NASF Preliminary Response to EPA’s Metal Finishing 

Study Questions – November 2015

This is intended to be a broad list. Not every question on here may be answerable. Note that the 

term “metal finishing facilities” is usually meant to cover facilities regulated under 40 CFR Part 

413 and part 433.

1. What are the applicability issues with the existing rule? (These are typically related to 

ambiguous wording in the 1983 TDD.) What is the best way to address the issues: 

letters, memoranda, guidance, and rulemaking? Does it make sense to deal with these 

issues at the national level? Examples:

a. Cleaning vs Etching – already covered by ELGs

b. Phosphoric acid cleaning vs chemical conversion coating (phosphating) -- already 

covered by ELGs

c. Powder Coating – not covered by ELGs

d. Brighteners – have been part of process for a long time

e. Revivation – primarily auto body shop cleaning and pretreatment process for 

removing grease and paint (heated alkaline electrolytic solution)

f. Zirconization – ecofriendly pretreatment process that is phosphate free and does 

not appear to present any significant concerns

g. Citric acid passivation – process removes iron and leaves chromium conversion 

coating in place and does not appear to present any significant concerns

2. What are the advances in surface finishing that can affect wastewater characteristics? 

Are new pollutants of concern being generated or used and then discharged in 

wastewater? The industry continues to implement good practices to reduce the 

amount of pollutants that are generated and discharged in wastewater.

3. What are the advances in process technologies that have reduced or eliminated the 

discharge of more toxic pollutants? Examples:

a. Replacements for cyanide plating chemistries 

b. Replacements for cadmium plating chemistries

c. Replacements for conventional water treatment chemicals that produce toxic 

sludge (e.g. eliminating the use of sulfides) and/or lower volumes of wastewater 

treatment sludge

d. Trivalent chrome decorative plating chemistries (i.e. alternatives to hexavalent 

chromium)

e. Cobalt-free, tri-chrome passivates

f. Organically stabilized electroless nickel (non-lead, cadmium, bismuth and 

antimony)

g. The zirconization process uses zirconium hexafluoride to deposit a zirconium 

oxide layer on the surface of the work piece; so, zirconium and flouride might be 

present in the corresponding wastewater stream

h. Also new aluminum coatings, zinc-nickel alloy coating, nickel fluorocarbon, 

trivalent chromium, and dry technologies such as high velocity oxygen fuel spray

The industry continues to implement a broad range of technologies to replace 

and/or improve plating processes to reduce or eliminate the discharge of 
potentially toxic pollutants. NASF can provide additional information on 

specific technologies, if appropriate.

4. What strategies are metal finishing facilities using to reduce water consumption or 

minimize wastewater discharge? How can effluent guidelines incentivize reduction in 

water consumption/wastewater generation? What are the advancements in pollution 

prevention practices (P2)? Examples:

a. Counter current flow operation

b. In-stream recovery operations

c. Segregated wastewater treatment and recycle

The industry has achieved significant reduction in water use. In 2006 EPA 

Sector Strategies Program reported that industry reduced releases to air and 

water by 58% over period of 1994 to 2003. See detailed responses to this section 

provided below.

5. Are POTWs receiving pollutants from metal finishing facilities that interfere with their 

operations or pass through? POTWs have continued to report that they do not have any 

significant problems associated with discharges from metal finishing operations and 

would not recommend any changes to existing ELGs.

a. How is today’s metal finishing industry handling chelated metals in their waste? 

What if they are using citric acid? Are there improvements in handling chelated 

waste since the 1983 ELG? Many chelated metals are treated with oxidizers 

before chemical precipitation process.

6. How can metal finishers achieve zero liquid discharge? How can the effluent guidelines

be crafted to incentivize that? See detailed response provided below.

7. What types of wastewater treatment technologies are being installed/operated in metal 

finishing facilities beyond the BPT technology, defined as hydroxide precipitation 

followed by clarification? How can they be most economically employed by metal 

finishers (e.g. when is end-of-pipe not always the best option?) Are there technologies 

now that are more affordable than conventional chem precip? (I have heard that disposing 

of solids from those systems is expensive, electrochemical techniques produce less 

waste.) Examples:

a. Dialysis

b. Electrodialysis, electrodeposition, and electrocoagulation

c. Reverse osmosis (and other membrane technologies)

d. New chemicals for use in chem precip systems (e.g. Compliance MX)

e. Ion exchange

f. Filtration (micro-, ultra-, nano-)

g. Other sorption techniques (biosorption, adsorption, nanosorption)

h. Evaporation

i. Biological treatment

See detailed discussion provided below in response to Question 4.

