MOBILE ON-SITE RECYCLING OF METALWORKING FLUIDS
by
Arun R. Gavaskar, Robert F. Olfenbuttel, and Jody A. Jones
Battelle
Columbus, Ohio 43201
Contract No. 68-CO-0003
Work Assignment No. 0-06
Technical Project Monitor
Johnny Springer, Jr.
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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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 taws, 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.
Passage of the Pollution Prevention Act of 1990 marked a strong change in the U.S.
policies concerning the generation of hazardous and nonhazardous wastes. This bill implements the
national objective of pollution prevention by establishing a source reduction program at the EPA and
by assisting States in providing information and technical assistance regarding source reduction. In
support of the emphasis on pollution prevention, the "Waste Reduction innovative Technology
Evaluation (WRITE) Program" has been designed to identify, evaluate, and/or demonstrate new
ideas and technologies that lead to waste reduction. The WRITE Program emphasizes source
reduction and on-site recycling. These methods reduce or eliminate transportation, handling,
treatment, and disposal of hazardous materials in the environment. The technology evaluation
project discussed in this report emphasizes the study and development of methods to reduce
waste.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
in
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ABSTRACT
This evaluation addresses the product quality, waste reduction, and economic issues
involved in recycling metalworking fluids through a mobile recycling unit. The specific recycling
unit evaluated is based on the technology of filtration, pasteurization, and centrifugation.
Metalworking fluid recycling was found to have good potential as a means of waste reduction and
cost saving. Product quality was evaluated by conducting performance tests and by chemical
characterization of the spent, recycled, and virgin fluids. The performance of the recycled fluid
appeared promising.
This report was submitted in partial fulfillment of Contract Number 68-CO-0003, Work
Assignment 0-06, under the sponsorship of the U.S. Environmental Protection Agency. This report
covers a period from December 1, 1990 to June 15,1992, and work was completed as of June
15,1992.
IV
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TABLE OF CONTENTS
Page
FOREWORD iii
ABSTRACT iv
LIST OF TABLES v.. vii
LIST OF FIGURES vii
ACKNOWLEDGEMENTS viii
SECTION 1
PROJECT DESCRIPTION 1
1.1 PROJECT OBJECTIVES 1
1.2 DESCRIPTION OF THE TECHNOLOGY . 2
1.3 DESCRIPTION OF THE SITE 2
1.4 SUMMARY OF APPROACH . . 4
1.4.1 Product Quality Evaluation 4
1.4.2 Waste Reduction Evaluation 4
1.4.3 Economic Evaluation 5
SECTION 2
PRODUCT QUALITY EVALUATION 6
2.1 ON-SITE TESTING 6
2.2 ANALYTICAL RESULTS . 8
2.2.1 Participates . . 8
2.2.2 Metallic Contaminants 10
2.2.3 Viscosity 11
2.2.4 pH . . t 14
2.2.5 Extreme Pressure Additives 14
2.2.6 Corrosion Properties . , . . 14
2.2.7 Tramp Oil Content and Emulsion Stability 18
2.2.8 Foaming Tendency . 18
2.2.9 Lubricity and Wear Preventive Characteristics 20
2.2.10 Bioresistance 20
2.3 PRODUCT QUALITY ASSESSMENT 25
SECTION 3
WASTE REDUCTION POTENTIAL 27
3.1 WASTE VOLUME REDUCTION , 27
3.2 POLLUTION REDUCTION 27
3.3 WASTE REDUCTION ASSESSMENT : 31
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SECTION 4
ECONOMIC EVALUATION 32
4.1 OPERATING COSTS COMPARISON ;• 32
4.2 ECONOMIC ASSESSMENT 34
SECTION 5
QUALITY ASSURANCE . 35
5.1 ON-SITE TESTING 35
5.2 LABORATORY ANALYSIS FOR COOLANT PERFORMANCE 35
5.3 LIMITATIONS AND QUALIFICATIONS 38
SECTION 6
CONCLUSIONS AND DISCUSSION 39
SECTION?
REFERENCES 41
LIST OF APPENDICES
APPENDIX A - WATER CONTENT ANALYSIS 42
VI
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LIST OF TABLES
TABLE 2-1. ON-SITE TESTING DESCRIPTION . 7
TABLE 2-2. ANALYSIS OF NON-DISSOLVED AND DISSOLVED SOLIDS 9
TABLE 2-3. TOTAL METALS CONTENT OF METALWORKING FLUIDS 12
TABLE 2-4. ANALYSIS.OF VISCOSITY '. 13
TABLE 2-5. CHEMICAL CHARACTERISTICS OF THE METALWORKING FLUIDS 15
TABLE 2-6. CORROSION TEST RESULTS OF THE METALWORKING FLUIDS 17
TABLE 2-7. TRAMP OIL SEPARATION AND EMULSION STABILITY . . 19
TABLE 2-8. FOAMING TENDENCY OF METALWORKING FLUIDS 21
TABLE 2-9. LUBRICITY AND WEAR CHARACTERISTICS
OF THE METALWORKING FLUIDS 22
TABLE 2-10. RESULTS OF MICROBIOLOGICAL TESTING 24
TABLE 3-1. WASTE VOLUME GENERATION 28
TABLE 4-1. OPERATING COSTS FOR DISPOSAL AND RECYCLING 33
TABLE 5-1. LABORATORY QA DATA FOR PERFORMANCE TESTS 36
TABLE 5-2. PRECISION DATA FOR METALS ANALYSIS 37
LIST OF FIGURES
Figure 1-1. Metalworking Fluids Recycling Process 3
VII
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ACKNOWLEDGEMENTS
The New Jersey Department of Environmental Protection is acknowledged for its
important contribution to this evaluation. Waily Dankmyer and Esfandiar Kiany from Safety-KIeen,
Inc. are acknowledged for their support during the evaluation. The authors wish to thank
Dr. Elliot S. Nachtman of Tower Oil and Technology, Inc. for his review of the draft report.
VIII
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SECTION 1
PROJECT DESCRIPTION
The objective of the Waste Reduction Innovative Technology Evaluation Program
conducted by the U.S. Environmental Protection Agency (U.S. EPA) is to evaluate, in a typical
workplace environment, examples of prototype or innovative commercial technologies that have
» •
potential for reducing waste. In general, for each technology to be evaluated, three issues should
be addressed.
First, it must be determined whether the technology is effective. Since waste
reduction technologies usually involve recycling or reusing materials, or using substitute materials
or techniques, it is of primary importance to verify that the quality of the recycled product is
satisfactory for the intended purpose. Second, it must be demonstrated that using the technology
has a measurable positive effect on reducing waste. Third, the economics of the new technology
must be quantified and compared with the economics of the existing technology. It should be
clear, however, that improved economics is not the only criterion for the use of the new
technology. There may be justifications other than saving money that would encourage adoption
of new operating approaches. Nonetheless, information about the economic implications of any
such potential change is important.
This evaluation addresses the issues involved in using a particular commercially
available technology offered by a particular manufacturer for recycling metalworking fluids
(machine coolants). The recycling unit used in this study is a mobile unit offered by Safety-Kleen
Corp. Other recycling units arid technologies (with varying capabilities) applicable to the same
wastestream (metalworking fluids) are also commercially available.
1.1 PROJECT OBJECTIVES
The goal of this study was to evaluate a technology that could be used to recycle
spent metalworking fluids (machine coolants) for reuse in machining operations. This study had the
following critical objectives:
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• Evaluate the effectiveness of the recycling unit in generating a metalworking fluid
of acceptable quality
• Evaluate the waste reduction potential of this technology
• Evaluate the cost of recycling versus the cost of current practice (disposal).
1.2 DESCRIPTION OF THE TECHNOLOGY
The mobile metalworking fluid recycling unit is operated by Safety-Kleen Corp., Elgin,
Illinois. Safety-Kleen provides fluid recovery services to a variety of businesses, primarily those
that generate relatively small quantities of fluid hazardous waste. The mobile service performs the
recycling on the generator's property, thus eliminating the need for transportation of potentially
hazardous wastes. Each mobile truck-mounted unit, operating off its own power, is capable of
processing fluid at a maximum rate of 300 gallons per hour. Heat for the pasteurization step is
drawn from the hot antifreeze of the truck.
