Merit Partnership Pollution Prevention Project for Metal Finishers
dsst Reverse Osmosis Applications
For Metal Finishing Operations


The Merit Partnership is a joint venture between the U.S.
Environmental Protection Agency (EPA) Region 9, state
and local regulatory agencies, private-sector industries,
and community representatives that was created to pro-
mote pollution prevention (P2), identify P2 technology
needs, and accelerate P2 technology transfer within vari-
ous industries in southern California. One of these in-
dustries is metal finishing, which is represented in the
Merit Partnership by the Metal Finishing Association of
Southern California (MFASC). Together, MFASC, EPA Re-
gion 9, and the California Manufacturing Technology
Center (CMTC) established the Merit Partnership P2 Project
for Metal Finishers. This project involves implementing
P2 techniques and technologies at metal finishing facili-
ties in southern California and documenting results. The
project is funded by the Environmental Technology Ini-
tiative and EPA Region 9.
This fact sheet provides technology transfer information
on reverse osmosis (RO) applications for metal finishing
operations in general and presents the results of a spe-
cific RO application case study conducted at a metal fin-
ishing facility in southern California.
WHAT IS REVERSE OSMOSIS?
Reverse osmosis (RO) involves separating water from a
solution of dissolved solids by forcing water through a
semipermeable membrane. As pressure is applied to the
solution, water and other molecules with low molecular
weights (specific weight of molecules allowed to pass
through is dependent on selected membrane), pass
MEMBRANE
Contaminant Buildup
Although "closing the loop" has many advantages, it
also has disadvantages: contaminant buildup.
Contaminants, such as unwanted metals from
preceding process operations, may "enter the loop"
as a result of drag-in and slowly accumulate in the
closed-loop operation, which may impact the
process chemistry. Therefore, bath monitoring is
essential to successful use of recycling systems such
as RO. Built-up contaminants may also precipitate
out of solution and cause membrane fouling.
PRESSURIZED
FEED
PERMEATE
J J J J J J

PERMEATE
CONCENTRATE
MEMBRANE
Figure 1. Reverse Osmosis Cross-flow Filtration
through micropores in the membrane. Larger molecules,
such as organic dyes and metal complexes, are retained
by the membrane. The purified stream that passes through
the membrane is called permeate, and the concentrated
stream containing a high concentration of dissolved sol-
ids is called concentrate. RO membrane systems feature
cross-flow filtration (illustrated in Figure 1) to allow the
concentrate stream to sweep away retained molecules
and prevent the membrane surface from clogging, or foul-
ing.
In the past, RO applications for electroplating operations
were mostly limited to final treatment of a combined
wastewater stream. Such applications typically involved
discharging the permeate to a POTW and returning the
concentrate to the head of the wastewater treatment sys-
tem. Because of the high flow rates associated with treat-
ing combined wastewater streams, large, costly RO units
were required. More recent metal finishing applications
of RO have involved installing RO units in specific pro-
cess operations, allowing return of the concentrate (re-
covered chemical solution) to the process bath and reuse
of the permeate (cleaned rinse water) as fresh rinse wa-
ter. By "closing the loop,"
valuable process chemicals
are recovered, and less
fresh water is needed. Fur-
thermore, a waste stream
is eliminated that would
otherwise be discharged to
the POTW.
Proven RO Applications
Copper Electroplating
Nickel Electroplating
Zinc Electroplating
Nickel Acetate Seal
Black Dye
-(ED ST.
9
proX*-

