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# OAR Box 1158 Prepped by RyanDugan



# Document

Number: 

# 65 ) ll-A- 9 Docket Number: 

# A-88-0 2

Printed 4/28/2008 2:34:14

PM Sheet 65of 349

# »EP A Unite d State s inv.ironme.nta l Protectio n Agenc y Technolog yTransfe r EPA/625/5-85/01 6 Septembe r198 5 Revise d 

## P. 2 

# Environmenta l Pollutio n £T? 2 

# Contro l Alternative s Reducin g Wate rPollutio n Contro l Cost s i n th e Electroplatin g Industw HjjjjSJLJi J JA N 

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Technolog yTransfe r EPA/625/5-85/0 1 ( 

# Environmenta l Pollutio n Contro l Alternative s Reducin g Wate rPollutio n Contro l Cost s i n th e Electroplatin g Industry

Septembe r1985

Thi s repor twa s prepare d jointl yb y Industria l Technolog yOivisio n Offic e o fWate rRegulation s an d Standard s Offic e o fWate r Washington , D C 2046 0 an d Cente rfo rEnvironmenta l Researc h Informatio n Offic e o fResearc h Progra m Managemen t Offic e o fResearc h an d Developmen t Cincinnati , O H 4526 8



# Z -P. 4

Cyanid e wast e Causti c - i Acid- i Causti c

Chrom e wast e

Acid/alkal i wast e 

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... V•>•_«_ •£La.- 

## ^|SS^^_" J *W7' . •.-_. . !a*%yt:J-'.'..."ir: Polyme r 

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# n •••S&i W 

# f l
Wastewate r discharg e

Neutralizatio n precipitatio n Rocculatio n

Averagin g Filte rcak

e .^ ^ t o approve d disposa l Sludg e thickenin g

Filtratio n Rgur e 1 . Conventiona l Wastewate rTreatmen tSyste m fo rElectroplatin g 

## Capita l Cost

s Th e uni tprocesse s show n i n Figur e 1 ar e use d extensivel yi n th e electroplatin g industry , an d a s a resul tthei rdesig n ha s becom e somewha tstandard
. Th e abilit yt o standardiz e ha s reduce d th e hig h cos to fsit e preparatio n an d constructio n throug h th e developmen to fskidmounte d packag e systems , complet e wit h al l hardwar e an d auxiliaries
. Installatio n cost s fo rpackag e system s usuall y rang e betwee n 1 0 an d 3 0 percen to f th e purchas e pric e ofth e equipmen t compare d wit h installatio n cost s o f 5 0 t o 10 0 percen to fpurchas e pric e fo rcomponen tsystems . Th e cost s presente d i n th e followin g section s assum e th e purchas e o fal l component s o fth e individua l systems . Cost s coul d b e reduce d b y usin g existin g pumps , tanks , an d instrumentation , bu tthes e ar e rarel y available
. Installatio n cost s wil l increas e a s a resul to fsite-specifi c requirement s relate d t o wastewate r collectio n systems , ne wbuildin g space , structura l modifications , o r th e relocatio n o fexistin g equipment
. Wastewate rCollection . Wastewate r fro m individua l platin g operation s mus tb e directe d t o th e appropriat e treatmen tcomponents , whic h ofte n entail s separat e wastewate r collectio n system s fo rchromium , cyanide , an d acid/alkal i wastes . Typically , a collectio n pip e syste m i s installe d paralle l t o th e platin g lin e s o tha tspen trins e water s ca n b e draine d t o on e o rmor e treatmen t sumps . Equipmen twashdow n an d spille d material s ar e collecte d i n a trenc h whic h als o lead s t o th e appropriat e sump . Th e treatmen t sum p i s equippe d wit h a level -P. 5

controlle d pum p tha t deliver s th e wastewate rt o th e treatmen t unit . I n addition , som e provisio n mus t b e mad e fo rcollectin g th e stron g cleanin g an d platin g chemica l solution s whic h ar e usuall yble d a t a slow , constan t rat e int o th e treatmen t syste m b ywa yofa n averagin g tan k

