United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-84-100 July 1984
SER& Project Summary
Investigation of Textile Dyebath
Reconstitution and Reuse
Jon F. Bergenthal and Anthony J. Tawa
About 80% of textile finishing mills
discharge their wastewater to publicly
owned treatment works. Most of the
wastewater receives little or no pre-
treatment before discharge. A variety of
wastewater recycle/reuse technolo-
gies, allowing these mills to reduce the
amount of wastewater and pollutants
discharged, were described in an earlier
(Phase I arid II) report.
This two-volume (Phase III) report
examines in detail one of these recycle
technologies, dyebath reconstitution
and reuse. This technology is considered
promising for several reasons: signifi-
cant environmental benefits, potential
for widespread application, low capital
cost, cost savings in textile dyeing,
and economic attractiveness.
Volume 1 gives results of a detailed
investigation of dyebath reconstitution
and reuse at a carpet mill. The results of
bench-, pilot-, and full-scale testing are
presented. Wastewater data document-
ing the pollutant reductions achieved
through dyebath reuse are presented.
The economic feasibility of implement-
ing the technology full-scale is addressed.
Volume 2 gives detailed procedures
and methods for implementing dyebath
reconstitution and reuse. It can be used
as an operations manual for other mills
wishing to investigate this technology.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
Over 100 x 10'
wastewater is discharged annually in the
gal. (3.8 x 10s m3) of
U.S. from the finishing of textile products.
An estimated 80% of textile finishing
mills discharge their wastewater to
publicly owned treatment works (POTWs).
Most of this wastewater receives either
no treatment or only primary treatment
(e.g., settling, screening, equalization, or
neutralization) before being discharged to
municipal sewers.
Major textile finishing operations
include fiber preparation (desizing,
scouring, mercerizing, bleaching), fiber
coloring (dyeing, printing), and functional
finishing. Wastewater results primarily
from preparation and coloring.
Many wastewater recycle/reuse tech-
nologies, allowing reuse of these waste-
waters, are described in detail in an ear-
lier report. One of these technologies,
dyebath reconstitution and reuse, ap-
pears to offer significant environmental
benefits and substantial cost savings to
the industry, and also has the potential
for widespread use within the industry.
This report investigates dyebath reconsti-
tution and reuse in detail.
Textile Dyeing
The vast majority of textile products are
colored by dyeing. In 1980, about 7.8 x
109 Ib (3.5 x 109 kg) of fibers were dyed.
For this dyeing, 171 x 106 lb(7.8x 10* kg)
ofdyestuffsand1.28x109lb(5.8x108kg)
of additives (auxiliary chemicals) were
used. Most auxiliary chemicals do not
exhaust during dyeing and are thus
discharged with the dyeing wastewater.
Dyestuffs, however, generally exhaust to
over 90% during dyeing. The often quoted
value for average dyestuff exhaustion
during dyeing is 95%. Assuming a 95%
exhaustion rate for the dyestuffs still
leaves about 8.5 x 106 Ib (3.9 x 106 kg) of
dyestuffs discharged annually in dyeing
wastewater.
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Dyeing can involve either continuous
or batch operations. About half of the
textile fibers dyed in the U.S. are batch
dyed. Certain products (e.g., knit fabrics,
hosiery, and yarn) are almost exclusively
dyed using batch processes. Large
amounts of carpet and some woven
fabrics are also batch dyed. Batch dyeing
remains popular due to its flexibility,
short-run capability, and ease of control.
Batch processes, however, are generally
inefficient in their use of water and auxil-
iary chemicals.
In typical batch dyeing, 1 -5 gal. (0.004-
0.02 m3) of water is used as dye liquor for
each pound (0.45 kg) of fiber dyed.
Auxiliary chemicals and dyes are added to
this dye liquor. Auxiliary chemicals can
include exhaust agents, leveling agents,
buffers, pH control chemicals, retarding
agents, wetting and dispersing agents,
carriers, softeners, lubricants, and pene-
trants. The total amount of auxiliary
chemicals added will vary depending on
the fiber and dyestuff types, but will
generally range from a few percent of the
fiber weight (2 or 3% o.w.f—of weight of
fiber) to as much as 50% where high
concentrations of exhaust agents are
required. Dyestuff quantities are generally
a few (less than 4) percent of the fiber
weight. After adding auxiliary chemicals
and dyes, the dyebath temperature is
raised to (and held at) the desired dyeing
temperature until dyeing is complete and
a level dyeing is achieved. The exhausted
dyebath, now containing only a few
percent of the original quantity of dyestuff
but still most of the auxiliary chemicals, is
dropped, and the dyed product is rinsed
with fresh water.
