EPA 440/1-72/ 001 -a
DEVELOPMENT DOCUMENT FOR
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
AND NEW SOURCE PERFORMANCE STANDARDS
FOR THE
FLAT GLASS
SEGMENT OF THE
GLASS MANUFACTURING
POINT SOURCE CATEGORY
£ \
U5£J
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
OCTOBER 1973
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Publication Notice
This is a development document for proposed effluent
limitations guidelines and new source performance
standards. As such, this report is subject to changes
resulting from comments received during the period of
public comments of the proposed regulations. This
document in its final form will be published at the
time the regulations for this industry are promulgated.
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DEVELOPMENT DOCUMENT
for
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
FLAT GLASS SEGMENT
of the
GLASS MANUFACTURING POINT SOURCE CATEGORY
Russell E. Train
Administrator
Robert L. Sansom
Assistant Administrator for Air & Water Programs
^1° "
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ABSTRACT
This document presents the findings of an extensive study of the flat
glass manufacturing industry by Sverdrup 5 Parcel and Associates, Inc.
for the Environmental Protection Agency for the purpose of developing
effluent limitations guidelines, Federal standards of performance, and
pretreatment standards for the industry, to implement sections 304, 306,
and 307 of the "Act."
Effluent limitations guidelines contained herein set forth the degree of
effluent reduction attainable through the application of the best
practicable control technology currently available and the degree of
effluent reduction attainable through the application of the best
available technology economically achievable which must be achieved by
existing point sources by July 1, 1977 and July 1, 1983, respectively.
The Standards of Performance for new sources contained herein set forth
the degree of effluent reduction which is achievable through the
application of the best available demonstrated control technology,
processes, operating methods, or other alternatives.
The development of data and recommendations in the documnet relate to
the flat glass manufacturing and automotive glass fabricating segments
of the glass manufacturing industry. These two segments are further
subdivided into six subcategories on the basis of production processes
and waste water characteristics. Separate effluent limitations were
developed for each subcategory on the basis of the level of raw waste
load as well as on the degree of treatment achievable by suggested model
systems. These systems include, coagulation, sedimentation, filtration
and certain in-plant modifications- Supportive data and rationale for
development of the proposed effluent limitations guidelines and
standards of performance are contained in this document.
iii
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CONTENTS
SECTION PAGE
I Conclusions 1
II Hecommendations 3
III Introduction 5
Purpose and Authority 5
Summary of Methods <5
General Description of Industry 14
Production and Plant Location 17
General Process Description 21
IV Industry categorization 27
V Water Use and Waste Characterization 2 9
Auxiliary Wastes 29
Sheet Glass Manufacturing 30
Rolled Glass Manufacturing 32
Plate Glass Manufacturing 32
Float Glass Manufacturing 38
Solid Tempered Automotive Glass 42
Fabrication
Windshield Fabrication 47
VI selection of Pollutant Parameters 55
VII control and Treatment Technology 59
Sheet and Rolled Glass Manufacturing 59
Plate Glass Manufacturing so
Float Glass Manufacturing 64
Solid Tempered Automotive Glass 68
Fabrication
Windshield Fabrication 73
VIII Cost, Energy, and Non-Water Quality Aspects 7 9
v
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Cost and Reduction Benefits 79
Energy Requirements 90
Non-Water Quality Aspects 91
IX Best Practicable Control Technology 93
Currently Available
Introduction 93
Effluent Reduction Attainable 94
Identification of Technology 95
Rationale for Selection 97
X Best Available Technology Economically iqi
Achievable
Introduction 101
Effluent Reduction Attainable 102
Identification of Control Technology 103
Rationale for Selection 105
XI New Source Performance Standards 107
XII Acknowledgements 109
XIII References 111
XIV Glossary 113
vi
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1
2
3
a
5
6
7
8
9
10
11
12
13
14
FIGURES
page
Data Retrieval Form 8
Sample Computer Format io
Flat Glass Industry 16
Location of Manufacturing Plants in 18
U.S., 1973
Sheet Glass Manufacturing 31
Rolled Glass Manufacturing 33
Plate Glass Manufacturing 35
Float Glass Manufacturing 39
Solid Tempered Automotive Glass 4 3
Fabrication
Windshield Fabrication 48
Wastewater Treatment - Plate Process 62
Wastewater Treatment - Float Process 66
Wastewater Treatment -
Solid Tempered Automotive Glass 70
Fabrication
Wastewater Treatment - Windshield 76
Fabrication
vi.i
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MB.
1
2
3
4
5
6
7
8
9
10
11
12
13
TABLES
Flat Glass Plants
Plants Visited
Primary Flat Glass Manufacturing
Production Data
Automotive Glass Fabricating
Production Data
Raw Wastewater, Plate Glass
Manufacturing Process
Raw Wastewater, Float Glass
Manufacturing Process
Raw Wastewater, Solid Tempered
Automotive Glass Fabrication
Raw Wastewater, Windshield
Fabrication Using Oil Autoclaves
Concentration of Wastewater Parameters 56
Water Effluent Treatment Cost - 81
Plate Glass
Water Effluent Treatment Cost - 83
Float Glass
Water Effluent Treatment Cost - 86
Solid Tempered Automotive Glass
Fabrication
Water Effluent Treatment Cost - 88
Windshield Fabrication
PAGE
11
13
IS
20
37
41
46
51
viii
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Recommended Monthly Average Effluent
Limitations Using Best Practicable
Control Technology Currently Available
Recommended Monthly Average Effluent
Limitations Using Best Available
Control Technology Economically
Achievable
ix
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SECTION I
CONCLUSIONS
That part of the glass manufacturing industry covered in this document
is classified into six subcategories. The first four subcategories
refer to primary glass manufacturing. The last two subcategories deal
with automobile window glass fabrication. The subcategorization is
based on (a) production process and (b) waste water characteristics.
Factors such as raw materials, age and size of production facilities,
and applicable treatment technology do not provide significant bases for
differentiation. The subcategories indicated, are as follows:
1. Sheet Glass Manufacturing
2. Rolled Glass Manufacturing
3. Plate Glass Manufacturing
4. Float Glass Manufacturing
5. Automotive Glass Tempering
6. Automotive Glass Lamination
Recommended effluent limitations and waste control technologies to be
achieved by July 1, 1977 and July 1, 1983, are summarized in Section II.
It is estimated that the investment costs of achieving the 1977
limitations and standards by all plants in the industry is less than
$900 thousand excluding costs of additional land acquisition. The costs
of achieving the 1983 level is estimated to be an additional $2.3
million over the 1977 level.
1
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SECTION II
RECOMMENDATIONS
The recommended effluent limitations for the pollutant constituents of
major significance are summarized below for the subcategories of glass
manufacturing source category included in this document.
Using the Best Practicable Control Technology Currently Available daily
maximum limits are as follows:
Sheet Glass
Rolled Glass
Plate Glass
kg/metric ton
(lb/ton)
Float Glass
g/metric ton
(lb/ton)
Automotive Glass
Tempering
g/sq m
(lb/ton)
Automotive Glass
Lamination
g/sq m
(lb/ton)
Suspended
Solids Oil COD
No waste water discharge
No waste water discharge
Total
BOD Phosphorus
2.76
(5.52)
2.0
(0.004)
1.95
(0.40)
4.4
(0.9)
0.90
(1.80)
0.7 2.0
(0.0014) (0.004)
0.64
(0.13)
1.76 4.9
(0.36) (1.0)
0.73
(0.15)
0.05
(0.0001)
0.98
(0.20)
PH
Between 6.0 and 9.0 (all subcategories)
3
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Using the Best Available Control Technology Economically Achievable, no
discharge of waste waters to navigable water is recommended for the
sheet, rolled and float glass subcategories. The daily maximum effluent
limitations recommended for the other subcategories are as follows:
Suspended Total
Solids Oil COD BOD Phosphorus
Plate Glass
Kg/metric ton
(lb/ton)
0.045
(0.09)
0.09
(0.18)
Automotive Glass
Tempering
g/sq m
(lb/ton)
0.24
(0.05)
0.24
(0.05)
0.49
(0.10)
Automotive Glass
Lamination
g/sq m 0.88
(lb/ton) (0.18)
0.88 4.9
(0.18) (1.0)
0.20
(0.04)
PH
Between 6.0 and 9.0 (all subcategories)
Recommended effluent limitations and standards of performance for new
point sources are no discharge for the sheet, rolled, plate, and float
subcategories and the Best Available Control Technology Economically
Achievable for automotive glass tempering and automotive glass
lamination.
4
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SECTION III
INTRODUCTION
PURPOSE AND AUTHORITY
Section 301(b) of the Act requires the achievement by not later than
July 1, 1977, of effluent limitations for point sources, other than
publicly owned treatment works, which are based on the application of
the best practicable control technology currently available as defined
by the Administrator pursuant to Section 304(b) of the Act. Section
301(b) also requires the achievement by not later than July 1, 1983, of
effluent limitations for point sources, other than publicly owned
treatment works, which are based on the application of the best
available technology economically achievable which will result in
reasonable further progress toward the national goal of eliminating the
discharge of all pollutants, as determined in accordance with
regulations issued by the Administrator pursuant to Section 304 (b) of
the Act. Section 306 of the Act requires the achievement by new sources
of a Federal standard of performance providing for the control of the
discharge of pollutants which reflects the greatest degree of effluent
reduction which the Administrator determines to be achievable through
the application of the best available demonstrated control technology,
processes, operating methods, or other alternatives, including, where
practicable, a standard permitting no discharge of pollutants.
Section 304(b) of the Act requires the Administrator to publish within
one year of enactment of the Act, regulations providing guidelines for
effluent limitations setting forth the degree of effluent reduction
attainable through the application of the best practicable control
technology currently available and the degree of effluent reduction
attainable through the application of the best control measures and
practices achievable including treatment techniques, process and
procedure innovations, operation methods and other alternatives. The
regulations proposed herein set forth effluent limitations guidelines
pursuant to Section 304(b) of the Act for certain subcategories of the
glass and asbestos manufacturing source category. They include float
glass, plate glass, sheet glass, rolled glass, automobile glass
tempering and automobile window glass fabrication.
Section 306 of the Act requires the Administrator, within one year after
a category of sources is included in a list published pursuant to
Section 306(b) (1) (A) of the Act, to propose regulations establishing
Federal standards of performance for new sources within such categories.
The Administrator published in the Federal Register of January 16, 197 3
(38 F.R. 1624), a list of 27 source categories. Publication of the list
constituted announcement of the Administrator's intention of
establishing, under Section 306, standards of performance applicable to
new sources within the flat glass industry subcategory as delineated
above, which was included within the list published January 16, 1973.
5
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SUMMARY OF METHODS USED FOR DEVELOPMENT OF THE EFFLUENT LIMITATIONS
GUIDELINES AND STANDARDS OF PERFORMANCE
Purpose and Authority
The effluent limitations guidelines and standards of performance pro-
posed herein were developed in the following manner. The point source
category was first categorized for the purpose of determining whether
separate limitations and standards are appropriate for different
segments within a point source category. Such subcategorization was
based upon raw material used, product produced, manufacturing process
employed, and other factors. The raw waste characteristics for each
subcategory were then identified. This included an analyses of (1) the
source and volume of water used in the process employed and the sources
of waste and waste waters in the plant; and (2) the constituents
(including thermal) of all waste waters; including toxic constituents
and other constituents which result in taste, odor, and color in water,
or aquatic organisms. The constituents of waste waters which should be
subject to effluent limitations guidelines and standards of performance
were identified.
The full range of control and treatment technologies existing within
each subcategory was identified. This included an identification of
each distinct control and treatment technology, including both inplant
and end-of-process technologies, which are existent or capable of being
designed for each subcategory. It also included an identification in
terms of the amount of constituents (including thermal) and the
chemical, physical, and biological characteristics of pollutants, of the
effluent level resulting from the application of each of the treatment
and control technologies. The problems, limitations and reliability of
each treatment and control technology and the required implementation
time was also identified. In addition, the non-water quality
environmental impact, such as the effects of the application of such
technologies upon other pollution problems, including air, solid waste,
noise and radiation were also identified. The energy requirements of
each of the control and treatment technologies was identified as well as
the cost of the application of such technologies.
The information, as outlined above, was then evaluated in order to
determine what levels of technology constituted the "best practicable
control technology currently available", "best available technology
economically achievable", and the "best available demonstrated control
technology, processes, operating methods, or other alternatives". In
identifying such technologies, various factors were considered. These
included the total cost of application of technology in relation to the
effluent reduction benefits to be achieved from such application, the
age of equipment and facilities involved, the process employed, the
engineering aspects of the application of various types of control
6
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techniques process changes, non-water quality environmental impact
(including energy requirements) and other factors.
Basis for Guideline Development
The data for identification and analyses were derived from a number of
sources. These sources included EPA and industry-supplied information;
published literature; and on-site visits, interviews, and sampling at
typical or exemplary plants throughout the United States. References
used in the guidelines for effluent limitations and standards of
performance on new sources reported herein are included in Section XIII
of this document.
Three types of waste water data were analyzed. These are RAPP data,
industry supplied data, and data derived from the sampling of typical or
exemplary plants. The data retrieval form illustrated in Figure 1 was
developed to aid in the collection of data during interviews and plant
visits and was supplied to the industry to indicate the types of data
required for the study.
The data was analyzed with the aid of a computer program which provided
the capability for summing the data for each plant where multiple
discharges existed, averaging the data for each plant where multiple
data sets were available and comparing and averaging the data for all
plants within each subcategory to determine values characteristic of a
typical plant. Input to the computer for each plant consisted primarily
of the plant production rate, the waste water flow rate, the
concentration of each constituent plant intake water, the average and
maximum concentrations of each constituent in the waste water, and some
descriptive information regarding existing waste treatment methods,
subcategory type, and sampling methods.
An example of the computer printout is the hypothetical summary of
effluent suspended solids data for plate glass plants using lagoon
treatment illustrated in Figure 2. The pound per day increase, mg/1
increase and pounds added per day per production unit are calculated.
Data from all of the plants listed is summarized in terms of the
average, standard deviation (SIGMA) and minimum and maximum values for
the data listed.
The name, location, and applicable manufacturing processes for the
plants contacted in this study are listed in Table 1. Twenty-three
plants supplied some type of usable information or data for computer
analysis. RAPP data was available and used for 10 plants.
Ten plants covering various manufacturing combinations were visited.
The subcategories covered are listed in Table 2 along with the type of
data collected. Six of the plants were sampled, some with more than one
subcategory. One plate, one float, 2 solid tempered automotive, and 3
laminating processes were sampled.
7
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m FLAT GLASS 0TUDT
Data Ittrlml ton ¦», 1
jMMmrj, 1973
A. fVT7 Itai
B. FlMrt fleaa cad location
C. Castas! - hnoaMl
• Tint ft nasal
0. Tllajtane Ho.
n MHTFACTtimQ IBOCBS CBABJCTl&ZZAnQS (Separata *Mt tm
each prooacs)
00
A.
».
C.
0.
ftooeu Type
Protfoctlcn Rata
Oparetlag Schedule
¦a^er or Xqplojees
I. Vatar Bugil Milts
1. Vbltse and Sonreea
2. QMS
(lislading ioIim)
a.
b.
o.
Out ftmimilfiB
d.
Clamp
a.
Sanitary (if available)
f.
Other
«.
toller titer
KFA mi GLASS STPDI (Caotd.)
fretreatsent Beqolrueata
a. Yolwe Treated
b. Season for Treatment
o. Describe Treatsnt Syrtea and Operation
d. Type nd (fciaatity of Cbe&ieals Qaad
a. Available Inforartlon an Treated Vatar (kality
A. %1ob and Source*
B. tMentcndl&g of Ho* and Why the Vatar la Coed is the Proceta
C. Does the douce Voltne aad Concentration of Vastevater Vtxy
Depending on the Type or Qnlity of Glass Produced or
Fabric atedf
D. Are Wastewater Characteristics Appreciably Different During
Start-up and Siutdoen as Compared to Horatl Operation!
K. Qisstity asd Mint of Application of Oil, Detergent ud
Other Cbeaicals Ceed Vhicb Itlght Inter the Wastewater Stress
t. Available Inforartlon on Untreated Wastewater Qiality
1. BOO
2. COD
3. Total SolIda
4. Suspended Solids
5. Dissolved Solids
6. Oil and Ore ado
7. Iteapfcorua
8. WAS
Available Uifviiaatlop on to Vstsr fcxallty
-1-
FIQOWE I
OATA RETRIEVAL FORM
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EPA PUT GIASS STUD? (Contd.)
9. Tenpereture
10.
11. Other (All nvaj-leblo lnforoatlon should be collected)
0. Treatment Ustfaods
1. Wastewater Source and Voluoo
2. Re wan for Treatment
3. Describe Treatment System and Operation
4. Typo ^wrtity of Chemicals Osed
5. Available Info mat Ion on Treated Wastewater (iiality
a. BOO
b. COD
c. Total Solids
d. Suspended SolIda
e. Dissolved Solids
f. Oil and Grease
g. Raospho rvs
b. NBAS
1. Temperature
J. &
k. Other (All available Information should be collected)
6. Is Any Kaon Toxic Material In the Vasteeater?
H. Vartevater Recycle
1. Is Asy Vaster iter Recycled Presently?
2. Can Wastewater be Recycled?
EPA PLAT GLASS STUDY (Cozxtd.)
I. In Plant Methods of Water Conservation and/or Waste
Reduction
J. Identify Any Air Pollution, Noise or Solid Tastes Resulting
froa Treatment or Other Control Ifetbods. Ho* Is the Solid
Waste Disposed of?
K. Cost Information (Related to vater pollution control)
1. Treatment Plant and/or EQulpcent Cost
2. Operating Costs (ftorsonnel, maintenance, etc.)
3. fc«r Costs
4. Estimated Equljncxrt Life
L. Vater Jtollution Control lfethods Being Considered for future
Application
III COO LI NO WATER
A. Process Steps Requiring Cooling Vater
B. Heat Rejection Requirements (BTU/bour)
C. Type of System (Once through or recycle)
D. Vater Teoperatures and Flo* Rate
1. input
2. Output
3. Flow Rate
E. Cooling Tower
1. Direct or Indirect
2. Slowdown Rate
3. Blowdown Control lfethod
4. Type and Quantity of Vater Treatment Chemicals Osed
3. Available Information on Blew down Water polity
?. Type and ftiantlty of Chemicals Used for Once Through
Cooling Vater Treatment
IT BOILER
A. Capacity
B. Blowdown
FIGURE I (CONTD.)
DATA RETRIEVAL FORM
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PART A AND B PARAMETERS OF INTAKE WATER AND DISCHARGE. BREAKDOWN 3Y PLANT
PLANT INF. EFF. CONC.
INF. EFFi
CONC. AVE. MAX LB/DAY INCREASE
MGD GPM MG/L MG/L MG/L AVE MAX
LBS ADDEO PER
MG/L INCREASE UNIT/DAY PRODUCT UNIT
AVE MAX AVE MAX
SAMPLE TYPE
ITEM NO.
530. TOTAL SUSPENDED SOLIDS
NAME* XYZ GLASS COMPANY
2.1 1458.33 11.
30.
NAME * ABC GLASS INDUSTRIES
5.96
4138.89 60.
75.
PRODUCTION" 100. TONS/DAY tLAGOON.PLATE
375. 332.766 6375.09 19. 364. 100.
PRODUCTION- 300. TONS/DAYtLAGOON.PLATE
425.
745.596 18142.8 15.
365 <
300.
3.32766 63.7509CQMP.MP227
2.48532 60.4761C0MP»MP275
8.06
5597.22
71.
105.
800.
1078.36
24517.9
34.
729.
400.
5.81298
124.227
4.03
2798,61
35.5
52.5
400.
539.181
12259.
17.
364.5
.200.
2*90649
62.1135
2 .72943
1895.44
34.6482
31.8198
35.3553
291.915
8321.04
2 . 82843
0.7071
141.421
0.59562
2.31556
5.96
413B.89
60.
75.
425.
745.596
16142.8
19.
365.
300.
3.32766
63.7509
2.1
1458.33
11.
30.
375.
332.766
6375.09
15.
364.
loo.
2.48532
60.4761
TOTAL
AVER.
SIGMA
MAX*
MlN.
FIGURE 2
SAMPLE COMPUTER FORMAT
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TABLE 1
FLAT GLASS PLANTS
Company Name Plant Location Applicable Processes
ASG Greenland, Tenn. P
Kingsport, Tenn. R
Okmulgee, Okla. S
Jeanette, Pa. S
Chrysler Detroit, Mich. L, T
CE Fullerton, Calif. R
Erwin, Tenn. R
Floreffe, Pa. R
St. Louis, Mo: R
Ford Dearborn, Mich. F, L, T
Nashville, Tenn. F, L, T
Fourco Fort Smith, Ark. S
Guardian Millbury, Ohio T
Carleton, Mich. F
Detroit, Mich. L
LOF E. Toledo, Ohio F, L, T
Rossford, Ohio F, P,* T
Ottowa, 111. F, L, T
Lathrop, Calif. F, L, T
PPG Creighton, Pa. L
Carlisle, Pa. F
Cumberland, Md. F, P
11
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TABLE I (Contd.)
FLAT GLASS PLANTS
Company Name Plant Location Applicable Process
PPG Meadville, Pa. F
Crystal City, Mo. F
Henryetta, Okla. S
Mt. Vernon, Ohio S
Clarksburg, W. Va. S
Mt. Zion, 111. S
Fresno, Calif. S
Greensburg, Pa. L
Crestline, Ohio T
Tipton, Pa. T
Safelite Wichita, Kans. L
Enfield, N. C. L
Safetee Philadelphia, Pa. L
Shatterproof Detroit, Mich. L
Note (1) F = Float Glass
P = Plate Glass (Including grinding and polishing)
R = Rolled Glass
S = Sheet Glass
L = Windshield Fabrication (laminating)
T = Solid Tempered Automotive Fabrication
12
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TABLE 2
PLANTS VISITED
Plant Types
Plate
Float
Rolled
Sheet
Automotive Tempering
Automotive Laminating
No. of Plants
1
1
1
1
1
2
Combined Float, Auto. Laminating
and Auto. Tempering
Combined Float, Plate and Auto.
