EVALUATION OF ULTRAFILTRATION TO RECOVER
AQUEOUS IRON PHOSPHATING/DEGREASING BATH
by
Gary D. Miller, Timothy C. Lindsey, Alisa G. Ocker
Hazardous Waste Research and Information Center
Illinois Department of Energy and Natural Resources
Champaign, Illinois 61820
Michelle C. Miller
Daily and Associates Engineers, Inc.
Champaign, Illinois 61820
Contract No. CR-815829
Project Officer
Paul Randall
Pollution Prevention Research Branch
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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NOTICE
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency (U.S. EPA) under Contract No. CR-815829 to the University of Illinois
and the Hazardous Waste Research and Information Center in Champaign, Illinois. It has been
subjected to the Agency's peer and administrative review process, and it has been approved for
publication as an EPA document. Approval does not signify that the contents necessarily reflect the
views and policies of the EPA, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and practices
frequently carry with them the increased generation of materials that, if improperly dealt with, can
threaten both public health and the environment. The U.S. Environmental Protection Agency (EPA) is
charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate
of national environmental laws, the agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and nurture
life. These laws direct the EPA to perform research to define our environmental problems, measure
the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing, and
managing research, development, and demonstration programs to provide an authoritative, defensible
engineering basis in support of the policies, programs, and regulations of the EPA with respect to
drinking water, wastewater, pesticides, toxic substances, solid and hazardous wastes, Superfund-
related activities, and pollution prevention. This publication is one of the products of that research and
provides a vital communication link between the researcher and the user community.
This report describes the results of laboratory and field testing of an ultrafiltration system to
recover and reuse an iron phosphating/degreasing bath. This pollution prevention project supports the
emphasis on reducing generation of hazardous waste by encouraging study and development of
methods to effectively use and recover aqueous cleaning solutions.
HI
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ABSTRACT
Pollution prevention efforts targeted the hazardous waste generated from a 5000-gallon iron
phosphating/degreasing bath used by a meta! fabricator to clean and precondition steel parts for
painting. With extended use, the buildup of emulsified oil in the bath reduced cleaning and
phosphating efficiency. Dragout of oil from the bath into the rinse water also pushed oil and grease
levels in the effluent over the allowable limit. When oil in the bath began to sacrifice product quality
and effluent levels edged closer to the maximum allowable limit, all 5000 gallons were dumped and
replaced. Periodic dumping, about three times each year, resulted in at least 15,000 gallons per year
of hazardous waste. Several waste minimization alternatives were considered, and ultrafiltration was
selected as the most promising technology to recover and reuse the bath and to reduce the total
amount of hazardous waste generated. Ultrafiltration has proven successful in similar industrial
applications with alkaline cleaning solutions, but the application of new membrane filtration technology
to this acidic, corrosive, high temperature bath was an innovative approach to pollution prevention.
This project was carried out in four stages: (1) initial assessment of the problem and evaluation
of alternatives, (2) bench-scale screening of ultrafiltration membrane candidates, (3) pilot-scale study
at the Illinois Hazardous Waste Research and Information Center (HWRIC), and (4) full-scale
implementation and testing onsite at the company's facility. Full-scale testing integrated the new
waste reduction scheme into the facility's production process by applying ultrafiltration directly to the
5000-gallon iron phosphating/degreasing bath. Ultrafiltration successfully removed oil contamination
from the bath and returned clean process solution back to the original 5000-gallon tank. Ultrafiltration
concentrated the hazardous component down to 10 gallons of oily waste and reduced hazardous waste
generation 99.8%. The concentration of oil in the bath was substantially reduced and maintained at
acceptable operating levels. Permeate flux rates exhibited excellent performance and were high
enough to compete with the constant input of oil from the production line. A significant portion of the
unused phosphating agents were also conserved although some surfactant was lost. Product quality
tests revealed that quality achieved during the full-scale ultrafiltration study was good for the facility's
application. The estimated payback period associated with implementing ultrafiltration was only 6.9
months. Results of this study were used to justify installing a permanent ultrafiltration system and
operating practices that would improve product quality.
This report was submitted in partial fulfillment of Contract No. CR-815829 under the
sponsorship of the U.S. Environmental Protection Agency. This report covers a period from February
1992 to November 1992 and work was completed as of November 1992.
IV
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TABLE OF CONTENTS
Foreward iii
Abstract iv
Figures vi
Tables vii
Abbreviations and Symbols viii
Acknowledgements ix
1. Introduction 1
Project Goals and Objectives 1
Industrial Participant 1
Problem Description 3
2. Process Background 6
3. Waste Reduction in the Metal Fabricated Products Industry
Waste Generation 9
Aqueous Cleaners 10
Ultrafiltration 13
4. Bench-Scale Membrane Screening
Methods and Materials 19
Bench-Scale Activities 19
Results and Discussion 21
5. Pilot-Scale Testing
Methods and Materials 23
Pilot-Scale Activities 25
Results and Discussion 26
6. Full-Scale Implementation and Testing
Methods and Materials 31
Full-Scale Activities 31
Results and Discussion 32
7. Quality Assurance 45
8. Economic Analysis 50
9. Conclusions and Recommendations 53
References 55
Glossary 57
Appendix 58
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FIGURES
Number
Page
1 Floor Plan of Cleaning and Painting Operations 2
2 Flow Diagram of Main Operations and Associated Waste Stream 4
3a Tubular Membrane Module .16
3b Spiral Wound Membrane Module 1 g
3c Hollow Fiber Membrane Module 1 Q
4 Bench-Scale Ultrafiltration Apparatus '.'.'.'.'.'.'.'.'. 20
5a Comparison of Wastewater Flux Rates During Bench-Scale Testing 22
5b Comparison of Normalized Flux Rates During Bench-Scale Testing 22
6 Continuous Scheme Ultrafiltration 24
7 Batch Scheme Ultrafiltration !!!!.'! 24
8 Modified-Batch Scheme Ultrafiltration '.'.'.'. 24
9 TOC in Process Tank and Permeate vs. Time
Using Clean Process Solution 27
10 Phosphate in Process Tank and Permeate vs. Time
Using Clean Process Solution 27
11 a TOC in Process Tank and Permeate vs. Time
Using Waste Process Solution 28
11 b Temperature Effect on Permeate TOC vs. Time
Using Waste Process Solution 28
12 Phosphate in Process Tank and Permeate vs. Time
Using Waste Process Solution 29
13 Calibration Curve for Dura-Gard TOC ['.'.'. 33
14a Oil and Surfactant TOC in Bath vs. Time ' ' 37
14b Oil and Surfactant TOC in Rinse vs. Time ' ' ' 37
14c Oil and Surfactant TOC in Process Tank vs. Time 38
14d Oil and Surfactant TOC in Permeate vs. Time '.'.'.'.'. 38
15 Phosphate in Bath, Process Tank, and Permeate vs. Time 40
16a Permeate Flux Rate vs. Time \\ 42
16b Permeate Flux Rate vs. Time (Extended Study) 42
VI
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TABLES
Number
1 Typical Materials Used and Types of Wastes
Generated in the Metal Fabricated Products Industry .............. 10
2 Membrane Candidates and Material Specifications ..................... 19
3 Product Quality Test Results ................................... 41
4 Sample Summary ........................................ ... 45
5 Precision Data for Full-Scale Sample Analysis ........................ 48
6 Accuracy Data for Full-Scale Sample Analysis ........................ 49
7 Assumptions for Economic Analysis ............................. . 50
8 Cash Flow Summary ........ . ................................. 51
9 Economic Summary ................................... ...... 52
VII
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ABBREVIATIONS
ASTM
cmc
COD
DAF
EDTA
EPA
HSWA
HWRIC
1C
IR
IRR
kW
L
MEK
mg
MIBK
mL
mm
MWCO
N
NPV
PHC
POTW
PPA
psig
PVDF
QAPP
RCRA
RPD
SARA
TCLP
TOC
TRI
UF
VOC
WRITE
SYMBOLS
Ca
CaCO3
Cr03
Fe2(P04)3
Mg
NaCI
NaOH
Na2SO4
PH
PK.
P04
ABBREVIATIONS AND SYMBOLS
American Society for Testing and Materials
critical micelle concentration
Chemical Oxygen Demand
Dissolved Air Flotation
Ethylenediaminetetraacetic acid + its sodium salts
Environmental Protection Agency
Hazardous and Solid Waste Amendments to RCRA
Hazardous Waste Research and Information Center
Ion Chromatograph
Infrared Spectrophotometer
Interest Rate of Return
kilowatt
Liter
Methyl Ethyl Ketone
milligrams
Methyl Isobutyl Ketone
milliliter
millimeter
Molecular Weight Cutoff
Normal
Net Present Value
Polyhydrocarbon
Publicly Owned Treatment Works
Pollution Prevention Act
pounds per square inch, gage
- Polyvinylidene di fluoride
Quality Assurance Project Plan
Resource Conservation and Recovery Act
- Relative Percent Difference
- Superfund Amendments and Reauthorization Act .
- Toxicity Characteristic Leaching Procedure
- Total Organic Carbon
Toxics Release Inventory
- Ultrafiltration
- Volatile Organic Compound
- Waste Reduction Innovative Technology Evaluation
Calcium
Calcium Carbonate
Chromic Acid
Iron Phosphate
Magnesium
Sodium Chloride *
Sodium Hydroxide
Sodium Sulfate
Log of Hydrogen ion concentration
Dissociation constant
Phosphate
viii
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ACKN 0 WLEDG EM ENTS
The U.S. Environmental Protection Agency and the Hazardous Waste Research and Information
Center acknowledge the important contributions made by the Civil Engineering Department at the
University of Illinois, R.B. White, Inc., Koch Membrane Systems, Inc., Arbortech Corporation,
Osmonics, Inc., DuBois Chemicals, Inc., and John Sparks of the U.S. EPA Global Change Division. The
support and cooperation of each of these people and organizations was greatly beneficial to this
project.
IX
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Section 1
INTRODUCTION
This project is one of five projects conducted under the State of Illinois - U.S. Environmental
Protection Agency's (EPA) Waste Reduction Innovative Technology Evaluation (WRITE) Program. It
represents a joint research effort of R.B. White, Inc., Bloomington, Illinois; the Illinois Hazardous Waste
Research and Information Center (HWRIC), the Department of Energy and Natural Resources,
Champaign, Illinois; the Civil Engineering Department at the University of Illinois; and the USEPA Office
of Research and Development, Cincinnati, Ohio.
Project Goals and Objectives
The purpose of this project was to evaluate potential technologies and operational modifications
that could reduce the amount of hazardous waste generated at a metal fabrication facility. HWRIC's
pollution prevention team worked with R.B. White, Inc., a sheetmetal fabricator, to develop a reduction
strategy for hazardous waste generated from operating a 5000-gallon iron phosphating/degreasing
bath. The goal of this project was to find an environmentally responsible means to extend the life of
the bath and thereby reduce hazardous waste generation. This project was carried out in four stages:
(1) initial assessment of the problem and evaluation of alternatives, in which ultrafiltration was
identified as the most promising technology to accomplish the project goal, (2) bench-scale screening
of ultrafiltration membrane candidates, (3) pilot-scale testing performed at HWRIC labs, and (4) full-
scale implementation and testing performed on site at R.B. White. The relative feasibility of
ultrafiltration as well as its capability to reduce waste generation were assessed on an engineering and
economic basis. Results of this project were used to justify installing a permanent ultrafiltration system
and operating practices that would improve product quality.
Industrial Participant
R.B. White, Inc. operates a sheetmetal fabrication facility that manufactures painted steel
shelving units. Figure 1 depicts a floor plan of R.B. White's metal working, cleaning, and painting
operations. Cold-rolled steel arrives at the plant from the steel mill coated with mill oils to protect the
bare metal from corroding or staining during storage and fabrication operations. The sheetmetal is
fabricated using various stamping and shaping operations which apply coolants and lubricants to the
metal working surface. Before being painted, the metal surfaces are cleaned to remove the mill oils
and metal working fluids and then preconditioned to bond well with the paint coating. Fabricated parts
are hung on a conveyor system that immerses the steel in a heated, aqueous iron
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Conveyor j
System ;
I
parts
loading
Parts
Flow !
X
Paint Spray ^
Booths \
Infrared Oven
Curing
unloading
parts
>_Air_Dryjng_
"funnel"
I
Finished Product
Inspection and Packaging
(D Spray
Rinsing
Iron Phosphating/
Degreasing Bath
Stamping and Shaping Operations
Ultrafiltration
Unit
Path of Fabricated Sheetmetal
Figure 1: Floor Plan of Cleaning and Painting Operations
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phosphating/degreasing bath. Surfactants in the bath clean away the mill oils, coolants, lubricants,
and shop soils while phosphating agents simultaneously deposit an amorphous coating that aids in
paint adhesion. Quality control in the bath is maintained by performing daily titrations which track the
level of chemicals in the bath. When the parts emerge from the bath, a fresh water spray rinses away
any oil residue and helps to prevent spotting. Parts are visually inspected to make sure they are free
from oil and display a uniform phosphate coating. The cleaned and phosphated parts are dried in a
forced-air drying tunnel, coated with enamel paint in a spray booth, and cured in an infrared oven. The
parts are then removed from the conveyor, and the adhesion quality of the paint coating is spot-
checked using a cross-hatch test. Finally, the finished product is boxed and shipped for distribution.
There are various point sources of waste generation in this process. Figure 2 illustrates a flow diagram
of the main operations and their associated waste streams. This project focused on the hazardous
waste generated from operating the 5000 gallon iron phosphating/degreasing bath and the resulting
rinse water discharge.
R.B. White has used the current mode of iron phosphating/degreasing for the past eight years.
This process was recommended by DuBois Chemicals (R.B. White's chemical supplier) on the basis that
phosphating and degreasing could be accomplished in a single tank by using two of their products:
Dura-Gard Soke and Tart liquid acid. Previously, the facility had operated separate degreasing and
phosphating tanks using trichloroethylene in the degreasing tank. In 1985, the company switched to
DuBois' aqueous iron phosphating/degreasing system to improve worker safety and reduce the
generation of organic solvent emissions and hazardous waste. Although switching to a single-stage
aqueous system eliminated the risks and liabilities associated with organic solvents, it introduced a new
waste disposal problem.