The recycling process, as presented in Figure 1 -1, consists of filtering, pasteurizing,
and centrifuging the spent fluid. The fluid is first sent through a 100-micron filter to remove any
large particulates. It is then pumped through a pre-heater and then a heat exchanger to kill bacteria
and fungi, as well as to reduce fluid viscosity before centrifuging. Centrifuging, where tramp oil
and other debris is separated from the usable fluid, is next. After cooling to the original
temperature, the fluid is tested for quality. Additives are then incorporated into the fluid to restore
performance. In the final step, the fluid flows through a 1 -micron filter to remove any remaining
particulates. The fluid is then returned to the client's clean holding tank for reuse. Of the vairious
classes of metalworking fluids, Safety-Kleen currently offers the process only for emulsions
("soluble oils"), synthetics, and semi-synthetics.
1.3 DESCRIPTION OF THE SITE
The above technology was evaluated at three different small- to medium-sized
machine shops (sites) in the Philadelphia, Pennsylvania, vicinity. The three sites were chosen from
among Safety-KIeen's customer base. Two of the sites used emulsion-type metalworking fluids.
The third site used a synthetic fluid.
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1.4 SUMMARY OF APPROACH
A Quality Assurance Project Plan (QAPjP), prepared at the beginning of this study
(Battelle 1991), describes the detailed approach and scientific rationale used to design the recycling
unit evaluation.
1.4.1 Product Quality Evaluation
Two types of metalworking fluids were evaluated - emulsion and synthetic. The main
purpose of these fluids in machining operations is to provide lubricity and cooling.
The approach used for evaluating product quality was as follows. At each of the three
sites evaluated, one sample each of the spent, recycled, and virgin fluids at their use
concentrations were collected and subjected to the same series of tests. A comparison between
the analyses of spent and recycled fluids indicates the improvement achieved by recycling. A
comparison between the analyses of recycled and virgin fluids indicates how closely the recycled
product approximates the virgin product.
The focus of this testing is to provide as broad a data base to potential were as
possible. Hence, within the available resources, the objective is to take fewer samples and run
several performance and characterization tests on each sample, rather than to take statistically
significant number of samples and run fewer analytical tests. Thus, the evaluation provides users
with an idea of the efficiency of the recycling process, and a comparison, based on a wide range of
characteristics, between the performance of recycled and virgin metaiworking fluids.
1.4.2 Waste Reduction Evaluation
The waste reduction potential of this technology was measured in terms of the
projected reduction in the amount of spent fluid generated by typical machine shops and requiring
disposal. The sidestreams from the recycling process itself are the tramp oil and filtration residue.
These were also accounted for.
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1.4.3 Economic Evaluation
The economic analysis includes a comparison of operating costs for the new
technology (recycling) with the costs for the current practice (disposal).
• 5
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SECTION 2
PRODUCT QUALITY EVALUATION
Two types of metalworking fluids were evaluated - emulsion and synthetic.
Emulsions, often called "soluble oils," consist of oil suspended in water by use of a surfactant. The
oil contributes the lubricating properties, while the water provides the cooling required during
»
machining operations such as cutting, grinding, etc. Synthetic fluids are chemicals that form true
solutions in water. Both emulsions and synthetics contain additives to improve specific properties
such as stability, corrosivity, foaming, and bioresistivity.
At each of the three sites evaluated, samples of the spent, recycled, and virgin fluids
at their use concentrations were collected and subjected to the same series of tests. The objective
was to compare the spent and recycled fluids to determine the improvement achieved by recycling.
The recycled and virgin fluids were compared to determine how closely the recycled product
approximates the virgin product.
2.1 ON-SITE TESTING
Table 2-1 describes the on-site testing conducted during this evaluation. Recycling
was performed at two machine shops that use emulsion-type fluids and at one machine shop that
uses synthetic fluids. The process for both types of fluid is the same except that different
additives are used. Of the two sites where emulsions were processed, the first site was one that
Safety-Kleen had serviced several times in the past. The second site was one that was being
serviced for the second time only. The reason for this type of site selection was to see if the fluid
quality changes over several recycles.
Samples of the spent, recycled, and virgin fluids were collected at each site. The
virgin fluid samples were prepared by diluting virgin concentrate obtained from each site with tap
water from the same site. At most sites that Safety-Kleen services, the concentrates are diluted to
a use concentration of approximately 3 to 5% in water to obtain the desired degree of lubricity and
cooling.
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TABLE 2-1. ON-SITE TESTING DESCRIPTION
Site Description
First
Machine shop where fluid had
been recycled several times in
the past.
Second
Machine shop where fluid was
being recycled for the second
time.
Third
Machine shop where fluid had
been recycled several times in
the past.
Fluid
Type
Emulsion
Emulsion
Synthetic
Site
Number
E1
E2
S1
Volume of
Fluid Recycled
(gallons)
175
55
100
Samples
Collected8
E1-S (spent)
E1 -R (recycled)
E1-V (virgin)
E2-S (spent)
E2-R (recycled)
E2-V (virgin)
S1-S (spent)
S1-R (recycled)
S1-V (virgin)
a One sample each of spent, recycled and virgin metalworking. fluid at the use concentration were
collected at each site.
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One sample at each site was obtained from the spent fluid storage tanks by means of
a bailer to ensure representative samples from all depths. Samples were shipped to the analytical
laboratory in coolers packed with ice to prevent microbial growth and degradation of the fluid. All
samples were refrigerated until the time of analysis.
2.2 ANALYTICAL RESULTS
The samples collected during the on-site testing were analyzed in the laboratory for
various characteristics. The tests and results are described below. The two spent emulsion
samples (E1-S and E2-S) had a floating tramp oil phase> This floating phase was separated in a
separatory funnel and the lower bulk liquid was analyzed because most of the following tests
cannot handle two phases. The performance of these spent fluid samples in the following tests is
therefore somewhat better than would be normally expected if the tramp oil phase were included.
No noticeable quantity of tramp oil was observed in the spent synthetic fluid samples.
2.2.1 Particulates
During machining, metallic and organic particles from various sources accumulate in
the metalworking fluid. High concentrations of these particulates adversely affect tool life, surface
finish, and chemical breakdown. Particles also provide substrates for microbial growth. Degree of
;
removal of particulates during recycling is shown in Table 2-2. Paniculate concentrations were
measured by ASTM D 2276-89. This method measures the change in weight of an 8-micron filter
membrane' (relative to a control filter) after filtration of the fluid. The filter is washed with
petroleum ether to remove any oily matter from the residue before weighing. The results are listed
as "total" particulates in Table 2-2. At all three sites, the results showed considerably lower
concentrations of particulates in the recycled fluids as compared with the spent fluids. The virgin
fluids had the lowest concentrations of particulates.
Although the ether wash of the filter removes most oily matter, there may still be
some organic residue (e.g., biomass) on the filter. Combusting the residue gets rid of this organic
residue. When the filtration residues were combusted, the resulting combustion residues are
shown in the column marked "inorganic" particulates in Table 2-2. In all samples, the "inorganic"
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TABLE 2-2. ANALYSIS OF NON-DISSOLVED AND DISSOLVED SOLIDS
Sample No.
E1-Sb
E1-R
E1-V
E2-Sb
E2-R
E2-V
S1-S
S1-R
S1-V
Non-Dissolved Particulate Concentration3
(mg/lOOmL)
Total
79.10
22.55
3.55
12.55
5.60
4.50
33.80
17.00
5.18
Inorganic
27.25
1.45
2.50
0.50C
3.00
2.00
14.50
1.95
0.78
Dissolved Solids
(Conductivity)
(umhos/cm2)
2,400
1,810
700
1,820
1,750
810
1,450
1,460
1,930
8 By ASTM D 2276. Participates smaller than 8 microns.
b Analyzed after skimming off and discarding the floating tramp oil.
0 Possible inhomogeneity giving a low value.
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values were lower than the corresponding "total" values. The "non-combustible" particulates
represent the inorganic fraction of the "total" particulates and provide some indication of
suspended metal particulates.
