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FATE OF EDCS IN WASTEWATER TREATMENT
AND EU PERSPECTIVE ON EDC REGULATION
Hansruedi Siegrist
1
,* Adriano Joss
1
, Thomas Ternes
2
, Jörg Oehlmann
3
*
1
Swiss Federal Institute for Environmental Science and Technology (EAWAG),
Überlandstrasse 133, PO Box611, CH-8600 Dübendorf, Switzerland
2
Federal Institute of Hydrology (BFG, Koblenz, Germany
3
University of Frankfurt am Main, Frankfurt, Germany
ABSTRACT
Municipal wastewater is one of the main exposure routes that brings the most important EDCs
like natural and artificial hormones via urine, ingredients of personal care products and detergent
via grey water (e.g. alkylphenol) and ubiquitous industrial chemicals (e.g. Bisphenyl A) into the
environment.
Whether trace pollutants can be eliminated in a WWTP depends on the biological treatment
standard (Ternes et al., 2004). In Europe, mainly activated sludge systems are installed for
biological treatment. Biological treatment has been developed step by step during the past 50
years starting from only BOD removal with short sludge retention times (SRT <4 days),
followed by nitrification and denitrification with an extension of the SRT to 10-15 d and finally,
in the last 15 years, introduction of anaerobic zones for P removal with total SRT = 15-25 d.
Degradation of EDCs is strongly improved with increasing SRT. Whereas natural hormones (E1
and E2) are partly degraded at SRT <5 days, EE2 is only significantly removed at SRT >10 days
(Andersen et al., 2003). Biofiltration reaches similar removal efficiencies if designed for nutrient
removal (Joss et al. 2004). With membrane bioreactors having SRT of more than 30 days an
increased alkylphenol degradation (>95%) was observed (Wettstein, 2004). Sorption plays only
a minor role if a compound is degraded.
In the raw wastewater the hormones are mainly responsible for the estrogenic effect. In the outlet
of nutrient removal plants the contribution of other EDCs like alkylphenols, bisphenols,
phthalates and today unknown compounds become important because hormones are degraded by
more than 95%. Even more so, since the strong focus on fish as the currently dominating sentinel
group for aquatic ecotoxicity testing and monitoring bears the risk of underestimating the
potential impact from non-steroidal estrogenic compounds for other aquatic wildlife groups,
particularly invertebrates (Oehlmann et al., 2005).
For sensitive receiving waters with low wastewater dilution or direct infiltration, partial
ozonation (2-10 gO
3
m
-3
, depending on the background DOC) can be an economic (<0.1 $ m
-3
)
but energy consuming solution (0.05-0.15 kWh m
-3
wastewater) allowing the removal of more
than 90% of the compounds (Huber et al., 2005) in the plant outlet. But before starting a broad
application of post ozonation the fate and effect of oxidation products should be extensively
investigated.
On long term, source control measures (ban of hazardous chemicals or labeling of consumer
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articles) and source separation (e.g. separate treatment of hospital and industrial wastewater)
should be established to reduce the load of hazardous compounds in the municipal wastewater
(Siegrist et al., 2003).
In the EU currently none of the environmental regulations are specifically dealing with
endocrine disrupting compounds although compounds with endocrine related functions are
mentioned in the EU Water Framework Directive. In the substance priority list of the EU only
alkylphenols, phthalates and triazines are mentioned as hazardous compounds. However, they
are included not due to their endocrine properties, but due to their overall toxicity. Within the
registration of pesticides, endocrine effects are covered in chronic effect studies. Nevertheless, it
is expected that current research projects focusing on EDCs will lead to environmental
regulations covering endocrine issues.
KEYWORDS
Endocrine disrupting compounds, estrogenicity, biological wastewater treatment, ozonation,
source control and separation, regulation.
INTRODUCTION
In the last forty years the treatment requirements for wastewater treatment plants (WWTP) have
been increasing, starting with the reduction of the organic pollution in the sixties, followed in the
seventies and eighties by the nitrification of the fish toxic ammonia to nitrate and nutrient
removal (nitrogen and phosphorus) to decrease the eutrophication of freshwater lakes and marine
coastal waters (Fig. 5). In parallel, measures at the source (e.g. pretreatment in industry, ban of
compounds) had been quite successful in reducing the load of heavy metals and certain persistent
industrial chemicals in the sewage, enhancing the agricultural use of hygenised and stabilized
sewage sludge.