t o avoi d upsettin g th e process . Wastewate rcollectio n cost s ar e highl yvariable . Aplan t ma yhave t o provid e a s man ya s fiv e separat e collection/sum p system s t o handl e thre e differen t kind s o fwastewate r plu s spen t cyanid e an d noncyanid e chemica l solutions . Cost component s fo rwastewate r collectio n ar e give n i n Tabl e 3 . Large rsump s ar e use d fo rchromiu m an d cyanid e wastewate rcollection ; i n fact , th e sum p itsel fma yb e use d a s th e treatmen t vesse l (thi s practic e i s rare) . I t shoul d b e pointe d ou t tha t custom-mad e concret e sump s ar e considerabl ymor e expensiv e t o construc t tha n th e preforme d sump s indicate d i n Tabl e 3 .
Tabl e 3 . Cost s fo rWastewate rCollectio n Collectio n conduit: " Linea rruns : 4"-$1.50/f t 6"-$2J0/f t 4"-$200.0 0 6"-$350.0 0 4"-$200.0 0 6"-$300.0 0 Eac hconnection :
Eac hbend : Collectio n sumps: ' 10 0 gallon s ...$2,00 0 30 0 gallon s .. . $2,50 0 50 0 gallon s .. . $3,00 0 1,000gallon s .. . $3,50 0 °PV C pipe . "Preforme d PVC ingroun d tan k wit h sum p pump , leve l contro l an d stee l gratin g cover . 198 4 data . Chromiu m Reduction . Chromiu m i s usuall ypresen t i n electroplatin g wastewate ra s trivalen t cnromiu m (Cr +3 ) o ras hexavalen t chromiu m (Cr +$ ) . Althoug h mos t heavymetal s ar e precipitate d readil ya s insolubl e hydroxide s i n th e neutralizer , hexavalen t chromiu m mus t firs t b e reduce d t o trivalen t chromium . Reductio n i s usuall yachieve d b y reactio n wit h gaseou s sulfu rdioxid e (S0 2 ) o ra bisulfit e solutio n (NaHS0 3 ) . Usin g sodiu m metabisulfit e (Na 2 S 2 O s ) , th e net reactio n involve s chromi c aci d an d sulfuri c aci d i n th e formatio n o f sodiu m sulfate , chromiu m sulfate , an d water : 3Na 2 S 2 O s + 4H 2 Cr0 4+ 3Hs>S04- » 3Na 2 S0 4+ 2Cr 2 (S0 4 ) 3 + 7H 2 0 Becaus e th e reactio n proceed s rapidl ya t lo wpH , a n aci d i s adde d t o maintai n th e chromi c aci d wastewate rbetwee n a p H o f2 an d 3 . T o preven t th e releas e ofsulfu r dioxid e durin g th e reaction , maintainin g th e p H nea r3 i s advised . I n additio n t o th e us e ofsulfu r dioxid e o rbisulfite s t o reduc e hexavalen t chromium , ther e ar e thre e commerciall yavailabl e method s tha t us e th e reducin g potentia l o firo n and/o riro n salts . Ferrou s sulfat e reduce s hexavalen t chromiu m accordin g t o th e followin g equation : 3Fe + 2 + C r + 6 . 3Fe + 3 + C r + 3 Th e us e o firo n i n thi s for m add s considerabl yt o th e volum e o fsludg e produce d b yth e treatmen t system . Thi s metho d i s rarel yuse d excep t wher e a n effluen t ofhig h chromiu m conten t i s locate d clos e t o a chea p an d abundan t sourc e offerrou s salts , suc h a s wast e pickl e liquo rfro m a stee l mill . Ferrou s salt s ma yals o b e generate d b ya patente d proces s employin g a n electrolyti c cel l havin g iro n anode s an d iner t cathodes : 

### 3Fe ° + 6e " 3Fe + 2 A s th e iro n anode s ar e dissolve d i n th e process , the ymus t b e replace d wit h ne wones . Whil e thi s proces s wil l als o produc e substantia l quantitie s o fexces s sludge , i t provide s a convenien t metho d o f continuousl ytreatin g lo w concentrations o fhexavalen t chromium , suc h a s migh t b e foun d i n coolin g towe rblow-dow n water s o ri n rinse s fro m chromat e conversio n coatings . Wit h highe r chromiu m concentration s i t i s difficul t t o economicallyproduc e th e require d ferrou s io n concentration s o n a flow-throug h basis .P. 6



### s o r

20 30 4 0 FLO WRAT E (gal/min ) 50 6 0 Legend : _—•» - Tota l installe d cos t

- TM " " Hardwar e cos t

Notes : Batc h units : Installe d cos t = 2 xhardwar e cost . Uni t consist s o ftw o 4-hou rreactio n tanks wit h necessaryauxiliaries . Continuou s units : Installe d cost = 1.2 5 xhardwar e cost . Uni t consist s o fequipmen t show n i n Figure 1 .
Rgur e 2
. Investmen tCos tfo rChromiu m Reductio n Unit s
Iron , i n th e for m o fsmal l piece s o f scra p steel , ma yals o b e use d t o directl yreduc e hexavalen t chromium
. Thi s patente d proces s i s controlle d b yadjustin g th e p H ofth e influen taccordin g t o it s hexavalen t chromiu m content . Ap H o f2. 0 t o 2. 2 wil l usuall yaccommodat e chromiu m loading s a s hig h a s 20 0 t o 30 0 ppm . Lowe rp H setting s woul d b e require d t o trea thighe rchromiu m concentrations
. Th e followin g equatio n represent s th e reductio n mechanism : 