8. We need information on the demographics, economics, and potential sub categorization

of the metal finishing industry. This industry includes many small entities that might 

struggle to afford advanced wastewater treatment installations. What sectors might 

include larger firms that are better able to afford advanced wastewater treatment? What 

new markets are metal finishing facilities operating in? How many facilities does that 

cover? What are good sources to use for demographic information about this industry or 
to identify facilities and scope of their operations? How is generation of wastewater 

related to facility size? Are large facilities producing most of the pollutants in metal 

finishing wastewater? NASF has provided EPA with some preliminary data on the 

decreasing number of metal finishing facilities and continues to work with POTWs to 

collect more of this data. In addition, EPA should refer to the industry comments and 

other rulemaking materials that were produced as part of EPA’ Metal Products and 

Machinery (MP&M) rule in which EPA concluded that no further regulation was 

warranted for the metal finishing industry.

9. Are metal finishing facilities sending their wastes to CWTs? Our understanding is that 

the vast majority have pretreatment and then discharge to POTWs. With the exception of 

when they need to dispose of spent plating baths, however this only happens once every 

five to ten years. The vast majority of facilities discharge to POTWs. Some facilities 

have NPDES permits and discharge directly in waters of the U.S.

10. Are there control authorities (at POTWs) that are imposing strict local limits and driving 

innovation in water use reduction and wastewater treatment at metal finishing facilities 

within their catchment area? Which regions/localities/states have been leading this 

charge? Metal finishing facilities have made great progress in reducing water use and 

this progress has been motivated primarily by the facility’s efforts to reduce costs and 

minimize its environmental footprint and potential long-term liabilities.

11. Are there air pollution control technologies that generate wastewater that is commingled 

and subsequently discharged with metal finishing wastewater? We are aware of 3 

NESHAPs that apply to this industry: 40 CFR Part 63 Parts N, T, and GG. With respect 

to the Chromium Electroplating NESHAP (Subpart N), facilities with wet scrubbers to 

control emissions do generate small amounts of wastewater that is processed in the 

facility’s wastewater treatment system that do not pose any issues in complying with the 

existing ELGs. Some scrubber systems also route the wash-down water back into the 

process tanks.

12. What facilities should we conduct site visits at to get a better idea of the current 

operations of the metal finishing industry? NASF is happy to help EPA identify metal 

finishing operations for site visits.
Detailed NASF Responses

Q4(1). What strategies are MF facilities using to reduce water consumption 

and/or reduce the amount of wastewater discharge?

Provided below is a list of pollution prevention (P2), best operating procedures in common use in 

our industry today. 

 

Process Solutions

1. Accurate and frequent solution analysis to maintain bath constituents at +/- 2% 

of recommended levels to prolong life of bath;

2. Use of statistical process control;

3. Removal of dropped parts;

 a) use of rack maintenance program

 b) use of barrel maintenance program

 c) operator training programs on the above

 d) rack/barrel systematic inspections

 e) scheduled removal/repair program

4. Use of DI water increased bath life and better plated product);

5. Bus bar maintenance;

a) Covered anode rails to prevent corrosion and solution contamination

b) Proper positioning with relation to exhaust systems to prevent above.

c) Plating of rails to prevent Cu corrosion

d) Plastisol coating of rails to prevent Cu corrosion

6. Control of operating parameters. This has changed significantly in recent years 

with the advent of PCLs to control temperature and feed rates of reagent 

chemicals. This results in the more efficient operation of the chemical reactions 

for the selected removal methodologies, i.e. not overdosing of OH in hydroxide 

ppt Rx thus coming closer to the minimum solubility for a selected pH range.