Problem Description
At R.B. White, simultaneous degreasing and phosphating in the same bath formed an oil-water
emulsion. With extended use, the buildup of oil and dirt in the bath reduced cleaning and phosphating
efficiency, and product quality was compromised. Without a clean surface, residual oil and dirt
adversely affected the adhesion and uniformity of the phosphate coating. Additionally, dragout of oil
from the bath into the rinse water raised oil and grease levels in the discharge. In the past, oil
skimmers were used to control oil slicks on the surface and prolong the life of the bath, but the
skimmers were only partially effective. When oil in the bath began to sacrifice product quality and the
discharge levels edged closer to the maximum allowable limit, the bath had to be replaced. Depending
on production rates, the bath typically lasted 3 to 4 months. Replacing the bath required a full day of
lost production time to take the process off-line, make arrangements with a waste transporter to drain
and dispose of the entire contents, and recharge the tank with 5000 gallons of fresh water and raw
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WASTE
PRECURSORS
PROCESSES
MAIN WASTES
GENERATED
Oil-based rust
inhibitor
Metal working fluids
Shop soils
Delivery of cold-rolled steel
Stamping and Shaping
Surfactants
+ Phosphating chemicals
4- Water
Scrap metal
Iron Phosphating/
Degreasing
Fresh water
Enamel paint
Cleaning solvents
h* Waste aqueous bath
with emulsified oil & dirt
t* Iron phosphate
precipitate sludge
»:* Free oil
Spray Rinsing
Forced-air Drying
Spray Enamel Painting
K ' a
Oven Curing
:* Rinse water
(discharged)
* Spent cleaning
solvents
< Overspray to |3aint
filters (landfilled)
Solvent vapors
(incinerated)
Figure 2: Flow Diagram of Main Operations and Associated Waste Streams
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materials. The spent bath was classified as RCRA hazardous waste because it failed Toxicity
Characteristic Leaching Procedure (TCLP) tests for xylene. Since land disposal of liquid wastes is
prohibited, the bath, sludge, and skimmed oil were incinerated in a cement kiln. Disposal costs
including transportation and incineration ran about $1 per gallon which came to $5000 per bath, or
about §15,000 per year in addition to the costs associated with lost production time and replacement
of water and raw materials.
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Section 2
PROCESS BACKGROUND
Iron phosphating/degreasing processes are widely used in the manufacture of metal products
to clean and precondition ferrous surfaces. Many metal fabricators and others that paint or coat steel
choose iron phosphating/degreasing processes because they effectively clean metal parts, provide an
excellent surface for paint adhesion, and protect against under-paint corrosion (Wittke, 1987). Iron
phosphate coatings have become increasingly popular in prepaint applications as existing and projected
EPA regulations require more stringent control and more expensive waste treatment methods for other
coatings such as chromated seals, zinc phosphate, and chromate conversion coatings {Phillips, 1990).
The goals and mechanisms associated with R.B. White's degreasing and phosphating process are
discussed below.
The goal of degreasing is to remove mill oils, metal working fluids, and any other shop soils
from the steel surface and prepare it for finishing. Degreasing agents can accomplish this in several
ways: detergency, solvency, chemical reaction, or mechanical action (USEPA, 1989). The aqueous
cleaning solution in use at R.B. White employs detergency in a heated {140°F), air-agitated bath.
In R.B. White's bath, degreasing is accomplished using nonionic surfactants that act at
interfaces between the metal, oil, dirt, and water. The surfactant molecules have hydrophobic "tails"
that penetrate the oil and dirt while their hydrophilic "heads" surround the particles and lift them away
from the metal surface and into the water phase. Nonionic surfactant molecules owe their "split
personality" (Wray, 1992) to long chain, hydrocarbon tails that more readily solubilize in oil than in
water and to oxygen-containing heads that rather prefer to hydrogen-bond with water molecules.
Surfactant molecules arrange themselves in chemically stable micelle formations, with their
hydrophobic tails oriented inward and their hydrophilic heads pointing out. The micelles disperse in
the water phase and form a stable emulsion that cleans the parts and prevents the oil and dirt from
redepositing on the metal surface (Morrison, Boyd, 1973). Micelles form as aggregates of 50 to 300
or more surfactant molecules depending on the nature, temperature, and concentration of the
surfactant. Micelle formation will only occur at or above a very narrow range of surfactant
concentration known as the critical micelle concentration (cmc). Below the critical micelle
concentration, there is not enough surface activity to provide efficient cleaning (Cutler, Davis, 1972).
Studies by Ginn and Harris (1961) have shown that maximum soil removal for nonionic surfactants
occurs at concentrations well above the critical micelle concentration. In R.B. White's degreasing
application, maintaining sufficient levels of surfactant in the iron phosphating/degreasing bath is an
important process control parameter to ensure good cleaning.
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Phosphating is a type of prepaint coating process used to simultaneously provide corrosion
-% i'"^ '-;ft. if*'
resistance and enhance paint adhesion to a metal surface. Phosphoric acid chemically bonds to the
metal surface to produce an amorphous conversion coating. The phosphate conversion coating is
nonconductive so it protects the metal surface from electrochemical oxidation that leads to rust and
corrosion. The matrix of the phosphate coating forms capillaries which increase the surface area and
provide a mechanical interlocking structure on which the paint can adhere (Phillips, 1990). Since the
phosphate layers contain surface breaks, immediate painting is imperative or corrosion may begin
within twenty-four hours following the phosphating operation (Paul, 1986).
The phosphate coating process chemically reacts in two steps. Phosphoric acid is added to
lower the bath pH to between 3.5 and 5 to dissolve a thin layer of metal from the part surface.
Solubilizing the metal consumes acid, and the local pH at the metal surface increases. At this higher
pH, phosphate salts bond with the solubilized metal ions to form an insoluble phosphate precipitate.
The precipitate deposits on the metal surface in an amorphous configuration. The two critical
parameters in this process are the solution pH and the concentration of phosphating agents.
Maintaining a solution pH between 3.5 and 5 is critical to ensure optimum reaction between the metal
surface and the phosphoric acid. Keeping the concentration of phosphating agents sufficiently high
is important to provide adequate coating and coverage, but excessive concentrations may produce a
coating that is undesirably loose and dusty (Phillips, 1990).
Parameters describing the quality of an iron phosphate coating include: (1) coating weight, (2)
rust creepage, and (3) paint adhesion. Coating weight is a measure of the mass of iron phosphate
(Fe3(PO4)2) deposited per unit area. Rust creepage is an indication of coating density and uniformity.
Paint adhesion is a measure of the strength of the bond between the phosphate and paint layers.
Imperfections in the coating can usually be traced to fluctuations in pH, changes in temperature, or an
imbalance of chemicals or contaminates in the bath (Phillips, 1990).
Several system configurations are available for iron phosphating/degreasing processes.
Systems may utilize vapor, spray, or immersion applications and range anywhere from one to seven
steps. Process designs may include a pickling step to remove rust and scale. Systems also have the
option of using distilled water or applying a seal coat in the final rinse. Selection is determined by
product quality requirements, soil removal capability, and production load. Traditionally, chemical
suppliers have recommended separate degreasing and iron phosphating steps when soils were difficult
to remove or when cleanliness was a particularly important quality parameter. Manufacturers would
rely on solvents or aqueous alkaline cleaners to degrease the parts, fresh water to rinse, iron phosphate
solution to coat, and more water to rinse. In many applications, adequate product quality can be also
be achieved by using a system configuration that combines the degreasing and iron phosphating
process into one step. This configuration relys on surfactants to function concurrently with iron
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phosphating agents in an aqueous solution. Companies like R.B. White switched to the one-step iron
phosphating/degreasing bath because it offered an alternative to solvent use and disposal, eliminated
separate cleaning and rinsing stages, and reduced water and space usage.
The 5000-gallon bath at R.B. White was charged with Dura-Gard Soke and Tart liquid acid
which contained nonionic surfactants, phosphate salts, phosphoric acid, and accelerators to promote
phosphate precipitation. The concentration of Dura-Gard Soke was checked daily with a simple
titration kit and conversion table to ensure that concentrations were maintained between 1.5 and 2.0
ounces of Dura-Gard per gallon. After the concentration of Dura-Gard was adjusted, pH was checked
with litmus paper. If the pH exceeded 3.5, it was adjusted to 3.5 by addition of Tart liquid acid. The
bath temperature was maintained at 140°F. During operation, a coarse bubble aeration system was
used to prevent bath stratification and provide complete mixing of all but the sludge settled on the tank
bottom. Oil skimmers were used to control oil slicks on the surface. Daily operations varied in length
from 8 to 16 hours per day, 5 to 6 days per week.
8
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Section 3
WASTE REDUCTION IN THE METAL FABRICATED PRODUCTS INDUSTRY
Waste Generation
The EPA's campaign for waste reduction is bringing change to industries through the 1984
Hazardous and Solid Waste Amendments (HSWA) to the Resource Conservation and Recovery Act
(RCRAj, the Toxics Release Inventory (TRI), the 1990 Pollution Prevention Act (PPA), and the more
recent 33/50 Program. The HSWA require industries to set up waste minimization programs and to
produce certified manifests demonstrating their waste reduction efforts. The TRI is a computerized
data base that tracks the routine and accidental release of approximately 300 toxic chemicals reported
by U.S. manufacturers. The 1990 PPA brought about stricter TRI industrial reporting requirements that
include providing information on pollution prevention efforts. The 33/50 Program is EPA's voluntary
pollution prevention initiative to reduce the Nation's releases of 17 TRI chemicals 33% by the end of
1992 and 50% by the end of 1995 (Hindin, Burch, Fort, 1992). Backed by federal legislation and
economic incentives, EPA's pollution prevention campaign has targeted several operations associated
with the metal fabricated products industry- Finding environmentally responsible solutions to the
industry's waste disposal problems has focused on source reduction (including process modifications
and raw materials substitution) and recycling.
The metal fabricated products industry is an integral part of aerospace, electronic, defense,
automotive, furniture, domestic appliance, and many other industries. The raw materials used in metal
fabrication range from common copper and steel to high grade alloys and precious metals. Typical
materials used and types of wastes generated from metal shaping, surface preparation, and surface
finishing operations are presented in Table 1.
Wastes generated from metal shaping operations include scrap metal and metalworking fluids.
In general, metal working fluids are petroleum-based fluids, oil-water emulsions, or synthetic emulsions.
With extended use, these metalworking fluids become spoiled and are often disposed as hazardous
waste. The fluids may be contaminated with cadmium, chromium, or lead depending on the metal
being tooled. In addition, the fluids may contain chemical additives such as chlorine, sulfur and
phosphorous compounds, phenols, cresols, and alkalies (Hindin, 1992).
Surface preparation operations generate wastes contaminated with solvents, heavy metals, and
oils. Concentrated solvent-bearing wastes may result from degreasing operations which produce
solvent-bearing wastewaters, air emissions, and solid-phase wastes. Chemical treatment operations
such as alkaline, acid, mechanical, and abrasive cleaning can generate waste streams contaminated
with oils or heavy metals (Hindin, 1992).
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Surface finishing operations result in plating-related wastes and painting wastes. Metal plating
and related metal deposition processes such as conversion coating account for the largest volume of
heavy metal- (cadmium, chromium, lead mercury, nickel) and cyanide-bearing wastes. Painting and
cleanup operations result in the direct release of solvents such as MEK, M1BK, toluene, xylene, and
many TRI regulated chlorinated solvents (Hindin, 1992).
Table 1: Typical Materials Used and Types of Wastes Generated in the Metal Fabricated Products
Industry (Hindin, Burch, Fort, 1992)
Operation
Typical Materials Used
Types of Wastes Generated
METAL WORKING
Cutting fluids
Lubricants
Inorganic/organic solvent
electrolytes
Heavy metals
. Heavy metal wastes
. Solvent wastes
. Waste oils
. Scrap metal, filings
SURFACE
PREPARATION
Cleaning
Acid/alkaline cleaners
Detergents
Organic degreasing and
cleaning solvents
Acid/alkaline wastes
Ignitable wastes
Solvent wastes
Still bottoms
Waste oils
Chemical Treating
Acid/alkaline cleaners
Etching/Pickling acids
Acid/alkaline wastes
Heavy metal wastes
Waste oils
SURFACE FINISHING
Electroplating
Acid/alkaline solutions
Heavy metal-bearing solutions
Cyanide-bearing solutions
Acid/alkaline wastes
Cyanide wastes
Heavy metal wastes
Plating wastes
Reactive wastes
Wastewaters
Conversion Coating
Phosphate salts
Chromate salts
Acid solutions
Chromium-bearing
wastewaters
Acid wastes
Painting
Paints
Solvents
Paint carrier fluids
Heavy metal paint wastes
Ignitable paint wastes
Solvent wastes
Still bottoms
Paint overspray waste
VOC emissions
Aqueous Cleaners
The EPA recommends various strategies for pollution prevention in the metal fabricated
products industries. Until now, waste reduction in surface preparation operations has focused on
10
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conserving or finding alternatives to organic solvent cleaners. For years, the metal finishing industry
has relied on organic solvents for cleaning metal parts.
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parts. In one case study, a major U.S. aerospace manufacturer successfully made the switch from a
1,1,1-trichloroethane vapor degreaser to an aqueous cleaning bath with only slight modifications and
little capital investment. In another case, a large plating firm replaced a two-stage solvent degreaser
and caustic bath with a single-stage, heated (140°F), aqueous cleaning bath (Quitmeyer, 1991). In
1985, R.B. White also made the switch from trichioroethane to a single-stage, heated (140°F), aqueous
degreasing/phosphating system and eliminated separate degreasing and rinsing operations.