Conductivity measurements are a measure of the dissolved solids (metallic impurities
and salts) content. Conductivity is tracked by metalworking fluid users as an indicator of the
variation in fluid quality over time (and use). A conductivity reading was taken on all samples
collected. For the emulsion-type fluids (Sites E1 and E2), the virgin samples showed much lower
conductivity as compared with the spent samples, indicating that the dissolved solids content of
the fluids increased over use. Recycling did not reduce the conductivity of the spent fluid
noticeably. This is because the smallest filter used in the recycling process is 1-micron. Dissolved
solids would pass through this filter.
This accumulation of dissolved solids over time and use can limit the number of times
a given batch of fluid could be recycled. When the dissolved solids content of the fluid becomes
approximately 2,600 ppm, the emulsion may start to break and water may separate out. This
study did not correlate the conductivity measurements (in umhos/cm2) to actual dissolved solids
concentrations (in ppm). Only the trends were observed. Addition of fresh inhibitors during normal
use or recycling could also raise dissolved solids levels.
In the synthetic fluid (Site S1), a conductivity trend was not so obvious. The virgin
sample showed a higher conductivity reading than the spent or recycled samples; this may mean
that the virgin fluid itself contains several dissolved additives that raise the conductivity reading.
Also, the virgin sample had been prepared with tap water, which would itself contribute in some
measure to the conductivity. One explanation for the results at Site S1 could be that the spent
coolant had originally been prepared with deionized water, whereas the virgin sample was prepared
with tap water.
2.2.2 Metallic Contaminants
Metallic contaminants enter the metalworking fluid during normal machining
operations. In fact, one of the functions of spraying the fluid is to carry away metal chips from the
work piece as they are formed. The metals accumulate in the spent fluid in suspended or dissolved
form. In suspended form they provide a substrate for microbial growth. In dissolved form they
contribute to increased levels of dissolved solids and hence emulsion instability.
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No really large metal chips or turnings (coils) were visually observed in the spent
samples collected, indicating that large pieces had settled out in,the bottom of the spent fluid
storage tank, and were not drawn into the sample. A total (suspended and dissolved) metals
measurements of the fluids was conducted by ICP analysis of the samples (Table 2-3). Aluminum
and zinc levels were somewhat reduced after recycling. Copper levels increased in the emulsion
samples after recycling; this is attributed to the fact that copper is an ingredient in one of the
additives introduced during recycling of emulsions. Lead levels remained fairly constant in the
spent and recycled samples; this is attributed to the fact that lead is often present in a solubilized
form and hence difficult to remove. Note that the virgin samples too had lead levels comparable to
those in the spent and recycled samples. Iron levels at-all three sites showed a slight increase after
recycling. A possible reason for this could be that the spent fluid solubilizes some iron encountered
in the recycling system (e.g., from the residue on the filters).
In general, metal levels in all the collected samples {spent, recycled, and virgin) were
too low to be of concern from a product quality point of view. Many of the larger metal particles
could have settled out in the spent fluid storage tank itself. Larger metal particles drawn into the
recycling unit would be expected to be removed by the filters as shown in Section 2.2.1.
Calcium and magnesium levels were also measured because these metals contribute to
water hardness and emulsion instability. Calcium and magnesium were not removed from the fluid
during recycling, indicating that these metals are mostly in the soluble form. High levels in virgin
samples indicate that calcium and magnesium enter the fluids through the make-up water (tap
water) used. Emulsion stability and bioresistance tests described in Sections 2.2.7 and 2.2.10,
respectively, indicated that the levels of metallic contaminants in the recycled fluids do not
significantly affect their performance.
2.2.3 Viscosity •
Viscosity (resistance to flow) is an important parameter for a lubricant. It determines
a fluid's flow and penetration characteristics, as well as the oil film thickness. Kinematic viscosity
of all samples collected was measured by ASTM D 445-71. Kinematic viscosity, measured in
centiStokes (cS), is a measure of the resistive flow of a fluid in relation to its density. The recycled
and virgin samples from all three sites had matching viscosities (Table 2-4) indicating that the
recycling process had restored this parameter. Spent sample E2-S was the only spent sample that
11
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TABLE 2-3. TOTAL METALS CONTENT.-QF METALWORK1NG FLUIDS
Sample
No.
E1-Sb
• E1-R
E1-V
E2-Sb
E2-R
E2-V
S1-S
S1-R
S1-V
Iron"
(ppm)
10.4
11.1
1.0
2.4
5.2
0.3
3.1
4.5
0.3
Copper"
(ppm)
1.4
2.3
0.6
0.1
2.7
0.0
9.2
7.2
0.0
Aluminum8
(ppm)
1.1 .
0.7
0.2
0.3
0.4
0.2
4.9
3.3
0.2
Lead"
(ppm)
0.21
0.19
0.17
0.21
0.19
0.17
0.41
0.37
0.33
Zinc3
(ppm)
1.7
0.6
0.1
0.1
0.3
0.0
1.6
1.0
0.2
Calcium8
(ppm)
37
20 .
20
53
40
140
70
14
50
Magnesium8
(ppm)
42
35
15
14
21
21
40
40
23
• Analyzed by EPA 6010 UCP).
b Analyzed after skimming off and discarding the floating tramp oil.
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TABLE 2-4. ANALYSIS OF VISCOSITY
Sample No.
E1-Sb
E1-R
E1-V
E2-Sb
E2-R
E2-V
,S1-S
' ;
S1-R
S1-V
Viscosity3
(cS)
0.77
0.85
0.81
0.69
0.81
0.77
0.77
0.75
0.75
• By ASTM D 445.
b Analyzed after skimming off and discarding the floating tramp oil.
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appeared to be noticeably out of range to start with; the viscosity of this fluid was restored during
recycling. The viscosity measurements also indicate that the recycling process succeeded in
returning the fluids to the required use concentration (concentrate:water ratio). The concentration
of the recycled fluid is adjusted during the recycling process by taking refractometer readings.
Small amounts of virgin concentrate is added to the recycled batch if necessary to restore the use
concentration.
2.2.4 pH.
The pH of a metalworking fluid is often monitored by users as an easily measured
indicator of fluid quality. A change in pH may indicate chemical degradation or degradation due to
microbial growth. The recycling process seeks to restore pH to a range of 8.5 to 9.5 using
appropriate additives. This alkaline pH improves emulsion stability and corrosion resistance
characteristics of the fluid. At the three sites tested, the pH of the recycled fluids (measured by
EPA Method 150.1) was returned to this range (Table 2-5) by the alkaline component of the fresh
additive. Note that at Sites E1 and E2, the spent fluid pH had degenerated to below 7. The
lowered pH indicates microbial growth (acids generated by microbial metabolism) and depletion of
alkalinity-building chemicals in the fluids.
2.2.5 Extreme Pressure Additives
Because many metalworking fluids contain what are known as extreme pressure (EP)
additives, the collected samples were analyzed for these compounds. EP additives are organic
molecules with sulfur and chlorine. They serve as solid lubricants with low binding energy. None
of the samples collected (Table 2-5) showed any elevated levels of either sulfur (ASTM D 129) or
chlorine (ASTM D 808), indicating that these additives were not present in the fluids used at the
three sites. Some sulfur was present, but was attributed mainly to the sulfonate emulsifier used.
2.2.6 Corrosion Properties
Corrosion characteristics are important parameters for water-based metalworking
fluids because of their effect on workpiece quality and tool life. Corrosivity of the fluids to ferrous
14
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TABLE 2-5. CHEMICAL CHARACTERISTICS OF THE METALWORKiNG FLUIDS
Sample No.
E1-S°
E1-R
E1-V
E2-S°
E2-R
E2-V
S1-S-
S1-R
S1-V
.
PH
6.71
9.58
8.60
6.57
9.32
1 • ^^^™^™^^"^^^^^^^^^^^^^3
Sulfur
Concentration8
(%)
< .003
0.021
0.011
< .003
0.014
8-44 0.011
8-52 o.009
8.52 o.OOS
8-39 I < .003
=
By ASTM D 129. Sulfur in extreme-pressure additives.
