© 2009 by Taylor & Francis Group, LLC 155 7 Treatment of Nanoparticles in Wastewater Kim M. Henry AMEC Earth & Environmental Kathleen Sellers ARCADIS U.S., Inc. Commercial products incorporating nanomaterials eventually reach the end of their usable life. Sunbathers w ash sunscreen containing titanium dioxide (TiO 2 ) nanopar- ticles from their skin; antimicrobial silver particles drain from washing machines in therinsecycle;paintsandcoatingsake;ormaterialsarelandlled.Whathappens tothosenanoparticlesattheendofproductlife?Inshort,nooneknows.Initialatten- tionhasfocusedonthefateofnanoparticlesinwastewatertreatment.Nanoparticles canenteramunicipalwastewatertreatmentplantasaresultofcommercialuseand discharge. Wastewater discharges from manufacturing processes also can contain nanoparticles.Asillustratedbyexamplesinthischapter,however,thedischargeand fateofnanomaterialsisdifculttoquantify. CONTENTS 7.1 Mass Balance Considerations 156 7.1.1 CaseStudy:SilverCare™ Washing Machine 157 7.1.2 Case St udy: Socks with Na no Silver 159 7.2 Treatment P roc esses 160 7.2.1 Sedimentation 160 7.2.2 Coagulation and Flocculation 161 7.2.3 Activated Sludge 162 7.2.4 Sand Filters 164 7.2.5 Membrane Separation 165 7.2 .6 Disin fection 165 7.3 Summary 165 References 166 © 2009 by Taylor & Francis Group, LLC 156 Nanotechnology and the Environment Thesameuniquepropertiesthatmakenanomaterialssopromisinginawide varietyofindustrial,medical,andscienticapplicationsmayposechallengeswith respect to wastewater treatment. In 2 004, because the toxicity of nanomaterials and theirfateandtransportintheenvironmentwerenotwellunderstoodatthetime, theBritishRoyalSocietyandtheRoyalAcademyofEngineeringrecommended that “factories and research laboratories treat manufactured nanoparticles and nano - tu besasiftheywerehazardous,andseektoreduceorremovethemfromwaste streams” [1]. Although t he body of research regarding the toxicity, fate, and trans- portofnanoparticleshasgrown[2],literaturesurveysin2006and2007indicatethat thebehaviorofnanomaterialsduringwastewatertreatmenthasnotbeenwellstudied [3, 4]. Anabstractforaresearchprojecttoevaluatetheremovalofvarioustypesof nanoparticles during wastewater treatment, which was funded by the U.S. EPA’s National Center for Environmental Research (NCER) for the period from 2007 to 2010, states: “Today, almost no information is available on the fate of manufactured nanoparticles during biological wastewater treatment” [5]. This chapter discusses the potential for various treatment processes to remove nanoparticles from waste streams. Ag eneral description of each process is provided, as well as an evaluation of how particular properties of nanomaterials can reduce or enhance the effectiveness of the process. Research  ndingsareprovidedwhere available, or an indication is given as to whether research is ongoing at the time of writing this book. While t he primary focus is treatment processes in a typical municipal wastewater treatment plant, many of these processes are used in industrial wastewater treatment. Certain p rocesses also may apply to drinking water treatment and,whererelevant,thendingsfromwatertreatmentresearcharealsodiscussed. 7.1 MASS BALANCE CONSIDERATIONS Concernsoverthepresenceofnanoparticlesinwastewaterstreams,whichcould eventually accumulate in sewage sludge or discharge to the environment in treated wastewater, must be put into context. The c oncentration of a nanomaterial in waste- water depends primarily on: The amount of local production or use of commercial products containing nanomaterials Whe therthenanomaterialsarexedinamatrix(suchasthecarbonnano- tu besinatennisracket)orfree(suchasTiO 2 nanoparticlesinsunscreen) Theamountofthefreenanomaterialintheproduct The fraction that is washed down the drain The degree of agglomeration or adsorption occurring in aqueous solution thatchangestheformofthenanoparticleorremovesitfromsolution Theextentofdilution Nostudieshavebeenpublishedofwhichtheauthorsareawarethatattemptto quantify the discharge of nanomaterials into wastewater treatment plants. Given t he recentgrowthoftheindustry,thewidevarietyofmaterialsenteringthemarket,and thecondentialityoftheirformulation,thiscomesasnosurprise. Two ca se studies • • • • • • © 2009 by Taylor & Francis Group, LLC TreatmentofNanoparticlesinWastewater 157 illustrate both the potential for nanomaterials to enter wastewater streams and the difcultyinmakingsuchanestimatewhenthedetailsofproductmanufactureare proprietary. Coincidentally, b oth examples concern the discharge of silver when washing clothes. 