Pollution Control and Resource Recovery for PC Plating Shops

Robert M. Burford, Consuitant, RMB Mfg. Co., 30 W. Lancaster Ave., Downingtown, PA 19335. (215) 269-6910

ABSTRACT

A review of present day regulations of EPA covering plating waste water and sludge disposal.

Detailed discussion of various waste streams and methods reconi- mended for recovery or reduction of waste losses and sludge generation.

A review of latest technology and equipment available for heavy metals removai from amiioniated and other chelated process chemicals. Reverse Osiimsis, Evaporation, ion Exchange arid electrodialysis are discussed a s recovery methods.

Ecomonic considerations are reviewed i n designiny a waste treatment and pollution control facility f o r pc plating shops. Particular emphasis is placed on water saving methods fcr rinsing needs and savings of up to 90% in water usage shown.

OVERVIEW

o having plating operations are r'aced with the cal, state and federal pollution control

lluticn control equipment is quite costly an6 the operation of these systems can add substantial costs to operating budgets. Proper planning of the pollution control system can zid

inciude recovery of yaluable metals, reduction of ~

educing operatiiig costs. ce recovery qust be included in the program.

To achieve optimum operating Resouxce,

megat ti on and water reuse.

Because most printed circuit shops have small process tanks and employ a wide variety of highly chelated chemicals, particulaf care must Be exercised in adopting resource recovery methods.

I.

EPA REGULATIONS

Surface water discharges are covered under the program identified as the National Pollutant Eischarge Elimination System (NPDES). Each plater must have a NPDES permit to be a legal operation. Platers discharging to sewers are covered by the Publicly Owned Treatment Works (POTW) pretreatment regulations. All platers must comply with the Resource Conservation and RecGvery Act ( R C m ) regulations. RCRA regulations ucveyn +ha = : - - - - - - L - -

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2 Fourth INTERNATIONAL PRINTED CIRCUITS CONFERENCE

All of these regulations require understanding on the part of the plating shop operators. In general, the cjoverment rules prohibit discharge of heavy metals and other related materials above certain specified limits. These limits are shown in charts in the appendix (Table I through Tabla VI.

Present rtgulations adopted are scheduled to be in effectnation- ally by October, 1982.

Platers should be planning arid budgeting their pollution control programs for adoption within the next few months to meet this schedule;

REVIEW OF PLATING FACILITY

The volume of water used in plating is the major factor used in design of a pollution control system. The xain objective of the facility review shall be to obtain accurate infornation sn all water needs for plating and identify the contamination levels.

The recoinmerlded first step for facility review is the preparation of a tank layout of the plating facility. Tile tank layout should show the volume and size of each tank to scale, with identification

-

5 of the chemical content, or product, in each tank.

Next, a flow diagram should overlay the tank laycut to reveal if the work flow is progressive and efficient throagh the existizg plating facility. If criss-crossing and back-tracking occur, strong coiisideraticn must be given to smoothing the work flow.

Xaving identified the total watzr volwne used in plating, it is necessary to define exactly how and where this waier vo lume is baing used. The water usage for each tank should be noted on a tank layout overlay.

The two overlays shall provide a good basis for making revisions in your plating facility that will result in more efficient work niovement and better water usage. Zowever, in those areas where water usage may still be excessive, it may be desirable to coiisider one or more of tile following means for reduction of water:

A. t!k!mWe r f l o w ' r i n s i h g (addition of rinse tanks) B. -ewbrestrictors c . s b&is~se~ *( I n termi t ten t )

Use of item listed above can reduce water needs by 50% or more, in many cases.

Having listed all. the chemicals 3r products in each tank we now must classify them. The first classification quickly adopted by platers is the recovery of valuable chemicals - such as gold from.go1d plating solutions. Silver from photcgraphic processes is also worthy of recovery.

3

For waete treatment considerations we nead to know which chemicals are duiiped as concentrated cr strong chemicals. We need to kilow the volume, concentration and frequency of Each duiip. Ke also nee5 to knov the chemical composition Gf such wastes. If the material is proprietary, then the chaTical supplier is required to reveal its composition or recommend a proper method for safe and efficieat disposal a s a waste.

Strong chemicals are treated separately or slowly added to the rinse water waste streams for disposal. Many strong chemiczls offer recovery opportunities that should be considered. For example: tions. sewer. These are considered to be "closed lsop" system and are highly rccomnended to pc platers.