By ASTM D 808. Chlorine in extreme-pressure additives.
Analyzed after skimming off and discarding the floating tramp oil
Chlorine
Concentration13
< 0.007
0.069
< .007
15
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metals was measured by the iron chip corrosion test (ASTM D 4627-86). A copper corrosion test
(ASTM D 130-88) was also performed.
In the iron chip test, cast iron chips are placed in a petri dish containing a filter paper
soaked with the metalworking fluid. The filter paper is examined the next day for rust stains. For
each fluid sample, the test was repeated for the use concentration (as-received), as well as 90%,
70%, 50%, 30%, and 10% of the use concentration (if necessary). A break-point can be
determined as the weakest concentration that left no rust stains on the filter paper. It provides a
relative measure of the corrosion inhibition strength of the fluid. In addition, a number of blank
runs (same procedure without any iron chips) were conducted to make sure that the fluids
themselves were not leaving any stains on the filter paper.
The results (Table 2-6) of the iron chip test on the virgin samples (E1-V, E2-V, and
S1-V) showed that E1-V and S1-V generated no rust at the use concentration (approximately 5%
solution of the concentrate in tap water). S1-V showed stronger corrosion inhibition since there
were no rust stains even at 30% of the use concentration. E2-V showed rust stains at the use
concentration itself, indicating that this virgin fluid had lower strength corrosion inhibition
properties compared with the other two.
All three spent samples showed rusting at the use concentration, which was expected
given their low pH values and high contaminant levels. Recycled sample E1 -R showed considerable
improvement over the spent sample (E1-S), indicating that its corrosion inhibition properties had
been restored. E2-R and S1-R showed some rust at the use concentration, indicating that stronger
iron corrosion resistance properties need to be imparted to these fluids.
In the copper corrosion test {ASTM D 130-88), a polished copper strip is immersed in
the fluid and heated at 100°C for 3 hours. Then, the test strip is removed, washed, and compared
with the ASTM Copper Strip Corrosion Standards. The test strip is then given a single rating of
1A, 1B, 2A, 2B, 2C, 2D, 2E, 3A, 38, 4A, 4B, or 4C. The 1A rating is the best, indicating almost
no tarnish on the strip, and the 4C rating is the worst, indicating heavy tarnish. All the collected
samples (Table 2-6) fared virtually the same with a high rating of 1A or 1B, indicating that none of
the samples had much effect on copper.
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TABLE 2-6. CORROSION TEST RESULTS OF THE METALWORKING FLUIDS
Sample No.
E1-S°
E1-R
E1-V
E2-S°
E2-R
E2-V
S1-S
S1-R
S1-V
Iron Chip .••
Corrosion Breakpoint*
Rust stains at use concentration
No rust stains at 50% of use concentration
No rust stains at use concentration
Rust stains at use concentration
Rust stains at use concentration
Rust stains at use concentration
Rust stains at use concentration
Rust stains at use concentration
No rust stains at 30% of use concentration
Copper
Corrosionb
1A
1A
1A
1B
1B
1A
1A
1A
18
a Analyzed by ASTM D 4627. Breakpoint is the lowest concentration tested that left no rust
stains on filter paper.
b Analyzed by ASTM D 130. The rating scale is from 1 to 4, where 1 indicates slight tarnish and
4 indicates corrosion. 1A indicates a light orange color (almost the same as the freshly polished
strip) and 1B indicates a dark orange color.
c Analyzed after skimming off and discarding the floating tramp oil.
17
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2.2.7 Tramp Oil Content and Emulsion Stability
Tramp oil is the non-emulsified floating oil that builds up in metalworking fluid sumps
from sources such as leaking equipment seals (hydraulic oils, gear oils) or from the workpiece itself.
These oils can contaminate the workpiece or generate smoke from the heat of machining. Tramp
oils are also the biggest contributors to fluid rancidity and odor. Rancid fluid promotes corrosion
and may cause skin irritation. Tramp oil is removed during the recycling process by the centrifuge.
Tramp oil in the samples was measured by allowing a known volume of fluid to sit for
4 hours at room temperature in a graduated cylinder. The top layer that separated out was
measured (Table 2-7). Spent samples E1-S and E2-S contained approximately 6% and 2% (by
volume) respectively of tramp oil. No phase separation was noticed in any of the recycled samples,
indicating the tramp oil had been removed. Virgin sample E1-V also showed some phase
separation, but this was attributed to some unemulsified concentrate in the fluid. No noticeable
quantity of tramp oil was noticed in any of the synthetic samples.
Often, excessive temperatures during operation, contamination, or formulation
deficiencies can affect the stability of emulsions. Emulsion stability was measured by ASTM D
3707-89. In this test, a fluid sample contained in a 100-mL graduated cylinder is placed in an oven
set at 85°C. The sample is examined after 48 and 96 hours for phase separation. This test was
conducted on the fluid samples after any tramp oil that separated out at room temperature was
discarded. The results (Table 2-7) showed small amounts of phase separation in spent samples E1-
S and E2-S. The recycled samples remained as a single phase even after 96 hours, indicating that
emulsion stability had been restored during recycling.
2.2.8 Foaming Tendency
Foam can be generated by agitation of the metalworking fluid caused by the
machining operation or by fluid transfer. Foaming can reduce effective film strength, reduce heat
transfer, and interfere with the settling of metal fines. Tendency of the fluids to foam was tested
by ASTM D 892-89. In this method, a fluid sample, maintained at a temperature of 75°F, is blown
with-air at a constant rate for 5 minutes, then allowed to settle for a maximum of 10 minutes. The.
test is repeated on fresh fluid at 200°F, and then, after collapsing of the foam, at 75°F.
18
-------
TABLE 2-7. TRAMP OIL SEPARATION AND EMULSION STABILITY
Sample
No.
E1-S
E1-R
E1-V
E2-S
E2-R
E2-V
S1-S
S1-R
S1-V
Tramp Oil Separation
(Room Temperature)
Total
Initial
Volume (mL)
898.
850
882
• 846
850
850
850
850
850
Upper Layer
Volume {mL}
After 4 Hours
51
0
22°
13
0
0
0
0
0
Emulsion Stability"
(Temperature = 85 °C)
Total
Initial
Volume (mL)b
100
100
100
100
100
100
NA
NA
NA
Upper Layer Volume
(mL)
After
48 Hours
1
0
0
1.5
0
0.7
NA
NA
NA
After
96 Hours
1
0
0
1d
0
od
NA
NA
NA
a By ASTM D 3707. An "NA" indicates not analyzed.
b After discarding the upper layer formed at room temperature.
c Unemulsified constituents.
d Upper layer that formed after 48 hours reduced or disappeared after 96 hours.
19
-------
From the results (Table 2-8), it can be seen that foam volume in the recycled samples
(E1-R, E2-R, and S1-R) was significantly higher than in the spent or virgin samples. This can be
attributed to the introduction of fresh emulsifier (surfactant) during recycling. A correction can be
made for this effect by adding an anti-foam agent during recycling. However, Safety-Kleen does
not typically add an anti-foam agent, unless the customer specifically reports a foaming problem.
2.2.9 Lubricity and Wear Preventive Characteristics
Lubricity and wear preventive characteristics of a metalworking fluid affect workpiece
quality and tool life. When a high degree of lubrication rat needed, straight oils are used instead of
emulsions, with a concomitant loss in cooling characteristics. Emulsions have moderate lubricity
and cooling characteristics for most general applications. Synthetic fluids contain special additives
to impart lubricity. , ' -
Lubricity and wear characteristics were measured by ASTM D 4172-88. In this test,
three 0.5-inch diameter steel balls are clamped together and covered with the metalworking fluid
(maintained at 167 F). A fourth ball (called top ball) is pressed with a force of 40 kgf into the
cavity formed by the three clamped balls for three point contact. The top ball is rotated at 1200
rpm for 60 minutes. The average size of the scar diameters worn on the three lower clamped balls
is measured and can be used as a parameter for comparing various fluids. The results are reported
in Table 2-9.
i ,
For Site E1, the recycled sample had a much lower average scar diameter than the
spent sample, but not as low as the virgin sample. This indicated that the recycled and virgin
samples had better lubricity and wear characteristics than the spent fluid, and the virgin sample
was slightly better than the recycled. The Site E2 samples showed no noticeable differences in
performance, although the recycled and virgin samples performed about the same. The presence
of some emulsified tramp oil could have improved the lubricity results of the spent sample E2-S.