Tempering
(1) - Individual process or subcategory
(2) - End-*of-Pipe including all process and
auxiliary wastes
Type of
Data Obtained
(2)
(1) (2)
No Process Waste
No Process Waste
(1) (2)
(1) (2)
(1) (2)
(1) (2)
13
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GENERAL DESCRIPTION OF THE INDUSTRY
Production Classification
The U.S. Bureau of Census, Census of Manufacturers, classifies the flat
glass manufacturing industry as Standard Industrial Classification (SIC)
group code number 3 211 under the more general category of Stone, Clay,
Glass, and Concrete Products (Major Group 32). The four-digit
classification code (3211) comprises industrial establishments primarily
engaged in manufacturing flat glass and flat glass products from
materials taken from the earth in the form of sand. This study also
includes some plants which are engaged in the fabrication of glass
products (automobile window glass) from purchased glass which is covered
under SIC group code number 3231, Glass Products, Made of Purchased
Glass.
Origin and History
Glass is thought to have been made in Persia 700 0 years ago and is known
to have been produced 2000 years ago in Egypt. It was first used for
gems and was later made into hollow vessels such as jars and vases. A
circular piece was used for a window in a bath house in Pompeii sometime
between 600 B.C., when the city was founded, and 79 A.D., when it was
destroyed by the eruption of Mt. Vesuvius. The glass was made by
casting and then drawn with pincers. The glass blowpipe was invented
at the beginning of the Christian era and led to two important methods
for manufacturing flat glass; the crown process and the cylinder
process. In the crown process (which was thought to have been invented
by the Syrians), a sphere was blown, an iron rod was attached to the
sphere opposite the blowpipe, and the blowpipe was cracked off. The
iron rod was then used to spin the reheated sphere until it opened to a
flat circular sheet. Glass-making was introduced in America by the
English, and the first glass factory in America was erected by the
beginning of the seventeenth century at Jamestown, Virginia.
During the nineteenth century, the crown process of making flat glass
was replaced by the cylinder process in which a cylinder was blown, the
ends were cracked off, the cylinder was split along the side, and then
reheated so that it could be opened into a flat sheet. The cylinder
process did away with the thick center and thick edge that were
characteristic of the crown process. In addition, larger sheets could
be formed. Various improvements were made in mechanizing the process,
including using compressed air for blowing.
In 1904, a patent was granted to Emile Fourcault in Belgium for a
process in which a flat sheet of glass could be drawn directly from a
bath of molten glass. Two other methods were developed for making sheet
glass at about the same time in America. These were the Colburn (or
Libbey-Owens) process and the Pittsburgh process. All three processes
are still in use and many improvements have been made since the original
14
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development. Although sheet glass has a high surface finish, the
surfaces are inherently wavy and are unsuitable for mirrors or large
windows in which undjstorted vision is desired. This fault can be
overcome by grinding and polishing the sheet glass, although ground and
polished glass is produced today by the plate process and, to a lesser
extent, by the rolled process.
The earliest plate glass was produced by a casting process invented in
France in the middle of the seventeenth century. The glass was melted
in pots, poured onto a casting table and then leveled to the reguired
thickness with a roller. The glass was allowed to cool and was then
ground with sand and water using finer grades of sand as the grinding
progressed. The glass was then polished with feltcovered wheels fed
with a fine abrasive slurry of iron oxide. These basic grinding and
polishing steps are in use today, although continuous processes are now
employed in manufacturing ground and polished plate glass. The latest
method for producing high optical-quality glass is the float process,
introduced by Pilkington Brothers Limited in 1959. The method gets its
name from that part of the process in which the glass is drawn across a
bath of molten tin. Heat is applied and, together with the effect of
gravity, a distortion-free sheet of glass is produced which has the high
surface-quality of sheet glass. Float glass is rapidly replacing ground
and polished plate glass.
Description of Manufacturing Methods
Manufacture of the basic sheet of flat glass from sand and other raw
materials is defined as primary flat glass manufacturing. Sheet,
rolled, plate, and float glass are primary flat glass products. The
primary glass sheets may be used directly or may be fabricated into
glass products as indicated in Figure 3. Among the many fabricated
products are mirrors and other coated glass, automotive and archi-
tectural tempered glass, windshields, and numerous speciality products
such as bulletproof glass, basketball backboards, and glass hot plates.
Tempered automobile glass and windshields are the only fabricated
products covered by this study.
Primary Flat Glass Manufacturing-
Flat glass is manufactured by melting sand together with other inorganic
materials and then forming the molten material to a flat sheet. Within
the primary flat glass industry, several distinct methods are used to
make flat glass. These are the float, plate, sheet, and rolled
processes. Although the raw materials and the melting operations are
essentially the same, each process uses a different method for forming
the molten glass into a flat sheet. In the float process, the glass is
drawn across a molten tin bath while in the plate process, rolls control
the initial thickness with the final thickness determined by grinding
and polishing. The glass is formed by a vertical drawing process in the
15
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PLATE (GAP)
SHEET
ARCHITECTURAL
FABRICATION
RAW MATERIAL STORAGE
RAW MATERIAL MIXING
MELTING
ROLLED
AUTOMOTIVE
WINDSHIELD
FABRICATION
FLOAT
SOLID TEMPERED
AUTOMOTIVE GLASS
FABRICATION
MISCELLANEOUS ft
ARCHITECTURAL
FABRICATION
CONSUMER
FIGURE 3
FLAT GLASS INDUSTRY
-------
sheet process. Finally, texturizing rolls are used to impart various
surface textures in the rolled process.
All primary glass may be used as architectural glass. Plate glass is
used in preference to sheet where a distortion-*free glass is desired.
Rolled glass is used where a decorative or translucent surface is
desired. Float glass is used for the same purposes as plate glass, both
of which can serve as the raw material for automobile window glass.
Fabricated glass is produced using all of the primary glass types.
Automobile Window Glass Fabrication-
Automobile window glass fabrication is divided into two processes.
Windshield laminating consists of bonding two layers of glass to an
inner layer of vinyl plastic. The major unit of equipment in the
process is the autoclave which is used to complete the bonding operation
under conditions of high temperature and pressure. The purpose of
laminating is to make the glass shatter resistant. Unlike windshields,
side and back lights (windows) are fabricated from solid pieces of
glass. The process includes edge grinding, bending and tempering. The
purpose of tempering (heating, followed by rapid cooling) is to increase
the strength of the glass over that of ordinary annealed glass and to
cause it to shatter into small rounded pieces, should it be broken.
PRODUCTION AND PLANT LOCATION
There are a total of 36 plants owned by 11 companies which manufacture
flat glass and fabricate automobile window glass in the United States
(See Figure 4 and Tables 3 and 4), with a combined daily processing
capacity of 10,700 metric tons (11,800 short tons) of primary flat glass
products and 173,0 00 square meters (1.86 million square feet) of
automotive glass products. The daily capacity of an average plant
engaged in primary flat glass manufacturing is 413 metric tons (455
short tons). These plants range in size from 54 metric tons (60 short
tons) per day to 109 0 metric tons (1200 short tons) per day.
The daily capacity of an average plant engaged in automotive glass
fabrication is 10,800 square meters. These plants range in size from
2,00 0 square meters (22,000 square feet) per day to 24,700 square meters
(266,000 square feet) per day.
Total employment in the industry is 24,000 with an average of 67 0
employees per plant. Plant employment ranges from about 100 to 2900.
It should be noted that employment figures are based on plant totals.
Many of the plants carry on production processes (such as architectural
glass fabricating) which are not covered by the study.
17
-------
ME
WASH
IV T
N DAK
MONT
MINN
NY.
OREG
iCT,
WIS
MICH
S. DAK
IDAHO
iNJ.
PA
WYO
IOWA
iEL
NEBR
OHIO
ILL
IND
'. VA
NEV
VA
UTAH
MO
COLO
KY
KANS
CALIF
N.C.
TENN
SC.
• OKLA
ARK
ARIZ
GA
N. MEX
ALA
MISS
LA
TEX
FLA
FIGURE A
LOCATION OF FLAT GLASS MANUFACTURING PLANTS WITHIN THE UNITED STATES, 1973
: r I
-------
TABLE 3
PRIMARY FLAT GLASS MANUFACTURING
PRODUCTION DATA
Number of Plants
Toal Capcity
(metric tons/day)
Average Plant Size
(metric tons/day)
Range (metric tons/day)
Total Capacity
(short tons/day)
Average Plant Size
(short tons/day)
Rnage (short tons/day)
Plants Discharging to
Municipal Treatment
Systems
Float
11
6430
5 80
330-1090
7080
640
360-1200
20%
Plate
3
970
330
250-390
1070
360
27 0-425
0%
Sheet
8
2720
340
150-600
3000
370
Rolled
5
670
140
55-230
740
150
170-660 60-250
No
Process
Waste
No
Process
Waste
19
-------
TABLE U
AUTOMOTIVE GLASS FABRICATING
PRODUCTION DATA
Number of Plants
Total Capacity (sq m/day)
Average Plant Size (sq m/day)
Range (sq m/day)
Total Capacity (sq ft/day)
Average Plant Size (sq ft/day)
Range (sq ft/day)
Plants Discharging to
Municipal Treatment
Systems
Laminating
11
75,200
6,900
65-15, 800
810,000
74,000
7,000-170,000
30%
Tempering
9
97,500
10,900
1,390-24,700
1,050,000
117,000
15,000-266,000
20%
20
-------
GENERAL PROCESS DESCRIPTION
Primary Flat Glass Manufacturing
Primary flat glass manufacturing consists of batching, melting, forming,
annealing, and cutting. Grinding, polishing, and washing are included
in the plate process, and washing is included in the float process. All
of the processes use water for cooling. The basic unit of production
for primary flat glass manufacturing is the metric ton (or short ton in
English units) and is based on the amount of glass drawn from the
melting tank.
These units were chosen because this is the most common measure of
production for primary glass manufacturing and the data will be readily
available for enforcement personnel. In some cases, production is
measured in terms of tons of raw material fed to the furnace, but this
is easily converted by subtracting the weight volatilized during the
melting process. A weight loss of 18% was assumed for this study.
Raw Materials-
The most common type of flat glass produced is the soda-lime type which
is also used for bottles, light bulbs, and eye glasses. The basic
composition remains the same, although there may be minor differences in
raw material composition depending on the manufacturer and the process
(float, plate, sheet or rolled). The principal ingredient is sand
(silica), which accounts for about half of the batch. Other major
ingredients are soda ash (sodium carbonate) , limestone (calcium
carbonate) , dolomite (magnesium carbonate) , and cullet. Soda ash is
added to reduce the viscosity of the melt and thus lower melting
temperatures. Limestone and dolomite are added to improve the chemical
durability of glass. Carbon dioxide is evolved from the soda ash,
limestone, and dolomite during the melting process, leaving sodium
oxide, calcium oxide, and magnesium oxide in solution with the silica
(silicon dioxide). The amount of evolution of carbon dioxide is about
18% by weight of the total charge less cullet.
Cullet is waste glass that is inevitably produced in the glass
manufacturing process, both inadvertently and intentionally, and may be
25% of the total amount of glass removed from the melting tank. The
cullet is reprocessed with the raw materials and actually improves the
melting qualities of the batch because of its tendency to melt faster
than the other ingredients, thus providing starting points from which
the melting can proceed. Other ingredients are often added to
21
-------
accomplish specific purposes. For example, iron oxide is added in small
amounts to produce the blue-^green color in tinted automotive glass.
Batchinq-
In the batching operation, the raw materials are brought together and
mixed to a homogeneous consistency. Good mixing is very important in
maintaining uniform physical properties in the finished product.
Likewise, impurities in the raw materials must be kept to a minimum to
avoid imperfections which result in rejection of the finished product.
Melting-
In the melting operation, the raw materials are continuously fed into
the refractory-lined melting tank where they are heated using fuel oil
or natural gas. Because of the high temperatures involved, all melting
tanks use large amcunts of cooling water to maintain structural
integrity.
Forminq-
Up to this point, the operations are essentially the same regardless of
process. As the molten glass progresses through the melting tank, it is
allowed to cool somewhat to facilitate removal from the tank in a
continuous ribbon. It is the manner in which the ribbon is removed from
the tank and the subsequent means used to effect dimensional control and
surface texture that distinguishes between the sheet, plate, rolled, and
float glass processes.
The glass is vertically drawn from the melting tank in the sheet glass
process. The drawing process is started by lowering a bar into the
molten glass and then pulling it out. The glass adheres to the bar and
forms a continuous ribbon as the bar is raised. The glass cools and
hardens as it is raised, after which powered rollers are applied to the
ribbon to maintain a continuous drawing operation. The thickness of the
glass is approximately inversely proportional to the drawing speed.
In the plate process, the molten glass flows by gravity to a pair of
water-cooled forming rolls which determine the thickness of the glass.
The rolled-glass operation is similar except that the rolls may be
texturized to impart a decorative and diffusing surface. Wired glass is
another product of the rolled glass operation. Two pairs of forming
rolls are used to produce two ribbons of glass. A wire mesh is inserted
between the two ribbons which are then brought together while the glass
is still hot and soft so that bonding occurs.
In the float process, the glass is passed out of the melting tank onto a
molten-tin surface. Heat and the force of gravity combine to provide a
product with optical qualities similar to that of ground and polished
22
-------
plate glass. The advantage of the float process over the plate process
is that grinding and polishing are not required.
Annealing-
Each of the primary manufacturing processes incorporates an annealing
lehr in which internal stresses are removed by heating the glass to a
uniform temperature followed by controlled cooling. Following
annealing, the glass is cut.
Grinding and Polishing-
Plate glass must be ground and polished to achieve the flat and parallel
surfaces that are required for good optical quality. Large rotary
grinding machines are used. The cast iron grinding tools are called
laps, and use a grinding medium which is a slurry of sand and water.
Coarse sand is used in the initial stages of grinding, but progressively
finer sand is used as the glass passes through successive grinding
stages. The grinding slurry is recycled through classifying equipment
which continuously grades the sand and feeds each section of the
grinding machine with a slurry of water and appropriately sized sand.
Sand and glass grindings that are too fine to use for grinding are
discharged in a continuous blowdown. It should be pointed out that the
classifying operation is sensitive to contamination. Contaminants may
cause an upset resulting in a shutdown of grinding operations. A matter
of days may be required to restore proper operation.
Polishing is accomplished with rotary equipment using animal felt as the
polishing surface and a slurry of water and iron oxide or cerium oxide
as the polishing medium. Grinding equipment and some polishing
equipment in use today is of the "twin" configuration in which both
sides of the glass are ground and polished concurrently. With "single"
polishing equipment, glass is conveyed through the polishing operation
on tables that have been coated with gypsum or some other supporting
medium to prevent movement of the glass. During grinding and polishing,
the glass thickness is reduced by approximately 15 percent.
Washing-
Washing is always performed in the plate process to remove residual
grinding slurry and polishing rouge. In some cases, float glass is
washed to remove sodium sulfate which forms on the glass as a result of
a chemical reaction with sulfur dioxide. The sulfur dioxide is sprayed
to prevent roller marks as the glass passes through the annealing lehr.
No washing is done as a part of the sheet and rolled glass primary
manufacturing processes. Sheet and rolled glass manufacturers may also
do some fabricating (usually architectural) in addition to their primary
manufacturing operations. In most cases, glass washing is required.
The washing is a fabricating step and, as such, is not a part of primary
manufacturing operations.
23
-------
Coolinq-
Large amounts of heat energy are used in the manufacturing of flat glass
and lead to large usages of cooling water to protect the equipment from
excessive temperatures. Cooling water is required for all melting
tanks, for the float bath in the float glass process, the forming rolls
in the plate glass and rolled glass processes, and for the drawing kiln
in the sheet glass process- In addition, cooling water is required for
the plant compressors and may also be used for the annealing lehr.
Heat energy that is dissipated by cooling water is called heat rejection
in this report. Heat rejection is defined as the heat energy leaving
the process in the discharge water minus the heat energy entering the
process in the intake water.
For primary manufacturing plants, most of the process waste heat is
dissipated directly tc the atmosphere. Based on information from one
source, the total heat energy required for manufacture of flat glass is
about 3,000,000 kilogram-calories per metric ton (11,000,000 Btu/short
ton) of glass removed from the melting tank. Average heat rejection by
means of cooling water systems is about 600,000 kg-cal/ metric ton
(2,200,000 Btu/short ton). Based on the large amounts of cooling water
required, some plants have found it advantageous to be located near
rivers while others use cooling towers or spray ponds to dissipate waste
heat.
It should be pointed out that the heat rejection values presented later
in this report are only estimates. Heat rejection is difficult to
define because of varying flow rates and varying temperatures which can
be caused by changes in intake temperature and in process operating
conditions. For example, cooling water requirements for melting tank
operations can vary over the life of the melting tank from one
rebricking to the next. Melting tanks require rebricking approximately
every four years. Over the course of the four years, the melting tank
brick work will degrade and molten glass leaks can occur in the walls.
A leak is repaired by locating an auxiliary cooler at the hole to freeze
the molten glass and, thus, plug the hole. The addition of the cooler
results in increased use of cooling water and, consequently, a higher
heat rejection rate.
Heat rejection was computed in two different ways. For a oncethrough
cooling system, it was necessary to determine the average intake and
average discharge water temperatures and the average flow rate. Unless
continuous monitoring was employed, the values had to be estimated.
Heat rejection for a recycling cooling system could be determined if the
cooling tower or spray pond make-up water flow rate was known. Make-up
requirements are an indication of the evaporation rate which is
proportional to the heat rejection rate.
24
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Automobile Window Glass Fabrication
— — _ ——^ — w y ¦' ¦ " M ^
Automobile window glass fabrication includes windshield laminating and
side and back light (side and back window) solid tempering. The basic
unit of production for automotive fabrication is expressed in square
meters (or 1000 sq ft in English units) of the surface area (one side)
of finished glass.
These units were chosen because they are used at all of the plants
studied to measure automobile glass production. Waste water volume and
characteristics are related to the square meters (square feet) of glass
fabricated.
Windshield Laminatinq-
Windshield laminating consists of bonding two layers of glass, which
have been cut and bent to the proper size and curvature, to an inner
layer of vinyl plastic. Bending is accomplished in a bending lehr.
Heat is applied to the glass and a form is provided to assure the proper
curvature. Mating panes are bent together to assure that both are of
the same curvature. A parting material is applied to the panes before
bending to prevent sticking.
Bonding of the two layers of glass to the vinyl plastic is done in two
steps, sometimes referred to as prepressing and pressing. Prepressing
is generally done with rollers. The large manufacturers do their final
pressing in an oil autoclave in which oil is the medium for transmitting
pressure and temperature changes to the windshield to induce bonding.
Oil autoclaves are typical for the industry.
Vinyl plastic sheet is purchased in rolls. Before assembling the
plastic into rolls, the manufacturer applies a coating of sodium bi-
carbonate tc prevent sticking of adjacent layers during shipment and
storage.
Cutting the glass leaves a sharp edge so that most manufacturers find it
desirable to seam (sand or rough grind) the edges for safety in
handling. Some manufacturers seam immediately after cutting while
others wait until after pressing.
Several washing operations are required. The glass is washed before
bending to remove contaminants that could be baked on the glass due to
the high temperatures in the bending lehr; before prelamination assembly
to assure cleanliness of the inner surfaces; and after pressing to
remove the oil which adheres to the glass. The prelamination wash has
been eliminated at some plants. Washing is also required to remove
bicarbonate of soda from the vinyl plastic prior to prelamination
assembly. If seaming occurs after autoclaving, the glass is again
washed before shipment to the customer.
25
-------
Large amounts of heat are required in the autoclave operation to produce
the temperatures necessary for bonding- Following lamination, non-
contact cooling water is used to cool the glass.
A few small manufacturers, producing windshields for the replacement
windshield and recreational and farm vehicle markets, are using air
autoclaves. In the air autoclave, air is the medium for transmitting
the required pressure and temperature changes to the windshield. The
advantage of the air autoclave is that it is not necessary to wash the
glass after autoclaving; however, increased handling may be required
with an air system. The trend in the industry is towards air
autoclaving. Some cf the large manufacturers have indicated that any
new laminating facilities will be equipped with air autoclaves.
Automotive Solid Tempering-
Production of automotive side and back lights consists of cutting, edge
grinding, seaming, drilling, bending, and tempering. The edges of side
lights that will be exposed after being assembled into the automobile
(the edges that are exposed when the window is rolled down) are ground
to a smooth radius for appearance and safety. The other edges may be
seamed to facilitate safe handling during subsequent fabricating steps.
Hole drilling is performed on some lights to provide for special
fabricating requirements of the automobile manufacturer. Bending is
accomplished in a bending lehr by heating the glass to achieve the
proper curvature, and the glass is tempered by rapid cooling after
heating. Either air or water quenching may be used. Tempered glass is
stronger than ordinary annealed glass and it breaks into tiny rounded
pieces that will not cut a person's skin. Cooling water is required in
the tempering hearth.
Edge grinding requires the use of a cooling solution which is recir^
culated through settling tanks to remove the glass solids. These solids
are disposed of as landfill. Washing is required before bending to
remove residue from the edge grinding and drilling operations.