7. Tank filtration. Promotes longer solution life; use of in & out of tank systems; 

containment of filtration systems;

8. Use of inert anodes where feasible

9. Contamination removal;

a) LCD electrolysis

b) Chemical treatments...pH adjustment, H2O2, polysulfide ppt, IX to 

selectively remove trap metals (Cr+3 solution)

c) Activated carbon for organics - batch or continuous

d) Carbonate freeze-out to extend life of CN solutions

10. Drag out reduction;

a) Use of drag out tanks

b) Installation of drip boards

c) Increase dwell hang time

d) Reduced removal rates from solutions

e) Optimum racking spatial orientation to promote solution drainage

f) Use of wetting agents (better drainage)
g) Reduction of solon viscosity; Increase solution temperature; better 

drainage

h) Installation of air knives

i) Use of spray rinses

j) Use of slots vs holes in barrel construction

k) Use of I/O doors for plating barrels

l) Proper rack & barrel maintenance

m) Position parts for racking to optimize rinsing

Rinsing System

1. Increased rinsing agitation; enhanced rinsing efficiency; pumps and eductors

2. Counter flow rinsing; F=D(CT/CR)to 1/n power

3. Air knives

4. Spray rinsing; generally need hot tanks > 140F

5. Reactive rinsing; use of same rinse water for acids and alkali

6. Barrel spray rinsing (proprietary system, Spray-Thru by hardwood Line Corp. of 

Chicago; good system works well but they are bear fans?*^&#!!)

7. Flow restrictors

8. Timers for on/off

9. Waste stream segregation; note little if any economic incentive for this

10. Conductivity controllers

Good Housekeeping

1. Keep floors clean and dry

2. Use secondary containment

3. Use overflow protection; level controls and dead man switches

4. Lined tanks for leakers

5. Storage tanks w/ labels for off-line work product

6. Pits to collect spills

7. Ventilation systems; updraft or down draft; Pros and cons of each. I prefer updraft 

for condensate return to process tank

8. Inventory control of chemicals; log sheets for sign out of chemicals and to ID site 

of use

9. Storage segregation of non-compatible chemicals

Q4(2). How can effluent guidelines incentivize reduction in water 

consumption and waste water generation, i.e. ultimately make less waste?

To reduce waste, reclaim and use valuable resources (metals), reduce costs in transporting 

hazardous materials, reduce the number of land sites required for eternal storage of F006 and 

protect our sources of drinking water there needs to be a regulatory methodology to incentivize 

the segregation of waste streams within MF facilities. If waste streams could be separated so as 

to create a stream that will produce a material that can be beneficially reused, and is not 

characteristically defined as hazardous, a massive amount of innovation would ensue. 
1. Waste stream segregation would occur to promote recycling of the inherent metallic 

content;

2. Cyanide bearing waste streams would be removed from mixing with non-cyanide 

bearing waste streams to create a non-hazardous sludge;

3. Hexavalent chromium bearing waste would be removed from mixing with other 

metallic bearing waste streams to create a non-hazardous sludge;

4. Cadmium bearing waste would be removed from mixing with other metallic bearing 

waste streams to create a non-hazardous sludge;

5. Less landfill sites for F006 storage would be consumed as more hydroxide sludge 

will be reintroduced into commerce to recycle metals;

6. If waste streams were segregated, they will also be concentrated to obtain a higher 

economic return. One does not want to treat water, rather the metallic content. This 

will promote water conservation;

7. As more metals are recycled energy requirements to mine, refine and transport new 

will diminish;

8. As facilities are allowed to recycle waste treatment sludge and receive an economic 

return, this will encourage more separation of waste streams to yield more return; 

facilities will then return to Item Number 1. Round and round we go;

9. Substitution of processes would be encouraged especially if the waste product from 

them was non-hazardous. Process R & D would be driven to use chelation systems 

that would create systems that no not use hazardous chelators;

Q4(3). Best Operating Practices for Pretreatment

The requirement to properly minimize waste during pretreatment requires a knowledge of the 

particular process, emission sources from the process, use of good operating processes, selection 

of technologies (often dependent on type of product being finished), process changes and 

alternate technologies if applicable.

