Evaluation of New and Emerging Waste-Managemel Technologies in the Metal Finishing Industry

~ ~~-

By J.D. Dietz

an operating metal finishing facility disqualified nologies that were not sufficiently developed.

Limited field sampling and analysis were perf0 three processes: buoyant media filtration," ze discharge,h and distillation solvent recovery.'

Buoyant Media Filtration Buoyant media filtration refers to a granular-b process. Liquid passes in an upflow mode throu with a density lower than that Of the filtrate. The held in place just below the liquid surface by a screen. Backwash of the filter isachieved by reve flow and subsequent fluidization of the media.

Test samples were obtained from full-scale operating facilities using three technologies-buoyant media filtration for clarification purposes, zero liquid discharge for electroplating wastewaters, and distillation solvent recovery for the small user. Limited field sampling and analysis indicate that all have the potential for greater use in pollution control.

nactment of federal legislation has resulted in the implementation of extensive pollution-control programs in the metal finishing industry. Effluent E limitations have been established for a number of

toxic metals (Cd. Cr, Cu, Pb, Ni, Ag, Zn), cyanide, total toxic organics (TTO), oil and grease, total suspended solids (TSS), and pH.

Although the effluent standards are based on application of 4 specific technology, the discharger has the option of selecting an alternative method of treatment. New processes for the treatment of finishing wastes and/or the

devel oped. This report represents a cooperative effort between the

U.S. EPA and the AESF. The principal objectives were to identify and evaluate new technologies in waste manage- ment. Attention was directed toward methods with the potential for treating effluent and residual solids. In some cases, the technologies incorporated a novel modification to conventional precipitation. Only new and emerging technologies were eligible for participation in the field characterization phase of the research. Also, the requirement for completing field sampling and analysis at

recovery of valuable wastewater components have been RETAINING SCREEN

BACKWASH VALVE

'Macrospheres, system developed by 3M, St. Paul, MN. 'ZLD. system developed by Zerpol Gorp, Hatfield, PA. 'System developed by Recyclene Products, San Francisco, CA. Fig. 1-Schematic diagram of buoyant media filter.

62 PLATING AND SURFACE FI

~

ualified tech- 1.

performed for I," zero liquid

r-bed filtration ,rc*;? a medid !. The media 1s by a retaining ' reversal of the &ia. This floh

7

.UENT WEIR

E R E D WATER 7AGE

4 I N I N G SCREEN

VANT MEDIA 1 t o 3.0 mp1 n i l

,ersal is easily achieved by withdrawing fluid by gravity ,,,the bottom of the filter (Fig. 1). rhe media utilized in this study is composed of very all, hollow beads. The shell of these beads consists of IIOW glass spheres held together with a phenolic resin &r. The spheres have diameters of 0.3 to 6 mm; xtures of any Size range are available. The sphere faces are very rough compared with alternative filter dia (e& sand). )otential applications of the technology include: effluent ilshing following conventional clarification, replacement conventional clarification, and modification of con- ,tlonal clarification to include a buoyant mediafilter at surface of an existing clarifier. full-scale buoyant media filter has been operating

lodical rod eoriginal mr ed )espite flow equalization, the influent composition and

were quite variable due to the frequent batch dis- trges of solutions from the production lines. Concurrent ?ration of all three production lines was not common. sause suspension of operation between shifts was Itlne, intermittent flow to the waste-treatment facility was 3erienced. The treatment system encompasses: equalization, (2) pumping at 60 gal/min, (3) chromium uction at pH 2.5 and an ORP of 280 mV, (4) neutralization/ tclpitation at pH 9, (5) flocculation with a polymer