26
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SECTION IV
INDUSTRY CATEGORIZATION
The segments of the flat glass industry covered by this study are
primary flat glass manufacturing and automotive glass fabrication. A
general distinction can be made between primary manufacturing and
automotive fabrication based on differences in raw materials used,
products produced, and production methods employed. These factors were
discussed in detail in the preceding paragraphs. The expression of
primary production in terms of weight and fabricated production in terms
of area is an indication of the basic difference.
The following factors were considered with respect to further sub-
categorization within the above two general categories:
Raw materials
Age and size of production facilities
Products and production processes
Waste water characteristics
Treatment methods
It is concluded that primary flat glass manufacturing should be sub-
categorized as float, plate, sheet, and rolled glass manufacturing and
that automobile window glass fabricating should be subcategorized as
windshield fabrication and solid tempered automotive glass fabrication.
Products and production methods are the primary bases for
subcategorization.
Raw Materials
The raw materials fcr primary flat glass manufacturing do not provide a
basis for subcategorization since they are essentially the same
regardless of the process and in themselves have no direct effect on
waste water quality. The same reasoning applies to automotive
fabricating in which the raw material is flat glass, generally from the
float process.
Age and Size of Production Facilities
Age is not a factor for the float process because it has only been used
since 1959. There are only three plate lines in the country. These are
the most modem as the older, less-efficient facilities have already
been phased out. Sheet and rolled glass plants are of varying age but
since no process water is used, age is not a significant factor except
27
-------
that the cooling water requirements are probably greater for older
melting tanks. Laminating and tempering facilities are continuously
being modernized so that plant age is not a factor in automotive
fabrication.
Waste water volumes and flow rates expressed in terms of production do
not vary significantly with respect to plant size. Basic process
equipment is generally the same for each subcategory throughout the
industry. The larger the plant, the more parallel equipment employed.
For these reasons, plant age and size are not a basis for subcate-
gorization.
Products and Production Processes
Readily identifiable production methods characterize the manufacturing
processes by which the various primary and fabricated products are made.
The float process is characterized by the molten tin bath; the plate
process by grinding and polishing; the rolled process by the texturizing
rolls; the sheet process by vertical drawing; the laminating process by
the oil autoclave; and the tempering process by edge grinding, hole
drilling, and tempering. Each of these processes has different
requirements for water, resulting in different waste water
characteristics and treatment requirements. Heat rejection requirements
also differ for the different manufacturing processes. The variation in
production methods forms a significant basis for subcategorization.
Many flat glass plants have more than one manufacturing process
contributing to the total waste stream. A typical multi-product plant
may have a float line as well as automotive laminating and tempering
facilities. This phenomenon is additional justification for
subcategorization by process. Performance standards will be recommended
a subcategory by subcategory basis. In this way, the total effluent
limitation for a multi-product plant can be determined by summation.
Waste Water Characteristics
Waste water volume and characteristics vary widely for the different
manufacturing processes. No process waste water is produced by rolled
and sheet glass manufacturing. A small volume of clean water results
from washing in the float process. Grinding and polishing in the plate
process produces large volumes of high suspended solids waste water.
Windshield fabrication produces a lower volume of oily waste water and
solid tempered automotive glass production results in a still lower
volume of somewhat cleaner waste water. The variation in waste volume
and characteristics is a basis for subcategorization.
Treatment Methods
Although waste water volume and characteristics vary significantly,
applicable treatment methods are all related to the removal of oil, and
suspended and dissolved solids. Some of the same treatment methods
apply to more than one subcategory and, therefore, variation in
treatment methods is cnly partial basis for subcategorization.
28
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SECTION V
WATER USE AND WASTE CHARACTERIZATION
Water is used to some extent in all of the subcategories covered by this
study. Cooling and boiler water are required at aj.1 plants. Washwater
is used in the plate, float, and automotive fabrication subcategories
for washing, and water is the transfer medium for grinding sand and
rouge in the plate process.
Plant water is obtained from various sources including the city water
supply, surface, or ground water. City water is used in almost all
cases where it is available, except for plate glass manufacturing where
large quantities of river water are used for grinding and polishing.
AUXILIARY WASTES
For the purposes of this study, non-contact cooling, boiler, and water
treatment waste waters are considered auxiliary wastes as distinguished
from process waste waters. Process waste water is defined as water
which has come into direct contact with the glass, and include such
sources as washing, quenching, and grinding and polishing.
Pretreatment requirements depend on the raw water quality and the
intended water use. Cooling water pretreatment practices may range from
no treatment to coagulation-sedimentation, filtration, softening, or
deionization. Generally, treatment is sufficient to prevent fouling of
the cooling system by clogging, corrosion, or scaling. Boiler water
treatment is related to boiler requirements, but removing the suspended
solids and at least a portion of the dissolved solids are generally
required. Filtration, softening, aeration, and deionization are done as
necessary. Washwater must be low in suspended and dissolved solids to
avoid spotting the glass. City water is used, where available, or water
from other sources is treated to obtain water of similar quality. In
some cases deionized water is required for final rinsing.
Waste waters from pretreatment systems are highly variable and depend
upon the characteristics of the water being treated. At two plants in
the same subcategory, therefore, no pretreatment may be required at one
while coagulation-sedimentation, filtration, and deionization may be
required at the other. For plants with the same system, the
pretreatment waste volume and characteristics are also proportional to
the concentration of pollutants removed.
Cooling and boiler systems, associated water treatment requirements and
waste water characteristics vary considerably among the plants in the
flat glass industry. Existing cooling systems include once-through and
direct-contact and indirect-contact recirculating systems. Highly
variable cooling water treatments are used in these systems. Boiler
29
-------
systems may also vary considerably in terms of chemical treatment and
blowdown. The volume and characteristics of cooling and boiler waste
waters are directly related to the make-up water characteristics and the
type of system employed.
Auxiliary waste waters are not unique to the flat glass industry. Many
manufacturing operations throughout industry use the same cooling,
boiler, and water pretreatment systems. Owing to their highly variably
volume and characteristics, auxiliary waste waters are not included in
the effluent limitations and standards of performance developed for
process wastes. Auxiliary wastes will be studied at a later date, and
characterized separately for industry in general. The values thus
obtained will be added to the limits for process waste water to
determine the effluent limitations and standards of performance for the
total plant.
In this report, cooling requirements will be discussed in terms of heat-
rejection requirements. Where appropriate, some of the types of systems
used may be discussed; however, no attempt will be made to define or
categorize the equipment and systems used, the cooling-water treatment
methods, or the effluent characteristics. Water pretreatment methods
will be discussed where applicable to process water treatment and washes
that may require deionized water will be noted.
SHEET GLASS MANUFACTURING
Sheet glass manufacturing operations may be defined as the processing of
raw materials to form thin glass sheets of saleable size. Figure 5 is a
flow diagram indicating water usage with respect to the manufacturing
steps. The manufacturing process has been defined in detail in Section
IV. Non-contact cooling water is used, but no process waste water is
produced by this subcategory.
Process Water and Waste water
t
The only water used in the process is 12 1/metric ton (10 gal/short ton)
added to the raw materials for dust suppression. This is evaporated in
the melting tank.
No process water is used and, therefore, no process waste water is
produced by the sheet-glass subcategory. However, it should be noted
that architectural tempering or other waste waterproducing fabrication
steps may be operated in the same facility in which sheet glass is
produced. The effects of fabrication steps must be considered when
analyzing the total effluent from a sheet glass facility.
Cooling
In the sheet glass manufacturing process, cooling water is required for
the melting tank, drawing kiln, compressors and the reannealing lehr.
-------
WATER
42 L/METRIC TON
10 GAL/SHORTTON)
COOLING WATER
KG-CAL
.772 X 106 METRIC TON
- BTU
(2.78 X 10b SHORT TON)
COOLING WATER
HEAVY GLASS
MELTING
DRAWING
ANNEALING
RE-ANNEALING LEHR
CUTOFF
CUTTING
PACKAGING
STORAGE
RAW MATERIAL STORAGE
MIXING
CONSUMER
FIGURE 5
SHEET GLASS MANUFACTURING
31
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Average heat rejection for plants using the Pennvernon process is
772,000 kilogram-calories per metric ton (2,780,000 Btu/short ton) with
a range of 741,000 kg-cal/metric ton (2,670,000 Btu/short ton) to
877,000 kg-cal/metric ton (3,160,000 Btu/short ton). Another sheet
glass plant, using the Fourcault process, reports heat rejection at
350,000 kg-cal/metric ton (1,260,000 Btu/short ton). The reason for the
difference in heat rejection between the Pennvernon process and the
Fourcault process is the relative proximities of the drawing kiln to the
melting tank. In the Fourcault process the molten glass flows in a
canal to the drawing kiln which is not as close to the melting tank as
in the Pennvernon process. By traveling the longer distance (by way of
canals) , the glass has an opportunity to cool so that not as much
cooling water is required in the drawing kiln. The Libbey-Owens process
is also used for making sheet glass. No heat-rejection data was
available from these plants.
ROLLED GLASS MANUFACTURING
Rolled glass manufacturing consists of melting raw materials and drawing
the molten glass through rollers to form a glass sheet. The major
process steps and points of water usage are listed in Figure 6. Non-
contact cooling water is used, but no process waste water is produced by
this subcategory.
Process Water and Waste water
Approximately 42 1/metric ton (10 gal/short ton) of water are added to
the raw materials for dust suppression. This water is evaporated in the
melting tank.
No process water is used and, therefore, no process waste water is
produced by the rolled glass subcategory. Fabricating operations
generally occur in conjunction with rolled glass manufacturing and
should be noted that numerous and highly variable waste water streams
may result. Although primary rolled-glass production is a dry process,
waste waters may be generated by a rolled glass facility because of
fabrication waste water.
Cooling
In the rolled-glass manufacturing process, cooling water is required for
the melting tank, forming rolls, annealing lehr and compressors.
Although no heat-rejection data is available for rolled glass plants, it
is expected that heat rejection requirements are similar to the plate
glass process because of similarities in process configuration.
PLATE GLASS MANUFACTURING
Plate glass manufacturing is the production from raw materials of a
high-quality thick glass sheet. This subcategory has historically been
32
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RAW MATERIAL STORAGE
MIXING
WATER
42 L/METRIC TON
(10GAL/SHORT TON )
COOLING WATER
(DATA NOT AVAILABLE)
MELTING TANK
COOLING WATER
FORMING ROLLS
ANNEALING
INSPECTION
CUTTING
CUT!
PACK)
riNG
\GING
CONSUMER
FABRICATION
FIGURE 6
ROLLED GLASS MANUFACTURING
33
-------
the greatest source of waste in the industry since large volumes of
high-suspended-solids waste water are produced. Owing to high
production costs and related water pollution problems, plate glass is
being replaced by float glass. Only three plate glass plants remain in
the United States. The major process steps and points of water usage
are shown in Figure 7.
The typical plate glass manufacturing plant may be located in any part
of the country and is at least 12 years old. Advanced plate glass
manufacturing technology is used, but this has not been improved since
the early 1960's when the advantages of the float process became
apparent. Production is continuous seven days a week.
Process Water and Waste water
Process water is used in the batch, grinding, polishing, and washing
operations. Approximately 4 2 1/metric ton (10/short ton) of water are
added to the raw materials for dust suppression. This water is
evaporated in the melting tank. Waste water results from grinding,
polishing, and washing the glass. River water is generally used for
grinding and polishing, but city or treated water is required for final
washing and rinsing.
Grindinq-
Grinding is the first step in the process to transform the rough glass
sheet into the finished plate-glass product. A sand slurry is used in
conjunction with large iron grinding wheels to actually grind down the
glass surface. Relatively coarse sand is used initially, with
progressively finer sand used as the glass proceeds down the grinding
line. Sand slurry is recycled from a gravity classifier. All of the
return from the grinders enters one end of the classifier, the sand
particles settle according to size, and the waste water overflows at the
other end. The grinding slurry is drawn from progressive segments of
the bottom of the tank. Sand classification is regulated by the
velocity of water passing through the tank and is controlled by both the
slurry drawoff rate and the tank overflow. Particles too small to
settle are removed in the overflow. This waste water stream is very
high in suspended solids consisting of fine sand, glass, and iron
particles. About Q7% of the flat glass waste water is contributed by
the grinding process.
Polishinq-
Polishing is similar to grinding except that smaller particles are used.
Rouge (ferric oxide) has generally been used as the polishing medium,
but at least one company uses cerium oxide. Neither grinding medium has
an apparent advantage in terms of raw wastewater characteristics. Felt
34
-------
WATER
42 (./METRIC TON
(10 GAL/SHORT TON)
COOLING WATER
RIVER WATER
RIVER WATER
WATER
RAW MATERIAL STORAGE
MIXING
*
>
*
MELTING
FORMING ROLLS
ANNEALING
CUTTING
GRINDING
POLISHING
WASHING
INSPECTION
CUTTING
PACKAGING
STORAGE
COOLING WATER
~ KG-CAL
.539 X 10® METRIC TON
c BTU
(1.94 X 10s SHORT TON)
WASTEWATER
39,900 L/METRIC TON
<9.570 GAL/SHORT TON)
87%
WASTEWATER
4.590 L/METRIC TON
(1.100 GAL/SHORT TON)
10%
WASTEWATER
1.3B0 L/METRIC TON
(330GAL/SHORT TON)
3%
CONSUMER
FIGURE 7
PLATE GLASS MANUFACTURING
35
-------
pads are used to apply the polishing medium to the glass surface and,
therefore, contribute some organic matter to the waste water stream.
The glass is ground first on one side and then on the other. A bedding
medium is required to evenly support the glass. Plaster of paris is
traditionally used for bedding; however, proprietary methods using a
reusable medium have been developed for the newer polishing lines.
Polishing contributes about 1056 of the plate glass waste water volume.
The major constituents include, rouge or cerium oxide, glass particles,
felt, and calcium sulfate if plaster of paris bedding is used.
Washing-*
The residue resulting from grinding and polishing is removed by a series
of washing steps. River water is generally used for the first rinse,
followed by an acid wash and a final rinsing with city water. The city
water rinse may be followed by a deionized water rinse. Washing
contributes about 3X of the plate glass waste water volume. The water
is clean as compared with the grinding and polishing waste water. The
initial wash contains significant suspended solids, but the final wash
is very clean. Acid carry-over is quickly neutralized by the other
waste streams which tend to be basic.
Waste Water Volume and Characteristics
some typical characteristics for the combined waste water stream are
listed in Table 5. In all cases except for pH, the values listed are
the quantities added to the water as a result of the plate glass
process, and concentrations in the influent water have been subtracted.
Flow—A variable volume of process water is used for plate glass
manufacturing. Flows range from 14,600 to 45,900 1/metric ton (3,500 to
11,000 gal/short ton) or 4,920 to 18,200 cu m/day (1.3 to 4.8 mgd). The
typical flow is 45,900 1/metric ton (11,000 gal/short ton). Water usage
is related to the type and age of the equipment used, with the highest
water usage at , the oldest plants. At plants built before water
conservation and pollution control were widely practiced, open channels
were provided for flushing away any wastes or spillage. Large
quantities of water are necessary to maintain sufficient velocity to
prevent settling. Extensive in-plant modifications will be required in
these plants to significantly reduce water usage.
Suspended solids—Suspended solids are the major waste water con-
stituents resulting from plate glass manufacture. The available data
shows a wide variation in concentration, but good correlation in terms
of pounds per ton. Approximately 690 kg/metric ton (1,375 lb/short ton)
of suspended solids are discharged. The major waste water source is the
grinding operation, with lesser quantities contributed by polishing and
washing.
36
-------
TABLE 5
RAW WASTEWATER (a)
PLATE GLASS MANUFACTURING PROCESS
Flow
pH
Temperature (b)
Suspended Solids
COD (b)
Dissolved Solids (b)
u>
-J
1+5 >900 1/metric ton
9
2.8 C
690 kg/metric ton
4.6 kg/metric ton
8.0 kg/metric ton
11.000 gal/short ton
6 F
1,375 lb/short ton
9.2 lb/short ton
16.1 lb/short ton
(a) Represents typical plate glass process wastewater prior to treatment.
Absolute value given for pH, increase over plant influent level given
for other parameters.
15,000
mg/1
100
mg/1
175
mg/1
(b) Indication of approximate level only; insufficient data are available
to define actual level.
-------
Other parameters—Limited information is available on other raw water
parameters. Although sufficient information is not available to
definitely establish the dissolved solids, BOD, COD, and temperature
levels, the data indicate these are insignificant as compared with
suspended solids. Detergents are not used and, therefore, no increase
in phosphorus should occur. While some lubricating oil dripping can be
expected from the process equipment, it cannot be detected in the large
volume of waste water.
Discussion—Plate glass manufacturing is generally a continuous
operation (24 hr/day 7 day/week), and the waste water flows, therefore,
are relatively constant. Polishing is done only part of the time in
some plants, and the suspended solids loadings are lower when polishing
is not on line but the waste water flow is not substantially reduced.
Waste water flows and characteristics are also not significantly
different during start-up or shutdown. The plate furnace is drained
every three to five years for rebuilding. At this time, the glass is
drained into a quench tank and cooled with water. Generally the quench
water evaporates and no discharge occurs. No toxic materials are known
to be contained in waste water from the plate glass manufacturing
process.
Cooling
In the plate glass manufacturing process, cooling water is required for
the melting tank forming rolls, annealing lehr and compressors. Two of
the three plate glass plants in the United States reported heat-
rejection data. They are 311,000 kg-cal/ metric ton (1,120,00 0
Btu/short ton) and 766,000 kg-cal/metric ton (2,760,000 Btu/short ton).
The wide variation in the two values cannot be explained. The larger
value is probably more representative of actual plate glass heat
rejection requirements.
FLOAT GLASS MANUFACTURING
1
The float process may be considered the replacement for plate glass
manufacturing. Float glass production is substantially less expensive
and process waste water has all but been eliminated. The major process
steps and points of water usage are illustrated in Figure 8. The
manufacturing process is more fully explained in Section IV.
The typical float glass plant may be located in any part of the country
and has been built since 1960. Both float and mirror washing are
practiced so that flows are approximately 30 51 higher than if float
washing alone is practiced. Float production is continuous seven days a
week, but the mirror washer is operated only as required.
38
-------
RAW MATERIAL STORAGE
MIXING
WATER
42 L/METRIC TON
(10 GAL/SHORT TON)
COOLING WATER
- KG- CAL
.475 X10 METRIC TON
COOLING WATER
. c P I U
<1.71 X 10b SHORT TON)
WASHING
RINSING
WATER
WASTEWATER
138 L/METRIC TON
(33 GAL ) SHORT TON)
MELTING
FLOAT BATH
INSPECTION
CUTTING
PACKAGING
STORAGE
ANNEALING
CONSUMER FABRICATION
FIGURE 8
FLOAT GLASS MANUFACTURING
3 )
-------
Process Water and Waste Water
Process water is used in the batch and in some cases for washing.
Approximately U2 1/metric ton (10 gal/short ton) of water are added to
the raw materials for dust suppression. This water is evaporated in the
melting tank. some plants wash the glass prior to packing, and this
constitutes the only waste water stream for this subcategory.
Washing-
Sulfur dioxide is sprayed on the underside of the glass sheet soon after
forming to develop a protective coating. Sodium sulfate is formed
which, in high enough quantity, will show up as a visible film on the
glass which may be removed by washing.
Some plants wash as part of the float process and others do not.
Generally, where they do not, the glass is to be fabricated in the same
facility, and washing is the first step in the fabrication process.
Glass to be used for mirror manufacture is always washed in a special
washer not directly connected to the float line. The available data do
not distinguish between regular washing and mirror washing, so both
types are considered to be part of the float process in this report.
The mirror washer effluent is probably of higher quality than the float
washwater, but the differences are not significant for this study.
Two basic types of washing systems are used. Most plants presently use
a one- or two-stage wash of city water quality followed by a deionized
water rinse. The water is heated to 52°-65°C (125-150° F) to prevent
glass breakage and to enhance dissolution of the soluble film. Maximum
recycle is practiced, with blowdown governed by dissolved solids
buildup. This system is typical of the industry.
An older three-stage system using detergents is still used at some
plants. The first stage is a recycled detergent wash followed by a
recycled city-water rinse and a recycled deionizedwater rinse. Blowdown
is governed by dissolved solids and detergent buildup.
Waste Water Volume and Characteristics
Some typical characteristics of float-glass washwater blowdown are
listed in Table 6. In all cases except for pH, the values listed are
the quantities added to the water as a result of the float glass
process, and concentrations in the influent water have been subtracted.
Flow—The volume of washwater discharge is influenced by make-up water
characteristics and mirror washing requirements. Flows range from 88 to
138 1/metric ton (21 to 33 gal/short ton) or 34 to 136 cu m/day (0.009
to 0.036 mgd), with the highest volumes recorded for plants that are
washing mirror glass. The typical flow is 138 1/metric ton (33
gal/ton). The volume of waste water discharged depends upon the
40
-------
TABLE 6
RAW WASTEWATER (a)
FLOAT GLASS MANUFACTURING PROCESS
Flow
138
l/metric ton
33
gal/ton
PH
8
Temperature (b)
37 C
98 F
Suspended Solids
2
g/metric ton
.OOlj-1
lb/short
ton
15
mg/1
Oil
• 7
g/metric ton
.001U
lb/short
ton
5
mg/1
COD
2
g/metric ton
.00U1
lb/short
ton
15
mg/1
BOD
.25
g/metric ton
.0005
lb/short
ton
2
mg/1
Phosphorus
(c)
Dissolved Solids
lU
g/metric ton
.028
lb/short
ton
100
mg/1
(a) Representative of typical float glass process wastewater. Absolute value given for
pH and temperature, increase over plant influent level given for other parameters.
(b) Indication of approximate level only; insufficient data is available to define
actual level.
(c) No information is available on wastewater containing phosphorus.