Vapor Degreasers

1. Avoid solvent degradation (extends life of solvent)

a) Accumulation of metal finds from work product

b) Avoid hot spots on heating elements

c) Avoid introduction of water.... On work product or from atmosphere

d) Avoid build-up of chlorinated/sulfonated lubricants

e) Avoid addition of acid from fluxes or previous acidic cleaners

f) Use solvents that are stabilized (Vapor Degreaser Grade)

g) Control pH which typically drops

2. Operating Requirements

a) Withdrawal rate 10 – 11 fpm

b) Limit volume loading to < 50% of solvent volume

c) Allow adequate time for parts to reach solvent temp; watch vapor level

d) On addition pump solvent into sump....Do Not Pour; rate of 5 – 10 gpm

e) Install and use cover as appropriate

f) Avoid spraying solvent when possible; If spray below vapor line

g) Require regular equipment inspection
h) Place parts in system as to promote drainage

i) Reduce ambient drafts over equipment to < 30 fpm

j) Remove degreasers away from doors and building exits

Aqueous Cleaning Systems

1. Operate and maintain temperature; it is the thermal energy that does the work

2. Add agitation....more is better

3. Maintain/clean all nozzles

4. Remove oil as necessary

5. Add oil skimmers

6. Add filtration to extend solution life

7. Lipophilic Filtration available for oil removable (very expensive)

8. Micro and ultrafiltration have been used to remove oils from a cleaner tank; $25k - $40K 

per tank; Cost prohibitive

9. Use low TDS water for M/U

10. Evaluate and optimize Surfactant for work flow

11. Maintain a log of tank dumps

12. Use liquid chemicals vs powders better solution rates

13. Regular chemical analysis

14. Require regular equipment inspection

Ultrasonic Aqueous Cleaning Systems

1. Maintain monitor temperature.... 50 – 80C

2. Frequency 20 – 40 kHz

3. Maintain energy density @ < 20 watts/gal

4. Avoid introduction of gases

5. Avoid introduction of energy absorbers...plastic, plastisol

6. Maintain dilute cleaning chemistries; < 1.5 opg

7. Use liquid chemicals vs powders better solution rates

8. Regular chemical analysis

9. Require regular equipment inspection

Electrolytic Aqueous Cleaning Systems

1. Maintain monitor temperature.... 50 – 80C

2. Use liquid chemicals vs powders better solution rates

3. Use low TDS water for M/U

4. Regular chemical analysis.... Maintain alkalinity

5. Add filtration to extend solution life

6. Lipophilic Filtration available for oil removable (very expensive)

7. Monitor and control CD

8. Maintain a log of tank dumps

9. Maintain all bus connections

10. Maintain electrodes

11. Monitor FOG concentrations

Substitutions in Solvent Cleaning (Not Common Practice)

1. NMP- N-Methylpyrrolidine; non-flammable; $30+/gallon
2. Terpene Systems

3. Methyl Siloxanes

4. Non-linear alcohols

5. Iso-propyl alcohol

6. Numerous other solvents with varying degrees of polarity; Need to evaluate health effects 

before use.

Biological Cleaners (Not Common Practice) 

1. Aqueous based cleaning system that uses bio-organisms (bugs)

2. Cleaning cycle- approximately 5 – 10 minutes

3. Operating temp 104 – 122F

4. No cleaner dumps

5. Must maintain pH 8.8 – 9.2 or GOOD BYE BUGS!!!

6. Removes aliphatic hydrocarbons and most aromatic rings

7. Removes chlorinated solvents

8. System is physically large therefore fitting into existing machines is problematic

9. By products are CO2, H2O and inert solids (“Bug waste”)

Use of acids in the pretreatment scheme of any finishing facility is a key component in the 

application of a suitable finish to the base material. The acid MUST be selected based on the 

substrate type, the type of surface oxide (scale) present and end use of the metal product. The 

article being processed often cannot be etched due to the inappropriate selection of an acid, to 

long of a cycle or operated at the wrong temperature. Therefore changes in acid type or 

formulation are difficult accept for fear of producing unacceptable product.

The P2 Opportunities that exist are:

1. Changes in process chemistry or operating procedure (Note warning above);

2. Bath maintenance;

3. Reducing water use;

4. Acid recovery.

Acids (Mineral, oxidizing or acid salts) are the least expensive portion of the MF process. 