During recent years, chemicals with estrogenic activity have received increasing attention due to
there occurrence in the aquatic environment and the growing concern that these endocrine
disrupting chemicals (EDC) may cause serious reproductive effects in aquatic organisms
(Spengler et al., 2001; Witters et al., 2001; Jobling and Tyler, 2003; Vethaak et al., 2005). EDCs
were found partly responsible for the impairment of the trout population below the discharges of
WWTPs (Escher et al., 1999).
Durrer et al. (2000) could detect a significant estrogenic activity in the inlet and outlet of
different Swiss WWTP (Figure. 1). The reduction of the estrogenic potency was only in the
range of 10-40% whereas with the human estrogen receptor D-test, hosted in a yeast strain,
Svenson et al. 2001 observed more than 60% reduction of the estrogenicity in WWTPs with
activated sludge treatment; for mechanical treatment no reduction of estrogenicity was observed.
The measured estrogenic potency of WWTPs in-/outlet was for both investigations in the same
range of 1-20 Estradiol equivalents (ng/l).
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Figure 1 – Estrogenic impact of mechanically and biologically treated wastewater of different
Swiss municipal wastewater treatment plant. A few of them (Focce Maggia, Focce Ticino,
Brissago, Bühler) are only partly nitrifying, the others are fully nitrifying but two are strongly
loaded with industrial wastewater (Kloten/Opfikon, Wattwil). It is clearly seen that the
estrogenic effect is only partly reduced. Study done with the proliferation of MCF-7 breast
cancer cell; 100% corresponds to the induction of 30 ng l
-1
of the natural hormone 17E-Estradiol
(Durrer et al., 2000).
0
10
20
30
40
50
60
70
Kl
ote
n/Op
f
i
k
on
F
o
ce Magg
i
a
Fo
c
e T
i
cino
Brissago
Ho
r
g
e
n
/
Ob
erri
e
d
e
n
W
att
wi
l
B
ü
h
l
e
r
W
a
rt
a
u
I
n
wil
Relative Estrogenic Impact (100%)
.
Mechanical treatment
Biolo
g
ical treatment
Relative estrogenic activity (%)
0
10
20
30
40
50
60
70
Kl
ote
n/Op
f
i
k
on
F
o
ce Magg
i
a
Fo
c
e T
i
cino
Brissago
Ho
r
g
e
n
/
Ob
erri
e
d
e
n
W
att
wi
l
B
ü
h
l
e
r
W
a
rt
a
u
I
n
wil
Relative Estrogenic Impact (100%)
.
Mechanical treatment
Biolo
g
ical treatment
Relative estrogenic activity (%)
Municipal wastewater is one of the main routes of emission into the environment for most
important EDCs like natural and synthetic estrogens via urine, as well as ingredients of personal
care products and detergent via grey (washing) water (e.g. alkylphenolpolyethoxylates, UV
filters), phytoestrogens from food processing and consumption (e.g. E-sitosterol, genistein) and
ubiquitous chemicals used in different industrial products getting in contact with water (e.g.
tubes, paintings, plastics releasing xenoestrogens like bisphenol A, organotin and phthalates)
(Johnson and Sumpter, 2001; Körner et al., 2001; Desbrow et al., 1998; Routledge et al, 1998;
Houtman et al., 2004).
What also has to be beard in mind is the loss of pollutants in the sewer system due to combined
sewer overflow (CSO) and exfiltration from leaky sewers into ground water. CSO brings less
than 1% of the total load in raw wastewater (Brombach et al., 1999). Assuming a 50 to 90%
elimination of EDCs during wastewater treatment, the CSO discharges maximal 2 to 10% of the
total load to surface water. Luckily, during storm water events rivers and creeks have an
increased flow that dilutes the effect of CSOs.
In the greater London region Bishop et al. (1998) estimate a wastewater loss of 5% by
exfiltration. Fenz et al (2004) calculated from monitoring results of the persistent pharmaceutical
Carbamazepine in groundwater and raw sewage an exfiltration rate of 1-4% expressed as
percentage of the dry weather flow. Other investigations in Germany (Stein, 1999) estimate the
exfiltration rate of public sewer system with 6-10%, which corresponds to a specific wastewater
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loss of about 15 l p
-1
d
-1
. The EDC load of by exfiltration corresponds to 10-100% of the WWTP
effluent load, assuming 50-90% EDC elimination.
