Zero Sludge/Zero Discharge Pretreatment Systems

?
L
DISCUSSION
Tratmcnt of many sdctute- or thallium-beuing wastes by alrady &sing chaniul treatment
proccss~
are applicable with minor modifications. In a few cases. n w trummt wbemer need to k
eontidered. This is panicularly Vue for orgmorncniC. organomercury, and orpanoxlmium
compounds.
The volumes oforgmomermry and orpnoseienium wastes are rcluively low. while the unounu of
urenic-bcuing wastes manageable by inanartion may k considerable. The tshnology in UK at
smelten u,remove uxnic oxida fmm sulfur dioxide laden smelter flue ~ p r c(which
r
are subKguently
used for sulfuric acid production) should prove directly applicabk to rcmonl of -c
oxide from
incinerator flue gases.
Cumntly. most commercial arsenk Oxide d m d h ma by impom. and it may be c c o n o m i d y
atUactive to develop a domestic source of arsenic oxide feedscock.Materials m v e r e d from comb=
tion of uxnic-bafing waster co& primarily of arsenic oxide and m o w acid. which could be
used u feedstock for commerc+dprodunion frdlities.
1.
SYSTEMS FOR THE METAL FINISHING AND PLATING
INDUSTRY
Mirk W. Davis, Rocas Enginm
Tom Sandy, Process Enginm
CH2M HILL
&Ilevut, Washington 98005
INTR0DUCn0N
A wide nriety of metals arc used in tbe meul f a g and pluinf indusuy. Although some of
t h e maah arc relatively benign. most are toxic to ather bumuu or wildlife.
Many marl finirhing and p h b g companies dbchgc their wxtcwater to municipal sewage treatment plants. Becaw m+ul conuminlnts a c c " l u e in the sludge pmdwcd by convcnrhal w e water vcltment syrtnns. thus awplicatiag dirposrl. prztreatmeot of the wastewater is required. The
Environmental P r o t d o n A g e s (EPA) pretreatment sundub for hcrvy maah and cyanide for
the deampluing and meul fhkhing categories arc prrvnted in Table I. Because state and local
governments may have stricter standards than those shown. it is important to identify aU penincnt
regulatory standards before designing a trcament systm.
.
US. Eurau of Miner. I986 Minerals Yewbook. Volume I. MetoLC und MincroLr. Washington.
D.C. f19861.
4.
71 ZERO SLUDGEIZERO DISCHARGE PRETREATMENT
. -,
V e n u Inc.. "Multimdia Assessment of the Inorganic Chemicals Indumy." Final Report Task 4.
Contract 68.W-Z4(W. for Industrid Envirrmmat RaovEb laboratory. Cincinnati. OH. USEPA
(1980).
K.. GrwmPnn H.. Herbst K.. and Rose B.. A m n u and Arsenic Compoundc in
Ullmanns ficyclopcdia of Indunriol Cheminry, VCH VorLpcgacllxhrft GMBH Weinheim.
Cammy. VOl. A-3. 113-141 (1989.
Dooovan. J.R.. and Salamone, J.M.. Su@ricA&mdSupiw Triox& in Kirk O t h m s f i w l , , .
@b of Chemical Tuhnolou. New York. John Wdy I o t a s c i ~22.
~ ~190-232
~.
(19%5).
Mellor. J.W.. A Comprehensive T m t k on Inorganic and Theorerid Chmrmry. Volume 5,
London. Longnuns G r a Inc.. 102-167 f I W_,.
.
Korasek. L.F., "Removal of Variow Toxic H a v y M a a h lad Cyanide from Water by M e m b r w
R o ~ t cW.J.
.
Cooper. Editor, Volume I. AM Arbor Pras. Ann
Proocrra" in Chmkty in WU~U
Arbor, Michigan, 261-280 (1981).
Elkin. EM.. Sclmiu" Kirk Othmcr ~ I o O p e i aof Chemic01 T u h o l o g ~Volume 20. New
York. John Wiley Intmcieoce, S7S-601 (1981).
5. Hanwh.
6.
7.
8.
9.
Tabk I.
Rchatllmt studub for tbc Fkmoplrtlg rod Mcul nmbbbg sOk.W'gOrkr'
€ktmplating EItllwot GIJddlna, "C
...
