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Evaporation- A Wastewater Treatment Alternative Page 1 of 5 <br /> Storm Water Solutions <br /> Published on Storm Water Solutions (hfp://www.estormwater.com) <br /> Home>Printer-friendly <br /> Evaporation - A Wastewater Treatment <br /> Alternative <br /> Submitted by kherda on December 28, 2000 <br /> Evaporation is being considered as an alternative process in an increasing number of <br /> wastewater treatment applications. It can be effective for concentrating or removing salts, <br /> heavy metals and a variety of hazardous materials from solution. Also, it may be used to <br /> recover useful by-products from a solution, or to concentrate liquid wastes prior to <br /> additional treatment and final disposal. Most applications of the technology also produce a <br /> high quality, reusable distillate-a very important feature where water conservation is a <br /> priority. <br /> During evaporation, a solution is concentrated when a portion of the solvent, usually <br /> water, is vaporized, leaving behind a saline liquor that contains virtually all of the dissolved <br /> solids, or solute, from the original feed. The process may be carried out naturally in solar <br /> evaporation ponds, or through the use of commercially available evaporation equipment. <br /> Solar evaporation ponds usually are limited by land availability and cost, potential odor <br /> problems, or meteorologic and climatological conditions, whereas mechanical evaporators <br /> are relatively compact, reliable and efficient. <br /> Design and Operation <br /> The evaporation process is driven by heat transferred from condensing steam to a <br /> solution at a lower temperature across a metallic heat transfer surface. The absorbed heat <br /> causes vaporization of the solvent, usually water, and an increase in the solute <br /> concentration. The resulting vapor may be vented to the atmosphere, or condensed for <br /> reuse. <br /> Mechanical evaporation is an energy-intensive way to concentrate liquids, and various <br /> energy alternatives should be considered in the selection of the most efficient evaporator. <br /> In an ideal system, one kilogram of condensing steam will evaporate one kilogram of <br /> water from the solution. Such a system has a steam efficiency, or economy, of 1:1 (1 kg of <br /> water removed for every kg. of steam applied). A simple evaporator system (Fig 1) has a <br /> single evaporation chamber, or effect, and is said to have an "economy of one." <br /> Evaporator economy can be increased by increasing the number of effects. A multiple <br /> effect system (Fig 2) uses the vapor from the first effect as the steam source for each <br /> subsequent effect. As the temperature decreases in each succeeding stage, evaporation <br /> continues because the pressure and boiling point also are reduced. <br /> http://www.estormwater.com/print/4458 11/28/2012 <br />