Therefore there is little incentive to change or extend the process to save an acid solution. For 

example, in one automated line the individual cells are 110 gallons. With the acid salt 

concentration at 12 opg and the cleaner at 16 opg and each component at approx. $1.100/lb., the 

makeup cost for electro-cleaner and acid pickle is $121.00 and $90.75 respectively ($211.75 

total). If the pretreatment where extended to conserve resources by whatever P2 method you 

choose, and the system fails to properly pretreat product creating rejects costs to strip and rework 

material could easily exceed $2500.00. Therefore why take the risk to extend a very inexpensive 

material at the risk of easily 10X the cost of the pretreatment chemistry. In addition, if product 

has to be stripped and reworked, the resulting strip solutions are often untreatable on site due to 

heavy chelation and must be shipped off site for incineration or other disposal technique. 

Therefore, a greater environmental liability is created by stripping the product because one tried 

to extend or save the cleaner or acid pickle. Operating prudence dictates to dump pretreatment 

frequently to produce a higher percentage of good product.
“In most cases bath maintenance and recovery technologies are applicable to very high 

volume pickling operations where significant chemical replacement costs are experienced. 

This is NOT the norm in most MF facilities, where smaller volumes of acids are in use. The 

costs of these technologies are usually prohibitive”*

 *Taken from NASF P2 Pollution Prevention Practices Course. 

In addition acid pickles are not made up with heavy metals as are plating baths, and become 

laden through use with none regulated metals (Fe, Al, Sn) thus reducing the incentive to apply 

expensive recovery techniques.

Acid Selection Considerations

1. Acid choice selections are often dictated by the dynamics stated above (What has been 

found to work and meets customers’ requirements.

2. Acid choice will also be dictated, by the amount of waste generated and ability to treat. 

For example, citric acid produces less waste(less substrate dissolved) but is a chelator and 

thus is difficult to treat. It is often shipped off site. Standard mineral acids win this 

decision battle every time.

Process Variables: Time, Temperature and Concentration

From a P2 prospective, lower acid concentration and less thermal energy are good. However, 

operation of chemistries in this fashion dramatically slows the process and increases the cost(less 

through put). Therefore from an economic perspective P2 loses.

Agitation

Agitation improves thru put by replenishing the acid next to the work piece with fresh acid. This 

technique is often used. Thus an acid bath can operate at a lower concentration if agitated. 

Agitation is a P2 technique that increases thru put and uses less acid.

Inhibitors 

Conventional acid pickling attacks the base as well as metal oxides on the surface of the base. 

This can be rapid thus loading the chemistry too fast with metal and etching the surface. In order 

to retard the action of the acid a class of materials is added to retard this action, inhibitors. 

Inhibitors can be metals or organic compounds. They have been in use for over 50 

years. Concentrations vary from 0.5% TO 6% depending upon the acid type, concentration, 

temperature and soil characteristics. Inhibitors are a P2 methodology in that they slow metal 

build up in acid pickles. Control of inhibitors can be difficult because they are often designed for 

an acid concentration and temperature range. If incoming material dictates a process alteration to 

effectively clean a substrate (lower pH or increased temperature) the inhibitor can be destroyed. 

The chemical formulations of inhibitors are often hidden from the user. Since there are questions 

from EPA regarding introduction of new pollutants of concern being introduced to wastewater 

(Question No 2), the organic chemicals being used as inhibitors would be a place to look.

Acid Rinsing P2

All of the P2 rinsing practices previously discussed apply to acid pickles and their associated 

rinse systems;

1. Drag-in minimization

2. Drag-out minimization
3. Reactive rinsing

4. Flow control with flow control valves, conductivity controllers

5. Counter flow rinses

6. Spray rinses

7. Agitation

8. Control of pH based on subsequent plating system; acidic pH 5-6 for Ni systems or pH 

of 9 – 10 preceding EN systems

Bath Monitoring (Maintain within 5%)

Analytical monitoring of acid chemistries will maintain bath life and create less waste. Monitor 

for:

1. Dissolved metal;

2. Monitor for inhibitor;

3. Perform FOG analysis;

4. Monitor acid concentration look for excessive water build up.

Acid Bath Technologies beyond BPT

These technologies have uses in recovering metals and acid from spent pickle baths. However as 

stated the economics of their installation costs, maintenance and operation almost never work in 

favor of the MF facility. The most common systems are:

1. Acid sorption

2. Diffusion dialysis

3. Electrowinning

Q6. How can a MF achieve zero liquid discharge? How can EFG be 

crafted to achieve this? 

