1. Innovative Resources Group
MetalsRemovalProcessCharleston,SouthCarolina
Removalof metalsfrom wastewater canbeaccomplishedeffectivelyby precipitatingthemetalsby
various chemicalmeansandremovingtheprecipitateswithclarificationmethods.IRG Systems offers
an improvedversion of the proven processby usingtubularmembranefilters(TMF).Thisresultsina
moreeffective andreliablesolidsseparationprocessandprovidesexceptionaleffluentquality.Use of
TMF alsoeliminatesthebulkyclarifierstypicallyusedin the processandmakesit possibleto provide
the entire system as a portablecontainerizedsolution.
Background
Industrial processescanoftenresult in wastewater contaminatedwithheavymetals(suchas Hg, Pb,
Zn, Ni, Cr, Cu, and Cd)that requiretreatmentpriorto dischargeorreuse.Basic treatmenttechnology
for metalsremovalis chemicalprecipitation.Byaddingspecific chemicalreagentstothe wastestream,
the chemicalsreactwithheavy metalsto form insolubleprecipitates.Theseprecipitatescanthenbe
separatedfrom the water with the appropriate solid/liquidseparationprocess.Conventionalseparation
equipmenttypicallyinvolves gravity separationmethods suchasan inclinedplateclarifier.Butgravity
settlinghas somedisadvantagesdueto the separationprinciple:
A chemicalcoagulanthasto be fed into
the wastewaterto form largersuspended
particlesto enhancetheseparation
process.Coagulantsbringthreeproblems:
higheroperationcost,largersludge
volume,and the possiblepresenceof
impuritiesinthe coagulants.
Separationperformanceislesseffective
dueto a lackof an absolutebarrier.
Separationperformanceisaffectedby changesinflowand temperature.
Tubularmembranefilter(TMF)modulesincombinationwithchemical precipitationprovideexcellent
reductionofheavy metalsdueto their absolutefiltration(0.1 micron)capabilityandtheir abilityto resist
fouling. TMF productwater(referredto as filtrate) is readyfor eitherdisposalinto existing municipal
waste systems or further treatment for plantreuse. Treatedeffluentlevelsof lessthan 1 ppm
suspendedsolidsandless than0.1 ppm metalsare typical.
Treatedfiltrateis readyfor reuse, not just for discharge.
Removalefficiencyis excellentwithtreatmentlevels morethanadequateto meetstringent
dischargestandards.
Less spaceisrequiredandsystem expansionisrelatively easy, often simplyby adding
membranemodules.
Less coagulantisrequired.
TheTMF filtrationprocessis muchmoreconduciveto automationasopposedtoclarification.
It canalso be started andstopped easilywithoutdegradationof treatedwater quality.
2. MetalsRemovalProcessCharleston,SouthCarolina
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ProcessDescription
Themetalsremovalprocessiscomprisedofthe followingsteps:equalization,chemicaladditionand
reaction,solidsseparation,solidsdewatering,filtrateneutralization, andmembranecleaning.Eachis
explainedinmoredetail belowandon the attachedflowdiagram.Pleasenotethis is a general
descriptionaseachsystem mayvary dependinguponthenatureof the waste stream and the metalsto
be removed.
Equalization-An equalizationtankis used to holdinfluentwastewater allowingfluctuationsin
water chemistryandflow to equalize. Volumeof this tank dependsuponinfluentwater
quantity, qualityandfluctuation.
Chemical Addition and Reaction -Severalmethodsmaybe usedfor chemicaladditionto
the waste stream dependinguponthenatureof the wastestream andthe types of metalsto
be removed.It maybe doneelectrolyticallyby meansofan electrocoagulationstep.Orit may
be doneby injectionofthe necessarychemical IndividualTMF Module reagentsfollowedby
mixing.Typically,oneor two reactiontanks are requiredafterchemicaladditionforpH
adjustment,oxidation/reductionreactions(onlyfor certainmetals),coagulantfeeding,etc.
SolidsSeparation -After sufficientchemical reactiontime,thewastestream enters a
recirculationtankwhich allowsthewastewaterwiththe precipitatedsolidstobe recirculated
throughthe TMF modules.Therecirculation tankisnormallydesignedtohave 2 to 5 minutes
of hydraulic retentiontime.Therecirculationpumpissized to provide enoughflowto maintain
a sufficientvelocityin the membranemoduletubestominimizemembranefouling. Therefore
the recirculationpumpcapacityismuchhigherthanactualsystem capacity.TheTMF modules
are connectedinserieswithmultipletrainsofmodulescomprisingthecompletesystem.The
numberof TMF modulesinseriesandthe quantity of separatetrains are determinedbywaste
stream conditions,flowrate, and selected membranefluxvalue.
SolidsDewatering -Thewastestream isrecirculatedthroughtheTMF modulesuntilthe
solidsconcentration reaches3%to5%. A portion of the concentratedwastestream isthen
transferred to a sludgethickenerequipped withafilter pressor centrifugeto separatethe
dewateredsolids.Supernatantfrom the dewateringprocessis transferred backto the
recirculationtank.