2.2.10 Bio resistance
A major factor in metalworking fluid spoilage (rancidity) is microbial growth. Microbial
growth is caused by the wide variety of nutrients and substrates present in the metalworking fluid
and by aeration during machining and transfer. Examples of metalworking fluid components that
act as nutrients are mineral oils, fatty acids, emulsifiers, etc. Waste metal chips and grinding swarf
20
-------
TABLE 2-8. FOAMING TENDENCY OF METALWORKING FLUIDS
Sample
No.
E1-Sb
E1-R
E1-V
E2-Sb
E2-R
E2-V
S1-S
S1-R •
S1-V
Temperature
°F
75 (I)
200 (II)
75 (III)
75 (I)
200 (II)
75 (III)
75 (I)
200 (II)
75 (III)
75 (I)
200 (II)
75 (111)
75 (I)
200 (II)
75 (III)
75 (I)
200 (II)
75 (III)
75 (I)
200 (II)
75 (III)
75 (I)
200-(ll)
75 (III)
75 (I)
200 (II)
75 (III)
Foam Volume (mL)
at End of 5-Minutesa
10
10
< 10
170
250
450
20
80
100
10
10
< 10
520
710
430
< 10
20
< 10
420
10
390
490
120
510
180
310
190
Foam Volume (mL)
at End of Settling"
0 after 26 seconds
0 after 6 seconds
0 after 1 8 seconds
0 after 298 seconds
0 after 161 seconds
60 after 10 minutes
0 after 56 seconds
0 after 45 seconds
0 after 535 seconds
0 after 29 seconds
0 after 5 seconds
0 after 1 6 seconds
370 after 1 0 minutes .
0 after 328 seconds
280 after 1 0 minutes
0 after 7 seconds
0 after 5 seconds
0 after 6 seconds
60 after 1 0 seconds
0 after 4 seconds
210 after 10 minutes
1 90 after 1 0 minutes
0 after 87 seconds
330 after 10 minutes
1 0 after 1 0 minutes
0 after 1 35 seconds
1 0 after 1 0 minutes
a By ASTM D 892.
b Analyzed after.skimming off and discarding the floating tramp oil.
21
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TABLE 2-9. LUBRICITY AND WEAR CHARACTERISTICS OF
THE METALWORKING FLUIDS
Sample No.
E1-Sb
E1-R
E1-V
E2-Sb
E2-R
E2-V
Average Wear Scar Diameter*
(mm)
1.26
0.83
0.64
0.97
1.18
1.17
• By ASTM D 4172.
b Analyzed after skimming off and discarding the floating tramp oil.
22
-------
provide a substrate for microbial growth. The problem is exacerbated by poor housekeeping that
leads to the presence of tramp oil, food, cigarettes, and other debris in the fluid. Rancid fluid
lowers pH, destabilizes emulsions, promotes rusting, and could cause skin irritation. Controlling
microbial growth is an important factor in extending the life of the fluid.
One way of controlling microbial growth is by the addition of measured amounts of
biocide. It is important, however, that the biocide used does not inactivate the other fluid
components and inhibitors and is not itself inactivated by the other fluid components. In the
recycling process, existing microbes are killed during the pasteurization step, the dead biomass is
removed during the centrifugation step, and a measured quantity of biocide is added to control
future microbial growth. ASTM E 686-85 evaluates the, effectiveness of biocides at use
concentrations. |n this test, the fluid at the use concentration and fortified with the biocide is
inoculated with a mixed population of bacteria and fungi. For this study, the inoculum was
prepared by culturing a sample of spent (spoilt) fluid. Iron filings are also added to the test fluid to
simulate the substrate. The fluid is aerated for 5 days, left unaerated for 2 days, and evaluated for
bacterial and fungal counts. The process is repeated over a six-week period. This simulates plant
conditions whereby the fluid is in use (aeration) during a five-day work week, and allowed to sit
(non-aeration) over the weekend. Aerobic microorganisms grow during the aeration phase and
start decaying during the non-aeration phase, especially if a floating layer of tramp oil cuts off
ambient air; this decaying biomass causes what is commonly called "Monday morning odor."
Recycled and virgin fluids from sites E2 (emulsion-type) and S1 (synthetic) were
subjected to this test/' No additional biocide was added to the virgin fluids, which were prepared
simply by diluting the virgin concentrate with tap water. Results are presented in Table 2-10.
Week 0 represents the microbial concentrations immediately after inoculation. Week 1 results
show that both bacterial and fungal populations were completely wiped out by the biocide in the
recycled samples. In the virgin samples, most of the microbial populations declined but were not
wiped out in Week 1. Fungal counts in Sample E2-V increased several orders of magnitude in
Week 1. This indicates that the virgin fluids needed to be fortified with supplemental biocides (a
normal practice in industry). No microbial growth was observed in the recycled samples even after
six weeks. None of the samples, recycled or virgin, showed any noticeable changes such as
change in appearance, emulsion break-up, or pH decline.
The ASTM method suggests using 107 bacteria CFU/mL as a reliable cutoff point
when evaluating biocide failure. By this criterion, both virgin samples demonstrated biocide failure
in the first week. Other sources have suggested 10* bacteria CFU/mL and 103 fungi CFU/mL as
23
-------
TABLE 2-10. RESULTS OF MICROBIOLOGICAL TESTING
Week
No.
0"
1
2
3
4
5
6
Sample
No.
E2-V
E2-R
S1-V
• S1-R
E2-V
E2-R
S1-V
S1-R
E2-V
E2-R
S1-V
S1-R
E2-V
E2-R
S1-V
S1-R
E2-V
E2-R
S1-V
S1-R
E2-V
E2-R
S1-V
S1.-R
E2-V
E2-R
S1-V
S1-R
pH
8.00
8.90
8.13
8.30
8.12
8.83
8.10
8.35
8.20
8.83
8.10
8.40
8.41
8.78
8.08
8.41
8.45
8.78
8.02
8.41
8.40
8.70
7.92
8.36
8.38
8.75
8.00
8.40
Bacteria3
(CFU/mL)
1.0 x 109
3. Ox 108
1.3 x 108
1.6 x 10s
5.9 x 107
< 10
>1.0 x 107est
< 10
2.8 x 107
< 10
6.1 x 108
< 10
1.8 x 107
< 10
5.8x 108
< 10
1.5 x 107
< 10
1.2 x 109
< 10
1.6x107
< 10
8.7 x 108
< 10
1.3 x 107
< 10
7.5 x108
< 10
Fungi"
(CFU/mL)
4.1 x 10*
< 10
1.0x 10a
6.5 x 10s
1.8x 108
< 10
2.6x 105
< 10
2.3 x 105
< 10
1.4x 108est
< 10
2.0 x 105
< 10
2.9 x 106
< 10
6.3 x 108
< 10
1.1 x 107
< 10
8.0 x 106
< 10
3.6x106
< 10
7.1 x 106
< 10
5.9 x 10s
< 10
• Analyzed by ASTM E 686.
b Immediately after inoculation.
24
-------
pass/fail criteria. Yet others have suggested 99.9% (three-log reduction) after 60 days as the
cutoff. By all these criteria, the recycled samples performed well. It is common practice for users
to supplement virgin fluids.with sump-side biocide additions.
In addition to the above test, ASTM recommended practices for safe handling of
metalworking fluids include recommendations and tests for acute toxicity, skin sensitization, and
eye irritation. These tests address the complete metalworking fluid constitution, including the
biocide. These tests were beyond the scope in this evaluation, but would be good adjuncts to the
above test.