There are a number of “advanced technologies” that can be applied to plating operations to move toward 

zero liquid discharge. Please note these technologies often only work on one or a small group of 

pollutants. None of these techniques cover all pollutants like hydroxide or sulfide precipitation. Some of 

these systems are:

1. Dialysis

2. Electro dialysis

3. RO

4. IX

5. Electrowinning

6. Evaporation

All of these suffer from two main faults. They are not universal to all pollutants and they are very 

expensive. Therefore they must be applied to a select group or type of analytes. 

Ion Exchange (IX) and Electrowinning: An Example

IX can remove metals from a waste stream but they do not remove all metals equally. Therefore on a 

finishing line to remove a group of regulated metals one may need several IX resins operating under very 

different conditions to capture all of the metals. For example, if a strong acid resin were to be used to 

capture metals, these resins have a preference for higher valence metals (not all metals are equal when 

presented to the resin). If a heavy metal selective chelating resin were used to capture metals (R-EDTANa + Ni+2 = (R-EDTA) 2Ni + 2Na), it has a poor selectivity in the presence of Cu+2 or Pb+2 ions. Thus 
if those 2 metals were present as in a line designed to plate on 360 brass the resin would be 61X more 

effective in picking up the Pb+2 or Cu+2 than the Ni+2!

Resins also have a finite capacity i.e., they can only hold so much metal before the system has to be 

regenerated (metal flushed off of the resin to restore it to its original capacity). Thus if a metal is removed 

from an effluent waste stream of a plating line, the metal is now captured and transferred to a different 

aqueous liquid stream than the plating line effluent. However, it still is in an aqueous solution that has to 

be addressed, albeit at an off-site facility. The water discharge may be reduced, but it is simply 

transferred to another facility that processes the metal finishing facility’s wastewater. After removing 

metals with IX or electrowinning, the wastewater could be neutralized and discharged without generating 

additional sludge as waste.

So how does one remove the soluble metal from liquid solution Number 2? One could precipitate it out, 

but this is not favored by EPA since precipitation makes a sludge which EPA wants to eliminate. 

Therefore, it could be plated out by using an electrowinning cell. One now invests in an electrowinning 

system to plate out the nickel. Cost of such a system could easily be $50,000 (function of size). This 

system will decrease the Ni concentration in the IX concentrate from approximately 4000 ppm to 10 ppm 

(99.75% removal efficiency) but, it still cannot be discharged. The 433 regulations require Ni to be at 

2.38 ppm on a 30 day average to discharge. Therefore, something still has to be done with the small 

amount of Ni: possibly precipitation, evaporation or bleed and feed.

So what has been accomplished in trying to remove nickel from this plating line and achieve zero water 

discharge?

1. Spent approximately $170,000 to purchase and install an IX & Electrowinning system;

2. System will reduce the Ni in the plating effluent to < 2.38 ppm which can be discharged, but 

there still is a discharge; nothing has been done to decrease the liquid outfall 

flow...NOTHING!

3. Transferred the nickel metal to a second aqueous media that cannot be discharged!

4. Have recovered approximately 99.75% of all nickel via Electrowinning. Payback on 

equipment is none existent.

5. The metal finishing facility may have achieved zero discharge, but the discharge has been 

transferred to a separate off-site facility.