In all these applications, the tank life of the aqueous cleaners is limited by the buildup of dirt
and oil in the bath. Cleaning effectiveness begins to deteriorate as dirt and oil accumulate in the water,
and the performance of other chemicals in solution is inhibited. Although the aqueous degreasers do
not carry the risks and liabilities associated with the disposal of waste organic solvent cleaners,
periodic replacement of the bath creates a different waste disposal problem. Aqueous degreasers form
stable oil-water emulsions that work well in cleaning but make them difficult to treat for disposal. The
emulsions contain levels of dirt, metal particles, and oil that are not acceptable to pour down the drain.
When pretreatment limits for wastewater discharge are exceeded, high oil content and chemical
oxygen demand (COD) keep the waste process solution from being treated at a publicly owned,
treatment works (POTW) by conventional biological treatment methods {Bailey, 1977).
Current disposal options for spent aqueous cleaning solutions include tankering to an offsite
treatment facility, incineration on or offsite, or discharge to a POTW. Tankering the waste process
solution to another site is a convenient but expensive option since more than 90% of the waste is
actually water. Tankering is also not a pollution prevention solution since it only transfers the problem
from one location to another. Incineration is another disposal option that can be used to burn the
waste oil despite its high water content. Incineration is commonly used, but the process requires
supplemental fuel and leaves no room for reuse or recovery of the spent bath (Bailey, 1977).
Discharge to a sanitary sewer is another option for disposal only as long as the wastewater
meets with effluent standards. An industrial facility may operate an end-of-pipe, wastewater
pretreatment plant before discharging spent cleaning solution to the POTW. A conventional
wastewater pretreatment plant might employ the following unit processes to remove oil from water
prior to discharge. Skimming can remove free oil from the surface, but sulfuric acid or lime may be
required to adjust the pH and help release free oil. Coalescing can separate water and dispersed oil
droplets that do not float to the surface, but this technique is only effective when surfactants are! not
present. Additional chemicals are required to overcome surface active agents and release the: oil.
Chemical emulsion breaking can be used when coalescing is not effective. Chemical emulsion breaking
begins by adding aluminum sulfate (alum) as a coagulant to destabilize the emulsified oil droplets. Lime
or caustic soda is used to raise the pH and form an insoluble aluminum hydroxide floe. Cationic
polymers may also be used with alum to eliminate the need for pH adjustment. The destabilized oil
12
-------
droplet:; then adsorb onto the alum floe surface. Dissolved air flotation (DAF) employs tiny bubbles
of air to carry the alum floe to the surface and over a clarifier weir (Springborn Laboratories, 1982).
The primary goal of this type of conventional, end-of-pipe pretreatment is compliance. Treated
water is discharged to the sewer while sludge produced during the process creates a new waste
disposal problem. With increasing environmental restrictions, landfilling the chemical sludge is
becoming less and less attractive as a disposal option. Alternatively, the sludge can be incinerated or
treated on site to recover the oil. Thermal oil recovery relies on heating the waste sludge to nearly the
boiling point to separate the oil, water, and sludge phases. The process may require a heat exchanger,
centrifuge, evaporator, acid, and additional chemicals (Springborn Laboratories, 1982). Since waste
emulsified oil solutions typically contain less that 10% oil, it usually does not pay to install such an
extensive oil recovery system (Cheng, 1983).
The rising costs associated with these disposal and pollution control techniques are the two
main incentives to extend the life of the aqueous cleaner baths (Wahl, 1979). Rather than wasting
valuable raw materials, the aqueous cleaners have the potential to be recycled again and again.
Depending on the physical characteristics of the bath solution, the life of the bath can be extended by
skimming contaminants off the top, settling heavier fractions to the bottom, or filtering out suspended
species (Quitmeyer, 1991). R.B. White found skimming only marginally effective, and no amount of
settling time would break the stable oil-in-water emulsion, but filtration did have potential for extending
the life of their aqueous cleaning bath.
Ultra-filtration
Conventional filtration techniques rely on depth or screen filters to remove oil and dirt from a
process solution, but conventional filter media clog easily. They require frequent backflushing or
disposal which result in additional wastes. Membrane filtration is a more advanced technique that
takes advantage of thin-film membranes and turbulent flow patterns to deliver a more consistent flow
rate and a higher quality filtrate than conventional filtration. One way that membrane filtration differs
from conventional filtration is that the direction of feed flow is tangential to the filter media rather than
perpendicular to it. Turbulent cross-flow across the membrane means oil and dirt are less likely to
build-up on the surface of the filter media and clog the flow (Bailey, 1977). The membranes
themselves are also revolutionary. Instead of thick beds of filter media, membranes are cast as thin
films with designated pore sizes ranging from atomic to macroscopic levels. Ultrafiltration is one class
of membrane filtration that uses membranes with pore diameters ranging from 10~9 to 10"8 meters.
This is smaller than the size of an emulsified oil droplet but much larger than the water molecules and
other dissolved species in an aqueous cleaning solution (Cheryan, 1986).
The ultrafiltration process works by producing two separate streams: concentrate and
13
-------
permeate. The permeate stream contains only the components in the feed solution small enough to
pass through the membrane pores. For an aqueous cleaning bath like R.B. White's, the permeate
would contain water, phosphating agents, and solubilized raw materials that did not react with the
membrane surface. The concentrate stream contains everything else that is rejected by the membrane.
At R.B. White, this would include emulsified oils, dirt, and water associated with the emulsion.
The recent development of more durable membranes, such as polyvinylidene di fluoride (PVDF),
has expanded the application of ultrafiltration beyond its origins in the food industry to successfully
handle industrial process solutions with extreme pHs, high temperatures, and high oil concentrations.
Because of its unique capabilities to concentrate oily wastewater and produce a clear filtrate,
ultrafiltration has emerged as a promising technology for extending the life of aqueous cleaners.
Ultrafiltration of oil-water emulsions is a more straight-forward method for removing and concentrating
oil are than any of the chemical or thermal techniques mentioned earlier. Ultrafiltration does not require
a stockpile of chemicals such as sulfuric acid, alum, lime, caustic soda, polymers, and other proprietary
chemicals. Instead, ultrafiltration produces a water phase that requires no further treatment and a
concentrated phase only a fraction of the original volume that can sustain combustion or be disposed
of efficiently. Ultrafiltration requires no heat input, low energy, and little operator attention (Wahl,
1979).
Each ultrafiltration application calls for a specific membrane type. Membranes used in
ultrafiltration are characterized by material of construction, pore size statistics, rejection, and flux. The
material of construction determines the acceptable range of chemical and physical parameters
(resistance to pH, temperature, pressure, solvents) that the membrane can withstand. Pore size
statistics describe the membrane's structure in terms of nominal pore size, pore size distribution, and
percent porosity- These parameters determine the minimum molecular weight cut-off (MWCO) which
is the minimum weight of a typical molecule that would be rejected by the membrane. Rejection
describes the degree to which ultrafiltration prevents components from passing through the membrane.
The rejection may change with use or aging of the membrane, but the % rejection may always be
determined by the following equation:
% Rejection = (CF - CP)/CF X 100% (E!q. 1)
where CF = concentration in feed solution
CP = concentration in permeate stream
Flux is defined as the volumetric flow rate of permeate per cross-sectional area per time. Flux is a
function of pressure, feed concentration, temperature, flow rate and turbulence in the feed channel,
and the tendency to foul (Cheryan, 1986). Rux determines the membrane surface area and pump
capacity requirements for a given wastewater flow rate or volume. Therefore, capital and operational
14
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costs are directly related to flux characteristics.
Membranes are cast in a variety 6f module configurations, each having particular advantages
and limitations. Spiral wound, hollow fiber, and tubular membranes are the most popular cross-flow
configurations. These configurations are designed to supply the greatest amount of surface area per
unit volume and flow channels that will accommodate the nature of the feed stream. Illustrations of
each are provided in Figure 3. The wide-channel tubular configuration is usually preferred for high
strength oily wastewaters. Although tubular membranes do not have the high surface area to volume
ratios that the other configurations do, the wide-channel tubular membranes provide good resistance
to cake formation and clogging by oil and particulates (Cheryan, 1986).
One of the greatest limitations of ultrafiltration membranes is their tendency to clog or foul.
Fouling is detected as the decrease in permeate flux over time and is a result of changes in the
membrane structure or interactions between the components of the feed stream and the membrane
surface. Fouling is mainly due to the accumulation of particles and adsorption of foulants on the
membrane surface and/or within the pores of the membrane itself. Almost all feed solutions will foul
a membrane to some extent, but optimizing the chemical compatibility of the feed stream and the
membrane material will help to reduce the effects of fouling. When a membrane shows signs of
fouling, the flux can largely be restored by cleaning the membrane to remove accumulated foulants like
oil, suspended solids, and metal precipitates. Mechanical cleaning employs sponge balls to remove
chemically precipitated species. Detergents work to breakup deposits on the membrane surface and
disperse them into solution. Solubilizing uses acids and chelating agents to dissolve stubborn foulants
like metal hydroxides or other chemical deposits {Pinto, 1978). Even with regular cleaning, a portion
of the flux may be unrecoverable because of irreversible fouling. The extent of irreversible fouling
determines the useful life of the membrane, which is also part of the operational cost associated with
the process (Cheryan, 1986).
The rate of fouling depends not only on the type of membrane and the nature of the feed
stream, but on the operating conditions as well. Fouling can be minimized by controlling pretreatment,
temperature, pressure, velocity, configuration, and concentration. Pretreatment of the feed stream
protects the membrane surface by straining out debris like suspended solids, grit, metal filings, and
cigarette butts. Temperature controls the viscosity of the feed stream and the adsorption of foulants
to the membrane surface. Increasing temperature within the recommended range for a membrane may
increase flux and decrease foulant adsorption. Transmembrane pressures are usually specified by the
membrane manufacturer to deliver optimal flux without compressing or changing the membrane
structure. Increasing the pressure within a certain limit will yield an increase in flux. Velocity in the
flow channel determines the degree of turbulence and, therefore, the likelihood of cake formation at
the membrane surface. High velocities at the membrane surface tend to shear off deposited material
15
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t'UKMEATE
-EPOXY REINFORCED /-BOOT SEAL
MEMBRANE-- FIBERGLASS SUPPORT TUBE
Figure 3a: Tubular Membrane Module (Cheryan, 1986) !
CONCENTBATEOUT
FEED IN
PERMEATE
SPACER
MEMBRANE FEED SPACER
Figure 3b: Spiral Wound Membrane Module (Cheryan, 1986)
OPEN END
Of FIBERS
EPOXY
TUBE SHEET
SNAP RING
XT RING SEAL
\
FEED
aow SCREEN
POROUS
BACK-UP DISC
SNAP RING
PERMEATE
END PLATE
FIBER
SHELL
XT RING SEAL
POROUS FEED END PLATE
DISTRIBUTOR TUBE
CONCENTRATE
Figure 3c: Hollow Fiber Membrane Module (Donnelly, Goldsmith,
McNulty, 1976)
16
-------
and prevent the formation of a fouling layer. Membrane configurations establish flow patterns to
minimize fouling from different types of feed streams. Choosing the best membrane configuration will
depend on the nature of the feed stream, the type of application, and the economies of scale.
Concentration of the feed stream determines the rate of permeate flux and the potential for cake
formation at the membrane surface. While it is possible to achieve 40 - 75% oil in the concentrate,
it may be more economical to settle for 40 - 50% since the rate of permeation decreases rapidly as
feed stream concentration rises. Higher feed stream concentrations also have,a greater potential to
foul the membrane, which leads to higher membrane cleaning and replacement costs (Bailey, 1977).
In industrial applications where ultrafiltration could be used to filter aqueous cleaning baths,
fouling will typically be due to oils, suspended solids, free surfactants, and metal precipitates (Pinto,
1978),, Research by Bhattacharyya, et. al. (1979) predicted fouling phenomena for oil-surfactant-water
conditions similar to those at R.B. White. Bhattacharyya experimented with ultrafiltration of oily-
surfactant waters using tubular, non-cellulosic membranes. The study was used to determine the
feasibility of using ultrafiltration aboard Navy ships to treat "bilge waters" to meet marine discharge
standards. The bilge oil Bhattacharyya used to mix the samples consisted mainly of fuel oil, lubricating
oils, and hydraulic oils. The experimental formulations were prepared at a neutral pH using distilled
water or river water and nonionic surfactants. Bhattacharyya worked at temperatures of 25 and 40°C
(77 and 104°F) and tested different combinations of feed streams: oil-water, surfactant-water, and
oil-surfactant-water.
From the test results, Bhattacharyya attributed fouling and flux decline to a cpmbination of gel
formation and adsorption of foulants on the membrane surface. In the oil-river water samples,
Bhattacharyya found that the interaction between oil and suspended solids resulted in the formation
of a gel layer that restricted permeate flux. Gel formation occurs when the interactions between the
oil droplets are strong enough to produce aggregates that eventually develop into a gel layer on the
membrane surface (Lee, 1984). With the dirt and other particulates in R.B. White's bath, the formation
of a gel layer was a possible source of fouling. In the surfactant-water samples, Bhattacharyya found
that free nonionic surfactants contributed to fouling and inhibited flux by physical adsorption and
micelle formation within the membrane pores. In R.B. White's application, this type of surfactant
stripping by the membrane was a concern for preserving the concentration of raw materials in the bath.
In the oil-surfactant-water systems,.Bhattacharyya found that there was less flux decline than in the
other two systems. With the surfactant and oil tied up in an emulsion, there was decreased adsorption
of free surfactant and oil on the membrane surface. However, since less free surfactant was available,
surfactant rejection was enhanced in the presence of oil. This scenario most closely represented the
actual conditions at the R.B. White facility. In general, the degree of adsorption depends on the type
and concentration of surfactant, other materials present in solution, and the type of adsorbent (oil,
17
-------
membrane, etc.). Adsorption of surfactant tends to decrease as temperature increases and as
concentrations rise above the critical micelle concentration (Cutler, Davis, 1972). By raising the
temperature to 40°C (104°F), Bhattacharyya found that flux increased due to lower viscosities and less
adsorption of oil and surfactants on the membrane without sacrificing oil rejection (Bhattacharyya,
Jumawan, Grieves, 1979). For the warmer operating temperatures (140°F) at R.B. White, this
observation was encouraging.
