Merit Partnership Pollution Prevention Project for Metal Finishers
Reducing Rinse Water Use
With Conductivity Control Systems
The Merit Partnership is a joint venture between U.S. Envi-
ronmental Protection Agency (EPA) Region 9, state and local
regulatory agencies, private sector industries, and community
representatives. The partnership was created to promote pol-
lution prevention (P2), identify P2 technology needs, and ac-
celerate P2 technology transfer within various industries in
southern California. One of these industries is metal finish-
ing, which is represented in the Merit Partnership by the Metal
Finishing Association of Southern California (MFASC). To-
gether, MFASC, EPA Region 9, and the California Manufac-
turing Technology Center (CMTC) established the Merit Part-
nership P2 Project for Metal Finishers. This project involves
implementing P2 techniques and technologies at metal finish-
ing facilities in southern California and documenting and
sharing results. Technical support for this project is provided
by Tetra Tech EM Inc. (formerly PRC Environmental Man-
agement, Inc.). The project is funded by the Environmental
Technology Initiative and EPA Region 9, and is implemented,
in part, through CMTC by the National Institute of Stan-
dards and Technology.
INTRODUCTION
Rinse operations significantly impact product finish and plat-
ing operations by removing concentrated process solutions
from part surfaces and minimizing dragin to subsequent op-
erations. At most metal finishing facilities, water continu-
ously flows through rinse tanks to provide proper rinsing.
However, many facilities use more rinse water than necessary,
which results in high water bills and wastewater treatment costs.
During metal finishing, as parts are removed from a process
bath and dipped into a rinse tank, the concentrations of chemi-
cals in the rinse water increase, thereby increasing rinse water
conductivity. Conductivity control systems monitor the con-
ductivity of the rinse water to maintain chemical concentra-
tions at levels that provide adequate rinsing and prevent exces-
sive dragin to subsequent process tanks. Conductivity control
systems reduce water use by adding water to rinse tanks only
when necessary instead of continuously at a constant rate.
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Figure 1. Conductivity Control System Components
CONDUCTIVITY CONTROL SYSTEMS
A conductivity control system consists of three main compo-
nents: (1) a conductivity sensor, (2) a conductivity analyzer,
and (3) a solenoid valve (see Figure 1). The conductivity sen-
sor is a probe placed in the rinse tank to measure rinse water
conductivity. The conductivity analyzer is the signal process-
ing unit that controls the system. The conductivity analyzer
receives input from the sensor and determines rinse water con-
ductivity. The conductivity analyzer features a programmable
or adjustable set point and deadband. When the rinse water
conductivity reaches the set point, the analyzer opens the sole-
noid valve to release water into the rinse tank, thereby reduc-
ing the conductivity of the rinse water. The deadband is the
conductivity range within which the solenoid valve will re-
main open after being activated by the analyzer. When rinse
water conductivity decreases to a level below the deadband,
the analyzer closes the solenoid valve to stop water flow to the
rinse tank (see Figure 2).
Benefits of Reducing
Rinse Water Use
The advantages of reducing
rinse water flow include:
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4- Decreased water use
4- Decreased wastewater generation
4 Decreased wastewater treatment chemical use
4 Decreased sludge generation
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be monitored before system installation to determine its con-
ductivity range (see Figure 5). Initially, conductivity control
system set points should be established at the high end of the
rinse water conductivity range. Set points can be increased if
process operations remain unaffected and further reductions
in rinse water use are desired. Set points can be reduced if
parts are not adequately rinsed or if dragin to subsequent pro-
cess tanks adversely affects process operations. A record of set
points, process bath conditions, and parts rejected because of
poor rinse quality should be maintained to help determine
optimal set points.
