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<br />I-'- <br />en <br /><:..:, <br />o <br /> <br />2.3.3 Quantities. Qualities and Disposal of Reverse Osmosis Waste. <br />An alternative to t~e use of ion exchange for boiler feed water preparation <br />is ~everse osmosis used in conjunction with a polishing mixed-bed ion exchanger. <br />The reverse osmosis-ion exchange system gives a completely different ~aste <br />than does ion exchange by itself. In a typical situation very few regenerant <br />chemicals are used and ~~e waste contains two streams. The first, and major <br />one, is about 4 times ~~e concentration of the source water and one-third the <br />volume of the product. water. The second stream, from the "polishing" ion <br />exchange. contains 1 to 2% total dissolved solids and has a volume ot 0.5 to <br />1% of the product water. <br />Reverse osmosis is more eX?ensive than ion exchange for large throughputs, <br />6 <br />but cheaper for small throughputs This means that reverse osmosis may be <br />preferred for plants which are about one-fift:." the "standard" size plants of <br />250 " 106 set/day"; i. e.. for plants below an output of about 2 :< 109 9tu!"r. <br />For larger plants reverse osmosis will be used when it results in savings i~ <br />''''''aste d.isposal~ <br />!f allowed, the reverse osmosis waste :rorn the larger plants may be <br /> <br />. <br />sui~able fc~ return to ~~e river. While the concentration of sal~s is up to 4 <br /> <br />times greater than in the river, the amount of dissolved material is nearly <br /> <br />the same as ~~at which was in the water withdrawn from the river because no <br /> <br />chemicals are added during ~~e treatment. Thus if returning salts to the <br />r~ver is acceptable, reverse osmosis should ~e considered for boiler feed <br />water treatment and the costs of an evaporation pond avoided. The cost of <br />reverse osmosis is decreasing relative to ion exchange and it may become as <br />cheap as ion exchange for large plants when the cost of waste disposal is <br />taken into account. However, in the Coloraco River Basin, because of the <br />regulations directed towards zero discharge of brackish water, it would seem <br />unlikely that discharge of concentrated reverse osmosis wastewater would be <br />allowed. <br /> <br />2.4 Cost of Evacoration <br />Evaporation has been mentioned above as the probably procedure for disposal <br />of ion exchange regeneran~ waste. Evaporation may also be considered for <br />disposal of other wastes such as cooling tower blowdown and so a separate <br /> <br />0- <br />.0 <br />