COMPARATIVE ESTROGENICITY OF SINGLE EDCS IN WWTP OUTLET
To estimate the potential impact of single EDCs on wildlife, the average, observed WWTP
effluent concentration has to be multiplied with its specific estrogenic potency. This procedure
would help to evaluate the effect of potential measures in urban wastewater management to
reduce the estrogenicity in WWTPs discharges (Houtman et al., 2004; Körner et al, 2001;
Desbrow et al. 1998, Routledge et al., 1998; Snyder et al., 2001).
The observed estrogenic potencies of EDCs depends strongly on the test system (in vivo vs. in
vitro) and the test organisms (e.g. human, mammalian, fish, snails; Figure 2). The estrogenic
potency of the synthetic 17D-Ethinylestradiol (EE2) is much larger for in vivo tests (vitellogenin
production in trouts) than for in vitro receptor tests, using 17E-Estradiol (E2) as a standard
reference (Sumpter et al., 2001).
Most studies analysed estrogenic effects in fish while other modes of endocrine modulation such
as androgenicity, antiandrogenicity, antiestrogenicity, interference with thyroid hormones and
further wildlife groups received by far less attention despite the occurrence of these EDC classes
in WWTP effluents and the fact that fish represent only a minor, although economically
important part of the aquatic biodiversity (Levy et al., 2004).
Reports on endocrine disruption in freshwater fish populations range from subtle physiological
and behavioral changes such as vitellogenin induction and courtship impairment to alterations in
sexual differentiation like the development of ovotestes. However, only few studies
demonstrated population-level consequences as a result of exposure to EDCs. Jobling and Tyler
(2003) have shown that roach (Rutilus rutilus) exposed to treated sewage effluent in UK rivers
are characterised by a reduced reproductive capacity, which in turn may have population-level
consequences. It is well documented for fish that the majority of observed endocrine disruption
effects in field populations is due to the exposure to natural and synthetic steroidal estrogens and
their breakdown products such as 17ß-estradiol (E2), estrone (E1) and 17Į-ethinylestradiol
(EE2) (Thorpe et al., 2003). Industrial chemicals with an estrogenic activity like plasticisers,
alkylphenols and their ethoxylates seem to contribute to the observed effects in wildlife fish to a
lesser extent (Thorpe et al. 2001).
Based on these results in fish it was concluded that a large fraction of the pollution which is
responsible for the observed endocrine disrupting effects in wildlife stems from natural and
synthetic steroid hormones excreted by humans, and the emission of those can hardly be
controlled without improvement of the sewage treatment technology (Jobling and Tyler 2003).
Indeed, it has been shown that the degree of feminization and other endocrine mediated
responses in wild fish can be predicted with high accuracy, based on the calculated exposure to
E1, E2 and EE2 using geography-reference chemical exposure prediction tools such as GREAT-
ER (Geo-referenced Regional Exposure Assessment Tool for European Rivers) (Schröder, 1997;
Schowanek et al., 2001).
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However, it is at least questionable whether natural and synthetic steroid estrogens and their
breakdown products are equally important as EDCs in wildlife groups other than fish. Even
between different fish species, the relative sensitivity to known EDCs and estrogenic effluents
may vary dramatically (Tyler et al., 2005). This potential bias in the discussion on the
contribution of the various estrogenic chemicals to the observed effects in natural populations is
fueled by the imbalance in current research and monitoring activities strongly focused on
endocrine disruption in fish. Other groups of aquatic organisms like amphibians and
invertebrates have found by far less attention, although the latter provide some of the best
documented examples of endocrine disruption in wildlife with proven population-level effects.
Further, with more than 95% of all known animal species, these represent an extremely
important part of the biodiversity (Oetken et al., 2004). Indeed, there is little evidence to suggest
that fish are more susceptible to EDCs relative to other wildlife groups: it has been shown that
substances affecting fishes as well as a number of other compounds have the potential to affect
invertebrates by interfering with their often unique endocrine systems (for review Oetken et al.,
2004). As yet, however, there is little information on the relative sensitivities of different wildlife
groups to these chemicals and their mixtures (as found in WWTP effluents).
Figure 2 – Specific estrogenic potencies of important EDCs in vitro and in vivo (Sumpter et al.,
2001; Oehlmann et al., 2005) compared to the estrogenicity of 17E-Estradiol.