7.1.1 CASE STUDY: SILVERCARE™ WASHING MACHINE Samsung’s SilverCare™ option on several models of washing machine uses silver ions to sanitize laundry. Samsung r eportedly spent $10M to develop this technology [6]. The d etails of the technology are, understandably, proprietary. Company litera- ture describes the technology in several ways. According t ooneaccount[6],thesys- temelectrolyzespuresilverintonano-sizedsilverions“approximately75,000times smallerthanahumanhair”;assumingthatahumanhairisapproximately60to120 micrometers (μm) wide [4], then the silver nanoparticles would be on the order of 1 nm in diameter. Elsewhere[7],Samsungdescribedtheirsystemasfollows: “[A] grapefruit-sized device alongside the [washer] tub uses electrical currents to nano- shavetwosilverplatesthesizeoflargechewinggumsticks.Ther esultingpositivelycharged silver atoms — silver ions (Ag + )—areinjectedintothetubduringthewashcycle.” Thesetwodescriptionsdifferenoughtomakeitunclearwhetherthesilverisreleased asatruenanoparticle(ca.1nmdiameter)orasionicsilver.(Silverhasanatomic diameterof0.288nmandanionicradiusof0.126nm[8],andthussilverionsare smaller than the nanoparticle size range of 1 to 100 nm.) Based o n the electrolysis process, both may be present. Key a ndMaas[9]indicatethatelectrolysisofasilver electrodeindeionizedwaterproducescolloidalsilvercontainingbothmetallicsilver particles(1to25wt%)andsilverions(75to99wt%).Thes ilver particles observed in colloidalsilvergenerallyrangeinsizefrom5to200nm;aparticle1nmindiameter would consist of 31 silver atoms. This i nformation suggests — but certainly does not conclusively prove — that the SilverCare™ washing m achine discharges a mixture ofsilverionsandsilvernanoparticles.Silverions,ratherthannanoparticles,may comprise most of the mass. Samsung has offered several indications of the amount of silver released when washing a load of clothing. T heir p roduct literature notes that electrolysis of silver generatesupto400billionsilverionsduringeachwashcycle[6,10].Thet wo chew- ing-gum sized plates of silver reportedly last for 3000 wash cycles [10]. Finally, S amsung reportedly has indicated that using a SilverCare™ washing machine for a yearwouldrelease0.05gsilver[11]. Withrespecttothesanitizingfunctionthatthisreleaseofsilverprovides,Sam- su ng has indicated that the silver ions “eradicate bacteria and mold from inside the washer” and “stick to the fabric” of clothes being washed to provide antibacterial functionforupto30days[10]. A S amsung representative stated that “silver nano ions can easily penetrate ‘non-membrane cell’ [sic] of bacteria or viruses and sup- presstheirrespirationwhichinturninhibit[sic]cellgrowth.Ont he other hand, Silver Nano is absolutely harmless to the human body” [6]. WhileSamsunghasmarketedthisantibacterialactionasabenettocustomers, someconsumershavebecomeconcernedaboutthepotentialconsequencesofusing © 2009 by Taylor & Francis Group, LLC 158 Nanotechnology and the Environment SilverCare™ products.Initialeffortstomarketthewashingmachinemetwithresistance inGermanyandthewashingmachinewastakenoffthemarketinSwedenforabrief timeduetoconcernsoverthepotentialtoxiceffectsofdischargingsilvernanoparticles from the use of these machines to wastewater treatment plants [11, 12]. Chapter 4 dis- cusses regulatory actions in the United States regarding such washing machines. Attemptstoquantifythedischargeofsilverfromusingthewashingmachine — and thus illuminate the potential effects on a municipal wastewater treatment plant—providearangeofanswersbasedontheavailabledata.Inadditiontothe information provided above regarding the mass and potential form of silver released, the following assumptions about wastewater generation were used to complete a con- servative mass balance: Eachwashcycleuses12.68gallonsofwater[13]. The typical residence generates approximately 70 gallons of wastewater per person per day [14]. Afour-personhouseholddoestwoloadsoflaundryperdayonaverage. Allthesilvergeneratedinthewashingmachineentersthesewage. Further,theauthorsmeasuredthesizeofastickofgumatapproximately0.2by1.8 by7.2cm,assumedthatthedensityofasilverbarwas10.4g/cm 3 [8], and