-------
dissolved-solids content of the makeup water. Blowdown rates are
manually adjusted and are generally held constant even though the square
meters of glass washed nray vary considerably. The flow is set so that
acceptable dissolved solids concentrations are maintained at the highest
washing rate. Dissolved solids in the wash prior to the deionized rinse
are generally limited tc 300 to 400 mg/1.
Waste water parameters—Elowdown from the float washer is of fairly high
quality, as can be seen from Table 6. The most significant increase of
14 g/metric ton (0.028 lb/short ton) or 100 mg/1 is noted for dissolved
solids. COD and suspended solids show increases of only 2 g/metric ton
(0.0041 lb/short ton). Trace quantities of BOD and oil are also
present. The available data indicate a pH range of 7.4-8.2 with a
typical pH of 8. Only cne temperature reading was available, this gives
an indication of the water temperature, but should not be taken as
typical. No information was available on the phosphorus content of
float washer effluent where detergents are used, but the use of deter-
gent is not typical. Deionizer regeneration is not considered process
waste water and, therefore, was not included in the characterization.
Discussion—Process waste water from the float subcategory is of fairly
high quality and is disposed of only because of the dissolved solids
concentration. There is no significant change in waste water
characteristics during start-up or shutdown. The float furnace is
drained every 3 to 5 years for cleaning. Molten glass is drained into a
quench tank and cooled with a water spray. The cooling water evaporates
and no discharge occurs.
Cooling
In the float glass manufacturing process, cooling water is required for
the melting tank, float bath, annealing lehr and the compressors.
Average heat rejection is 475,000 kg-cal/metric ton (1,710,000 Btu/short
ton) removed from the melting tank with a range of 4 00,0 00 kg-cal/metric
ton (1,440,000 Btu/short ton) to 561,000 kg-cal/metric ton (2,020,000
Btu/short ton) .
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
Solid tempered automotive fabrication is the fabrication from glass
blanks of automobile backlights (back windows) and sidelights (side
windows). The major process steps and points of water usage are
illustrated in Figure 9. A detailed description of the manufacturing
process is given in Section IV.
The typical solid tempered automotive glass fabrication plant may be
located in any part of the country and uses process equipment that has
been modified within the last 10 to 15 years. Production schedules are
variable, but in many cases the plant is operated five or six days a
week for 24 hours a day.
42
-------
MAKE UP
TEMPLATE CUTTING
RECIRCULATION
SETTING TANKS
WATER
NEfll IGIRI F V I
AMOUNT
FOR DUST SEAMING
CONTROL
WASTEWATER
£
EDGE GRINDING
E
COOLING
SOLUTION
COOLING
SOLUTION
T~W
SOLIDS
TO LAND
DISPOSAL
WATER
DRILLING
WATER
COOLING WATER
WASt
HING
BENDING
TEMPERING
^ WASTEWATER
20 L / SO M
(490 GAL f 1000 SQ FT)
41%
WASTEWATER
28.9 L/SQ M
(710 GAL / 1000 SQ FT)
59%
COOLING WATER
(DATA NOT AVAILABLE)
AIR COOLING
QUENCHING
•WATER
~ WASTEWATER
3.1 L/SO M
( 77 GAL /1000 SQ FT)
NOT TYPICAL
INSPECTION
PACKAGING
STORAGE
CONSUMER
FIGURE 9
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
43
-------
Process Water and Waste Water
Water is used in solid tempered automotive fabrication for seaming,
grinding, drilling, quenching, cooling, and washing. The washwater is
the major source of contaminated waste water.
Seaminq-
Seaming is a light grinding to remove the sharp edges on backlights. In
some cases, a fine spray of water is used to hold down the dust.
Edge Grindinq-
Edge grinding is used to form the smooth rounded edge on the exposed
surfaces of sidelights. An oil-water emulsion coolant-solution is used
which also serves to flush away the glass particles. All plants recycle
the coolant through a gravity sedimentation chamber where the glass
particles settle and are removed along with free floating oil and scum.
The coolant is continuously recycled and the only blowdown from the
system is the carry-over that remains cn the glass. In the typical
plant, the settled sludge and skimmings are collected for disposal as
landfill; a few plants, however, discharge this waste to the waste water
system. About 11.2 g/sq m (2.3 lb/1000 sq ft) of dry sludge is
produced.
Drilling-
Holes are drilled in sidelights for window handles and brackets. Water
is used in this process to cool the drill and to flush away the glass
particles. The typical flow is 20 1/sq m (U90 gal/1000 sq ft).
Washinq-
washing is required to remove residual coolant and glass particles. One
or two washing^ steps may be used before the bending furnace, depending
on the plant set up. Where the plant is set up on a production-line
basis, the glass goes directly from edge grinding through drilling and
washing to tempering, and only one washer is used. The edging or
drilling and seaming lines may also operate independently of the
tempering line, in which case washing occurs following drilling and
seaming and again befcre tempering. More water is used in the two-stage
process, but the pollutant loadings are not significantly different.
Both once-through and recycling washers are used, two or more stages may
be used with each recycling from its own reservoir. Make-up water is
added to the last stage and waste water is discharged from the first
stage. The recycle systems reduce the water usage, but the quantity of
waste products is not reduced. The washwater is heated to accelerate
removal of oily residues. Recycling is limited by the build-up of oil
44
-------
and suspended solids. A typical plant uses one or two wash steps, with
some recycling. The typical flow is 28.9 1/sg m (710 gal/1000 sq ft).
Quenchincj-
Rapid cooling is required by the tempering process. Air cooling is
typical, but quenching is also done with a water spray. Quench water is
considered a process waste because the water comes in direct contact
with the glass. Very little, if any, contaminants are picked up. The
only apparent benefit of water quenching is that less space is required
than for air cooling. About 3.1 1/sq m <77 gal/1000 sq ft) is used
where quenching is employed.
Waste Water Volume and Characteristics
Some typical characteristics of the combined waste water resulting from
solid tempered automotive fabrication are listed in Table 7. In all
cases except for pH, the values listed are the quantities added to the
water as a result of solid tempered automotive fabrication. The
background level in the influent water has been subtracted. The
significant parameters are BOD, suspended solids, and oil.
Flow-EProcess waste water flows vary significantly, ranging from 40.7-
105 1/sq m (1000 to 2,600 gal/1000 sq ft) or 492-1551 cu m/day (0.13 to
0.41 mgd). The typical flow is considered to be 49 1/sq m (1200
gal/1000 sq ft). As stated above, the waste water flow rates are
influenced both by the number of washing steps employed and by
recycling. The high flcw-rate is indicative of a plant which does not
recycle water.
Suspended solids—Suspended solids are added to the waste stream in the
form of glass particles resulting from seaming, grinding, and drilling.
A typical plant generates 4.9 g/sq m (1 lb/1000 sq ft). Some decrease
in suspended solids loading may be expected if dry seaming is practiced,
but a quantitative estimate of the reduction is not available.
Oil--Almost all the oil is contributed by the grinding solution carry-
over, with trace qunatities added by miscellaneous machine lubricants.
Typical plant waste water contains .64 g/sq m (.13 lb/1000 sq ft).
Biochemical Oxygen Demand--A small quantity of BOD is contributed to the
waste water by the oil in the coolant solution carry-over and to a much
lesser extent by traces of oil entering the wastewater stream as a
result of machinery lubrication. The typical raw waste water loading is
0.73 g/sq m (0.15 lb/1000 sq ft).
Other parameters-i-some information is also available on pH, temperature,
COD, and dissolved solids. Limited data are available for temperature
and COD, but BC (17 F) and 1.22 g/sq m (0.25 lb/ 1000 sq ft) are
indicative of the increases to be expected. A pH of nearly 7 was
45
-------
TABLE 7
RAW WASTEWATER (a)
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
Flow
k9
1/sq
m
1200
gal/1000 sq ft
PH
7
Temperature (b)
8 C
IT F
Suspended Solids
1+.9
g/sq
m
1
lb/1000 sq ft
100
mg/1
Oil
.61+
g/sq
m
.13
lb/1000 sq ft
13
mg/1
COD (b)
1.22
g/sq
m
.25
lb/1000 sq ft
25
mg/1
BOD
.73
g/sq
m
.15
lb/1000 sq ft
15
mg/1
Dissolved Solids
b.9
g/sq
m
1
lb/1000 sq ft
100
mg/1
(a) Representative of typical solid tempered automotive process wastewater. Absolute
value given for pH, increase over plant influent level given for other parameters.
(b) Indication of approximate level only; insufficient data is available to define
actual level.
-------
recorded in all cases, indicating that pH is not a problem in solid
tempered automotive glass fabrication. The dissolved solids increase of
1.9 g/sq m (1 lb/1000 sq ft) is higher than was expected. Water
treatment regenerants and boiler blowdown (which are combined with the
process wastewater stream for much of the sample data) are assumed to
have contributed at least in part to the dissolved solids increase.
Discussion-xNo significant variations in waste water volume or
characteristics are experienced during plant start-up or shutdown, and
there are no known toxic materials in waste water from the solid
tempered automotive glass manufacturing process.
Cooling
Cooling water is required at some solid tempered automotive glass plants
for the tempering hearth and quenching. Although no data is available,
heat rejection for these operations can be expected to be low with
respect to the other subcategories.
WINDSHIELD FABRICATION
Windshield fabrication is the manufacturing of laminated windshields
from glass blanks and vinyl plastic. Oil resulting from oil autoclaving
is the major constituent in this waste water. The major process steps
and points of water usage are illustrated in Figure 10. A detailed
description of the manufacturing process is given in section IV.
The typical windshield fabrication plant may be located in any part of
the country and uses oil autoclaves. Air autoclaves have been installed
at some new plants, but oil autoclaves are still used for 90% of the
windshields produced. The production schedule is variable and ranges
from an eight hour five-day week to a 21 hour six-day week.
Process Water and waste water
Water is used in windshield fabrication for cooling, seaming, and
washing. Three or four washes are required when oil autoclaves are
used. Initial, vinyl, and post-'lamination washes are required in all
cases. The prelamination wash has been eliminated by some plants.
Seaming-
Wet or dry seaming may be used in the windshield fabrication process.
With wet seaming, a sirall volume of water is used for dust control and
to flush away the glass particles produced. About 8.2 1/sq m (200
gal/1000 sq ft) of finished windshields is used.
47
-------
WASTEWATER
8.2L/SQM '
<200 GAL/1000 SO FT)
5°ta
WATER
~ WASTEWATER
81.5 L/SQ M
(2000 GAL/1000SQ FT)
47%
WATER
PARTING MATERIAL
APPLICATION
WATER
' WASTEWATER
16.3 L/SQ M
(400GAL/1000 SQ FT)
9%
VINYL INSERTS
WASTEWATER
28.5 L/SQ M
(700 GAL/1000 SQ FT)
16%
RECYCLED OIL
COOLING
WATER
* COOLING WATER
49.3 X103 KG-CAL/SQ M
(18.2 X 103 BTU/ SQ FT)
RECYCLED
SEPARATION
OIL
WATER
WASTEWATER
40.7 L/SO M
(1000 GAL/1000 SQ FT)
23%
SOLIDS TO
LAND . -
DISPOSAL y
WASTEWATER
NEGLIGIBLE AMOUNT
VINYL WASH
WASHING
RINSING
SEAMING
VINYL ASSEMBLY TACKING
PRELAMINATION
WASH ft RINSE
FINAL WASH A RINSE
TEMPLATE CUTTING
BENDING
AUTOCLAVING
DRAINING
CONSUMER
FIGURE 10
WINDSHIELD FABRICATION
48
-------
Initial Wash-
The first wash occurs early in the manufacturing process, following
cutting and seaming. Traces of cutting oil, residual glass particles,
and any dust which may have accumulated on the glass while in storage is
removed. Only water, which is generally heated, is used. No detergents
or other cleaning compounds are required.
Various types of washers are used. In some cases, once-through
washwater is discharged directly to the sewer. Newer plants generally
use recycling washers to reduce water usage. The waste water flows vary
from 28.5 to 138 1/sq m (700 to 3100 gal/1000 sq ft) of finished
windshields. The typical flow is 81.5 1/sq m (2000 gal/1000 sq ft).
Prelamination Wash-
The two pieces of glass used to form a windshield are bent as one unit,
and a parting material is used to prevent the two pieces from fusing
during the bending process. The parting material is usually washed
before the vinyl sheet is inserted, but in some cases a material is used
that does not require washing. The exact nature of the parting
materials used and the details of their application and removal are
considered proprietary by the industry.
The prelamination washer also serves to clean the glass surface of any
dirt or spcts since they cannot be removed following lamination. A
three-stage washer is usually used. The first stage is a detergent wash
followed by a city-water rinse and a final demineralized-water rinse.
Deionized rinse water is the only makeup to the system. It is recycled
through the stages and discharged as blowdown from the detergent wash.
All stages are heated. Water usage is about 16.3 1/sq m (400 gal/1000
sq ft) of windshields produced. The limited data available indicate a
hot waste water with relatively high phosphorus, moderate dissolved-
solids, and low organic and suspended solids increases.
Vinyl Wash-
The plastic used for laminating is shipped from the manufacturer in
rolls. Sodium bicarbonate is used as a parting material to keep the
plastic from sticking and is removed in a two- or threestage washer.
The three-stage system uses two city-water washes in series followed by
a deionized-water rinse. The two-stage system is used where relatively
low dissolved-solids water is available and consists of two city-water
rinses in series. Highly variable quantities of water are used for
washing plastic, ranging from 12.2 to 285 1/sq m (300 to 7000 gal/1000
sq ft). The typical flow rate is 28.5 1/sq m (700 gal/1000 sq ft). The
waste water is high in dissolved solids because of the sodium
bicarbonate. The data also indicate a COD of 100 mg/1 or 2.8 g/sq m
(0.58 lb/1000 sq ft) based on the typical flow. The high COD is
unexpected and has not been explained.
49
-------
Post-Lamination Wash-
Residual oil from the laminating autoclaves is removed in a series
washing operation. Two basic systems are employed in the industry. In
one case only washing is accomplished. In the second case, the washing
is done in two stages with dry seaming in between washing steps. The
waste water characteristics are similar for both systems. For the
purposes of this report, both systems will be grouped and discussed as
one process.
Washwater for each stage is recycled out of a reservoir. In some cases,
flows are countercurrent with blowdown from the following stage serving
as makeup for the preceding stage.
The old method of post-lamination washing, still used at some plants, is
to use a detergent wash as the first stage followed by two city-water
rinses and possibly a final deionized-water rinse. Large quantities of
detergent are required with this system, and very oily emulsified waste
water is produced.
Using a hot-water rinse before the detergent wash has been found to cut
detergent usage by up to 95%. Most of the oil is removed by the hot
water, and proportionately less detergent is required to emulsify the
residual oil. Although the same quantity of oil remains in the waste
water stream, the majority is free oil and is more readily removed than
emulsified oil.
The waste water flows are the same for both methods. The typical post-
lamination washer flow is 40.7 1/sq m (1000 gal/1000 sq ft) of
windshields produced. Waste water characteristics are also similar for
both methods, except higher phosphorus concentrations resulting from
higher detergent usage are expected where an initial detergent wash is
used.
Oil Separation System-
Small amounts 'of water are picked up by the autoclave oil from
condensation, cooling water leaks, and other sources. The oil and water
separate in the oil storage tanks and the water is removed to a second
tank where further gravity separation takes place. The oil is recycled
to the autoclaves and the water is either discharged to the sewer or to
the autoclave washwater treatment system. The stream accounts for only
one to two percent of the total waste water flow.
Waste Water Volume and Characteristics
Some typical characteristics of the combined waste water stream
resulting from windshield fabrication are listed in Table 8. In all
cases except for pH, the values listed are the quantities added to the
water as a result of windshield fabrication. The influent water
background levels have been subtracted. These data apply to a plant
50
-------
TABLE 8
RAW WASTEWATER (a)
WINDSHIELD FABRICATION USIUG OIL AUTOCLAVES
Flow
175
1/sq
m
1+300
gal/1000 sq ft
pH
7-8
Temperature
18.9 C
1+0 P
Suspended Solids
u.i+
g/sq
m
• 9
lb/1000 sq ft
25
mg/1
Oil
298
g/sq
m
6l
lb/1000 sq ft
1700
mg/1
COD
298
g/sq
m
6l
lb/1000 sq ft
1700
mg/1
BOD
5.9
g/sq
m
1.2
lb/1000 sq ft
33
mg/1
Total Phosphorus
.98
g/sq
m
.2
lb/1000 sq ft
5.6
mg/1
(a) Representative of typical process wastewater from the fabrication of windshields
using oil autoclaves. Absolute values are listed for pH; the increase over plant
influent level is given for other parameters.
-------
where an initial hot-water rinse is used for the post-lamination wash.
No information is available for plants using an initial detergent wash.
Flow—Waste water flow rates from plants considered typical of the
windshield fabrication process vary from 52.9 to 492 1/sq m (1300 to
12,100 gal/1000 sq ft) of windshields produced. This corresponds to 454
to 2195 cu m/day (0.12 to 0.58 mgd). The variability is due to the type
of washers used (once-through as opposed to recycling) and to the
dissolved^solids content of the plant water. Less recycling can be
practiced where influent dissolved solids are high. The typical flow is
175 1/sq m (4300 gal/1000 sq ft) .
Suspended solids--Suspended solids are contributed to windshield
fabrication waste water as a result of seaming. Carry-over results,
even when dry seaming is used. The data indicate a typical reported
value of 137 g/sq m (28 lb/1000 sq ft) or 780 mg/1. This figure is much
higher than the actual suspended-solids level because of oil
interference since free oil tends to collect on the filter used in the
suspended solids determination, causing high readings. The actual
typical suspended solids are estimated at 4.4 g/sq m (0.9 lb/1000 sq ft)
or 25 mg/1.
Oil—Almost all the oil is contributed by the laminating process, with
trace amounts resulting from machinery lubrication. The typical loading
is 298 g/sq m (61 lb/1000 sq ft).
Chemical Oxygen Demand—A significant COD is noted as a result of the
high oil content from the post-lamination wash. Almost the entire
loading of 298 g/sq m (61 lb/1000 sq ft) may be attributed to oil. As
indicated above, some COC is also contributed by the vinyl washwater.
pH—The pH for all of the plants for which data was received ranged
between 7 and 8. Sodium bicarbonate, removed from the vinyl, is the
only constituent added which would be expected to significantly affect
pH. Sufficient dilution is provided by the other waste waters so that
little effect is noted.
Phosphorus—Phosphorus results from detergents used in the preassembly
and post-lamination washes. The available information on phosphorus
loading shows substantial variation, indicating variable detergent
usage. No basis is available for defining phosphorus or detergent
limitations; therefore, the typical phosphorus value is based on the
plants with high phosphorus loadings. The typical value is 0.98 g/sq m
(0.2 lb/1000 sq ft).
Other parameters—Limited information is available on BOD and
temperature characteristics for raw windshield-lamination wastewater.
The data indicate a EOD loading of 5.9 g/sq m (1.2 lb/1000 sq ft) or 33
mg/1. As with COD, the BOD can be attributed to the oily waste water
temperatures. These show an average discharge temperature immediately
52
-------
following the process of 38.9°C (102°F) or 18.9°C (40°F) over the
influent temperature. Sufficient data is not available to give an
indication of the dissolved-solids levels.
Discussion--No significant variations in waste water volume or
characteristics are experienced during plant start-up or shutdown, and
there are no kncwn toxic materials in waste water from the windshield
fabrication process.
Cooling
Cooling water is required for autoclave operations and the compressors.
Data is available from two plants. Values are 40,100 kg-cal/sq m
(14,800 Btu/sq ft) and 58,600 kg-cal/sq m (21,600 Btu/sq ft) of
fabricated automotive glass. The average heat rejection is 49,300 kg-
cal/sq m (18,200 Btu/sq ft).
53
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
Subcategories causing significant pollution in this portion of the flat
glass industry are plate glass manufacturing, solid tempered automotive,
and windshield fabrication. The major waste water constituents are the
result of various types of grinding and oil autoclaving. Less
significant dissolved-solids are contributed by parting materials used
at several points in these processes for glass or plastic separation.
The major parameters cf pollutional significance for the combined group
of subcategories are:
Suspended Solids
Oil
BOD
COD
pH
Total Phosphorus
Temperature
Dissolved Solids
These do not occur in all cases for all subcategories, or may be less
significant in one subcategory than in another. Table 9 lists the
typical concentrations by subcategory. With the exception of
detergents, these are the only constituents known to be added. On the
basis of the data collected, no toxic or hazardous substances are
contained in these process waste waters.
SUSPENDED SOLIDS
Suspended solids are contained at various concentrations in plate,
float, and automotive fabrication waste waters. Suspended solids are
regulated in almost all cases where effluent limitations are imposed
since they are aesthetically unappealing, and contribute to turbidity
and in some cases sludge deposits in the receiving body of water.
Typical raw waste concentrations range from 15 mg/1 for float to 15,00 0
mg/1 for plate glass manufacturing.
55
-------
TABLE 9
CONCENTRATION OF WASTEWATER PARAMETERS
PRIMARY FLAT GLASS MANUFACTURING AND AUTOMOTIVE GLASS FABRICATION
TYPICAL RAW WASTEWATER CONCENTRATION (a)
Rolled
Glass
Suspended Solids, mg/l
Oil, mg/l
COD, mg/l
BOD, mg/1
pH
Total Phosphorus, mg/l
Temperature F
Dissolved Solids, mg/l(d)
w
CO
-------
OIL
Oil is contributed to flat glass waste waters as a result of laminating,
edge grinding, and miscellaneous machinery lubrication. At least traces
of oil appear in all process waste water, but significant quantities are
contained in solid tempered automotive and windshield fabrication
wastes. Free oil will float, causing an aesthetically unappealing scum
or sheen on the water. The State of Illinois limits oil discharge to 15
mg/1. Public Health Service Drinking Water Standards, by limiting
carbon chloroform extract (CCE) to 0.2 mg/1, allow virtually no oil
concentration in drinking water. Raw waste water concentrations in this
study range from traces resulting from machinery lubrication to 13 mg/1
for solid tempered automotive and 1700 mg/1 for windshield fabrication.