18
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Section 4
BENCH-SCALE MEMBRANE SCREENING
Methods and Materials
The laboratory bench-scale activities served as an initial screening of candidate membranes to
asses their respective flow rates and chemical compatibility. The key parameters for membrane
evaluation focused on flux and fouling characteristics and permeate quality.
Ultrafiltration equipment used in this study was provided by a variety of well-known equipment
and membrane manufacturers. The laboratory bench-scale study utilized an Amicon dead-end, stirred-
cell ultrafiltration assembly (Model 8200, 180 mL capacity) with a nitrogen pressure source. The
bench-scale apparatus was used to screen a variety of 62 mm diameter disk membranes for flux rates
and chemical compatibility. A summary of the disk membranes tested is presented in Table 2, and a
diagram of the bench-scale apparatus appears in Figure 4. Permeate flux rates were determined by
weighing the permeate as it filtered through the stirred cell over time. Permeate was collected in a
beaker located on a Sartorius analytical balance (Model LC 12000s). The balance was connected to
a computer via a RS-232 cable, and mass measurements were sent in prescribed time intervals to a
Lotus 1-2-3 spreadsheet.
Table ?.: Membrane Candidates and Material Specifications
MODEL
NO.
HG05
SNO4
PM10
PM30
M2
M3
VENDOR
Osmonics
Osmonics
Amicon
Amicon
Enviro-Process
Enviro-Process
MATERIAL OF
CONSTRUCTION
Polysulfone
Cellulose Acetate
Polysulfone
Polysulfone
Teflon
Teflon
MWCO
2,000
20,000
10,000
30,000
20,000
500
MAXIMUM
PRESSURE
(psi)
400
150
70
70
80
200
MAXIMUM
TEMPERATURE (°C)
100
60
100
100
* No limit specified
* No limit specified
Bench-Scale Activities
Samples for the bench-scale study were collected from the iron phosphating/degreasing bath
while it was relatively dirty. Samples were drawn from twelve locations in the tank along the surface,
middle, and bottom using a Scienceware polyethylene dipper. The dead-end, stirred ultrafiltration cell
19
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Pressure from
Nitrogen Source
Disk Membrane
Magnetic Stirrer
Permeate
Beaker
Electronic Balance
Computer B
Data via
RS-232 Cable
Figure 4: Bench-Scale Ultrafiltration Apparatus
(Laine, Hagstrom, Clark, 1989)
20
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was used to test six different membranes for clean water flux, process solution flux, and flux recovery
at consistent transmembrane pressures in triplicate. First a clean water flux test was run with 180 mL
distilled/deionized water to establish an initial flux. The process solution flux test directly followed to
characterize a representative flow rate of process solution through the membrane. Flux recovery was
determined by rinsing the membrane and filtering a second 180 mL aliquot of distilled/deionized water.
The deterioration of process solution flux with time and the net difference in initial flux and flux
recovery were used as a measure of fouling that occurred during filtration.
Sample quality for the bench-scale testing was defined by the partition-gravimetric method for
oil and grease (USEPA Method 413.1). At this stage, oil and grease tests were performed without
sufficient analysis to actually differentiate between oil/grease and non-ionic surfactants because the
contract lab used was unaware of the importance of specifying these components separately (see
Quality Assurance section). Oil and grease analyses were performed on permeate, concentrate, and
unfiltered process solution samples. Results are still considered valid to the extent that they were used
to determine the relative efficiency of each membrane to remove emulsified oil contamination in the
process solution and last without fouling.
Results and Discussion
The results of the bench-scale flux tests are summarized in Figures 5a and 5b. Figure 5a
compares the relative wastewater flux rates of each membrane candidate. Model M2 (Teflon 30,000
MWCO) produced the highest flux rates with Model SN04 (Cellulose Acetate 20,000 MWCO) running
a close second. Figure 5b shows that both candidates displayed competitive flux recovery, but
iai values set the M2 Teflon model out front. J represents the permeate flux, and the value
aae/Jiniti.1 "s an indicator of the loss in permeate flux from clean water to wastewater. The relative
loss was much less for the M2 Teflon model than the SN04 Cellulose Acetate which indicates the M2
Teflon membrane underwent the least fouling in the bench-scale test.
Oil and grease levels in the permeate as measured by the USEPA Method 413.1 were
consistently low, typically less than 40 mg/L for all membrane candidates. As discussed in the Quality
Assurance section of this report, a portion of the oil and grease measurements was attributed to the
presence of free surfactant in the permeate.
The overall best performance was given by the M2 Teflon 30,000 MWCO membrane from
Enviro-Process Systems. Even though the SN04 Cellulose Acetate membrane appeared to be a close
competitor, manufacturer's ratings indicated that the cellulose acetate would not have withstood the
extreme conditions at the R.B. White facility with long-term use. Attractive features of the M2 Teflon
model for this application were its resistance to extreme pH, its ability to withstand high temperatures,
and its durability in the presence of industrial wastewater components.
21
-------
j:
E
"c
"2
o
E
1
n
E
2
x
J3
U.
n
to
CO
£
M2
MATERIAL: Teflon
SN04
PM30
MWCO:
PM10
Polysulfone
10,000
Cellulose Polysulfone Teflon
Acetate
30,000 20,000 2,000 500
Membrane Model
Figure 5a: Comparison of Wastewater Flux Rates
During Bench-Scale Testing
X
3
o
O
E
o
0.4-
0.2-
Javerage/Jinitial
Jrecovery/Jinitial
where J = flux
0.0
M2 SN04 PM30 M3 PM10
MATERIAL: Teflon Cellulose Polysulfone Teflon Polysulfone
Acetate
MWCO: 30,000 20,000 30,000 500 10,000
Membrane Model
Figure 5b: Comparison of Normalized Flux Rates
During Bench-Scale Testing
22
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Section 5
PILOT-SCALE TESTING
Methods and Materials
Although dead-end filtration is useful for bench-scale screening, pilot- and full-scale membrane
cartridges typically use hollow fiber, spiral wound, or tubular configurations (see Figure 3, Sect. 3).
Due to the high concentration of suspended solids and other impurities associated with the process
solution, a tubular configuration was chosen for the pilot- and full-scale tests. Although tubular
membranes do not have the high surface area to volume ratios that other configurations do, the wide-
channel, cross-flow nature of the tubular membranes provides good resistance to cake formation and
clogging by particulates. Additionally, tubular membranes offer the advantage of being able to use
rubber sponge-balls in cleaning. A pilot-scale, tubular module made of the Enviro-Process M2 Teflon
was not available, so other membrane suppliers were contacted to find a suitable replacement. Koch
Membrane Systems' 5'HFP-276-PNO PVDF 100,000 MWCO membrane was recommended in the one-
inch tubular configuration with 1.1 square feet of membrane area. Like Teflon, PVDF is capable of
withstanding high temperatures and extreme pHs. The PVDF 100,000 MWCO was greater than the
30,000 MWCO tested for the Teflon membrane, but the PVDF surface was negatively charged to repel
emulsified oil droplets. The larger nominal pore size would also permit higher permeate flux rates and
permeation of unused surfactants and phosphating agents. The pilot-scale ultrafiltration unit utilized
the Osmonics PES/OSMO-O5T-SSXX model capable of operating at pressures between 40 and 60 psig
within a pH range of .5 to 13.
Three types of large-scale operating schemes can be used in pilot- and full-scale applications:
continuous, batch, and modified-batch. Scheme selection depends on the size of the operation, the
availability of space, and the nature of the process solution.
The continuous scheme implies a dead-end filtration configuration or a system with internal
recycle (see Figure 6). Permeate is returned directly to the bath as contaminants continuously
accumulate at the membrane surface and within the system plumbing. This scheme does not bear the
additional capital cost of a separate holding tank for the permeate, but continuous or dead-end filtration
is likely to significantly shorten the useful life of the membrane due to the rapid accumulation of
foulants.
The batch scheme filters process solution one tank at a time. Rgure 7 illustrates a schematic
of the batch set-up. When process solution is pumped from the feed tank through the UF system,
some of the flow permeates through the membrane into a separate tank while the majority of the flow
is recirculated back to the feed tank for further concentration. As the flow is recirculated, more and
more solution is permeated through the membrane until only a fraction of the original solution volume
23
-------
Feed Tank
(5000 gal bath)
I Pump
Figure 6: Continuous Scheme Ultrafiltration
Feed Tank
(5000 gal bath)
Concentrate
Pump
Figure 7: Batch Scheme Ultrafiltration
Pump
£ nj "a?
oj m c
J= 0 0
D. £ o
t
Process Tank
(55 gal)
Pump
^Permeate to separate
holding tank
Concentrate
Membrane
Permeate to bath
Figure 8: Modified-Batch Scheme Ultrafiltration
24
-------
remains in the feed tank. This type of set-up was tested in HWRIC's pilot lab facility using a 55-gallon
feed tank. For a batch scheme to work on a full-scale operation, the entire bath would have to be
filtered into another 5000 gallon holding tank and then returned to the operating tank all at once.
Periodic batch filtration uses membranes more efficiently and helps to prolong the useful life of the
membranes. However, this option involves down time as well as the additional capital costs associated
with a separate holding tank and greater membrane capacity.
The modified-batch scheme is a cross between the batch and continuous schemes. This
scheme utilizes an intermediate process tank which is only a fraction of the size of the primary feed
tank. A schematic of the modified-batch scheme is depicted in Figure 8. The oily bath is first fed into
the process tank and then sent through the ultrafiltration system. The clean permeate is continuously
returned to the bath while the concentrate is recirculated back to the process tank for further
concentration. As the permeate is filtered into the bath and the process tank gets low, solution is
pumped from the bath into the process tank to keep it full. When levels in the process tank reach
sufficient concentration, a batch-down procedure can be used to further concentrate the contents of
the process tank. During a batch-down, flow to the process tank is stopped, and the contents of the
process tank are allowed to concentrate down as described for the batch scheme. The modified-batch
scheme was chosen in the full-scale testing for its cost efficiency, lack of disruption to the production
process, and limited space requirements.
Pilot-Scale Activities
A batch scheme ultrafiltration system was set up at HWRIC's pilot lab facility to filter bulk
samples of process solution. The pilot-scale system was intended to model the flux and fouling
characteristics that might be expected in a full-scale operation.
A preliminary pilot test was conducted on clean process solution to determine the selective
permeation of raw materials through the PVDF membrane. Since the two essential components of
Dura-Gard Soke are phosphating agents and surfactants, it was important to monitor the fate of these
chemicals under the influence of ultrafiltration. Twenty gallons of clean process solution were prepared
with distilled water at 2.5 ounces Dura-Gard/gallon and filtered through the UF pilot unit.
A second pilot-scale test was used to evaluate the effectiveness of the UF equipment regarding
removal of emulsified oil and raw materials from the waste process solution. A 50-gallon sample was
collected from R.B. White's iron phosphating/degreasing bath and shipped to HWRIC by a DOT licensed
hazardous materials transporter. This solution was filtered through the UF pilot-scale unit, and
transmembrane pressure, concentrate flow, permeate flux, and influent temperature were monitored
during the test.
In both pilot-scale tests, one-liter samples of permeate and inflow were collected in glass
25
-------
bottles at 1-hour intervals. Permeate flux and temperature were measured every 15 minutes. Samples
of the concentrate, permeate, and unfiltered process solution were analyzed for oil/grease and
surfactant by TOC (Standard Method 5310 B) and for phosphate by titration (Standard Method 2310
B).
Results and Discussion
Results of the preliminary pilot test with clean process solution helped to identify the extent
of selective permeation of raw materials through the membrane. Since the process solution was clean
and uncontaminated by oil, Dura-Gard surfactants accounted for the only TOC contribution to the
system. Figure 9 shows that during the course of the test, surfactant TOC levels steadily rose in the
process tank while levels in the permeate showed a predominantly downward trend with the exception
of the last sampling point. Without emulsified oil in the process solution, all the surfactants were free
and able to interact with the membrane structure. The build up of free surfactant TOC in the feed tank
indicated that the PVDF membrane was selectively filtering out some free surfactant from the process
solution. As less and less surfactant permeated through the membrane, it appeared that the surfactant
molecules were adsorbing to the membrane surface and forming micelles in the membrane pores.
Interactions between free surfactant and membrane structures were described by Bhattacharyya, et.
al. and are summarized in the Waste Reduction section of this report. It is interesting to note,
however, the sudden increase in TOC/surfactant for the final permeate data point. During the
preliminary pilot test, the temperature of the feed stream rose from 25 to 51 °C (77 to 124°F) and
concentration nearly doubled from 490 to 950 mg/L TOC. As predicted by Bhattacharyya (1979),
adsorption of free surfactant on the membrane was reduced as temperature and concentration
increased. For the full-scale testing, this was encouraging, and an increase in surfactant permeation
was expected due to the warmer operating temperatures (app. 140°F) at R.B. White. As illustrated
in Figure 10, phosphate levels in the process tank and the permeate remained relatively constant during
the course of the test. Phosphate values for permeate were only slightly lower than in the process
tank, indicating that the phosphating agents were not selectively removed by the PVDF membrane to
a significant degree. On the other hand, the surfactant component did show signs of selective removal
by the PVDF membrane.
Results of the second pilot-scale test conducted on the 50-gallon sample of waste process
solution are presented in Figures 11 and 12. Figure 11a depicts the steady increase of TOC in the
process tank and permeate with time. As TOC levels built up in the tank, more and more clean
permeate was filtered out and the oily process solution concentrated down. During the test
temperatures rose from 24 to 54°C (75 to 130°F) and paralleled the rise in permeate TOC (see Figure
11 b). Exactly what percentage of the TOC could be attributed to oil/grease or surfactant was unclear,
26
-------
it- *
I
w
O)
1
Q.
U
o
1000
900-
800-
700 -
600-
500
190
400
120
0.0
2.0
en
E
(B
Q>
£
I
O
TOC in Process Tank
TOC in Permeate
0.5 1.0 1.5
Elapsed Time (hours)
Figure 9: TOC in Process Tank and Permeate vs Time
Using Clean Process Solution
e
'a
a.
to
o
JK
Q.