conser- vativelyassumedthattheentiremassofsilverinthetwoplateswouldbeentirely consumed within the 3000-cycle lifetime. Asarstapproximation,theamountofnanosilverparticlesthatcouldentera wastewater treatment plant from the use of SilverCare™ in w ashing clothes could range from 0.001 micrograms per liter (μg/L) to an extreme upper bound concentra- tionof9μg/L.Thelowestestimateisbasedonthereportedreleaseof0.05gsilver peryearandtheassumptionthatonly25%ofthemasswouldcomprisenanoparticles (rather than ions) of silver. The highest estimate is based on complete consumption ofthetwosilverplatesduringtheunitlifetimeandtheassumptionthat75%ofthe silverwasinnanoparticulateform.Theactualconcentrationofnanoparticleswould be lower than either of these estimates due to adsorption and agglomeration. Labora- to ryexperimentswithsolutionsof25-nmand130-nmsilverparticlesshowedthat uponvortexmixing,thesilveragglomeratedintoparticlesrangingupto16μmin diameter, well outside the nanoparticle range [15]. Further, the mass balance calcula- tionsdonotaccountfordilutionbysourcesofwastewaterotherthandomesticsew- agefromhomesusingSilverCare™ washing machines. Dilution from other sources wouldalsodecreasetheconcentrationofsilvernanoparticles.Thus,theupperbound estimateof9μg/Lshouldberegardedasanextremeupperbound. Whateffectcouldthisdischargeofsilverhaveonthemicroorganismsina wastewater treatment plant? As d escribed previously, silver has antimicrobial prop- erties. At the time this book was written, the authors could not identify published benchmarksthatenabledthemtodirectlycomparetheestimateddischargeofsilver nanoparticlestolevelsthatareeither“safe”or“toxic”tomicroorganismsatasew- agetreatmentplant.Theacuteambientwaterqualitycriterionforsilver,whichwas not derived specically for nanoparticles, is 3.2 μg/L [16]. This concentration is comparable to the upper bound estimate of the discharge of silver nanoparticles into • • • • © 2009 by Taylor & Francis Group, LLC TreatmentofNanoparticlesinWastewater 159 wastewater from using the SilverCare™ system; however, as noted above, that upper bound estimate was quite conservative. As d escribed below, research on the toxicity of silver nanoparticles provides further relevant information. Rojoetal.[17]assayedthetoxicityofcolloidalsilvernanoparticlesinthe5-to 20-nmsizerangetozebrashembryos. T hey t ested solutions containing between 1and5000μg/Lsilvernanoparticles.Theirinitialtestsshowednoeffectondevel- opment or survival of the embryos in the rst 2 weeks. Subsequent e xperiments monitored effects on eight selected genes. At t he highest nanosilver concentrations tested,theresearchers“foundacleareffectongeneexpressioninmostcases.”Those c oncentrations were, however, orders of magnitude higher than the estimated levels of silver nanoparticles in wastewater described above. Otherresearchershaveworkedwithmammaliancelllinestotestthetoxicityof silver nanoparticles. Hussain e t al. [18] tested the effect of solutions containing 10 to 50 μg/L silver nanoparticles (15 nm) on PC-12 cells. This n euroendocrine cell line originated from Rattus norvegicus (N orwegian rat). The research team observed decreasedmitochondrialfunctioninthePC-12cellsuponexposuretothesilver nanoparticles. Skebo e tal.[15]showedthatratlivercellscouldinternalizesilver nanoparticles (25, 80, 130 nm) but that agglomeration of nanoparticles can limit cell penetration. Finally, B raydich-Stolleetal.[19]testedtheeffectsof15-nmsilver nanoparticlesonacelllineestablishedfromspermatogoniaisolatedfrommice.The n anoparticles reduced mitochondrial function and cell viability at a concentration between5and10μg/mL(or5000and10,000μg/L).Ther esearchers estimated the EC50, or the concentration that would provoke a response half-way between the baseline and maximum response, at 8750 μg/L. This l evel is orders of magnitude higher than the rst approximation estimates of silver nanoparticles in wastewater from using the SilverCare™ s ystem. 