CHEMICAL OXYGEN DEMANE
Some COD is contributed by all of the process waste waters, and the
values range from 15 mg/1 for float glass to 1700 mg/1 for the typical
windshield fabrication plant. In most cases, COD is a direct result of
the oil concentration. Because BOD concentrations are low, COD is a
more accurate measure of organic content for flat glass waste water.
BIOCHEMICAL OXYGEN DEMAND
At least trace concentrations of BOD are present in all of the process
waste streams. Insignificant loadings cccur for plate and float glass
and at least measurable concentrations are recorded for solid tempered
automotive and windshield fabrication. BOD is inferior to COD as a
measure of organic pollution, because of the low concentrations recorded
in the flat glass industry and the absence of organic loading, except
for oil. However, COC data was not available for all subcategories.
pH
Except for plate/ glass manufacturing, pH is not a significant pollutant.
pH levels of 6-9 are generally considered acceptable, and these are
readily achieved in all the other subcategories. Plate glass wastes
tend to be alkaline, and in some plants acid treatment is used to reduce
the pH to 9.
TOTAL PHOSPHORUS
Phosphorus is contributed to the windshield waste water stream and, in
some cases, to float waste water through the use of detergents.
Phosphorus discharge may contribute to the eutrophication of some bodies
of water where background phosphorus concentrations limit algae growth.
Total phosphorus is also a measure of detergent usage.
57
-------
TEMPERATURE
Most of the washing operations in flat glass manufacturing and
fabrication require warm-to-hot water and at least one stage of the
washwater is generally heated- Some data on water temperatures
immediately following the washers has been presented in this report.
Temperature increases at this point are much greater than at the end of
the pipe immediately before the receiving stream. Dilution with once-
through cooling water and natural cooling in the sewer pipe tend to
reduce discharge temperatures to less than 4.7°C (10° F) over ambient,
substantial temperature increases may adversely affect aquatic
organisms; insufficent data is available at the present time, however,
upon which to base limitations. These will be set at a later date.
DISSOLVED SOLIDS
Dissolved solids are critical for all washing operations, and the
concentrations must be kept low enough so that spotting of the glass
does not occur. Deionized water is used in some cases for a final
rinse. Because low dissolved solids is a process consideration,
relatively small concentrations of dissolved solids are discharged in
the process waste water. Glass is inert and, therefore, dissolved-
solids sources are limited to calcium sulfate in the plate process,
sodium sulfate in the float process, various parting materials used in
fabrication, and to concentration increases due to evaporation. Owing
to the relatively low concentration, limited dissolved-solids data have
been collected by the industry. Much of the industry includes the
auxiliary wastes in the process-waste stream, making it difficult to
determine the dissolved solids contributed by the process. The
contribution by auxiliary wastes, which are not covered by this study,
is generally more significant. The major concern for dissolved solids
is in a recycle system where removal is necessary because of the low
washwater dissolved-solids requirements.
58
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SECTION VII
CCN1ROL AND TREATMENT TECHNOLOGY
As indicated in Chapter V, the major constituents requiring treatment
for primary flat glass manufacturing and automotive fabrication are
suspended solids and oil. The treatment methods presently employed have
been developed for this purpose. Effluent values are given as monthly
averages except as noted.
No process waste water and, therefore, no treatment is required for the
rolled and sheet subcategories. In all cases, polyelectrolyte addition
with lagoon sedimentation is practiced for plate glass manufacturing.
Upgrading the lagoon system and partial recycle are methods of reducing
waste loads from the plate process. Float waste water is of high
quality and presently is not treated. Solid tempered automotive glass
waste water is also net treated but oil and suspended solids must be
reduced. Flotation and centrifugation are used to reduce the oil
discharged by the windshield fabrication process. Additional treatment
will further reduce and assure low discharge levels in the flat glass
industry. In some cases, treatment technologies developed for other
industries will have to be used.
SHEET AND ROLLED GLASS MANUFACTURING
No process waste water is produced by the sheet and rolled glass sub-
categories. The manufacturing processes are dry with process water used
only in the batch for dust ccntrol.
Both subcategories have significant cooling requirements and use
substantial quantities of cooling water. Although cooling systems are
not specifically covered in this report, one system related to water
pollution control will be discussed briefly.
i
Several sheet glass plants are eliminating a pollution problem by
disposing of chromium treated cooling tower blowdown in the batch.
Approximately 42 1/metric ton (10 gal/short ton) can be disposed of by
this method. This is especially interesting in view of the adverse
affect of chromium on glass quality. At a low concentration, which has
not been defined, chromium causes "stones" or imperfections in the
glass. Apparently, this concentration is not exceeded in sheet glass
or, more likely, the imperfections are not significant because the glass
is thinner and of lower quality than other types of primary glass.
Discussions with glass industry personnel have indicated great re-
luctance to consider disposal of cooling tower blowdown, especially
chromium treated, in the batch for plate, float, or rolled glass. These
glasses are thicker and of higher quality and it is thought that
noticeable imperfections in the glass will result. An unsuccessful
59
-------
attempt at batch disposal could be quite costly. Glass melting is a
continuous process with a large volume of melted glass contained in the
furnace. If an undesirable concentration of some contaminant is
introduced into the glass furnace, it might result in a week or two of
production of unusable glass to dilute the furnace contents to an
acceptable level.
Disposal of other glass plant auxiliary wastes in the batch such as
boiler blowdown and softener and deionizer regenerants is also within
the realm of possibility, however, none of these has as yet been
demonstrated. Washwater, especially from the float process, should also
be amenable to batch disposal. Although batch disposal is not a cure-
all for primary glass waste water disposal (the volume of process and
auxiliary waste water discharge far exceeds the 42 1/metric ton (10
gal/short ton) maximum that can be accepted by the batch),
experimentation within the industry should be encouraged. Batch
disposal of cooling tower blowdown for sheet glass manufacturing has
been demonstrated and should be applicable at many plants. It is too
early, however, to predict universal applicability and each process
should be considered on an individual basis.
PLATE GLASS MANUFACTURING
Plate glass manufacturing produces a large volume of waste water, high
in suspended solids with lesser concentrations of dissolved solids, BOD,
and COD. Waste water sources and characteristics are described in
Section V. Plate glass manufacturing is rapidly being replaced by the
float process. Float glass is of similar quality, but is less expensive
to produce and process waste waters are insignificant compared to the
plate process. Only three plate glass plants remain in this country and
at least two of these may be closed by 1977.
Owing to the high operating costs and pollution load, no new plate glass
facilities are anticipated. The industry trend of replacing plate glass
with float glass' has shown that plate glass manufacturing can be
successfully eliminated, therefore, only treatment technologies for
reducing pollutant loadings from existing plate glass plants will be
discussed.
In-Plant Modifications
No apparent in-plant modifications of pollutional significance have been
developed for the plate glass manufacturing process. The three
remaining plants are relatively modern by plate standards. Plate glass
technology development ended with the advent of the float process. Sand
and rouge recovery systems are based on the latest technology.
In one case, cerium oxide rather than iron oxide is used as the pol-
ishing medium. This plant also has the most efficient waste water
treatment of all of the plate glass plants indicating the possible
6(3
-------
beneficial effects of cerium oxide. Cerium oxide has a higher specific
gravity than rouge which may account for better settlability. The
switch from rouge to cerium oxide was made for reasons other than
pollution control and comparative effluent data before and after the
change do not exist. Although insufficient information is available to
conclude that cerium oxide is more easily removed from plate waste
water, this method might be considered where problems are experienced
with iron oxide removal.
Existing Treatment Systems (Alternative A)
Each of the three remaining plate glass plants use lagoon treatment with
polyelectrolyte added to. the influent waste water. The typical flow
rate is 45,900 1/metric ton (11,000 gal/short ton) or 18,168 cu m/day
(4.8 mgd) and the suspended solids loading is 690 kg/metric ton (1,375
lb/short ton) or 15,000 mg/1. A cationic polyelectrolyte is added to
the influent sewer with mixing accomplished through the natural
turbulance of the water. The typical lagoon is square, has an area of
approximately 5.26 ha (13 acres) and a working depth of 2.44 m (8 feet).
Available data indicate the highest efficiency presently available using
this system is 99.69S suspended solids reduction to produce an effluent
concentration of 2.5 kg/metric ton (5 lb/short ton) or 54 mg/1. The COD
is reduced approximately 90% to 0.4 5 kg/metric ton (0.9 lb/short ton) or
10 mg/1. Additional treatment methods can be employed to further reduce
effluent suspended solids levels.
Additional Treatment Methods
Several methods for upgrading existing plate glass lagoon systems to
increase suspended solids removal efficiency are apparent. Improved
polyelectrolyte addition and a two-stage lagoon system should reduce
suspended solids to 30 mg/1. An additional reduction to less than 5
mg/1 can be accomplished by sand filtration of the lagoon effluent. The
filter volume can in turn be reduced by recycling the lagoon effluent
back to the grinding and polishing process. These methods of treatment
are illustrated in Figure 11.
Lagoon Improvements (Alternative B) -
It should be possible to reduce lagoon effluent suspended solids to 30
mg/1 or 1.38 kg/metric ton (2.75 lb/short ton) by improving coagulant
mixing and using a two-stage lagoon system. The maximum daily discharge
from this system will be 60 mg/1 or 2.76 kg/metric ton (5.5 lb/short
ton. A mixing tank is added at the lagoon influent to assure proper
polyelectrolyte dispersion. The mixing is for one minute or less and is
of sufficient velocity that essentially instantaneous mixing of the
polyelectrolyte is assured.
61
-------
WATER
POLYELECTROLYTE
FLASH MIXER
BACKWASH TO
PRIMARY MIXER
RETURN TO
GRINDING
SURFACE
DISCHARGE
SAND
FILTER
PUMP
STATION
GRINDING
POLISHING
WASHING
SECONDARY
LAGOON
PRIMARY
LAQOON
POLYELECTROLYTE
FLASH MIXER
FIGURE 11
WASTEWATER TREATMENT
PLATE PROCESS
62
-------
The lagoon is divided into two stages by constructing an additional
levee. This will produce two lagoons of 2.H3 ha (6 acres) each in the
typical plant. The two-stage system will reduce the effects of wind
action which is a major cause of low effluent quality. A second mixing
tank with provision for adding additional polyelectrolyte between the
lagoon segments is provided. It is not certain that the second
polyelectrolyte addition step will be necessary, but the equipment is
included for cost estimating purposes.
The minimum allowable lagoon surface area and detention time is not
known. The data from existing one-cell lagoon systems indicate no
correlation between surface area or detention time and suspended solids
removal. This may be due to poor design, lack of solids removal, or
other factors. The lowest effluent concentration was produced in the
lagoon with the shortest detention time. This lagoon was used as the
basis for the recommended improvements. The other lagoon systems,
having a longer detention time, if properly operated, should have no
trouble achieving the same effluent levels.
Many polyelectrolytes are on the market, but laboratory testing is
required to determine the most efficient one for each application.
Based on current practice in glass plants, a liquid cationic poly-
electrolyte is most effective, although some inorganic coagulants may
also be effective. The latter should be avoided, if possible, where
recycle is considered because of the dissolved solids increase.
Coagulation and sedimentation are widely employed for both water and
waste water treatment. An effluent concentration much less than 30 mg/1
suspended solids is achieved in many systems. Although most
conventional systems are operated in specially designed tanks, there is
no evidence to indicate that a lagoon system with sufficient protection
against short circuiting and wind cannot achieve an average effluent of
30 mg/1 suspended solids.
Filtration (Alternative C) -
Lagoon effluent suspended solids can be further reduced to less than
0.23 kg/metric ton (0.46 lb/short ton) or 5 mg/1 by rapid sand
filtration. The entire lagoon effluent is filtered through a standard
gravity sand filter at an assumed 163 1/min/sq m (4 gpm/sq ft). The
filter backwash is recycled to the head of the lagoon for suspended
solids removal.
Rapid sand filtration is a widely used and thoroughly proven technology.
Such filters are used extensively in water treatment plants following
coagulation and sedimentation. Suspended solids levels substantially
below 5 mg/1 are almost the rule in the water treatment industry and
similar values have also been achieved for the filtration of secondary
sewage effluent. Other filters such as mixed media, pressure, and
upflow filters are also available and may be more desirable in some
63
-------
cases, but rapid sand filters are chosen for illustrative purposes
because more background information on cost and treatment efficiency is
available.
Filtration and Recycle (Alternative D) -
The volume of water requiring filtration can be substantially reduced by
recycling the lagoon effluent back to the grinding process. Recycle is
not presently employed in the industry, but there is adequate reason to
believe that it is feasible especially if lagoon effluent suspended
solids are reduced to 30 mg/1. In most cases, this is a lower
concentration than the raw river water presently being used.
A liberal 20% blowdcwn from the recycle system is assumed to allow for
any unforeseen dissolved solids problems. It is likely that a lower
blowdown rate can and will be achieved to reduce filtration
requirements. The filtered effluent suspended solids concentration will
still be 5 mg/1 or less but, owing to the 80% volume reduction, the
effluent loading will te reduced to 0.045 kg/metric ton (0.09 lb/ short
ton). COD will be reduced to 0.09 kg/metric ton (0.18 lb/short ton).
FLOAT GLASS MANUFACTURING
Float glass manufacturing is rapidly replacing the plate glass process
as the method for producing high quality thick glass sheets. Conversion
to the float process has drastically reduced pollution loadings related
to the manufacture of this type of glass. Washing is required for some
types of glass and this is the only process waste water resulting from
float glass production. Raw waste suspended solids loadings are reduced
from 690 kg/metric ton (1,375 lb/short ton) for plate glass to 2
g/metric ton (0.0041 lb/short ton) for float glass. The waste water
loading for other parameters is equal to or less than that for suspended
solids. More detailed information on waste water characteristics is
presented in Section V. The typical flow is only 138 1/metric ton (33
gal/short ton) or 13 6 cu m/day (0.036 mgd). Owing to the high quality,
float washwater is presently not treated.
In-Plant Modifications
Until several years ago, detergents were used in the float washer. In
an effort to reduce phosphorus discharge and prevent foaming in the
receiving body of water, most plants have now found that sufficient
washing can be accomplished without detergents. Non-detergent washing
is now typical. There is no evidence to indicate that elimination of
detergents in the float wash is detrimental to the product or the
process. Elimina.ticn of detergents in the float wash is believed
possible in all cases.
Recycling washer systems are typical for the industry. Recycling,
although having no effect on the quantity of pollutants discharged, does
64
-------
conserve water and should be encouraged. A typical system involves one
or two stages of city water washing and a final, totally recycled
deionized water rinse. Dissolved solids are removed in the first washer
stages and any residual that might cause spotting is removed by the
deionized water rinse. Deionizer regeneration requirements are governed
by the buildup of dissolved solids in the preceding wash. The more
dissolved solids carried over into the final rinse, the more picked up
and thus removed by the deionizer.
Recycle and Treatment Methods
Waste water phosphorus loadings can be eliminated by discontinuing the
detergent wash and all effluent loadings can be eliminated by recycling
the washwater to other processes. Dissolved solids is the limiting
factor governing discharge from a recycling float washer system.
Dissolved solid removal is required if the water is recycled for
washing. Where no detergents are added, the washwater is of high
quality and can be recycled to the batch and cooling tower. These
systems are illustrated in Figure 12.
Detergent Elimination (Alternative A)-
The use of detergents for float glass washing can be eliminated without
any adverse effects on the manufacturing process as discussed above.
Although this is an in-plant modification, by reducing phosphorus, it
has the same effect as treatment and is considered as such for the sake
of continuity in this report. Elimination of detergent essentially
eliminates phosphorus from float process waste water as no other source
is known. No data is available on the quantity of phosphorus presently
discharged, but elimination of detergents will achieve essentially 100%
removal. With credit given for evaporation, trace phosphorus, and
analytical error, a typical plant can achieve an effluent phosphorus
concentration of 0.05 g/metric ton (0.0001 lb/short ton) or 0.5 tng/1.
Recycle to Batch' and Coding Tower (Alternative B) -
Float glass washwater, where no detergents are used, is of high quality
and can be recycled as batch water or cooling tower 'makeup. The data
indicate very low increases of all contaminants result from washing.
The dissolved solids will average 300 to 100 mg/1 and the concentration
of other constituents will be less than 15 mg/1. The exact temperature
is not known, but in one case was measured at 37°C (98°F) . With the
exception of temperature, these characteristics are not significantly
different from those of the city water presently being used in the batch
or as cooling tower makeup.
Washwater can be collected and pumped through overhead piping to the
batch house or cooling tower. The maximum flow acceptable for the batch
is 42 1/metric ton (10 gal/short ton). The remaining 96 1/metric ton
(23 gal/short ton) may be pumped to the cooling tower. Batch and
65
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WATER
FLOAT
WASHER
RECYCLE TO
BATCH OR COOLING
TOWER
RETURN TO
FLOAT WASHER
DIATOM ACEOUS
EARTH
FILTER
REVERSE
OSMOSIS
T
+
BRINE
EVAPORATION
I
I
+
SOLIDS TO
PERMANENT
STORAGE
FIGURE 12
WASTEWATER TREATMENT
FLOAT PROCESS
66
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cooling tower disposal of float washwater has not been demonstrated, but
owing to the high quality of this waste water, there are no apparent
reasons why this disposal method should not be implemented.
Total Recycle {Alternative C) -
It is theoretically possible to recycle the washwater back to the washer
following dissolved solids removal. Three dissolved solids removal
systems are sufficiently developed at present to be considered currently
available. These are ion exchange, electrodialysis, and reverse
osmosis. Ion exchange is already used extensively for final rinse water
treatment; however, this process significantly increases the total
dissolved solids loadings when regeneration wastes are considered.
Current research and development effort in dissolved solids removal
technology center cn reverse osmosis. Significant improvement and
future development of this process are anticipated. For these reasons,
reverse osmosis is selected for dissolved solids removal in this report.
It is assumed that reverse osmosis will concentrate the dissolved solids
approximately five tines and produce a waste water flow rate of 20% of
the initial volume treated. This waste water stream must be disposed of
if any net pollution reduction is tc be achieved. It may be possible to
discharge this waste water to the batch, but this has not been
demonstrated. The proven method of evaporation to dryness will be
assumed in this report.
A complete recycle system using reverse osmosis might be set up as
follows. The washwater discharge will first pass through a diatomaceous
earth filter with an oil absorptive media to reduce both oil and
suspended solids to less than 5 mg/1. Both of these constituents have
an adverse effect on the reverse osmosis membranes. The filter is a dry
discharge type, and spent diatomaceous earth is discharged at
approximately 15% dry solids content, suitable for land disposal.
Following filtration, dissolved solids are removed by reverse osmosis.
The water is forced at high pressure through a semipermeable membrane
that retains most of the dissolved ions. Product water is returned to
the washer and the waste brine is evaporated. The steam is condensed
and also returned to the washer and the salt residue must be stored
permanently in lined basins to prevent ground water contamination.
No total recycle systems have been demonstrated or contemplated in the
flat glass industry. At the present time, reverse osmosis is used
mainly for boiler water treatment, generally in competition with ion
exchange. With the present state of the art, it is* impossible to
accurately predict the feasibility of the system without pilot plant
data. Even if technically feasible, the cost/ benefit ratio will be
high. Capital and operating costs are high, relatively large amounts of
energy are required, and two types of solid waste must be disposed of on
land. The untreated washwater contains only 300-400 mg/1 dissolved
67
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solids and less than 15 mg/1 of other constituents. In most cases these
concentrations will not significantly affect the receiving stream.
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
Solid tempered automotive glass fabrication produces a waste water with
significant quantities cf suspended solids, and lesser quantities of oil
and BOD. The BOD is the result of oil contamination. Typical raw waste
water characteristics are:
Suspended Solids 100 mg/1
Oil 13 mg/1
BOD 15 mg/1
These and other waste water characteristics are more fully described in
Section V. The typical flow rate is 49 1/sq m (1200 gal/1000 sq ft).
None of the plants studied presently treat solid tempered automotive
waste water.
In-Plant Modifications
In-plant modifications may reduce waste water volume and loading. Most
plants presently collect the sludge removed from the coolant recycle
system for disposal as landfill; however, in a few cases this is
discharged to the sewer system imparting an unnecessary load on the
treatment system. The method of collection and dewatering used by most
plants is a chain-driven scraper system which scrapes the sediment to
discharge at one end of the tank and skims the floating material for
discharge at the other end. The combined sludge is collected in a
portable container for hauling to landfill. The sludge has an
approximate moisture content of 90X and is well suited for land
disposal.
In some plants, cooling water is sprayed directly onto the glass.
Although little contamination is picked up in this quenching process,
the water is in contact with the glass and is, therefore, a process
waste water. Quenching may be replaced by air cooling thereby reducing
the volume of waste water requiring treatment.
Waste water volumes, but not the quantity of pollutants discharged, can
be reduced by using recycling washers. Generally older washers tend to
be of the once-through type, while new equipment is generally recycling
with a two-stage system most common. Water is pumped over the glass
from two separate reservoirs, and make-up water is added to the second
wash tank. Overflow from second tank goes to the first wash tank and
overflow from this tank is discharged to the sewer.
Sufficient water pressure and volume is required for the washer sprays
to dislodge and flush away glass particles, oil, or dirt that might be
on the glass. Recycling does not significantly affect these
68
-------
requirements until the concentration of contaminants increases to the
point where residue is left on the glass. Some recycling can be
employed in all plants, even where dissolved solids are high. Only one
recycle will cut the waste water flow to half that required for a once-
through system.
