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- Membrane

Y Solution of (B)

FIGURE 7.7 Schematic of membrane ultrafiltration process. [From U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Coil Coating Point Source Category (Canmaking Subcategory), Final report 440/1-83/071, Washington, DC, November 1983; U.S. EPA, Coil Coating Forming Point Source Category, available at http://www.access.gpo.gov/nara/cfr/waisidx_03/40cfr467_03.html, 2008.]

TABLE 7.16

Removal of COD, TSS, TS, and Oil and Grease from Coil Coating Wastewater by Ultrafiltration

Parameter Feed (mg/L) Permeate (mg/L)

Oil (freon extractable) 1230 4

COD 8920 148

TSS 1380 13

Total solids 2900 296

Source: U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Coil Coating Point Source Category (Canmaking Subcategory), Final report 440/1-83/071, Washington, DC, November 1983; U.S. EPA, Coil Coating Forming Point Source Category, available at http:// www.access.gpo.gov/nara/cfr/waisidx_03/40cfr467_03.html, 2008.

TABLE 7.17

Removal of Heavy Metals from Coil Coating Wastewater by Membrane Filtration

Manufacturers' Specific Metal, mg/L Guarantee

Plant 19066

Plant 31022

Aluminum Chromium6+ Chromium (total) Copper

0.01

0.018

0.043

Predicted Performance

TABLE 7.17 (continued)

Manufacturers' Predicted

Specific Metal, mg/L Guarantee Plant 19066 Plant 31022 Performance

TABLE 7.17 (continued)

Manufacturers' Predicted

Specific Metal, mg/L Guarantee Plant 19066 Plant 31022 Performance

Iron

0.1

288

0.3

21.1

0.263

0.30

Lead

0.05

0.652

0.01

0.288

0.01

0.05

Cyanide

0.02

<0.005

<0.005

<0.005

<0.005

0.02

Nickel

0.1

9.56

0.017

194

0.352

0.40

Zinc

0.1

2.09

0.046

5.00

0.051

0.10

TSS

632

0.1

13.0

8.0

1.0

Source: U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Coil Coating Point Source Category (Canmaking Subcategory), Final report 440/1-83/071, Washington, DC, November 1983; U.S. EPA, Coil Coating Forming Point Source Category, available at http://www.access.gpo.gov/nara/cfr/ waisidx_03/40cfr467_03.html, 2008.

Source: U.S. EPA, Development Document for Effluent Limitations Guidelines and Standards for the Coil Coating Point Source Category (Canmaking Subcategory), Final report 440/1-83/071, Washington, DC, November 1983; U.S. EPA, Coil Coating Forming Point Source Category, available at http://www.access.gpo.gov/nara/cfr/ waisidx_03/40cfr467_03.html, 2008.

6. The type of clarification used comprises eight sedimentation tanks (note: dissolved air flotation can also be used for clarification).

7. The sedimentation hydraulic detention time is 3.9 h.

8. The sedimentation hydraulic loading rate is 733 L/h/m2.

9. The operation mode is continuous, 24 h/d. 10. The pollutant removal data are as follows:

Initial Concentration Reduction (%)

TSS

34 mg/L

82

Iron

2 mg/L

50

Tin

0.02 mg/L

55

Oil and grease

20 mg/L

10

Cobalt

0.5 mg/L

60

Cadmium

8 mg/L

99

Lead

200 mg/L

>99

1,1,1-Trichloroethane

2400 mg/L

88

Trichloroethylene

2700 mg/L

93

1,1-Dichloroethylene

530 mg/L

87

1,2-irans-Dichloroethylene

16 mg/L

38

Ethylbenzene

2 mg/L

>99

Isophorone

170 mg/L

35

Tetrachloroethylene

4 mg/L

50

Toluene

29 mg/L

83

7.8.11 Full-Scale Wastewater Treatment Case History: Galvanized Subcategory

A full-scale wastewater treatment plant system has performed well for treatment of the wastewater generated from coil coating galvanized subcategory operations. The process principles and operational data of the full-scale treatment of a galvanized subcategory wastewater are summarized as follows:

1. The process flow diagram consists of chromium reduction, chemical precipitation, and clarification.

2. The sources of theories and principles for chromium reduction using an acid, chemical precipitation using a base, and clarification can be found in Refs. 8 to 10.

3. The flow rate of the wastewater treatment facility is 174,000 m3/d.

4. The acid used for chromium reduction is sulfuric acid.

5. The base used for neutralization and chemical precipitation is lime (note: sodium hydroxide can also be used for neutralization and chemical precipitation).

6. The type of clarification used comprises eight sedimentation tanks (note: dissolved air flotation can also be used for clarification).