Dyebath Reuse
The exhausted dyebath may be used for
subsequent dyeings, thus using the
auxiliary chemicals for more than one
cycle of dyeing. This results in production
cost savings and also decreases the
volume of wastewater and quantity of
pollutants discharged. To reuse the
dyebath, a method was needed for
analyzing the exhausted dyebath to
determine the quantities of dyestuffs
remaining and thereby the quantities to
add for the next dyeing.
Much of the development of the
dyebath analytical techniques and recon-
stitution methods was performed at the
School of Textile Engineering at the
Georgia Institute of Technology in the
1970s. The success of this development-
al work led to several full-scale demon-
strations, also by Georgia Tech.
The work under Phase III of EPA's
Textile Wastewater Recycle/Reuse pro-
ject expands on earlier work on dyebath
reconstitution and reuse:
1. It examines the application of dyebath
reuse at a mill that is fairly typical of
many dyehouses, yet is not a "per-
fect" candidate for this technology.
• Dye formulations had to be modi-
fied to use a smaller number of
• dyestuffs before reconstitution
became technically feasible.
• Quality control requirements are
strict at this mill, thus posing a stiff
test of the ability of dyebath reuse
to produce acceptable dyeings.
• Overflow rinsing is typically used
at this mill, thereby affecting not
only the dyebath analysis/recon-
stitution methods, but also the
economics of dyebath reuse.
2. It presents a detailed examination of
the techniques used not only in full-
scale testing but also in the develop-
ment and testing of the technology at
this mill. These techniques can be
directly applied by other mills wish-
ing to examine the feasibility of
dyebath reuse.
3. It presents the first development of
environmental data for this waste-
water recycle/reuse technology.
Thus, the environmental benefits of
dyebath reuse can be quantified for
the first time.
4. It updates the equipment used in
dyebath analysis to include a modern
desktop computer, a commercially
available interface for the spectro-
photometer/computer, and software
written in the BASIC computer
language to allow for greater com-
prehension and adaptability to a
variety of desktop computers.
Volume 1 of this report details the
results of a study of dyebath reuse
implementation at a carpet mill. Volume 2
is a dyebath reuse operations manual,
providing information on the technology
to mills interested in adopting dyebath
reuse.
Dyebath Reuse Studies
To develop information on full-scale
implementation and costs of dyebath re-
constitution and reuse, a demonstration
of the technology was performed at a
carpet mill, Mill C-2 of earlier studies. Mill
C-2 performs atmospheric batch dyeing
primarily of nylon carpet, discharging
about 1 x 106 gal./day of wastewater to
the municipal collection system.
Two popular, large-volume carpet styles
were selected for dyeing using dyebath
reuse procedures. The dye recipes for
these styles had recently been reformu-
lated to utilize a small number of dyestuffs.
Many of the different shades now have
recipes containing varying amounts of
the same three dyestuffs. This is an
essential step in implementing dyebath
reuse since the residual dyes in the dye-
bath from the just completed dyeing must
be the same ones that are to be used in
dyeing the next shade.
The dyebath was analyzed using a visi-
ble-light spectrophotometer. Dyestuff ab-
sorbance coefficients were determined in
the laboratory for each dyestuff. These
coefficients are the k-values in the Lam-
bert-Beer equation:
A = kC
where A - absorbance of the dyestuff,
and C = concentration of the dyestuff.
These values were then used to analyze
exhausted dyebaths to determine the
amounts of dyestuffs that remained at the
end of a dyeing. A desktop computer was
programmed to perform all the calcula-
tions needed to determine how much dye
remained in a used dyebath and how
much had to be added to perform the next
dyeing. In this way, the actual procedures
needed to reuse a dyebath could be carried
out in only a few minutes by dyehouse
personnel.
Twenty-six series of dyeings were per-
formed with dyebath reuse, each series
consisting of 5-10 dyeings using the same
dyebath.
