applications of nano‐biotechnology in wastewater treatment.pdf

ApplicationsofNanobiotechnologyinwastewatertreatment

Water is one of the most important resources for sustaining human life.Exclusivityofwaterisconsideredcentraltoevolutionoflifeonearth.Reliableandsustainablesupplyofwater isoneofthemostbasichumanitariangoalsandyetremains a challenge to meet globally. Major civilizations developed aroundriverine systems due to availability of ample supply of water and fertile land.Providingcleanandaffordablewatertomeethumanneeds isagrandchallengeofthe21stcentury.Worldwide,watersupplystrugglestokeepupwiththe fastgrowing demand, which is aggravated by population growth, global climatechange,andwaterqualitydeterioration.Theneedfortechnologicalinnovationtoenable integrated water management cannot be overstated. Nanotechnologyholdsgreatpotential inadvancingwaterandwastewater treatment to improvetreatment efficiency as well as to augment water supply through safe use ofunconventional water sources. Developments in nanotechnology have startedproviding reliable solutions forwater andwastewater treatment. The range ofcandidate nanomaterials, properties and mechanisms that enable theapplications,advantagesand limitationsascompared toexistingprocesses,andbarriers and research needs for commercialization will be discussed here.Application of biotechnology knowledge for development of antimicrobialnanomaterials, reduction of pollutants in water using nanomaterials andnanomaterials for removal of contaminants are some of the fieldswhich haveapplicationofbiotechnology.

CurrentandPotentialapplicationforwaterandwastewatertreatment

Nanomaterialsaretypicallydefinedasmaterialssmallerthan100nm inat leastone dimension. At this scale, materials often possess novel sizedependentproperties different from their large counterparts which might already beexplored forthewatertreatmentpurposes.Thesepropertiesmayrelateto thehigh specific surface area, such as fast dissolution, high reactivity, and strongsorption, or to their discontinuous properties, such as super paramagnetism,

localized surface plasmon resonance, and quantum confinement effect. Mostapplicationsarestillinthestageoflaboratoryresearch.

1) AdsoptionAdsorption iscommonlyused to removeorganicand inorganiccontaminants inwaterandwastewatertreatment.Nanosorbentsprovidesignificantimprovementoverconventionaladsorberntswiththeirextremelyhighspecificsurfaceareaandassociatedsorptionsites,short intraparticlediffusiondistance,andtunableporesizeandsurfacechemistry.a) Carbonbasednanoadsorbents OrganicremovalCNT isbetterthanactivatedcarbon forremovalofvarious

organicwastes chemicals. Its high adsorption capacity ismainly due to thelarge specific surfaceareaand thediversecontaminantCNT interactions. Inaqueousphase,CNTformaggregatesduetohydrophobicityoftheirgraphiticsurfaces. These aggregates contain interstitial spaces and grooves forwithhighabsorptionenergy fororganicmolecules.CNTshavemore capacity forabsorptionororganicbulkymoleculesbecauseof largepores inbundlesandmoreaccessiblesorptionsites.Theyabsorbpolarorganiccompoundsduetodiverse contaminantCNT interactions like hydrophobic effect, pipiinteractions (for polycyclic aromatic hydrocarbons, Polar aromaticcompounds), hydrogen bonding(for compounds with COOH, NH2, OHfunctional groups), covalent bonding and electrostatic interactions (forpositivelychargedorganiccontaminantslikeantibiotics).

HeavymetalremovalOxidizedCNTshavehighadsorptioncapacityformetalionswith fast kinetics. The surface functional groupsofCNTs absorbmetalions through electrostatic interactions and chemical bonding. Thus, surfaceoxidationcansignificantlyenhancetheabsorptioncapacityofCNTs.Theymaynotbeagoodalternativeforactivatedcarbonaswidespectrumadsorbents,but since their surface chemistry can be tuned to target specificcontaminants, they may have unique applications in polishing steps toremove recalcitrant compounds or in preconcentration of trace organiccontaminants for analytical purposes. Recently it was found that sand

