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<br />..."nO <br />{...I '-' <br /> <br />42 <br /> <br />METROPOLITAN WATER DISTRICT <br /> <br />raise the silica content to such a level that dissolution of this ele- <br />ment from the zeolite would be reduced to a minimum. At the end <br />of the fiscal year more than 1,700,000 gallons of water had been <br />softened per cubic foot of the newer zeolite, in service for slightly <br />more than three years, Its operation continued to be satisfactory, <br />although a general, though gradual, decrease in exchange capacity, <br />loss of volume, and increase in salt consumption were observed. <br />Due to the high percentage of fines in the three softener units con- <br />taining the revivified original zeolite, the attrition losses were suf- <br />ficiently high to require the consolidation of this material into two <br />units, New, high-capacity, organic exchange material was placed <br />in the unit emptied, and enough new siliceous zeolite was purchased <br />to bring the remaining nine units up to proper volume. After three <br />months of continuous operation and 220,000 gallons of water soft- <br />ened per cubic foot of material, the new organic exchanger was <br />proving very satisfactory. <br /> <br />Research 1Vo,'k <br /> <br />The detailed investigations into the characteristics of the several <br />kinds of cation exchangers were continued. Much valuable infor- <br />mation has been accumulated relative to exchange capacity and <br />salt requirements under different conditions of regeneration and <br />concerning resistance to breakdown under the condition of low <br />chlorine residual usually present in District softener influent water, <br />Vapor absorption experiments were conducted to determine the sur- <br />face area and diameter of the pore char.nels of several siliceous <br />zeolites and resinous exchangers. <br />Details of the plans for the larger experimental electrolytic water <br />softening unit were revised in preparation for the start of con- <br />struction in the ensuing fiscal year, Delay in construction of this <br />unit was unavoidable because of the activities of the contractor <br />during construction of the softening and filtration plant expansion, <br />Tests to determine the efficacy of chlorine-activated sodium sili- <br />cate as an aid to coagulation under District conditions of lime <br />softening were completed, and the process was put into use on a <br />plant scale. <br />Laboratory t~sts werE' rnn t.o netermine the chlorine demand of <br />the water entering the San Diego aqueduct, and recommendations <br />were made for the most economical dosage of chlorine to be applied <br />in order to maintain satisfactory conditions in the pipe line. <br /> <br />, <br />~ <br />