United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/114 August 1993
vxEPA Project Summary
Mobile Onsite Recycling of
Metalworking Fluids
Arun R. Gavaskar, Robert F. Olfenbuttel, and Jody A. Jones
Product quality, waste reduction, and
economic issues were evaluated for a
technology designed to recycle metal-
working fluids. Emulsion-type fluids
were tested at two sites and a syn-
thetic fluid was tested at a third site.
The specific recycling unit being evalu-
ated is based on the technology of fil-
tration, pasteurization, and centrifuga-
tion. This recycling unit is mounted on
a truck that goes from site to site, per-
forming the recycling at each
customer's location. The customer is
charged a fixed fee for the service. Met-
alworking fluid recycling was found to
have good potential as a way to reduce
waste and save money. The product
quality achieved by this unit was ac-
ceptable for the applications studied.
Product quality was evaluated by con-
ducting performance tests and by
chemical characterization of the spent,
recycled, and virgin fluids. Performance
tests included tests for corrosion re-
sistance, emulsion stability, foaming
resistance, lubricity, and biological re-
sistance.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
The objective of the Waste Reduction
Innovative Technology Evaluation (WRITE)
Program conducted by the U.S. Environ-
mental Protection Agency (EPA) is to
evaluate, in a typical workplace environ-
ment, examples of prototype or innovative
commercial technologies that have poten-
tial for reducing wastes. The goal of the
metalworking fluid recycling study was to
evaluate (a) the quality of the recycled
coolant, (b) the waste reduction potential
of the technology, and (c) the economic
feasibility of the technology.
The mobile metalworking fluid recycling
unit is operated by Safety-Kleen Corp.*
Elgin, IL. Safety-Kleen provides fluid re-
covery services to a variety of businesses,
primarily those that generate relatively
small quantities of fluid waste. The mobile
service performs the recycling on the
generator's property, thus eliminating the
need to transport potentially hazardous
wastes. Each mobile truck-mounted unit,
operating off its own power, is capable of
processing fluid at a maximum rate of 300
gal/hr.
The recycling process (Figure 1) con-
sists of filtering, pasteurizing, and centri-
fuging the spent fluid. The fluid is first
sent through a 100-u, filter to remove any
large particulates. It is then pumped
through a preheater and then a heat ex-
changer to kill bacteria and fungi, as well
as to reduce fluid viscosity. Centrifuging,
where tramp oil and other debris are sepa-
rated from the usable fluid, is next. Addi-
tives are then incorporated into the fluid to
restore performance. In the final step, the
fluid flows through a 1-p. filter to remove
any remaining particulates. The fluid is
* Mentionof tradenamesorcommercial products does
not constitute endorsement or recommendation for
use.
^ZZ> Printed on Recycled Paper
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Vacuum
Hose
150 Micron.
Main
Filter
Chamber
• Remdte Filter' '
Chamber'* Caddy
Customer
Recyctabte
fluid
Storage
Container
Recirculate
Clean
Fluid
Holding
Tank
i
f
Pump
Customer
Chan
Ftuftf
Storage
Container
Fluid Test
Pass
Fail
Customer
Waste
Container
Outside
Van
To
Centrifuge
Bypass
Centrifuge
Figure 1. Metalworking fluids recycling system flowchart.
then returned to the client's clean holding
tank for reuse.
The technology was evaluated at three
different small- to medium-sized machine
shops (sites) in the Philadelphia, PA, vi-
cinity. The three sites were chosen from
among Safety-Kleen's customer base. Two
of the sites (called E1 and E2) used emul-
sion-type metalworking fluids. The third
site (called S1) used a synthetic fluid. At
each site, one sample each of the spent,
recycled, and virgin fluids (at their use
concentrations) was collected and sub-
jected to the same series of tests. The
comparison between the spent and re-
cycled fluids indicates the improvement
achieved by recycling, and a comparison
between the recycled and virgin fluids in-
dicates how closely the recycled product
approximates the virgin product. A limited
number of samples was taken at each
site because the objective was to conduct
a broad spectrum of analytical tests on a
few samples, rather than a statistical com-
parison based on a large number of
samples.
