Raw Materials and Wastes for Dyeing and Printing
Processes
Table 9 shows the auxiliaries required for
different dyes and Table 8 shows the amount of water
used and liquor rations of dyeing machines.
Wastewater generation from a typical dyeing
facility is estimated at 3800 to 7500 m3
per day. Including the dyeing, post scouring and
rinsing processes, approximately 100 to 150 m3
of wastewater per tonne of product are produced for
disperse dyeing, while 125 to 170 m3 per
tonne is more typical for direct and reactive dyeing.
The primary source of wastewater is spent dyebath
and washwater, which contain by-products (hydrolyzed
dye), some intact dye, and auxiliary chemicals. In
addition to process water and chemicals, a major
source of toxic pollutants in wastewater is cleaning
solvents used in dyeing and printing machine cleaning,
such as oxalic acid, hydrochloric acid and carbon
tetrachloride.
With the abundance of individual dyes and the wide
range of dyeing equipment in use today, it is
difficult to summarize waste stream characteristics.
In general, wastewater from batch dyeing is high in
volume and pollutant load, and tends to contain heavy
metals, aromatics, and halogenated hydrocarbons from
the dyebath makeup. All are toxic to aquatic life. In
addition to the dyestuff itself, many auxiliary
chemicals are used to aid in dye transfer; the
majority of these chemicals, including unreacted
color, are discharged with the spent bath
Table 8: Water Use
and Liquor Rations of Dyeing Machines
| Dyeing Machine |
Water consumption (m3/tonne) |
Liquor/goods ratio |
| Continuous |
137 |
1:1 |
| Beck |
234 |
17:1 |
| Jet |
200 |
12:1 |
| Jig |
100 |
5:1 |
| Beam |
167 |
10:1 |
| Package |
184 |
10:1 |
| Paddle |
292 |
40:1 |
| Stock |
167 |
12:1 |
| Skein |
250 |
17:1 |
As mentioned earlier, dyes and
auxiliaries used in printing are similar to those
used in fabric dyeing. However, the colour
application techniques are quite different. In the
most commonly used technique, pigment printing, the
main source of waste is from the cleanup, during
which unused printing paste is removed from the
screen. Consequently, proper planning of paste use
and housekeeping are major issues in minimizing waste
in printing operations. Volatile organic compounds
from the paste composition are generated. Table 11
gives, according to reference 33, the characteristics
of a typical textile fabric printing run,
characteristics for different printing equipment and
sources of mineral spirit emissions.
Table
9: Auxiliaries Required for Satisfactory Dyeing
| Chemical Auxiliary |
Acid |
Direct |
Basic |
Disperse |
Mordant |
Premetalized |
Reactive |
Sulfur |
VAT |
| Acetic acid |
x |
|
x |
x |
x |
x |
x |
(1) |
x |
| Ammonium acetate |
x |
|
|
|
|
|
|
|
|
| Ammonium phosphate |
x |
|
|
|
|
|
|
|
|
| Ammonium sulphate |
x |
|
|
|
x |
x |
|
|
|
| Aromatic amines |
|
x |
|
|
|
|
|
|
|
| Buffer |
|
|
|
|
|
|
x |
|
|
| Defoamer |
|
|
|
x |
|
|
|
|
|
| Dispersing agents |
|
|
|
x |
|
|
|
|
|
| Formic acid |
x |
|
x |
|
x |
x |
|
|
|
| Gelatin |
|
|
|
|
|
|
|
|
x |
| Hydrochloric acid |
|
x |
|
|
|
|
|
|
|
| Hydrogen peroxide |
|
|
|
|
|
|
|
x |
x |
| Leveling or retarder
