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<br />. <br /> <br />I. <br /> <br />. <br /> <br />f\) <br />W <br />tv <br />~ <br /> <br />or trickling filtration could be used as the secondary treatment. <br /> <br />Trickling filters were considered for the purpose of this study. <br /> <br />Activated carbon filteration would be used to remove essentially all of <br /> <br />the suspended solids remaining after secondary treatment. <br /> <br />Since <br /> <br />preliminary cost comparisons give reverse osmosis a cost advantage <br /> <br />over both electrodialysis and vertical tube evaporator-multistage flash <br /> <br />processes, reverse osmosis demineralization would be used. <br /> <br />Conditions assumed for New River water at the International <br /> <br />Boundary include 7,000 mg/I total dissolved solids (TDS), 0.08 mg/I <br /> <br />iron, 400 mg/I calcium, 80 mg/I potassium, 1,500 mg/I sodium, 2,600 <br /> <br />mg/I chlorine, 600F temperature, dissolved oxygen content at or near <br /> <br />zero, biochemical oxygen demand exceeding 850 mg/I, and fecal <br /> <br />coliform levels exceeding 110 million colonies per 100 ml. This would <br /> <br />be the worst condition expected since average TDS levels are between <br /> <br />4,000 and 5,000 mg/I and Mexico is trying to improve the quality. <br /> <br />Alamo River Facility <br /> <br />Alamo River water quality conditions make membrane processes <br /> <br />more viable than distillation, but neither reverse osmosis or electro- <br /> <br />dialysis has an advantage based on costs. A reverse osmosis process <br /> <br />was considered. Primary treatment, which would consist of screens, <br /> <br />grit chambers, and clarifiers, would be required because of the high <br /> <br />suspended solids content. <br /> <br />A water sample taken from the Alamo River east of Brawley on <br /> <br />December 10, 1976, gave the following analysis: <br /> <br />22 <br />