Environmental Engineering Reference
In-Depth Information
a.shorter.leaching.time.might.result.in.lower.concentrations.than.were.measured.in.
the.experiment.
The.difference.in.the.volume.of.wash.water.alone.might.account.for.
dilution.by.a.factor.of.25;.additional.dilution.by.other.sources.of.wastewater.would.
reduce.the.concentration.still.further.
The.most.dificult.variable.to.quantify.would.
be.the.number.of.socks.washed.per.load.of.laundry.(although.as.any.parent.would.
attest,. that. variable. could. increase. the. estimated. discharge. of. silver. by. at. least. an.
order.of.magnitude.over.the.estimate.from.washing.a.single.sock).
As. these. examples. show,. estimating. the. discharge. of. nanomaterials. from. the.
use.of.commercial.products.is.no.simple.matter.
The.mass.or.concentration.released.
to.the.environment.depends.on.the.amount.and.availability.of.the.material,.among.
other.factors,.and.such.proprietary.information.can.be.dificult.to.obtain.
The.p
os-
sible.effects.of.exposure.can.only.be.inferred.from.the.developing.toxicological.data-
base.
Some. research. is. beginning. to. produce. information. on. the. possible. fate. of.
nanomaterials. once. released;. the. next. section. of. this. chapter. describes. the. fate. of.
nanomaterials.in.a.municipal.wastewater.treatment.plant.
. 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.
suspended. solids. by. settling. or.
sedimentation
,. and. to. skim. off. loating.
greases
Biological.treatment,.to.promote.degradation.or.consumption.of.dissolved.
organic.matter.by.microorganisms.cultivated.in.
activated sludge
.or.trick-
ling.ilters
Chemical.treatment,.to.remove.other.constituents.by.chemical.addition,.or.
to.destroy.pathogenic.organisms.by.
disinfection
Advanced. treatment,. to. remove. speciic. constituents. of. concern. by. such.
processes.as.activated.carbon,.
membrane separation
,.or.ion.exchange
•
•
•
Similar. processes. are. used. in. drinking. water. treatment..
Coagulation
,. by. the.
addition.of.alum.and.other.chemicals,.removes.suspended.solids.that.cause.turbidity.
and.objectionable.taste.and.odors..The.
loc
.formed.during.coagulation.is.removed.
by.sedimentation..
Sand ilters
.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.
incorporate.sand.iltration.)
Disinfection
.removes.bacteria.or.microorganisms.[21].
Processes.indicated.in.italic.font.above.are.discussed.with.regard.to.their.poten-
tial.to.remove.nanoparticles.from.waste.streams.
7.2.1 s
edimentatiOn
Sedimentation.or.settling.is.intended.to.remove.suspended.inorganic.particles.that.are.
1.µm.in.size.or.greater.
Because.of.their.size,.free.non-agglomerated.nanoparticles.