PoUuClnc
Cyanide, t o "
COPW
Pretmtmmt St.odyd-€xidec soclrce (PSES)
Avcrrga of M y
Maximum
Valuerfor((!) .
for any
conrcnnive M
m
Dalryr Shall Not E x a d
AnyIbY
I .9
I .O
4.1
2.7
2.6
chrome. toul
7.0
4.0
Zinc
4.2
2.6
0.4
0.7
Nickel
Lad
cadmium
Total meulr
4.5
0.6
13
10.5
6.8
2.77
3.38
0.69
3.98
0.43
2.61
120
0.86
Cyanide. amenable
1.71
2.07
0.43
2.38
0.24
I .48
0.65
0.32
.
For less cban 1O.OOO GPD efflwc. the cyanide limitsarc 5.0 mg/L (muday) and 2.7 m d L
(4-day average). A h . l a d and cadmium are the only restricted metals.
....
i
44th h d u e lndwriafWasfeCon&mc~ R n w d i n y .
Printed in U S A .
0 1990 Lewis Publishers. lac.. Chelsea. Michigan 481 18.
649
.
Table II.
Meld C o l c c n t n l h Unlls 1. Wutc E x t m from a FOO6 Tmad W l d W a d
Concentration
M d
Cadmium
Chromium (total)
Lead
Nickd
Silver
(mdL)
0.066
5.2
0.51
0.32
0.072
om
W A W
In addition to these pretreatment requirements. the €PA recently restricted the disposal of elmroplating wastewater sludge (EPA Hazardous Waste No. FOO6) and p r o p o d treatment standards that
would allow duposal. Thac standards r q u i r c that FUO6 sludge be treated so that a laboratorygenerated leachate will have co~mtrationsof cadmium. chromium, lead. nickel, and silver below
those shown in Table II. Additional restrictions arc expected to be published thh year and n u t year.
The combination of stringent wastewater pmreatmmt standards and sludge d u d constmints
has led many metal finishing and plating annpaaies to invenigate zero dxhargdzcro sludge M t ment systems. This chapler -d
methods to recover m a d s tither as pure mcul or as a muable
solution, thus diminuing or drastically reducing the amount of sludge disposal rquired. Also. waste
mini"
techniques a d wastewater treatment methods that can produce lower effluent metal
concentrations than those rchimble by conventional treatment &e.. prccipifation proceua) are
d i d .
MFTAL FINISHING/PUTINC WASITWATER CONCENllUTlONS
Generally, metal finishing and p l h g wastewaters can be categorized into one of three areas.
cuadc Riul.g
A schematic of 8 three-stage cascade rime is shown in Figure 1. Rimewater flows countacurrenrly
to the movement of metal parts with wa~ermakeup to the last rinse stage and rinsewater discharge
from the firs rim stage. By using this rinsc xhanc. the discharged rinsewater has a higher metal
concentntioa and a lower volume than a three-stage rinse -em where all three rinses haw separate
makeups and diuhuges. For the three-stage-de
rinse shown in Figure I. the dwharged nmew8ter metal concentration wwld be about three tima more concentrated and rinxwater volume would
be about one-third.
Became k wastewater volume. primarily consisting of rinsewater. usually is the most importlnt
factor in treatment equipment sizing. a reduction in ri-tn
volume can significantly reduce the
size of downstream treatment equipment.
0 b r k n " d ~
M U Plating Baths
These dcctroplating or elmroles plating baths contain high concentrations of the m d being
plated. Baawe of the buildup of impurities and ba* chemistry degradation. t h e baths are pcriodia l l y dumped (once per week to once pa year). M d concentrations range from IO to 400 e/L for
m d electroplating baths and from IO to IS0 g/L for elecvoleu baths.
For plating and finishing operationschat are intermittent. ondemmd rinsing. as shown in Figure 2.
can reduce rimewater volumes. On-demand rinse system use manual initiation and automatic shutoff
of rinsewater. Automatic shutoffs generally M on a tima. and the manual stan can be a foot pedal or
a hand nit&. Ondemand rinsing prevents rinsewater from being left on while the rinse bath is no(
being used. As for cascade rinsing, the redudon in wastes v d u m a will greatly affect the size of
downsvcrm VQtment equipment.
McW Flclbhlag Baths
Bath Refmrbhbin#
+hex baths usually M used to vat or apply a protective coating to the surface of base material
prior to plating o r other m d fdhing. Over time. meul impurities build up so that the bath must be
dumped. Berides metal contarninants that build up due to dissolution of the parts being treated. some
surface costing baths use chromic aad. thus adding chrome as a contaminant. Metal concentrations
in these baths range from 0.1 to 5
ut.
Rinsewater
n e s e wastewaters are produced by rinsing paru after a m d finishing or plating srep. ~ i n waer
x
will usually haw mnal concentrations that are from 100 to 1.ooO times more dilute than the m a r l
finishing or plating bath.
