Biomedical Engineering Reference
In-Depth Information
1995
2025
Water withdrawal as percentage of
total available
Over 40%
40%-20%
20%-10%
Less than 10%
FIGURE 19.1
(See. color. insert.). Water. withdrawal. rate. as. a. percentage. of. total. available. water,. projected. until. 2025.. (From.
Service,.R.F.,.
Science
,.313,.1088-1090,.2006..With.permission.)
and.diarrhea..In.addition,.it.has.been.estimated.that.over.20.million.people.are.affected.by.
Arsenic.poisoning.in.the.Bengal.region.of.the.Indian.subcontinent.(including.Bangladesh)..
Given.these.brief.statistics,.it.is.not.surprising.that.there.is.a.renewed.focus.on.developing.
new.technologies.for.water.puriication.
2,5
Among.the.many.challenges.that.exist.toward.generating.high-quality.potable.water,.
desalination.of.saltwater.has.been.identiied.as.a.key.step.toward.making.progress.for.
developing.sustainable.sources.for.freshwater.
6
.However,.to.create.effective.desalina-
tion.and.subsequent.distribution.strategies,.it.is.important.to.review.how.the.water.is.
distributed.around.the.planet..The.total.available.water.on.earth.is.approximately.1.4.
×.10
21
.L.(or.about.3.3.×.10
8
mi
3
)..Of.this.seemingly.enormous.water.supply,.over.99%.
of.the.water.is.currently.inaccessible.to.human.use,.and.more.than.97%.of.the.earth's.
water. exists. in. oceans,. bays,. seas,. and. saline. aquifers. as. large. reservoirs. of. saltwa-
ter.. In. fact,. several. estimates. place. the. approximate. supply. of. usable. freshwater. at.
~0.7%,.or.about.9.8.×.10
18
.L..While.this.may.appear.to.be.a.large.number,.accounting.
for.population.increases,.demands.on.freshwater.for.agriculture.and.industry,.poten-
tially. changing. climate,. declining. freshwater. quality. from. worldwide. contamination.
via. industrial,. municipal,. and. agricultural. discharge,. and. increasing. energy. needs.
leads. to. a. rather. bleak. picture. for. future. availability. of. clean. water. for. human. use..
Consider. a. recent. editorial. review
6
. that. reports. data. from. the. World. Meteorological.
Organization. (WMO):. the. combination. of. uneven. population. and. water. distribution.
is. causing. rapidly. increasing. water. withdrawal. rates. as. a. fraction. of. total. available.
water.(Figure 19.1),.and.it.is.projected.that.by.2025.(only.15.years.from.now).most.of.
the.world's.population.will.be.facing.serious.water.stresses.and.shortages..Therefore,.
the. ability. to. affordably. and. sustainably. desalinate. water. can. resolve. many. of. the.
impending.and.projected.water.crises..The.purpose.of.this.chapter.is.to.provide.a.suc-
cinct.literature.review.of.the.current.and.emerging.state.of.science.and.technology.for.
water. desalination,. with. a. particular. focus. on. achieving. the. highest. possible. energy.
eficiency.in.water.desalination.