7.1.2 CASE STUDY: SOCKS WITH NANO SILVER Several manufacturers market socks impregnated with nanosilver particles as an antibacterial agent. Westerhoff’s [ 20] team at Arizona State University measured the amountofsilverthatvedifferentbrandsofsockscouldreleasewhenwashed.They simulatedwashingbyplacingthesocksindeionizedwaterfor24hours(hr)onan orbital mixer, removing, drying, and then rewashing the socks three times (for a total of four wash cycles). F our o f the test socks initially contained silver at 2.0 to 1360 μg/g sock. The  fthsockcontainednomeasurablesilver.Theamountofsilverthat leachedoutofthesilver-bearingsocksafterfoursimulatedwashcyclesrangedfrom 0to100%.Thec oncentrationofsilverinthewashwaterrangedfromlessthan1to 600μgin500mLwashwater,orupto300μg/L.Ther esearch team noted that it was difcult to distinguish between silver ions, silver nanoparticles, and aggregated silver nanoparticles in the wash water. These initial laboratory results are difcult to extrapolate to the concentration ofsilverthatmightresultinsewagefromwashingsockscontainingsilvernanopar - ticles. As n oted above, the typical wash cycle uses more than 12 gallons of water (ratherthan500mL)andrunsformuchlessthan24hr,suggestingthatdilutionand © 2009 by Taylor & Francis Group, LLC 160 Nanotechnology and the Environment ashorterleachingtimemightresultinlowerconcentrationsthanweremeasuredin theexperiment.Thedifferenceinthevolumeofwashwateralonemightaccountfor dilutionbyafactorof25;additionaldilutionbyothersourcesofwastewaterwould reducetheconcentrationstillfurther.Themostdifcultvariabletoquantifywould bethenumberofsockswashedperloadoflaundry(althoughasanyparentwould attest,thatvariablecouldincreasetheestimateddischargeofsilverbyatleastan orderofmagnitudeovertheestimatefromwashingasinglesock). As these examples show, estimating the discharge of nanomaterials from the use of commercial products is no simple matter. The m assorconcentrationreleased totheenvironmentdependsontheamountandavailabilityofthematerial,among otherfactors,andsuchproprietaryinformationcanbedifculttoobtain.Thep os- sibleeffectsofexposurecanonlybeinferredfromthedevelopingtoxicologicaldata- base. Some r esearchisbeginningtoproduceinformationonthepossiblefateof nanomaterials once released; the next section of this chapter describes the fate of nanomaterialsinamunicipalwastewatertreatmentplant. 7.2 TREATMENT PROCESSES Municipal wastewater treatment plants are designed to accelerate the natural pro- cesses that remove conventional pollutants, such as solids and biodegradable organic material, from sanitary waste. Treatment processes include: Physical treatment, to screen out or grind up large-scale debris, to remove suspendedsolidsbysettlingorsedimentation, and to skim off oating greases Bi ologicaltreatment,topromotedegradationorconsumptionofdissolved organicmatterbymicroorganismscultivatedinactivated sludge or trick- ling lters Chemical treatment, to remove other constituents by chemical addition, or to destroy pathogenic organisms by disinfection Ad vanced treatment, to remove specic constituents of concern by such processes as activated carbon, membrane separation, or ion exchange Similarprocessesareusedindrinkingwatertreatment.Coagulation,bythe addition of alum and other chemicals, removes suspended solids that cause turbidity and objectionable taste and odors. The oc formed during coagulation is removed by sedimentation. Sand lters or other porous media such as charcoal subsequently remove smaller particles that remain in suspension. (While more commonly used in water treatment than wastewater treatment, some wastewater treatment systems do incorporatesandltration.)Disinfection removesbacteriaormicroorganisms[21]. Processes indicated in italic font above are discussed with regard to their poten- ti al to remove nanoparticles from waste streams. 7.2.1 SEDIMENTATION Sedimentationorsettlingisintendedtoremovesuspendedinorganicparticlesthatare 1μminsizeorgreater.Becauseoftheirsize,freenon-agglomeratednanoparticles • • • • © 2009 by Taylor & Francis Group, LLC TreatmentofNanoparticlesinWastewater 161 willnotberemovedduringsettling,unlessbytheactionofcoagulantsorocculants or by the adsorption of the nanoparticles onto large particles [3]. For f urther discus- sion of the forces affecting the settling of nanoparticles, see Chapter 6. 7.2.2 COAGULATION AND FLOCCULATION Coagulation and occulation are typically used to remove solids in water treatment; certain wastewater treatment applications can include these processes. Coagulation ca nfacilitatetheremovalofnanomaterialspriortosedimentationormembrane separation [3]. Coagulationreferstothenetreductioninelectricalrepulsiveforcesatparticle surfaces to allow them to agglomerate. In a treatment plant, operators rapidly mix acoagulant(suchasaluminumorironsalts,orlong-chainpolyelectrolytes)intothe water to destabilize colloids. Flocculation i s the process of aggregating those par- ticles by chemical bridging between particles. After t he coagulation step, water is slowlymixedtoallowparticlestocollideandoctoform.Sedimentationr emoves theoc,ormembraneseparationcanbeusedtopolishthewater. Huangetal.