EffluentNeutralization -Manymetalsremovalapplicationsrequiretheadditionofchemical
reagentsthat raisethe pH of the waste stream. In those cases,the filtrate mustbe pH
adjustedby addingcarbondioxideorotheracid.
MembraneCleaning -As is the casewithany membrane treatmentprocess,themembrane
doesneed to be cleaned periodically.Thesystem is thereforeequippedwithanintegral
membranecleaninplace(CIP)system. TheCIP system is comprisedofcleaningtanks,a
cleaningpump,andrelatedpipingandvalves.
3. MetalsRemovalProcessCharleston,SouthCarolina
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ProcessOperation
TheTMF system hasthree operationmodes:service,backpulse,andchemicalcleaning.Asimple
descriptionofeachoperationmodeisdescribedbelow.Again,pleasenote this is a generaldescription
as eachsystem mayvary dependinguponthenatureof the waste stream andthe metalsto be
removed.
ServiceMode -Thewastestream flowsby
gravity or is pumpedfrom theequalizationtank
into the reaction tankswith relevant chemical
dosing andnecessarypH/ORP monitoring.
Gravity flow into the recirculation tankthen
takes place.Thewaterwith precipitatedmetals
is drawnout of the tank by the process
(recirculation)pump.Themembranefiltration
processseparatesthe suspended solidsfrom
the liquid.Thesuspended solidsareretainedby
the membranes,concentratedinthere-
circulating stream,andreturnedto the recirculationtank.Filtratethat has passedthru the membranes
goesto addedprocessing(suchasneutralization)ordischarge.Sludgeintherecirculationtankissent
to a sludgethickenerandthen to a filter press or centrifugebypneumatic diaphragmpump.
BackpulseMode -After the system runs undernormalconditionsfora set periodof time, usually5-30
minutes,the recirculationpumpisshutdownandan automatic valve on the filtrate pipingisclosed.A
solenoidvalve opens,allowing7-15psiof air to pushfiltrate from the backpulsecolumn,installedon
filtrate piping,into the moduletrain for approximately10seconds.Becausethetrainis flooded,the air
pressureinto the pipingforcesfilteredwater throughthe membranetubesintheoppositedirectionof
the normalfiltrationflow, dislodgingsuspendedsolidsthat mayhave collectedonthemembrane
surface.
Chemical Cleaning -After the system hasbeen runfor several days or weeks,filtrate flowrate will
decreasedueto normalmembranefoulingthatis not removedby the backpulsemode.When
degradationofperformancehas MultipleTMF Trainsreachedaspecifiedlimit,chemicalcleaningis
executedmanuallyor automaticallyto regainpropermembrane performance.DuringCIP,chemical
solutionsare circulatedthroughthemembranemodulesviathe cleaningpump. Cleaningchemicals
includingsodiumhypochlorite,acids,andsodium hydroxidearetypicallyused to dissolve contaminants
from the membranesurface.
4. MetalsRemovalProcessCharleston,SouthCarolina
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EffectivenessofTreatmentMethod
Thetablebelowlistsactualtest resultsfrom four separatewaste streams.Pleasenote that actual
results willvary with eachapplication.
WasteStream 1 WasteStream 2 WasteStream 3 WasteStream 4
Influent
pH: 2.63
Cu: 36.6 mg/l
Ni: 0.993 mg/l
Cr: 0.464 mg/l
Fe: 0.418 mg/l
Conductivity:
2590 μs/cm
pH: 8.34
Cu: 0.075 mg/l
Ni: 87.1 mg/l
Conductivity:
454 μs/cm
pH: 2.99
Cu: 0.821 mg/l
Ni: 0.18 mg/l
Cr: 221.6 mg/l
Fe: 1.054 mg/l
Conductivity:
846 μs/cm
pH: 3.16
Cu: 12.2 mg/l
Ni: 81.5 mg/l
Cr: 293.1 mg/l
Fe: 0.692 mg/l
Conductivity:
2940 μs/cm
Filtratepriorto
Neutralization
pH: 11.07
Cu: not detected
Ni: not detected
Cr: not detected
Fe: not detected
Conductivity:
1303 μs/cm
pH: 9.12
Cu: not detected
Ni: 0.107 mg/l
Conductivity:
512 μs/cm
pH: 11.78
Cu: 0.01 mg/l
Ni: not detected
Cr: not detected
Fe: not detected
Conductivity:
2610 μs/cm
pH: 9.99
Cu: not detected
Ni: 0.088 mg/l
Cr: 0.211 mg/l
Fe: not detected
Conductivity:
3770 μs/cm
SystemCapacity
Dueto the availableTMF modulesizes,the maximumcapacityof one individualtrainis limitedto
approximately250,000gallonsperday. However, multipletrainscancompriseasinglesystem.
Therefore virtuallyanysize system is possibleupwardsofseveral milliongallonsperday.