The extent of recycle is limited by oil and suspended solids buildup.
It is theoretically possible to remove these contaminants using a
diatomaceous earth filter with oil absorption media. This type
equipment is discussed below in more detail. Complete recycle is
limited by dissolved solids buildup, with at least one company believing
that 300-400 mg/1 is the allowable maximum concentration.
Treatment Methods
The major contaminants to be removed from solid tempered automotive
glass are suspended solids and oil. Treatment may be accomplished at
the individual washer or at end of pipe. It may be beneficial to
consider individual treatment for new sources, but owing to limited
floor space, end of Fipe treatment is most practical for existing
plants. Location of the treatment system does not influence the degree
of pollutant reduction.
Coagulation-sedimentation and filtration are common methods for reducing
suspended solids and oil that are applicable to solid tempered waste
water. These treatment methods and a recycle system using reverse
osmosis will be discussed and are illustrated in Figure 13. For cost
estimating pruposes, no waste water treatment is considered to be
treatment Alternative A.
Coagulation Sedimentation (Alternative B) -
Coagulation and sedimentation is commonly used in the water industry for
suspended solids removal. Solid tempered automotive glass wastewater is
not unlike some of the river water commonly treated except for the
higher oil content. It should be possible, using a properly designed
system and the correct coagulant to achieve an effluent suspended solids
concentration of 2 5 mg/1.
A solids contact coagulations-sedimentation system with sludge dewatering
by centrifugation is assumed. Solids contact differs from conventional
coagulation-sedimentation in that a portion of the sludge is returned to
provide more surface area for trapping the newly coagulated particles.
Numerous organic and inorganic flocculants and flocculant aids are
available and individual testing will be required in each case to
determine the optimum chemicals and addition rate. Polyelectrolytes are
preferable to inorganic flocculants because they do not contribute
dissolved solids. Owing to the nature of the waste water, however, it
is likely that an inorganic flocculant such as alum or a coagulant aid
such as bentonite clay will be required. Design parameters cannot be
69
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MAKE-UP
WATER
EDGE
GRINOING
RECIRCULATION
SETTLING TANKS
r
i
4-
SOLIDS TO
LAND DISPOSAL
t
I
»
DRILLING
WASHING
QUENCHING
CENTRIFUGE
CHEMICAL
COAGULATION
T
A
DIATOMACEOUS
EARTH
FILTRATION
WATER
RETURN TO
PROCESS
REVERSE
OSMOSIS
1
1
+
BRINE
EVAPORATION
I
SOLIDS TO
PERMANENT STORAGE
FIGURE 13
WASTEWATER TREATMENT
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
70
-------
accurately predicted without at least laboratory scale studies. Con-
ventional design rates can be assumed.
Sludge will be dewatered by centrifugation. It is difficult to
accurately predict the sludge volume or moisture content without
experimental data. A conservative estimate of the volume expressed in
terms of production is 21 cu cm/sq m (0.07 cu ft/1000 sq ft) with an 80%
moisture content. Sufficient capacity for all equipment will be
required so that effluent quality is maintained when portions of the
equipment are down for maintenance.
Coagulation-sedimentation for suspended solids removal is a well-
established process that can be successfully applied to solid tempered
automotive glass waste water. An effluent of 25 mg/1 suspended solids
or 1.22 g/sq m (0.25 lb/1000 sq ft) should be readily achieved and the
maximum daily concentration should not exceed 4 0 mg/1 or 1.95 g/sq m
(0.4 lb/1000 sq ft). It is likely that oil and, therefore, BOD will
also be removed, especially if inorganic coagulants are used, but
lacking substantiating evidence, no credit is given for oil and BOD
removal. Dissolved solids will be increased somewhat if inorganic
coagulants are used.
Filtration (Alternative C) -
A further decrease in suspended solids and oil can be achieved by
filtering the settled effluent through a diatomaceous earth filter with
a media especially treated for oil removal. This type of filter is
commonly used to remove oil from boiler condensate.
The diatomaceous earth filtration system will consist of the filter,
precoat tank, and a slurry tank for continuously feeding diatomaceous
earth. The filter will be of the dry discharge type so that the sludge
will not require dewatering. Sufficient units will be provided so that
the system will continue to function with one unit down for cleaning or
maintenance. Experimentation on solid tempered automotive waste water
will be required to develop exact design parameters, but the approximate
filter rate will be 20.1 to 40.7 1/min/sq m (0.5 to 1 gpm/sq ft) and
approximately 0.9 kg (2 lb) of diatomaceous earth is required per 0.4 5
kg (1 lb) of oil removed. Oil, rather than suspended solids, is
expected to be limiting; therefore, approximately 1.28 g/sq m (0.26
lb/1000 sq ft) of diatcmaceous earth will be required.
71
-------
Effluent oil and suspended solids should be reduced to well below 5 mg/1
by diatomaceous earth filtration. The BOD reduction resulting from oil
removal can only be estimated. An effluent BOD of 10 mg/1 is assumed
although actual values will probably be lower. These loadings expressed
in terms of typical plant production are as follows:
Suspended Solids .24 g/sq m (0.05 lb/1000 sq ft)
Oil .24 g/sq m (0.05 lb/1000 sq ft)
BOD .49 g/sq m (0.1 lb/1000 sq ft)
COD will probably be reduced in equal or greater proportion than BOD.
Equivalent effluent levels can also be achieved using sand filtration,
as described for plate glass (waste water treatment), if sufficient oil
is removed in he coagulation-sedimentation process. Inorganic
coagulants such as alum will absorb oil. Trace quantities of oil are
commonly removed by coagulation-sedimentation in water treatment plants.
The quantity of oil removed and the conditions for removal cannot be
accurately stated without experimental data. Another consideration is
oil fouling of the sand media. Oil will tend to coat the sand
particles, and if sufficient quantities reach the filter, special
cleaning procedures may be required. Due to the unknown factors related
to sand filtration, a diatomaceous earth filtration system is used for
cost estimating.
Total Recycle (Alternative D) -
As in all cases for the flat glass industry, it is theoretically
possible to completely recycle the treated effluent following dissolved
solids removal. No such system is presently employed in the industry
and only very general assumptions on the type of equipment required and
the treatment efficiency can be made.
Filtered effluent can be passed through a reverse osmosis unit with 80S
of the flow returned to the plant. The other 20%, consisting of waste
brine, is evaporated with the steam condensed and returned to the plant
and the salt permanently stored in a lined lagoon. The reverse osmosis
system is similar for all flat glass applications and is discussed more
fully in the float glass treatment section.
Dissolved solids data from the solid tempered automotive subcategory is
limited and difficult to interpret because high dissolved solids from
auxiliary waste streams are included. The maximum allowable dissolved
solids concentration is also unknown. It is certain, however, that
maximum possible recycle will be practiced* prior to reverse osmosis.
For cost estimating purposes,a conservative estimate of half of the
typical flow or 24.4 1/sq m (600 gal/1000 sq ft) will be assumed to be
treated by reverse osmosis.
72
-------
Only limited benefit, in terms of pollution reduction, will be achieved
by going to a complete recycle system. Parameters other than dissolved
solids have essentially been eliminated by prior treatment. Available
data indicate a 100 mg/1 or 4.9 g/sq m (1 lb/1000 sq ft) dissolved
solids increase at present water usage, which may be considered
insignificant. Relatively large capital, operating, and power costs are
required for reverse osmosis and and an expensive landfill is needed for
salt storage.
WINDSHIELD FABRICATION
Oil is the major contaminant to be removed from windshield lamination
waste water. The oil contributes to a high organic loading as measured
by COD. Lesser quantities of suspended solids and phosphorus are
contributed as a result of seaming and detergent washing. Typical
concentrations of these parameters are as follows:
Oil 1700 mg/1
COD 1700 mg/1
Suspended solids 25 mg/1
Phosphorus 5.6 mg/1
The typical flow rate is 175 1/sq m (4300 gal/1000 sq ft) . More
detailed information on raw waste water characteristics may be found in
Section V.
A combination of in-plant modification and end-of-pipe treatment will
most efficiently reduce pollutant concentrations. Oil and phosphorus
concentrations can be significantly reduced by modifying washing
techniques. Residual oil and suspended solids can be reduced by
filtration. An alternate to much of the oil removal equipment is the
use of air autoclaves. In theory, zero discharge can be accomplished by
using reverse osmosis for dissolved solids removal.
In-Plant Modification
In-plant modifications can significantly contribute to a reduction of
waste water volume and to the quantity of oil and phosphorus discharged.
Reduction of waste water volume through recycling and reuse, though not
reducing the quantity of pollutants discharged, will reduce the size of
required treatment units. Windshield fabrication waste water is almost
entirely the result of washing operations. Three or four washes are
required, depending on the production process, but the number of washes
does not significantly affect waste water volume. Of much greater
significance is the extent of washwater recycle. The same general
considerations govern windshield washwater recycle as govern solid
73
-------
tempered washwater recycle. Older washers tend to be of the once-
through type and some type of recycling is generally provided on new
equipment. The typical plant employs some recycling, but water usage
has not been minimized. Recycle is limited by factors, such as the
manufacturing process and background dissolved solids concentration,
that vary from plant to plant and cannot be generalized. It is probable
that maximum recycle will be practiced wherever possible to minimize
treatment costs.
As described in Section V, it is now typical in the industry to use an
initial hot water rinse in the post lamination wash to reduce detergent
usage and to eliminate the large volume of emulsified oil that is
produced when an initial detergent wash is used. This practice should
become standard and is assumed as part of all treatment methods.
The limited available data on effluent phosphorus concentrations show
increases from near zero to 0.98 g/sq m (0.2 lb/1000 sq ft) indicating
significant variation in detergent usage. Insufficient information was
available to define the reasons for variable detergent usage, but it is
apparent that some plants are producing acceptable windshields with much
lower phosphorus discharges than others. Two exemplary plants are
discharging less than 0.2 g/sq m (.04 lb/1000 sq ft) and, therefore, it
can be assumed that other plants can develop the technology to reduce
phosphorus to this level.
Another method for reducing oil contamination to trace levels is to use
air rather than oil autoclaves. Air autoclaves are now used for
windshield lamination by several small manufacturers, but are not
typical of the industry- Greater handling problems and apparently more
manpower are required for air autoclaves. It was impossible to obtain
the background data necessary to determine the relative cost of the two
systems. However, one company has indicated that its analysis has shown
a trade off for new plants between the cost of extra handling using air
autoclaves and treatment requirements using oil autoclaves. It is
possible to reduce oil to trace levels by using diatomaceous earth
filtration as indicated below.
Replacement of existing oil autoclaves would be expensive in terms of
the investment required and the loss of production during the change
over. It is likely, however, that owing to the reduction in water usage
and elimination of a potential pollution problem, air autoclaves will be
installed in new plants.
Treatment Methods
Primary methods of windshield fabrication washwater treatment involve
removal of the oil from post-lamination washwater. Most of the oil can
be removed by centrifugation, plain flotation in an American Petroleum
Institute (API) separator, or dissolved air flotation. Suspended solids
and residual oil can be removed by oil absorptive media filtration. In
74
-------
theory, it is possible to go to complete recycle by removing dissolved
solids. The progression of treatment methods is illustrated in Figure
14. Phosphorus concentrations will be lowered by reducing detergent
usage as indicated above. An initial hot water rinse is assumed for all
treatment methods. Fcr cost estimating purposes, no waste water
treatment is considered to be treatment Alternative A.
Lamination Washwater Treatment (Alternative B) -
When an initial hot water rinse is used, the oil removed collects in the
initial wash reservoir. The oil is not emulsified since no detergents
are used and can readily be removed by gravity separation. A cream
separator type centrifuge is used for oil removal at one exemplary plant
and this method is the most efficient and economical of those observed.
Oil and water are drawn from the surface of the hot water rinse
reservoir and passed through a centrifuge commonly used in the dairy
industry for cream separation. Concentrations of up to 50% oil are
reduced to less than 50 mg/1. The oil is sufficiently free of water to
be returned to the autoclaves and the water is returned to the hot water
rinse reservoir. A cartridge filter is used prior to the centrifuge to
minimize cleanouts due to solids build-up, but this feature is optional
as the suspended solids content is low.
Sufficient oil is removed so that the only blowdown from the initial hot
water rinse is the residual carried over on the glass. So little oil
reaches the second stage detergent wash that carryover on the glass is
also the only blowdown cr loss from the detergent wash. As a result,
the only waste water from this exemplary post-lamination washer is
blowdown from the third-stage recycle rinse tank and once-through final
rinse water. The rinse water passes through an API separator, but
little removal takes place in this unit. An API separator is a good
safety feature, however, for trapping any oil that might accidently be
discharged and will be included in cost estimates for this system. Oil
and COD levels,> for the typical total plant effluent, can be reduced to
1.76 g/sq m (0.36 lb/1000 sq ft) and 4.9 g/sq m (1 lb/1000 sq ft),
respectively, or a reduction of over 98% in both cases. No credit is
taken for phosphorus and suspended solids removal with this system.
Similar effluent quality can be obtained by treating with dissolved air
flotation although at higher cost because more sophisticated equipment
and chemicals are required. With this system, presently in operation at
another exemplary plant, oil is not removed at the initial hot water
rinse tank, but blowdown from this and all the wash and rinse tanks is
collected and treated by dissolved air flotation. Free oil is removed
by belt skimmers prior to the flotation unit.
The raw waste water is treated with polyelectrolyte to break any
emulsion and combined with a portion of the treated effluent that has
been pressurized and saturated with air. This mixture is discharged
into the flotation cell. When the pressure is released, small bubbles
75
-------
MAKE-UP
WATER
OIL TO
REUSE
WATER
INTERMITTENT I
, USE !
API
SEPARATOR
SLUDGE TO
LAND DISPOSAL
DIATOMACEOUS
EARTH
FILTER
OTHER
PROCESS
HOT WATER
PRERINSE
DETERGENT
WASH
INITIAL AND
FINAL RINSE
CENTRIFUGE
RETURN TO
PROCESS
REVERSE
OSMOSIS
1
•
1
BRINE
EVAPORATION
T
i
SOLIDS TO
PERMANENT STORAGE
FIGURE 14
WASTEWATER TREATMENT
WINDSHIELD FABRICATION
76
-------
are formed which cause the oil to float. A disadvantage of this system
is that both skimmings and sediment are produced. These are not
suitable for reuse and are disposed of as landfill. No information is
available on the characteristics of this sludge.
A continuously recycling initial hot water rinse with oil removal has
been successfully demonstrated. This system or the alternate dissolved
air flotation system can be implemented throughout the industry. The
equipment is readily available and can be installed on existing
equipment without any interruption of normal operations. Cost estimates
in Section VIII are based on the centrifuge system.
Filtration (Alternative C) -
Residual oil and suspended solids can be reduced to trace quantities by
filtration in either of two systems that are available. The entire
windshield fabrication waste water stream may be filtered through oil
absorptive diatomaceous earth or only the laminating washwater may be
filtered through oil absorptive diatomaceous earth and the total waste
water stream filtered through sand or an equivalent media. The
diatomaceous earth filters are the same type discussed for solid
tempered automotive glass treatment. Sand filters are discussed in the
section on plate glass treatment.
More process steps are required for sand filters because the filter
backwash must be dewatered. It is assumed that the backwash would be
treated by batch coagulation-sedimentation and that the resulting sludge
would be dewatered by centrifuge. Approximately a 2036 solids sludge
would be obtained by this method. No additional equipment is required
with the diatomaceous earth filters as these discharge a dry cake that
is suitable for land disposal. The diatomaceous earth filtration system
is somewhat less expensive and is used for cost estimating purposes.
Waste water effluent quality is assumed to be the same for both systems.
Oil is reduced at least 50% compared to the above discharge and 99+%
compared to the raw waste water for a residual loading of .88 g/sq m
(0.18 gal/1000 sq ft) or 5 mg/1 based on the typical flow rate.
Suspended solids is reduced at least 80% compared to the raw waste water
for a typical effluent concentration of 5 mg/1 and, therefore, has the
same residual loading as for oil. The effluent loadings are
conservatively estimated because neither system has been demonstrated in
the flat glass industry. No credit is taken for COD reduction as most
of the residual at this point is assumed to be contributed by the vinyl
washwater and not by oil. This technology has been demonstrated in
other industries and can be successfully employed for windshield
fabrication waste water treatments.
Total Recycle (Alternative D)-
77
-------
As with the other subcategories, it is theoretically possible to totally
recycle windshield fabrication waste water following reverse osmosis.
No system of this type has been demonstrated or anticipated by the
industry for windshield fabrication waste water. Many factors are
related to the feasibility of a reverse osmosis system and it can only
be assumed that such a system is technically feasible for windshield
lamination effluent.
The anticipated system is similar to those indicated for float glass and
solid tempered automotive glass fabrication. Maximum recycle would be
achieved prior to reverse osmosis, but this is assumed to account for
only a 3 3% reduction because significant recycle is already practiced in
the windshield fabrication process. The reverse osmosis product water
will be recycled to the manufacturing process. Waste brine will be
evaporated with the steam returned to the process and the residual salt
permanently stored in a lined lagoon.
Capital and operating costs for a dissolved solids removal system will
be high and land will be permanently wasted for salt storage. Little
benefit in terms of pollution reduction will be achieved because waste
water dissolved solids concentrations are low.
78
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SECTION VIII
COST, ENEFGY, AND NON-WATER QUALITY ASPECTS
COST AND REDUCTION BENEFITS OF ALTERNATIVE TREATMENT AND CONTROL
TECHNOLOGIES
Investment and operating costs for the alternative waste water treatment
and control technologies described in Section VII are presented here.
The cost data include the traditional expenditures for equipment
purchase, installation, and operation and where necessary, include solid
waste disposal. No significant production losses due to the
installation of water pollution control equipment are anticipated. The
costs are based on a typical plant for subcategories where no treatment
is practiced and on an exemplary plant where treatment is employed. In
some cases production rates and waste water volume are adjusted to be
more representative of the industry subcategory.
Investment costs include all the equipment, excavations, foundations,
buildings etc., necessary for the pollution control system. Land costs
are not included because the small additional area required is readily
available at existing plants. In all cases, the lagoon systems used for
plate glass waste water treatment are already in operation and no
additional land costs are required.
Costs have been expressed as August 1971 dollars and have been adjusted
using the national average Water Quality Office - Sewage Treatment Plant
Cost Index. The cost of capital was assumed to be 8% and is based on
information collected from several sources including the Federal Reserve
Bank. Depreciation is assumed to be 20 year straight line or 5% of the
investment cost. Operating costs include labor, material, maintenance,
etc., exclusive of power costs. Energy and power costs are listed
separately. August 1971 energy costs were assumed to be $.018 per
kilowatt-hour for electricity and $l/million BTU for the steam required
for brine evaporation.
Six subcategories have been defined in the development document. Costs
for each subcategory will be covered separately. The various
alternative treatment systems will be discussed and factors that might
affect the cost will be indicated. No process waste water results from
sheet and rolled glass manufacturing and, therefore, no treatment costs
result for these subcategories. Cost for the other subcategories are
summarized below.
Plate Glass Manufacturing
The typical plate galss manufacturing plant may be located in any part
of the country and is at least 12 years old. Advanced plate glass
manufacturing technology is used but this has not been improved since
79
-------
the early 1960*s when the advantages of the float process became
apparent. Annual production at the plant is approximately 150,000
metric tons. Costs and effluent quality for the four treatment
alternatives are summarized in Table 10.
Alternative A - Lagoon with Polyelectrolyte Addition
Alternative A is the treatment universally practiced at plate glass
plants and includes polyelectrolyte addition to the raw waste water
followed by sedimentation in a one cell lagoon.
Costs. No additional cost.
Reduction Eenefits. Suspended solids are reduced 99.6/6
and COD is reduced 90%.
Alternative B - Lagoon Improvements
Alternative B consists of partition of the existing one cell lagoons
into two cells in series with polyelectrolyte addition at the entrance
to each
Costs. Incremental investment costs are $57,000 and total
annual costs are $32,800 over Alternative A.
Reduction Benefits. The incremental reduction of suspended
solids compared to Alternative A is 7056. Total reduction
of suspended solids is 99.8*.
Alternative C - Filtration
Alternative C is sand filtration of the lagoon effluent resulting
from Alternative B.
Costs. Inqremental investment costs are $472,000 and total
annual costs are $14 2,500 over Alternative B.
Reduction Benefits. The incremental reduction of suspended
solid compared to Alternative B is 83%. Total reduction
of suspended solids is almost 100%.
Alternative D - Filtration and Recycle
Alternative D is recycle of the lagoon effluent resulting from
Alternative B to the plate glass grinders and sand filtration of a 20%
blow-down prior to dishcarge to the receiving stream. Owing to the
lower operating cost fcr Alternative D, the annual cost for this system
is less than for Alternative c.
80
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TABLE 10
WATER EFFLUENT TREATMENT COSTS
FLAT GLASS MANUFACTURING
PLATE GLASS
Alternative Treatment or Control Technolo-
gies :
Investment
Annual Costs:
Capital Costs
Depreciation
Operating and Maintenance Costs
(excluding energy and power costs)
Energy and Power Costs
Total Annual Cost
A
($1,000)
B C
D
0
57.
529.
656.
0
4.6
42.3
52.5
0
2.9
26.5
32.8
0
22.7
99.7
49.7
0
. 2.6
6.8
3.5
0
32.8
175.3
138.5
Effluent Quality:
Effluent Constituents
Raw
Waste
Load
Resulting Effluent
Levels
Flow ( l/metrie ton)
45,900
45,900
45,900
45,900
9,200
Suspended Solids ( kg/metric ton)
690.