Chemical companies will cften reclaim copper etch solu- Many such processes m e designed ss that no waste goes to

Acid dips alsc cac be recovered by removing the copper by ion- exchange cr crystallization. Approximately 80% sf the acid is reused thus lowering acid purchasss arid saving cost of neutral- izing chmicals while putting copper ir, a fcrm where recovery of the metal is feasible.

Sorre electroless plating baths also lend themselves to metals recovery and to recovery cf chelating chemicals.

Copper carried over into rinse waters c2n also 5e recovered u s i n g ds for closed loo? rinsing.

All of the above ry Kiethods, plus others aot specified, should be considered during the design phase of a pollution control program.

The cost - payback evclluition on each recovery system must not ignorc the ever-rising ccst of sLudge disposal. It is expected that as EFA defines proper disposal methods, sludge disposal costs will be the largest single c o s t in your pollution control program. Therefore, any payback evaluation of six years or less is 2 very wcrthy candidate for acceptance in your pollution control program today.

Special care must also be given when evaluating payback 02 recovery system to the ease cr difficulty cf postponed adoption. For example, if counterflow rinses are nezded as a part of a recovery system, but you decide to postpcne adoption of thc system to lower capital zxpenditures, you are then faced wikh a potential larger cost in the future so that the extra tanks can be included. In cases like this, the extra tanks should be put in, or space left fo r them i2 the plating room design.

Having gathcred the facts and evaluated the possibilities, yc?u may now adopt your plating room tank laycut. include a l l auxilliary equipment such as filters, rectifiers, etching machines, deburring machines, pcllution control equipment, recovcry equipment, chemical storage, etc. all in true scale.

A proper layout should

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Fourth 1HTERNATK)IWL PAINTED CIRCUITS CONFERENCE 4

DESIGN OF POLLUTION CONTROL SYSTEM

Now you hava your plating room layout completed. The first step in your polluticn control prograq io to. isolate the plmbing an& &b2ageh~fsa?..deaeh "closed lcopl' system.

,I

- Gold - All rinse waters shculd circulate through a gold recovery chamber. Gold filter is also a closed loop. Recsvery: filter cartridges and ion-zxchange cartridges are processed for go12 recovery. Recovery can be dcne "in house" or with a trusted supplier who will faithfully account for all gold processed and charge a reasonable fce for such service.

No water to sewer.

Silver - Photographic: The silver contained in scrap film and in some photo chemicals can be reclaimed by companies whc specislize in this work f o r hospital X-rays and other large users of phcto silver. equipment for "in house" recovery of photo- graphic silver. Platinq: In small systenis the most cost effective recovery is the use of counterflow rinsing. silver recovery. icn-exchange cartridges can be processed for silver recovery either "in house" or by outside contractors.

PC platers may purchase

Ion-exchange can also bc used for The filter cartridges and

Nickel - Electroless: Electrcless nickel is a highly chelated material. Rinse waters ccntaining this solution must receive a treatment suited to releasing the ccmplexed nickel. This will require a drainage line to an area suited to this type chemical treatment. troless nickel solution shall be placed in a separate holding tank for special handling. Watts Nickel: Rinses from this tank may go directly to neutralization and precipitation. Filter cartridges used on the Watts nickel are disposed of as scrap nickel. Most pc nickel plating operations are too small to consider nickel recovery. (Wood's) should be treated as a complexed metal in the waste treatment system.

Copper - Mechanical: There are several sources of valuable copper to be recovered after mechanical treatment in the pc shop. Ali scrap from lamina- tions shall be saved f o r copper recovery. routing and drill wastes shall be saved for copper recovery. The water used in deburring or brushing operations shall be filtered an2 reused as a

The spent elec-

The sulfaxiate nickel bath

All

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5

Copper (Continued)

water to waste trcaLment or sewer. cartridges containing copper are disposed of with scrap copper as a solid waste.

Filter

Chmical - Elsctroless: All rinses f r o m electroless copper must go tc thc special trea"Jnent required to break metal complexes. must be collected in a scparate holding tank for special handling.

The spent electroless copper

Chemical - Acid: plating tank may 50 directly to neutralization and precipitation for trea+aent. used on Acid Copper tank can be disposed of as scrap copper.

