Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 256 of 331

organic materials, such as alum or ferrous sulfate, or organic polymers, or some combination of the two; 4. The precipitated solids are pumped from the clarifier to a secondary system for further dewatering; the dewatering system may be anything from a sludge consolidation pit to a plate and frame filter press. The waste treatment system allows suspended solid pollutants to settle out of the water stream for collection and, in addition, can remove dissolved, dispersed, or otherwise-distributed contaminants by treating them (typically chemically) to separate them from the water in the waste stream. Examples of these contami- nants include oils and greases dispersed by surfactants and metals made soluble by chelants. Once these dispersed materials have been "destabilized," the normal methods of collection in the waste treatment system allow the "solids" to settle out. Other additives such as polymers are added to increase the settling rate of the "solids" by increasing the density/weight of the particles. The net result is the removal of all materials infiltrating the water stream from the point of entering the facility to the point of leaving it. With the ever-increasing regulations con- cerning the contents of discharged water, it may often be the case that the effluent water is of a higher overall quality than the influent. These systems can be run effectively with a minimum of effort on the part of the organic finisher by rec- ognizing what pollutants enter the stream within the plant and how each impacts the treatment program. By working with the various chemical suppliers within the functional areas, problems of treatment for the finisher should be mini- mized and discharge limits in all areas easily met. 255

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