2.5
1.38
.23
.045
COD ( kg/metric ton)
4.6
.45
.45
.45
.09
Flow ( l/sec )
210
210
210
210
40
Suspended Solids ( mg/l )
15,000
54
30
5
5
COD ( mg/l.)
100
10
10
10
10
81
-------
Costs. Incremental investment costs are $127,000 over
Alternative C but total annual costs re $36,800 less
than Alternative C.
Reduction Benefits. Incremental reductions are 8056 for
suspended solids and COD compared to Alternative C.
Total reductions are essentially 100% for suspended
solids and 9895 for COD.
Three plate glass plants remain in operation in the United States. All
of these plants practice Alternative A treatment but none of the other
alternatives are practiced at present. There is no apparent benefit for
phasing costs within an alternative. However, where one alternative
includes a previous alternative, the earlier alternatives may be built
first.
The cost of Alternative B is not expected to vary significantly between
plants. The cost of Alternative C and D will vary somewhat depending on
the volume of water filtered. A reduction in plant water usage,
although theoretically possible, is not practical because extensive
inplant modifications will be required. For this reason, costs are
based on the plant having the highest flow rate and will be somewhat
less for other plants. Another unknown factor is the amount of blowdown
required for the recycle system. A liberal 2056 blowdown is assumed.
Filtration costs will be reduced if the allowable blowdown can be
reduced.
The age of equipment and process employed do not significantly affect
costs. No process changes are required and significant engineering or
non-water quality environmental impact problems are not anticipated.
Float Glass Manufacturing
The typical float glass manufacturing plant may be located in any part
of the country and has teen built since 1960. Annual production is
approximately 360,00 metric tons. Three alternative methods of
treatment are disucssed. Costs and effluent quality are summarized in
Table 11.
Alternative A - No Waste Water Treatment or Control
Alternative A is the elimination of detergent usage in the float washer.
As can be seen, the waste water is of high quality and all plants
presently discharge this water untreated.
Costs. None.
Reduction Benefits. Close to 100% phosphorus reduction.
82
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TABLE 11
WATER EFFLUENT TREATMENT COSTS
FIAT GLASS MANUFACTURING
FLOAT GLASS
Alternative Treatment or Control Technolo-
gies:
A
($1,000)
B
C
Investment
0
7.
134.
Annual Costs:
Capital Costs
0
.6
11.
Depreciation
0
.4
6.7
Operating and Maintenance Costs
(excluding energy and power costs)
0
2.
28.4
Energy and Power Costs
0
.1
12.5
Total Annual Cost
0
3.1
58.6
Effluent Quality:
Effluent Constituents
Raw
Waste
Load
Resulting Effluent
Levels
Flow (l/inetric ton)
Suspended Solids (g/metric ton)
Dissolved Solids (g/faetric ton)
COD (g/netric ton)
138
2
14
2
138
2
14
2
No Discharge
No Discharge
Flow (l/sec) 1.6 1.6 qj
-------
Alternative B - Recycle to Batch and Cooling Tower
Alternative B includes recycle of the float washwater to the batch and
cooling tower. Process waste water discharge is elimianted. The waste
load recycled to the hatch will become part of the glass and the waste
load recycled to the cooling tower will constitute a portion of the
cooling tower blowdown.
Costs. Incremental investment cost are $7r000 and total
annual costs are $3,100 over Alternative A.
Reduction Benefits. Elimination of process waste water discharge.
Alternative C - Total Recycle
Alternative C is the total recycle of waste water back to the process
following treatment using diatomaceous earther filtration for suspended
solids removal and reverse osmosis for dissolved solids removal. Waste
brine is evaporated to dryness and residual salt permanently stored.
Sufficient suspended and dissolved solids are removed so that the water
can be reused for float washing* No liquid wastes are discharged.
Costs. Incremental investment costs.re $127,000 and
total annual costs are $55,500 over Alternative B.
Reduction Benefits. Waste water discharge is totally eliminated.
Reduction of suspended solids, COD, phosphorus and all other
pollutant constituents of 100%.
About half of the float glass plants produce process waste water in the
form of washwater. Washing is not required at the other plants and no
process waste water is produced. Washing is necessary where practiced
and cannot be eliminated on the bases of the information gathered for
this study.
No cost is associated with Alternative A. The evidence gathered
indicates that detergent can simply be eliminated from the process. The
cost of Alternatives E and C will depend upon the quantity of glass
produced and the allowable dissolved solids build-up. The typical plant
is one of the largest float plants so that the costs should be somewhat
conservative with respect to the entire subcategory. The high cost of
Alternative C is the result of dissolved solids removal and waste brine
disposal. These costs could be only roughly estimated since no system
of this type is presently in operation. . Each of the alternatives is a
separate system and there is no benefit to be derived from cost
phasing.
As discussed in the Development Documents the age of equipment and the
process employed do not significantly affect costs. No process changes
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are required and no significant engineering or non-water quality
environmental impact problems are anticipated.
Solid Tempered Automotive Glass Fabrication
The typical solid tempered automotive glass fabrication plant may be
located in any part of the country and uses process equipment that has
been modified within the last 10 to 15 years. Annual production is 3.5
million square meters. Cost and effluent quality for the four treatment
alternatives discussed are summarized in Table 12.
Alternative A - No Waste Water Treatment or Control
Alternative A is no waste water treatment or control. The waste water
is of relatively high quality except for suspended solids. At the
present time, no plants treat solid tempered automotive waste water.
Land disposal of coolant sludge is assumed, as this is almost
universally practiced in the industry.
Costs. None.
Reduction Benefits. None.
Alternative B - Coagulation-Sedimentation
Alternative B is solids contact coagulation-sedimentation of all process
waste water, centrifugation of waste sludge and land disposal of
dewatered waste solids.
Costs. Incremental investment costs are $81,000 and total annual
cost are $24,100 over Alternative A.
Reduction Benefits. Effluent suspended solids are reduced 75%.
Alternative C - Filtration
Alterantive C is oil absorptive diatomaceous earth filtration of the
effluent from Alternative B. The spent diatomaceous earth is also
disposed of as landfill.
Costs. Incremental investment costs are $68,000 and total annual
costs are $18,000 ever Alternative B.
Reduction Benefits. Incremental reduction of suspended solids is
80%. Total reductions of suspended solids, oil and BOD are 95, 62,
and 33% respectively.
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TABLE 12
WATER EFFLUENT TREATMENT COSTS
FLAT GLASS MANUFACTURING
SOLID TEMPERED AUTOMOTIVE GLASS FABRICATION
Alternative Treatment or Control Technolo-
gies;
($1,000)
C
D
Investment
0
81.
149.
364.
Annual Costs:
Capital Costs
0
6.5
11.9
29.1
Depreciation
0
4.1
7.5
18.2
Operating and Maintenance Costs
(excluding energy and power costs)
0
11.7
17.9
53.4
Energy and Power Costs
0
1.8
4.8
25.7
Total Annual Cost
0
24.1
42.1
126.4
Effluent Quality:
Effluent Constituents
Raw
Waste
Load
Resulting Effluent
Levels
l
Flow
HM m)
49
49
49
49
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Alternative D - Total Recycle
Alternative D is the further treatment of the effluent from Alternative
C using reverse osmosis. The waste brine is evaporated and the residual
salt permanently stored. Sufficient suspended and dissolved solids are
removed so that the water can be reused in the manufacturing process.
No liguid wastes are discharged.
Cost. Incremental investment costs are $215,000 and total annual
costs are $84,300 over Alternative C.
Reduction Benefits. Reduction of suspended solids, oil, BOD and all
other pollutant constituents of 100%.
The volume of water to be treated depends on the amount of recycling
practiced. More extensive recycling at the typical plant is
representative of the better plants in this subcategory. A further
reduction in water usage may be possible but is not assumed in the cost
estimate. For those plants presently using more water than the typical
plant, higher cost may be required for increase treatment cost or for
in-plant modifications to reduce water usage. The costs recorded here
are representative cf an above average size plant with moderate water
recycling and reuse practices. A flow reduction of 50% prior to the
reverse osmosis system in Alternative D is assumed.
None of the treatment methods is presently practiced in the flat glass
industry. The technology is transferred from other industries and for
this reason the cost estimates may be somewhat rough. This is espe-
cially true for the reverse osmosis system in Alternative D, where many
unknowns had to be assumed. There is no apparent benefit for phasing
costs within an alternative; however, where one alternative includes
other alternatives, the earlier alternatives may be built first.
The age of equipment and the process employed do not significantly
affect costs. N,o process changes are required and no significant
engineering or non-water quality environmental impact problems are
anticipated.
Windshield Fabrication
The typical windshield fabrication plant may be located in any part of
the country and uses oil autoclaves. Annual production is 750,000
square meters. Cost and effluent quality for the four treatment
alternatives discussed are summarized in Table 13.
Alternative A - No Waste Water Treatment or Control
Alternative A is no waste water treatment or control.
Costs. None.
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TABLE. 13
WATER EFFLUENT TREATMENT COSTS
FLAT GLASS MANUFACTURING
WINDSHIELD FABRICATION
Alternative Treatment or Control Technolo-
gies
($1,000)
J3 C
Investment
0
32.
115.
317.
Annual Costs:
Capital Costs
0
2.6
9.2
25.4
Depreciation
0
1.6
5.8
15.8
Operating and Maintenance Costs
(excluding energy and power costs)
0
8.
13.6
48.5
Energy and Power Costs
0
2.4
4.2
33.1
Total Annual Cost
0
14.6
32.8
122.8
Effluent Quality:.
Effluent Constituents
Raw
Waste
Load
Resulting Effluent
Levels
Flow (l/6q m)
175
175
175
175
Oil (g/kq m)
298
298
1.76
.88
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Reduction Benefits. None.
Alternative B - Lamination Washwater Treatment
Alternative B is modification of the post lamination washer sequence to
provide a continuously recycling initial hot water rinse, oil removal by
centrifugation of the recirculating hot rinse water, recycle of oil back
to the process, and treatment of other post lamination rinse waters by
gravity oil separation. Other process waters are not treated.
Neligible waste solids are produced.
Costs. Incremental investment costs are $32,000 and total annual
costs are $14,600 over Alternative A.
Reduction Benefits. Oil is reduced by 99.456 and COD is reduced by
98.1%.
Alternative c - Filtration
Alternative C includes cil absorptive diatanaceous earth filtration of
all process waste water in addition to the treatment system discribed
for Alternative B. The spent diatomaceous earth is disposed of as
landfill. Phosphorus is reduced by more vigorous inplant detergent
control and improved washing techniques.
Costs. Incremental investment costs are $83,000 and total annual
costs are $18,200 over Alternative B.
Reduction Benefits. Incremental reductions are 5056 for oil and 80%
for suspended solids. Total reductions are 99.1% for oil, and 80%
for suspended solids and phosphorus.
Alternative D - Total Recycle
Alternative D is total recycle and reuse of the water following reverse
osmosis treatment for dissolved solids removal. The waste brine is
evaporated and the residual salt is permanently stored.
Costs. Incremental investment costs are $202,000 and the total
annual costs are $90,000 over Alternative C.
Reduction Benefits. Reduction of oil, COD, suspended solids,
phosphorus and all ether pollution constituents of 100%.
As with the other subcategories, the volume of water treated and, there-
fore, the cost of treatment is related to the amount of recycling that
can be practiced. Approximately the same absolute 1/sq m are required
at all plants, but the quantity discharged can be reduced by using re-
cycling washers. Relatively more recycle is presently practiced for
windshield fabrication than for other subcategories but it may still be
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possible by using recycling washers in all cases and by carefully
controlling flow to further reduce usage. The typical plant is of less
than average size and practices moderate water recycling and reuse.
Costs may be as much as 4 times higher for the larger plants because fo
the higher water volume. A flow reduction of 33% prior to the reverse
osmosis system in Alternative D is assumed.
New plants will probable use air rather than oil autoclaves. This will
reduce the waste water flow rate by approximately 2396 and eliminate the
need for Alternative E treatment.
The technology for Alternatives C and D was transferred from other
industries and is presently not practiced in the flat glass industry.
The cost estimates for these alternatives may be somewhat rough because
of the unknowns involved. This is especailly true for the reverse
osmosis system in Alternative D. There is no apparent benefit for
phasing costs within an alternative; however, where one alternative
includes other alternatives, the earlier alternatives may be built
first.
It is possible, but not likely that some modification of the washers may
be required to effect the detergent reduction indicated for Alternative
C. No equipment modification was required at the exemplary plant where
this technology is used but it is possible that modification will be
required if another type of washer is used. Other considerations such
as the age of equipment or the process employed do not significantly
affect cost and no significant engineering of non-water quality
environmental impact problems are anticipated.
ENERGY REQUIREMENTS OF TREATMENT AND CONTROL TECHNOLOGIES
The energy required to implement in-plant control measures at a typical
flat glass plant is 5 kw or less. The energy requirements are almost
entirely for pumping to recycle washer water.
The energy requirements of the end-of-pipe treatment technology are
relatively low for conventional operations such as coagulation-
sedimentation and filtration, but are much higher for total recycle
systems incorporating reverse osmosis or evaporation. Typical energy
requirements for conventional treatment are 45 kw or less. The energy
requirements may run as high as 1000 kw for a total recycle system
because of the energy required for evaporation.
No information was provided by the industry relative to the energy
requirements of individual manufacturing plants. Large quantities of
energy are used in primary glass production to produce the high
temperatures required fcr glass melting and annealing and numerous large
horsepower motors are needed for grinding and polishing in the plate
process. Less energy is required for automotive fabrication. The
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additional energy required to implement conventional control and
treatment technologies is less than 1% of process requirements for
primary manufacturing and is estimated to be less than 10% of process
requirements for automotive fabrication.
NON-WATER QUALITY ASPECTS OF TREATMENT AND CONTROL TECHNOLOGIES
Air Pollution
There are no significant air or noise pollution problems directly
associated with the treatment and control technologies. The waste
waters and sludges are odorless and no nuisance conditions result from
their treatment or handling. Incineration is not used in the treatment
technologies so no air pollution is caused by this source. Water vapor
resulting from the evaporation of reverse osmosis brines is expected to
be relatively pure.
A non-water quality aspect of perhaps greater significance than air
pollution is the high energy required for total recycle systems. In
view of the limited availability of clean energy sources and the air
pollution problems associated with other energy spurces, the benefits
derived from a total recycle system should also be weighed against the
energy required to operate such a system.
Solid Waste Disposal
Landfilling of properly dewatered sludges from the flat glass industry
is an appropriate means of disposal. The wastes are largely inorganic
and incineration, ccmposting, or pyrolysis would not be effective in
reducing their volume. The dewatered solids are relatively dense and
they are stable when used as fill material. If disposed of using proper
sanitary landfill techniques, solids from flat glass manufacturing
should cause no environmental problems.
With the exception of plate glass manufacturing, the volume of sludge
associated with the various control and treatment technologies is
relatively small. The lagoons used for plate glass suspended solids
removal also serve as sludge disposal sites. The levees are generally
raised to keep pace with the rising sediment level. At older plate
plants large areas of low-lying land have been filled in. In some cases
this is reclaimed as park land by spreading topsoil over the dry sludge
solids.
Three types of waste solids are produced by the treatment systems
indicated for the float, solid tempered automotive, and windshield
manufacturing processes. These are (1) coagulation-sedimentation
sludges associated with tempering waste waters, and (2) spent dia-
tomaceous earth, and (3) brine residue associated with at least one
treatment alternative for each of the subcategories. The coagulation-
sedimen-feation sludge is assumed to be dewatered by centrifuge to about
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20% dry solids and the typical volume produced is estimated to be 0.38
cu m/day (13.5 cu ft/day).
Spent diatomaceous earth has an estimated moisture content of 85%, but
is dry to the touch. This material is stable and should be suitable for
landfill. Estimated production of diatomaceous earth waste is less than
0.23 cu m/day (8 cu ft/day) for each of the subcategories.
The salt residue that will be produced by a total recycle system will
present the biggest disposal problem. To prevent ground water
contamination, it must be permanently stored in lined basins. Only as
much water as will evaporate can be allowed into the basin. The land
used for salt storage will be permanently spoiled. The salt residue
produced by the tempering and laminating processes is conservatively
estimated to be 0.56 cu m/day (20 cu ft/day). Salt storage costs are
directly related to the cost of land and the type of lining used.
The cost for hauling the coagulation sludge and diatomaceous earth to
landfill, assuming a commercial disposal firm is used, is $60 to $100 a
month. Disposal costs are variable depending on the equipment used and
distance to the disposal site.
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SECTION IX
EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION OF
THE BEST PRACTICAELE CONTROL TECHNOLOGY CURRENTLY AVAILABLE
EFFLUENT LIMITATIONS GUIDELINES
INTRODUCTION
The effluent limitations that must be achieved July 1, 1977 are to
specify the degree of effluent reduction attainable through the ap-
plication of the Best Practicable Control Technology Currently
Available. Best Practicable Control Technology Currently Available is
generally based upon the average of the best existing performance by
plants of various sizes, ages, and unit processes within the industrial
category or subcategory. This average is not based upon a broad range
of plants within the flat glass industry, but based upon performance
levels achieved by exemplary plants.
Consideration must also be given to:
a. The total cost of application of technology in relation
to the effluent reduction benefits to be achieved from
such application;
b. the size and age of equipment and facilities involved;
c. the processes employed;
d. the engineering aspects of the application of various
types of control techniques;
e. process changes;
f. non-water quality environmental impact (including energy
requirements).
Also, Best Practicable Control Technology Currently Available emphasizes
treatment facilities at the end of a manufacturing process, but also
includes the control technologies within the process itself when the
latter are considered to be normal practice within an industry.
A further consideration is the degree of economic and engineering
reliability which must be established for the technology to be
"currently available". As a result of demonstration projects, pilot
plants, and general use, there must exist a high degree of confidence in
the engineering and economic practicability of the technology at the
time of commencement of construction or installation of the control
facilities.
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EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION OF BEST
PRACTICABLE CONTROL TECHNOLOGY CURRENTLY AVAILABLE
Based on the information contained in Sections III through VIII of this
document, a determination has been made of the degree of effluent
reduction attainable through the application of the Best Practicable
Control Technology Currently Available for the flat glass manufacturing
industry. The effluent reductions are summarized here.
Suspended Solids
A principal pollutant constituent in waste waters from the manufacture
of plate glass and the fabrication of solid tempered automotive glass is
suspended solids. Application of this technology will reduce suspended
solids levels by 99,8% for plate glass manufacturing and 75% for solid
tempered automotive glass fabrication. The low percentage for
automotive tempering is an indication of the high quality of the raw
waste water.
Suspended solids will not be significantly reduced by the application of
this control technology to float glass manufacturing and to windshield
fabrication waste waters.
Oil
At least trace amounts of oil are present in all flat glass waste waters
with the highest concentration resulting from windshield fabrication.
This control technology will reduce oil levels in windshield fabrication
waste waters by 99.4%, but will not effect significant oil removal for
the other subcategories.
Oxygen Demanding Materials
Oxygen demand in the flat glass industry is related to the oil content
of the waste water. COD levels will be reduced 90% in plate glass and
98% in windshield waste waters using this control technology. The BOD
or COD for the other subcategories will not be reduced, but the levels
are already low by conventional standards.
EH
With the exception of plate glass manufacturing, the pH of the flat
glass waste waters falls within the accepted range of 6 to 9. In some
cases, raw plate glass waste water may have a pH level above 9, but
neutralization is already universally practiced where necessary.
Total Phosphorus
Some phosphorus may be present in float glass and windshield fabrication
waste waters as a result of detergent usage. This control technology
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eliminates detergent usage in the float process, but no treatment or
control is applied to windshield fabrication wastewaters.
Process waste waters from the float and automotive glass fabrication
subcategories may show some temperature increase because of heated
washwater requirements. Application of this control technology will not
result in significant temperature reduction.
Dissolved Solids
Dissolved solids increase somewhat as a result of all of the glass
manufacturing processes. The average typical increase is about 100
mg/1. High dissolved solids in the process water cannot be tolerated
because almost all of the water is used for washing and high dissolved
solids leave a residue on the glass. For this reason, flat glass
process waste water will always be of high quality with respect to
dissolved solids. This control technology does not reduce dissolved
solids.
IDENTIFICATION OF THE BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE
In-plant control measures as well as end-of-pipe treatment techniques
contribute to the best pollution control technology currently available,
although emphasis is cn end-of-pipe treatment. Water recycle and reuse,
although not a significant factor in this technology, will tend to
reduce the cost of end-of-pipe treatment facilities.
The Best Pollution Control Technology Currently Available for the
subcategories of the flat glass industry is summarized below.
Recommended effluent limiatations are summarized in Table 14. These
limitations are daily maximums except where noted.
t
Sheet Glass Manufacturinc[
No process waste water results from the sheet glass manufacturing
process, therefore, no waste water or waste load should be discharged.
Rolled Glass Manufacturing
No process waste water results from the rolled glass manufacturing
process, therefore, no waste water or waste load should be discharged.
Plate Glass Manufacturing
The control technology is partition of existing one-cell lagoons into
two cells in series with provision for polyelectrolyte addition at the
entrance to each cell. This is to provide more efficient coagulation
95
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TABLE 14
vo
-------
and to reduce the effects of short circuiting and wind action on
sedimentation. Effluent limitations for suspended solids are 1.38
kg/metric ton (2.75 lb/short ton); for COD, 0.45 kg/metric ton (0.9
lb/short ton); and pH of between 6.0 and 9.0.
Float Glass Manufacturing
The control technology is elimination of detergent usage from the float
washing process. Effluent limitations for suspended solids and COP are
2 g/metric ton (0.0041 lb/short ton); for oil, 0.7 g/metric ton (0.0014
lb/short ton); and for total phosphorus, 0.05 g/metric ton (0.0001
lb/short ton).