Rinses from the a c i d copper - Filter cartridges

Recovery: percentage of copper in the wastc materials, recovery bezomzs a feasible ccnsideration due to:a) of copper andjb) reduction of sludge waste. This will be discussed later in this paper.

Eecausc pc plating shops have such a high

the value

Tin-Lead Tin-Lead plating is carried o u t normally in a fluzl- boric acid scjlution to promote soldering operations. The rinse waters and strip solutions f o r tin-lead are disposed of in the neut ra l iza t ion-prec ip i ta t iof i system.

Activators, Catalysts and Others: Some of the remzining solutions m a y have complexing agents, most will not. Where possible, complexing agents should be avoided. One popular bath in FC shops is Ammonium Pcrsulfate plus Sulfuric Acid. This can be substituted with Iiydrogen Peroxide and Sulfuric Acid which offers G

copper recovery opportunity and avoids one complex- ing agent.

Disposal of the concentrate baths shall be directed t o the holding tank. The rinse waters from these tanks shall go to waste treatment for complexed chemicals as a safety measure.

Photo Resist & Strip Screening: ALL PHOTO RESIST SQLUTIONS AND STRIPPERS MUST 3E DISPOSED OF IN SEPARATE TREATMENT SYSTEM. cals will foul waste treatment system.

Photo resist. and strip-,ing chemi- pumps and piping in ii conventional.

.Solvent System: trichlor developer and methylene chloride with alcohol as the stripper. and fume scrubbers will provide a closed loop,

These system frequently use 1.1.1

U s e of distillation stills

leaving still 11boftnmc81 Fn+- 2 : -----l

Fourth INTERNATIONAL PAINTED ClRCUlTS CONFERENCE

Semi-Aqueous System: developer with a solvent fcr stripping. The solvent can be recovered in a solvent recovery still.

These systems use carbonate

Aqueous System: of high pH. of the caustic-potash will resillt in a cjelat/inoua mass that may be disposed of to incinerator. The water will have high BOD 2nd should 50 directly to sewer, by-passing normal waste treatment.

This is a caustic-potash stripper Once loaded with resist, neutralizatiQn

Average rinse tank size - 50 gallons.

A. CLEANING AYD PREP LINE (5000 sq. ft./8 hrs.)

P,sOCESS

1. Alkaline Cleaner 2 . Rinse

4 . Rime

6. Rinse 7. 13% HC1 8. Post Activation

- 3 . APS & H2SO4

5. 10% H2S04

9. Electroless Copper 10. Rinse 11. Electroless Copper 12. Rinse

1 4 . Rime 13. 10% H2S04

CISBOSAL

Holding Tank Treatment System Holding Tank Treatment System Acid Recovery Copper/Water Recovery Holding Tank Izolding Tank Special Treatment System Special Treatmerit System Acid Rscovery Copper/Water Recovery

B.

C.

Estinated Rinse to Waste Treatmect - 6 GPM COPPER PLATING LINE (After cleaning)

PROCESS

1. Rinse 2 . Copper Plate (CUSO~) 3 . Rime 4 . 10% H2SO4 5 . Rinse

D I S POSPL

Copper/Water Recovery NONE (filtration) Copper/Water Recovery Acid Recovery Copperfiater Recovery

Estimated Rinse to. Waste Treatment - NOKE

THROUGH HOLE PLATING & TIN-LEAD (TWO Lines)

PROCESS

'1. Acid Clean 2 . Rinse 3 . APS/HzSO4*

CISPOSAL

Holding Tank Treatment System Holding Tank

7

I I

i C. THROUGH HOLE PLATING & TIN-LEAE ( C o n t i n u e d )

4 . R i n s e * Treatment System 5. 1 0 % H2SO4 A c i d R e c o v e r y 6 . R i n s e C o p p e r / W a ter R e c o v e r y 7. C o p p e r P l a t e ( C u S O 4 ) NONE ( F i l t r a t i o n ) 8. R i n s e C o p p e r / W a t e r R e c o v e r y 9. C o p p e r P l a t e ( C u S 0 4 ) NOXE ( F i l t r a t i o z )

1 0 . P r e - D i p (HBF4) H o l d i n g Tank 11. R i n s e Treatment System 1 2 . T i n - L e a d P l a t i n g

NONE 13 . R i n s e T r sa tmen t Sys tern

E s t i m a t e s R h s e t o Waste Treztmcnt - 8 GPM (Two l i n e s )

D. TAB PLATING - P C PLATING SHOP

PROCESS DISPOSAL 1 A.