### Fe ° + C r + 6 

### Fe + 3

### + C r + 3 Becaus e th e iro n an d chromiu m

reac to n a one-to-on e basis , rathe r tha n a three-to-on e ratio , th e slud g _ produce d b ythi s proces s i s significantl yles s tha n tha tgenerate d i n th e othe rprocesse s usin g iron
. Th e lo wcos to fscra p stee l allow s thi s proces s t o compet e favorabl y wit h th e cos to fsulfu rdioxid e treatment , whil e eliminatin g th e potentia l o freleasin g hazardou s gas . Hardwar e an d installatio n cost s fro m package d continuou s an d batc h chromiu m reductio n unit s ar e show n i n Figur e 2
. Cost s includ e storag e an d fee d system s fo rth e treatmen t reagents , a s wel l a s th e cost s fo r hardware , piping , instrumentation , an d utilit yconnections
. Th e continuou s uni tcost s ar e base d o n usin g sodiu m metabisuifit e a s th e reducin g agen tan d a wastewate r retentio n volum e o f3 0 min
. Fo rver y smal l flows , simple ran d les s costl y batc h system s ar e feasible
. Th e batc h syste m cost s includ e tw o reactio n tank s eac h size d t o hol d 4 h o fwastewate rflo wan d equippe d wit h hig h leve l alarms , portabl e p H an d oxidatio n reductio n potentia l (ORP ) meters , a portabl e mixer , an d storag e tank s an d fee d pump s t o ad d sodiu m metabisuifit e an d sulfuri c aci d t o th e reactio n tanks
.P. 7



### Cyanid e Oxidation . Dilute cyanid e rins e stream s resultin g fro m platin g operation s an d cyanid e dips mus t also b e treated separatel yt o oxidiz e th e highl ytoxi c cyanide , first to les s toxi c cyanate , the n t o harmless bicarbonates an d nitrogen . Th e oxidizin g reagent i s usuall ychlorin e ga s (Cl 2

### ) o rsodiu m hypochlorit e (NaOCI) . Usin g chlorine , th e typica l reactio n i n th e first stag e involves sodiu m cyanid e (NaCN ) an d sodiu m hydroxid e (NaOH) : Cl 2 

### + NaC N + 2NaOH- + NaCN O + 2NaC I + H 2 

### 0 an d i n th e secon d stage : 3CI 2 

### + 2NaCN O + 5NaO H - * 6NaC I + C0 2 

### + N 2 

### + NaHC0 3 

### + 2H 2 

### 0 Whe n sodiu m hypochlorit e is used , th e typica l reactio n i n th e first stage is : NaOC I + NaC N - * NaCN O + NaC l an d i n th e secon d stage , 3NaOC I + 2NaCN O + H 2 

### 0- > 3NaC I + N 2 

### + 2NaHC0 3 

### I n mos t continuou s systems , i t is preferabl e t o conduc

t th e operation s i n two series-connected reactio n tank s rathe rtha n i n stage

s i n on e tank. I n th e first stage , th e p H i s adjusted betwee n 9 an d 1 1 usin g a n alkal i such a

s causti c soda o rlime . Th e p H i n th e secon d reactio n chambe ri s controlled t o approximatel y8.5 . Sodiu m hypochlorit

e i s added continuously t o bot h stages . Deman d i n eac h stag e is determined b

ymeasurin g ORP . Th e reactio n tim e needed is approximatel y3 0 t o 6 0 mi n i n eac h stage . Figur e 3 show s cos t curve s fo r continuou s an d manua l batc h cyanid e oxidatio n units . Th e continuou s uni t cos

t i s fo ra uni t whic h use

s sodiu m hypochlorit

e a s th e oxidizin g agent . Th e cos t include s storag e an d feed system s forth e treatmen t reagents . Th e batc h syste m cos

t i s fo ra syste m wit h two 4 h reactio n tank

s an d th e auxiliaries required t o ad d sodiu m hypochlorit e an d contro l pH . Again , fo rver

ysmal l flows , simple r an d les s costlybatc h system s ar e feasible . A

t wastewate rflowrates belo w2 0 gal/mi n (76 l/min ) batc h unit s appea rt o b

e mor e costeffectiv e tha n continuou s units .

50

40

o o o 53 0 t O < JrZ U J 5 t tn 2 0 U J 

### > Z

1 0

0 TM



### • ' ^^^ 

# Xl/"

^ ^ unit s ^ ^ 

# y^ ^ rlT *<? <T ^ 

### J ' ' // ** 

# y >

/^ Batc h unit s f 

### , ' 

# y s s

I I 

### i I I

1 0 2 0 3 0 40 5 0 FLO WRAT E (gal/min ) Legend : 

### , 1 •Tota l i .'stalle d cos t = • = = Hardwar e cos t

Notes : Batc h units : Installe d cost = 2 xhardwar e cost . Uni t consist s oftw o 4-hou rreactio n tanks wit h necessaryauxiliaries . Continuou s units : Installe d cost = 1.2 5 xhardwar e cost . Uni t consist s ofequipmen t show n i h Figure 1 . 

