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<br />~.... <br />en <br />Ul <br />w <br /> <br />2.8.2 <br /> <br />Disoosal <br /> <br />~s indica~ed on Figure 2-1, most plans do not include disposal of blowdown <br />to ~he river. Current and proposed regulations in the ColoradO River Basin are <br />directed towards zero discharge. The Lurgi designs of E1 paso)2 and wesco33 do <br />not have any effluent discharges. The usual plant will use blowdown to wet <br />down the coal ash for disposal and will try to control the cooling system ~o <br />ensure that the plant stays in balance. Por the example shown in Figure 2-2, <br />the cooling tower was operated in such a way as to use all of ~~e blowdown fer <br />ash disposal. <br />For the purposes of this study, we do not count the ultL~ate disposal <br />procedure relevant. 1f, for any chosen disposal procedure, the blowdcwn is <br />too dirty or teo salty, then additional treatment is needed. <br /> <br />2. a. 3 <br /> <br />Treatments ~~d Costs <br /> <br />Because cooli~g tower blowdown is supersaturated, t~e ~05t probable <br />procedure for ~ re~oval is evaporation. If forced eva?oration is used, ~~e <br />organic ~atter will distill wi~~ ~~e water and if this is not good enough, it <br />must be ra~oved, probably before ~~e evapora~or. Impounernent and natural <br />evaporation is also possible~ The flow rate of blowdown is ~'e same as the <br />flow rate of ion exchange waste and the discussion for ion exchange was~e <br />applies. Here again, if organic contamination of the pond ~esidue is unacceptable, <br />then organic ~emoval is required~ At this time we do not know what level cf <br />organic ccntam~nation is unacceptable. <br />Consider ~~e organic removal possibilities, one-by-one, basing the dis~~ssion <br />on 1000 gals of blowdown. <br />Biolcoical treatmen~ will probably be functional in the blowdown stream. <br />However, there will be present biocides to cor.trol sli~e i~ t~e cooling system <br />and these may interfere or render smooth operation difficult~ It is possi~le, <br />but not probable, that the high salt concentration will interfere. More <br />important is the fact that biological treatnent removes BOD and not COD. In <br />an activated sludge process, non-biodegradable contamination is removed by <br />adsorption onto the sludge. Probably this will happen much less in the cooling <br />tower and ~~e ratio COD/BOD will be higher in the blowdown than in the makeup. <br />Consequently, biological treatment should probably be placed in the makeup. <br />If this were done 3000 to 7000 gals would have to be treated per 1000 gals of <br />blowdown at a cost of $2.4 to S5.6/1000 gals blowdown (= $782 to $1826/acre-:tl. <br />We can say lit~le about the quality of the effluent water, but we expect it to <br />be medium good. <br /> <br />46 <br />