Product Quality Evaluation
The main purpose of metalworking flu-
ids in machining operations is to provide
lubricity and cooling without causing cor-
rosion or other problems. Through use,
the fluids lose some measure of these
functions because of the accumulation of
contaminants and microbes. The recycling
process attempts to restore these func-
tions.
Degree of removal of nondissolved and
dissolved particulates during recycling is
shown in Table 1. High concentrations of
these particulates affect tool life, surface
finish, and chemical breakdown. Particles
also provide substrates for microbial
growth. At all three sites, the results
showed considerably lower concentrations
of nondissolved particulates in the recycled
fluids (E1-R, E2-R, and S1-R) as com-
pared with concentrations in the spent flu-
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Table 1. Analysis of Non-Dissolved and Dissolved Solids
; Non-Dissolved Solids Concentration
(mg/100 mL.)
Sample No.
Total
Inorganic
Dissolved Solids
(Conductivity)
(umhos/cm2)
E1-S"
E1-R
E1-V
E2-S»
E2-R
E2-V
S1-S
S1-R
S1-V
79.10
22.55
3.55
12.55
5.60
4.50
33.80
17.00
5.18
27.25
1.45
2.50
0.50 c
3.00
2.00
14.50
1.95
0.78
2,400
1,810
700
1,820
1,750
810
1,450
1,460
1,930
ByASTM D 2276. Particulates smaller than 8 microns.
Analyzed after skimming off and discarding the floating tramp oil. E1-S = spent emulsion, site 1;
E1-R = recycled emulsion, site 1; E1-V= virgin emulsion, site 1; etc.
Possible inhomogeneity giving a low value.
ids (E1-S, E2-S, S1-S). The accumulation
of very small participates over time and
use could limit the number of times a
given batch of fluid could be recycled.
Conductivity of the samples was measured
as an indicator of the dissolved solids
levels in the fluids. Dissolved solids levels
remained approximately the same after
recycling, which indicated the effect of con-
taminant precipitation and fresh additive
introduction.
Users of metalworking fluid often moni-
tor the pH as an easily measured indica-
tor of fluid quality. A change in pH may
indicate chemical degradation or degra-
dation due to microbial growth. The recy-
cling process seeks to restore pH to a
range of 8.5 to 9.5. This alkaline pH im-
proves emulsion stability and corrosion
resistance characteristics of the fluid. At
the three sites tested, the pH of the re-
cycled fluids was returned to this range.
Corrosion characteristics (Table 2) are
important parameters for water-based met-
alworking fluids because of their effect on
workpiece quality and tool life. The results
of the iron chip corrosion test (ASTM D
4627) on the virgin samples (E1-V, E2-V,
and S1-V) showed that E1-V and S1-V
generated no rust at the use concentra-
tion (approximately 5% solution of the con-
centrate in tap water). In this test, the
lower the concentration of the fluid in wa-
ter at which there is no rust, the better the
corrosion resistance. S1-V showed stron-
ger 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 corro-
sion inhibition properties compared with
the other two. Recycled sample E1-R
showed considerable improvement over
the spent sample (E1-S), indicating that
Table 2. Corrosion Test Results of the Metalworking Fluids
Sample No.
E1-SC
E1-R
E1-V
E2-SC
E2-R
E2-V
S1-S
S1-R
S1-V
Iron Chip
Corrosion Breakpoint '
Rust at use concentration
No rust at 50% of use concentration
No rust at use concentration
Rust at use concentration
Rust at use concentration
Rust at use concentration
Rust at use concentration
Rust at use concentration
No rust at 30% of use concentration
Copper
Corrosion "
1A
1A
1A
1B
1B
1A
1A
1A
1B
Analyzed by ASTM D 4627. Breakpoint is the lowest concentration tested that left no rust stains
on filter paper.
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.