The first 15 series (bench-scale dye-
ings) provided opportunities to become
familiar with dyebath reuse concepts and
procedures, to test the shade-matching
capability of dyebath reuse, and to resolve
problems while still on a small scale. Six
shades from each of the two carpet styles
were selected for dyeing. For each shade,
the dyebath was reused until a series of
five dyeings was completed. This accounted
for the first 12 series. The final three
bench-scale series each started with a
light shade and gradually progressed to
darker shades as the dyebath was reused.
The dyed carpet samples from these bench-
scale dyeings were analyzed with a Diano/
Hardy II spectrophotometer to evaluate
the ability of dyebath reuse to produce
acceptable shade matches. Results were
very good.
Following the success of the bench-
scale dyeings, eight additional dyebath
reuse series were conducted using a
pilot-scale beck(vat). The pilot-scale beck
and dyeing procedures more closely re-
semble full-scale dyeing than bench-scale
dyeing. Thus, the pilot-scale dyeing would
provide an opportunity to test dyebath
reuse under conditions that approximate
full-scale dyeing, and resolve any prob-
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ems. Both single- and multi-shade series
were dyed for each carpet style. The
ihade matching, levelness, and color fast-
ness results (primary measures of product
quality) of the dyed samples were very
jood.
The final three series were full-scale
dyeings conducted in a 6,000-gal. (22,700-1)
atmospheric beck. The first series had
o be aborted after three dyeings due to
an unexpected yarn lot change. The re-
naming two series were multi-shade
Jyeing series consisting of 6 and 10
Jyeings, respectively. The process was
nonitored carefully to calculate the sav-
ngs in water, energy, dye, and chemical
jse due to dyebath reuse. Shades were
natched successfully in all dyeings. The
:arpets produced were of first quality.
3oth the number of adds and redyes were
vithin the mill's typical frequency for
hese styles. Thus, the full-scale experi-
nents demonstrated that the ease of
)btaining satisfactory dyeings with re-
:onstituted baths was comparable, if not
superior, to that of conventional dyeing.
Environmental Benefits
Wastewater samples were collected
luring both the pilot- and full-scale dye-
ngs. Results of the full-scale data (below)
:haracterize the potential environmental
senefits of dyebath reuse:
Percent Reduction
in Discharge
3ollutant Series 25 Series 26
:low (gal./lb)
BOD
:OD
rss
TDS
'henolics
Total-P
24
13
32
47
25
0
28
34
33
33
0
43
0
44
The concentrations of various pollutants
in the dyebath increased as the dyebath
was reused. This is suspected to be due to
the buildup of yarn finishes that are
removed from the carpet during dyeing.
Despite these higher concentrations, the
net effect of dyebath reuse is to reduce
the mass of pollutants actually discharged,
as compared to conventional dyeing. The
lack of suspended solids reduction in
Series 26 is an exception to this observa-
tion that cannot be explained. This net
reduction is due to the smaller amounts
of auxiliary dyeing chemicals needed to
perform reuse dyeings.
The larger reductions in wastewater
volume and pollutant discharge in Series
26, as compared to Series 25, were due to
attempts to reduce the volume of over-
flow cooling water used in the dye cycle.
Less cooling water results in less dilution
of the dy.ebath. Consequently, smaller
amounts of auxiliary chemicals are needed
to reconstitute the dyebath for reuse. This
results in both wateruse/discharge and
pollutant discharge reductions. Further
optimization in this area will result in
even greater environmental benefits.
Economic Analysis
In general, dyebath reuse has favorable
economics due to its relatively low capital
cost and significant cost savings. Payback
periods of about 1 year are common for
this technology.
An economic analysis was conducted
for dyebath reuse implementation at Mill
C-2. The cost savings due to dyebath
reuse were calculated based on data
collected during the full-scale tests. The
calculated savings averaged $23.85 and
$28.60 per dye cycle for the two carpet
styles, or about $0.011 to $0.012/lb of
carpet. About 65% of these savings are
due to reduced auxiliary chemical require-
ments. Energy savings account for an-
other 20%. Water and sewer use savings
account for the remaining 15%. Future
optimization of the reuse dyeing proce-
dure, by reducing the amount of overflow
cooling water used, could easily increase
the per-cycle cost savings to over $30.