Things to Consider When Selecting Components
Considerations that affect the type of conductivity con-
trol system components selected include the following:
~	Conductivity range of the rinse water: Analyzers
and conventional conductivity sensors are de-
signed to measure certain conductivity ranges.
~	Analyzer mounting configuration: Analyzers are
equipped with special hardware for mounting on
an instrument panel, flat surface, or pipe.
~	Analyzer mounting location: Analyzers are avail-
able with NEMA 4X water- and corrosion-resis-
tant enclosures for installation near process tanks.
~	Number of channels on the analyzer: Some
analyzers are capable of accepting inputs from two
sensors so that water flow in two rinse tanks can
be controlled.
~	Chemical concentrations in the rinse tank: The
chemical concentrations in the rinse tank, which
are determined by the type and volume of dragin
from preceding processes, can affect the type of
sensor selected. Electrodeless sensors may be
more appropriate in rinse tanks with high chemi-
cal concentrations because they do not foul.
CASE STUDY: ARTISTIC PLATING AND METAL
FINISHING, INC.
The Merit Partnership sponsored a P2 project that involved
installing and evaluating conductivity control systems at Ar-
tistic Plating and Metal Finishing, Inc. (Artistic), a medium-
sized metal finishing facility in Anaheim, California. The
main objective of the Artistic P2 project was to evaluate the
effectiveness and benefits of using conductivity control sys-
tems on various metal finishing processes. The Artistic facility
performs copper, nickel, and chrome electroplating on a hand-
operated rack line and copper electroplating on a manually-
operated barrel hoist line. The facility specializes in electro-
plating zinc die-cast parts for commercial customers, and op-
erates up to three shifts per day. Wastewater is sent to an on-
site wastewater treatment system (WWTS). Treated wastewater
is discharged to the local publicly owned treatment works and
sludge (filter cake) is disposed of off site.
Conductivity Controlled Rinse Tanks at Artistic
4 Acid activation (three) 4 Nickel (three)
4- Copper cyanide (two) 4 Chromium (one)
Nine conductivity control systems were installed at the Artis-
tic facility. Three conductivity control systems were purchased
from the Foxboro Company (Foxboro), three from Great Lakes
Instruments (GLI), and three from Cole-Parmer Instrument
Company (Cole-Parmer). The Foxboro and GLI conductivity
control systems use electrodeless sensors and the Cole-Parmer
conductivity control systems use conventional sensors. The
Foxboro and GLI systems have analyzers with digital displays
that allow accurate programming of set points and deadbands
and easy system calibration and operation. The Cole-Parmer
systems do not have displays, and analog set points and
deadbands are adjusted by turning screws in the sensors. Un-
like the Cole-Parmer systems, the Foxboro and GLI systems do
not include solenoid valves; therefore, valves for these systems
were purchased separately from a hardware supplier.
CASE STUDY SYSTEM SETUP
The analyzers for the conductivity control systems on the rack
line at the Artistic facility were mounted on a common con-
trol panel (see Figure 6). Cables from the analyzers to the
sensors and solenoid valves were run below the floor grating
and protected from moisture by conduit. The analyzers for
the conductivity control systems on the barrel line were
mounted on a nearby wall. Artistic monitored rinse water
conductivity for 3 weeks before system installation to deter-
mine the operating conductivity range of each rinse tank. Based
on this information, the
initial set point on all
analyzers were set at 1,200
microSiemens per centi-
meter ([xS/cm), with a
deadband of 50 [xS/cm.
During 3 months of op-
eration, no negative pro-
duction impacts oc-
curred (inadequate rins-
ing or dragin to subse-
quent process tanks). Ar-
tistic may therefore even-
tually raise the set points.
Conductivity control system maintenance includes monthly
calibration checks performed by comparing the conductivities
measured by the conductivity control systems with those mea-
sured by a calibrated, hand-held conductivity meter. During 3
months of operation, the sensors did not need cleaning. One
of the Cole-Parmer conductivity control systems malfunctioned
because of a manufacturer's defect. This system was returned
to the distributor for replacement.