'he filter was piped in parallel with a slant-tube clarifier. xlbility was provided for loading the filter with floc- ated wastewater or effluent from the clarifier. During the npling program, the clarifier was loaded at 60 gal/min 5gal/min/ft2) when the filter was not in use. The filter was oloaded at 1.5 gal/min/ft' (40 gal/min) while receiving a rtlon of the total flow. The filter bed had a cross-sectional haof 26.5 ft' with a media depth of 12 in. Valves to permit pass of either unit allowed independent field testing of

clarifier and filter. A backwash flow rate of 17.4 1 min/ft' was employed, representing a total backwash ume of 7.5 gal/ft2. Theresults of grab sampling for influent, clarifier effluent, 3 filter effluent are summarized in Table 1. These data iresent a cumulative statistical analysis for the 71 grab nples collected over a four-day period. Several analyses rota1 chromium were not incorporated in the statistical mmary because temporary problems were encountered :h the chromium reduction system. Evaluation of per- 'mance under such conditions would probably not be Xesentative due to excessive levels of soluble chromium. 3ased on the grab samples, it is apparent that con- lerable variation w x eAperienced in both influent and 'dent concentrations. The grab sample data were t!tstically evaluated to determine whether the reported "erences in effluent concentration between the filter and arlfler were significant. The clarifier appeared to suffer a :re Pronounced variation in effluent quality than the filter Oiew of the greater standard deviation of effluent values. . ;difference was determined to be significant for Zn, P, ?and Cr. The average and maximum effluent concentra- :nSwere also normally greater during operation with the a'lfier. This difference was determined to be significant 'Zn and Cr. Testing of the clarifier and filter was not

~~~~~ ~

(6) sedimentation, and (7) filtration.

'rm 727, American Colloid. Skokie, IL.

conducted with side-by-side experimental units receiving identical wastewater inputs; each unit was tested sequentially.

Advantages and Limitations The buoyant media filter in operation was demonstrated to be a viable alternative to the existing slant-tube clarifier. Both systems were capable of removing particulate metal hydroxide precipitates to the required effluent standards for this application. Removal of soluble materials was negligible; therefore, compliance would depend on the success of preceding chemical reduction and precipitation p _ r o c e s ~ s , I h F ? ~ h a r ~ i s t i ~ of &be Buoyan~wdia fitter ~ ~

were similar in this respect to the conventional system. Analysis of numerous grab samples over the extended

eriod i r compared with the slant-tube clarifier. This

observation is significant in view of the highly variable nature of the wastewaters at this particular metal finishing operation. Numerous batch dumps of cleaning or plating solutions were experienced throughout an operating day. A radical variation in influent wastewater characteristics was noted, with an extreme variation in solids and hydraulic loading on the two solids/liquid separation systems. The demonstrated stability of the filter under these conditions is an important advantage.

Removal of soluble metal species was not expected during a physical operation such as gravitational sedimentation or filtration. This process limitation was documented. Adding buoyant media filtration to an existing system would not appreciably improve performance in those instances in which the principal metal species remaining after chemical precipitation was not in a particulate form.

Zero Liquid Discharge The zero-liquid-discharge (ZLD) process recycles treated effluent as rinsewater. High-purity rinsewater is produced by condensation of steam generated by a boiler receiving treated rinsewaters as feed. Residual salts and solids are removed from the system as boiler blowdown and metal hydroxide sludge, respectively. These streams are removed by contract hauling and disposal.

Chemical treatment of the rinsewaters is conducted in a batch mode, with sequential treatment in a single reactor for cyanide oxidation, chromium reduction, metal hydroxide precipitation, and sedimentation. Certain restrictions are imposed on the selection of reagents employed for chemical treatment in order to reduce the input of dissolved species to the recovery loop of the system. Hydrogen peroxide is used for the oxidation of cyanide in lieu of the conventional chlorine compounds, which would result in unacceptable levels of chloride in the system. Sodium hydrosulfite is used for chromium re- duction because a pH near neutral (5 to 8 ) is effective. This eliminates the requirement for adding large quantities of salts for reducing the pH to optimum levels for reaction with bisulfite salts or sulfur dioxide. Precipitation of the metal species is achieved by adding sodium hydroxide. Sodium salts are better than calcium salts for avoiding scaling problems in the boiler.