;
.
The type of treatment these wastewaters receive depends primarily on the meul concentrations. For
waste baths with high metal concentrations. mctaLr can often be recovered directly; for rinsewaters. a
concentration step usually is required prior to metal recovay.
WMTE MINIMIZATION TECHNIQUES
There arc many methods to minimize the generation of wastewaters and reduce the frequency of
bath dumping. Of these methods. only cascade rinsing, ondcmand rinsing, and refurbishing of
plating and finishing baths are dixusred in this chapter. These techniques should be considered first
for any wastewater pretreatment system because they tend to be more cost-effective than metal
recovery from wastewater.
Bath refurbishing system are used to remove impuritia Ih.c buildup in metal finishing or plating
baths in o r d a to m e n d the life of the bath. ThcK systems tend to be economic for large volume metal
finishing or plating operations where baths are dumped once a day or more. Electrodialytic and
electrolytic ncovcrg are two major proa*ccs used in bath refurbishing. In particular, one patented
elmrodiiytic raovcry system has the ability to separate meul cations. such as copper. from acid
baths. This laves the bath relatively pure and minimize the dump frequency.
M d impurities m o v e d by the refurbishing system may rquire further treatment to produce a
nonhazardous sludge. The systems d i d later in this chapter may be suitable for additional
treatment.
ZERO SLUDGE WASTEWATER TREATMENT SYSTEMS
Although wastewater volume can be significantly reduced by the above minimization techniques.
wastewater will still r q u i r e pretreatment to reduce m d concentrations prior to discharge. This
section discusses methods to treat these wastewaters.
Mon zero sludge system cohciu of the following steps:
Waste segregation is wd to isolate individual metals.
Ion exchange is wd to reduct wastewater mual concentrations below discharge levels and to
concentrate the metal contaminant for subsfquent recovery.
Electrowinning is used to recover metal from plating baths and IX regenerant.
t=
8
T8bk ill.
Table IV. Ek*mrimlm Mdal Removal R.ce
Effluent Maal
Removal Rat?
Concentration
(md-1
Meal
(Ib/hr/ft')
0.04 10 0.06
10 10 100
Cadmium
600 t o l.m
0.04 to 0.20
CWpr
c2
COPperb
0.03 to 0.Mb
Nickel
0.03 to 0.04
1.mto 3.OOo
1.000 to 3.000
Zinc
0.03 to 0.04
Typical I X R a l a Mcu) Capacitia
Meial
Cadmium
COPPcr
Chrome (Ill)
Chrome (VI)b
Nickel
'Capaatia are for a chelating resin unlcss noted.
Wakly basic anion achange resin.
Capacity Range
(lb/ft'p
0.8 to 2.0
0.5 to 1.0
0.5 to 1.0
1.0 to 2 . 9
0.8 to 2.0
~-
Rate capacity for high surface area dectrowinner.
Electrodialytic systems arc wed for chrome recovay (as chromic acid) from s p a t maal tracing
baths.
Each of t h e e steps is d
e further in the following sections.
Another type of elmrovinner uses cathode with much greater (narly two to four tima) surface
area than parallel plate ath&. ThtK dearowinnas am used to treat wwewater with low c o m trations, similar 10 IX syumu. P d b k uses for t h a c dmrowinnerrinclude treatment of the effluent
of parallel plate dmrowinnen. allowing dire3 d s h a r g e instead of nwcling.
A schematic of an IWekcrrowin treatment system b shown in figure 3. Trpid flow nter and
m a l l concentratioru arc shown.
scyrlrh
Many metal finishing and plating operatioar have more than one maal contaminant present in their
wastewater. Segregation of the different wastewaters Kcording to their m a r l contaminant is important kaw the metab arc easier to sell or mue and arc m e valuable if they are relatively pure.
Also. combinations of metals may k difficult to recover becauserequired procesr conditions (such as
pH) may k different for differmt maals. Once metals are mixed together in a single wastewater
stream. it kcoma much more diffmlt to separate them than it would be if the wastewater streams
are initially segregated.
Besides segregation by metal, streams should also be qucgated by concentration. Usually, waste
streanu with high metal concentrations (such as dumped metal plating baths) can be directly clectrotwinned. Wastewater stream with low meul concmtrationr (such as rinsewaters) usually arc concencrated by ion uchmgc (IX), and the IX regenerant is electrowinned. Waste streams that fall between
thae two extremes may be treated either way. depending on the composition of the wastewater.
atarodhlytk SM-
Elcctrodialylic systems are fairly MU tahnoiogy that have been dmlopcd to M t waste m*.l
plating and meul finishing baths. A number of appliutionr for this technology have been ralited.
and more applications currcnrly are being developed. Only one of these applicatioru b dircruccd in
chis chapter.