15200
14800
14400
14000
13600
13200
12800-
12400
a Process Tank
-« Permeate
0.0
2.0
0.5 1.0 1.5
Elapsed Time (hours)
Figure 10: Phosphate in Process Tank and Permeate vs Time
Using Clean Process Solution
27
-------
D)
E
M
O
P
o
4000
3000-
2000-
1000
100
-90
-80
-70
r60
50
2468
Elapsed Time (hours)
10
TOG in Process Tank
TOC in Permeate
O)
^
o
"5
i
u
o
Figure 11a:
TOC in Process Tank and Permeate vs Time
Using Waste Process Solution
100
o
O)
c
o
2
o
a.
c
30-
20
Temperature
TOC in Permeate
02468
Elapsed Time (hours)
Figure 11 b: Temperature Effect on Permeate TOC vs Time
Using Waste Process Solution
28
-------
0>
E
4>
«*
CO
JZ
o.
o
Q.
5800
5600-
5400-
5200-
5000 -
4800-
4600-
4400-
4200
Phosphate in Process Tank
Phosphate in Permeate
4 6
Elapsed Time (hours)
10
Figure 12: Phosphate in Process Tank and Permeate vs Time
Using Waste Process Solution
29
-------
but research by Bhattacharyya and results of the first preliminary pilot test led to the assumption that
perhaps increasing levels of surfactant TOC were passing in the permeate along with some oil.
As demonstrated by the two pilot-scale tests, the interactions of free and combined surfactant
with the membrane surface are completely different. The preliminary pilot test with clean process
solution demonstrated that free surfactant tended to foul the membrane, increasing surfactant
rejection. When temperature and concentration in the feed tank increased, surfactant adsorption
occurred to a lesser extent. In the second pilot-scale test with the waste process solution, more
surfactant was tied up with the emulsified oil droplets and was not available to adsorb onto the
membrane surface. Only a small fraction of free surfactant was actually present in the waste process
solution; most of it became physically associated with the oil during the rigorous mixing in the process
tank. With the waste process solution, less fouling was attributed to adsorption of surfactants and
formation of micelles on the membrane, and an increase in temperature seemed to encourage
permeation of surfactant.
Figure 12 illustrates the relationship between phosphate levels in the process tank and
corresponding levels in the permeate in the second pilot-scale test with the waste process solution.
The graphs show an upward trend in phosphate levels for both concentrate and permeate with time.
Values for both data sets were relatively close, confirming the free passage of phosphating chemicals
through the PVDF membrane. The increasing levels of phosphate with time were not anticipated in
the preliminary pilot test with the clean process solution. This may be an indication that the
phosphating agents were somehow associated with the emulsified oil or other rejected components
in the feed tank and passed through as concentrations rose in the feed tank.
Results from both pilot tests indicated that UF would be effective in removing emulsified oil
contamination while conserving some valuable raw materials. Data confirmed that phosphating agents
were conserved during ultrafiltration. Levels in the permeate were only slightly less than the levels in
the feed stream. The interactions of free and combined surfactants with the membrane surface
indicated that some free surfactant was selectively removed by the PVDF membrane, but the presence
of oil in the full-scale application was expected to minimize fouling caused by surfactant adsorption
and micelle formation within the membrane structure.
30
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Section 6
FULL-SCALE IMPLEMENTATION AND TESTING
Methods and Materials
The full-scale in-plant testing featured an ultrafiltration system provided by Koch Membrane
Systems (Model UF-4) equipped with 4 of the same 1" tubular PVDF membranes {100,000 MWCO,
4.4 sq. ft. total area) utilized in the pilot phase. The modified batch scheme was chosen for the full-
scale in-plant test (see Fig. 1, Sect. 1 and Fig. 8, Sect, 4).
Full-Scale Activities
Results from the pilot study were used to develop a full-scale, modified-batch test conducted
onsite at R.B. White's facility- The full-scale test applied ultrafiltration directly to the 5000 gallon iron
phosphating/degreasing bath. The objective was to directly measure the effect of ultrafiltration on the
process solution under actual plant conditions. The full-scale test took into account the constant input
of oil from the production line and the daily addition of bath chemicals. Additionally, the full-scale test
also helped identify and develop solutions to problems with the ultrafiltration equipment and anticipate
operating changes that should be made on a permanent unit.
Transmembrane pressure, flux, and temperature were monitored during the test as samples
were taken. A daily log sheet was utilized to keep records of chemical additions to the bath. Samples
of inflow (from the intermediate process tank) and permeate were collected daily in 1 -liter glass bottles
and stored in a 4°C cold room. Samples of the bath were collected every third day from five different
locations 1 foot deep along the length of the tank using a transfer pump. All samples were collected
in the morning prior to production start-up. This helped to nullify any fluctuations in process solution
quality that occurred during the day under actual production conditions. Rinse water samples were
also collected every third day from the catch basin located downstream of the iron
phosphating/degreasing tank. These samples helped to determine whether oil was clinging to the parts
as they emerged from the bath and if UF would help to control compliance problems with the
discharge. All samples from the full-scale study were analyzed for oil/grease and surfactant by TOC
and for phosphate by titration (see Quality Assurance section). A representative group of 20 full-scale
samples were analyzed for orthophosphate by 1C and for oil/grease and surfactant by the
extraction/infrared technique (Standard Method 5520C). A sample of the make-up water supply was
also tested for Ca/Mg hardness to identify hardness levels that might contribute to higher surfactant
usage.
To determine the impact of the UF system on product quality, DuBois Chemicals ran a series
of 6 steel test plates through the iron phosphating/degreasing bath during the UF experiment. The test
31
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plates were analyzed for coating weight, rust creepage, paint thickness, and paint adhesion as
described in the Quality Assurance section.
Permeate flux rates were recorded daily, and the time required for the UF unit to filter the entire
5000 gallons of process solution was calculated. When it had been determined that the UF unit had
processed 5000 gallons of permeate, a batch down of the contents in the intermediate process tank
was performed. The feed line from the 5000-gallon bath to the process tank was shut off, and the
UF unit concentrated down the 55-gallon process tank to approximately 10 gallons of oily waste.
Data obtained from the full-scale modified batch test was used to determine whether UF would
be a viable option for waste reduction at the R.B. White plant. Technical, operational, and economic
aspects associated with the UF equipment were examined to evaluate the feasibility of this technology
to improve R.B. White's metal fabrication operation.
Results and Discussion
Results of the full-scale testing on site at R.B. White provided a more complete picture of how
ultrafiltration impacted the 5000 gallon iron phosphating/degreasing bath and the quality of the parts
it produced. For the scope of this report, the time frame for experimental data was limited to the time
that was required to filter the first 5000 gallons of permeate and to proceed to batch down. This
covered a test period of 11 days. A total of 180 UF operating hours was required to process 5000
gallons of bath solution.
When field testing began, the iron phosphating/degreasing bath had not been replaced in over
3 months. The aqueous solution was murky with dirt and oil, and large patches of free oil floated on
the surface. The changes that took place over the next 11 days of ultrafiltration testing produced a
dramatic effect. Surface oil slicks disappeared and were replaced by a clean, light foam. The bath
solution was visibly clearer, and plant personnel testified that it looked like a freshly recharged bath.
Product quality tests also revealed that quality of the steel parts was improved significantly as a result
of the cleaner process solution maintained by the ultrafiltration system.
In order to quantify this exceptional improvement, results of the full-scale testing were analyzed
one-step further than the bench- and pilot-scale tests, paying particular attention to the separate TOC
contributions of oil and surfactant. Since standard analytical test methods were not adequate to make
the important distinction between oil/grease and surfactant for reasons detailed in the Quality
Assurance section of this report, analysis of the field data took a new approach. A mass balance was
developed to provide a more realistic representation of the events that took place over those 11 clays.
The mass balance utilized TOC data, records of chemical additions, and an estimation of the daily
production load. The analytical information on TQC provided a base line for total oil/grease and
surfactant levels in the bath, process tank, permeate, and rinse water. Daily records of the chemical
32
-------
500
.3- 400 -
"w
E
o
o
*»*
C3
"5
3
0)
300-
200 -
100
Best Fit: y = 20.974 + 22.436X RA2 = 0.999
6 8 10 12 14 16 18 20 Dura-Gard (g/L)
1.0 1.5 2.0 2.5 Dura-Gard (oz/gal)
Figure 13: Calibration Curve for Dura-Gard TOC
33
-------
additions of Dura-Gard Soke provided an accurate measure for the amount of TOC added as surfactant
to the bath during the course of the full-scale test (see Figure 1 3 for calibration curve of Dura-Gard
TOC). An estimation of the daily production load provided a practical and realistic value for .the amount
of oil that was washed off in the bath during 8 full days of production.
The daily production load was calculated by dividing the oil TOC in the bath at the start of the
test by the number of working days since the bath had last been dumped. The oil TOC in the bath at
the start of the test was extrapolated from titration data that was used to determine Dura-Gard
concentrations in the bath. The titration was actually a measure of the level of phosphating agents
in the bath, but this method was also valid for tracking the level of surfactant before ultrafiltration
began. According to DuBois, both the phosphating agents and surfactants are consumed at the same
rate under normal operating conditions. On the morning of the full-scale start-up, the bath titrated at
0.80 ounces Dura-Gard per gallon. Using the titration data, the level of surfactant was computed from
the calibration curve in Figure 1 3 as 1 55 mg/L, and the level of oil was calculated as the difference
between total TOC (422 mg/L) and surfactant TOC (1 55 mg/L). This value of oil TOC (267 mg/L) was
converted to mass units (267 mg/L x 3.785 L/gal x 5000 gal) and divided by 71, the number of
working days since the bath had last been dumped. The estimated production load was computed as
0.07 12 kg oil/day.
Once UF testing was implemented, the titration was no longer a reliable indicator of surfactant
or oil levels. The selective rejection and permeation of surfactant and phosphating agents by the UF
membrane resulted in different consumption rates for each component, so the mass balance was
developed to characterize the levels of oil and surfactant in the bath thereafter.
MASS IN - CHANGE IN MASS = MASS OUT (Eq. 2)
where MASS INn = (n(0) + m(S)}KW9d + {(O + S)^ + (0 + S)^},,^
CHANGE IN MASSn = {(0 + S)procew + (O + S),lut)fl0 + (0 + S)Mm}n
tank
MASS OUTn = {(0 + S)^ + (0 + S)rima}n
n = number of working days (n = 0 to 8) . ;
m = number of Dura-Gard additions (90 Ibs) in n days (m = 0 to 5)
O = oil TOC mass
S = surfactant TOC mass
Known Values: nntS),,^ TOC added as Dura-Gard surfactant
Measured Values: {(O + S)tath> ^oc^ ,*}
Estimated Values: {(S),^,}^,, Initial surfactant TOC mass
o Initial oil TOC mass
Daily production load
34
-------
Unknown Values: {(O + S),lra8, ,lud(J)>, . Wm}n
Ratio of 0 to S
The known, measured, and estimated values of TOC mass account for the major contributions
to the mass balance equation. The unknown values of {(O + S)rirw>i auivti ,Wm}n and {(0 + S)rirwjn,0
made up a smaller fraction of the mass balance and were difficult to determine analytically. The TOC
mass in the rinse was not calculated due to lack of consistent measurements for the volume of rinse
water; the mass of sludge produced was not possible to measure under field conditions; and the
skimmed oil did not lend itself to a homogeneous sample that could be analyzed by the HWRIC's TOC
analyzer. These unknown values of {(0 + S)rlw. ,ludBe, .Wm}n and {{O + S)rlme}n=0 were combined into
a single loss factor, k, to complete the mass balance. Still, one key assumption had to be made for
the unknown ratio of O to S. A quantitative relationship needed to be defined for the ratio of oil/grease
to surfactant in each facet of the mass balance equation: bath, process tank, and rinse. Without
analytical laboratory data to affirm the relative concentration of each component in the separate test
streams, insight into the physical chemistry of nonionic surfactants was used to fit together the final
pieces of the puzzle.
Surfactant molecules associate with an oil phase in an amount proportional to the concentration
of oil present and the conditions of mixing. Hundreds of surfactant molecules may surround a single
droplet of oil to form a micelle, but the amount of surface area on the oil nucleus determines the
number of bonding sites for the surfactant's hydrophobic tails. When sufficient surfactant is available,
the critical micelle concentration (cmc) is reached, and the surfactant molecules effectively emulsify
the oil in an aqueous phase. There is a direct and consistent correlation between the amount of
surfactant and the amount of oil in an emulsified solution (Cutler, Davis, 1972). Of course, the
presence of free surfactant or oil not associated with the emulsion would bias the balance between
the oil to surfactant ratio. Based on field observation during the full-scale testing, the only times free
oil was visible were on the first day in the bath and in the process tank there after. At all other times,
the absence of free oil indicated that the balance of oil to surfactant favored excess surfactant. In
terms of the mass balance, this observation led to a conservative estimate for reporting the amount
of surfactant, attributing a higher percentage of the total TOC to oil.
The mass balance assumed that the ratio of oil/grease to surfactant in each test stream (bath,
process tank, rinse) was equivalent to the ratio of oil to surfactant in the total system at time n. The
ratio of 0 to S was defined using the daily production load, surfactant additions, and initial bath
conditions. An example calculation follows.
