of metals and possibly other hazardous or radioactive (e.g. uranium, radon) constituents. If the water requires pretreatment (e.g. lowering of pH for adsorption processes, or raising it for lime-softening) the waste situation becomes more complicated.

The most common metals of concern in drinking water are iron and manganese, which present similar challenges when found in solution, often appear in tandem. Chemical oxidation converts iron and manganese to insoluble hydroxides and oxides, and the precipitates can then be extracted from solution by sedimentation or filtration. The common oxidants used for iron and manganese removal are oxygen, chlorine, chlorine dioxide, ozone and potassium permanganate. The effectiveness of oxidation on iron and manganese hinges on several key factors: the pH of the solution, the reductive potential of the solution, the presence of naturally occurring organic material (NOM), and the ionic strength of the solution. Manganese is substantially more stable than iron in solution and manganese is autocatalytic where iron is not. Due to the complex chemistry involved in the removal of iron and manganese with oxidation, design and testing on the bench and pilot scale are strongly encouraged.

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Best Practice Guide on Metals Removal from Drinking Water by Treatment

Coagulation and flocculation are used to form precipitates that adsorb natural organic matters and some inorganic materials such as phosphates, arsenic compounds and fluoride. Aluminum sulphate (alum), ferric iron salts, organic polymers (polyelectrolytes) are widely used as coagulants in the water treatment plants.

Oxidative chemicals such as chlorine, ozone or potassium permanganate can be added prior to the primary coagulant to improve the coagulation by oxidizing dissolved organics. All the coagulants have an optimum operation pH range. The Guide describes how heavy metals, existing as cations in water, form insoluble hydroxides and carbonates and precipitate. This is achieved usually by adding caustic soda or lime to adjust the pH according to the maximum metal insolubility.

Metal precipitates or metals adsorbed onto coagulated particles can be removed by both sedimentation and flotation. The sedimentation process is based upon the settlement of the suspended solids by gravity and consequently settleable solids are removed from water as sludge at the bottom of a circular or rectangular tank. General parameters used for the design of sedimentation tank are surface loading rate, retention time, tank depth and flow rate and tank. The major advantage of sedimentation is that it uses only gravity to separate the flocs from water and is therefore cost effective with a low energy usage. The major disadvantages of sedimentation are the long separation time required and the large amount of land area required.

The flotation process uses gas bubbles to increase the buoyancy of suspended solids. To obtain efficient flotation, the pH and chemical dosage of the coagulation process should be optimized. The time and degree of agitation used for flocculation process also affect the performance of flotation process.

A typical treatment train consists of an oxidant dose followed by a detention basin and finally rapid filtration or pressure filtration. The differing chemistries and reaction kinetics of iron and manganese has impacts on filter design. For systems utilizing oxidation for removal of iron and manganese, proper selection of the filter media and design of the filtration unit is important. Filter media (type and size), filter area and depth, hydraulic and solids loading rate and backwashing regimes are all important aspects of filter design. Autocatalytic removal of manganese can take place in a filter and can be critical for manganese removal. An investment in filter pilot testing can provide significant.

Electrochemical treatment is an emerging technology used for the removal of organic and inorganic impurities from water and wastewater. Electrochemical processes involve redox reactions, where oxidation and reduction reactions are separated in space or time. Usually the electrochemical treatment of water is concerned with electron transfer at the solution/electrode interface applying an external direct current in order to drive an electrochemical process. Electrocoagulation is the electrochemical production of destabilisation agents (usually Al or, Fe ions) that neutralize the electric charge of suspended pollutant. Electrochemically generated metallic ions from these electrodes can undergo hydrolysis near the anode to produce a series of activated intermediates that are able to destabilize finely dispersed particles present in the water/wastewater to be treated. Electrochemical treatment methods have a future as advanced technologies for additional treatment of potable water domestically and remote areas.

Zeolites are the best natural filter medium available for treatment of water for metals removal. They offer superior performance to sand and carbon filters, giving purer water and higher throughput rates with less maintenance required. The application of zeolites provides an economical means of removing mixed heavy metals from water. Physical and/or chemical regeneration of used zeolitic adsorbents facilitate the protection of natural environment, provided that the used regenerant can be disposed of safely. Activated carbons are non-selective sorbents and presence of the competing ions could reduce the efficiency of metal removal. All activated carbon filters, do not naturally reduce the levels of soluble salts (including nitrates), fluoride, and some other potentially harmful minerals like arsenic (unless specially designed) and cadmium. The overall water quality (turbidity or presence of other contaminants) affects the capacity of activated carbon to adsorb a specific contaminant.

Executive summary

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The Guide describes ion exchange as a reversible chemical reaction where an ion from solution is exchanged for a similarly charged ion attached to an immobile solid particle. These solid ion exchange particles are either naturally occurring inorganic adsorbents or synthetically produced organic resins. The synthetic organic resins are the predominant type used today because their characteristics can be tailored to specific applications. After using, ion exchangers can be cleaned by chemical or thermal processes and reused.

Membrane separation processes are considered emerging technologies capable of improving on the performance of traditional processes such as granular filtration, precipitation, disinfection, biological treatment, and to assist in complete elimination of emerging pollutants. The Guide describes how, within the broad family of membrane separation processes, there are “loose” membrane-based technologies (Microfiltration (MF) and Ultrafiltration (UF)), and “tight" membrane separation processes (Nanofiltration (NF) and Reverse Osmosis (RO)) which require higher levels of pressure to enable free water passage with simultaneous rejection of particulate and even dissolved materials. The advance in membrane science and technology and their high and reliable separation efficiency, make this class of processes very suitable for the removal of heavy metals and related substances.

The Guide describes how physical and chemical processes are applied for arsenic removal in drinking waters: chemical co-precipitation, adsorption, ion exchange, and membrane filtration. Reduced inorganic As(III) should be converted to As(V) to improve its removal and a high Fe:As ratio promotes arsenic removal. The most effective method for arsenic removal in the case of large-scale water utilities is the coagulation with ferric or alumina salts. In addition, adsorption and ion exchange are becoming increasingly popular for arsenic removal in small-scale treatment systems.

The integration of different physical, chemical and/or biological processes into the so-called “hybrid” process creates new advantageous applications in the removal of metals and related substances from ground and surface water. The most known hybrid application is the combination of pressure driven membrane processes such as MF and UF with high capacity sorbents or special metal-bonding agents (polyelectrolytes, surfactants, polyamino acids, natural biopolymers such as chitosan) which substantially increases the separation selectivity and efficiency. The membrane bioreactor process is the best example of the success of hybrid membrane treatment.