## 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 th at the

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

4 13 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 rule making ? Does it make sense to deal with these issues at the national level? Examples:

a. Cleaning vs Etching

– already covered by ELGs

b. P hosphoric acid cleaning vs chemical conversion coating (phosphating)

-- already covered by ELGs

c. Powder Coating

– not cover ed 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 proces s 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 poll utants 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 p lating 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. alternativ es 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 ofpotentially toxic pollutants. NASF can provide additional information on specific technologies, if appropria te

. 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 wate r use. In 2006 EPA Sector Strategies P

rogram reported that industry reduced releases to air and water by 58% over period of 1994 to 2003. See detailed response s to this section provided below.

5. Are POTWs receiving pollutants from metal finishing facilities that interfere with their operations or pass through? PO TWs 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 guideline s be crafted to incentivize that? See detailed response provided below.

7. What types of wastewater treatment technolog ies are being installed /operated in metal finishing facilitie s beyond the BPT technology, define d 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 , e lectrodeposition , and electrocoagulation

c. R everse osmosis (and other membrane technologies)

d. New ch emicals 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 d emographics, economics, and potential sub categorization of the metal finishing industry. This industry includes many small entities that might struggle to afford advanced wastewater treatment installati ons. 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 in formation about this industry orto identify facilities and scope of their operations? How is generation of wastewater

related to f

acility size? A re large facilities p roducing most of the pollutants in metal finishing wastewater ? NASF has provided EPA wi th 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 ha ve 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 p ermits 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 a rea? 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 environ mental footprint and potential long

- term liabilities.

11. Are there air pollution control technologie s that generate wastewater that is commingled and subsequently discharge d 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

o perations of the metal f

i nishing 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 consumpt ion 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 mainta in 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 pa rameters. 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 ine rt 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 conti nuous 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 rac king 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 har dwood 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 st reams 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 c hromium 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 s ludge;

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 retu rn. 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 e specially 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 properl y 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

alte rnate 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 typical ly 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 inspectionh) Place parts in sy stem 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; i t 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

1 2. 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+/gallon2. 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 syste m 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, i f 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 prohibi tive”*

*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 app ly 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

th rough 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 agi tated. 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% d epending 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 concentra tion 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. Sinc e 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 minimization3. 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 chemistrie s 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 t oward 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 analyt es.

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 v ery 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

- EDTA

Na + Ni+2 = (R

- EDTA) 2Ni + 2Na), it has a poor selectivity in the presence of Cu+2 or Pb+2 ions. Thusif those 2 metals were present as in a line designed to plate on 360 brass the resin would b e 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). T hus 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 neutra lized 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 concentra tion 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 N i to be at 2.38 ppm on a 30 day average to discharge. Therefore, something still has to be done w ith 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 insta ll 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 t he liquid outfall

flow...NOTHING!

3. Transferred the nick el 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 econo mically 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 alterna tive 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.

P lating 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 ch emical systems on a co nsistent 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 re turned 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 constit uents(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 spat ter, 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 f rom 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, S O4, 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 a n enormous chemical, electro

- che mical 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 hard est 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 (w aste).

T o 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, el ectro

- winning and systems to reduce the oxidizer concentration.

The cost of implementing such systems is beyond the reach of most metal finishing facilit ies . 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 remov ing the waste products create s 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 i ndividual 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 ma y 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.