Biomedical Engineering Reference
In-Depth Information
21.5 Nano-EnabledApproach
The.typical.surface.area.of.the.porous.ceramics.used.can.be.signiicantly.increased.through.
the.growth.of.nanomaterials.in.the.pores.of.this.ilter.material..This.can.increase.the.sur-
face. area. by. 50. to. 200. times. and. even. higher,. thus. providing. a. very. effective. medium.
that.only.requires.short.contact.times.between.the.contaminant.and.the.active.ilter.agent..
This.in.turn.greatly.enhances.the.iltration.media.performance.and.reduces.the.amount.
of.media.needed.
How. effective. the. nano-enabled. media. will. be. frequently. determines. both. the. cost. and.
footprint.of.the.system..For.a.given.set.of.conditions.and.contaminant.levels,.key.factors.are
•.
How long must the water remain in contact with the ilter media?
. This. is. typically.
referred.to.as.empty.bed.contact.time.(EBCT),.and.
shorter is better
.since.it.reduces.
the.size.of.the.system.and.its.capital.cost..Effective.iltration.media.need.shorter.
contact.times.
. . Metals.(e.g.,.Se,.As,.Pb).are.removed.in.1-2.minutes.vs..a.normal.10-.to.20-min-
ute.time.
. . Removing.contaminants.more.quickly.lowers.system.capital.cost.by.40%.or.more.
•.
How long will the ilter media last?
.This.is.typically.referred.to.as.the.number.of.bed.vol-
umes.(BV).of.contaminated.water.passed.through.a.system.before.the.contaminant.
in.the.water.being.discharged.(efluent).exceeds.the.allowable.limit..
More BV is bet-
ter
.since.it.determines.how.frequently.the.media.must.be.replaced.or.regenerated.
. . Nanomedia.for.removing.Se.and.P.lasted.10.times.longer.than.conventional.media.
•.
What are the operating costs of a system using a particular media?
Operating.costs.can.
include.energy.in.the.form.of.electricity.or.pressure,.as.well.as.replacement.cost.
of.the.media..High.low.rates.without.pressure.increases.are.also.better.and.desir-
able..If.pressure.to.low.water.through.the.media.bed.is.higher,.the.operating.costs.
will.increase.
The. type. of. nanomaterial,. along. with. the. methods. used. to. prepare. and. grow. these.
materials. onto. the. porous. substrate,. and. also. the. composition. of. the. porous. material,.
will. largely. determine. performance. for. removal. of. speciic. contaminants.. Active. agents.
like.manganese.oxide.can.be.used.to.change.the.valence.state.of.metal.ions.in.water.(e.g.,.
using.manganese.oxide.to.oxidize.arsenic.from.the.+3.to.the.+5.state),.which.can.be.more.
easily.removed.by.reaction.with.nano-iron.oxide.hydoxide.compounds..Nano-iron.oxide.
compounds.are.widely.used.to.break.down.organics,.pesticides,.and.such.materials.into.
nonhazardous. compounds.. Often. reactions. are. enhanced. through. the. addition. of. other.
nanomaterials,.such.as.copper.or.copper.oxide.
Coupled. with. application-speciic. nano-engineered. agents,. the. resulting. media. can.
effectively.remove.phosphates,.heavy.metals,.lead,.arsenic,.and.other.pollutants.as.water.
lows.through.or.into.the.porous.ilter.media..Porous.ceramics.also.can.be.made.to.sup-
port.thin,.nanostructured.membranes.with.thicknesses.under.100.nm..Figure.21.6.shows.
a.cross.section.of.a.membrane.supported.on.a.porous.alumina.substrate..These.ceramic.
membrane. ilters. can. provide. eficiency. beneits. and. low. rates. shown. in. the. laboratory.
to.be.100.times.higher.than.those.of.conventional.reverse-osmosis.iltration.membranes,.
which. have. the. potential. to. reduce. the. waste. of. signiicant. quantities. of. water. now.dis-
posed.of.during.water.cleanup.with.the.membrane.technology.