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1
7
b
-E
2
E
E2
E1
17a-E2
E3
Nonylphenol
E1-Sulf
a
te
Geniste
i
n
1
7
b
-E2
-su
l
fa
te
B
i
s
p
h
e
n
o
l
A
E2-Glu
c
uronide
NP1EC
Di
butyl
p
ht
h
ala
t
e
Estradiol Equivalente [ng/l]
In vitro tests
In vivo (vitellogenin)
In vivo (water snail)
The comparison of threshold concentrations for the induction of endocrine-mediated effects
highlights the considerable differences in sensitivity of fish and aquatic invertebrates to various
classes of estrogenic chemicals. For bisphenol A (BPA) Sohoni et al. (2001) determined in a
multi-generation study with fathead minnows (Pimephales promelas) a no observed effect
concentration (NOEC) for reproduction of 16 µg/L, while the corresponding value in the
freshwater ramshorn snail (Marisa cornuarietis) was 8 ng/L according to Oehlmann et al.
(2005), indicating that prosobranch snails are by a factor of 2,000 more sensitive to this
estrogenic chemical than fish. This difference seems to be at least partially due to structural
differences of estrogen receptors in fish and mollusks. In contrast to these industrial chemicals,
fish and mollusks seem to be almost equally sensitive to estrogenic steroids such as EE2: a
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NOEC of 1 ng/L for reproductive effects was found in M. cornuarietis (Schulte-Oehlmann et al.,
2004) as well as for full life-cycle test with zebra fish (Danio rerio; Young et al. 2002).
The average WWTP effluent concentration presented in Figure 3 could be significantly lower for
well functioning nutrient removal plants with increased SRTs (see below), assuming that the
inlet is not strongly polluted with industrial wastewater.
Figure 3 – Average WWTP effluent concentrations of selected EDCs (Desbrow et al. 1998,
Routledge et al, 1998, Snyder et al, 2001; Sumpter et al., 2001; Johnson et al., 2005)
0.1
1.0
10.0
100.0
1000.0
10000.0
1
7
b-E2
EE2
E1
17a-E2
E3
N
on
ylp
he
nol
E1-Sulfate
Ge
n
ist
ei
n
1
7b-E2-sulfate
B
i
sph
en
o
l
A
E
2
-G
l
ucuro
ni
de
NP1
EC
Dibutyl phthalate
Average concentrations [ng/l]
Figure 4 – Estrogenicity of important EDCs calculated with the product of the average
concentration presented in Figure 3 and the specific estrogenic potency presented in Figure 2.
0.00001
0.0001
0.001
0.01
0.1
1
10
100
17b
-
E2
EE2
E1
17a-E2
E3
Non
y
l
p
heno
l
E1-Sulfa
t
e
Genistein
1
7b
-
E2-
s
ulf
at
e
Bisphe
n
ol A
E2-Glucuronide
NP1
EC
Di
bu
t
y
l
phthalate
Estradiol equivalents [ng/l]
In vitro
In vivo (vitellogenin)
In vivo (water snail)
Consequently, the strong focus on fish as the dominating sentinel group for aquatic ecotoxicity
testing and monitoring bears the risk of underestimating the potential impact from non-steroid
estrogenic compounds for other aquatic wildlife groups, particularly invertebrates. For mollusks
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the existing evidence points to an almost equal toxicological potential of estrogenic industrial
chemicals. Because the concentrations of xenoestrogens such as BPA, phthalates, alkylphenols
and their ethoxylates in WWTP effluents generally exceed those of natural and synthetic steroids
it can be expected that they are more important as endocrine disrupters at least for particular
invertebrate groups.
FATE OF EDCS IN WASTEWATER TREATMENT
Whether EDCs and other trace substances can be eliminated in a wastewater treatment plant
depends essentially on the level of development of the biological purification stage. In the last 40
years, biological wastewater purification has been adapted step by step to the tightening
wastewater discharge regulations. This is described in Figure 5 using the most commonly
employed activated sludge system (>80% of the WWTPs in Europe).
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Figure 5 - Historical development of the activated sludge method. Over the course of time,
several processes have become integrated in the: At the beginning, sewage plants were designed
only for the decomposition of organic substances. Since the 1960s, phosphate was removed by
chemical precipitation in order to reduce the phosphate loading of lakes. Nitrogen, originating
mostly from urine, has been eliminated since the end of 1970s. By means of the nitrification
process, ammonium which is toxic for fish is converted to the less critical nitrate. Nitrate,
however, carries the risk of nitrogen over-fertilization of the coastal waters. Therefore, since the
1980s, nitrification has, in most cases, been supplemented with a partial denitrification in which
the nitrate is converted to molecular nitrogen. The biological phosphate elimination through an
upstream anaerobic zone was introduced in the 1990s. This brings about enrichment in the
sludge of bacteria with polyphosphate storage.
