Removal of Pollutants by a Combination of Lime Precipitation Sedimentation and Filtration at Plant Ba

Pollutant (mg/L)

Chromium

Copper

Nickel

Zinc

Iron

Raw Wastewater

5900 170 3300 2900 22900

Treated Effluent

38 11 180 35 400

Percent Removal

95 99 98

Source: U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Aluminum Forming Point Source Category, Vols. 1 & 2, U.S. EPA, Washington, DC, 1984; U.S. EPA, Aluminum Forming Point Source Category, 2008. a Treated effluent performance reported for the period 1974-1979.

processes can be used for separation of the freed oil together with other pollutants from the wastewater. This specific set of treatment data documents the efficiency of the emulsion breaking and ultrafiltration treatment system. Again, Appendix B shows that the preliminary treatment system of emulsion breaking and ultrafiltration can achieve over 90% of O&G, TSS, COD, TOC, benzene, 2,4,6-trichlorophenol, bis-(2-ethylhexyl) phthalate, diethyl phythalate, tetrachloroethylene, and PCB.

Appendix C documents the U.S. EPA data on full-scale treatment of aluminum forming wastewater by chemical precipitation and clarification. It is important to note that Appendixes A and B present the preliminary treatment performance by which main organics are removed. The preliminary treatment step will not remove heavy metals in a significant amount. Accordingly, the system presented in Appendix C is a secondary treatment system following the preliminary treatment step. Appendix C shows that in the secondary treatment system consisting of chemical precipitation, sedimentation clarification can further achieve over 90% removal of oil and grease, and total toxic organics (TTO), such as fluoranthene, methylene chloride, 2,4-dinitrophenol, n-nitrosodiphenylamine, chrysene, and pyrene. Although lead was removed by 69%, the removal of other major heavy metals (chromium, copper, mercury, nickel, and zinc) was insignificant.

Appendix D presents the U.S. EPA data on a full-scale treatment of aluminum forming waste-water by chromium reduction, chemical precipitation, and sedimentation clarification. Chromium reduction, as described in detail by Wang, Hung and Shammas,9 is an important step prior to

Top view

Inlet

Skimmed oil to sump fi I I I Outlet

fi I I I Outlet

Inlet

Outlet

1 Trash trap (inclined rods)

2 Oil retention baffles

3 Flow distributors (vertical rods)

4 Oil layer

5 Slotted pipe skimmer

6 Adjustable overflow weir

7 Sludge sump

8 Chain and flight scraper

Inlet

Outlet

1 Trash trap (inclined rods)

2 Oil retention baffles

3 Flow distributors (vertical rods)

4 Oil layer

5 Slotted pipe skimmer

6 Adjustable overflow weir

7 Sludge sump

8 Chain and flight scraper

FIGURE 5.1 Typical gravimetric API oil-water separator. (Source: Wikipedia Encyclopedia, API Oil-Water Separator, http://en.wikipedia.org/wiki/API_oil-water_Separator.)

chemical precipitation and clarification. The treatment system documented in Appendix D consists of the following:

1. Chromium reduction using sulfuric acid

2. Neutralization and chemical precipitation using lime and/or sodium hydroxide

3. Sedimentation for clarification

http://en.wikipedia.org/wiki/API_oil-water_Separator.)"/>
FIGURE 5.2 Typical parallel plate oil-water separator. (Source: Wikipedia Encyclopedia, API Oil-Water Separator, http://en.wikipedia.org/wiki/API_oil-water_Separator.)

TABLE 5.15

Removal of Pollutants by Sodium Hydroxide Precipitation

Pollutant (mg/L)

Chromium

Copper

Iron

Lead

Manganese Nickel Zinc TSS

Raw Wastewater

Treated Effluent

BDL 17 880 120 0.05 31 12 12,000

Percent Removal

Source: U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Aluminum Forming Point Source Category, Vols. 1 & 2, U.S. EPA, Washington, DC, 1984; U.S. EPA, Aluminum Forming Point Source Category, 2008. BDL, below detection limit. a Approximate value.

It should be noted that dissolved air flotation (DAF) is a more effective process for clarification.8-10 As shown in Appendix D, with an additional step of chromium reduction, the secondary treatment system effectively removed chromium (over 99%), copper (89%), cadmium (64%), lead (67%), and zinc (77%).

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