One w of dcctrodialyric systems is for rccovay of chrome (as chromic acid) from mcu) u a l k
baths (and their corresponding rinsovltm)containing chromic add. These baths must k p c r i o d i d y
dumped when Vivaient chrome concentrations become too high. thus reducing the OXiditing
of the mnol treating bath. k i d a trivalent and hexavalent chrome (as chromate). these baths have
metal impuritiCS faulting from dissolution of the m a d puu being treated. One common impurity is
copper.
A schematic of a chrome recovery Wtem is shown in Figure 4. The spcnt m d trating baths .re
collected and bled into the waste rinsewater stream. The combined stream is then pumped lfvough
loa Exchmge
Ion C X C ~ ~ I Q C systems scrve two primary purposes. Firs!. IX systems are used to reduce m*rl
c~ncmtraUo
in~the wastewater to k l o w discharge limits. allowing the I X effluent to be dixharged.
Second. IX is used to concentrate the removed m a d (typically S.OOO to 10.000 mg/L) $0 that
downstream recovery systems. such as electrowinning, are more effective. IX is most suitable for
wastewater Urams that are high in volume but low in m a d concentration (1 to 1W mg/L). such as
rinsewater.
In addition to rinsewaters. mmnl treating baths that contain highly corrosive acids are often bled
into the IX influent. Directly c l a winning t h e e baths is possible, but expensive. corrosion-resistant
materials may be required. ALO ae chemical compasition of these baths may interfere with the
electrowinning process. making it ;a
efficient.
Approximate metal capaatia of IX resins are shown in Table Ill.
Elmrori.uiw
r'---
J
Elmrowinning is used to remove metal contaminanu from plating baths, IX regmerant. and some
meul treating baths. A separate electrowinner is required for each metal because different bath
conditions (such as pH) are raquircd and because of varying removal rata. Mad is removed by
+ plating it onto cathodes emened in the electrowinning tank. Recovered maal is then removed from
the cathodc so the cathode can be rcwed. Reusable cathodes are generally made of stainla steel. An
alternative is to w disposable cathodes, which consist of a thin copper foil.
Typical removal rates for parallel plate electrow'nnm M shown in Table IV. Beuuv removal
rates depend on the metal concentration. electrowinning below cemin concentrations (shown in Table
I v ) becoma impractical. Therefore. instead of electrowinning to below dischuge limits, the effluent
of the electrowinner usually is recycled back to the IX system.
It is i m p o m t to .+~sessthe potential buildup of contaminants in the treatment system due to
,
recycling. The concentration of any metal contaminant that is removed by I X but not by electrowinn~ingwill wcntually build up. requiring periodic purging of the treatment system.
electrowinner rumple.
Flcure 4. Chrome exchange eirctrodi*iytk
example.
iaticln and anion ton exchangers in
anion I X removes chromate.
%rich.
llic
cation I S remove\ trivalertt chtoiiic
.ir1c1 .aWrx+r. rhc
~
The caiion exchange regenerant is trwied in an electrdialyiic recovery unit ihai ~ r i ~ l i r dJr .haich
trcstmeni tank and an elcoirodialytic membrane cartridge immcrwd in thc treatment tank The outer
*urface ol the cartridge is a cation-celectivc membrane. A caiistic wlution i s circiit:iid thrc>uuh the
in\& ut the cartridge. which also ccmtains the cathode. The anode IS tmtncr\erl ,lrrecilv i n the
treatment tank. Applying a potential to the cell causes copper IO move 3cross !he nlemhfaar mto the
c'austtc rolution, where the copper prectpttates as copPcr hydroxide. The transier 01 trivalcrir chrome
(which has a much lower electromottve poicntial than copper) across thc rncmhranc I\ # t ~ i i a l l yless
than 0.1%.
instead of transferring across the membrane. trivalent chrome is oridired to chromaie at ihc anode.
n u s . at the completion of batch trearment the maloricy of the coppcr (greater than W l 1 haa been
removed. and the trivalent chrome has becn convened to chromate. This solution i s (hen returned to
the anion I X inffucnl for recovery of chromate.