JANUARY 2002 REVISION

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Permeate
Cartridge
Filters
cm
I Recycle
I Tank
RO Membrane
Modules
Strainer
Concentrate
Feed
Solution
Pressure Booster
Pump
Optional
Pretreatment
Before Implementing RO . . .
Before implementing RO, low-cost P2 techniques
and other good operating practices such as pro-
cess monitoring should be adopted. For example,
countercurrent rinsing should be implemented to
reduce the required rinse water flow rate. This
will reduce the RO feed flow rate, and as a result,
smaller, less costly RO units and pretreatment sys-
tems can be used.
acetate membranes are limited to a fairly narrow pH range
(2.5 to 7) and a lower maximum temperature (about 85°F),
and such membranes are biologically degradable. The
type of RO membrane and module needed depends on
feed solution characteristics and the desired performance
of the RO unit. RO vendors or consultants often select an
off-the-shelf unit that is most appropriate for a given ap-
plication. Pilot tests are often necessary before a full-
scale RO system is implemented.
Figure 2. Basic Components of an KO Unit
RO UNIT COMPONENTS
Figure 2 shows a basic RO unit. The essential compo-
nents include a strainer, a pressure booster pump, car-
tridge filters, and the RO membrane modules. The strainer
removes large, suspended solids from the feed solution to
protect the pump. The booster pump increases the pres-
sure of the feed solution; typical operating pressures range
from 150 to 800 pounds per square inch (psi). Commer-
cially available cartridge filters are used to remove par-
ticulates from the feed solution that would otherwise foul
the RO units. Filter pore sizes are typically between 1 and
5 microns.
Membranes are assembled in modules, each of which com-
pacts a membrane of large surface area within a cylindri-
cal shell of small volume. The type of commercially avail-
able module most applicable to metal finishing operations
is the spiral-wound module. Although a number of mem-
brane materials are under development, two commercially
available membrane materials are currently in common
use: aromatic polyamides and cellulose acetate. The aro-
matic polyamide membranes used in spiral-wound mod-
ules typically take the form of thin-film composites. Such
a membrane consists of a thin film of membrane bonded
to layers of other porous materials that support and
strengthen the membrane. Thin-film composites can be
applied over a relatively broad pFI range (2 to 11), can
tolerate a maximum temperature of about 160°F, and are
more durable than single-material membranes. Cellulose
Pretreatment Considerations
Depending on the feed characteristics, optional pretreat-
ment considerations include:
pH Adjustment: If the feed solution pH is outside the
acceptable range for the membrane or near the solubil-
ity minimum of the feed solution ions, pH adjustment
may be necessary to avoid damaging or fouling the mem-
brane.
Oil and Grease (O&G) Separation: O&G may be
present in the feed as a result of drag-in from other pro-
cesses. If the feed contains O&G it should be removed
using an oil-water separator or a coalescer.
Disinfection: Feed shouldbe disinfected to prevent bac-
teria from building up and fouling the membrane; ultra-
violet (UV) light is preferable to chlorine to avoid a
subsequent dechlorination step.
Temperature Adjustment: If the feed solution tempera-
ture is greater than the maximum allowable tempera-
ture for the membrane, heat exchangers or other devices
can be used to cool the feed solution and prevent mem-
brane damage.
RO UNIT OPERATION AND MAINTENANCE
RO unit operation involves adjusting valve and pump
settings to control the pressure and flow rates of the feed
and concentrate streams. The most significant RO main-
tenance requirement is membrane cleaning or replace-
ment as a resultof fouling. Membrane fouling results
from poor feed solution characteristics, which are con-
trolled largely by some of the pretreatment steps discussed
above. When fouling is prevented or minimized by ef-
fective pretreatment, RO unit maintenance requirements
are minimal. For example, cartridge filters may require
periodic maintenance or replacement.
COST CONSIDERATIONS
The capital and installation cost for an RO unit is highly
variable depending on application. As illustrated by the
case study below, an RO unit used for a multi-line elec-
troplating application with flow rates of 10 to 15 gallons
per minute (gpm) can cost approximately $50,000.
Smaller units with a 3 to 5 gpm flow rate may cost be-

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tween $10,000 and $20,000. Basic costs cover the strainer,
pressure booster pump, cartridge filters, RO membrane
modules, plumbing, and installation. The capital cost of
an RO system increases with the amount of pretreatment
required (see "Pretreatment Considerations" on previous
page). Many RO units are compact and have low floor
space requirements. For example, a 3 gpm unit needs
only 6 square feet (ft2) and a 12 gpm unit needs 27 ft2- of
floor space. Operation and maintenance (O&M) costs
for RO units are relatively low. Because RO units are
automated, little operator attention is required and there-
fore labor costs are low (less than 3 hours a month). Main-
tenance costs are driven by membrane cleaning and re-
placement schedules', which are dictated by influent char-
acteristics and pretreatment effectiveness, To prevent mem-
brane fouling,, cartridge filters typically are changed once
a week and the RO membrane is cleaned once a month.
Applying RO to existing process lines may also involve
other costs associated with rearranging tanks, replumbing
water and process chemistry lines, and other modifica-
tions to create space or adjust rinse water flows.
RO CASE STUDY:
PERFECTION PLATING AND ECOSYSTEMS
With a goal of eliminating nickel from their wastewater.
Perfection Plating (Elk Grove Village, Illinois) purchased
an RO system from Ecosystems of Costa Mesa, California,
in December 2000 to treat rinse water from its nickel baths.
Perfection Plating installed the RO system to improve its
treatment of nickel-bearing wastewater compared to con-
ventional chemical precipitation and to assure that its ef-
fluent is well below its discharge limits to account for
normal operational variations. Perfection Plating provides
electroplating services to a variety of industries, including
automotive and electronics, and specializes in plating elec-
trical connectors and switches. Perfection Plating has ap-
proximately 70 employees and operates two shifts per
day. The facility is approximately 65,000 ft?and includes
several barrel, rack, and reel-to-reel nickel sulfamate plat-
ing lines. The nickel rinse water is consolidated and fed
into one RO system. The wastewater originates from the
first tank of each multi-stage, counter-current rinse, and
the RO unit returns reclaimed rinse water (permeate) to
the final rinse bath and the concentrated chemicals (con-
centrate) to the process baths. Figure 3 is a photograph
of the RO unit and Figure 4 shows the RO system schematic.

