Environmental Engineering Reference
In-Depth Information
Over.the.next.several.decades,.federal,.state,.and.local.governments.and.pri-
vate.industry.all.over.the.world.have.to.spend.billions.of.dollars.annually.to.
clean.up.sites.contaminated.with.hazardous.wastes.and.petroleum.products.
from.a.variety.of.industrial.sources..At.the.current.level.of.site.cleanup.activ-
ity. in. the. United. States. (about. $6-8. billion/annum),. it. would. take. at. least.
35.years.to.complete.most.of.the.cleanup.work..In.particular,.MGP.cleanup.
costs.have.been.documented.to.range.from.a.few.hundred.thousand.dollars.
to. $86. million. for. a. single. site;. most. tend. to. be. in. the. $3-10. million. range..
Should. all. 30,000-45,000. sites. need. cleanup,. the. estimated. cost. would. be.
$26-128. billion.. The. increasing. cost. of. these. technologies,. therefore,. forces.
us.to.look.for.the.potentially.low-cost.technologies.such.as.bioremediation.
ApproachesforRemediationofPAHsin
Metal-ContaminatedSystems
Since. 1970s,. research. on. biological. degradation. of. PAHs. demonstrated. that.
bacteria,.fungi,.and.algae.possess.catabolic.abilities.that.may.be.utilized.for.
the.remediation.of.soils.contaminated.with.PAHs..However,.co-occurrence.of.
metals.and.PAHs.in.soil.complicates.the.bioremediation.process..The.strate-
gies.for.remediation.of.soil.contaminated.with.either.hydrocarbons.or.heavy.
metals.have.undergone.considerable.improvement.in.recent.years;.however,.
in. real. ield.situation,. cost.of. treatment. offsets. the. application. of.commonly.
used. remediation. techniques. such. as. land. removal,. incineration,. or. land.
illing..Also,.some.remediation.processes.are.slow.due.to.the.presence.of.het-
erogeneous.mixture.of.organic.and.inorganic.contaminants..This.is.because.
very.few.existing.techniques.(such.as.chemical.oxidation,.microbial,.or.phy-
toremediation).can.deal.with.both.metals.and.organic.compounds..However,.
the.eficiency.of.these.techniques.has.not.been.explored.completely.and.opti-
mized. for. mixed. contaminants. in. soils.. This. remains. to. be. an. unexplored.
area. in. remediation. research.. Bioremediation. approaches. that. involve. PAH.
degradation.in.the.presence.of.metals.must.consider.microbial.mechanisms.of.
metal.resistance.(Hettiarachchi.et.al..2000),.microbial.degradation.(Roane.et.al..
2001),.biosurfactants.(Fraser.2000),.and.abiotic.methods.like.addition.of.natu-
ral.materials.to.reduce.metal.toxicity.(Malakul.et.al..1998,.Sandrin.et.al..2000).
Conclusion
Pollutants. generally. occur. as. mixtures. at. any. contaminated. site.. The. for-
mer.MGP.sites.are.typical.examples.of.such.sites.contaminated.with.various.
inorganic. and. organic.chemicals.. The. available. reports.clearly. indicate. that.
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