2.3 PRODUCT QUALITY ASSESSMENT .;.
The product quality of the recycled fluids can be considered as a function of (a) the
level of contaminants and (b) the concentrations and efficacies of the various components of the
fluid (the base oil or chemicals, corrosion inhibitors, biocides, and other additives). The
performance tests conducted in this evaluation (namely, lubricity and wear, iron corrosion, copper
corrosion, bioresistance, foaming tendency, and emulsion stability) are a measure of the integral
effect of both the contaminant levels as well as the fluid components. The levels of particular
contaminants that can be tolerated in the recycled fluids are difficult to judge in isolation, and are
often affected by the properties of other fluid components. Hence, a combination of chemical
characterization and performance testing is used in this evaluation.
The recycling process brings about considerable improvement in fluid quality, making
recycling a technically feasible option. The above testing showed good results for recycled fluid
characteristics such as viscosity, lubricity, wear resistance, pH, paniculate removal, and
bioresistance. The recycled fluid showed some tendency toward foaming and iron corrosion as
compared to the virgin fluid; these could possibly be adjusted by appropriate additives. One
limitation of this recycling process is that dissolved components of the spent fluid are not removed
before adding fresh additive. There is, therefore, some potential for old and new additives
clashing.
Some solubilized contaminants (such as calcium, magnesium, etc.) remain in the
recycled fluid because the smallest filter (1 micron) in the recycling unit does not remove them.
However, the levels of these contaminants in the fluids at the three sites evaluated did not appear
to affect their performance. Dissolved solid levels in the fluids need to be monitored periodically by
25
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the user to determine when a given batch of fluid (after several recycles) is to be discarded.
Dissolved solids level (as conductivity) is a fairly simple measurement on the shop floor.
Some accumulation of contaminants is noticeable between fluids at Site E1 (which
had been recycled several times) and Site E2 (which had been recycled only twice). For example,
paniculate and dissolved solids levels (Table 2-2) were higher in the spent and recycled fluids at
Site E1 than at Site E2. Metallic contaminants (e.g., iron, aluminum, zinc, and magnesium)
appeared to be higher at Site E1 than at Site E2 (Table 2-5). On the other hand, calcium levels
appeared to be higher at Site E2 than at Site E1. Thus, other factors such as tap water, type of
machining operations, use patterns, etc. may also affect contaminant accumulation.
Further testing could include observation of. the recycled fluids during use. Parameters
such as workpiece quality and tool life could be evaluated over an extended period of time to
evaluate the long-term performance of recycled fluids, especially because the recycled fluid showed
a slight tendency towards ferrous metal corrosion. Tests for acute toxicity, skin sensitization, and
eye irritation could be done to ensure that the biocide and other additives introduced during
recycling do not present an occupational hazard.
Currently, there are no published standards for recycled fluids. Each user has to
evaluate his/her own requirement based on the same factors used in selecting a virgin fluid brand. •
At the three test sites evaluated in this study, recycled fluids appeared to satisfy the functional
requirements of the users.
26
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SECTION 3 .
WASTE REDUCTION POTENTIAL
Waste reduction potential was measured in terms of (a) volume reduction and
(b) pollutant reduction. Volume reduction addresses the gross wastestream (such as metalworking
fluid and tramp oil). Pollutant reduction involves individual pollutants {such as surfactants and
heavy metals) in the gross wastestream. Volume reduction affects environmental resources (e.g.,
landfill space) expended during disposal. Pollutant reduction addresses the specific hazards of
individual pollutants.
3.1 WASTE VOLUME REDUCTION
The waste volume reduction potential of this technology involves the amount of spent
metalworking fluid prevented from being disposed of into the environment (e.g., landfilling).
Table 3-1 lists the various wastestreams and waste volumes measured at the three sites evaluated
in this study. On an average, Safety-Kleen visits each customer once every 10 weeks and recycles
an average of 250 gallons of spent fluid per visit. Thus, there is potential for an annual reduction
of 1,250 gallons from these typical customers.
Approximately 4 gallons of tramp oil per visit, on average, are generated during
recycling. This tramp oil can either be disposed of by the customer or is hauled away for a nominal
charge by Safety-Kleen for use as supplemental fuel. Sludge residue generated on the filters is
carried away by Safety-Kleen at no charge and later reclaimed for its metal value. Metal chips on
the filters are placed in the customer's metal recycling bin (personal communication with Wally
Dankmyer, Safety-Kleen, Inc.).
3.2 POLLUTANT REDUCTION
Metalworking fluids may contain several components that could be detrimental to the
environment. Emulsion-type fluids are made up of an oil of mineral, vegetable, or synthetic origin
27
-------
TABLE 3-1. WASTE VOLUME GENERATION
Waste Type
Current Practice:
(Disposal)
Spent Metalworking Fluid
Recvclinn:
Spent Metalworking Fluid
Tramp Oil
•
Residue on Filters
Site
E1
E2
S1
Average15
E1, E2, S1
Average13
E1
E2
S1
Average1*
Average3
Amount Generated
Per Visit"
(gallons)
175
55
100
250
0
0
10
2
4
4
Variable
B On an average, Safety-Kleen visits each customer once every 10 weeks.
b Average per customer based on all Safety-Kleen customers.
28
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dispersed in water by means of a surfactant. Synthetic fluids are solutions that use synthesized
hydrocarbons (e.g. polyalphaolefins) or long-chain alcohols instead of mineral oils. In addition to
these basic components, all fluids contain additives that impart specific properties. Typical
additives include surfactants (e.g. sulfonates), anti-foam agents (e.g., siloxane), corrosion inhibitors
(e.g. amines), odor suppressants (e.g. pine oil), and extreme pressure additives (e.g. sulfur,
chlorine, phosphorus compounds).
In rare cases, metalworking fluids may be discharged to natural waters under a
National Pollutant Discharge Elimination System (NPDES) permit. Discharges to natural waters
could also result from leaks or spills. Typically, metalworking fluids are treated in an on-site
industrial wastewater treatment system or a Publicly Owned Treatment Works (POTW) prior to
discharge. Waste disposal is a growing concern because of increasing costs and environmental
concerns.
Of the two types of metalworking fluids, the emulsion type fluids are generally easier
to treat. The emulsion type fluids are treated by adding acid to reduce the pH to the range of 2 to
5. Inorganic salts such as calcium chloride, alum, or ferric chloride are then added to help
coagulation. The pH is then raised into the range of 8 to 9 by addition of caustic, lime or soda ash.
Sometimes cationic and anionic polymers are used to help the emulsifying and coagulation process.
Emulsion breaking and coagulation results in an oily sludge, which, depending on economics, may
be disposed of or recycled.
The synthetic fluids use synthesized hydrocarbons that form true solutions with water.
Therefore, it is not possible to remove the organic materials by emulsion breaking. As a result, the
synthetic fluids are more difficult to treat. The dissolved organics contribute significant quantities
of oxygen demand which is normally removed by a biological process. The unexpected arrival of a
high concentration of a waste with high oxygen demand can upset the operation of the biological
digestion portion of a treatment plant.
Environmental concerns arise due to fundamental properties of metalworking fluids,
whether they are released to a natural water body or to a treatment system. The major
characteristics of concern are:
• Biochemical Oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Fats, Oils, and Grease
• Total Suspended Solids
. • Toxicity and potential to induce cancer
29
-------
BOD measures the dissolved oxygen consumed by biological activity to degrade the
organic and inorganic contaminants. COD measures the oxygen consumed when the contaminants
are oxidized in a potassium dichromate/sulfuric acid solution. The COD test involves a powerful
oxidizing agent and therefore determines the oxygen demand for both biodegradable and non-
biodegradable compounds. COD is not directly representative of oxygen demand in natural
systems but can be measured more quickly and repeatably than BOD.
When waste containing degradable compounds enters a body of water or a biological
treatment system, natural purification by biological activity begins to occur. Microbes use organic
contaminants as a carbon and energy source. Dissolved oxygen in the water is consumed to
sustain respiration. While exact interpretation of the significance of BOD and COD depends on the
characteristics of the receiving water or treatment system, they generally indicate the oxygen
consumed by the waste as it decomposes. Most water systems can tolerate some additional
oxygen demand. However, an abrupt introduction of a new source of biodegradable chemicals may
deplete dissolved oxygen faster than it can be replenished by dissolution from the air. Reduced
dissolved oxygen concentration can cause fish kills in natural waters or failure of the biotreatment
system in a water treatment plant.
