Removal of Persistent Organic Pollutants and Compounds of Emerging Concern in Public-Owned Sewage Treatment Works: A Review - Environmental Contamination: Health Risks and Ecological Restoration - page 150

such.as.a.quaternary.amino.(-.NR 4 ) + ,.are.now.increasingly.being.used.as.
coagulants. for. water. treatment. to. neutralize. the. negatively. charged. par-
ticulate. solids.. Once. suspended. particles. are. locculated. into. larger. par-
ticles,.they.can.usually.be.removed.from.the.liquid.by.sedimentation..The.
removal.of.POPs.and.CECs.during.the.primary.sewage.treatment.process.
for. a. compound. takes. into. account. the. two. main. sorption. mechanisms.
(Ternes.et.al..2004):
•. Absorption:. It. is. the. interaction. of. the. organic. groups. of. the. POPs.
and.CECs.with.the.cell.membrane.of.the.microorganisms.and.lipid.
fractions.of.the.sludge.
•. Adsorption:. It. is. the. physical. binding. of. ions. and. molecules. onto.
the. surface. of. another. molecule. through. electrostatic. interactions.
of. positively. charged. groups. of. a. compound. with. the. negatively.
charged.surfaces.of.the.microorganisms..
Any. chemical. that. binds. to. particles. and. compounds. with. high. lipid.
solubility.and.positively.charged.species.can.be.removed.by.the.primary.
treatment. process.. In. contrast,.compounds.that.are.highly. dissolvable. in.
water.or.have.negatively.charged.compounds.tend.not.to.be.removed.by.
this. process.. Highly. hydrophobic. contaminants. are. most. likely. to. enter.
POSTW. already. bound. to. particulate. matter. and. remain. undetected. in.
the.purely.liquid.portion.of.the.inluent..A.detailed.study.was.conducted.
on.the.effectiveness.of.the.primary.treatment.process.(Snyder.et.al..2007).
involving.the.investigation.of.36.targeted.compounds..The.indings.indi-
cated.that.less.than.20%.was.removed.for.34.of.these.targeted.compounds.
by.coagulation.with.alum.or.ferric.chloride..DDT.and.Benzo(a)pyrene.were.
the.exceptions..The.removal.rates.were.in.the.range.of.20%-50%.for.DDT.
and. 50%-80%. for. Benzo(a)pyrene.. Previous. studies. have. also. indicated.
that.coagulation.and.softening.are.generally.ineffective.for.the.removal.of.
CECs.(AWWRF.2007).
The secondary treatment process .was.designed.to.substantially.degrade.the.
biological. contents. of. the. sewage. that. originates. from. human. waste,. food.
waste,. soaps,. and. detergent.. This. process. relies. on. the. metabolic. activ-
ity.of.a.mixed.population.of.bacteria.to.degrade.organic.material.in.water..
Microorganisms.select.many.organic.and.natural.compounds.for.food.and.
growth. in. their. metabolic. processes.. It. could. take. place. in. aerobic,. anoxic,.
or. anaerobic. environments.. An. anoxic. environment. is. a. condition. where.
oxidized. forms. of. nitrogen. (e.g.,. nitrate). serve. as. electron. acceptors. in. the.
absence. of. molecular. oxygen,. whereas. in. anaerobic. environments. neither.
oxygen. nor. an. oxidized. form. of. nitrogen. is. present.. Microorganisms. use.
inorganic.and.organic.electron.acceptors.in.anaerobic.environments.
CECs. are. usually. present. in. trace. quantities. that. are. insuficient. in. pro-
viding.a.primary.substrate.for.the.growth.of.microorganisms..The.removal.
and.transformation.of.POPs.and.CECs.using.biological.treatment.cannot.be.