Adsorptive and Chemical Pretreatment of Reactive ... - ACS Publications

Chapter 7

Adsorptive and Chemical Pretreatment of Reactive Dye Discharges 1

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D. L. Michelsen , L. L. Fulk , R. M. Woodby, and G. D. Boardman Downloaded by UNIV OF NORTH CAROLINA on June 6, 2013 | http://pubs.acs.org Publication Date: February 22, 1993 | doi: 10.1021/bk-1993-0518.ch007

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Department of Chemical Engineering and Department of Civil Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0211

The color from navy cotton reactive cold pad/batch and exhaust/jet dyeing processes using primarily C.I. Reactive Black 5 can be substantially lowered by the use of sorbents, flocculating polymers, reducing agents, and anaerobic biodegradation. Of the reducing agents sodium hydrosulfite, thiourea dioxide, sodium formaldehydesulfoxylate, and sodium borohydride, sodium hydrosulfite is the most economical, but the amount of thiourea dioxide needed to produce the same color change for both effluents is the least. Reduction via anaerobic digestion provides comparable color and increased TOC removal over chemical reduction of pad/batch rinse water. The amounts of sorbents and flocculants needed proved to be expensive and likely too massive for dye house effluents. As the amount of cotton textiles dyed in this country has increased, the amount of color discharged into surface waters has increased. The cotton reactive dyes for the intense and bright colors favored today are difficult to remove from process water because of their high water solubility and chemical stability of the hydrolyzed form in wash waters (7). This leads to residual color in wastewater treatment plant effluents and colored surface waters, which are aesthetically unacceptable, if not toxic. Our studies of color and total organic carbon (TOC) removal have been applied to a dark navy cotton reactive mixture of monoazo and disazo compounds used for dyeing 50/50 or 95/5 cotton/polyester fleece produced by a local textile manufacturer. This shade of navy is named Navy 106 by that plant. The dye mixture, consisting of black, red, and yellow dyes, is applied either by a cold pad /batch process or by an exhaust/jet process. The cold pad/batch dyed knit fabric is rinsed of excess dye and auxiliaries in a slack washer; this washer effluent was used for some of the treatment studies. The polyester in the 50/50 blends is first dyed in a jet machine, washed, and dried before padding. When the cotton of the 50/50 blend fleece is dyed in a jet machine, the polyester is first dyed and washed in the 0097-6156/93/0518-0119$06.00/0 © 1993 American Chemical Society In Emerging Technologies in Hazardous Waste Management III; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

Downloaded by UNIV OF NORTH CAROLINA on June 6, 2013 | http://pubs.acs.org Publication Date: February 22, 1993 | doi: 10.1021/bk-1993-0518.ch007

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EMERGING TECHNOLOGIES IN HAZARDOUS WASTE MANAGEMENT III

same machine. The dye cycle effluent from the cotton dyeing in the jet machine was the other source of samples for treatment. The Navy 106 mixture consists primarily of the bireactive C.I. Reactive Black 5, a disazo dye with two vinyl sulfone reactive groups. Much smaller quantities of a Remazol Red and a Remazol Golden Yellow, both azo dyes from HoechstCelanese, are used to obtain the dark navy shade. C.I. Reactive Black 5, one of the largest selling dyes in the world, is purchased in the salt form (1). Upon mixing in a caustic medium the salt form is converted to the vinyl sulfone or reactive form (2). This vinyl sulfone form can either react with the nucleophilic cotton fiber hydroxyl groups by a Michael type 1-4 addition or hydrolyze in water to form the very water soluble, but colorful, chemically unreactive, hydroxyl form (3) that is quite stable (7). The pollution problem is further complicated by the frequent use of considerable sodium silicate and organic auxiliaries in pad dyeing, or sizeable amounts of sodium chloride, sodium carbonate, or sodium sulfate in jet dyeing to improve the mass transfer of the vinyl sulfone reactive dye molecules to the cellulose active sites. Sorption Studies Since the volume of process water used in textile dyeing operations is so large, one reasonable method of separating and reducing the volume of contaminated material would be sorption (adsorption and/or absorption) of the dye molecules onto a solid or into a liquid that is or can become insoluble. The segregated waste solid or liquid dye concentrate could then be treated by some form of chemical or aerobic oxidation, chemical or anaerobic reduction, and/or incineration to destroy the refractory species. Recycling of the adsorbent might also be possible. The effluent of vinyl sulfone reactive dye bathes and washes contains the hydrolyzed form of this cotton reactive group with a terminal hydroxyl group that permits hydrogen bonding. In a strongly basic environment the hydroxyl group loses a hydrogen ion resulting in negative species, which are electrostatically attracted to cationic or basic functional groups on solids or liquids. This scenario is supported by our laboratory tests. A series of room temperature laboratory tests at pH of 10.4 (the pH of the process water), 7.5, and 4.6 with 22 different solids were conducted in which 20,000 parts per million (ppm or mg/L) adsorbent was placed in the Navy 106 slack washer discharge. These were shaken at room temperature for a day. The ADMI color value and TOC were determined on the treated effluent after filtering through a 1.2 micron glass microfibre filter to obtain a clear liquid. Data from these adsorption studies are shown on Table I. The ADMI color value units were used to evaluate the extent of color removed by the different treatments (2). This ADMI system is more accurate than other color systems because it is somewhat independent of hue (3), but most sensitive to red. To determine the ADMI color value of a liquid, a spectrophotometer is used to measure the percent transmittance of the liquid at 438, 540, and 590 nm. A series of equations using the Adams-Nickerson color difference equation are used to calculate the ADMI value from the transmittances. The treatment performance is

In Emerging Technologies in Hazardous Waste Management III; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