4
Figure 6. Analyzer Panel at
the Artistic Facility

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CASE STUDY COSTS
The costs for conductivity control systems ranged from $290
to Si,140 per system. Other hardware, such as mounting equip-
ment, conduit, and wiring, cost an additional $100 to $250
per system. Installation was performed by an outside contrac-
tor for $400 to $600 per system. System operation and main-
tenance activities are currently performed by a contractor but
may eventually be performed by Artistic staff.
Typical Conductivity Control System Costs

Conventional"
Electrodeless'
Capital
$290
$1,140
Additional Hardware
$100
$ 250
Installation
$400
$ 600
Total (per system)
$790
$1,990
a Conventional sensor, analyzer with no display, and analog set point and deadband
b Electrodeless sensor, analyzer with digital display, and programmable set point and
deadband


Although the conventional conductivity control systems re-
quire less capital cost, Artistic believes the electrodeless sys-
tems are likely to be more cost-effective in the long term be-
cause they are easier to operate and maintain.
CASE STUDY RESULTS
The conductivity control systems were installed at the Artistic
facility in August 1996 and after 2 weeks of adjustment have
performed effectively. Analyzers with digital displays and pro-
grammable set points were easiest to use and allowed better
control of rinse water flow than analyzers with no display and
analog set points. During 3 months of conductivity control
system operation, no adverse impacts on process quality were
observed. The conductivity control systems have resulted in
the following benefits: (1) decreased rinse water use, (2) de-
creased wastewater generation, (3) decreased WWTS treatment
chemical use, and (4) decreased WWTS sludge generation.
Decreased Rinse Water Use and Wastewater Generation : After
3 months of operation, the conductivity control systems have
reduced rinse water use and resulting wastewater generation at
Artistic by 43 percent (see Figure 7). According to the facility
production manager, production was steady during this pe-
riod. Artistic has saved a total of $390 per month on city
water purchase and sewer discharge fees.
5 80,
£
>, 40,
Average Water Use
Before: 129,000 gal./week
After: 74,000 gal./week
Conductivity Control
System Installation
5/6 5/20 6/3 6/17 7/8 7/22 8/5 8/19 9/3 9/16 9/30 10/14 10/28 11/11
Week (1996)
Decreased Wastewater Treatment Chemical Use and Sludge
Generation: Conductivity control systems significantly reduce
overall rinse water use and wastewater volume; therefore, if
dragout remains constant, the average concentration of metals
in the wastewater will increase. Studies have shown that treat-
ing smaller volumes of more concentrated wastewater can re-
duce treatment chemical use and associated costs. This effect
is realized because electroplaters use treatment chemicals in
quantities that greatly exceed stoichiometric requirements. Re-
ducing wastewater volume and treatment chemical use may
also reduce the volume of sludge (filter cake) generated because
a significant portion of sludge mass can be attributed to treat-
ment chemicals (for example, lime) and their reactions with
naturally occurring ions (for example, carbonates, phosphates,
and sulfates) present in water that are removed during treat-
ment.
In addition, reduced wastewater generation will result in a lower
flow rate through the WWTS, which can increase retention
time in the treatment tanks and improve WWTS performance
and efficiency, further reducing treatment chemical require-
ments. Because the evaluation period was not long enough to
allow adequate sludge generation data to be gathered and be-
cause the facility changed the type of flocculant used in the
WWTS, sludge reduction was not quantified.
Conductivity Control System Results
Per Month	Monthly
Rinse Water Use
Wastewater Discharge
WWTS Chemical Use
WWTS Sludge
Before
516,000 gal.
516,000 gal.
$4,000
After
296,000 gal.
296,000 gal.
$3,200
Savings
$280
$110
$800
Not Quantified
Total Cost for Nine Systems = $14,500
Total Savings = $14,300/year
Payback Period = 1.0 year
For more information on the Merit Partnership, this case study,
or conductivity control systems, contact the following
individuals:
Laura Bloch (EPA Region 9)
at
(415)
744-2279
John Siemalc (CMTC)
at
(310)
263-3097
Dan Cunningham (MFASC)
at
(818)
986-8393
Kipton Kahler (Artistic)
at
(714)
632-1496
Kevin Quaclcenbush (Foxboro)
at
(508)
378-5177
Joseph Novak (GLI)
at
(414)
355-3601
(Cole-Parmer)
at
(800)
323-4340
Figure 7. Rinse Water Use at Artistic Decreased 43%
Assistance for this fact sheet was provided by
Tetra Tech EM Inc.

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