2. 3 . 4 . 5. 6. ?. 8 .

Tin-Lead S t r i p R i n s e 1 0 % H2S04 R i n s e N i c k e l P l a t e R i n s e G c l d P l a t e R i n s e

Est imated R i n s e

F i g u r e 1

F i g u r e 2

Hold ing T a n k T r e a t m e p t System A c i d R e c o v e r y C o p p e r / W a t e r R e c o v e r y NOXE ( F i l t r a t i o n ) T r e a t m e n t System NONE ( F i l t r a t i o n ) Separate R e c o v e r y

t o Waste Treatment - 1 0 GPM

WORK FLOW PLATING ROSM LAYOUT

A C I D RECOVERY PLATING ROOM LAYOUT

F i g u r e 3 101:-EXCHANGE RECOVERY UNIT

F igure 4 COPPER/WATER RECOVERY UNIT

F igu re 5 VC RECOVERY UNIT

PLATING ROOM U Y O ' J T

F igure 6' HOLDING TANK & WASTE TFCEATMENT

F igure 7 HY-BOY TREATMENT U N I T F igu re S SET-L-FLOC C L A R I F I E R F igure 9 LEAF PILTER/SLUDGE DEWATER F igu re 16 "AQUA-LOOP" DESALINATTON PLANT

.

EFFLUENT P A W T E R S img/L) Comments Phosphorus i P ) 2

F ~ ~ r t h INTERNATIONAL PRINTED CIRCUITS CONFERENCE

Metal c o n c e n t r a t i o n s are based on a n a l y s i s of ac id i f i ed s o l u t i o n s , expressed i n t o t a l metal c o n t e n t .

t TABLE i. D I R E C T DiSCHARGE EFFLUENT CONCENTRATION L i M I T S I

FOR R I M E WATER FLOW OF 89 L/m2 OPERATION*

r y a n i d e , T o t a l

luoride luminum admium hromium, cr+6 hromium, C r T

ead icicel i i v e r

1 0 . 6 0 . 1 i Soluble and

Suspended Sol ids 1 2 1 1 1 2 1

40

U n i t s are l i t e rs p e r s q u a r e meter of work p r o c e s s e d per o p e r a t i o n .

I

I

I

1-day max. 4-day avg. Cyanide, amenable t o

c h l o r i n a t i o n 5 .0 2.4 Lead 0.6 0.4 Cadmium 1.2 0.7

a

September 7 , 197

TABLE 11. SMALL PLANT PRETREATMEEiT STANDAFUS (mg/L)

LESS THAN 38,060 L il0,OOO gai.)/CZLLENUAR DAY

t

TABLE 111. LARGE PLANT PREYREATMXNT STILf-DAKDS img/L>

MORE TXAN 3 6 , 0 0 0 Ljday ( 1 0 , 0 0 0 ga l . /dayj I barmeter 1-day max. 4-day avq.

1.9 l . G 4.5 2.7

4.2 2.6

1.2 0.7 1.2 0.7

10.5 6.8

n iae , T o t a l

4.i 2.7 7.0 4.0

0.6 0 . 4

o m i u m , T o t a l

(CU, Ni, Zn & Crj

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TABLE V. MASS DISCHARGE PKETHEAI'MENT STANUARDS

Fourth INTERNATIWAL PRINTED ClRCUrrS CONFERENCE

September 7, 1379

TABLE IV. uPTiONAL PitETKEA'I'MENT S'I'ANDARDS (mg/L)

1-day max. 4-day avg.

0.6 0.4 ,ead 1.2 0.7 ladmiurn

'otai suspended soiids 20.0 13.4 H 7.5-10.0

:yanfde, Total 1.9 1.r

tipulations: NO ~ r + ~ , no strong chelating agents, iime neutralization.

Parameter 4-day avg. Max. 1 day yanide, Total OPPer ickel hromium, Total Zinc ' ead admiurn iiver otal Metals i (Cut Ni, Zn & Cr)

39 105 10G 156 102 16 29

267

29

74 176 160 273 164 23 47 410

4 7

ECONOMIC CONSIDERATIONS

The first capital consideration will be the changes required in your existing placing facility to optimize the pollution control and recovery program. depend on the status of his plating operations at the time the pollution control evaiuation becomes necessary. ‘need few or no changes in his shop. changes in the shop.