Fats, Oils, and Grease in the waste stream can cause problems. Free oil and grease in
natural waters can coat and foul skin, feathers, or gills of animals. Similar fouling and flow
blockage can occur in equipment at water treatment plants. Most cities do not allow any floatable
grease in waste water entering their treatment systems. The other oils, fats, or fatty acids are not
as harmful as oil and grease but can still foul natural ecosystems. The oil and grease will increase
sludge volume in a water treatment plant. Water treatment plants typically limit the inlet
concentration of vegetable oils, fats, and fatty acids to 150 mg/l.
Total Suspended Solids measures the total filterable paniculate matter in the fluid.
High levels of suspended solids can increase the turbidity of natural waters. Suspended solids
increase the amount of sludge that results from a water treatment system.
Surfactant additives emulsify oil in rnetalworking fluids. Different surfactants vary
widely in terms of aquatic toxicity and ease of biodegradation. Surfactants accumulate within and
on the surfaces of aquatic organisms (such as the gills of fish) and interfere with the function of
these organs (Smjth 1989). Biocide additives are used in rnetalworking fluids also. The main
categories of these biocides include: alkane derivatives, formaldehyde condensates,
isothiazolinones, morpholine compounds, oxazolidine compounds, phenols, pyridine derivatives, and
quaternary ammonium compounds. Release of biocides into an aqueous or soil waste stream can
30
-------
cause detrimental environmental effects. For example, Dowicide 1 (0-phenylphenol) can form
mutagens (Ames positive) when exposed to nitrites and nitrates in an aqueous environment
irradiated by sunlight (Suzuki et al., 1990). Low levels of Dowicide 1 have also been detected in
citrus {Ito et al., 1979). Disruption of plant leaf cells upon contact with Busan 77 caused by the
disorganization of cellular membranes has been reported (Towne et al., 1978). The inherent
toxicity or mutagenic properties of many biocides to the organisms that they would encounter, if
released into the environment, preclude the disposal of many of these compounds into soil or water
wastestreams.
As discussed above, metalworking fluids are typically processed in a wastewater
treatment system. Under normal operations processing1 the fluid increases the volume of sludge
from the treatment plant. The possible presence of high oxygen demand and free mineral oil and
grease will increase the required complexity of the treatment system and may result in occasional
operating upsets. In rare instances of direct release, the oxygen demand and free mineral oil and
grease may damage aquatic life in the receiving water. Thus, there is a measurable pollution
prevention accruing from recycling metalworking fluids.
X
3.3 WASTE REDUCTION ASSESSMENT
Although most water-based metalworking fluids are about 95% water at use
concentration, there is concern about the detrimental effect of some of the fluid components listed
above on the environment. Many states such as California, New Jersey, and Connecticut consider
spent coolants as hazardous waste. In most other states, spent fluids are disposed in accordance
with state'regulations for oily wastes unless the TCLP test shows high levels of metallic
contaminants, in which case the fluid is disposed of as hazardous waste. Recycling enables the
recovery and reuse of most of .the metalworking fluid components, thus, reducing waste.
According to a 1991 study by the Independent Lubricant Manufacturers Association
(ILMA 1991), the volume of metalworking fluids (concentrate) manufactured in the U.S.A., has
increased steadily from 67 million gallons in 1985 to 92 million gallons in 1990. By extending the
life of metalworking fluids through on-site recovery, considerable amounts of fluid can be prevented
from going to waste. The actual total volume of fluids going to waste, in some cases, may be as
much as 20 times, higher, since many types of fluids are diluted into 3 to 5% solutions in water.
31
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SECTION 4
ECONOMIC EVALUATION
From the point of view of a small generator of spent metalworking fluid waste, the
economic evaluation of this mobile recycling process consists only of a comparison between the
operating costs for disposal versus those for recycling. There are no capital costs because the
generator does not have to purchase and install any capital equipment, other than perhaps a
holding tank to store the recycled fluid. Clean 55-gallon drums often suffice for this purpose.
4.1 OPERATING COSTS COMPARISON
The evaluation involved comparing the operating cost of disposal to the cost of the
recycling (summarized in Table 4-1), from the point of view of a typical small generator who
generates 250 gallons of spent fluid every 10 weeks (1,250 gallons/year). If the generator were to
have the spent fluid hauled away by a waste disposal company (in the New Jersey/Pennsylvania
area), the cost would be about $1.05/gallon if a TCLP test showed the fluid to be non-hazardous.
This cost would rise to $6.00/gallon if the TCLP test showed the fluid to have hazardous levels of
metals. In addition to this base disposal cost, there would be an annual analytical charge of $900
for the TCLP test and $385 for other miscellaneous analysis (such as fuel value). The typical small
generator would therefore pay $2,600/year if the TCLP test was negative, or $8,785/year if the
fluid was hazardous.
The charge for the recycling service is $1.25/gallon. The typical generator would
therefore pay $1,565/year for five recycling visits (250 gallons/visit) to process 1,250 gallons/year.
On average, 4 gallons of tramp oil is generated per visit (20 gallons/year). Because of its fuel
value, tramp oil is hauled away at a charge of $0.15/gallon ($3/year). The total annual cost of
recycling for the typical small generator, therefore, is approximately $1,570/year.
32
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TABLE 4-1. OPERATING COSTS FOR DISPOSAL AND RECYCLING
Cost Element
Disposal:
Spent Fluid Disposal
if non-hazardous
if hazardous
Hazardous Analysis
- TCLP
other
Total
Recyclina: -' -•
Fluid Recycling Charge
Tramp Oil Disposal
Filtration Residue
- Total
Amount Generated
Per Year
(gallons)
1,250
1,250
V
1
1,250
20
Variable
Unit
Cost
($)
1.05
6.00
900
385
1.25
0.15
0
Total
Cost
($)
1,315
7,500
900
385
2,600a
1,565
3
0
1,568
a If non-hazardous. The total cost of disposal would be $8,785 if TCLP testing showed it to be
hazardous.
33
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By recycling 1,250 gallons/year, the typical generator potentially reclaims and reuses
approximately 1,200 gallons of valuable product; the slight difference being accounted for by
systemic losses due to tramp oil removal, residual fluid in the recycling process lines, etc. Virgin
fluid concentrate costs about $9/gallon (generally $7-11/gallon). This concentrate is usually diluted
to a 5% use concentration in tap water. Thus, the generator realizes a recycled product worth
$540/year; in other words, $540/year are saved in virgin fluid purchase costs.
4.2 ECONOMIC ASSESSMENT
The annual saving for the typical small generator is $1,572 if the spent fluid is non-
hazardous. This saving reflects the difference between total disposal ($2,600) and recycling
($1,568) costs, plus recycled product value ($540). If the spent fluid is hazardous, the total
disposal cost rises from $2,600 to $8,785 and the annual saving goes up to $7,757. Thus, it is
economically beneficial for a small generator to recycle through mobile services rather than dispose,
if it is determined that the recycled fluid quality is acceptable for the specific application.
34
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SECTION 5
QUALITY ASSURANCE
A Quality Assurance Project Plan (QAPjP) was prepared and approved by the EPA
before testing began (Battelle 1991). This QAPjP contains a detailed design for conducting this
study. The experimental .design, field testing procedures, and laboratory analytical procedures are
»'
covered. The QA objectives outlined in this QAPjP are discussed below.
5.1 ON-SITE TESTING
On-site testing was conducted as planned in the QAPjP.
5.2 LABORATORY ANALYSIS FOR COOLANT PERFORMANCE
Allanalysis was performed as planned, except that a duplicate analysis (to determine
precision) for the emulsion stability test was not conducted. All samples were additionally analyzed
for calcium and magnesium because high levels of these metals are associated with water
hardness, and can lead to unstable emulsions.