Analyzed after skimming off and discarding the floating tramp oil.
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. All of the collected samples (Table
2) fared virtually the same in the copper
corrosion test (ASTM D 130) with a high
rating of 1A or 1B, indicating that none of
the samples have much effect on copper.
Tramp oil is the nonemulsified floating
oil that builds up in metalworking fluid
sumps from sources such as leaking equip-
ment 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. Table 3 shows
the results of the tramp oil analysis. Spent
samples E1-S and E2-S contained ap-
proximately 6% and 2% (by volume) re-
spectively of tramp oil. No phase separa-
tion was noticed in any of the recycled
samples, indicating the tramp oil had been
removed. Virgin sample E1-V showed
some phase separation, but this was at-
tributed to some unemulsified concentrate
in the fluid.
The results of emulsion stability testing
at elevated temperature (Table 3) showed
small amounts of phase separation in
spent samples E1-S and E2-S. The re-
cycled samples remained as a single
phase even after 96 hr, indicating that
emulsion stability had been restored dur-
ing recycling.
Foaming can reduce effective film
strength, reduce heat transfer, and inter-
fere with the settling of metal fines. Ten-
dency of the fluids to foam was tested by
ASTM D 892-89. Foam volume in the
recycled samples (E1-R, E2-R, and S1-R)
was significantly higher than that in the
spent or virgin samples. This can be at-
tributed to introducing fresh emulsifier
(surfactant) during recycling. A correction
can be made for this effect by adding an
antifoam agent during recycling. Safety-
Kleen, however, does not typically add an
antifoam agent unless the user specifi-
cally reports a foaming problem.
At all three sites, the recycled and vir-
gin fluid viscosities were very close (Table
4); this indicated that the recycling pro-
cess had restored this parameter. The
viscosity measurements also indicate that
the recycling process succeeded in re-
turning the fluids to the required use con-
centration (oihwater ratio). The concentra-
tion of the recycled fluid is adjusted during
the recycling process by taking refracto-
meter readings. More virgin fluid is added
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Table 3. Tramp Oil Separation and Emulsion Stability
Tramp Oil Separation
(Room Temperature)
Emulsion Stability'
(Temperature = 8S°C)
Sample
No.
E1-S
E1-R
E1-V
E2-S
E2-R
E2-V
S1-S
S1-R
S1-V
Total
Initial
Volume of
The Fluid
Samples (mL)
898
850
882
846
850
850
850
850
850
Volume
(mL) of
Upper Layer
Separating
Out
After 4 Hr
51
0
22 c
13
0
0
0
0
0
Upper Layer Volume
(mL)
Total
Initial
Volume (mL)"
100
100
100
100
100
100
NA
NA
NA
After
48 Hr
1
0
0
1.5
0
0.7
NA
NA
NA
After
96 Hr
1
0
0
1"
0
0"
NA
NA
NA
By ASTM D 3707. An NA indicates not analyzed.
After discarding the upper layer formed at room temperature.
Unemulsified concentrate.
Upper layer that formed after 48 hr reduced or disappeared after 96 hr.
to the recycled batch if needed to restore
the use concentration.
Lubricity and wear preventive charac-
teristics of a metalworking fluid affect
workplace quality and tool life. Lubricity
and wear characteristics were measured
by the standard "four-ball test" (ASTM D
445) (Table 4). For Site E1, the recycled
sample caused a much lower average scar
diameter than did the spent sample, but
not as low as the virgin sample. This indi-
cated that the recycled and virgin samples
had better lubricity and wear characteris-
tics than the spent fluid and that the virgin
sample was slightly better than was the
recycled. The Site E2 samples showed no
noticeable differences in performance, al-
though 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.
A major factor in metalworking fluid spoil-
age (rancidity) is microbial growth. In the
recycling process, existing microbes are
killed during the pasteurization step, the
dead biomass is removed during the cen-
trifugation step, and a measured quantity
of biocide is added to control future micro-
bial growth. ASTM E 686-85 evaluates
the effectiveness of biocides at use con-
centrations. No microbial growth was ob-
served in the recycled samples even after
6wk.