The ZLD system is characterized by large tank volumes to accommodate batch treatment. A simplified schematic diagram of the process is provided in Fig. 2. Al l influent wastewaters are collected in one of the two batch reaction tanks. A treatment cycle is initiated when the capacity of

one of the tanks is exhausted. The tanks are designed to hold the entire wastewater flow for three days. Influent wastewaters are diverted to the alternate tank during a batch-treatment cycle. Oils are skimmed from the surface and collected in a chamber between the two batch- treatment tanks.

After chemical treatment for cyanide oxidation, chro- mium reduction, and hydroxide precipitation, the pre- cipitated solids are allowed to settle overnight in the batch reactor. Settling aids are not normally used. Supernatant is withdrawn and retained as makeup for the rinsing opera- tion. This supernatant is stored in the clear-water storage tank.

The precipitated solids are removed from the batch reactor and transferred to a gravity thickener. The thickener has sufficient capacity to permit withdrawal and disposal of sludge on an infrequent basis. The facilities surveyed disposed of sludge from the thickeners at intervals of two to six months.

A portion of the effluent (approximately one-third the flow) from the batch-treatment process is directed to a boiler for steam production. The remaining batch effluent (two-thirds of flow) is used directly as rinsewater. The steam is used throughout the plant for various process applications such as heating hot water rinses and plating

solutions, and evaporating water from collected 11 blowdown

The input concentration of.dissolved salts to the boll extremely high (several tholtsand mg/L). This level off in a boiler feed would be 'f general concern if precaur and safeguards were no. mployed to control thechen composition of the boiler feed stream. Specifically, a c concentration (several mg/L) of residual cyanic purposely left in the effluent from the batch-treatii process. This residual cyanide acts as an oxygen scaverr inhibiting corrosion of boilersurfaces. Additional chemi (e g , chromium) may be added to the boiler feecc necessary to prevent scaling and to assure proper br function Nominal residual quantities of chromium (seu mg/L) may be desirable after batch treatment for reason

Salts are removed from the system periodically as bl blowdown Thickening and evaporation of the blowdl stream is achieved in a separate tank from which Sal$! removed several times a year.

A source of makeup water is required to compensatii the water evaporated from the plating solutionsand for removed from the process via the disposal of sludge salts. The presence of small amounts of calcium Or nl nesium in the raw water source may result ill

PLATING AND SURFACE FIN~S

i'

64

ation of these ions to objectionable levels.

0 the extended hydraulic detention in treatment components, successful water conservation and uction are essential factors for the attainment of a

ere taken at three facilities. Although the flows at these installations were less than ay, implementation of strict water-conserva- s in conjunction with installation of the ZLD

drained pieces, so dragout was minimal. w- W w a p f e e w e & *

of finishing processes, including cadmium, zinc, and silver (barrel and rack) plating; passivation of

gram was approximately 2500 gal/day. ng and Wire Co., acaptive plating operation in rrel plates zinc and cadmium on steel, nickel

an abnormally high concentration of . A small leak in a heating coil in one of

tive levels of copper, cyanide and TDS the system (Le., influent, effluent, condensate, blowdown). The cyanide concentrations, in

tal concentrations after batch treatment values permissible for discharge. The

recycled for rinsing purposes, the critical te to the maintenance of acceptable product

heating coil leaked.

nide was somewhat greater than the company xperienced, but the treated effluent and

e levels were consistent with objectives to Corrosion effects. I t is apparent from the n of data on dissolved solids that the boiler

optimal at the time condensate grab ed. Considerably smaller values for

Due to the presence of high residual metal concen- trations, the treated effluent and condensate quality would not be compatible with discharge options. As previously noted, the appropriate concern is related to possible effects on product quality. Satisfactory product quality was maintained during the sampling program with these corresponding characteristics for rinsewater makeup sources.