1950
Return flow
Effluent
Excess
sludge
Secondary
clarifier
Influent
Activated
sludge tank
Sludge age
(Days)
BOD
Elimination
2 – 4 20 - 40
1960
1970
1980
1990
2000
P-Precipitation
Nitrifikation
Denitrification
anaerobic anoxic
Nitrification
Denitrification Nitrification
Biological
P-Elimination
Tank volume
(L/person)
Nitrification
8 - 12 80 - 140
Fe, Al
10 - 15 100 - 160
14 - 20 140 - 200
Fe, Al
1950
Return flow
Effluent
Excess
sludge
Secondary
clarifier
Influent
Activated
sludge tank
Sludge age
(Days)
BOD
Elimination
2 – 4 20 - 40
1960
1970
1980
1990
2000
P-Precipitation
Nitrifikation
Denitrification
anaerobic anoxic
Nitrification
Denitrification Nitrification
Biological
P-Elimination
Tank volume
(L/person)
Nitrification
8 - 12 80 - 140
Fe, Al
10 - 15 100 - 160
14 - 20 140 - 200
Fe, Al
The most important elimination processes for trace pollutant elimination are:
x the sorption to suspended solids in the waste water, which are removed by sedimentation as
primary and secondary sludge in the primary and secondary clarifiers respectively;
x the decomposition or transformation of substances through microorganism in the biological
step, designated as mineralization or transformation;
x stripping during aeration: this process is negligible for the micropollutant under
consideration, as the mostly large, lipophilic and often charged molecules feature low
volatility.
x photo-oxidation in polishing ponds and receiving waters
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Sorption
In the case of sorption of organic trace substances, a distinction is made between (Figure 6):
x absorption: hydrophobic interactions of the aliphatic and aromatic groups of a compound
with lipophilic cell membranes of microorganisms and fat fractions of the sludge;
x adsorption: electrostatic interactions of positively charged groups of chemicals with the
negatively charged surfaces of microorganisms.
The quantity sorbed by a substance (C
sorb
), can be expressed by a simplified linear model. It is
dependent upon the sorption constant K
d
, the concentration of the suspended solids SS (g
SS
L
-1
)
to which the substance can adhere and the amount of the substance present in dissolved form
(C
diss
):
C
sorb
= K
d
· SS · C
diss
The sorption constant K
d
has the unit L g
SS
-1
. In case of predominantly hydrophobic interactions,
K
d
can be estimated from the octanol-water distribution coefficient, while if electrostatic
interactions are important, it must be determined by means of sorption trials.
A substance which sorbs relatively well to suspended solids is the antibiotic norfloxacin (Figure
3) (Golet et al., 2003). The sorption is based to a large extent on electrostatic interactions
between the positively charged amino group of norfloxacin and the negatively charged surfaces
of microorganisms. In a study carried out in the sewage plant Zürich city, EAWAG was able to
confirm that with an excess sludge production of 0.15 g/l, up to 80 % norfloxacin is sorbed to the
secondary sludge. The reason for this high sorption is that microorganisms represent the greater
proportion of the suspended solids in secondary sludge, resulting in a sorption constant K
d
| 25
l/g. For primary sludge however, the sorption constant of norfloxacin is only K
d
| 2, because in
spite of having the same concentration of suspended solids, primary sludge contains essentially
fewer microorganisms but has a large fat fraction instead. Thus, only ca. 20 % norfloxacin is
sorbed to the primary sludge. For EDCs, such as bisphenol A and estrogens, the proportion
sorbed is essentially smaller (Figure 7).
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Figure 6 – Sorption model for hydrophobic compounds and chemicals with positively charged
groups.
lipophilic cell membrane
Bacterium
negatively loaded surface
HN
NN
F
OO
OH
Adsorption of a bivalent compound
(
e.g. Norfloxacin) or a positevely
loaded compound onto the surface
Absorption of a hydrophobic compound
(
e.g. Nonylphenol) into the lipophilic membrane
O
H
lipophilic cell membrane
Bacterium
negatively loaded surface
HN
NN
F
OO
OH
Adsorption of a bivalent compound
(
e.g. Norfloxacin) or a positevely
loaded compound onto the surface
HN
NN
F
OO
OH
Adsorption of a bivalent compound
(
e.g. Norfloxacin) or a positevely
loaded compound onto the surface
Absorption of a hydrophobic compound
(
e.g. Nonylphenol) into the lipophilic membrane
O
H
O
H
Figure 7 - Sorption constant to the suspended solids and sorbed fractions of selected compounds
in the inflow as well as in the primary and the secondary sludges with reference to the raw
influent load assuming no biological degradation. K
d
values estimated from Andersen et al.