The performance tests conducted in this
evaluation (viscosity, lubricity and wear,
iron corrosion, copper corrosion,
bioresistance, foaming tendency, and
emulsion stability) are a measure of the
integral effect of both the contaminant lev-
els as well as the level of additives and
Table 4. Lubricity and Wear, and Viscosity 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
Viscosity '
(cs)
0.77
0.85
0.81
0.69
0.81
0.77
0.77
0.75
0.75
Average Wear Scar Diameter b
(mm)
1.26
0.83
0.64
0.97
1.18
1.17
NA
NA
NA
By ASTM D 445. An NA indicates not analyzed.
Analyzed after skimming off and discarding the floating tramp oil.
other fluid components. The levels of par-
ticular 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 and
additives. The recycling process brings
about considerable improvement in fluid
quality, to make recycling a technically
feasible option. The recycled fluid showed
some tendency toward foaming and iron
corrosion when compared with the virgin
fluid; but these could possibly be adjusted
by appropriate additives. Some solubilized
contaminants (such as calcium, magne-
sium, etc.) remain in the recycled fluid
because the smallest filter (1 |i) in the
recycling unit does not remove them. The
levels of these contaminants in the fluids
at the three sites evaluated did not, how-
ever, appear to affect their performance.
Retention of solubilized constituents in re-
cycled fluids also has the potential for old
and new additives to clash if they are
mismatched.
Currently, there are no published stan-
dards 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 ap-
peared to satisfy the functional require-
ments of the users.
Waste Reduction Potential
The waste volume reduction potential
of this technology involves the amount of
spent metalworking fluid kept from being
disposed into the environment (either by
landfilling or by onsite wastewater treat-
ment and sewer disposal). On an aver-
age, Safety-Kleen visits each user once
every 10 wk and recycles an average of
250 gal of spent fluid per visit. Thus, there
is potential for an annual reduction of 1,250
gal from a typical small user. Approxi-
mately 4 gal of tramp oil per visit are
generated during, recycling. This tramp oil
is hauled away at a competitive fee by
Safety-Kleen for use as supplemental fuel.
Residue generated on the filters (mostly
metal chips) is transferred to the user's
waste metal bin and later reclaimed for its
metal value.
According to a 1991 study by the Inde-
pendent Lubricant Manufacturer's Asso-
ciation, the volume of metalworking fluids
(concentrate) manufactured in the United
States, has increased steadily from 67 mil
gal in 1985 to 92 mil gal in 1990. By
extending the life of metalworking fluids
through onsite 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
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be as much as 20 times higher than the
manufacturer volumes, since many types
of fluids are diluted into 3% to 5% solu-
tions in water.
Economic Evaluation
The economic evaluation compared
costs for recycling versus costs for dis-
posal. Recycling costs included the onsite
service charge for the customer arid tramp
oil disposal cost. Disposal costs included
spent fluid disposal cost and hazard analy-
sis costs. The annual savings for a typical
small user, who recycles 1,250 gal/yr of
metalworking fluid was approximately
$1,600, if the spent fluid was nonhazard-
ous, and $7,800, if the spent fluid was
hazardous (by the Toxicity Characteristic
Leaching Procedure).
Conclusions
This evaluation found that recycling of
metalworking fluids is a good option for
small- to medium-sized plants with ma-
chining operations. In the absence of pub-
lished standards for recycled fluids quality
and performance, the user has to evalu-
ate the recycled product by the same cri-
teria used to select a virgin brand. In addi-
tion to the testing performed in this evalu-
ation, shop-floor testing of the recycled
fluids over an extended period of time to
determine the effect on workpiece quality
and tool life would be desirable.
The full report was submitted in fulfill-
ment of Contract No. 68-CO-0003 by
Battelle Memorial Institute under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
•&U.S. GOVERNMENT PRINTING OFFICE: 1993 - 750-071/80049
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