Solid Tempered Automotive Glass Fabrication
The control technology is coagulation-sedimentation of all process waste
waters with land disposal of dewatered waste solids. Effluent
limitations for suspended solids are 1.22 g/sq m (0.25 lb/1000 sq ft);
for oil, 0.64 g/sq m (0.13 lb/1000 sq ft); and for BOD, 0.73 g/sq m
(0.15 lb/1000 sq ft) .
Windshield Fabrication
The control technology is modification of the post-lamination washer
sequence to provide a continuously recycling initial hot water rinse,
oil removal by centrifugation of the recirculating hot rinse water,
recycle of oil back to the process, and treatment of other post-
lamination rinse waters by gravity oil separation. Negligible waste
solids are produced. Effluent limitations for suspended solids are 4.4
g/sq m (0.9 lb/1000 sq ft); for oil, 1.76 g/sq m (.36 lb/1000 sq ft);
for COD, 4.9 g/sq m (1 lb/1000 sq ft); and for total phosphorus, 0.98
g/sq m (0.2 lb/1000 sq ft).
RATIONALE FOR THE SELECTION OF BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE
Engineering Aspects of Application
In all cases, this control technology has been applied in the glass
industry or in another industry where the characteristics of the water
treated are sufficiently similar to provide a high degree of confidence
that the technology can be transferred to the glass industry.
The derivation and rational for selection of the control technology are
described in detail in Sections V and VII. These may be briefly
summarized as follows:
Plate Glass Manufacturing
Existing treatment of plate glass waste waters is uniformly inadequate
and must be upgraded. The recommended lagoon modifications and the
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resulting effluent limitations are based on company experience and
engineering judgement. The recommended effluent concentrations are
being achieved part of the time in existing plate glass lagoon systems
and there is no evidence to indicate that these levels can not be
achieved using the proposed technology.
Float Glass Manufacturing
Elimination of detergents from the float washer will result in a high
quality waste water suitable for discharge without further treatment.
The detergent wash has already been eliminated at most plants and there
is no evidence to indicate elimination of detergents is detrimental to
the product or the manufacturing process. Of the six plants that
presently wash float glass, four have already eliminated detergents.
Solid Tempered Automotive Glass Fabrication
None of the plants studied presently treat solid tempered automotive
waste water. Treatment for suspended solids removal is required prior
to discharge. The recommended coagulation-sedimentation technology is
commonly used for removing suspended solids from both water and waste
water. Company experience and engineering judgement indicate that this
treatment technology and the resulting effluent limitations can be
successfully applied for solid tempered automotive waste water
treatment.
windshield Fabrication
One plant is presently achieving the recommended effluent limitations
using the technology indicated for treating post lamination wash water.
It is also possible tc achieve the same effluent quality using dissolved
air floatation but at higher cost. The equipment for either system is
readily available and can be installed on existing washers without any
interruption of normal operations.
Total Cost of Application
Based on the information presented in Section VIII of this document, the
industry as a whole would have to invest approximately $900,000 to
achieve the effluent limitations prescribed herein. The increased
annual costs of applying this control technology are approximately
$345,000 for the industry.
Size and Age of Equipment
The size of plants within the same subcategory is not sufficiently
different to substantiate differences in control technology based on
size. All glass plants are continuously modernized so that age of
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equipment and facilities does not provide a basis for differentiation in
the application of this control technology.
Processes Employed
All plants in a given subcategory use very similar manufacturing
processes and produce similar waste water discharges. The control
technology for a given subcategory is compatible with all of the
manufacturing processes presently used in that subcategory.
Process changes
A minor process change is required in one subcategory for the
implementation of this technology. It will be necessary for the plants
in the windshield fabrication subcategory that are still using an
initial detergent wash as part of the post-lamination washing sequence
to eliminate this wash in favor of a recycling hot water rinse. As far
as is known, this can be accomplished without any additional equipment
by simply eliminating phosphorus frcm the first stage washer. This
technology is presently employed by a number of windshield fabrication
plants.
Major changes in the production process are not anticipated. It should
be noted, however, that minor process changes to adjust for automobile
model changes are required yearly for automotive glass fabricating
plants. These generally do not significantly affect waste water volumes
or characteristics. This technology can be applied so that upsets and
other fluctuations in process operations can be accommodated without
exceeding the effluent limitations.
Non-Water Quality Environmental Impact
There is no evidence that application of this control technology will
result in any unusual air pollution or solid waste disposal problems,
either in kind or magnitude. The costs of avoiding problems in these
areas are not ' excessive. The energy required to apply this control
technology represents only a small increment of the present total energy
requirements of the industry.
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SECTION X
EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION OF
THE BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE
EFFLUENT LIMITATIONS GUIDELINES
INTRODUCTION
The effluent limitations that must be achieved July 1, 1983, are to
specify the degree of effluent reduction attainable through the
application of the Best Available Technology Economically Achievable.
This control technology is not based upon an average of the best
performance within an industrial category, but is determined by
identifying the very best control and treatment technology employed by a
specific plant within the industrial category or subcategory, or where
it is readily transferable from one industry process to another.
Consideration must also be given to:
a. The total cost of application of this control technology
in relation to the effluent reduction benefits to be
achieved from such application;
b. the size and age of equipment and facilities involved;
c. the processes employed;
d. the engineering aspects of the application of this
control technology;
e. process changes;
f. non-water quality environmental impact (including energy
requirements).
Best Available Technology Economically Achievable also considers the
availability of in-prccess controls as well as control or additional
end-of-pipe treatment techniques. This control technology is the
highest degree that has been achieved or has been demonstrated to be
capable of being designed for plant scale operation up to and including
"no discharge" of pollutants.
Although economic factors are considered in this development, the costs
for this level of control are intended to. be the top-of-the-line of
current technology subject to limitations imposed by economic and
engineering feasibility. However, this control technology may be
characterized by some technical risk with respect to performance and
with respect to certainty of costs. Therefore, this control technology ~
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may necessitate some industrially sponsored development work prior to
its application.
EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION OF BEST AVAILABLE
TECHNOLOGY ECONOMICALLY ACHIEVABLE
Based on the information contained in Sections III through VIII of this
document, a determination has been made of the degree of effluent
reduction attainable through the application of the Best Available
Technology Economically Achievable. No discharge is attainable for the
sheet and rolled glass subcategories as is indicated in Section IX. The
effluent reductions attainable for the other subcategories are
summarized here.
Suspended Solids
Suspended solids are reduced by more than 95% for the plate, float, and
solid tempered automotive glass subcategories by this technology. The
incremental increase over the levels achieved using the Best Practicable
Control Technology Currently Available is 80% or greater. This
technology effects an 80% suspended solids reduction in windshield
lamination waste water. The lower percent reduction is a result of the
high quality of the raw waste water.
Oil
This technology reduces oil discharged from the float glass process by
100%, from the windshield fabrication process by 98%, and from the
solids tempered glass process by 62%. The incremental increase for
windshield fabrication over the application of the Best Pollution
Control Technology Currently Available is 50%. The lower reduction
achieved for the solid tempered process is due to the low oil
concentration in the raw waste water.
Oxygen Demanding Materials
The COD discharged by the plate and float glass processes is reduced by
98% or more with this technology, but no reduction is achieved for
windshield fabrication waste waters. The incremental increase in COD
removal over the level achieved using the Best Practicable Control
Technology Currently Available is 80% for the plate glass process.
This technology reduces the BOD in solid tempered automotive glass waste
water by only 33% because the raw waste water is of very high quality.
Total Phosphorus
With this technology, total phosphorus discharged by the float glass
process is reduced 100% and phosphorus discharged by the windshield
fabrication process is reduced 80%. Phosphorus is not a significant
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constituent in plate glass and solid tempered automotive glass waste-
waters.
Other Pollutant Constituents
Temperature and dissolved solids, which are discussed in Section IX, are
not significantly reduced by this technology.
IDENTIFICATION OF BEST AVAILABLE CONTROL TECHNOLOGY ECONOMICALLY
ACHIEVABLE
Both in-plant controls and end-oiSpipe treatment technology constitutes
the Best Available Pclluticn Control Technology Economically Achievable.
This technology is summarized below and recommended daily average
effluent limitations are listed in Table 15.
Plate Glass Manufacturing
The control technology is improvement of existing lagoon systems as
described in Section IX, return of 80% of the lagoon effluent to the
grinding operation, sand filtration of the remaining 20%, and return of
the filter backwash to the head of the lagoon system. Effluent
limitations for suspended solids are 0.045 kg/metric ton (0.09 lb/short
ton) and for COD are 0.09 kg/metric ton (0.18 lb/short ton).
Float Glass Manufacturing
——~
The control technolcgy is return of float washwater to the batch and
cooling tower, thereby eliminating discharge of process waste water to
navigable waters.
Solid Tempered Automotive Glass Fabrication
The control technology is coagulation-sedimentation of all process waste
waters as described in Section IX followed by oil absorptive
diatomaceous earth filtration. Waste solids are disposed of to
landfill. Effluent limitations for suspended solids and oil are .24
g/sq m (0.05 lb/1000 sq ft) and for BOD are 0.49 g/sq m (0.1 lb/ 1000 sq
ft) .
Windshield Fabrication
The control technology is recycle of the post-lamination washer initial
hot water rinse and gravity separation of the remaining post-lamination
rinse waters as described in Section IX, .oil absorptive diatomaceous
earth filtration of the total - process waste water discharge, and
reduction of detergent usage. Effluent limitations for suspended solids
and oil are 0.88 g/sq m (0.18 lb/ 1000 sq ft), for COD 4.9 g/sq m (1.0
lb/1000 sq ft), and for phosphorus are 0.2 g/sq m (0.04 lb/1000 sq ft).
103
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TABLE 15
o
RECOMMENDED DAILY AVERAGE EFFLUENT LIMITATIONS USING
BEST AVAILABLE CONTROL TECHNOLOGY ECONOMICALLY ACHIEVABLE
Suspended Total
Solids COD Oil BOD Phosphorus pH
Sheet Glass No waste water discharge
Rolled Glass No waste water discharge
Float Glass No waste water discharge
Plate Glass
kg/metric ton 0.045 0.09 - - 6-9
lb/short ton 0.090 0.18
Solid Tempered
Automotive Glass ,
g/sq m 0.24 - 0.24 0.49 - 6-9
lb/1000 sq ft 0.05 0.05 0.10
Windshields
g/sq m ,0.88 4.9 0.88 - 0.20 6-9
lb/1000 sq ft 0.18 1.0 0.18 0.04
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RATIONALE FOR THE SELECTION OF BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE
Total Cost of Application
Based upon the information contained in Section VIII A of this document,
the industry as a whole would have to invest up to an estimated maximum
of $3,200,000 to achieve the effluent limitations prescribed herein.
The increased annual ccsts to the industry would be approximately
$1,000,000.
Size and Age of Equipment and Facilities
As discussed in Section IX, differences in size and age of equipment and
facilities in the industry do not play a significant role in the
application of this control technology.
Processes Employed
The manufacturing processes employed within each subcategory of the
industry are basically similar and the differences will not influence
the applicability of this control technology.
Engineering Aspects of Application
This level of technology is not achieved by any plants in the industry
at the present time. However, as indicated in Section VII of this
document, there is a high degree of confidence that this technology can
be implemented in the industry by 1983. The treatment and systems are
now used in other industries and this technology can be readily
transferred to the flat glass industry. The derivation and rational for
selection of the control technology are described in detail in Section
VII. These may be briefly summarized as follows:
Plate Glass Manufacturinq
Rapid sand filtration is a thoroughly proven technology that is used
extensively in the water treatment industry. Effluent concentrations
below the proposed effluent limits are commonly achieved. The lagoon
effluent should be suitable for recycle because the suspended solids
level is in most cases lower than the concentration of the raw river
water presently being used.
Float Glass Manufacturing
Float glass process waste water where no detergents are used, is of high
quality and can be' recycled as batch or cooling tower make-up. With the
exception of temperature, the waste water characteristics are not
significantly different from the city water presently being used for
this purpose.
105
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Solid Tempered Autmotive Glass and Windshield Fabrication
Oil absorbtive diatomaceous earth filtration is the additional treatment
technology recommended for both the solid tempered automotive and
windshield fabrication subcategories. This technology is commonly used
to remove oil and suspended solids from boiler water condensate and
effluent concentrations of less than 5 mg/1 are readily achievable for
both parameters. There is no evidence to indicate that this technology
can not be applied to waste water treatment in the glass industry.
Process Changes
Only one process change is effected by this control technology.
Reduction of detergent usage in the windshield fabrication process is
required. Although the exemplary plant upon which this technology is
based required no equipment modification to achieve the technology, it
is possible, but not anticipated, that equipment modification may be
required in other plants. Recycling of water is not required by the
technology, but it is likely plants will reduce water usage to a minimum
to reduce treatment costs.
Non-Water Quality Environmental Aspects
The application of this control technology will not create any new air
or land pollution problems, but will require approximately 2.5 times
more energy than is required for the application of the Best Practicable
Control Technology Currently Available. This is still estimated to be
less than 10SS of the energy required for the manufacturing process.
106
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SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
The term "new source" is defined to mean "any source, the construction
of which is commenced after the publication of the proposed regulations
prescribing a standard of performance." New sources from the sheet,
rolled, float, and solid tempered automotive glass and windshield
subcategories should achieve the effluent limitations prescribed as
attainable through the application of the Best Available Technology
Economically Achievable. This technology reduces the concentration of
pollutant constituents to trace levels and no other technology is
indicated that will further reduce these levels by virtue of new
construction.
New sources in the plate glass subcategory should achieve no discharge
of process waste waters to navigable waters. This regulation will most
probably prevent the construction of any new plate glass plants. This
type of glass can be produced more economically and with almost no water
pollution by the float process with the technologies recommended in this
document. For this reason, the effluent limitations attainable for
float glass manufacturing should also be applied for new plate glass
manufacturing sources. Owing to the high operating costs associated
with plate glass production, new source construction would be very
unlikely even without effluent limitations.
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SECTION XII
ACKNOWLEDGMENTS
The Environmental Protection Agency wishes to acknowledge the
contributions to this project by Sverdrup & Parcel and Associates, Inc.,
St. Louis, Missouri. The work at Sverdrup & Parcel was performed under
the direction of Dr. H.G. Schwartz, Jr., Project Executive; Richard C.
vedder, Project Manager; and assisted by Troy Kniffin, Daphne English,
David Graeflin, and Charles Rogge.
Appreciation is extended to the many people in the flat glass industry
who cooperated in providing information and data.
Special mention is made of the following company representatives who
gave of their time in developing the information for this document: Mr.
Raymond Smith of ASG Industries, Mr. Paul Schmitt of CE Glass, Mr.
Victor Sussman and Mr. Kenneth Bradford of Ford Motor Company, Mr. Henry
Walker of Fourco Glass Company, Mr. Richard Alonzo of Guardian
Industries, Mr. Werner Ganz and Mr. William Hupp of Libbey-Owens-Ford
Company, Mr. James Destefano and Mr. James Elliott of PPG Industries,
Mr. Charles Stevenson of Safelite Industries, and Mr. Dan Baraszu of
Shatterproof Glass Corporation.
Appreciation is expressed to those in the Environmental Protection
Agency who assisted in the performance of the project: Robert Dellinger,
Frances Hansborough, Jane Mitchell, John Riley, George Webster, Ernst
Hall, Arthur Mallon, Martin Knittel, John Insigna, and Edward Kimball.
109
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1
2
3
4
5
6
7
8
9
10
11
12
13
SECTION XIII
REFERENCES
Betz Handbook of Industrial Water Conditioning, Betz
Laboratories, Philadelphia, Pa., 1962.
Dietz, A. G. H., Engineering Laminates. John Wiley S Sons,
New York, 1949. ""
Handbook of Chemistry and Physics - 38th Edition. Chemical
Rubber Publishing Co., P. 503 & 533, l3?6.
Hardenbergh, W. A. and Rodie, E. B., Water Supply and Waste
Disposal. International Textbook, Scranton, Pa7, 1963.
Industrial Waste study Report: Flat GlassT Cement. Lime.
Gypsum, and Asbestos Industries, report to Environmental
Protection Agency by Sverdrup & Parcel and Associates,
Inc., 1971.
Johns-Manville Technical Data Sheet No. FF-214. New York
Lynam, B., Ettelt, G., and McAloon, T., "Tertiary Treatment
at Metro Chicago by Means of Rapid Sand Filtration and
Microstrainers", Journal Water Pollution Control
Federation. 11, No. 2, P. 247, 1969.
Methods for Chemical Analysis of Water and Wastes. Environ-
mental Protection Agency, National Environmental
Research Center, Analytical Quality Control Laboratory,
Cincinnati, Ohio, 1971.
Patterson, W. L. and Banker, R. F., Estimating Costs and
Manpower Requirements for Conventional Waste water
Treatment Facilities. Black and Veatch, Consulting
Engineers for the Office of Research and Monitoring,
Environmental Protection Agency, 1971.
Persson, R., Flat Glass Technology, Butterworths, London, 1969.
Porter, J. W., Hopkins, A. N., Fisher, W. L., "An Economic
and Engineering Analysis of Municipal Waste water
Renovation", Water. 90. No. 64, P. 246, 1968.
Probstein,.R. F., "Cesalinization", American Scientist.
Society of Sigma Xi, New Haven, Conn., May - June, 1973.
Sewage Treatment Plant and Sewer Construction Cost Indexes,
111
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o
Environmental Protection Agency, Office of Water
Programs Operations, Municipal Waste water Systems
Division, Evaluation and Resource control Branch.
14. Shand, E. B., Glass Engineering Handbook, McGraw-Hill,
New York, 1958. '
15. Smith, Robert, Cost of Conventional and Advanced Treatment
of Waste water. Federal Water Pollution Control ~r"'"
Administration, U.S. Department of the Interior, 1968.
16. Smith, Robert and McMichael, Walter F., Cost and Performance
Estimates for Tertiary Waste water Treating Processes.^"
Federal Water Pollution Control Administration, U.S.
Department of the Interior, 1969.
17. Standard Industrial Classification Manual. Office of
Management and Budget, U.S. Government Printing Office,
Washington, D.C., P. 136 - 138, 1972.
18. Standard Methods for the Examination of Water and Waste water,
13th Edition, American Public Health Association,
Washington, E.C., 1971.
19. Water Treatment Plant Design, American Water Works Association,
New York, 1969.
112
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SECTION XIV
GLOSSARY
Act
The Federal Water Pollution Control Act Amendments of 1972.
Annealing
Prevention or removal of objectionable stresses by controlled cooling
from a suitable temperature.
Batch
The raw materials, properly proportioned and mixed, for delivery to the
furnace.
Blowdown
A discharge from a system, designed to prevent a buildup of some
material, as in a boiler to control dissolved solids.
Category and Subcategory
Divisions of a particular industry which posses different traits which
affect water guality and treatability.
Cooling Water
Water used primarily for dissipation of process heat. Can be both
contact or non-contact, and is usually the latter.
Cullet
Broken glass generated in the manufacturing or fabricating processes.
Diatomaceous Earth
The skeletal remains cf tiny aquatic plants, commonly used as a filter
medium to remove suspended solids from fluids. Specially treated
diatomaceous earth can be obtained for the removal of emulsified oil
from water.
Fabrication
Used in this report in conjunction with processes which use flat glass
as the raw material, such as windshield laminating.
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Felt
Material, animal in origin, used in polishing pads for applying the
polishing medium (iron oxide or cerium oxide slurry) in polishing plate
glass.
Laminating
A process of constructing in layers to produce a product with composite
properties which are different from those of the components, as in
automotive windshields which are made shatter-resistant by laminating.
Lap
A large iron grinding wheel used in conjunction with a graded sand
slurry for grinding plate glass.
Lehr
A long tunnel^shaped oven for annealin.g glass by continuous passage.
Manufacturing
Used in this report in conjunction with the primary float, plate, sheet
and rolled processes.
New Source
Any building, structure, facility, or installation from which there is
or may be a discharge of pollutants and whose construction is commenced
after the publication of the proposed regulations.
Process Water
Any water which comes into direct contact with the intermediate or final
product. Includ'es contact cooling, washing, grinding and polishing,
etc.
Seaming
A light grinding or sanding process for removal of the sharp edges
produced by cutting of the glass, primarily for safety in handling.
Supernatant
The layer floating above the surface of a layer of solids, as the liquid
phase in a solids-separating centrifuge.
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Surface Waters
Navigable waters. The waters of the United States including the
territorial seas.
Tempered Glass
Glass that has been rapidly cooled from near the softening point, under
rigorous control, to increase its mechanical and thermal endurance.
Washer
A process device used for water cleaning of the product.
Waste water
™ — - jl —
Process water or contact cooling water which has become contaminated
with process waste and is considered no longer usable.
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CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
ENGLISH UNIT
by
CONVERSION
TO OBTAIN (METRIC UNITS)
METRIC UNIT
acre 0.105
acre - feet 1233.5
British Thermal Unit 0.252
BTU/short ton 0.278
BTU/square foot 2.71
feet 0.3048
gallons 3.785
gallons/minute 0.0631
gallons/1000 square feet 0.0407
gallons/short ton 4. 17
horsepower 0.74557
inches 2.54
pounds 0.454
pounds/1000 square feet 0.00489
pounds/short ton 0.5
million gallons/day 33785.0
square feet 0.0929
tons (short) 0.907
hectares
cubic meters
kilogram - calories
kilogram - calories/
metric ton
kilogram - calories/
square meter
meters
liters
liters/second
liters/square meter
liters/metric ton
kilowatts
centimeters
kilograms
kilograms/square meter
kilograms/metric ton
qubic meters/day
square meters
metric tons (10000 kilograms)
116
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