[22]performedjarteststoevaluatetheoptimaldosageofthe coagulant poly-aluminum chlorate (PACl) and the optimum pH required to remove nanoscale silica from chemical mechanical polishing wastewater generated from semiconductor manufacturing. Prior t o use, the silica present in the polishing slurry hasauniformparticlesizeof100nm.Aftert he polishing process, the colloidal sil- ica particles present in the wastewater range in size from 78 to 205 nm and, without pretreatment,canpenetrateandclogthemicroltrationmembrane. The r esearchers foundthatsupernatantfromthejartestshadthelowestturbiditywhenthepHwas around6andtheconcentrationofPAClwasgreaterthan10mg/L. At p H6,the PAClactstoneutralizethenegativelychargedsilicaandtodestabilizethecolloidal particles. Supernatant r epresentative of the range of optimal conditions identied in thesettleabilitytestswasthensubjectedtolterabilitytestingbymeasuringthetime to pass 50 mL of the supernatant through the microltration membrane. This t esting conrmedthatapHof6andaPAClconcentrationof30mg/Lproducedtheshortest ltration time. The coagulation enlarged the particle size such that nearly all the par - ti cles were greater than 4000 nm in diameter. Although s ubsequent microltration througha500-nmmembraneremovedapproximately95%ofthesilica,silicastill remainedinthetreatedwastewaterataconcentrationof44mg/L[22]. Kvinnesland and Odegaard [23] studied the effect of different polymers on the coagulation and occulation of humic substances present in water primarily as nanoparticles less than 100 nm in size. For t hepurposesoftheirstudy,theydened coagulation as the process by which the nanoparticles formed aggregates that could beremovedbya100-nmlter,andocculationastheprocessbywhichtheparticles furtheragglomeratedforremovalbyan11,000-nmlter. The researchers found that thevedifferentpolymersachievedthesamemaximumremovalofnanoparticles via coagulation (approximately 95% removal). The c oagulation was achieved by the additionofcationicchargeregardlessofthetypeofpolymerapplied.Removalo f thehumicsubstancesbyocculationvariedaccordingtothechargedensityofthe different polymers [23]. © 2009 by Taylor & Francis Group, LLC 162 Nanotechnology and the Environment InaprojectfundedbyNCERfortheperiodfrom2004to2007,Westerhoffet al.[24,25]areresearchingthefate,transformation,andtoxicityofmanufactured nanomaterials in drinking water. As p artoftheirresearch,theyhaveconducted jar tests of coagulation, occulation, sedimentation, and ltration to evaluate the removalofmetaloxidenanoparticlesduringtypicaldrinkingwatertreatmentpro - cesses. The metal oxide nanoparticles are present in solution as stable aggregates that range in size from 500 to 10,000 nm [24]. Metal c oagulants(alum)andsalt (magnesium chloride) were added to solutions of commercial metal oxide nanopar- ti cles, lab-synthesized hematite nanoparticles, and cadmium quantum dots. Accord- in gtoapaperpresentedattheNSTI-Nanotech2007Conference[25],“removalof nanomaterials by coagulation, occulation and sedimentation processes was rela - ti vely difcult.” More t han 20% of the commercial metal oxide and the laboratory- synthesized hematite nanoparticles remained in the water following these processes. Fo r all the nanoparticles tested, microltration through a 0.45-μm lter following sedimentation removed additional nanoparticles. However, 5 to 10% of the initial concentrationofparticlesremainedaftercompletionofthesimulateddrinkingwater treatment process [25]. Thepresenceofotherconstituentsinthewatercanaffectthecoagulationand occulation of nanoparticles. In a presentationtotheNationalInstituteofEnviron- mental Health Sciences, Westerhoff suggests that dissolved organic matter (DOM) present in water may stabilize nanoparticles by inhibiting the formation of aggre - gates.TheDOMthusaffectstheremovalofnanoparticlesduringsedimentation and ltration [20]. For e xample,Fortneretal.