Treatment of Nanoparticles in Wastewater - Nanotechnology and the Environment - page 162

In.a.project.funded.by.NCER.for.the.period.from.2004.to.2007,.Westerhoff.et.
al.. [24,. 25]. are. researching. the. fate,. transformation,. and. toxicity. of. manufactured.
nanomaterials. in. drinking. water. As. part. of. their. research,. they. have. conducted.
jar. tests. of. coagulation,. locculation,. sedimentation,. and. iltration. to. evaluate. the.
removal.of.metal.oxide.nanoparticles.during.typical.drinking.water.treatment.pro-
cesses. The. metal. oxide. nanoparticles. are. present. in. solution. as. stable. aggregates.
that. range. in. size. from. 500. to. 10,000. nm. [24]. Metal. coagulants. (alum). and. salt.
(magnesium.chloride).were.added.to.solutions.of.commercial.metal.oxide.nanopar-
ticles,.lab-synthesized.hematite.nanoparticles,.and.cadmium.quantum.dots. Accord-
ing.to.a.paper.presented.at.the.NSTI-Nanotech.2007.Conference.[25],.“removal.of.
nanomaterials. by. coagulation,. locculation. and. sedimentation. processes. was. rela-
tively.dificult.” More.than.20%.of.the.commercial.metal.oxide.and.the.laboratory-
synthesized.hematite.nanoparticles.remained.in.the.water.following.these.processes.
For. all. the. nanoparticles. tested,. microiltration. through. a. 0.45-µm. ilter. following.
sedimentation. removed. additional. nanoparticles. However,. 5. to. 10%. of. the. initial.
concentration.of.particles.remained.after.completion.of.the.simulated.drinking.water.
treatment.process.[25].
The.presence.of.other.constituents.in.the.water.can.affect.the.coagulation.and.
locculation.of.nanoparticles. In.a.presentation.to.the.National.Institute.of.Environ-
mental.Health.Sciences,.Westerhoff.suggests.that.dissolved.organic.matter.(DOM).
present. in. water. may. stabilize. nanoparticles. by. inhibiting. the. formation. of. aggre-
gates. The. DOM. thus. affects. the. removal. of. nanoparticles. during. sedimentation.
and.iltration.[20]. For.example,.Fortner.et.al..[26].have.conducted.research.on.the.
factors.that.affect.the.formation.of.nano-C60,.the.water-stable.aggregate.that.forms.
when.fullerenes.(C60).come.in.contact.with.water. Their.research.shows.that.the.pH.
of.the.water.affects.the.particle.size.of.the.nano-C60,.and.the.ionic.strength.affects.
the.stability.of.the.nano-C60.in.solution.[26].
Similarly,. multi-walled. carbon. nanotubes. are. hydrophobic. and. would. be.
expected.to.aggregate.and.settle.out.in.water. However,.researchers.at.the.Georgia.
Institute.of.Technology.have.observed.that.multi-walled.nanotubes.adsorb.to.organic.
material.that.occurs.naturally.in.river.water,.forming.a.suspension.that.persisted.for.
the.month-long.period.of.observation. The.natural.organic.matter.appeared.to.be.a.
better. stabilizing. agent. than. sodium. dodecyl. sulfate,. a. surfactant. often. applied. in.
industrial.processes.to.stabilize.carbon.nanotubes.[27]. This.type.of.interaction.of.
nanoparticles.with.constituents.in.natural.waters.would.likely.affect.their.removal.
7.2.3 a Ctivated s ludge
Some.nanoparticles.can.be.removed.by.adsorption.to.activated.sludge.[3]. A.research.
project.funded.by.NCER.for.the.period.from.2007.to.2010.will.address.the.fate.of.
manufactured.nanoparticles.during.biological.wastewater.treatment. The.investiga-
tors.(Westerhoff,.Alford,.and.Rittman.of.Arizona.State.University).indicate.that.the.
objective.of.their.research.is.to.quantify.the.removal.of.four.types.of.nanoparticles.
(metal-oxide,.quantum.dots,.C60.fullerenes,.and.carbon.nanotubes).during.wastewa-
ter.treatment. Batch.adsorption.experiments.will.be.performed.using.whole.biosol-
ids,. cellular. biomass. only,. and. extracellular. polymeric. substances. from. biological.