Report No DWI0640
THE DECLINE OF pH IN WATER DISTRIBUTION SYSTEMS
This study investigates the decline in pH of a soft water during supply. The fieldwork and laboratory data confirmed and quantified the pH decline in soft water that has had the pH increased by lime addition. A pH of 9.0 can decline to 7.5 during distribution. The role of humic acid as a causative agent of pH decline is examined in detail by modified jar test experiments and the development of a dialysis technique. The results of these experiments showed that binding occurred between the humic acid and calcium ion. This binding is reflected in a decline of pH in the water. The extent of binding between the calcium ions and humic acid was dependent on the contact time between the ions and acid.
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