The anion exchange regenerant. which is primarrly wdium chromate. is converted 11) chromic acid
in a similar electrodialytic recovery unit. Regenerant or sodlum chromaie IS converccd to chromic actd
by the removal of sodium cations through a cation selective membrane and the pr(\diic.tionof hydro.
gcn cations at the anode. The net result is a solution of chromic actd of a proprit<rnsl concentration
and purity as the original sodium chromate regenerant.
CONCLUSIONS
Provrded that wastewaters can be segregated into separate metal-bearing streams. ion exchange.
electrowinning. and el~rodialyttcunit procasa. when used together on metal plating and finishtng
nnscwaters and bath dumps. can provide an effluent in compltancc wtth regulatory pretreatment
standards. produce little to no sludge. and enahlc recovery and/or reux of relecicd metals and acids.
REFERENCES
Envlronmental protection Agency. Code oJFedera1 Regulocronr. Tttk 40 Porrs J33 und 4 / 3 (July
7. 1987).
2. Ennronmmtal Protection Agency. Code of Federol Regubrrons. Tule Jn Parr3 16l.H ond
I.
268 41 (August 17. 1988).
72
1 ItEATMKN'T OF STOHM HIINOFF Ilk' O I L W
.
SEPA HAT I oN
FLOTATION. FILTRATION. ANI) ADSORPTION.
PART A: WASTEWATER TREATMENT
',
.
R
1,awrcncc K. Wanp. Director
I-cnox Inwtute for Research Inc.
Lenox. Massachusetts OIZJO
William J. Mahency. Technical Director
tmperial Oil Company Inc.
Morgmville. N e w J m e y 07751
The fcasibitity of removing soluble arsenic I + $1 and urhcr conventional pollutants from combined
storm runorf and process wastewater by oil-water wparation. dissolved air floiazton (DAF) filtration.
and granular activaicd carbon (GAC) adsorption *as iully demonstrated for an oil blending company
in a northea,tern state.
The oil separated from the raw combined uastcumcr by the American Petroleum Institute (API)
oil-water separators was virgin. and was. therefore. skimmed off. dried and reused.
The uil.uarer separator effluent containing I . O l ny, L of arsenic. 3 NTU Or turbidity. 50 units of
color. :y I mp. L o i oil and grease tO&G). and Y 1 mq 1. of chemical oxygen demand tCOD) was fed
to a D~Filariliertsupracell) for removal oi rrsenic D\ 90 1%. turbidity by 30%. color bv 43%. O&G
bv 4 3 . 3 dnd COD by 32.5%. Either l-ernc chloridc or fernc sulfate was an effective coagulant for
arsenic rcmobal
The same oil-water reparazor effluent was d1w ,ucccssiullv treated by a DAF4ltratJon clarifier
(Sandfloat). Reductions of arsenic. turbidity. L.olilr. O&G. and COD were YO.6%. 93.3%. 98"s.
74.7we rnd SI 3%. rcspcctivcly.
Although Supracell and Sandfloat both Jcmon.tratcd to bc excellent prctrcalment processes. GAC
post-ireaimcnr removed 100% of solublc arsenic
This chapter summarizes and discusses the tcchntial data on combined trcatmcnt of storm-run and
process uater by the innovative treatment systems
PRETREATYEYT BY PILOT FI.VT.-\TION AND FUTVTION SYSTEM
The pilot plant system shown in Figure I was set up for this research. The system consisted of a
rapid mi.xingchamber. a rectangular static hvdraulic ilocculator (L x W x H = 102 in x 16 in x IO
in = 159 OS i m x 40.64 cm x 25.40 cml. J dissdbed atr flotation unit (Krofra Supr3ccll Model SPC
3; I)iamctcr = 0.91 m = 3 ft: Depth = 5 5 88 cm = 22 in). and three sand filters (28 cm of quartz
~ the heart of the entire pilot plant
rand 3s filter bed). The pilot dissolved air flotation unit ( D A was
rvuem. Thc following were the typical pilot plant operational conditions:
Inilucni:
Combined storm runoff uater and process water. pretreated by the existing A P I oilwater separators. and 5pikcd with soluble arsenic when necessary
Chtmlcals: 15 mg/L of sodium aluminate {as AI:O,), and IS mg/L of either ferric chlorid or
ferric sulfate (as Fe)
$2
Continuous influent flow 39 62 m: hr ( 9 gpm)
Continuou, DAF effluent flow 39 23 m' hr ( 8 934 gpm)
C o i l i " m s DAF sludge flow 0 29 m' h r (0(Ma gpm)
Caiiiinuous DAF recycle flow (I B m' hr 11spm)
655
'