[26]haveconductedresearchonthe factors that affect the formation of nano-C60, the water-stable aggregate that forms when fullerenes (C60) come in contact with water. Their r esearch shows that the pH ofthewateraffectstheparticlesizeofthenano-C60,andtheionicstrengthaffects thestabilityofthenano-C60insolution[26]. Similarly, multi-walled carbon nanotubes are hydrophobic and would be expected to aggregate and settle out in water. However, r esearchers at the Georgia InstituteofTechnologyhaveobservedthatmulti-wallednanotubesadsorbtoorganic material that occurs naturally in river water, forming a suspension that persisted for the month-long period of observation. Thenaturalorganicmatterappearedtobea betterstabilizingagentthansodiumdodecylsulfate,asurfactantoftenappliedin industrial processes to stabilize carbon nanotubes [27]. This t ype of interaction of nanoparticleswithconstituentsinnaturalwaterswouldlikelyaffecttheirremoval. 7.2.3 ACTIVATED SLUDGE Somenanoparticlescanberemovedbyadsorptiontoactivatedsludge[3].Aresearch projectfundedbyNCERfortheperiodfrom2007to2010willaddressthefateof manufactured nanoparticles during biological wastewater treatment. The i nvestiga- tors (Westerhoff, Alford, and Rittman of Arizona State University) indicate that the objectiveoftheirresearchistoquantifytheremovaloffourtypesofnanoparticles (metal-oxide, quantum dots, C60 fullerenes, and carbon nanotubes) during wastewa - ter treatment. Batch a dsorption experiments will be performed using whole biosol- ids, cellular biomass only, and extracellular polymeric substances from biological © 2009 by Taylor & Francis Group, LLC TreatmentofNanoparticlesinWastewater 163 reactors and full-scale wastewater treatment reactors. Nanoparticles also will be added to laboratory-scale bioreactors to quantify biotransformations to the nanopar- t i cles and toxicity to the microorganisms. E lectron m icroscopy imaging will be used toevaluatetheinteractionsbetweenthenanoparticlesandthebiosolids[5]. No NCER progress reports were available for the research of Westerhoff, Alford, andRittmanatthetimeofwritingthisbook. H owever, t he investigators hypothesize in their research abstract that “dense bacterial populations at wastewater treatment plants should effectively remove nanoparticles from sewage, concentrate nanopar - ticles in biosolids, and/or possibly biotransform nanoparticles. T he r elatively low nanoparticle concentrations in sewage should have negligible impact on the waste- w at er treatment plant’s biological activity or performance” [5]. P reliminary r esults [20]hintatthepossiblebehaviorofC60fullerenesinsewagetreatment.I ni nitial tests, the research team mixed a solution of C60 aggregates and biomass in water, then ltered the solids and measured C60 levels to determine the amount sorbed to biosolids. T hese r esults were incorporated into mass balance modeling that simulated the operation of a wastewater treatment plant at steady state. T he r esults indicated that22%ofC60wouldadsorbtobiosolidsandtheremainderwouldbedischargedin the efuent. Westerhoff [20] noted that the model estimates must be validated with laboratoryandeldmeasurements. Ivanov et al. [28] conducted research to evaluate whether microbial granules presentinabiolmcouldremovenano-andmicro-particlesfromwastewaterand whether calcium enrichment, which is typically applied to wastewater with high organicloading,couldenhancetheremovalofsmallparticles. C alcium i ons enhance theformationofmicrobialaggregatesbydecreasingthenegativesurfacechargeof thecells.Therefore,particleremovalbymicrobialgranuleswasevaluatedfordif - fe rent calcium concentrations. T wo l aboratory-scale sequencing batch reactors, one with no calcium supplement and the other with a calcium concentration of 100 mg/L, were inoculated with aerobic sludge and operated in parallel. The inuent consisted of synthetic wastewater. A erobic g ranules from the reactors were incubated with particlesuspensionsofdifferentsizes:100-nmuorescentmicrospheres,420-nm uorescent microspheres, and stained cells of Escherichia coli. Researchers used a confocal laser scanning microscope, a ow cytometer, and a uorescence spectrom- e t ertomeasuretherateofparticleremovalandtheaccumulationofparticlesinthe microbial granules. Theresultsshowedthattheadditionofcalciumdidnotenhance the removal of microspheres from the wastewater. M icrospheres w ere adsorbed to the surface of the granules but the depth of penetration did not vary with the calcium concentration, as it did for the E. coli cells [28]. Ivanov et al. concluded that the behavior of inorganic nanoparticles in aerobic wastewater treatment is different from thebehaviorofbiologicalcells. Researchers have shown that at certain concentrations, some nanoparticles may betoxictobacteria. Forexample,Fortneretal.