7. The sedimentation hydraulic detention time is 3.9 h.

8. The sedimentation hydraulic loading rate is 733 L/h/m2.

9. The operation mode is continuous, 24 h/d. 10. The pollutant removal data are as follows:

Initial Concentration Reduction (%)

TSS

170 mg/L

88

Iron

44 mg/L

96

Aluminum

1.8 mg/L

62

Oil and grease

54 mg/L

61

Manganese

0.38 mg/L

76

Copper

14 ^g/L

>99

Chromium

1300 ng/L

92

Lead

260 ng/L

>99

Zinc

2000 ng/L

95

1,1,1-Trichloroethane

3100 ng/L

19

Trichloroethylene

3800 ng/L

21

1,2-trans-Dichloroethylene

34 ^g/L

44

7.8.12 Full-Scale Wastewater Treatment Case History: Aluminum Subcategory

A full-scale wastewater treatment plant system has performed well for treatment of the wastewater generated from coil coating aluminum subcategory operations. The process principles and operational data of the full-scale treatment of the aluminum subcategory wastewater are summarized as follows:

1. The process flow diagram consists of chromium reduction, chemical precipitation, and clarification.

2. The sources of theories and principles for chromium reduction using an acid, chemical precipitation using a base, and clarification are detailed in Refs. 8 to 10.

3. The flow rate of the wastewater treatment facility is 3930 L/d.

4. The acid used for chromium reduction is sulfuric acid.

5. The base used for neutralization and chemical precipitation is sodium hydroxide (note: lime can also be used for neutralization and chemical precipitation).

6. The type of clarification used consists of tube plate settlers (note: dissolved air flotation can also be used for clarification).

7. The operation mode is continuous, 24 h/d.

8. The pollutant removal data are as follows:

Initial Concentration

TSS Iron

Phosphorus Oil and grease

93 99

Initial Concentration

Phenol, total

Aluminum

Manganese

Cadmium

Chromium

Copper

Nickel

Zinc

Lead

Bis(2-ethyhexyl)phthalate

Diethyl phthalate

Hexavalent chromium

330,000 ng/L

96 99

7.9 WASTEWATER TREATMENT LEVELS VERSUS COSTS

The investment cost, operating and maintenance costs, and energy costs for the application of control technologies to the wastewater of the coil coating industry have been analyzed. These costs were developed to reflect the practical application of technologies in this industry. A detailed presentation of the cost methodology and cost data is available in the literature.119

Application of the wastewater treatment technologies can fall into one of the following legal categories:

1. The best practicable control technology (BPT) currently available under the U.S. Federal Act Section 304(b)(1)

2. The best available technology (BAT) economically achievable under the U.S. Federal Act Section 304(b)(2)(B)

3. The best conventional pollutant control technology (BCT), under U.S. Federal Act Section 304(b)(4)

The available industry-specific cost information is characterized as follows. Unit operation/unit process configurations have been analyzed for the cost of application to the wastewater of this industry. Recommended unit process configurations for BPT and BAT levels of treatment and their costs are summarized briefly in the following sections.

7.9.1 BPT Level Treatment

7.9.1.1 Suggested BPT

The BPT treatment train for the steel, galvanized, and aluminum subcategories of wastewater consists of chemical oxidation of cyanide and chemical reduction of chromium for cyanide- and chromium-bearing wastestreams; oil skimming, chemical precipitation with lime, and sedimentation of combined wastestreams; and a vacuum filter to dewater sludge. For the purpose of cost estimates, cyanide oxidation was assumed to be a required treatment process only for the aluminum subcategory, because of the presence of cyanide in the chromating bath applied to aluminum. Chromium reduction was included in the system costs for all subcategories to treat chromium wastes from the chromic acid sealer and conversion coating rinses, where appropriate.

7.9.1.2 System Component of the Suggested BPT

Cyanide oxidation consists of a reaction with sodium hypochlorite under alkaline conditions in either a batch or continuous system. A complete system includes reactors, sensors, controls, mixers, and chemical feed equipment. Chromium reduction consists of reaction with sulfur dioxide under acid conditions for continuous systems and reaction with sodium bisulfite under acid conditions for batch systems. A complete system consists of reaction tanks, mixers and controls, and chemical feed equipment. Oil is separated from process wastewater by gravity in a baffled rectangular concrete tank and removed by a skimming device. Chemical precipitation and sedimentation may be by either a continuous or batch treatment system. A continuous system includes chemical storage and feeding equipment, a mix tank for reagent feed addition, a flocculator, and settling tank with associated equipment. A batch treatment system consists of dual tanks and chemical storage and feeding equipment.

7.9.1.3 Unit Cost of the Suggested BPT

Total annual unit costs consisting of annual cost of capital, depreciation, operation and maintenance cost, and energy cost for medium, low, and high flow rates are summarized in Table 7.18.

7.9.2 BAT Level of Treatment

7.9.2.1 Suggested BAT

The BAT level of treatment consists of all components of BPT except segregation and recirculation of quench wastewater. The combined wastewater after sedimentation is treated in multimedia filters and then discharged.

7.9.2.2 System Components of the Suggested BAT

Quench waste recirculation requires installation of a cooling tower to lower the temperature of the quench wastewater stream. The multimedia filter system for the final polishing of effluent includes a backwash mechanism, pumps, control media, and the filter structure.

7.9.2.3 Unit Cost of the Suggested BAT

Total annual unit costs for the complete BAT system, which includes components described in the BPT system for the three different flow rates, are summarized in Table 7.19.

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