### Figur e 3 . Investment Cos

t fo rCyanide Oxidatio n Unit s 

## ( oP. 8

Neutralization/Precipitation . Wast e stream s fro m eac h o fth e variou s meta l cleanin g an d platin g operation s ar e combine d i n th e neutralize rwit h th e effluen tfro m th e chromiu m reductio n an d cyanid e oxidatio n units
. Becaus e th e heav y metal s ar e onl ysolubl e unde racidi c conditions , th e p H i s adjuste d t o a rang e o f9. 0 t o 9.5 , a twhic h th e metal s precipitat e a s hydroxides
. Afterth e p H i s adjusted , a smal l amoun t( 1 t o 5 mg/l ) o fa coagulatin g agen tsuc h a s aluminu m sulfate , ferrou s sulfate , o rcalciu m chlorid e i s adde d t o th e wastewate rt o facilitat e precipitation
. Man ytype s o fneutralizatio n system s ca n b e designe d wit h variou s degree s o fautomatio n an d controls , dependin g o n th e magnitud e an d variabilit yo fth e flo w an d it s pH
. Becaus e a chang e o f1 p H uni trepresent s a tenfol d chang e i n hydroge n io n concentratio n an d a hundredfol d chang e i n solubilit yfo r som e metals , maintainin g th e p H i n th e narro wrang e wher e maximu m remova l o fpollutant s i s realize d i s critical , thoug h difficult , especiall y whe n th e neutralize rfee d i s subjec t t o wid e variation
. Asingle-stage , continuou s neutralizer , i n whic h al l th e alkal i suc h a s lim e o rcausti csod a i s fe d int o a singl e reactio n vessel , i s suitabl e fo rmos telectroplatin g applications
. I fth e wastewate ri s subjec tt o rapi d change s i n flo wrat e o rpH , however , a multistag e neutralize ri s required
. I n th e multistag e units , mos to fth e alkal i i s adde d i n th e firs tvesse l t o increas e th e p H t o 6
. Fina l p H adjustment s o f th e wastewate rar e mad e i n th e remainin g reactio n vessel s t o promot e precipitatio n an d t o enhanc e th e settlin g characteristic s ofth e meta l hydroxides
. T o maintai n adequat e p H control , th e retentio n tim e fo rtypica l neutralizatio n i s 1 5 t o 3 0 min
. Th e efficien tus e o flim e require s a minimu m o f3 0 mi n becaus e lim e react s mor e slowl y tha n sodiu m hydroxide
. Figur e 4 show s hardwar e an d tota l installe d cost s fo ra continuou s neutralizatio n uni ttypicall yuse d i n th e electroplatin g industry
. Thi s uni t i s singl e stag e wit h pH-controlle d additio n o fcausti csod a an d sulfuri c acid
.

4 0

__ . 30 o

tn O 

### u 2 0

> z 1 0 Tota l installe d cos t

I I 2 0 4 0 6 0 FLO WRAT E (gal/min ) Notes : Installe d cost = 1.2 5 xhardwar e cost . Cost doe s not includ e flocculatio n system . 8 0 10 0

Figur e 4
. Investmen tCos tfo rContinuou s Single-Stag e Neutralization /

Precipitatio n Uni t



## 1

### Clarification . Meta l hydroxide s an d othe rinsolubl e pollutants ar e removed fro m th e wastewate rb y gravit ysettlin g and/o rfiltration . Th e remova l efficienc

ydepend s o n th e settlin g rat

e o fth e suspende

d solids i n th e wastewate rfeed . Typically , som e o fthese solid s settl e ver

y slowl ybecaus

e o fthei rsmal l siz

e an d thei rsligh t densit

ydifference compared wit h th e water . Becaus e a n economica l desig n ofth e clarifie r limits th e retentio n tim e i n th e settlin g chamber , som e leve l o f suspende

d solid s wil l appea ri n th e overflow .

6 0

5 0

S 4 0 o o t V) OINVESTMENTCTirotoO oo

0 

### -

i i

2 0 4 0 

### T o enhanc e th e settlin g characteristics o

fth e suspende

d solids , a flocculatin g agent , usually a n organi c polymer , is added i n a fiocculato rwhere th e wastewate ris agitated gentl yt o allowth e solid s t o agglomerate . Th e wastewate rthe n enter s th e clarifie rwhere th e solid s settl e out . Th e solid s i n th e underflo wcan b e discharged to a holdin g tan k

fo rsubsequent dewatering .

Tota l installe d cos t

^^r ^ Hardwar e cos t P. 9 1



### Th e optima l dose

s o fflocculatin g agents , hardware specifications , an d solid s remova l efficiencies ar e usuall yestimated base

d o n laborator ytests conducted b

yth e equipmen t vendor . Figur e 5 show s hardwar e an d tota l installed cost s fo r flocculatio n an d clarificatio n unit s typica l o fthose use

d i n th e industry . These cost

s ar e presented a

s a functio n o

fvolumetri c flowrate ; the y also reflec

t th e effec

t o n uni t cost

s o f solids-settlin g rates an d th e leve l o f solid s allowe d i n th e effluent . Th e unit s ar e assumed t o hav

e a separat

e flocculatio n tank , a polyme rfeed system , a "lamella " (o rslant-tube separator) , an d a zon e i n whic h sludg e collects befor

e bein g discharged . These units ar e mor e widel yuse

d tha n simple rrectangula r settlin g chambers .

Notes : Installe d cos t= 1.2 5 xhardwar e cost . Cos tinclude s plate-typ e clarifie rwit h flocculatin g l 1 1 l c h 6 0 8 0 10 0 12 0 FLO WRAT E (gal/min )

: 

### igur e 5 . Investment Cos t fo rFlocculation/Clarificatio n Unit s

1 0 ambe ran d polyme rfee d system . 

