Environmental Engineering Reference
In-Depth Information
reactors. and. full-scale. wastewater. treatment. reactors. Nanoparticles. also. will. be.
added.to.laboratory-scale.bioreactors.to.quantify.biotransformations.to.the.nanopar-
ticles.and.toxicity.to.the.microorganisms. Electron.microscopy.imaging.will.be.used.
to.evaluate.the.interactions.between.the.nanoparticles.and.the.biosolids.[5].
No.NCER.progress.reports.were.available.for.the.research.of.Westerhoff,.Alford,.
and.Rittman.at.the.time.of.writing.this.topic. However,.the.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. The. relatively. low.
nanoparticle.concentrations.in.sewage.should.have.negligible.impact.on.the.waste-
water.treatment.plant's.biological.activity.or.performance”.[5]. Preliminary.results.
[20].hint.at.the.possible.behavior.of.C60.fullerenes.in.sewage.treatment. In.initial.
tests,.the.research.team.mixed.a.solution.of.C60.aggregates.and.biomass.in.water,.
then.iltered.the.solids.and.measured.C60.levels.to.determine.the.amount.sorbed.to.
biosolids. These.results.were.incorporated.into.mass.balance.modeling.that.simulated.
the.operation.of.a.wastewater.treatment.plant.at.steady.state. The.results.indicated.
that.22%.of.C60.would.adsorb.to.biosolids.and.the.remainder.would.be.discharged.in.
the.efluent. Westerhoff.[20].noted.that.the.model.estimates.must.be.validated.with.
laboratory.and.ield.measurements.
Ivanov. et. al.. [28]. conducted. research. to. evaluate. whether. microbial. granules.
present.in.a.bioilm.could.remove.nano-.and.micro-particles.from.wastewater.and.
whether. calcium. enrichment,. which. is. typically. applied. to. wastewater. with. high.
organic.loading,.could.enhance.the.removal.of.small.particles. Calcium.ions.enhance.
the.formation.of.microbial.aggregates.by.decreasing.the.negative.surface.charge.of.
the.cells..Therefore,.particle.removal.by.microbial.granules.was.evaluated.for.dif-
ferent.calcium.concentrations. Two.laboratory-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.inluent.consisted.
of. synthetic. wastewater. Aerobic. granules. from. the. reactors. were. incubated. with.
particle. suspensions. of. different. sizes:. 100-nm. luorescent. microspheres,. 420-nm.
luorescent.microspheres,.and.stained.cells.of. Escherichia coli . Researchers.used.a.
confocal.laser.scanning.microscope,.a.low.cytometer,.and.a.luorescence.spectrom-
eter.to.measure.the.rate.of.particle.removal.and.the.accumulation.of.particles.in.the.
microbial.granules. The.results.showed.that.the.addition.of.calcium.did.not.enhance.
the.removal.of.microspheres.from.the.wastewater. Microspheres.were.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.
the.behavior.of.biological.cells.
Researchers.have.shown.that.at.certain.concentrations,.some.nanoparticles.may.
be.toxic.to.bacteria. For.example,.Fortner.et.al..[26].have.shown.that.nano-C60.inhibits.
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]. As.noted.previously,.silver.also.can.have.antimicrobial.activity.
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