Environmental Engineering Reference
In-Depth Information
Oxygen.or.hydroxy.radicals.are.very.active.substances.with.high.oxidation.
ability.. Some. additives.were.applied.to.generate.these.radicals.by.UV. irra-
diation,.such.as.hydrogen.peroxide..The.UV-H
2
O
2
.system.has.been.applied.
to.produce.hydroxy.radicals.in.the.degradation.of.DMP.(Balabanovich.and.
Schnabel.1998)..The. results.of.experiment.indicated. that.a.higher.degrada-
tion. eficiency. was. obtained. when. DMP. was. exposed. to. UV-H
2
O
2
. system,.
with.over.98%.of.DMP.removed.in.45.min;.in.contrast,.only.60%.of.removal.
was.achieved.under.direct.irradiation.using.UV.for.60.min.
Other.oxidation.methods.such.as.Fenton.reaction.were.also.under.investi-
gation.for.their.potential.application.(Halmann.1992)..The.Fenton.reaction.is.
based.on.the.system.of.Fe
2+
-H
2
O
2
.and.is,.accordingly,.called.Fenton.reagent..
Under. the. irradiation. condition,. by. absorbing. the. photon. energy. the. Fe
2+
.
can.activate.hydrogen.peroxide.to.yield.the.hydroxy.radical,.which.is.highly.
oxidative. in. aquatic. environment.. The. hydroxy. radical. with. highly. oxida-
tive.ability.is.a.main.component.in.the.oxidation.process.involved.with.the.
degradation.of.PAEs..Zhao.et.al..(2004b).used.the.Fenton.reaction.to.oxidize.
DMP.and.demonstrated.that.the.Fenton.system.proceeded.more.eficiently.
in. acidic. condition. (pH. 3.0). than. in. neutral. condition,. attaining. over. 81%.
removal.in.120.min.(Figure.15.2).
Biotic Degradation
Apparently,.abiotic.degradation.of.PAEs.has.merits.such.as.faster.degrada-
tion.and.higher.eficiency..However,.the.disadvantages.are.also.obvious:.high.
investment. costs.as.well.as. the.cost.of.long-term. maintenance..As. a.result,.
in.many.wastewater.treatment.plants,.the.biotic.degradation.treatments.are.
commonly. chosen. for. organic. chemical. degradation.. While. reviewing. the.
biodegradation.studies.on.PAEs,.several.aspects.should.be.noticed,.such.as.
aerobic. or. anaerobic. conditions,. the. study. methods. used. (inoculum. test,.
water.sample.degradation.test,.and.soil/sludge.sample.test),.the.microorgan-
isms.involved,.the.enzymatic.mechanism,.and.the.degradation.pathway.
Aerobic Degradation
Many. research. works. that. studied. PAE. degradation. in. laboratory. were.
based. on. aerobic. condition. because. of. its. easy. operation. and. short. experi-
mental.periods.(Chauret.et.al..1995,.Shah.et.al..1998,.Wang.et.al..2003,.Zeng.
et.al..2004)..The.experimental.instrument.and.culture.medium.were.exposed.
in. the. ambient. air. containing. oxygen.. The. target. chemicals. were. precisely.
measured. and. added. to. the. prepared. mineral. salt. medium. (MSM),. which.
contained. the. essential. inorganic. elements. required. for. microbial. growth..
The. inoculum. was. normally. enriched. from. environments,. including. fresh.
waters,. soils,. sediments,. active. sludge,. and. so. on. and. incubated. using.
an. incubation. shaker.. The. list. of. microorganisms. and. their. degradation.
substrates.surveyed.were.listed.in.Table.15.4.
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