### :



# 8

.- J

## P.1 0

Manuall yshifte d low-pressur e recessed-plat e filte rpres s wit h capabilitie s fo rfillin g disposa l drum s directly
. Sludg e Handling . Th e solid s fro m clarifier s ar e typicall ydischarge d t o sludg e holdin g tank s a tsolid s concentration s o f0. 5 t o 3% ; overflo wfro m th e tan k i s recycle d t o th e clarifie ro rt o th e flocculatio n tank
. Usually , meta l hydroxid e solid s wil l concentrat e t o approximatel y3 t o 5 % solid s i n th e sludg e holdin g tank s i fsufficien tretentio n tim e i s allowed
. Th e tank s mus tals o provid e adequat e volum e t o stor e th e sludg e befor e i ti s shippe d t o a disposa l sit e o rtransferre d t o anothe rdewaterin g stage . Figur e 6 show s th e investmen t fo rsludg e holdin g tank s a s a functio n o ftan k

volume
. Furthe rconcentratio n o fth e thickene d sludg e require s th e us e o f mechanica l dewaterin g equipment
. Centrifuges , rotar yvacuu m filters , bel tfilters , an d filte rpresse s hav e bee n use d t o dewate rmeta l hydroxid e sludge
. Th e applicabilit y o fa particula rdewaterin g devic e fo r a specifi csludge , an d th e degre e o f cak e drynes s th e devic e wil l achieve , ca n b e determine d b ybench-scal e test s conducte d b yth e vendo rusin g th e intende d fee d material
. Figur e 7 present s th e uni tcost s fo r recesse d plat e filte rpresse s a s a functio n o fth e filter-cak e volum e o f th e unit
. Th e fee d volum e capacit yo f th e uni ti s als o given , base d o n a fee d solid s concentratio n o f2% , a cak e solid s concentratio n o f20% , an d a pres s cycl e o f8 h
. Th e cost s show n i n Figur e 7 d o no tinclud e installatio n o rauxiliar yequipmen t associate d wit h th e press , becaus e thes e cost s ar e highl yvariabl e an d site-specific
. Item s tha twil l contribut e t o th e cos to finstallatio n include :

•Hig h pressur e fee d pump(s ) (ofte n quote d an d supplie d wit h th e filter ) •Sludg e fee d storag e tank s •Filtrat e retur n line s (t o clarifier ) •Cake solid s handlin g equipment
.

1 1 

# qP.1 1

3 0

o o 

### 5 2 

### ° OT

. OINVESTMENTo

0 t

1 1 1 100 0 200 0 300 0

VOLUM E (gal ) Tota l investmen tcos t

Hardwar e cos t



### I I 400 0 500 0 Notes : Base d o n carbo n stee l construction . Cost s includ e fiber-reinforce d polyeste r tan k an d diaphrag m pump .
Rgur e 6 . Investmen t Cos t fo rSludg e Storage/Thickenin g Unit s

40 0

= 5 30 0ME(g D O > 20 0 U J _« _ 

### < c c H E 10 0

0 

### y / ' / / f Manua l



### " /

lll l 1 0 2 0 3 0 4 0

EQUIPMEN TCOS T($1,000 ) 

### / / / " Automati c

1 5 0 6 50 0

37 5gal/h)
2 250 - Z. —i O 

### > U l LL
. 12 5

D Notes :

Cos tinclude s carbo n stee l frame , poly propylen e plate s an d filte rcloths
. Installatio n cost s no tincluded
. Cak e volum e base d o n 1 V Vthic k sludg e cakes
. Fee d volum e capacit ybase d on : fee d solid s = 2% ; cak e solid s = 20% ; cycl e tim e = 8 hours
.
Figur e 7 . Hardwar e Cos t fo rRecesse d Plat e Filte rPresse s

1 2 

### \ 0P.1 2



## Operatin g Cost

s Althoug h th e investmen tcost s fo r conventiona l wastewate rtreatmen t system s depen d principall yo n wastewate rflo wrate , th e operatin g cost s depen d o n th e followin g factors :

•Sludg e disposa l an d municipa l sewe rfee s •Wastewate rtreatmen tchemica l cost s •Operatin g an d maintenanc e labo r cost s •Utilit ycost s (primaril yelectricit y t o operat e pump s an d agitators ) •Overhea d cost s an d depreciation
. O fthese , sludg e disposa l an d chemica l cost s offe rth e bes t opportunitie s fo rreducin g operatin g cost s sinc e labo ran d utilit y requirement s ar e usuall yfixed
. Th e cos tcomponent s o fthes e an d othe r operatin g cost s ar e describe d below ; Tabl e 4 show s th e assumption s fo r thes e evaluations
. Tabl e 4 . Basi s fo rEconomi cEvaluations 3 Basi s Annua l operating costs :

Operatin g labo r Supervisio n Maintenanc e Genera l plan t overhea d Depreciatio n (10-yea rstraigh t line ) Taxe s an d insuranc e Utilit ycharges :