35
-------
MASS IN - CHANGE IN MASS = MASS OUT
(n(0) + mtS)}.^ + {(O + S)taUl}n.0 - {(0 + S)procOM}n = {(O + S)^}n + k
where k = {{0 + S),lud89 + (0 + S)tklm + (0 + S)rirtM}n - {(0 + S)rinM}n,0
For n = 8 days
m = 5 additions
= .0712 kg oil/day (daily production load)
= -989 kg surfactant
o = 5.06 kg oil TOC (initially)
{(S)b«h}n=.o = 2-94 k9 surfactant TOC (initially)
{(O + S)proc«}n.8 = 3.96 kg TOC
{<0 + SltaJn^ = 6.43 kg TOC |
Substituting these values and solving for the loss factor, A:, gives:
8(.0712) + 5(.989) + (5.06 + 2.94) -3.96 = 6.43 + k
(.570 + 4.94) + (5.06 + 2.94) - 3.96 - 6.43 = k = 3.12 kg TOC
Grouping the O and S terms of the first two quantities separately and adding gives the total
measurable TOC in the mass balance system at n = 8:
OTOWI = (-570 + 5-06) = 5-63 k0 oil TOC
STOUI = (4.94 + 2.94) = 7.88 kg surfactant TOC
Calculating the ratio of 0 to S at n = 8 gives:
O/S = 5.63/7.88 = .714/1 or 0 = 41.7% and S = 58.3%
Following the assumption that the ratio of oil/grease to surfactant is equivalent for each test
stream (bath, rinse, process tank, permeate) gives:
Jn-e = 41 .7% (340 mg/L TOC) = 142 mg/L oil TOC
{(S)b.th}n-8 = 58.3% (340 mg/L TOC) = 198 mg/L surfactant TOC
{(O)rlma}n»8 = 41 .7% (1 1 mg/L TOC) = 4.58 mg/L oil TOC
{(S)rln«}n=8 = 58.3% (1 1 mg/L TOC) = 6.42 mg/L surfactant TOC
{(0)proe<>tt}n.8 = 41.7% (19000 mg/L TOC) = 7918 mg/L oil TOC
{(S)pr0ee«}n»8 = 58.3% (1 9000 mg/L TOC) = 11082 mg/L surfactant TOC
{(OUmMte}n,8 = 41 .7% (1 60 mg/L TOC) = 66.7 mg/L oil TOC
m.atJn-B = 58.3% (160 mg/L TOC) = 93.28 mg/L surfactant TOC
Figures 1 4a and 1 4b show the change in TOC levels of oil and surfactant in the bath and rinse
water over the course of the 1 1 -day experiment. When the field testing began, the bath had not been
replaced in over 3 months and free oil could be seen floating on the surface. At the start of the* field
36
-------
400 -
o»
E
O
o
300-
200-
100
Increased
Dura-Gard
additions
a Total TOG
Surfactant TOC
Oil TOC
0 20 40 60 80 100 120 140 160 180 200
Operating Time (hours)
Figure 14a: Oil and Surfactant TOC in Bath vs Time
o>
E
0 Total TOC
Surfactant TOC
Oil TOC
10-
5-
0 20 40 60 80 100 120 140 160 180 200
Operating Time (hours)
Figure 14b: Oil and Surfactant TOC in Rinse vs Time
37
-------
TO
E,
O
20000
15000 -
10000-
5000-
Q Total TOG
Surfactant TOO
a Oil TOG
-iiir
0 20 40
-T
60
-iiiiir
80 100 120 140 160 180 200
Operating Time (hours)
Figure 14c: Oil and Surfactant TOG in Process Tank vs Time
200
150-
O
100-
m Total TOC
Surfactant TOC
Oil TOC
-»r
20
rii'i"r
40 60 80 100 120 140 160 180 200
Operating Time
Figure 14d: Oil and Surfactant TOC in Permeate vs Time
38
-------
test, levels of oil/grease averaged 267 mg/LTOC and surfactant levels averaged 155 mg/LTOC. The
:« --» -
bath titrated at 0.80 ounces Dura-Gard per gallon which was we!! below normal operating parameters.
Under normal conditions, the bath is maintained at a Dura-Gard concentration of 1.5 to 2 ounces per
gallon. On the third day, oil TOC in the bath had dropped by 157 mg/L to 109 rng/L. On this day, the
bath composition was still low at 0.79 oz. Dura-Gard/gal as measured by titration in HWRIC's
laboratory. Apparently, R.B. White's simple colormetric test kit was not very precise in measuring
Dura-Gard levels in the bath. HWRIC field personnel alerted plant operators and provided R.B. White
with a more precise titration apparatus for testing the level of raw materials in the bath. The new test
apparatus included a pipette, buret, and pH meter for more accurate sampling and pH measurements
than the simple test kit could provide. The same titration procedure used in the lab was also used in
the field and is described in the Quality Assurance section of this report.
After ultrafiltration testing began, R.B. White personnel began adding more Dura-Gard to the
bath, and phosphate levels and surfactant TOC concentrations increased substantially. The rise in
phosphate levels in the bath shown in Figure 15 confirmed this surge in raw chemical addition.
Phosphate levels in the bath, permeate, and process tank rose simultaneously with the increase in bath
concentrations. The close correlation between phosphate levels in the separate test streams
demonstrated that virtually all the phosphating agents were recovered by the ultrafiltration equipment.
However, only a fraction of the unused surfactants managed to permeate through the membrane.
Figures 14c and 14d reveal the discrepancy of surfactant TOC in the process tank and permeate. As
predicted by the two pilot-scale tests, ultrafiltration was preferentially removing surfactant.
In addition to the effects of ultrafiltration, increased surfactant consumption may have been
aggravated by high calcium and magnesium levels in the make-up water supply. Results of the
hardness analysis on the make-up water identified 158 mg/L as CaCO3, which qualified the make-up
supply as a very hard water. High levels of Ca and Mg precipitate soaps and surfactants like those in
R.B. White's bath and increase surfactant consumption although low pH levels help to minimize the
effect. For R.B. White a water softening system might be beneficial, but the expense of purchasing
such a system would outweigh the cost of additional surfactant usage that R.B. White had already
become accustomed to before ultrafiltration was implemented.
Since Dura-Gard Soke only contained 2-3% surfactant by weight, compensating for surfactant
lost to ultrafiltration by adding more Dura-Gard could have resulted in excessively high phosphate
concentrations that would have contributed to loose and dusty coatings. At this point, it became clear
that Dura-Gard and Tart alone could not maintain the chemical balance in the bath. DuBois Chemicals
recommended a neutral cleaning additive, IPI-27, that contained the surfactant component found in
Dura-Gard Soke along with very low levels of phosphates. Since there was no good way to detect
levels of surfactant in the bath without laboratory analysis, it was suggested that plant operators
39
-------
CO
0.
o
JC
CL
7000
6000-
5000
4000 n
3000-
2000
Increase in Phosphate due to
increased Dura-Gard additions
Q Phosphate in BATH
Phosphate in INFLOW
B Phosphate in PERMEATE
0 20 40 60 80 100 120 140 160 180 200
Operating Time (hours)
Figure 15: Phosphate Levels in Bath, Inflow, and
Permeate vs Time
40
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develop their own gage for adding the surfactant component, IPI-27, on an as-needed basis. Operators
could even add excess surfactant as a safety factor td ensure clean part quality. Koch Membrane
Systems representatives indicated that excess surfactant would not irreversibly harm the membrane,
and DuBois Chemicals representatives saw no danger in excess surfactant interfering with the
phosphating process. The only loss seemed to be the extra money spent on adding too much
surfactant. Relative to the cost of the other raw materials, this added cost would be minimal.
Results of the coating weight, rust creepage, paint thickness, and paint adhesion tests
conducted by DuBois Research Laboratory and R.B. White personnel on samples of steel parts indicated
that acceptable product quality was achieved during the UF full-scale test. No previous product quality
records were kept on file, but conversation with DuBois laboratory personnel and R.B. White plant
operators confirmed that the product quality achieved during the UF full-scale test was good for R.B.
White's application for controlled indoor air environments. Product quality test results appear in Table
3.
Table 3: Product Quality Test Results
PRODUCT QUALITY TEST
Coating Weight
Rust Creepage 1 18"
Salt Fog 5%
Humidity 96%
Paint Thickness
Paint Adhesion
RESULTS (averages)
50.4 mg/ft2
Passing at 24, Failed at 48 hrs
Passing at 504 hrs
1 .6 mil
Good*
* Only qualitative data available from R.B. White personnel.
Permeate flux rates exhibited excellent performance during the full-scale operation. Rgure 16
shows the change in permeate flux with time and the approach to steady-state. According to Koch
Membrane Systems representatives, R.B. White's acidic iron phosphating/degreasing bath produced
much higher permeate flux rates than alkaline cleaning baths in similar UF applications. The
combination of acidic conditions (pH = 3.5 to 4.5), high temperature (140°F), relatively low oil
concentrations (267 mg/L in a dirty bath), and surfactant usage contributed to a very favorable
performance. High temperatures functioned to lower water viscosity and reduce free surfactant
adsorption while encouraging higher flux rates. The presence of surfactants also helped to keep the
membrane surface clean by tying up the oil and dirt in an emulsion.
41
-------
o
o>
x
a
a>
E
t«
o
a.
40
35-
E 30 J
25-
20
Figure 16a:
50 100 150
Elapsed Time (hours)
Permeate Flux Rate vs Time
200
40
CO
o>
X
UL
»
35-
30-
25-
20
Temporary flux increase
due to cleaning filter trap
Batch-down performed and
process tank refilled with
more dilute process solution
-O-Q-B-
100 200 300 400
Elapsed Time (hours)
500
600
Figure 16b: Permeate Flux Rate vs Time (Extended Study)
42
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During the 180 hour operating period of the full-scale UF test, permeate flux rates remained
steady and the membranes were never cleaned. Data collection was completed, but the UF system
was kept on line to evaluate the equipment's long-term performance. After several weeks the
permeate flux began to decline rapidly. Attempts to clean the membranes with alkaline cleaner (KLD-
Koch Liquid Detergent), diluted Tart (phosphoric acid plus surfactant), and rubber sponge balls were
jet
not effective in restoring flux. These cleaners were designed to remove oil, but apparently the oil was
not the primary cause of fouling and flux decline. The other major component in the bath that had the
potential to foul the membranes was the iron phosphate precipitate. A two-stage cleaning regime with
rubber sponge balls was prescribed. Sodium bisulfite was used in the first stage to reduce the iron
species to its more soluble state. Citric acid in the second stage acted as a chelating agent to combine
with the iron and prevent it from redepositing on the membrane surface. After lime pH adjustment,
the spent sodium bisulfite and citric acid cleaners were acceptable to pour down the drain. This
cleaning regime provided excellent flux recovery, but the high flux rates only lasted a few hours.
About this time, the centrifugal pump on the full-scale UF system began to show accelerated
signs of wear and tear. At least one pipe plug had been completely eaten away, and the pump casing
was leaking badly. The pump was made of cast iron and did not fare well under the corrosive
conditions of the bath and cleaning chemicals. The pump was taken off-line and replaced with a
stainless steel pump. When the interior of the old cast iron pump was examined, the inside had
severely corroded and the impeller had almost completely disintegrated. The bath and cleaning
chemicals had dissolved the iron from the pump and precipitated an iron phosphate coating on the
membrane surface. The accelerated iron corrosion and deposition from the cast iron pump kept the
membranes from staying clean for longer than a few hours. When the pump was replaced with a
stainless-steel one and the membranes were cleaned weekly, permeate flux rates were restored and
maintained.
In addition to membrane life, another long term concern pertained to regular maintenance on
the 5000 gallon tank. Since ultrafiltration had been implemented, periodic emptying of the tank was
eliminated. Previously, emptying the tank allowed plant personnel to recover lost parts from the tank
floor and remove the scale and sludge that had accumulated on the tank and heating element surfaces.
The scale and sludge consisted mainly of iron phosphate precipitate and undissolved Dura-Gard Soke
powder. DuBois recommended that the scale and sludge be removed periodically to reduce
contamination and improve heating element efficiency. Without emptying the tank, R.B. White needed
an alternative means of performing regular tank maintenance.
Plant personnel found that they could recover lost parts just by running a long pole with a hook
at one end along the bottom of the tank and fishing out the steel parts and hangers. The heating
elements were removable and could be cleaned without emptying the tank. With slight design
43
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modifications, the sludge that settled on the bottom of the tank could be removed using a slow-moving
sludge scraping mechanism and a sludge pump at a low point in the tank. Another alternative for
regular tank maintenance might involve renting or purchasing a 5000 gallon holding tank to use every
other year to store bath solution from the 5000 gallon process tank while regular tank maintenance
is performed. This way R.B. White could empty the tank, clean away sludge and lost parts, and still
save the bath solution. For the meantime, R.B. White has chosen to go with a third alternative.
DuBois Chemicals has recommended a liquid form of Dura-Gard Soke known as Secure Soke. This was
intended to reduce the amount of sludge accumulated in the tank by eliminating the undissolved Dura-
Gard component.
44
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Section 7
QUALITY ASSURANCE
A Quality Assurance Project Plan (QAPP) was prepared and approved by the U.S. EPA before
testing began (Miller, Lindsey, 1992). The QAPP contains a detailed design for conducting this study.
The experimental matrix, sampling and testing procedures, and laboratory analytical procedures are
delineated in the QAPP. The analytical objectives of the QAPP are discussed below. With the
exception of analytical difficulties involved in the oil/grease analysis, QA objectives for this project
were not only met but expanded to include more complete sample characterization.
The original intent, as outlined in the QAPP, was to analyze all samples for oil and grease in
order to determine the proficiency of ultrafiltration to remove oil contamination from the iron
phosphating/degreasing bath. As the project progressed, it became apparent that samples should also
be analyzed for concentrations of surfactant and phosphating agents to determine if valuable raw
materials were being filtered out along with the oil. Additionally, steel test panels were analyzed for
product quality during the full-scale study. Analysis of samples from the bench-, pilot-, and full-scale
studies included tests for oil/grease, polyhydrocarbons (PHC), total organic carbon (TOO,
orthophosphate, EDTA hardness, coating weight, rust creepage, paint thickness, and paint adhesion.
Table 4 presents a summary of sample types and analyses.
Table 4: Sample Summary
PHASE
Bench Scale
Pilot Scale
Full Scale
SAMPLE TYPE*
Process Solution
Concentrate
Permeate
Inflow
Permeate
Process Solution (Bath)
Inflow (Process Tank)
Permeate
Rinse Water
Raw Water Supply
Phosphated Steel Panels
Painted Steel Panels
SAMPLES
19
18
18
18
22
20
10
10
5
1
3
3
ANALYSIS
Oil/Grease
Oil/Grease
Oil/Grease
TOC, Phosphate
TOC, Phosphate
Oil/Grease, PHC, TOC, Phosphate
Oil/Grease, PHC, TOC, Phosphate
Oil/Grease, PHC, TOC, Phosphate
Oil/Grease, PHC, TOC, Phosphate
EDTA Hardness, TOC
Coating Weight
Rust Creepage, Thickness, Adhesion
Liquid samples were stored at 4°C in glass bottles with Teflon-lined caps;
holding times did not exceed 2 months.