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AntimicrobialNanomaterialsThe antibacterial nanoparticles are classified into three general categories:naturally occurring antibacterial substances, metals and metal oxides, andnovelengineerednanomaterials.Thesenanoparticlesinteractwithmicrobialcellsthroughavarietyofmechanisms.Thevarioustypesofantimicrobialnanomaterials are reviewed in this paper. The nanoparticles can eitherdirectly interact with the microbial cells, e.g. interrupting transmembraneelectrontransfer,disruptingorpenetratingthecellenvelope,oroxidizingcellcomponents,orproducesecondaryproducts(e.g.reactiveoxygenspecies(ROS)ordissolvedheavymetalions)thatcausedamage.AntimicrobialNanomaterialsandDisinfectionMechanismsVarious antimicrobial nanomaterials and their disinfecting mechanisms arereviewedfromliteratureasfollowing.1)ChitosanandPeptidesSynthesizednanoparticlesofnaturallyoccurringchitosanandpeptideshavemany potential applications in low cost water disinfection systems. Theantibacterialmechanismofnaturalpeptides isosmoticcollapse through theformation of nanoscale channels in bacterial cell membranes. Theantimicrobial properties of chitosan nanoparticles have been explained byvarious mechanisms. One theory proposes increase in membranepermeability and eventual rupture and leakage of intracellular componentswhenthepositivelychargedchitosanparticlesreactwithnegativelychargedcellmembranes as the chief antimicrobialmechanism.AnothermechanismproposeschitosanpenetratescellmembranewallsandbindswithDNAandthus inhibits RNA synthesis in cells. Potential applications of nanoscalechitosanandpeptidesincludesurfacecoatingsofwaterstoragetanksorasanantimicrobialagentinmembranes,sponges.2) Silver Nanoparticles Nanoparticles of silver release large quantities ofsilver ions (Ag+)when they interactwithbacterialcells.These ionsareveryreactiveand form reactiveoxygenspecies (ROS)within thecellsby reactingwith thiol groups in the enzymes. ROS formation renders the respiratory

enzymes inactive leading to cell death. The structural integrity andpermeability of the cell membrane is compromised by Ag + ions whichaccumulate inside themembrane by forming pits causing large increase inmembranepermeability.Ag+ionsalsopreventDNAreplicationbydamagingDNAandRNA.SilverionsalsoshowphotocatalyticactivityinpresenceofUVradiation and this isuseful indisinfectionofmicrobes.Many currentwaterpurification and disinfection systems use membranes impregnated withnanoscalesilverparticles.3)Ti02NanoparticlesTi02showsexcellentphotocatalyticactivityinpresenceofUVradiation.TheantibacterialactivityofTi02ismainlydueto ROS production, especially hydroxyl free radicals and peroxide formedunder UV irradiation by means of oxidative and reductive sequence ofchemicalreactionstakingplacewithinacell.OneoftheimportantfeaturesofdisinfectionusingTi02nanoparticlesistheirabilitytoshowphotocatalyticactivityeven inpresenceofvisiblesunlight.ThiscanbeenhancedbydopingTi02withvariousmetals.Ti02iswidelyusedinmanydisinfectionapplicationsnowadays.Ti02 issuitable forapplications inwatertreatmentbecause it isstable inwater,nontoxicby ingestionand lowcost.Ti02canbeappliedasathinfilmcoatedonareactorsurfaceoramembranefilterorasasuspensioninaslurryUVreactor.4)ZnONanoparticlesSimilartoTi02,nanosizedZnOalsoshowshighUVabsorption efficiency and photocatalytic activity. One of the mainmechanismsofphotocatalyticdegradationbyZnOisattributedtogenerationofhydrogenperoxidewithinthecells.Conclusion Clean water is essential and critical for all human activitiesranging from simple household chores to the very complex industrial andagricultural processes. Current water distribution and supply concepts areinefficientowingthevariousdrawbacksofthesesystemswhichincludelargedemandonresources,lowefficiencyinwaterpurificationandtreatment,highcost of operating the plant, chances of contamination during transport toremote locations etc.Currentwaterpurification andwastewater treatmentmethodscancontroltheorganicandinorganicwastesfromwater.But,these

methods are energy intensive and uneconomical because of nonreusablemembranesandfilters,inabilitytocompletelypurifywater,inabilitytomakereuseoftheretentate,etc. Variouskey issuesandchallengesstillremain insuccessfulincorporation,scalingupandcommercializationofnanotechnologyapplications in inhibiting thebacterialpathogens, removalofheavymetals,xenobiotics leading to water purification and wastewater treatment. Theability to synthesize cost effective nanomaterials and their availability atindustrial scale will determine the progress rate at which nanotechnologyapplications are accepted on industrial level. This chapter gives an overallglimpse of the applications of nanobiotechnology in controlling the waterqualityinwastewater.

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