Electricity Coolin g wate r(coolin g tower ) Stea m Ne t operating saving s ($/yr )
Ne t saving s afte rtaxe s ($/yr ) Retur n o n investmen t Cas h flo w($/yr ) Paybac k perio d (yr) $9/ h $12/ h 6 % ofinvestmen t 0.5 8 (operatin g + supervisory+ maintenanc e labor) ; maintenanc e labo r- 0.3 7 x(maintenanc e cost) 10 % o finvestmen t 1 %ofinvestmen t $0.08/kWh r $0.25/1,00 0 ga l $6.00/1,00 0 I b Operatin g cost reductio n resultin g fro m investmen t minu s increas e i n fixe d an d operating cost fo rne wsyste m Net operating saving s x0.5 4 (assume s 46 % ta xrate ) Ne t saving s afte rtaxe s * tota l installe d investmen t Ne t saving s afte rtaxe s + depreciatio n Tota l installe d investmen t + cas h flo w *N o interes t o n capita l i s include d i n th e economi c analyses .

1 3 

# wP.1 3

Sludg e Disposa l an d Municipa l Fees . Installatio n o fwastewate rtreatmen t system s result s i n th e discharg e o f tw o streams : overflo wfro m th e clarifie ran d sludg e fro m th e clarifie r o rdewaterin g equipment
. Th e cost s associate d wit h thes e discharge s ar e site-specific , an d depen d o n th e availabilit yo floca l disposa l site s t o receiv e th e sludg e an d o n municipa l sewe rcosts . Thes e cost s ar e expecte d t o escalat e i n th e futur e a s ne wregulation s ar e implemented
. Fo rth e overflo wfro m th e clarifier , typica l sewe rfee s fo ra majo rcit ya s presente d i n Tabl e 1 ar e $1.20/1,00 0 gal
. Figur e 8 show s th e direc t relationshi p o fwastewate rflo wrate s an d thes e sewe rfees
. Th e cos to fhaulin g th e sludg e t o a license d hazardou s wast e landfil l wil l depen d o n th e volum e o fsludge , th e distanc e hauled , an d th e sludg e composition
. I n mos tareas , th e cost s o fsludg e disposa l ar e currentl yi n th e rang e o f$.5 0 t o $1.00/gal , bu t ther e ar e case s wher e disposa l cost s ru n a s hig h a s $2.00/gal
. Figur e 9 show s th e annua l disposa l cost s fo r eac h 10 0 Ib
. (4 5 kg ) o fsolid s generate d dail yove ra rang e o f sludg e concentration s an d disposa l costs . Fo rexample , i f10 0 I b o fsolid s ar e generate d dail ya ta concentratio n o f6 % an d a ta disposa l cos to f$1.00/gal , th e annua l cos tfo rdisposa l wil l b e $60,00 0 (poin tAo n Figur e 9)
. Th e disposa l cos tsaving s achievabl e b ythickenin g ca n als o b e estimate d b yusin g Figur e 9 t o calculat e th e differenc e betwee n th e disposa l cost s a tth e presen tconcentratio n an d a tth e projecte d fina l concentratio n afte rthickening
. Fo r example , a plan tno wdispose s o f 10 0 Ib/ d (45. 4 kg/d ) o fdr ysolid s a s a sludg e wit h a concentratio n o f6 % solids
. Fro m Figur e 9 , th e disposa l cos to f10 0 Ib/ d a t$1.00/ga l woul d b e $60,00 0 pe ryear . I fa filte rpres s performanc e tes tpredict s a sludg e concentratio n o f25 % solids , sludg e disposa l cost s woul d decreas e t o $14,000
. Th e disposa l cost s save d a s a resul to fgreate rdewaterin g o fth e sludg e (fro m 6 t o 25 % solid s concentration ) woul d the n b e $46,00 0 ($60,00 0 minu s $14,000)
.

50

4 0(000($1-SEWERFEECOo

1 OT 8 2 0ANNUAL

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lll l 0 2 4 6 8

CLARIFIE R OVERFLO WRAT E (1.00 0 gal/h l Notes : Operatin g 480 0 h/yr . Sewe rfe e = $1.20/100 0 gal . Wate rus e fe e no t included . I 1 0

Figur e 8
. Annua l Sewe rFe e a s a Functio n o fClarifie rOverflo wRat e



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100 0 rr f 100

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J I I I 1 1 l l J — I I I J-i l $2.00/ga l sludg e disposa l cos t .$1.00/ga l sludg e disposa l cos t ,$0.60/ga l sludg e disposa l cos t

. 1 I I u l 0. 1 1. 0 1 0

CONCENTRATION SOLID S I N SLUDG E (wt% ) 10 0
Rgur e 9 . Annua l Cos tfo rDisposa l o fIndustria l Sludg e

(pe r10 0 I b dr ysolid s generate d pe rday )

Filte rpres s hoppe rwit h 40 % solid s filte rcake
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60 0

50 0000)($1 Z ^ U J 5 i — OT U J >

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100

0 —$2.00/ga l disposa l cos t

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_1 $1.00/ga l disposa l cos t 