45
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Laboratory analyses of the samples collected during this three-phase project were modified as
new information came to light. Oil and grease analysis as prescribed by USEPA Method 413.1
(Methods for Chemical Analysis of Water and Wastes, 1983) was complicated by the presence of
nonionic surfactants in the process solution. As the project progressed, it became evident that: the
nonionic surfactants in the process solution would interfere with the accuracy of this analytical
procedure. The surfactants contributed to a persistent, stable emulsion layer in the separatory funnel
that inhibited complete solvent extraction. Attempts to break the emulsion were time-intensive and
only partially successful. Glass beads, glass wool, Na2S04, NaCI, heating, freezing, pH adjustment
centrifugation, and continuous solvent-solvent extraction were not effective in breaking the emulsion
or achieving complete extraction.
In addition to the problems associated with the emulsions, the surfactants also contributed
false readings regarding the amount of oil and grease present. No known solvent will .selectively
dissolve only oil and grease. With the USEPA partition-gravimetric method (Method 413.1), freon
extraction not only dissolved oil and grease but other organics as well (Clesceri, Greenberg, Trussed,
1989). In this case, biodegradable nonionic surfactants were extracted along with the oil and grease
in the process solution. When the extract was distilled, the residue reflected the combined;total mass
of oil/grease plus surfactant. Since each component carried a different meaning, measuring the
quantity of the two components separately as oil/grease and surfactant was important.
Standard Method 5520 C extraction/infrared technique (Standard Methods for the Examination
of Water and Wastewater, 1989) goes one step beyond the USEPA partition-gravimetric method to
differentiate between oil/grease and other organics. This method utilizes solvent extraction plus
infrared spectroscopy. Analysis of the solvent extract by infrared spectrophotometer is capable of
discerning oil and grease as polyhydrocarbons (PHC) apart from nonionic surfactants. A representative
group of 20 full-scale samples were analyzed using this method, but the same problems associated
with the extraction procedure kept these samples from providing any conclusive data.
During the course of this study, laboratory personnel found that standard methods, would not
be adequate for analyzing the industrial process solution. Following standard protocol for defining and
reporting levels of oil and grease provided false and misleading information. In-house laboratory staff
worked on new methods and combinations of methods that would give a more accurate indication of
the samples' make-up. Their research went beyond the scope of this pollution prevention project, but
HWRIC staff will continue to research the analysis of similar industrial solutions in hopes of establishing
a more complete and accurate procedure for analyzing oily-detergent wastewaters.
Due to the complications involved in the oil and grease analysis, another analytical test was
developed for the complete set of pilot- and full-scale samples. Analysis for total organic carbon (TOO
was used as a surrogate test for combined levels of oil/grease and non-ionic surfactant. Analysis by
46
-------
TOC provided an accurate, efficient, and repeatable test for combined oil/grease and surfactant
concentrations. Under the circumstances? TOC provldeS the best indicator of the ability of
ultrafiltration to remove organic species, whether oil or surfactant, from the process solution. A mass
balance was then developed to describe the fate of each component. Analysis for TOC was conducted
by the Rosemount Analytical Dohrmann DC-190 TOC Analyzer according to the Combustion-Infrared
Method (Standard Method 5310 B). The TOC Analyzer was calibrated with 1000 ppm potassium
hydrogen phthalate (KHP) giving a reference standard of 999.7 ppm C as KHP with a typical recovery
of 986.4 +/- 25.57, standard deviation = 2.592 %. Method blank results were below the 10 ppm
detection limit. Samples were diluted according to strength.
In addition to testing for oil/grease and surfactant, samples were analyzed for phosphate
concentrations to determine whether ultrafiltration might selectively remove the valuable phosphating
agents from solution along with the emulsified oil. Concentrations of PO4 were determined by Ion
Chromatograph (1C) analysis using the Dionex Ion Chromatograph. The 1C was calibrated with
potassium phosphate. Samples were prefiltered with a solid phase extraction cartridge (C18) to
remove oil that might interfere with the 1C equipment. Due to the time and expense involved with the
1C testing, only a representative group of 20 full-scale samples were analyzed for orthophosphate by
1C. The remaining samples were analyzed for PO4 by using the same titration procedure R.B. White
plant personnel relied on for checking levels of phosphoric acid (free and combined) in the bath.
Samples were titrated with .1 N NaOH to the second pK, endpoint of 9.2. For the 20 representative
samples, a consistent ratio was defined between the volume of titrant required to reach the endpoint
and the known P04 values determined by 1C. This ratio was used to calculate concentrations for all
remaining samples. P04 data and data reduction procedures from the titrations and 1C testing are
presented in the Appendix.
For the onsite, full-scale testing, the make-up water supply for the iron phosphating/degreasing
bath was also tested for calcium/magnesium hardness. Hardness testing was used to determine the
potential for surfactant loss due to precipitation caused by calcium or magnesium in the water. The
EDTA titrimetric method (Standard Method 2340 C) was used to determine the level of water
hardness. These results were utilized to determine if a water softening system would be beneficial in
conserving surfactant in the long run.
Besides waste reduction, the primary objective of this study was to preserve product quality
by ensuring the steel parts were being cleaned and a good phosphate coating was being formed.
Quality control tests were performed by the chemical supplier and R.B. White personnel while the full-
scale ultrafiltration system was in operation. Standard tests included coating weight, rust creepage,
paint thickness, and paint adhesion. Coating weight was determined using DuBois Research
Laboratory's own method (Gortsas, 1993). Briefly described, steel test parts were processed through
47
-------
the iron phosphating/degreasing bath during normal operation. The parts were dried, weighed, and
measured. The phosphate coating was stripped with chromic acid (Cr03), and the parts were
reweighed. The net difference in weight gave milligrams phosphate coating weight per square foot.
Rust creepage was determined according to ASTM methods B117 and D2247-87. For these tests,
steel test parts were processed through the complete production line. Painted test parts were scored
and subjected to a either a 5% salt fog or 96% humidity. Rust creepage from the score was reported
as passing/failing for 1 /8" creepage at 24, 48, and 504 hours. Paint thickness was measured by the
Zorelco 757 coating gage and calibrated with a standard film thickness. Paint adhesion was checked
by R.B. White plant personnel using the cross-hatch test which involved scoring the paint and applying
a piece of tape to the scratch. Adhesion quality was observed as the tape was pulled away, and
results were qualitatively reported.
Tables 5 and 6 present the precision and accuracy data for the full-scale sample analysis
performed by HWRIC and DuBois labs. Due to the complications discussed earlier, data from the
oil/grease and PHC analyses was not used in the final evaluation.
Table 5: Precision Data for Full-Scale Sample Analysis (Typical values)
PARAMETER
TOC
Oil/Grease"
PHC"
Orthophosphate
EDTA Hardness
Coating Weight
RUST CREEPAGE
Salt Fog 5%
Humidity 96%
Paint Thickness
NO.
2
13
REGULAR
SAMPLE
440 mg/L
42 mg/L
LABORATORY
DUPLICATE
430 mg/L
FIELD
DUPLICATE
39 mg/L
PRECISION
RPD = 2.3%
RPD>7.4%
Data from the oil/grease and PHC analyses were not utilized due to
complications in laboratory procedures.
46
14
100
114
111
113
112
6055 mg/L
3641 mg/L
158.1 44 mg/L
53.2 mg/ft2
1/8" at <48hr
1/8" at >504hr
1 .6 mil
6095 mg/L
158. 144 mg/L
N/A
N/A
N/A
N/A
3799 mg/L
N/A
5 1.6 mg/ft2
1/8" at <48hr
N/A
1 .4 mil
RPD = 0.7%
RPD = 4.2%
RPD=0%
RPD=3.0%
RPD=0%
N/A
RPD = 13%
Oil and Grease analysis (USEPA Method 413.1) measures oil plus surfactant.
PHC analysis (Standard Method 5520 C) differentiates between oil and surfactant.
48
-------
Table 6: Accuracy Data for Full-Scale Sample Analysis (Typical values)
PARAMETER
TOC
Oil/Grease*
PHC"
Orthophosphate
EDTA Hardness
Coating Weight
RUST CREEPAGE
Salt Fog 5%
Humidity 96%
Paint Thickness
ID
NO.
REGULAR
SAMPLE
MATRIX
SPIKED
SAMPLE
MATRIX
SPIKED
VALUE
ACCURACY
(%
RECOVERY)
No data was obtained for spiked samples because oil would not stay
emulsified or remain in solution.
Data from the oil/grease and PHC analyses were not utilized due to
complications in laboratory procedures.
3'
100"
114
111
113
112
3905 mg/L
158.1 44 mg/1
as CaC03
53.2 mg/ft2
1/8" at <48hr
1/8" at >504hr
1 .6 mil
1 1 54 mg/l
1000 mg/L
as CaC03
N/A
N/A
N/A
N/A
1018 mg/l
1 004 mg/L
as CaCO3
N/A
N/A
N/A
N/A
88.3%
100.4%
N/A
N/A
N/A
N/A
Oil and Grease analysis (USEPA Method 413.1) measures oil plus surfactant.
PHC analysis (Standard Method 5520 C) differentiates between oil and surfactant.
Bath
b Raw water supply
49
-------
Section 8
ECONOMIC ANALYSIS
The costs and benefits associated with installing an ultrafiltration system at the R.B. White
facility were analyzed to determine the economic feasibility of this technology. Assumptions regarding
inflation rate, discount rate, federal tax rate, depreciation schedule, project life, and various operating
expenses were entered into a LOTUS spreadsheet program (General Electric, 1987) which calculated
a number of economic indices. The assumptions utilized in these calculations and their sources are
presented in Table 7.
Table 7: Assumptions for Economic Calculations >
(based on 1992 conditions)
ITEM
Inflation Rate
Discount Rate
Federal Tax Rate
Labor Rate
Power Costs
Depreciation Schedule
Project Life
Raw Materials Costs*
Down Time Costs"
Salvage Value
Waste Disposal Costs
FACTOR
4%
7.72%
34%
$15/hour
$.10/kw
7 years
20 years
$900/bath
$1000/bath
$0
$1 /gallon
SOURCE
Consumer price index
10 year treasury bill rate + 0.5%
General Electric, (1987) ;
R.B. White
Illinois Power i
General Electric, (1987)
Koch Membrane Systems, Inc.
R.B. White
R.B. White
Koch Membrane Systems, Inc.
R.B. White
* Raw Materials Costs include phosphating and degreasing chemicals required to charge a fresh
bath.
** Down Time Costs include costs associated with lost production incurred during bath cleaning
activities.
Table 8 provides estimates of the capital and operating expenses as well as the cost savings
that could be anticipated as a result of investment in an ultrafiltration system. These estimates assume
that the phosphating/degreasing bath would have to be disposed of and recharged at a frequency of
once every 2 years following installation of the ultrafiltration system. This contrasts with the schedule
utilized prior to installation of the ultrafiltration system which involved disposing of and recharging the
50
-------
to c
CO 4
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O T
CO
Is
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8
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88
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icals
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51
-------
bath at a frequency of at least 3 times per year. Additionally, it was assumed that the wasted bath
could be discharged directly to the sanitary district (following neutralization of its acidic conditions for
a minimal cost) as a result of ultrafiltration processing. This is appropriate since the bath would no
longer contain significant quantities of emulsified oil which had prevented discharge of the spent bath
prior to utilization of ultrafiltration.
As shown in Table 8, installation of an ultrafiltration system would require significant capital
expenditures (approximately $12,000) associated with purchasing and installing the equipment.
Additionally, significant operating expenses associated with cleaning and replacing the membranes,
equipment maintenance, and power consumption would be incurred over the projected 20 year life of
the equipment. However, substantial savings associated with reduced raw materials usage, reduced
plant down time, and reduced waste disposal costs would repay the capital and operating expenses
several times over.
Based on the estimated expenditures, savings, and economic conditions described above, the
financial analysis program (General Electric, 1987) was utilized to calculate the economic indices
described in Table 9. As shown, the economics associated with installing an ultrafiltration;system at
the R.B. White facility are very favorable. It is estimated that the payback period associated with this
technology is only 6.9 months. The net present value and implied rate of return indices are $152,143
and 178%, respectively. Therefore, investment in an ultrafiltration system at the R.B. White facility
represents a very attractive economic alternative.
Table 9: Economic Summary
Capital Invested
Payback Period
Net Present Value (NPV)
Interest Rate of Return (IRR)
$12,000
6.9 months ,
$152,143
178%
52
-------
Section 9
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
The overall evaluation of this pollution prevention project was based on ultrafiltration
performance, product quality, and economics. Results of the full-scale ultrafiltration study indicated
that the concentration of oil in the iron phosphating/degreasing bath was substantially reduced and
maintained at acceptable operating levels. Virtually all of the unused phosphating agents were
conserved although a portion of the unused surfactants was not. Permeate flux rates exhibited
excellent performance during the acidic (pH = 3.5), high temperature (140°F) operation and were high
enough to continuously process the constant input of oil from the production line. The entire 5000
gallon bath was processed in 180 ultrafiltration operating hours. Coating weight, rust creepage, and
paint adhesion tests conducted by DuBois Research Laboratory and R.B. White plant personnel on
samples of steel parts indicated that product quality achieved during the full-scale study was good for
R.B. White's application. Based on the estimated expenditures and savings, the payback period
associated with this pollution prevention technology was only 6.9 months.
By using ultrafiltration, the R.B. White will reduce its hazardous waste generation by at least
15,000 gallons per year, a 99.8% reduction. In addition, the company will no longer have periodic
problems exceeding allowed oil and grease levels in their rinse water discharge to the sanitary district.