The results for James Spring and Wire indicate a more dilute raw wastewater, reflecting relatively greater water use than at the other facilities. Dragout was relatively low, also, due to the ease with which the pieces in the barrel lines could be drained. I t was immediately apparent from the datathat little metal was removed during batch treatment. A definitive explanation for this observation was not available almough a sofids/liquid separation problem was suspected due to an elevated suspended-solids concentration. Also, the possibility of non-representative sampling cannot be Zf iMated.

The reported data for cyanide were consistent with the objective of retaining a residual throughout the steam loop to minimize corrosion. The condensate quality (as indexed by TDS) was much better at James Spring and Wire than at the other facilities. The treated effluent quality was not compatible with discharge. Satisfactory product quality was reported during the sampling period while using rinsewaters with the reported characteristics.

ZLD: Pros and Cons The obvious advantage of a ZLD system is compliance with present and future effluent regulations (including those for TTO). Protection of receiving' waters and publicly owned treatment works (POTW) is assured in spite of process upsets, accidental releases, or unanticipated variations in influent wastewater composition. For example, a leak in a heating coil resulted in an excessive cyanide concentration

RINSEWATER CLEAR WATER

STORAGE

BLOWDOWN

STORAGE BOILER SALTS

DISPOSAL

I CONDENSER "$~$~:' I-, RINSEWATER

Fig. 2-Schematic diagram of zero-liquid-discharge system.

987 65

in the wastewater at Pioneer Metal Finishing, but there was no liquid discharge of cyanide although elevated levels were reported in the sludge and blowdown. Security and stability were cited by the companies as principal reasons for selecting the ZLD system.

Because the process is conducted in a batch mode, existing personnel can be assigned to operate the wastewater treatment system at convenient times and without significant interruption of prior duties. This advantage would be shared by all batch processes with comparable cycle times. The manpower commitments were reported to vary from 2 to 5 hr/week/shift for each facility. Periodic monitoring of condensate quality must be performed throughout boiler operation to maintain the quality of the rinsewater source.

The extended detention that is available from the large tank volumes affords some flexibility in timing of treatment

operations. Each reaction tank is large enough to contam all flows for at least a three-day period. This allows timefoi adjusting chemical doses, repairing and maintaining equipment, and troubleshooting, when necessary. The extended detention provides the operator with more than one opportunity to identify an optimum chemical dose thereby avoiding overdoses.

Several important constraints that would restrict apgk cation of theZLD system were identified. Certain chemicals were not compatible with the boiler. This constraint may require abandonment of these compounds in plating and cleaning solutions. Boiler feed chemicalscould conceivably mitigate the foaming problem, but, again, may restrict thm selection of plating or cleaning compounds.

The success of the ZLD system requires recirculation 01 treated effluent and condensate as rinsewater makeup This practice did- not impair product quality at the three

66 _- PLATING AND SURFACE FINISHIN(

cilities surveycc Tsewater sour ,eration. The IH I the reused w a lanyfinishing ai f a continuous; he variability in: erformance \hi

perations in wt- Because the p)

$10 discharge, ecessary. Succ: eatment procct eeded for oper.. ?mporary malfi. ause an inferrii torage of conc. lterruption (se dverse conseqll The economii

'eduction in flovl 0 accommodat W e tank capal Mas prudent to Toses and subs

Buildup of sal Wh product qu cyanide oxidatit \he high cost of content of the Stantial decline %lout by add Or drainage of pi In the process Removal of calc

also neces:

Distillation SO olstiilation of '"dustry for seF

"q1L 1987

L

igh to contain allows time for I maintaining xessary. The iith more than hemical dose,

restrict appli- tain chemicals onstraint may in plating and Id conceivably lay restrict the

?circulation of jater makeup. :y at the three

FACE FINISHING

acilities surveyed. Specifications for the quality of the ,n%water source must be evaluated for each plating eration. The level of dissolved salts and other impurities nthe reused water streams would not be compatible with nanyfinishing activities. In these cases, auxiliary treatment fl a continuous makeup water stream may be essential. rhevariability in condensate quality due to irregular boiler Srformance would also be a concern for finishing )perations in which high-quality rinsewaters are essential. Because the process depends on water reuse to achieve

discharge, careful attention to a water balance is Ecessary. Successful operation of the boiler and batch- reatment process is imperative to generate the water ieeded for operation of metal finishing production lines. A emporary malfunction of the treatment system should not ruse an interruption in production due to the available itorage of condensate and treated effluent. A prolonged nterruption (several days) of the water supply may have idverse consequences on production.