[26]haveshownthatnano-C60inhibits the growth of bacterial cultures at concentrations of 0.4 mg/L or more and decreases aerobic respiration rates at 4 mg/L. Other research supports the antibacterial activity of nano-C60 water suspensions, indicating that suspensions formed by four different processes exhibited minimum inhibitory concentrations ranging from 0.1 to 1.0 mg/ L[29]. A sn oted previously, silver also can have antimicrobial activity. © 2009 by Taylor & Francis Group, LLC 164 Nanotechnology and the Environment 7.2.4 SAND FILTERS Brownian diffusion is the dominant mechanism governing the transport of nanopar- ticles through the granular lter. As t heypassthroughthelter,nanoparticlesare removedfromtheuidstreambyseveralprocesses,including: 1. Brownian diffusion causes the nanoparticles to agglomerate into larger par - ti cles or to agglomerate with the lter grains. 2. Nanoparticles are immobilized by gravitational sedimentation because theirdensityishigherthanthatoftheltermedium,ortheowvelocityis reducedwithinthelterbed. 3. Nanoparticles are intercepted by physical contact with the lter medium [30].Attachmentofparticlestotheltermediumisaffectedbyavarietyof forces, described by the term “attachment efciency,” as discussed further below [31]. The attachment efciency ( F)istheratiooftherateofparticledepositiontothe rate of particle collisions with the lter medium [31]. This parameter is governed byvariousphenomena,includingvanderWaalsforces,theforcesofsolvency,and electrostatic repulsive forces (see Chapter 6). When F is less than unity, conditions are not conducive to particle attachment. When F equals unity, no barriers to particle attachment exist. When F isgreaterthanunity,particlesmaybeattractedtothesur- face of the lter medium over small distances. However, f or very small nanoparticles lessthan2nminsize,therelativeeffectsoftheforcesgoverningtheparameterF can b e unpredictable and different from those of larger particles. If s maller nanoparticles aggregate to form colloidal material, as has been observed for C60 fullerenes and someotherparticles,thebehaviorofthematerialwithinagranularlterwilldiffer fromtheresponsepredictedbasedonthesizeoftheoriginalmanufacturedparticle. Therefore,researchershaveconcludedthatdirectmeasurementofthemobilityof nanoparticlesiscurrentlythemostaccuratemeansbywhichtoquantifytheirbehav - io rinporousmedia[32]. Nanoparticlemobilitywithinaporousmediumisafunctionnotonlyofsize,but also of surface chemistry [32]. Lecoanet, Bottero, and Wiesner [30] conducted labo- ratoryexperimentstoquantifythemobilityofeightdifferentmanufacturednanoma- te rialsinaporousmediumofglassbeads,whichtheresearchersindicatedwouldbe representativeofawatertreatmentplantlterorasandygroundwateraquifer. Their r esults indicated that different forms of nanoparticles with the same composition have different mobilities. For e xample, of the carbon-based particles tested, single-walled nanotubes and fullerols (hydroxylated C60) passed through the porous medium more rapidly than the colloidal aggregate form of C60 knownasnano-C60.Thesolubi- lizedformsoftheparticlesaremoremobilethanthesuspendedform[33]. Conditions in the waste stream, such as pH and ionic strength, will also affect the behavior of nanoparticles in water and the attachment efciency of nanoparticles passing through a lter medium [31]. As n otedabove,Fortneretal.[26]observed thatthepHandionicstrengthofwateraffect,respectively,theparticlesizeandsta- bi lityofthenano-C60insolution. [...]