This project has successfully demonstrated the ability of membrane filtration to reduce
industrial waste generation and recover valuable raw materials in a metal fabricating operation. This
application introduces another innovative waste reduction technique to the metal fabricated products
industry that could benefit the many plants nationwide that use aqueous cleaner systems like the iron
phosphating/degreasing process at the R.B. White facility. The ultrafiltration system implemented in
this project saves money, maintains good product quality, and reduces waste generation.
Recommendations
Many industries are facing tougher laws and tighter restrictions on solvent use and hazardous
waste generation. Along with the environmental concerns come the rising costs of liability,
compliance, and waste disposal. Developing cleaner production techniques will call upon innovative
ideas and creative engineering to build the environmentally responsible industry of the future.
The metal fabricated products industry needs to examine its present methods of operation and
set goals for cleaner production. Using iron phosphate and alternative coating chemicals can
modernize a metal coating operation as existing and projected EPA regulations require more stringent
53
-------
control and more expensive waste treatment methods for chromated seals, zinc phosphate, and
chromate conversion coatings. Making the switch from solvent to aqueous cleaners holds the potential
to reduce solvent waste, improve worker safety, and avoid stricter environmental regulations. Learning
to extend the life of aqueous process solutions opens the door to recovery technologies like
ultrafiltration that could save money in raw materials and waste disposal. In-plant evaluation and
testing can provide useful information for customizing a recovery scheme to fit an industry's specific
needs. Developing and implementing new ideas can bring about innovative solutions, but the industry
should be aware of limitations and special concerns. The issues of membrane fouling, sludge build-up
and disposal, regular tank maintenance, proper chemical balance, and raw material substitution need
to be dealt with on a case-by-case basis.
When industry cooperates and works with the EPA and equipment dealers, environmentally
responsible solutions to generating hazardous and industrial process wastes can be found. With the
advent of water-based cleaners, waste minimization and pollution prevention have become realistic and
attainable goals for the metal fabricated products industry.
54
-------
REFERENCES
Bailey, P.A. The Treatment of Waste Emulsified Oils by Ultrafiltration: Proceedings of the Filtration
Society. Filtration and Separation. January/February 1977, pp. 53-55.
Bhattacharyya, D., A.B. Jumawan, and R.B. Grieves. Ultrafiltration Characteristics of Oil-Detergent-
Water Systems: Membrane Fouling Mechanisms. Separation Science and Technology. Vol. 14, No.
6, pp. 529-549, 1979.
Cheng, S.C., B.O. Desai, C.S. Smith, H.D. Troy, T.E. Ctvrtnicek, W.H. Hedely. Alternative Treatment
of Organic Solvents and Sludges from Metal Finishing Operations. Cincinnati, Ohio: U.S. EPA.
September 1983. EPA/600/2-83/094. PB84-102151.
Cheryan, Munir. Ultrafiltration Handbook. Lancaster, Pennsylvania: Technomic Publishing Co., Inc.
1986.
Clesceri, Lenore S., Arnold E. Greenberg, R. Rhodes Trussed. Standard Methods for the Examination
of Water and Wastewater. Baltimore, Maryland: Port City Press. Seventeenth Edition, 1989.
Cutler, W.G. and R.C. Davis. Detergencv: Theory and Test Methods. Surfactant Science Series: Vol.
5. New York: Marcel Dekker, Inc. 1972.
Donnelly, R.G., R.L. Goldsmith, K.J. McNulty, D.C. Grant, M. Tan. Treatment of Electroplating Wastes
by Reverse Osmosis. Cincinnati, Ohio: U.S. EPA. September 1976. EPA 600/2-76-261.
General Electric. Financial Analysis of Waste Management Alternatives. Fairfield, Connecticut. 1987.
Gortsas, Louis A. Phosphate Coating Weights. DuBois Research Laboratory, Sharonville, Ohio 45241.
1993.
Grinn, M.E., E.L. Brown, and J.C. Harris. Journal of the American Oil Chemistry Society. Vol. 38,
1961.
Hindin, D.A., W.M. Burch, and D.L. Fort. Pollution Prevention Options in Metal Fabricated Products
Industries: A Bibliographic Report. Washington, D.C.: U.S. EPA. January 1992.EPA/560/8-92/001 A.
Laine, Jean-Michel, James P. Hagstrom, Mark M. Clark, and Joel Mallevialle. Effects of Ultrafiltation
on Membrane Composition. Journal of the American Water Works Association. November 1989. pp.
61-67.
Lee, Soobok, Yves Aurelle, and Henry Roques. Concentration Polarization, Membrane Fouling and
Cleaning in Ultrafiltration of Soluble Oil. Journal of Membrane Science. Vol. 19, 1984, pp. 23-38.
Mehta, Suresh and Thomas Besore. Alternative to Organic Solvents in Metal-Cleaning Operations.
Savoy, Illinois: Hazardous Waste Research and Information Center. July 1989.
Miller, G.D. and T.C. Lindsey. Quality Assurance Project Plan for Hazardous Waste Reduction for a
Commercial Iron Phosphating/Degreasing Bath. Cincinnati, Ohio: U.S. Environmental Protection
Agency. February 1992.
Morrison, Robert and Robert Boyd. Organic Chemistry. Third Edition. Boston, Massachusetts:
Allynand and Bacon, Inc. 1973. pp. 1059-1062.
55
-------
Paul, Swaraj. Surface Coatings: Science and Technology. Chichester: John Wiley and Sons, 1986.
Pinto, Steven D. Ultrafiltration for Dewatering of Waste Emulsified Oils. Lubrication Challenges in
Metalworking and Processing: Proceedings, First International Conference. IIT Research Institute,
Chicago, Illinois. June 7-9, 1978.
Phillips, Dick. Practical Application of the Principles Governing the Iron Phosphate Process. Plating
and Surface Finishing, Vol. 77, No. 3, March 1990, pp. 31-35.
Springborn Laboratories, Inc. Emulsified Industrial Oils Recycling. U.S. Department of Energy. April
1982. DOE/BC/10183-1.
Quitmeyer, JoAnn. Aqueous Cleaners Challenge Chlorinated Solvents. Pollution Engineering. Vol. 23,
No. 13, December 1991, pp. 88-91.
Ultrafiltration Saves Oil, Cleans Waste. Iron and Steel International, p. 391, December 1979.
Viego, Armando. Ultrafiltration System Saves $200,000 per Year in Disposal Costs. Plant Services.
July 1980, pp. 26-27.
Wahl, James R. and Lawrence S. Gould. How to Extend the Life of Washer Baths. Industrial Finishing.
September 1979, p. 47.
Wittke, William J. Phosphate Coatings. Metal Finishing Guidebook Directory. 1987. ;
Wray, Thomas K. Soaps and Detergents. Hazmat World. Vol. 5, No. 8, 1992. pp. 82-83.
U.S. EPA. Guides to Pollution Prevention: The Fabricated Metal Products Industry. Washington, D.C.:
U.S. EPA. July 1990. EPA/625/7-90/006.
U.S. EPA. Methods for Chemical Analysis of Water and Wastes. 1983.
U.S. EPA. Waste Minimization in Metal Parts Cleaning. Washington, D.C.: U.S. EPA. August 1989.
EPA/530-SW-89-049.
56
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GLOSSARY
(Cheryan, 1986)
Concentrate : the portion of the feed solution that is rejected by the membrane
Flux : the volumetric flow rate of permeate per cross-sectiona! area per time
Fouling : detected as the decrease in permeate flux over time and is a result of the changes in
the membrane structure or interactions between the components of the feed stream
and the membrane surface
MWCO : molecular weight cut-off, the minimum weight of a typical molecule that would be
rejected by the membrane
Permeate : the portion of the feed solution that passes through the membrane
Rejection : describes the degree to which ultrafiltration prevents components in the feed solution
from passing through the membrane
57
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APPENDIX Numerical Data from Figures in Text
Figure 5a: Comparison of Wastewater Flux Rates During Bench-Scale Testing
MEMBRANE MODEL MASS FLUX
(grams permeate/minute)
M2 Teflon 1.100
(30,000 MWCO)
SN04 Cellulose Acetate 1 .080
(20,000 MWCO)
PM30 Polysulfone .704
(2,000 MWCO)
M3 Teflon .209
(500 MWCO)
PM 10 Polysulfone .198
(10,000)
Rgure 5b: Comparison of Normalized Flux Rates During Bench-Scale Testing
MEMBRANE MODEL NORMALIZED FLUX
"t«cov«v'»'lnltltl
M2 Teflon .423 .869
(30,000 MWCO)
SN04 Cellulose Acetate .284 .921
(20,000 MWCO)
PM30 Polysulfone .017 .001
(2,000 MWCO)
M3 Teflon .275 .886
(500 MWCO)
PM 10 Polysulfone .009 .020
(10,000)
58
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Figure 9: TOC in Process Tank and Permate vs Time Using Clean Process Solution
ELAPSED TIME TOC (mg/l):
(hours) Permeate Process Tank
0.00
0.33
0.68
1.02
1.35
1.90
170
180
160
140
130
170
490
520
550
620
720
950
Figure 10: Phosphate in Process Tank and Permeate vs Time Using Clean Process Solution
ELAPSED TIME PHOSPHATE (mg/J):
(hours) Permeate Process Tank
0.00
0.33
0.68
1.02
1.35
1.90
13376
13693
13456
13218
13851
14010
13693
13930
13851
13930
Figure 11 a: TOC in Process Tank and Permeate vs Time Using Waste Process Solution
Permeate Process Tank
ELAPSED
TIME (hrs)
0.00
0.18
0.52
0.77
1.02
1.28
1.53
2.53
3.53
4.53
5.32
7.53
8.53
TOC
(mg/l)
52
53
56
56
57
56
57
60
69
79
85
81
91
ELAPSED
TIME (hrs)
0.63
2.28
3.28
4.28
5.28
6.28
7.28
8.28
9.28
TOC
(mg/l)
790
810
870
980
1200
1400
1800
2300
3100
59
-------
Rgure 11b: Temperature Effect on Permate TOC vs Time Using Waste Process Solution
ELAPSED
TIME (hrs)
0.00
0.18
0.52
0.77
1.02
1.28
1.53
2.53
3.53
4.53
5.32
7.53
8.53
TOC
(mg/1)
52
53
56
56
57
56
57
60
69
79
85
81
91
TEMP
24.0
24.0
25.5
27.0
29.5
31.5
34.5
40.0
46.0
50.0
53.0
50.5
51.0
Rgure 12: Phosphate in Process Tank and Permeate vs Time Using Waste Process Solution
Permeate Process Tank
ELAPSED
TIME (hrs)
0.77
2.53
3.53
4.53
5.32
7.53
8.53
PHOSPHATE
(mg/l)
4828
4749
4947
4947
5026
5184
5184
ELAPSED
TIME (hrs)
0.63
2.28
3.28
4.28
5.28
7.28
8.28
0.0
66.5
132
180
422
232
340
340
155
123
200
198
PHOSPHATE
(mg/l)
4986
4986
5144
5144
5224
5382
5382
Rgure 14a: Oil and Surfactant TOC in Bath vs Time
TOC (mg/l):
OPERATING
TIME (hrs) Total Surfactant Oil
267
109
140
142
60
-------
Figure 14b: Oil and Surfactant TOC in Rinse vs Time
TOC (mg/1):
OPERATING
TIME(hrs) Total Surfactant Oil
0.0 21 8 13
66.5 844
132 11 7 4
180 11 6 5
Figure 14c: Oil and Surfactant TOC in Process Tank vs Time
TOC (mg/l):
OPERATING
TIME (hrs) Total Surfactant Oil
0.5
18.5
42.5
66.5
85.0
108.0
132.0
158.0
180.0
710
4700
6300
7100
5900
8000
12000
1600
19000
261
2301
3351
3752
3325
4482
7078
9387
11088
449
2399
2949
3348
2575
3518
4922
6613
7912
Figure 14d: Oil and Surfactant TOC in Permeate vs Time
TOC (mg/l):
OPERATING
TIME (hrs) Total Surfactant Oil
0.5
18.5
42.5
66.5
108.0
132.0
158
180
67
42
39
42
75
150
170
160
25
21
21
22
42
88-
100
93
42
21
18
20
33
62
70
67
61
-------
Rgure 15: Phosphate Levels in Bath, Inflow, and Permeate vs Time
PHOSPHATE Img/l):
OPERATING
TIME (hrs) Bath Inflow Permeate
0.0 3617 3958
185 3245 3166
42*5 3007 2849
66'.5 3562 3799 3561
85.0 3483 3324
108.0 4353 4749
1320 6142 6094 6332
158.0 6094 6253
180.0 6008 6174 6055
Rgure 16: Permeate Flux Rate vs Time
ELAPSED
TIME (hrs)
18.5
42.5
66.5
108.0
132.0
158.0
180.0
252.0
276.0
300.0
324.0
348.0
516.0
FLUX
(gal/hr)
39.1
32.1
31.0
31.0
29.0
26.1
27.3
27.3
27.3
27.3
27.3
26.5
25.0
62
-------
Data Correlation for Phosphate Analysis by Titration and 1C
SAMPLE TYPE
Volume PO4 (mg/1)
Titrant (mL) by 1C
RATIO
3
6
7
17
21
22
30
34
33
42
43
46
53
54
55
67
70
71
AVERAGE 782.1
(Volume of Titrant, ml) x {Ratio = 782.1, mg/l/ml) = P04 mg/1
Bath
Permeate
Inflow
Bath
Permeate
Inflow
Bath
Permeate
Inflow
Inflow
Permeate
Bath
Bath
Inflow
Permeate
Bath
Permeate
Inflow
4.4
5.2
5.0
4.5
4.6
4.8
7.9
8.0
7.7
7.8
7.6
7.6
7.8
7.8
7.6
9.7
9.4
9.3
3937
4091
4028
3455
3642
3736
6333
6161
5129
5588
6248
6357
5760
5428
6145
8011
7790
6909
894.8
786.7
805.6
767.8
791.7
778.3
801.6
770.1
666.1
716.4
822.1
836.4
738.5
695.9
808.6
825.9
828.7
742.9
63
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