(2003), Wettstein (2004), Ying et al. (2003), Golet et al. (2003), Joss et al. (2005a) and Ternes et
al., 2004.
Compound K
d
(L g
SS
-1
) sorbed fraction in %
Bisphenol A 0.3 7 4 3
17E-Ethinylestradiol
0.4 - 1 9-20 5-12 4-9
Nonylphenol, Tonalide 5 - 10 55-72 33-43 22-29
Norfloxacin 2 / 25 33 20 57
Secondary sludge
0.10 gSS L
-1
Primary sludge
0.15 gSS L
-1
Primary clarif.
Activated sludge
Raw wastewater
0.25 gSS L
-1
=
=
Sorbed fraction =
C
sorb
+C
diss
C
sorb
K
d
·SS·C
diss
C
diss
+K
d
·SS·C
diss
1 + K
d
·SS
K
d
·SS
C
tot
C
sorb
=
Compound K
d
(L g
SS
-1
) sorbed fraction in %
Bisphenol A 0.3 7 4 3
17E-Ethinylestradiol
0.4 - 1 9-20 5-12 4-9
Nonylphenol, Tonalide 5 - 10 55-72 33-43 22-29
Norfloxacin 2 / 25 33 20 57
Secondary sludge
0.10 gSS L
-1
Primary sludge
0.15 gSS L
-1
Primary clarif.
Activated sludge
Raw wastewater
0.25 gSS L
-1
=
=
Sorbed fraction =
C
sorb
+C
diss
C
sorb
K
d
·SS·C
diss
C
diss
+K
d
·SS·C
diss
K
d
·SS·C
diss
C
diss
+K
d
·SS·C
diss
1 + K
d
·SS
K
d
·SS
1 + K
d
·SS
K
d
·SS
C
tot
C
sorb
C
tot
C
sorb
=
Biological treatment
As the discussed trace substances mostly occur in wastewater in concentrations of 10
-5
-10
-9
g/l,
biological degradation is only possible when the microorganisms have a primary substrate
available. In the case of biological degradation of trace substances, a distinction is made between
(Figure 8):
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x co-metabolism, in which the bacteria break down or convert the trace substances only partly
and do not use it as a carbon source; and
x mixed substrate growth, in which the bacteria use the trace substances as a carbon and energy
source, and hence totally mineralize it.
Figure 8 – Model for biological degradation or transformation (co-metabolism) with primary
substrate.
Pollutant is only
transformed
(no carbon source)
Cometabolism :
• Growth only with primary substrate
• Enzyme system used for transformation of pollutant
• e.g. Dechlorination of chlorinated hydrocarbons
Pollutant is only
transformed
(no carbon source)
Cometabolism :
• Growth only with primary substrate
• Enzyme system used for transformation of pollutant
• e.g. Dechlorination of chlorinated hydrocarbons
ng/lmg/l
Pg/l
Conzentration
Pollutant is
mineralized
(Carbon- and
energy source)
Substrate growth
(Pollutant = Substrate)
Growth limit
Mixed substrate
• Primary substrate needed
• Existing Enzyme system used
for pollutant degradation
Mixed substrate
• Primary substrate needed
• Existing Enzyme system used
for pollutant degradation
The transformation or decomposition of a substance can take place under aerobic and/or
anaerobic conditions. It arises through the (by chance) affinity of a trace substance with the
bacterial enzymes in the activated sludge. The decomposition was shown to increase with the
age of the sludge (Figure 9).
Figure 9 – Effect solid retention time of the activated sludge in the activated sludge tanks
(sludge age) for the biological degradation or transformation of trace compounds.