Table 5-1 describes the QA data (based on precision) on the performance tests. All
performance data was within acceptable precision. Table 5-2 describes the pecision data for the
metals analysis. Precision for the metals analysis was within the accceptable range. No matrix
spikes or method blanks were 'reported for metals because analysis was done by the standard
additions method.
Water content analysis of the metalworking fluid samples was planned and results are
reported in Appendix A.1. This analysis was performed by the Karl-Fischer titration method (ASTM
D 1744). This method is predominantly used for determining water content (up to 0.1 %) in
petroleum products. Because water content of the fluid samples was high (> 90%), this method
was found to be unsuitable; and results could not be corroborated by observations made during on-
site testing. However, other parameters (e.g., viscosity) can be used to indicate that water content
of the samples was appropriate.
35
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TABLE 5-1. LABORATORY QA DATA FOR PERFORMANCE TESTS
Parameter
Participate
Concentration
Conductivity
pH
Iron Chip
Corrosion
Precision Requirement
for this Study
Relative percent deviation should
be no more than 30%
Relative percent deviation should
be no more than 25%
Relative percent deviation should
be no more than 5%
Duplicates must target the same or
consecutive dilution
Duplicate
Results
86.50; 79.95
1750; 1980
6.57; 6.62
Target same
dilution
Precision8
Acceptable
Yes
(7.9%)
Yes
(12%)
Yes
(0.8%)
Yes
Precision
regular-duplicate
(regular H- duplicate)/2
36
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,c
•> i
TABLE 5-2. PRECISION DATA FOR METALS ANALYSIS
Parameter
Aluminum
Copper
Iron
Lead
Zinc
Sample No.
SK-E1S
SK-E1 S
SK-E1S
SK-E1S
SK-E1 S
Regular Sample
(ppm)
' 1.14
1.39
10.43
0.21
1.65
Duplicate
(ppm)
0.98
1.45
10.78
0.21
1.65
Precision
(RPD)a
15.1%
4.2%
3.3%
0.0%
0.0%
8 Relative Percent Difference
regular-duplicate
(regular + duplicate)/2
37
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5.3 LIMITATIONS AND QUALIFICATIONS
QA objectives mentioned in the QAPjP (Battelle 1991) were met, and the results of the
on-site and laboratory testing can be considered as a valid basis for drawing conclusions about
product quality and waste reduction. One limitation of this evaluation is that the scope did not
include shop-floor testing of recycled fluids over an extended period of time to determine workpiece
quality and tool life. The shop-floor testing of the recycled (and virgin for comparison) fluids would
be an essential step for all users. Also not included in the scope were tests for occupational
hazards (skin irritation, etc.) from the recycled fluids. All these additional factors are also the same
considerations that a user would evaluate while choosing a virgin brand.
Data for economic analysis were mostly obtained from Safety-Kleen's charges for its
various services. Any assumptions made are specified so that the readers can adjust them to their
own case.
38
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SECTION 6
CONCLUSIONS AND DISCUSSION • .
This evaluation found that recycling of metalworking fluids is a good option for plants
with machining operations. The recycled fluid quality was determined to be satisfactory for the
applications at the three sites serviced. Waste generation was reduced and a valuable resource
(metalworking fluid) was recovered. Mobile (on-site) recycling makes economic sense for smalt
generators who may find purchasing and running their own recycling equipment too expensive.
There are many aspects to the process of extending the life of metalworking fluids;
recycling is one of them. Many fluid users, large and small, are beginning to institute a fluid
management system. This system begins with an examination of all plant operations with a view
to consolidating the number of different fluids used. By testing different brands, a plant may be
able to reduce the number of different fluids used without compromising workpiece quality.
Consolidation of fluids enables users to focus on fewer waste types. Plants often find that
consolidation makes recycling more viable.
Plants have also found that converting from a central fluid collection system, to a
decentralized system facilitates better segregation of waste fluids. This makes recycling easier.
Another practice that is being abandoned is that of collecting waste oil and waste metalworking
fluids through a common system.
It is recognized in industry that using deionized water instead of tap water contributes
to longer fluid life by avoiding contaminants that make their way into the fluid through tap water
(such as calcium, magnesium/chlorides, sulfates, and bacteria). Regular fluid monitoring with
parameters such as concentration, pH, conductivity, etc. also helps to improve fluid life. If
monitoring indicates a problem, it can be immediately addressed (e.g., by adding more virgin fluid
concentrate or biocide). Good housekeeping to prevent extraneous materials such as dirt, food,
cigarettes, cleaners, and solvents from getting into the fluid is a good practice.
On-site recycling installations are often implemented progressively to improve fluid life.
First a filter may be installed to separate out paniculate material. Various devices to separate out
tramp oil, such as coalescers or skimmers, may be the next feature. Pasteurization units
accompanied by sump-side biocide addition may also be installed. The advantage of on-site
39
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installation is that the system and the additives can be tailored to the user's specific needs. F'or
small generators who do not want to purchase and operate these pieces of equipment, the mobile
recycling service is a good option. Currently, users generating as little as 55 gallons of used
coolant per month to as much as 1000 gallons of used coolant per month have been using this
service. :
In 1990, 92 million gallons of metalworking fluid (concentrate) were manufactured in
the U.S.A. (ILMA, 1991). The total volume of fluid going to waste, in some cases, may be 20 or
more times higher, because many fluid concentrates are diluted 20 or more times in water before
use. Considerable amounts of this fluid can be prevented from going to waste by on-site recycling.
40
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SECTION 7
REFERENCES
Battelle. Quality Assurance Project Plan (QAPjP) for an Industrial Fluids Recycling Study.
Columbus, Ohio, 1991.
Burke, J. M. 1990. "Wastewater Treatment of Metalworking Fluids: Three Options" in Waste
Management and Wastewater Treatment of Metalworkino Fluids. Independent Lubricant
Manufacturers Association. Alexandria, Virginia.
Childers, J. C., S-J Huang, and M. Romba. 1990. "Metalworking Fluid Additives for Waste
Minimization" in Waste Management and Wastewater Treatment of Metal working Fluids.
Independent Lubricant Manufacturers Association. Alexandria, Virginia.
Ito, et al. 1979. J. Food Prot.. Vol. 42, pp. 292-293.
Nachtman, E. S. 1990. "Metalworking Lubrication Definitions" in Waste Management and
Wastewater Treatment of Metalworkina Fluids. Independent Lubricant Manufacturers Association.
Alexandria, Virginia.
Passman, F. J. 1990. "Selection of Preservatives for Use in Industrial and Metalworking
Lubricants" in Waste Management and Wastewater Treatment of Metalworkina Fluids. Independent
Lubricant Manufacturers Association. Alexandria, Virginia.
Smith, B. 1989. Pollutant Source Reduction: Part n - Chemical Handling. American Dvestuff
Reporter. Vol. 78(4), pp. 26-30.
Suzuki, J., S. Toshiyuki, A. Ito, and S. Suzuki. 1990. "Mutagen Formation and Nitration by
Exposure of Phenylphenols to Sunlight in Water Containing Nitrate or Nitrite Ion." In: Bull. Environ.
Contam. Toxicol. Vol. 45, pp. 516-522.
Towne, C. A., P. G. Bartels, and J. L. Hilton. 1978. "Interaction of Surfactant and Herbicide
Treatments on Single Cells of Leaves." In: Wjedjjd., Vol. 26, pp. 182-188.
ILMA. 1991. "Report on the Volume of Lubricants Manufactured in the United States by
Independent Lubricant Manufacturers in 1990". Presented to the Independent Lubricant
Manufacturers Association 1991 Annual Meeting, September 28-October 1, 1991.
41
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APPENDIX A
WATER CONTENT ANALYSIS
42
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APPENDIX A-1. WATER CONTENT ANALYSIS
Water Content
Sample Number
-^•^•HHHM
SK-E1S
"•^™^~^™«^
SK-E1R
—•^•^-••^
SK-E1V
•"•"•—••••••
SK-E2S
™^—n^™«
SK-E2R
^«^^
SK-E2V
^H^HH^H^H^M
SK-S1S
^•^•M^WI^B^K
SK-S1R
"•^•"^^^^^
SK-S1V
43
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