Environmental Engineering Reference
In-Depth Information
agglomerates.were.mobile.over.the.pH.range.of.1.to.12..The.mobility.of.the.particles.
was.not.affected.except.around.the.pH.of.zero.point.charge.(pH.=.5.9);.at.this.pH,.the.
agglomerates.settled.out.of.suspension..However,.the.researchers.noted.that.this.initial.
mobility.might.allow.nanoparticles.to.cross.redox.zones.and.to.move.to.regions.of.dif-
ferent.solution.chemistry.or.surface.charge,.resulting.in.uneven.distributions.
Elliott.and.Zhang.[28].performed.a.ield.demonstration.to.evaluate.the.effective-
ness.of.nanoscale.bimetallic.particles.(Fe/Pd).in.degrading.chlorinated.hydrocarbons..
They. injected. the. nanoparticle. suspension. into. a. test. area. of. a. well-characterized.
chlorinated.hydrocarbon.plume.and.monitored.TCE,.total.iron,.and.dissolved.iron.
concentrations..They.experienced.minimal.clogging.of.the.injection.well.and.noted.
that.the.nanoparticle.plume.traveled.at.an.apparent.velocity.of.0.8.m/d,.exceeding.
the. natural. seepage. velocity. of. 0.3. m/d.. They. concluded. that. recirculation. of. the.
groundwater.prior.to.injection.and.dispersion.of.the.nanoparticles.had.contributed.
to. this. latter. effect. [28].. The. movement. of. nanoscale. particle. plumes. at. velocities.
faster.than.the.natural.migration.rate.of.the.contaminant.plumes.has.been.observed.
at.other.sites.[29].
While.past.research.has.focused.on.the.behavior.of.nanoparticles.in.aquifers.and.
other.saturated.porous.media,.ongoing.research.projects.are.looking.at.the.behav-
ior.of.nanoparticles.in.both.saturated.and.unsaturated.soils..The.NCER.has.funded.
research.projects.on.the.following.topics:
•
Agglomeration,.retention,.and.transport.behavior.of.manufactured.nanopar-
ticles.in.variably.saturated.porous.media.[30]
Fate. and. transport. of. carbon. nanomaterials. in. unsaturated. and. saturated.
soils.[31]
•
The. 2006. progress. report. is. available. for. the. latter. project,. which. focuses. on.
nano-C60.and.fullerol..During.the.irst.year.of.the.project,.researchers.at.the.Georgia.
Institute.of.Technology.conducted.40.column.experiments.to.evaluate.the.effects.of.
low.rate,.soil.particle.size,.and.inluent.concentration.on.transport.of.nano-C60.in.
water-saturated.sand.or.glass.beads..They.found.that.the.rate.of.attachment.of.nano-
C60.to.the.porous.medium.depended.on.the.number.of.available.deposition.sites..At.
low.ionic.strength,.nano-C60.behaved.like.a.non-reactive.tracer.and.passed.through.
the.sand,.consistent.with.the.behavior.predicted.by.DLVO.theory..The.second.year.
of.research.will.look.at.transport.in.a.natural.medium,.in.the.presence.of.surfactants.
and.dissolved.organic.matter.[31].
. ConClusions
Laboratory.and.ield.studies.to.date.show.how.nanomaterials.interact.with.each.other.
and. with. other. environmental. constituents. to. affect. their. fate. and. transport.. The.
physicochemical.properties.of.the.nanoparticles,.either.as.engineered.or.as.modiied.
by.reactions.in.the.environment,.may.lead.to.transport.behavior.that.is.dificult.to.
model.precisely..Environmental.variables.such.as.the.pH.and.ionic.strength.of.the.
aqueous.solution,.the.presence.of.dissolved.organic.matter,.and.the.organic.carbon.
content. and. grain. size. of. the. soil. strongly. affect. the. migration. and. disposition. of.
