An experimental investigation into filter ripening: contact filtration of lowland reservoir water. by Michael John Chipps A thesis submitted to the University of London for the degree of Doctor of Philosophy February 1998 Department of Civil and Environmental Engineering University College London Gower Street London W Cl E 6BT ProQuest Number: U642225 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest U642225 Published by ProQuest LLC(2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT Pilot rapid gravity filters, treating lowland reservoir water, were operated to examine chemical, physical and biological influences on filter ripening. Ripening occurred if, after backwashing, filtrate turbidities showed an initial peak, then improvement to a minimum value. Backwash ing using collapse pulsing prevented biological fouling of media, and ensured constant starting head losses for three years. Ripening was examined using sand roughing filtration and dual media contact filtration with pre-ozonation and iron (III) sulphate coagulation. Turbidity removal data from sand filters showed that ripening behaviour varied with seasonal changes in applied loading. Biological maturation of filter media over several months caused improved turbidity removals. Subsequently, ripened turbidity removals varied proportionally with water temperature. Within a filter run ripened turbidity removal was independent of load at constant flow rate, but varied inversely with flow rate. Dual media filters showed ripening behaviour in roughing and contact filtration modes. Iron dosing produced superior turbidity removals. A novel coagulation control method was devised, based on the shape of the filtrate turbidity curves. Ripening time varied inversely with coagulant dose, but higher doses caused turbidity breakthrough. A temporary initial overdose could control ripening. Pre-ozonation enhanced roughing and contact filtration, but did not change the time taken to achieve maximum removals. With contact filtration ripened removals were a fixed proportion of the applied turbidity in winter, but filtrate turbidity was independent of load in summer, achieving <0.2 NIL). Flow rates of 12, 17 and 22 m.h'^ produced identical ripening curves, indicating a complex relationship between flow rate and particle capture. This was confirmed with data showing inconsistent relationships between turbidity, particle loading and ripening, and poorer ripening behaviour on longer filter runs. Further detailed particle size data were required. Six definitions of ripening were examined but none was satisfactory as ripening behaviour changed with chemical treatment and seasonal factors. TABLE OF CONTENTS ABSTRACT ......................................................................................................................................... 2 TABLE OF CONTENTS ..................................................................................................................... 3 TABLE OF TABLES ............................................................................................................................ 7 TABLE OF ILLUSTRATIONS........................................................................................................... 10 ACKNOWLEDGEMENTS ................................................................................................................ 16 DEDICATION .................................................................................................................................... 17 CHAPTER 1. INTRODUCTION......................................................................... 18 CHAPTER 2. RIPENING IN RAPID GRAVITY FILTRATION OF POTABLE WATER ....................................................................23 2.1 INTRODUCTION ................................................................................................ 23 2.1.1 WATER TREATMENT OBJECTIVES .......................... 23 2.1.2 CAUSES OF WATER-BORNE DISEASE ................................................. 25 2.1.3 FAILURE OF FILTRATION PLANTS TO PROTECT PUBLIC HEALTH .................................................................................................. 26 2.2 RAPID GRAVITY FILTERS IN WATER TREATMENT ................................. 29 2.2.1 PRINCIPLES OF RAPID GRAVITY FILTRATION ..................................... 32 2.2.2 MECHANISMS OF RAPID GRAVITY FILTRATION ................................. 35 2.2.3 THE FILTER CYCLE ................................................................................. 41 2.2.4 PHASES OF A FILTER CYCLE ............................................................... 42 2.3 THE DEFINITION OF RIPENING ..................................................................... 44 2.4 RESEARCH INTO FILTER RIPENING ........................................................... 47 2.5 OBSERVATIONS OF FILTER RIPENING ......................................................49 2.5.1 THE HISTORY OF RIPENING OBSERVATIONS ..................................... 49 2.5.2 FILTRATE IRON CONCENTRATION ....................................................... 50 2.5.3 RIPENING OF SUSPENDED SOLIDS ...................................................... 51 2.5.4 RIPENING MEASURED BY FILTRATE TURBIDITY ................................ 51 2.5.5 RIPENING MEASURED BY PARTICLE COUNTERS ............................. 51 2.5.6 RIPENING OF BACTERIA ....................................................................... 52 2.5.7 RIPENING OF ALGAE ............................................................................. 53 2.5.8 RIPENING OF PARTICULATE ORGANIC CARBON .............................. 53 2.5.9 RIPENING OF GIARDIA CYSTS AND CRYPTOSPORIDIUM OOCYSTS ............................................................................................... 54 2.6 THE CAUSES OF FILTER RIPENING ........................................................... 54 2.6.1 THE INFLUENCE OF BACKWASHING ON FILTER RIPENING ............. 55 2.6.2 BACKWASH REMNANTS AND THE PRE-RIPENING PHASE ................ 56 2.6.3 EXPERIMENTS WITHOUT BACKWASHING ........................................... 58 2.6.4 THE INFLUENCE OF THE INFLUENT WATER ON RIPENING .............. 59 2.6.5 FILTER RIPENING SEQUENCE INCORPORATING BACKWASH CONDITIONS AND INFLUENT WATER ........... 59 2.7 OPTIMUM RIPENING TIME ............................................................................ 61 2.8 THE SIGNIFICANCE OF FILTER RIPENING ............................................... 61 2.9 THE SIGNIFICANCE OF TURBIDITY ........................................................... 62 2.10 HEAD LOSS AS INDICATOR OF RIPENING ........................................... 64 2.11 CONTROLLING FILTER RIPENING ........................................................... 65 2.11.1 CHEMICAL METHODS OF CONTROLLING RIPENING........................ 67 2.11.2 PHYSICAL METHODS OF CONTROLLING RIPENING ........................ 68 2.11.3 BIOLOGICAL CONTROL OF FILTER RIPENING ................................. 72 CHAPTER 3. EXPERIMENTAL CONDITIONS ..............................................73 3.1 INTRODUCTION ................................................................................................ 73 3.2 WATER SOURCES AND MANAGEMENT.................................................... 74 3.3 FILTER COLUMNS ........................................................................................... 75 3.3.1 CONTROL STRATEGY AND INSTRUMENTATION ................................ 80 3.3.2 OZONE GENERATORS AND CONTACTORS......................................... 81 3.3.3 IRON DOSING EQUIPMENT .................................................................... 82 3.3.4 TURBIDIMETERS ..................................................................................... 85 3.3.5 DIFFERENTIAL PRESSURE TRANSDUCERS AND MANOMETERS ....................................................................................... 86 3.3.6 FLOW MEASUREMENT .......................................................................... 87 3.3.7 FILTER MEDIA ......................................................................................... 88 3.3.8 DATA COLLECTION ............................................................................... 89 3.4 PILOT PLANT OPERATIONAL DATA ........................................................... 91 3.4.1 INFLUENT WATER QUALITY ................................................................... 91 3.4.2 RIVER THAMES WATER CHEMISTRY ................................................... 95 3.4.3 TURBIDITY MEASUREMENT ................................................................... 96 3.4.4 OZONE PRODUCTION MEASUREMENT ................................................ 97 3.4.5 CALIBRATION OF IRON DOSING EQUIPMENT ..................................... 99 3.5 DISCUSSION .................................................................................................. 102 3.5.1 TURBIDITY MEASUREMENT ................................................................. 102 3.5.2 OPERATION OF OZONE EQUIPMENT