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Pollution Prevention and Control Technologies for Plating Operations


Section 2 - General Waste Reduction Practices

2.6 REUSE OF TREATED RINSEWATER

Some shops responding to the Users Survey indicated that they reuse treated wastewater in their rinse tanks. Most of the reported reuse of treated wastewater is practiced at shops with conventional treatment (i.e., hydroxide precipitation) (PS 054, PS 091, PS 109, PS 123, PS 128, PS 199). This reuse is generally done in non-critical rinses (e.g., PS 199 reuses effluent in rinses following alkaline soak cleaners and acid dips). Some shops filter the treated wastewater before reusing it (e.g., PS 123 pumps it through a sand filter). Two shops reused the filtrate from a filter press as rinse water (PS 109 and PS 168).

Those contemplating the reuse of chemically treated water should be cautioned that a hydroxide precipitation process generates an effluent that is high in dissolved solids (e.g., sodium) that will contaminate subsequent process tanks. More extensive treatment is needed to produce a suitable quality of water for most rinsing needs. For example, two shops responding to the Users Survey reuse treated water after: (1) hydroxide precipitation/ion exchange (PS 068) and (2) hydroxide precipitation/ultrafiltration/reverse osmosis (PS 233). Ion exchange is generally not a good choice of technology for recycling treated wastewater. The treated wastewater will contain a high concentration of anions that must be removed to produce a reasonable water quality. Applications of ion exchange recycling are discussed in Sections 3.4 and 6.5.2. Membrane filtration, a viable option for effluent recycling, is discussed in Section 6.5.3.


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