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# " 1 f I / $0.50/ga l disposa l cos t 1 1 .____»

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5 1 0 1 5 2 0 2 5 30 CONCENTRATIO N O F DEWATERE D SLUDG E (% solids ) Notes : Assume s 10 0 lb/da ydrysolid s generated . Assume s 40 % RO I (pretax) . RO I = (disposa l cost saving s - fixe d cost ) + capita l investment . Fixe d cost include s depreciation , taxes . insuranc e an d maintenance . Utilit y an d labo rcosts not included . I n a 2 % solution , 10 0 I b solid s = 60 0 gal . 5 % = 23 2 gal . 10 % = 11 2 gal . 39 % = 3 2 gal .
Figur e 10 . Capita l Cos tJustificatio n fo rSludg e Dewaterin g Equipmen t
Mechanica l dewaterin g o fmeta l hydroxid e sludge s ca n achiev e solid s concentration s i n th e rang e o f 1 5 t o 50%
. Figur e 1 0 show s th e capita l investmen ttha tcoul d b e justifie d fo rdewaterin g equipmen t t o concentrat e a sludg e containin g onl y2 % solids
. Th e cos treductio n use d t o calculat e thi s retur n o n investmen t(ROI ) di d no ttak e int o accoun tvariabl e operatin g costs , suc h a s utilit ycost s an d operatin g labor , whic h fo rmechanica l dewaterin g device s coul d b e significant
. Thes e additiona l cost s woul d resul ti n a lowe rROI
. T o illustrat e th e investmen t justificatio n fo rth e mechanica l dewaterin g o fa dilut e sludge , assum e a plan tgeneratin g 10 0 Ib/ d o fdr ysolid s wa s abl e t o concentrat e it s sludg e fro m 2 t o 20 % solid s wit h a filte rpress . Th e annua l disposa l cos t woul d b e reduce d fro m $180,00 0 t o $16,00 0 base d o n a disposa l cos to f $1.00/ga l (Figur e 9)
. Th e maximu m capita l investmen tjustifie d t o achiev e thi s saving , usin g Figur e 10 , i s $270,000
. Figur e 7 show s th e cos t o ffilte rpresse s a s a functio n o fcak e voium e an d feed-processin g capacity
. Usin g th e feed-processin g capacity , th e pres s fee d rat e woul d equal : 1001 b solid s ga l sludg e 8.341 b xI b sludg e y

0.0 2 I b solid s d
_7 5 ga l sludg e

_ __ Fro m Figur e 7, th e minimu m siz e commercia l uni tcoul d dewate rthi s fee d rat e an d woul d cos t$16,000
. Assumin g th e tota l installe d cos to f th e syste m i s twic e th e pres s cost , o r $32,000 , th e RO I woul d b e wel l i n exces s o fth e 40 % use d a s a basi s fo r Figur e 10
.



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Wastewate rTreatmen t Chemica l Costs . Thes e chemica l cost s ar e dependen to n th e concentratio n o f pollutants , th e volumetri cflo wrat e o fth e wast e stream , an d th e type s o f chemical s chose n fo rwastewate r treatment . Becaus e th e additio n o f chemical s involve s a chemica l reactio n wit h th e pollutants , th e type s o ftreatmen tchemical s selecte d wil l produc e differen tus e rates , volume s o fsludg e fo r disposal , an d remova l efficiencies
. Eac h o fthes e factor s affec tth e operatin g cost s an d mus tb e considere d b yth e plater
. Commo n treatmen treagent s use d i n th e electroplatin g industr yar e sodiu m bisulfit e (NaHS0 3 ) fo r chromiu m reduction , sodiu m hypochlorit e (NaOCI ) fo rcyanid e oxidation , an d causti csod a fo r neutralization /

precipitation
. Thes e chemicals , an d th e chemica l cost s give n i n Tabl e 1 , wer e use d t o provid e th e cos tmode l fo r conventiona l wastewate rtreatmen t show n i n Figur e 11
. Thi s mode l enable s th e use rt o calculat e th e consumptio n o ftreatmen tchemical s (consumptio n factor ) an d th e associate d cos t(cos tfactor) , base d o n th e volumetri cflo wrat e o fth e wastewate rbein g treate d an d mas s flo wo feac h pollutant
. Th e sludg e disposa l cos tmode l (show n i n Figur e 12 ) ca n b e use d t o determin e th e dr ysolid s generate d b y precipitatio n o fth e heav ymetal s containe d i n th e wast e stream . Figur e 1 2 als o indicate s th e disposa l cos tfo reac h poun d o fmeta l precipitated , assumin g th e resultin g sludg e i s 20 % solid s an d th e disposa l cos ti s $1.00/gal
. Man ytreatmen tsystem s us e hydrate d lim e fo rneutralizatio n instea d o fsodiu m hydroxide ; som e system s us e sod a ash
. Th e selectio n o fneutralizatio n chemical s i s usuall y base d o n convenienc e an d price
. Th e choic e o fneutralizatio n reagen twil l affec tth e volum e o fsludg e generated , th e cost s o fsludg e disposal , an d th e investmen tcos tfo r storag e an d handlin g fo reac h chemical
. Acos tcompariso n o fth e variou s neutralizin g reagent s i s show n i n Tabl e 5
. Lim e requirement s an d chemica l an d sludg e disposa l cost s ca n b e estimate d usin g th e mode l i n Figur e 13 , whic h i s simila r t o th e model s develope d i n Figure s 1 1 an d 1 2 fo rcausti cneutralization
. Th e cos tmodel s i n Figure s 11,12 , an d 1 3 ca n b e use d t o determin e th e incrementa l cost s associate d wit h removin g eac h poun d o fpollutan t an d treatin g eac h gallo n o f wastewate renterin g th e system . Thes e model s ca n als o b e use d t o predic tth e impac to fwate rus e reductio n programs , chemica l recycl e systems , an d othe r modification s o n th e cost s o f operatin g a wastewate rtreatmen t system .