These costs will vary with each piater and

Some platers may Others may require major

11

The adoption of weter-savirrg devibes as listed earlier is gener- ally a low oost project and usually will not exceed $5,008 or &&O,OO$. For platers using city water and sewers, this cost can be recovered within a few months of operation. Lower flow rates will also reduce capital costs on pollution control or recovery equipment. You, therefore, benefit: two ways by saving water.

in the Example Layout you will note that there are three ( 3 ) piping systems used to isolate various waters and chemicals. In

, a shop of this type the piping system will cost approximately $20,000. Some platers will do their own drain piping and reduce this cost by as mucn as one half. You will also note that a collection sump is needed in some systems. Each sump represents a cost of approximately $1,000.

CHEMICAL DESTRUCT SYSTEM

A large percentage of platers, in order to conserve capital, will use only a chemical destruct system initially, and later add methods of acid and water recovery as economics justify these expeditures. Using the Example Layout and an estimated total water flow of 60 GPM, the chemical destruct system is made up of:

Sump Pumps ana Transfer Pumps Cnemicai Treatment Tanks & Mixers Chemical Feed Tanks and Controis Clarifier, filter press & polishing filter

This equipment will cost approximately $L30,000. Operating costs will include labor for two shifts of operation and chemicals totalling approximately $3&,0001per year. Sludge generation will amount to as much as l O G to 200 ibs per day of 40% solids using the hydrated lime treatment, and cost $50 to $100 per drum for landfilLor other disposal.

Smaller pc shops, presently operating at 10 GPM ‘ W O O 0 GPDj for a single shift operation can, by careful planning of water use, r ~ ~ , , . 2 & Q a ; . . . ~ ~ ~ 1 l o n s , pem day. This amount of water allows the plater to adopt a batch treatment system. A batch treatment of 2000 gailons will consist of:

sump rumps Treatment Tank with Mixer

12 Fourth INTERNATIONAL PRINTED CIRCUITS CONFERENCE

pH Indicator with Chem-Feed Pumps Work Platform, Centriiuge or tiravity Filter

This equipment can be purchased r'or approximately $20,060. Operating costs will inciude labor and cnemicais totailing approx- imately $12,000 per year. Sludge generation will approximate 25 gallons per day of 8-i2% solids with disposal cost of $50--.to Si00 per drum.

For small pc shops using batch treatment, recovery methods are not cost effective and tnerefore are not normally recommended.

RECOVERY METHODS

GOLU

SILVEK

NICKEL

COPPER

As earlier described, gold is an obvious candidate for recovery. The two most popular methods are ion- exchange and electrowinning. Gold rinse tanks are usuaily smail and flow rates of water iow. Cost or gold recovery equipment is approximately $5,000 and recovery of costs occurs in the first 3 to 6 months of operation as a rule. Cost for gold recovery is higher if an outside contractor is used to carry out recovery work.

Photographic. Photographic silver can be recovered by purchase of equipment suited to this purpose. 'rhe approximate cost of such equipment is $iO,OOO and will generally pay for itself within one year of operation.

Nickel is used in snail qunatitles by most pc piaters. The amounts lost to waste are also small. Aithougn there are severai metnods of recovery avaiiabie, there is no cost-effectiveness to nickel recovery.

It is not unusuai for a large pc plating shop to generate as much as 2G lbs. of copper per day in waste waters. Over a year of operation, this can amount to abouc 5000 lbs. of copper per year. This amount of copper however, translates into ,4 . i8QG0 lbs. of sludge per year. This converts to approximateiy Si5,OOO per year in present day sludge disposal costs. *rhus, ir: copper can be recovered the savings can become

$i5,000 in siudge disposal 5,600 in copper value

$ZO,OOO P138

Associated with copper recovery wili be the recovery of acid and rinse wacer. Assuming an annual value of $;5,G00 savings for each of these items we now have annual savings oi approximateiy $30,000.

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I 13

4

When a. water savings occurs, total water usage is reduced, thus lowering the flow of waste water pctssing througn the chemical aestruct treatment piant. copper, acid and water recovery are programmed into initial design the total flow can be reduced from 60 t i P M to approximately 30 GPM as shown on the Example Layout.