The economics of ihe process dictate a substantial !eduction in flow. The treatment system had little flexibility to accommodate flows in excess of design values due to linite tank capacities. A minimum batch cycle of two days was prudent to allow for proper identification of chemical doses and subsequent separation of solids and liquids.

Buildup of salts in the system also resulted in difficulties with product quality. Consequently, peroxide was used for cyanide oxidation instead of chlorine compounds. Due to Ihe high cost of peroxide, all efforts to reduce the cyanide content of the raw wastewater corresponded to a sub- stantial decline in treatment costs. Measures to reduce dragout by adding counterflow rinses, improving racking Or drainage of pieces, and reducing cyanide concentrations

the process solutions were desirable in this regard. Removal of calcium and magnesium from makeup waters was also necessary to maintain boiler function.

htillation Solvent Recovery Distillation of organics is widespread in the chemical mdustry for separating various compounds. The recovery

'RlL 1987

of valuable solvents by distillation is also practiced; however, substantial volumes of spent solvent are normally required to justify the expense of development and operation.

A small-scale batch-distillation unit for recovering solvents with a boiling point of less than 205" C (400" F) was introduced in 1981. The apparatus contains a heating element, a condenser, and a storage reservoir for recovered solvent. An innovative feature is that residue from the distillation operation is recovered in a nylon or Teflon bag, which can be removed easily from the boiler in much the same manner as a liner is removed from a garbage can. The residual material remaining after distillation is thus packaged for final disposal. The system has been installed in a variety of industries to recover solvents such as Freon, trichloroethylene, 1,1,1 -trichloroethane, naphtha, methyl ethyl ketone, toluene, and lacquer thinner.

The units are available with capacities of 14 to 35 gal/batch. A continuous-feed model with a capacity of 20 gal/hr was recently introduced. The limited capacity provides small generators an economical alternative for recovery, thereby reducing the costs for the purchase of virgin solvent and the treatment and disposal of spent material. All unitsare rated in accordance with the National Fire Protection Association's Class I, Div. 1, Group D, environment.

The W.A. Parsons Co., Durham, CT, is engaged in the fabrication of various sheet-metal pieces. Operations include painting and curing processes. A 14-gal distillation unit was used to recover a solvent blend containing 20 percent toluol, 20 percent butanol, 15 percent ethylene glycol mono ethyl ether acetate (cellosolve acetate), and 45 percent naphtha. Generation rates of spent solvent did not exceed 100 galhonth.

A closed-loop cooling system (Fig. 3) was installed to reduce water requirements. The unit required a flow of 20 gal/hr, a maximum temperature of 27" C (80" F), and a water pressure of 10 to 110 psi. The power requirements were 110 V ac, 60 Hz at 8 A.

The spent solvent was collected in a drum until a

67

Representatives of W.A. Parsons Co. indicated that recovered and virgin solvents yielded satisfactory resul

Two-Year Payback The economic features of the solvent recovery system quite attractive in light of the reported payback perio two years. Another significant advantage of the process reduction in the volume of hazardous materials for dispc Recovery and reuse of these organic compound definitely preferable to disposal from the standpoin environmental contamination and consumption of

Some technical complications preclude the use of tb systems for applications that would require temperat1 greater than 205O C f400" F). S e p " nf cacapou with similar boiling points could not be expected I

sufficient amount was available to warrant operation of the recovery unit. The batch operation included a 12-hr distillation cycle followed by a cooling period of several hours. A turnaround of 1 batchlday was feasible. A selected summary of the data is presented in Table 5. The reported values represent three batch cycles.

The composition of the recovered solvent generally approximated that of the virgin and spent solvents. A nominal systematic increase in the percentage of cellosolve acetate at the expense of toluol and butanol was observed.

SPENT SOLVENT

I RECYCLENE U N I T

SINK

REUSE

Fig. 3-Process flowsheet of distlilatlon solvent recovery.

68