How to Stop all Liquid Outfall

If one wants to stop the liquid outfall from a plating line, the 2 most realistic methods are to:

1. Evaporate all of the water coming from the line; 

2. Return the entire outfall back to the line.

Evaporation

If this line used 4 running CFR operating at 3gpm, it uses 5,760 gal per shift (46,080 lbs.’ of water per 

shift). To evaporate this amount of water would require 50,853,888BTUs/shift. This would mean the use 

of an evaporator with the capacity of approximately 20 MBTUs (30% efficient) running at full capacity 

for the entire shift!!! (1103.6 BTU required to evaporate 1 pound of water starting at 75 F). The cost of 

fuel and equipment makes this economically not feasible. Even if one did evaporate the water, the solid 

residue would still be a waste outfall from the line (F006) and have to be hauled away. Evaporation of an 

entire plating line effluent is not practical. Therefore, the only other alternative is to return all of the water 

used back to the plating line.
Water Return

If one returned all of the water to the line, space would have to be made in the line to accept 5,760 gallons 

per shift i.e., would have to evaporate rinse water tanks and plating baths to accept that volume, which as 

discussed above is not feasible in most cases. However, if one wanted to try this methodology and 

assuming that it could happen there are chemical concerns of an even greater concern than evaporation 

costs.

Plating lines collect and generate a large amount of chemical species that are detrimental to its continued 

operation. For a line to operate these chemical “species” (aka waste products) must be controlled and 

removed from the lines chemical systems on a consistent basis, which can pose significant 

technological challenges.

The following is a list of some of the waste products and adverse chemicals that would be introduced 

and accumulated into a plating line during operation if all water was continuously returned to the line. 

1. Cleaner chemistry: Na, K, OH, silicates, phosphates carbonates, sequestering agents, 

surfactants, contaminants (oil + grease from work flow);

2. Acid chemistry: Cl, SO4, nitrates, perchlorates, peroxides, metal alloying constituents(Cd, Pb, 

Si, P, Co, Ni, Cu, Zn, Cr, As, Sb, Bi, C, Mo, and a myriad of others), the base metals of the 

work (typically Al, Cu, Zn Fe, Ni, Cr, Co, Ag, Pb and a myriad off others) organic contaminants 

from the metals being pickled i.e. brazes, weld spatter, fluxes, oxidizers added to the acid baths 

(permanganate, potassium peroxymonosulfate, peroxide and others), organic 

inhibitors(petroleum products, complex organic molecules) and depolarizers;

3. Electroplating baths: The main metal being deposited from the bath will be dragged out of the 

bath on product along with its associated anion and chelators in use to adjust deposition 

potentials. This opens the list of metals to most transition metals in addition to a long list of 

anions from the simple(Cl, SO4, CN) to complex carboxylic acids, EDTA, amines, aromatic 

ringed compounds etc. In addition most plating systems contain a number of proprietary organic 

additives to modify the deposit properties from brightness, to ductility, to density, to hardness, 

to throw etc. These compounds not only exist but decompose into a plethora of innumerable 

sub-products of unknown composition.

To remove the list of chemicals discussed above, analyze the return water for their presence, and control 

their concentration is an enormous chemical, electro-chemical and technological challenge. A 

complete list of the “advanced” systems discussed above, and then some, would have to be applied to the 

line to continuously remove these contaminants. The plating baths would be the hardest hit as 

contaminant levels increased within their chemical systems. It would take a short time until the deposits 

from these baths would deteriorate to the point that the plated product would be rejects (waste) and the 

baths would have to be replaced (waste).

To remove this list of contaminants and achieve zero discharge, an extensive combination of technologies 

would be required, including IX, ED, RO, ultra-micro and nano filtration, carbon absorption, acid 

sorption, dialysis, lipophilic filtration, electro-winning and systems to reduce the oxidizer concentration. 

The cost of implementing such systems is beyond the reach of most metal finishing facilities. The 

operational costs of staff and maintenance are staggering. The irony of implementing all of these systems

in the name of zero discharge is that the process of removing the waste products creates their own 

waste!! The waste on the finishing line does not come out at the end of the system as an Foo6 waste 

water treatment sludge, but from individual units such as, brine, anode sludge, spent carbon, spent

solutions, water unusable due to high TDS, etc. 
A small number of metal finishing facilities have achieved zero water discharge. The success of these 

operations is a function of facility design (new construction is preferable over retrofitting existing 

operations), type of plating processes (generally fewer different types of plating processes are better), 

commitment and availability of capital resources, and geography (warmer climates may allow for some 

passive evaporation). Unfortunately, the success of zero water discharge is not readily transferrable to 

most metal finishing operations due to economic and technological feasibility or logistics at existing 

facilities.