Environmental Engineering Reference
In-Depth Information
in.the.nitrifying.activated.sludge,.which.has.a.higher.SRT.(49.days).than.
the.conventional.activated.sludge.(SRT.of.6.days)..In.nitrifying.activated.
sludge,. the. percentage. of. removal. of. iopromide. reached. 61%,. whereas.
average.removal.was.negligible.in.conventional.activated.sludge..For.tri-
methoprim,.removal.was.limited.to.about.1%.in.the.conventional.activated.
sludge,.whereas.in.the.nitrifying.activated.sludge.the.removal.increased.
to.50%.(Batt.et.al..2006).
In. Table. 8.4,. different. removal. eficiencies. can. be. seen. for. ive. antibiot-
ics. (tetracycline,. cephalexin,. norloxacin,. erythromycin,. and. trimethoprim).
from.four.different.sewage.treatment.works.(STW).(Wan.Chai,.Stonecutters.
Island,. Tai. Po. and. Shatin. sewage. treatment. facility). in. Hong. Kong. (data.
extracted.from.Gulkowska.et.al..2008)..The.existing.Wan.Chai.district.sewer-
age.system.was.designed.and.built.before.1970,.which.at.present.is.mainly.
used.as.a.preliminary.screening.facility.that.screens.for.suspended.matter.
with.a.diameter.of.more.than.6.mm..No.removal.eficiency.of.any.antibiotics.
would.be.expected,.and.this.was.conirmed.by.the.data.from.Wan.Chai.STW..
On.the.other.hand,.Stonecutters.Island.sewage.treatment.facility.is.a.chemi-
cally.enhanced.primary.treatment.facility.in.which.chemicals,.including.fer-
ric.iron.and.polymeric.coagulants.for.water.treatment,.are.used.to.treat.the.
sewage;. however,. the. solid. retention. time. (SRT). was. less. than. 2.h.. As. dis-
played.in.Table.8.4,.there.was.no.observable.removal.eficiency.for.any.of.the.
antibiotics..Tetracycline,.cephalexin,.and.norloxacin.were.demonstrated.to.
have.good.sorption.property;.hence,.a.reasonable.removal.eficiency.would.
be.expected.in.those.three.antibiotics.during.the.primary.treatment.process.
(Huang.et.al..2001,.Golet.et.al..2002,.2003,.Karthikeyan.and.Meyer.2006)..No.
observable.removal.eficiency.could.be.detected.for.tetracycline,.cephalexin,.
and. norloxacin. from. Stonecutters. Island. chemically. enhanced. primary.
treated. efluent.. Therefore,. it. would. be. beneicial. if. further. investigations.
could.be.conducted.to.establish.the.cause.of.such.outcomes..Both.Shatin.and.
Tai. Po. STW. are. secondary. treatment. facilities. that. also. include. processes.
for.primary.sedimentation.of.suspended.matter.and.biological.treatment.of.
sewage..As.demonstrated.in.Table.8.4,.signiicant.eficiencies.were.observed.
in.the.removal.of.tetracycline,.cephalexin,.and.norloxacin..The.removal.of.
these. may.be.principally.attributed. to. their. sorption. properties,. whereas.a.
less.signiicant.amount.may.be.justiied.by.biological.degradation..The.HRT.
for.the.Tai.Po.facility.was.reported.as.16.h,.but.it.was.reported.to.be.21.h.in.
the.case.of.Shatin.facility..There.were.better.removal.eficiencies.for.all.the.
investigated.antibiotics.at.the.latter.facility,.which.may.be.explained.by.the.
HRT.being.5.h.longer.than.the.former.facility..Apparently,.HRT.is.also.one.
of. the. major. factors. in. determining. the. removal. eficiencies. of. antibiotics..
The. HRT. was. longer. than. 15.h. for. secondary. treatment. plants. (Shatin. and.
Tai.Po),.but.the.solid.retention.time.was.only.1-2.h.for.the.primary.treatment.
plant.(Stonecutters.Island.STW)..The.extremely.low.concentration.found.at.
the.Tai.Po.facility,.96.ng/mL,.for.tetracycline.in.the.inluent.sample.may.be.
an.anomaly,.as.all.other.STWs'.inluent.concentrations.for.tetracycline.were.
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