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Pollution Prevention and Control Technologies for Plating Operations
Section 2 - General Waste Reduction Practices
2.5 RINSEWATER REDUCTION
The results of the Users Survey show that many plating shops have made significant strides in reducing water use. Sixty-eight percent of the respondents indicated that they have reduced flows by implementing pollution prevention. For shops that were able to quantify their achievements, the average flow reduction was approximately 20,000 gpd (or about 30%). Some shops were reluctant to make estimates of flow reduction because process and production changes that have occurred during the same time period make such estimates difficult (includes at least 19 shops). The following shops achieved the most dramatic flow reductions (all of these shops reduced their flows by 50,000 gpd or more or by 90% or more) (shown are the original and current flow rates and the year of the original flow rate data):
- PS 022: from 140,000 gpd to 70,000 gpd (50% reduction since 1980)
- PS 036: from 52,700 gpd to 2,700 gpd (95% reduction since 1978)
- PS 059: from 90,000 gpd to 10,000 gpd (89% reduction since 1977)
- PS 118: from 232,630 gpd to 42,630 gpd (82% reduction since 1983)
- PS 139: from 127,000 gpd to 52,000 gpd (59% reduction since 1986)
- PS 150: from 400,000 gpd to 100,000 gpd (75% reduction since 1986)
- PS 172: from 150,000 gpd to 70,000 gpd (53% reduction since 1975)
- PS 184: from 121,000 gpd to 11,000 gpd (91% reduction since 1982)
- PS 207: from 68,000 gpd to 18,000 gpd (74% reduction since 1986)
- PS 213: from 130,000 gpd to 50,000 gpd (62% reduction since 1985)
- PS 250: from 91,000 to 11,000 gpd (88% reduction, base year not given)
- PS 268: from 87,000 gpd to 17,000 gpd (80% reduction since 1987)
- PS 292: from 160,000 to 60,000 gpd (63% reduction since 1985)
- PS 296: from 1,900,000 gpd to 1,700,000 gpd (11% reduction, base year not given)
- PS 298: from 160,000 gpd to 90,000 gpd (70% reduction since 1990)
- PS 309: from 25,000 gpd to 1,450 gpd (94% reduction since 1984)
A summary of the Users Survey data relative to methods for reducing rinse water use is presented in Exhibit 2-16.
Although the plating industry as a whole has significantly reduced water use during the past 10 to 15 years, many plating operations can further reduce water use by improving the efficiency of their rinsing operations. The advantages of reducing water use include: (1)Êlowering operating costs by reducing the size of water bills; (2) reducing the quantity of treatment chemicals used (treatment chemical use is mostly dependent on the mass of contaminants, but a portion of treatment chemical use is related to hydraulic loading (see Section 6 which covers end-of-pipe treatment); (3) potentially improving the removal efficiency of waste treatment systems; and (4) reducing the needed size of future end-of-pipe treatment systems and certain types of recovery technologies.
Central to the reduction of rinse water use is the required quality of water used in rinsing. Simply reducing the flow rate of water in a rinse system, without regard to water quality, may cause loss of plating quality or appearance or it may cause the contamination of the next tank in the plating sequence. Various rinse water quality criteria are presented in the literature. These are discussed in Section 2.5.3.1.
Various methods of water use reduction have been identified in the literature and throughout the Users Survey. These methods have been categorized into three groups: (1) optimizing the rinse tank design; (2) controlling the rate of rinse water use; and (3) using alternative rinsing configurations. The following is a discussion of each group.