... affect their mobility in porous media Typical surface coatings include polymers, polyelectrolytes, and surfactants, and are often applied with the intention of improving the delivery or mobility of the nanoparticles Because these coatings can affect the surface charge of the nanoparticles or stabilize the particles against aggregation, they may reduce the ability of the filter medium to remove the nanomaterials... processes The extent of that removal, and the potential toxic effects of those nanomaterials, vary substantially between materials Particle size, concentration, and surface properties, as well as the other characteristics of the wastewater, can affect removal REFERENCES 1 The Royal Society and the Royal Academy of Engineering 2004 Nanoscience and Nanotechnologies: Possible Adverse Health, Environmental and. .. wastewater and water treatment Presented at Nanotechnology — Applications and Implications for Superfund, Session 6: Nanotechnology — Fate and Transport of Engineered Nanomaterials National Institute of Environmental Health Sciences, Superfund Basic Research Program, U.S Environmental Protection Agency 16 August 21 U.S Environmental Protection Agency 2000 The History of Drinking Water Treatment EPA-816-F-0 0-0 06... samsung.com/customer/usa/jsp/faqs/print.jsp?AT_ID =70 294 (Accessed September 21, 20 07) 14 Tchobanolglous, G and F.L Burton 1991 Wastewater Engineering: Treatment, Disposal and Reuse, 3rd edition, Chapter 4, p 27 Metcalf & Eddy, Inc New York: McGraw-Hill Publishing Company 15 Skebo, J.E., C.M Grabinsky, A.M Schrand, J.J Schlager, and S.M Hussain 20 07 Assessment of Metal Nanoparticle Agglomeration, Uptake, and Interaction using High-Illuminating... aggregate more soluble and thus potentially more mobile Future research activities will include applying ultraviolet radiation and chlorine to water containing nano-C60 [38] 7. 3 SUMMARY At this early point in the nanotechnology revolution, we know little about the fate of nanomaterials at the end of useful product life The amount of nanomaterial released to the environment may be limited by the relatively... Proceedings of the 20 07 Nanotechnology Conference and Trade Show, ISBN 1420061836, 2: 678 –680 26 Fortner, J.D., D.Y Lyon, C.M Sayes, et al 2005 C60 in water: Nanocrystal formation and microbial response Environ Sci Technol., 39:43 07 4316 27 Hyung, H., J.D Fortner, J.B Hughes, and J.H Kim 20 07 Natural organic matter stabilizes carbon nanotubes in the aqueous phase Environ Sci Technol., 41: 179 –184 28 Ivanov,... in fouling the membrane Particles less than 100 nm in size can pass through the membrane The smaller particles must be pretreated by coagulation prior to the microfiltration (see discussion above), or treated by other means [3] Figure 7. 1 shows the ranges over which these various forms of filtration can generally be effective 7. 2.6 DISINFECTION A research project funded by the NCER for the period from... 24, 20 07) 4 U.S Environmental Protection Agency 20 07 USEPA Nanotechnology White Paper EPA 100/B- 07/ 001 5 Westerhoff, P., T Alford, and B Rittman 20 07 EPA grant description: Biological fate and electron microscopy detection of nanoparticles during wastewater treatment http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/8402/report/0 (Accessed September 23, 20 07) ©... Huang, C., W Jiang, and C Chen 2004 Nano silica removal from IC wastewater by pre-coagulation and microfiltration Water Sci Technol., 50(12):133–138 23 Kvinnesland, T and H Odegaard 2004 The effects of polymer characteristics in humic substances removal by cationic polymer coagulation Water Sci Technol., 50(12):185–191 © 2009 by Taylor & Francis Group, LLC 168 Nanotechnology and the Environment 24 Westerhoff,... focuses on the fate and transformation of C60 nanoparticles in water treatment processes In the 2006 progress report, the investigators, Kim and Hughes, documented the results of applying dissolved ozone, a common disinfectant reagent, to a suspension containing the aggregate nano-C60 The products of this treatment were highly oxidized, soluble fullerenes [38], suggesting that disinfection has the effect . because the toxicity of nanomaterials and theirfateandtransportintheenvironmentwerenotwellunderstoodatthetime, theBritishRoyalSocietyandtheRoyalAcademyofEngineeringrecommended that “factories and. LLC 164 Nanotechnology and the Environment 7. 2.4 SAND FILTERS Brownian diffusion is the dominant mechanism governing the transport of nanopar- ticles through the granular lter. As t heypassthroughthelter,nanoparticlesare removedfromtheuidstreambyseveralprocesses,including: 1 nano-C60, the water-stable aggregate that forms when fullerenes (C60) come in contact with water. Their r esearch shows that the pH ofthewateraffectstheparticlesizeofthenano-C60,andtheionicstrengthaffects thestabilityofthenano-C60insolution[26]. Similarly,