Summary and Recommendations Three technologies for the management of wastes in finishing industry wereevaluated with limited field samp and analysis. Evaluation of the processes in the spel application selected for study may not provide suffic information to assess applicability in all segments of industry, although the information developed through type of program provides a starting point for the gen evaluation of any new or emerging technology.

The buoyant media filtration system was effectivi place of a clarifier. Extended studies to evaluate mc durability and size, as well as alternate backwash pract (frequency, duration, and hydraulic loading), would beneficial.

The development of a complete material and ent balance for the zero-liquid-discharge process wc require an extended presence. A detailed examinatiol identify energy requirements for boiler operat throughout the summer and winter would be desirabl full characterization of the boiler function and waterqur of the condensate cannot be established on the basisof limited sampling effort in this study. Completion (

material balance would also require consideration of slu and salts production over a compositing period responding to the characterization duration of the infll and reuse streams.

Long-term operating data would be required to ass maintenance and repair costs for the solvent distilla unit. Such data were not readily available due to the SI history of operation.

Acknowledgments The financial support of the US. EPA under Contract( 810787-01-0 and the AESF is gratefully acknowledged. analytical work was performed by Christopher M. Chern a graduate student at the University of Central Florida.

About the Author Dr. John D. Dietr is an assistant professor in the Civil Engineering and Environmental Sciences Dept., University Of

Central Florida, P.O. Box 25000, Orlando, FL 32816. His ted and research interests are in municipal and industrial waste management. Dr. Dietz holds degrees in civil and environmer engineering from the University of Illinois and Clemson, andl registered professional engineer in Florida and Mississippi.

PLATING AND SURFACE FINIS^

/ /

11

11

-

Evaluation of New and Emerging Waste-Manage! Technologies in the Metal Finishing Industrl

By J.D. Dietz

Test samples were obtained from full-scale operating facilities using three technologies-buoyant media filtration for clarification purposes, zero liquid discharge for electroplating wastewaters, and distillation solvent recovery for the small user. Limited field sampling and analysis indicate that all have the potential for greater use in pollution control.

three processes: buoyant media- filtration,A ZE discharge,h and distillation solvent recovery.'

Buoyant Media Filtration Buoyant media filtration refers to a granular-bedl process. Liquid passes in an upflow mode througll with a density lower than that of the filtrate. The! held in place just below the liquid surface by a I I

screen. Backwash of the filter is achieved by rever flow and subsequent fluidization of the media. TI

nactment of federal legislation has resulted in the implementation of extensive pollution-control programs in the metal finishing industry. Effluent limitations have been established for a number of

toxic metals (Cd, Cr, Cu, Pb, Ni, Ag, Zn), cyanide, total toxic organics (TTO), oil and grease, total suspended solids (TSS), and pH.

Although the effluent standards are based on application of E? specific technology, the discharger has the option of selecting an alternative method of treatment. New processes for the treatment of finishing wastes and/or the recovery of valuable wastewater components have been developed.

This report represents a cooperative effort between the U.S. EPA and the AESF. The principal objectives were to identify and evaluate new technologies in waste manage- mwt . Attention was directed toward methods with the potential for treating effluent and residual solids. In some cases, the technologies incorporated a novel modification to conventional precipitation. Only new and emerging technologies were eligible for participation in the field characterization phase of the research. Also, the requirement for completing field sampling and analysis at

"Macrospheres. system developed by 3M, St. Paul, MN. hZLD, system developed bv ZerDol CorD.. Hatfield. PA.

INFLUENT

EFFLUENT WEIFJ

FILTERED WATEi STORAGE

, RETAINING SCR!

1 BUOYANT MEDIA i (0.4 t o 3.0 mr'

'System developed by Recyclene Products. San Francisco, CA.

62 PLATING AND SURFACE FI

Fig. 1-Schematic diagram of buayant media filter.

:ollected boiler

s to the boiler IS

his level of salts n if precautions rol the chemica cifically, a sma!’ ual cyanide IS

)atch-treatmen: jgen scavenger : i ~ ~ a i chemica:s boiler feed a5

re proper boiler wmium (severd atment for thl5

ldically as bel!?' f the blowdow” I which salts arc

,ccumulation of these ions to objectionable levels. Due to the presence of high residual metal concen- ;onsequentlY, a water-softening System is essential for trations, the treated effluent and condensate quality would ,,iOtaining proper boiler function if the source water is not be compatible with discharge options. As previously lard Due to the extended hydraulic detention in treatmen!