Operating costs for dyebath reuse are
relatively low. Yearly operating costs of
$5,000 were estimated for Mill C-2,
based on 2,400 reuse dyeings per year.
This results in operating costs of about $2
per cycle.
Capital costs for equipping two dye-
becks at Mill C-2 for dyebath reuse were
estimated to be $70,500. This cost
includes a pump, an elevated 6,000-gal.
(22,700-1) storage tank, piping, valves,
controls, and analytical equipment
including a spectrophotometer and a
computer.
With an allowance of $10,000 for
developmental costs, the net payback
period is calculated to be 1.5 years:
Capital Cost $70,500
Development Cost 10,000
Total Capital $80,500
Yearly Savings $60,000
(based on $25/cycle)
Yearly O&M Costs 5,000
Net Savings $55,000
Payback Period =
80,500 = 1.5 years
55,000
Outlook for Use in Industry
As noted earlier, batch dyeing accounts
for half of the total amount of textile
dyeing. Due to the higher water and
chemical usage of batch dyeing, well
over half of the wastewater volume and
pollutant loading from dyeing results
from batch dyeing.
In certain industry sectors, dyeing is
performed almost exclusively by batch
operations: mills in these sectors can be
regarded as potential users of dyebath
reuse technology. These sectors include
knit fabric, hosiery, and yarn finishing. A
large amount of carpet dyeing is still
performed in batch operations, although
there is a trend toward producing more
continuous-dyed/printed carpeting. Most
large woven-fabric finishing mills employ
continuous dyeing, though some smaller
mills still have significant batch dyeing
operations. Overall, many mills can
potentially adopt this recycle technology.
Dyebath reuse has been tested or
demonstrated with a wide variety of
products and textile fibers, including
nylon hosiery and carpet; polyester fabric,
carpet, and yarn; acrylic yarn; and cotton
fabric. Dyestuff classes that have been
tested or demonstrated include acid,
basic, direct, disperse, and reactive.
At many mills, not all production will be
amenable to dyeing by dyebath reuse.
However, eve.n the conversion of a few
machines to this recycle technology will
have substantial cost and environmental
benefits. A mill that is ideally suited to
employ dyebath reuse technology will
generally dedicate only half of its dye
machines to reuse dyeing, to ensure
maintenance of flexibility in production.
The major obstacle to further use of this
technology appears to be the lack of
detailed information on evaluating and
implementing the technology. Volume 2
is an operations manual that should fill
this gap.
Operations Manual
The operations manual (Volume 2) first
introduces the reader to the concepts and
procedures of dyebath reuse. It then
presents a procedure that allows the
reader to determine if dyebath reuse is
applicable to his dyehouse. A preliminary
economic analysis can also be conducted.
The next topic is the development of an
evaluation program. Suggestions are
given on the content and scope of tests
necessary to evaluate the feasibility of
dyebath reuse.
Subsequent sections of the manual
introduce the concept of light absorbance
and how it is used to analyze dyebathsfor
their dyestuff content. The procedures for
analyzing and reconstituting dyebaths for
additional dyeings are then presented.
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Specifications for equipment and supplies
are provided.
The use of desktop computers to
perform the calculations for dyebath
reuse is discussed. Equipment is listed,
and a dyebath reuse computer program
written in BASIC is provided.
The final sections of the manual
discuss laboratory and full-scale dyebath
reuse experiments. Troubleshooting
guides are provided. Options and sugges-
tions for full-scale design and implemen-
tation of dyebath reuse are given.
The manual provides enough informa-
tion and guidance to assist textile mill
operators who are interested in evalua-
ting or implementing this technology.
J. Bergenthal and A. Tawa are with Sverdrup and Parcel and Associates, Inc.,
St. Louis, MO 63101.
Robert V. Hendriks is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Investigation of Textile
Dyebath Reconstitution and Reuse:"
"Volume 1. Technical Report," (Order No. PB 84-206 465; Cost: $16.00)
"Volume 2. Operational Manual," (Order No. PB 84-206 473; Cost: $ 16.0O)
The above reports will be available only from: (cost subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
US GOVERNMENT PRINTING OFFICE. 1984—759-015/7753
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
CHICAGO 1L 60604
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