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<br />~.."" <br />en <br />w:::.. <br />M':>o <br /> <br />be ~he most economical of the processes we have studied. A PH05h~-W plant for <br />the exemplar! Lurgi stream would require about $107 of equipment (installed), <br />consume 1.6 lb steam per gal wastewater treated, and have a cooling water <br />consumption (by evaporation) of 0.1 gal per gal wastewater treated. Cooling <br />water consumption can be reduced by 60\ by using air coolers, but a~ additional <br />capital cost. The total operating cost is $7.4 x 106 per year, or $7.80/1000 <br />gals of feed water, or 9.4~/106 Stu product output6 Credit for ammonia sales <br />cover the cost of this treatment. <br />The same column can yield a product water having about 14 ppm ammonia if <br />the stripping steam rate is doubled at an additional cost of about $2.7/1000 <br />gals. As stated in the preceding section, we have not studied t~is aspect. <br />The additional cost of $2.7/1000 gals is a maximum. It may be cheaper to use <br />a larger column and less steam or to follow stripping with biological nit~i2ication. <br /> <br />Solvent Extraction <br /> <br />In solvent extraction a solvent is intimately mixed with t~e ~aste~ater <br />in contacting devices in ~hich the phenols are transferred to the solvent <br />phase. The mixture ~~en enters settlinq vessels to separate the solvent and <br />~ater streams. Several stages are required eo achieve adequate phenol removal. <br />As a typical example, ~~o trains of six mixer settler stages each plus solvent <br />recovery ~quipment costing $14.6 x 106 (installed) are required to remove 99\ <br />6 <br />of the phenol from a 2,000 gpm, 6,000 ppm phenol wastewater stream. Such a <br /> <br />stream could oe obtainec from a Lurgi commercial scale qasification plan~~ <br />maintenance amounts to $2.93 ~ 106 per <br /> <br />The cost in capital <br /> <br />inves t:nen t and <br />6 <br />gals treated . <br /> <br />Costs are not dependent on influent concent~a~ion, <br /> <br />year, or $2.80/1000 <br /> <br />but costs can be decreased by reducing the removal efficiency. The lowest <br />acceptable removal efficiency, as determined by both water reuse and environmental <br />constraints. is not known. <br /> <br />At 80' efficiency only one or two theoretical stages are required, and <br />the number cf stages is not strongly dependent on the distribution coefficient <br />of the solvent. At 99' efficien~ll six to seven theoretical stages are <br />required, al~~ough these can be reduced either by increasing the amount of <br />solvent used. or by using a solvent with a higher distribution coef:icien~. <br />As the solvent distribution coefficient is increased, the number of stages <br />and/or the amount of solvent for a given removal efficiency can be decreased. <br /> <br />39 <br />