p m components, SUCCeSSfUl Water conservation and reduction are essential factors for the attainment of a

r L ~ condition. Samples were taken at three facilities. Although the

,astewater flows at these installations were less than 0,000 gal/day, implementation of strict water-conserva- on measures in conjunction with installation of the ZLD ,rO~ess reduced the flow almost 90 percent. 1 , NJ, is a J O ~ S ~ I O P ,eallng primarily in decorative plating of copper, nickel and hromium on zinc, brass, steel and cast iron. The major

BCk plating well-drained pieces, so dragout was minimal. he observed flow was 10,000 gallday for a two-shift peration. plate-Rite Co., Folcroft, PA, is a jobshop engaged in a

ariety of finishing processes, including cadmium, zinc, opper and silver (barrel and rack) plating; passivation of IalnleSS and corrosion-resistant steel; zinc and manganese

phating; black oxide coating; and chemical conversion eating on aluminum. The wastewater flow during the ampling program was approximately 2500 gal/day. JamesSpring and Wire Co., acaptive plating operation in

faer, PA, barrel plates zinc and cadmium on steel, nickel nd copper alloy. The wastewater contained large ,uantities of oil by comparison with the other facilities urveyed. The estimated daily flow was 4500 gal. The results of the analysisfor the composite samples are

lven in Tables 2-4. The sampling results for Pioneer Metal ,nishing indicated an abnormally high concentration of epper and cyanide. A small leak in a heating coil in one of l e copper plating baths was discovered after sample Jlection was concluded. This anomaly produced non- ;,xesentative levels of copper, cyanide and TDS voughout the system (i.e., influent, effluent, condensate, i d boiler blowdown). The cyanide concentrations, in articular, exceeded target values for both treated effluent nd condensate. The residual metal concentrations after batch treatment

id not approach values permissible for discharge. The Jality of the condensate would also preclude discharge Je to cyanide and copper contamination. Because these ‘reams are recycled for rinsing purposes, the critical 3ncerns relate to the maintenance of acceptable product dality rather than compliance with an environmental ‘andard. Satisfactory product quality was maintained oen the heating coil leaked.

performance data from Plate-Rite closely resembled %red operating conditions. The reported value for “hent cyanide was somewhat greater than the company Jrmally experienced, but the treated effluent and :ndensate levels were consistent with objectives to

-fi lmlze corrosion effects. It is apparent from the ’lamination of data on dissolved solids that the boiler .’flOrmance was not optimal at the time condensate grab LtWleS were collected. Considerably smaller values for 3s would be anticipated during ideal boiler operation.

)lhether the reported data were representative of boiler *hnance or indicative of a temporary upset with an asociated loss of solids in the steam output cannot be *ermined.

’* 7w7

. . . . .

n e - &

noted, the appropriate concern is related to possible effects on product quality. Satisfactory product quality was maintained during the sampling program with these corresponding characteristics for rinsewater makeup sources.

The results for James Spring and Wire indicate a more dilute raw wastewater, reflecting relatively greater water use than at the other facilities. Dragout was relatively low, also, due to the ease with which the pieces in the barrel lines could be drained. It was immediately apparent from the data that little metal was removed during batch treatment. A definitive explanation for this observation was not available

the possibility of non-representative sampling cannot be eliminated.

The reported data for cyanide were consistent with the objective of retaining a residual throughout the steam loop to minimize corrosion. The condensate quality (as indexed by TDS) was much better at James Spring and Wire than at the other facilities. The treated effluent quality was not compatible with discharge. Satisfactory product quality was reported during the sampling period while using rinsewaters with the reported characteristics.

ZLD: Pros and Cons The obvious advantage of a ZLD system is compliance with present and future effluent regulations (including those for TTO). Protection of receiving waters and publicly owned treatment works (POTW) is assured in spite of process upsets, accidental releases, or unanticipated variations in influent wastewater composition. For example, a leak in a heating coil resulted in an excessive cyanide concentration

SLURRY TANK 8 TANK TANK A

I

BLOWDOWN

STORAGE Z BOILER + SALTS

r--l I I . DISPOSAL

PROCESS

CONDENSER ‘ONDENSATE STORAGE RINSEWATER

Fig. 2-Schematic diagram of zero-liquid-discharge system.