7. MICHELSEN ET AL.

Pretreatment of Reactive Dye Discharges

111

[ΟΙΟ S t r u c t u r e

S t r u c t u r e

of

of

Parent

Vinyl

Remazol

Sulfone

Black

Remazol

Β

Black

Β

S0,CH„CH,0H

OIQ S t r u c t u r e

of

Hydrο

I y ζ βd

Remazol

B l a c k

Β


122


Table I. Removal of Color and TOC from Navy 106 Slack Wash Water Discharge Using Solid Adsorbents, Room Temperature pH = 10.4 Description As is


TM-399

ADMI

TOC

ADMI

4165

274

4486

1752

Wheat bran

2368

Chitosan, sea cure 543

2250 3116

Chitin, VNS-379 (Vanson)

2142 2510

Crab meal

2331 2306

TOC 290

197

99

Rice germ crushed

pH = 4.6

pH = 7.5

306

3060 753

277

1298 mi

4481 65 3097

323

2534 1223 361

ADMI

2228 219

609 923

1650 1305

193

577

1657 1335

410

1937

Ground hydrolyzed pig hair

3902 2944

910

1358

322

3241

Crab meal, treated with HC1, and trypsin

2291 2160

273

1407

222

1063

Sludge, dewatered Blacksburg

2728

1266

1562

695

3986

Partially hydrolyzed human hair

1814

Oat bran

2475

Crab meal (low HC1)

1785 (c)

Peanut shells

3712 3015

4033

1030

3208 1641

3175 385 1044

1657

484

3208 1992

4285 260


7. MICHELSEN ET AL.


123

Table I. Continued

pH = 10.4 Description Chitin, Kodak

ADMI

TOC

ADMI

2418 3397

242

3208 2674

209

1789

2215

620

Meat and bone meal Downloaded by UNIV OF NORTH CAROLINA on June 6, 2013 | http://pubs.acs.org Publication Date: February 22, 1993 | doi: 10.1021/bk-1993-0518.ch007

pH = 4.6

pH = 7.5 TOC

ADMI 1361 2777

Ducon chitosan

2536 (c)

2797

1337

Sea cure 140

2150 (c)

2579

611

Vermiculite

2545

Organic brown rice

2394

White pine needles

3377

Millet

2345

Oxycellulose

2987

4372 874

406

3911

275

2726

4441

445

4225

4093 3983

229

3598

3907 2611



124


then determined by changes in ADMI values before and after treatment. For all our studies, a Bausch & Lomb Spectronic 20 was used to measure the transmittances. Since many of the solid adsorbents tended to disintegrate partially into solution, the net TOC was determined by subtracting the TOC of a filtered reagent blank from the final TOC of the sample. All TOC's were determined by a Shimadzu TOC-5000 total organic carbon analyzer. The tests at pH 7.5 and 4.6 were conducted with Navy 106 slack washer effluent after first decanting to remove the precipitated silicates. In general, the color of the Navy 106 was removed more effectively by sorption as the pH decreased. The product which performed best was TM-399, a bentonite clay modified with a quaternary ammonium surfactant produced by Technical Minerals in Jackson, Mississippi. We were unable to regenerate the TM399 by removing the sorbed dyes with hot water, basic solution, acidic solution, or combinations of these. The natural products which were most effective for color removal are protein based substances such as rice germ, wheat bran, chitosan, chitin, crab meal, hydrolyzed pig hair, and crab meal treated with acid and trypsin to isolate the chitin crudely. While color removal was effective, the dye solution often partially disintegrated the adsorbent so that the TOC after pretreatment was greater than the TOC of the untreated dye wastewater. These tests were conducted within closed containers under more or less anaerobic conditions. The most active anaerobic activity (judged by the foulness of the odors) and color removal occurred in solutions containing crab meal, meat and bone meal, dewatered sludge from the Blacksburg POTW, and pig hair. Earlier testing of color removalfroma number of dye wastes showed pig hair at a concentration of 1 g in 60 mL of dye water readily went anaerobic. Color removal was essentially complete in two days by both anaerobic reduction and sorption. Color removals from the slack wash water as a function of ppm sorbent are shown in Figure 1 for TM-399, activated carbon (BL Pulverized from Calgon Carbon Corp.), chitosan (Sea Cure 543), and pure chitin (VNS-379). A carbon dosage of about 2500 ppm changed the colorfrom4100 to 900 ADMI units. These products are all too expensive to use and are required in excessive quantities. Even at an estimated $0.10 per pound, impure chitin from crab meal represents an unappealing choice. A total of 12,000 ppm would be needed for 56% color removal, or 100,000 lb at a cost of $10,000 per million gallons of slack water treated. A sample of navy jet dye bath effluent was diluted 1 to 20. The pH was lowered from 11.8 to 7.0 with hydrochloric acid. The resulting solution was agitated with varying amounts of activated alumina (Fisher), activated carbon (BL Pulverized from Calgon Carbon Corp.), TM-399, and chitosan (practical gradefromcrab shells, Sigma). The initial and final ADMI color values are plotted in Figure 2. Activated carbon performed best with color changes of 4000 to 1500 ADMI color units with a dosage of 150 ppm, and changes of 4000 to 5 ADMI with a dosage of 2500 ppm. Alumina and the TM-399 yielded similar results. In this test chitosan was the poorest performer. However, Smith and Hudson found that crab shell derivatives with up to 80% chitosan rapidly adsorbed all color from dye bathes of all classes except the basic ones (4).


7.


MICHELSEN ET AL.

125

5000

Ο Activated c a r b o n • T M - 3 9 9 sorbent V Chitosan • Chitin

4000

D >

3000


_o Ο Ο

2000

Ο • .

Adsorptive and Chemical Pretreatment of Reactive ... - ACS Publications

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