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Cyanid e Wast e gal/mi n IbCN " I b Metal * 

# • Oxidatio n (NaOCI . 7. 5 I b NaOCI / IbC N $4.50/I b C N Chromiu m Wast e gal/mi n IbCr* 6 

# • Reductio n (NaHS0 3 , H 2 S0 4 ) c 3 I b NaHSO^ b Cr" 6 2 I b H2S0«/l b Cr* 6 0. 3 I b NaHSO . 100 0 ga l 0. 2 I b H2SO4/IOO O ga l 

### $i.oo/ibcr6 $.10/100 0 ga l 

# • Neutralizatio n (NaOH) d 1.51 b NaOH/100 0 ga l $.20/100 0 ga l



### * Precipitatio n (NaOH ) 2. 3 I b NaOH/l b C r 2. 0 I b NaOH/l b Meta l

Legend : Proces s Ste p (Treatmen t Reagent ) Consumptio n Facto r Cost Facto r $.30/l b C r $.26/l b Meta l 

### * Flocculatio n (Polyelectrolyte ) 0. 1 lb/100 0 ga l $.20/100 0 ga l 

# j * Clarificatio n Sludg e Storag e 

# • Dewaterin g 

# t Disposa l Wastewate r Discharge ' Acid/Alkal i Wast e gal/mi n I b Metal * 

### * Neutralizatio n (NaOH)' ' 1.01 b NaOH/100 0 ga l $.13/100 0 ga l

* L b meta l expresse d a s I b o fmeta l io n

C

C Chromiu m reductio n usin g Su 2 :

Reductio n <S0 2 , H 2 SO J 2 I b SOa/l b Cr' 6 0.2lbSOj/1000ga l 0.2lbHjSO4/1000ga l $.28/l b Cr* 6 $.07/100 0 ga l
Cyanid e oxidatio n usin g Cl 2 :

Oxidatio n (Cl 2 , NaOH ) 7 I b Clj/l b C N 8 I b NaOH/l b C N $1.67/lbC N Lime i s als o commonl yused ; a usag e Figur e 11 . Consumptio n an d Cos tFactor s fo rWastewate rTreatmen tChemical s

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Cyanid e Wast e (gal/min . I b Metals )
Chromiu m Wast e (gal/min , I b Cr)
Acid/Alkal i Wast e (gal/min , I b Metals ) Precipitatio n (NaOH ) I b dr ysolid s generate d I b ofmeta l precipitate d C r1.9 8 N i 1.5 8 C u 1.5 3 C d 1.3 0 Fe 1.6 1 Z n 1.5 2 A l 2.8 9 Flocculation / Clarificatio n 

# I
Sludg e Storage/ Dewaterin g

Notes : I b meta l expresse d a s I b o fmeta l ion . Disposa l cost at $1.00/gal . 

# 1 20 % Solid s
Soli d Wast e Disposa l Cos t ($/1 b o fmeta l treated ) C r N i C u C d Fe Z n A l $1.1 8

0.9 2 0.9 0 0.7 8 0.9 6 0.9 2 1.7 2 Figur e 12 . Generatio n an d Cos tFactor s fo rSludg e Disposa l

Tabl e 5 . Cos tCompariso n o fCommo n Alkalin e Reagent s Wastewate r Discharg e

Agen t Sodiu m hydroxid e (caustic ) Sodiu m carbonat e (sod a ash ) Hig h calciu m hydrat e (hydrate d lime ) Hig h calciu m lim e (quicklime ) Chemica l formul a NaO H Na_C0 3 Ca<OH> 2 Ca O Pric e

($/ton ) $26 0 (98 % NaO H equivalent ) $12 0 (58 % NasCOj ) $5 0 (96 % pure ) $40(96 % pure ) lb/l b HjSO < neutralize d 0.82 6
1.90 0.78 8 0.59 5 Relativ e cost 9. 0
9.5 8 1.6 5 1.00 Proces s equipmen t require d

an d sequenc e fo ruse ofreagent s Causti c storag e —

Neutralize r
Sod a as h storag e —

• Slurr ytank—* Neutralize r Hydrate d lim e storag e — » Slurr ytan k

— Neutralize r Quicklim e storag e - » Slakin g - • Slurr yTank- » Neutralize r

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