Sludge age (SA)
< 5 d 17E-Estradiol
Estrone
5 -15 d 17D-Ethinylestradiol
Nonylphenol,
Bisphenol A
not degradable at SA
< 20d Carbamazepine
Biological degradation or
transformation
100%
0%
SA
minimum
Sludge age (SA)
< 5 d 17E-Estradiol
Estrone
5 -15 d 17D-Ethinylestradiol
Nonylphenol,
Bisphenol A
not degradable at SA
< 20d Carbamazepine
Biological degradation or
transformation
100%
0%
SA
minimum
The reason is that with increasing slusge age the bacterial biocoenosis becomes more diversified
since slower growing bacteria can accumulate in the sludge. This is demonstrated for instance
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with the contraceptive 17Į-ethinylestradiol (Andersen et al., 2003). A significant decomposition
is only detectable when the activated sludge age in the aerobic part of the plant is 8-10 days old
(Figure 10), On the contrary the natural estrogens are also degraded at low sludge age (Ternes et
al., 1999). With increasing sludge age the bacteria compete for more complex, less easily
degradable compounds. However, the decomposition of the trace substances can be impaired in
spite of a high sludge age. This may be the case when easily degradable substrates are present in
the sludge or during periods of increased substrate loads. The natural estrogens 17ȕ-estradiol and
estrone are mineralized in both the aerobic and the anoxic part of the biological purification
stage (Figure 11). On the other hand, the synthetic 17Į-ethinylestradiol decomposes only under
aerobic conditions (Andersen et al., 2003). Natural and synthetic estrogens are also degrading
under methanogenic conditions in the mesophilic digester (Carballa, 2005).
Due to the significant degradation of the natural and synthetic estrogens in the activated sludge
system and in the digester, the sorbed fraction on the excess and digested sludges are negligible
(Figure 10 und 11) despite the significant K
d
value (Figure 7).
Figure 10 – Measured mass flux of 17D-ethinylestradiol (EE2) in g/d at the municipal WWTP
Wiesbaden (300’000 person equivalents, sludge age of 11-13 days; Andersen et al., 2003). Adler
et al. (2001) estimated the conjugated (glucoronide, sulfate) EE2 quantities to be about 35% of
the non-conjugated EE2. The estimated inlet load of 0.7 g/d yields 2.3 mg/person and day, in
good agreement with the average consumption in Germany (50 kg EE2 per year for totally 80
million inhabitants).
Primary
clarifier
Raw
wastewater
Secondary
clarifier
Primary
effluent
Secondary
effluent
Denit 1
Nitrification
Primary sludge
Digester
Digested sludge
Denit 2
Secondary (excess) sludge
dissolved
adsorbed
conjugated (estimation)
internal recirculation and return sludge
< 0.07
<0.03
0.04
0.54
0.35
1.2
0.4
0.3
< 0.1
0.7
0.5
(
a
0.2) (
a
0.2)
1.3
1.5
0.5
<0.17
<0.14
7
< 0.03
<0.05 (estimated from K
d
)
Primary
clarifier
Raw
wastewater
Secondary
clarifier
Primary
effluent
Secondary
effluent
Denit 1
Nitrification
Primary sludge
Digester
Digested sludge
Denit 2
Secondary (excess) sludge
dissolved
adsorbed
conjugated (estimation)
internal recirculation and return sludge
< 0.07
<0.03
0.04
0.54
0.35
1.2
0.4
0.3
< 0.1
0.7
0.5
(
a
0.2) (
a
0.2)
1.3
1.5
0.5
<0.17
<0.14
7
< 0.03
<0.05 (estimated from K
d
)
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Figure 11 – Measured mass flux of estrone (E1) and 17E-estradiol (E2) in g/d at the municipal
WWTP Wiesbaden (see comment to Fig. 10). Adler et al. (2001) estimated the conjugated
(glucuronide, sulfate) estrogen quantities for municipal WWTP inlet to be about 130% of the
non-conjugated compounds. The conjugated quantities are partly hydrolysed in the sewer system
and the remainder in the first reactor. The estimated inlet load of 14 g/d corresponds to about 45
Pg/person and day.
