Biomedical Engineering Reference
In-Depth Information
removed. after. 500. days,. while. the. AA. no. longer. removed. phosphorous. after. 50.
days..Phosphorous.nutrients.come.from.septic.systems,.agricultural.products,.and.
industrial.and.municipal.wastes,.and.cause.algae.growth.in.water.
•.
Selenium
(Se).represents.a.primary.inorganic.pollutant.that.can.occur.in.U.S..West.
Coast. groundwater. and. is. found. in. oil. reinery-produced. water,. irrigation,. and.
mining.wastewater,.and.in.power.plant.ash.ponds..Se.concentration.in.oil.rein-
ery-produced.water.varies.from.~50.ppb.to.over.2,000.ppb.with.different.species.
(selenide. (Se
-2
),. selenite. (Se
+4
),. selenate. (Se
+6
)).. Selenate. (Se
6+
,. SeO
4
2-
). and. selenite.
(Se
4+
,
.
SeO
3
2-
).are.found.in.produced.water..While.selenium.is.an.essential.nutrient.
for.humans.and.animals,.it.can.be.toxic.in.higher.doses.
. . Surface-functionalized. (modiied). porous. ceramic. with. nano-iron. was. found.
to.remove.Se.from.synthetic.water.samples.and.actual.challenge.water.samples..
The. synthetic. water. samples. contained. selenite. and. selenate. (50/50);. the. chal-
lenge. water. samples. from. oil. reinery. water. had. 50. ppb. selenium. (selenite. and.
selenate).and.a.high.concentration.(~400.ppm).of.sulfate.(SO
4
2-
),.which.is.consid-
ered.a.primary.competition.ion.for.selenate.due.to.the.similar.molecular.struc-
tures.. Hydrocarbons. and. high. concentrations. of. solids. in. the. challenge. water.
samples. also. provide. obstacles. to. selenium. removal.. The. media. proved. to. be.
effective.in.lowering.Se.from.50.ppb.to.5.ppb.(detectable.limit).with.bed.volumes.
(BV).of.over.40,000.(a.long.life).at.a.contact.time.of.2.minutes..No.other.media.are.
commercially. available. with. a. similar. performance.. Media. were. also. shown. to.
lower.Se.from.220.ppb.to.50.ppb.with.a.1-minute.contact.time.and.a.useful.life.
of. over. 100,000. BV.. In. comparison,. testing. reported. by. the. U.S.. Environmental.
Protection.Agency.(EPA).on.activated.alumina.reduced.selenium.in.groundwater.
from.200.ppb.to.50.ppb.at.a.15-minute.contact.time,.but.it.only.had.a.life.of.1,200.
BV..Selenium.is.considered.dangerous.to.wildlife.and.people,.and.the.EPA.limit.
for.drinking.water.is.5.ppb.
•.
Arsenic
. is. a. serious. contaminant. that. needs. to. be. lowered. in. many. sources. for.
drinking. water.. While. many. methods. exist,. they. are. often. cost-prohibitive..
Nanomaterials.have.great.potential.for.use.in.preparing.effective.iltration.media..
Nano-enabled.media.were.shown.to
lower.arsenic.from.over.50.ppb.to.5.ppb.with.
a.2-minute.contact.time..The.Safe.Drinking.Water.Act.requires.arsenic.levels.to.be.
10.ppb.
.
. It.has.been.shown.that.a.combination.of.nano-manganese.oxide.ibers.combined.
with.nano-iron.oxide.(shown.in.Figure.21.7).is.exceptionally.effective.at.removing.
arsenic. (and. lead). from. water.
6
. This. technology. was. prepared. on. the. porous.
ceramic. media. and. provides. a. cost-effective. approach. with. a. very. fast. removal.
rate. of. arsenic. and. lead. from. water.. Small. column. tests. were. done. at. a. contact.
time.of.0.5.minute.using.National.Sanitation.Foundation.(NSF).“challenge.water”.
containing.50.ppb.arsenic..This.medium.was.almost.equivalent.in.eficiency.for.
the.removal.of.As(III).and.As(V)..As(III).is.much.more.toxic.and.harder.to.remove.
than.As(V);.however,.the.manganese.oxide.ibers.cause.preoxidation.of.As(III).to.
As(V).prior.to.sorption.of.the.As(V).by.nano-iron,.thus.removing.the.need.for.a.
preoxidation.step.during.pretreatment..The.life.of.the.media.was.twice.that.of.a.
commercially.available.iron-containing.medium.
.
. More. than. 4,000. municipal. communities. obtaining. water. from. wells. need. to.
reduce.arsenic.too,.as.well.as.many.commercial.businesses.relying.on.well.water.
