Operation and Optimisation of Media Filters

Practical Guide to the Operation and Optimisation of Media Filters

SE ND CO N

IO

IT ED Peter Mosse and Bruce Murray

Contents Foreword Acknowledgements General Introduction Chapter 1

Chapter 2

Chapter 3

Hazards, Risks And Control Points...................................................................6

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Hazards And Drinking Water ....................................................................................6 Pathogens Are The Main Hazards In Drinking Water................................................6 Other Hazards...........................................................................................................9 Control Points..........................................................................................................10 Critical Limits And Target Criteria............................................................................ 11 Corrective Actions, Incident And Emergency Management Plans...........................12 Monitoring...............................................................................................................13 Responsibilities.......................................................................................................13

Filtration....................................................................................................................14

• Filtration And Public Health.....................................................................................14 • The Filtration Process.............................................................................................15 • Operating Criteria And Performance Parameters . .................................................16

Filter Optimisation.................................................................................................18

1. Collect Relevant Drawings And Manuals.................................................................18 2. Establish Filter Run Times (Prepare A Filter Run Profile)........................................19 3. Establish The Filter Backwash Time ......................................................................21 4. Observe Filter Operation And Backwashes Regularly.............................................22 5. Measure Rates........................................................................................................23 6. Inspect The Media...................................................................................................24 a. Periodically Inspect The Surface Of A Filter After A Backwash........................27 b. Deep Bed Investigations..................................................................................27 c. Refilling A Filter After Draining.........................................................................28 d. Use Fine Mesh Filters To Determine Which Filter May Be Damaged...............28 e. Some Examples Of Problems With Filters........................................................29 7. Bed Fluidity And Bed Expansion.............................................................................31 8. Inspect The Plenum Space Or Filtered Water Channel...........................................34 9. Keep Filter Walls And Launders Clean....................................................................35 10. Measure Metal Concentrations In The Filtered Water:...........................................36 11. Minimise Particle Breakthrough..............................................................................36 12. Calibrate Differential Pressure Gauges, Flow Meters And Turbidity Meters...........39 13. Minimise The Filter Ripening Period.......................................................................39 14. Reduce The Risks Associated With Wastewater Recycling....................................40 15. Optimise Chemical Dosing.....................................................................................41 • Storing Filters Offline...............................................................................................42

Reduction Of Plant Flow...................................................................................42

Cycling Filters...................................................................................................43

Long Term Storage Of Filters...........................................................................43

Dry Storage......................................................................................................44

Wet Storage.....................................................................................................44

Returning A Filter To Storage...........................................................................45 • Pressure Or Enclosed Filters...................................................................................45 4

Chapter 4

Filter Backwashing................................................................................................47

Chapter 5

Monitoring Filter Function..................................................................................51

Chapter 6

Chapter 7

• Short Term Monitoring Of Filter Function: SCADA Trends.......................................51 • Long Term Monitoring Of Filter Function.................................................................52 • Other Measures.......................................................................................................55

Fixing Filters............................................................................................................56

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Filter Media. .............................................................................................................61

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Chapter 8

Chapter 9

Repeated Backwashing...........................................................................................57 Surface Scraping . ..................................................................................................57 Jet Lancing..............................................................................................................58 Caustic Washing......................................................................................................58 Chlorine Treatment..................................................................................................58 Managing Media Downstream Of The Filters..........................................................59 Topping Up Filter Media..........................................................................................60

Media Sieving..........................................................................................................61 Effective Size...................................................................................................63 Uniformity Coefficient.......................................................................................63 Physical Properties..................................................................................................63 Filter Coal.........................................................................................................63 Filter Sand For Dual Or Monomedia Filters......................................................64 Coarse Sand And Filter Gravel.........................................................................64 Granular Activated Carbon...............................................................................65 Filter Media Selection And Design..........................................................................66 Filter Media Life.......................................................................................................67

Rebuilding Filters. .................................................................................................68

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Getting Started........................................................................................................68 Dismantling The Filter.............................................................................................70 Remove All Traces Of Sand ...................................................................................72 Replacing Nozzles...................................................................................................72 Inspecting Nozzles..................................................................................................73 Checking The Air Scour Pattern..............................................................................74 Rebuilding A Filter...................................................................................................75 Relaying The Filter Media.......................................................................................76 Recommissioning The Filter....................................................................................78

Closing Words. .......................................................................................................79

References.........................................................................................................................................80 Appendices

Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5 Appendix 6 Appendix 7

Types of Filters........................................................................................................81 Calculation Of Filtration Rates And Backwash Rates...............................................83 Filter Entry Hazard Identification And Risk Assessment..........................................85 Example Filter Entry Permit.....................................................................................86 Filter Inspection Requirements................................................................................88 Filter Inspection And Assessment Procedure..........................................................89 Filter Inspection Record Sheets...............................................................................93 5