Biomedical Engineering Reference
In-Depth Information
supplies..At.the.same.time,.groundwater.supplies.in.the.United.States,.and.especially.in.
some.third.world.countries,.have.serious.contaminants..Arsenic.is.found.to.be.a.natural.
groundwater. contaminant. in. many. areas. of. the. world. (especially. in. Bangladesh,. where.
25%.of.the.population.is.at.high.risk)..Arsenic.levels.in.the.United.States.exceed.the.new.
standard. in. thousands. of. communities.
2
. Lack. of. access. to. clean. water. and. sanitation. in.
developing. countries. remains. a. high. development. priority,
3
. and. increased. emphasis. is.
being.given.to.point-of-use.water.treatment.methods.
Traditional. approaches. for. water. treatment. include. iltration. to. remove. trash,. sinkers,.
and.loaters;.chemical.locculation.to.remove.suspended.solids.(and.to.change.dissolved.
solids.into.suspended.solids.for.removal);.ion.exchange/sorption.to.remove.low-concentra-
tion.materials.that.locculants.cannot.address.cost-effectively;.aeration.to.remove.dissolved.
gases.and.high.vapor.pressure.dissolved.liquids;.and.disinfectation.(and.dechlorination)..
Specialty.treatments.may.include.desalination.(brine.and.salt.water.for.drinking).or.demin-
eralization.(lab.and.industrial.processes)..While.these.conventional.approaches.work,.they.
are.often.expensive,.especially.for.smaller.communities..Demand.for.water.reuse.is.rap-
idly.increasing,.and.this.trend.will.continue,.especially.for.nonpotable.applications.
New.approaches.are.in.demand.and.are.continually.being.examined.to.supplement.tra-
ditional.water.puriication.methods,.where.the.cost.for.using.conventional.water.treatment.
facilities. is. not. sustainable. in. the. future.. Infrastructure. in. some. municipalities. is. aging.
and.contributes.to.up.to.50%.of.water.being.lost.during.transport..Better.solutions.need.
to. be. lower. in. overall. cost,. durable,. and. more. effective. for. the. removal. of. contaminants.
from. water,. either. in. situ. or. in. water. puriication. systems.. It. is. in. this. context. that. both.
higher-performance. bioiltration. and. nano-enabled. technologies. are. being. examined..
These. consist. of. iltration. materials. that. have. enhanced. performance. arising. from. high.
concentrations.of.beneicial.facultative.bacteria,.higher.speciic.surface.area,.and.an.abun-
dance.of.surface.state.electrons.found.in.ilms.and.parts.containing.nanomaterials..These.
bio. and. nano-enabled. technologies. will. play. a. signiicant. role. in. water. treatment. in. the.
future.
21.2 Bioremediation
Bioremediation. (using. beneicial. bacteria). has. historically. offered. an. environmentally.
elegant.method.for.dealing.with.waste.streams.where.longer.contact.times.can.be.used,.
especially. for. management. of. nitrogen. compounds.. For. waste. gas. cleanup,. bioremedia-
tion.is.favored.over.more.expensive.and.environmentally.damaging.technologies,.such.as.
thermal.incineration.and.chemical.treatment.
For.improved.bioremediation.systems,.bacteria.carriers.are.needed.that.provide.higher.
surface.areas.to.allow.signiicantly.more.room.for.growth.of.active.biocolonies.of.benei-
cial.bacteria.than.traditional.media.available.today..More.surface.area.available.generally.
increases.the.rate.of.bioiltration.action..Conventional.media,.such.as.urethane.foam,.plas-
tic. materials,. or. many. ceramics,. have. only. moderate. surface. areas. available. for. bacteria.
growth,. which. limits. their. effectiveness,. often. leading. to. undesireable. clogging. due. to.
excessive.bacteria.growth..Alternatively,.a.highly.porous.ceramic.containing.a.hierarchy.
of.interconnected.pores,.ranging.from.millimeters.to.nanometers.in.size,.is.available.for.
both.bioremediation.and.nano-enabled.iltration..This.ceramic.typically.has.over.5.times.
the.surface.area.available,.compared.with.open.urethane.foams,.and.frequently.20.times.