Table 1
Specifications of Ecosystems Nickel RO Unit
Dimensions
Footprint: 3 ft. by 9 ft. (27 ft2)
Height: 6 ft.
Power
20 HP, 230V, 47 amps
Flow Rate:
12 gpm
Operating Pressure:
500 psi
pH Range:
4 to 8
Max. Temperature:
110°F
Nickel (Ni)	RO System
Process Lines
\-4		U	
~
RO Nickel
concentrate
Treated
RO Permeate
Consolidated
Rinse Water Effluent
for RO Feed
Ecosystems
RO System
A
Figure 3. Perfection Plating's RO System
Figure 4. RO System Schematic at Perfection Plating

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CASE STUDY COSTS AND PERFORMANCE
Capital and installation costs including engineering sup-
port during installation and start up for the RO system
totaled $45,000. O&Mcosts include power, filter replace-
ment, system maintenance (pumps, fittings, etc.), and mem-
brane cleaning. For example, both the reclaimed perme-
ate and concentrate pumps must periodically be flushed
to assure the reclaimed rinse water and chemicals are not
contaminated. Cartridge filters are replaced every week,
costing $10.20 per month. Perhaps the most intensive
maintenance proce-
dure is the monthly
cleaning of the RO
membrane. A
deionized water and
sulfuric acid solu-
tion, with a pH of
no less than 2.0, is
filtered through the
system. Sulfuric
acid is added until
the pH stabilizes at
2.0 using no more
than 1 gallon of sul-
furic acid. Then, the
same process is re-
peated using a caus-
tic solution, maintaining the pH at 11.0. In total, cleaning
the RO membranes costs $114 per month (including deion-
ized water and chemicals) and takes 2 hours to complete.
With proper membrane selection and maintenance, an RO
membrane will last for 2 to 5 years; membrane replace-
ments for the Perfection Plating system cost approximately
$1,800.
Table 2 lists the operational savings associated with Per-
fection Plating's RO unit. The savings are based on data
from the 6 months before and after the RO unit was in-
stalled, during which time production at Perfection Plating
remained constant. In addition to simplifying the waste-
water treatment process by eliminating nickel treatment,
the RO system provided other environmental and eco-
nomic benefits.
/ By returning the concentrate to the process baths,
Perfection Plating reduced their monthly nickel
chemistry additons by over 80 percent, saving
$1,939 per month.
/ Rinse water use for the nickel lines decreased from
200,000 gallons to just 2,000 gallons per month,
saving $345 per month.
/ The system eliminated the wastewater discharge
fees associated with the nickel lines, saving an ad-
ditional $50 per month.
/ Other savings associated with reduced wastewa-
ter treatment costs (treatment chemicals and filter
cake associated with conventional chemical pre-
cipitation of nickel bearing rinse waters) were
achieved but were not quantified and are there-
fore not included.
Perfection Plating's RO system has a simple payback pe-
riod of approximately 2 years not including RO system
depreciation.
RO LESSONS LEARNED
After 6 monthes of operation Perfection Plating has in-
corporated several techniques to enhance O&M for the
RO unit. These include:
(1)	Adding a bypass valve to the cartridge filter unit so
that employees could replace the cartridge filters
while the RO system is in operation;
(2)	Using the cartridge filter unit bypass valve while
cleaning the RO membranes to prevent the materi-
als cleaned from the RO membranes from lodging
in the cartridge filters during back flushing and then
coming loose and fouling the membranes once the
unit is put back into operation; and
Table 2
Monthly Saving

Before
After
Savings
Chemical Additions:
200 gal
200 gal
$1,939
Water Use:
200,000 gal
2,000 gal
$345
Discharge Savings:
200,000 gal
0
$50
Total Savings:
$2,334/month
Less Operation and Maintenance Costs:
$541/month
Net Savings:
$l,792/month ($21,504/year)
Simple Payback = approximately 2 years
RO Case Study Costs
Capital and Installation
$45,000
Monthly O&M
Power	$276
Cartridge filters	$ 10
Pump maintenance	$ 41
RO unit cleaning	$114
Labor (2 hours)	$ 50
Membrane Replacement $ 50
(prorated)
Total = $541
(3) Using a sulfuric acid and a caustic cleaning solution
to improve RO membrane cleaning and the length
of operation between cleanings.
For more information about RO or the Merit
Partnership, contact the following individuals:
Leif Magnuson (EPA Region 9) at (415) 972-3286
Taoward Lee (Ecosystems)	at (714) 646-7552
Gary Holzer (Perfection Plating) at (847) 593-6506
Assistance for this fact sheet was provided by
Tetra Tech EM Inc.

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