If

A chemical destruction plant sized for 36 GPM will cost approximateiy $iOO,OOO, resuiting in a net capital savings of $30,000 to be applied toward recovery equip- ment.

The cos t of recovery equipment for copper acid and some water will be as follows:

Acid Recovery unit (ion-exchange) $ 3 0 , 0 0 0 Copper/Water Recovery (evaporatorj ioo,ooo

(and eiectrowinning) 5,000 $ 135,000

The evaporator selected is a "low energy" unit. working 8

On the vapor recompression principle. These units utilize l/iOth the energy normaliy associated with conventional vacuum evaporators.

The estimated annual operating costs of the units listed will be $iO,OOO/'yr. based on the fact that they are f u l l y automdtic and run on continuous cycle.

The ~l..cost-efr'tactiveness of copper recuvery from a 50GO square feet per 8 hours plating operation will be :

aquipment COSK $ i35,OOO -30,000

Net cost difference $ 105,000 --- iess capital savings

OPh'RA'I'ING COST SAVINGS (Chem-Destruct)

less "necwery Casts -1?, OCO/yr. Net Savings $ 20,COO/yr.

$ 30,OOS/yi-.

/

The payback therefore, will be,S305,600 ciivided ;Oy S a 4 x Q - e G --5.,-25 years+

Taking into consideration that siudge disposal. costs wili probably increase in the next five years and copper will increase in vaiue as well a s capital equipment costs, this looks iike a very attractive investment at this time.

14 Fourth INTERNATIONAL PRINTED CIRCUITS CONFERENCE

TIN-LEAD & ACTIVATORSjCATALYSTS will riot offer any cost-effective recovery opportunities at this time. be combined with Nickel and other wastes not recovered.

These was$es to

i 3 T C H I N G S O i U T l O N S

Most chemical suppliers and most suppliers of etcn machines nave recovery processes available through counterfiow rinsing and otner methods. Since these units represent a "closecl loop" they are strongly recom- mended to pc shop operators. Cooperation with the chemical supplier wiil provide you with a recovery credit and eliminate a disposai problem.

UEBURRING & BRUSHING

Equipment suppliers or' duburring and brushing machines frequently offer a "closed loop" water reuse system. These systems include a good quality micro-filter that traps copper particies and reuses the water. This water is never dumped. This is a highly recommended step to take for each of your deburring/brusning machines.

PHOTO RESIST & STRIP SCREENING

As much as possible this waste shall be treated as a batch if an aqueous solucion is useci. Tne aqueous solution can be treated to cause the photo resist to coagulate and be removed as a solid waste for iaciner- ation. The rentairling water is then neutraiized and discnarged directly to sewer, by-passing the chemical destruct treatment unit.

For solvent type systems, the solvents shall be recov- ered in a distillation unit or sent to a soivent reprocessor.

The cost of either type treatment equipment will be approximately $lG,OOO.

WATER K E U S E

The ultimate savings will be the reuse of water after heavy metals removal in chemical destruction systems.

Water discharged from the chemical destruct system can be reused in your plating line without further treat- ment. However, continued reuse of such water wili build salt content to an unacceptable ievel. Therefore, by using desalinizing equipment on a "side stream" basis, salt can be Continuniis iv rnmn.rrn i l 2 n ~ 1 --I-----:

PC '81, JUIW~-4, 1981, Naw YO&, NY

There are several acceptable methods of desalinizing sucn as:

Reverse Osmosis Ion-Exchange Evaporation

Or' these R-0 appears most acceptable because it can run on a continuous basis, does not require frequent back- washing and is a low energy system.

For a 30 GPM system such as shown in the Example Layout, the following equipment:

5000 gallon storage Water Pump syscem k-0 uesal Unit...

wouid cost approximately S50,OCO and recovery approx- imately 85% of the water.

For critical rinsing operation the R-0 unit can provide high purity water.

, The cost-effectiveness of water reuse is determined by the cost of water at your location. If you pay $3Q,QoO per year for use of 6 . 5 miilion gallons per year, your water reuse investment can have a payback Q . L . J . ~ ~ ~ years.

rf you also pay a surcharge in addition to your water biil, your payback can be more rapid.

There are other recovery methods available that have not been discussed in detail. Yhis review is offered to show pc platers some of the opportunities available for masource recovery as reiated to poilution control.

15