agents |
x |
|
x |
x |
|
|
|
|
x |
| Oxalic acid |
|
|
x |
x |
|
|
|
|
|
| Penetrating agents |
|
|
|
|
x |
x |
|
|
|
| Potassium dichromate |
|
|
|
|
x |
x |
|
|
|
| Sequestering agents |
|
x |
|
x |
|
|
|
|
|
| Sodium acetate |
|
|
x |
|
|
|
|
|
|
| Sodium carbonate |
|
x |
|
|
|
|
x |
x |
|
| Sodium chloride |
|
x |
|
|
|
|
x |
x |
|
| Sodium dichromate |
|
|
|
|
x |
x |
x |
|
|
| Sodium hydrosulfite |
|
|
|
|
|
|
x |
|
x |
| Sodium hydroxide |
|
|
|
|
|
|
|
|
x |
| Sodium nitrate |
|
x |
|
|
|
|
|
|
|
| Sodium Sulfate(2) |
x |
|
x |
|
x |
x |
|
|
|
| Sodium sulfide |
|
|
|
|
|
|
x |
|
|
| Soluble oil |
|
|
|
|
|
|
|
x |
|
| Sulfuric acid |
x |
|
|
x |
x |
|
|
|
|
| Urea |
|
x |
|
|
|
x |
|
|
|
| Wetting agent |
|
x |
|
|
|
|
|
|
|
Table 10:
Application Calls and Suitability for Natural and
Synthetic Fibers
| Dye Class |
Wool |
Cotton |
Cellulose Derivatives |
Polyamide |
Polyester |
Acrylics |
| Basic |
x |
x |
x |
x |
x |
x |
| Direct |
|
x |
|
|
|
|
| Sulfur |
|
x |
|
|
|
|
| Azoic |
|
x |
x |
|
|
|
| Ingrain |
|
|
|
|
x |
|
| Vat |
|
x |
x |
|
|
|
| Acid Leveling |
x |
|
|
x |
|
|
| Acid milling |
x |
|
|
x |
|
|
| Mordant |
x |
(x) |
|
x |
|
|
| Metal Complex |
x |
|
|
x |
|
x |
| Disperse |
|
|
|
x |
|
x |
| Reactive |
(x) |
x |
x |
x |
x |
|
| Pigment |
|
|
|
x |
x |
x |
X=suitable; (X)=of secondary
importance. Pigments may be applied to any substrate
by the use of adhesives.
Table
11: Typical Textile Fabric Printing Run
Characteristics (1) and Sources of Mineral Spirit
Emissions from a Typical Textile Fabric Printing
Run
| |
|
Roller
|
Rotary
Screen |
Flat
Screen |
| |
Units |
Range |
Avg. |
Range |
Avg. |
Range |
Avg. |
| Characteristics
of the run |
| Wet Pickup Rate(1) |
Kg/Kg |
0.51-0.58 |
0.56 |
0.10-1.89 |
0.58 |
0.22-0.83 |
0.35 |
| Fabric Weight (2) |
Kg/m2 |
|
0.116 |
|
0.116 |
|
0.314 |
| Mineral Spirits added to
print paste |
weight % |
0-60 |
26 |
0-50 |
3 |
|
23 |
| Print Paste used in run (3)
|
Kg |
673-764 |
741 |
137-2497 |
764 |
787-2975 |
1254 |
| Mineral Spirits used in
run (4) |
Kg |
0-458 |
193 |
0-1249 |
23 |
181-684 |
288 |
| Source
of emissions |
| Wasted mineral spirits (potential
water emissions) (5) |
Kg |
0-28 |
12 |
0-77 |
1 |
11-42 |
18 |
| Overprinted mineral spirit
fugitives (6) |
Kg |
0-16 |
7 |
0-44 |
1 |
6-24 |
10 |
| Tray and barrel fugitives
(7) |
Kg |
0-1 |
1 |
0-4 |
0 |
1-2 |
1 |
| Flashoff fugitives (7) |
Kg |
0-7 |
3 |
0-19 |
0 |
3-10 |
4 |
| Dryer emissions (7) |
Kg |
0-405 |
170 |
0-1105 |
21 |
160-606 |
255 |
Length of run=10,000 m, fabric width=1.14
m, total fabric area=11,400 m2,
line speed=40 m/min, distance, printer to oven = 5 m.
(1) Wet pickup ratio is a method of yield
calculation in which mass of print paste consumed is
divided by mass of fabric used.
(2) Only average fabric weight is presented.
(3) Print paste used per fabric area
multiplied by area of fabric printed.
(4) Print paste used in run multiplied by
mineral spirits added to print paste, weight percent.
(5) Estimate provided by industry contact.
(6) Estimated on the basis of 2.5cm of
overprint on each side of fabric.
(7) Emission splits calculated from
percentages provided by evaporation computations.