Primary clarifier
Raw
wastewater
Secondary clarifier
Primary
effluent
Secondary
effluent
Denitrification
Reactor 1 Reactor 2
Nitrification
Primary sludge
Digester
Digested sludge
Secundary sludge (excess sludge)
dissolved
sorbed
conjugated (estimation))
Internal recirculation and return sludge
< 0.13
0.55
0.12
(
a
8)
5.4
5.8
5.2
11.4
2.3
3.0
2.3
total
a
14
<0.9
8.6
(
a
8)
6.2
< 0.2
0.3
0.4
0.1
<0.6 (estimated from K
d
)
Primary clarifier
Raw
wastewater
Secondary clarifier
Primary
effluent
Secondary
effluent
Denitrification
Reactor 1 Reactor 2
Nitrification
Primary sludge
Digester
Digested sludge
Secundary sludge (excess sludge)
dissolved
sorbed
conjugated (estimation))
Internal recirculation and return sludge
< 0.13
0.55
0.12
(
a
8)
5.4
5.8
5.2
11.4
2.3
3.0
2.3
total
a
14
<0.9
8.6
(
a
8)
6.2
< 0.2
0.3
0.4
0.1
<0.6 (estimated from K
d
)
Due to the low concentrations of trace substances, the degradation occurs mostly as a first order
reaction, including sorption on suspended solids yields:
r
deg
= k
deg
· SS · C
diss
= k
deg
· SS ·
SSK1
C
d
tot
=
SSK1
k
d
deg
· SS · = k
deg
’
· SS · C
tot
with k
deg
= degradation rate constant (L g
SS
-1
d
-1
)
SS = concentration of activated sludge in the tank (g
SS
L
-1
)
C
tot
= C
sorb
+ C
diss
= C
diss
(1+K
d
·SS) = sum of dissolved and sorbed concentration
For a completely stirred reactor (CSTR) fully mixed tank and a plug flow, batch reactor or SBR
follows:
CSTR:
influent
effluent
C
C
=
1
d
deg
SSK1
HRTSSk
1
¸
¸
¹
·
¨
¨
©
§
plug flow, SBR:
influent
effluent
C
C
=
exp
¸
¸
¹
·
¨
¨
©
§
SSK1
HRTSSk
d
deg
with HRT = V
activated sludge tank
/Q
inlet
= hydraulic retention time (d; for the SBR only the active
time without sedimentation and decantation has to be included)
SS·HRT = SP·SA (g L
-1
d
-1
), SP = excess sludge production (g
SS
L
wastewater
-1
), SA = sludge
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age (d)
A logic consequence of the above formula is that the degradation efficiency is improving with
increasing HRT. HRT is increasing with decreasing parasite water (infiltration water, rain water or
drinking water that dilutes the wastewater). Therefore measures reducing infiltration of clean water
into the sewer system could improve the degradation efficiency (e.g. separation and infiltration of
rain water if geologically feasible and reduction of sewer leaks by good maintenance).
For nutrient removal plants with SS·HRT
aerob
§ 3 g L
-1
·0.33 d = 1 g L
-1
d and EE2 removal, where a
k
deg
of about 5-10 L g
-1
d
-1
was observed (Joss et al., 2005b), a partition of the aerobic tank volume
or a sequencing batch reactor is superior to a fully mixed tank (Figure 12).
Figure 12 – Expected relative micropollutant removal for typical municipal nutrient removal
WWTPs. Assumptions: HRT = 0.33 days; sludge recycle twice the influent flow; sludge age and
concentration indicated next to the respective curves.
CAS: conventional activated sludge
treatment plant;
CSTR: completely stirred reactor with one or three cascaded compartments;
MBR: membrane bioreactor; SA: sludge age; SS: suspended solids concentration. For the MBR
the same k
deg
is considered although it could be increased due to the higher SA (Joss et al.,
2005b).
0.01 0.1 1 10 100
0.1%
1%
10%
100%
Degradation constant
k
biol
[L gSS
-1
d
-1
]
Residual load in the effluent
MBR
SA
25-30d
SS
8g L
-1
CAS
SA
10-15d
SS
3.5g L
-1
1 CSTR CAS
3 CSTR CAS
Plug flow CAS
1 CSTR MBR
3 CSTR MBR
Plug flow MBR
MEASURES AT THE SOURCE
EDCs from the combined sewer overflow and many EDCs that are only partly eliminated in the
WWTP end up in the surface water and a substantial fraction (5-10% of the total load, 10-100% of
the WWTP effluent load, assuming 50-90% EDC removal in the WWTP) exfiltrates from the sewer
system directly into the groundwater. This pollution could only be significantly reduced with
measures at the source or with source separation and separate treatment of strongly polluted
wastewater fractions.
k
deg
[L g
SS
-
1
d
-
1
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Ban of industrial EDCs and Eco-label for consumer products
Because the concentrations of xenoestrogens such as BPA, phthalates, alkylphenols and their
ethoxylates in WWTP effluents generally exceed those of natural and synthetic steroids it can be
expected that they are important endocrine disrupters at least for particular invertebrate groups.
Where industrial chemicals are identified as causative agents, a practical program of tighter
regulation for their discharge and/or a switch to alternative chemicals (which do not act as EDCs
and could acquire an ecolabel) is needed.
Improving the environmental assessment
Up to now, the eco-toxicological assessment of a chemical compound has mostly been based on
the determination of the acute or chronic toxicity in the environmental system. However,
substances used because of their hormonal effect, as well as substances suspected of exercising a
secondary hormonal effect in addition to their principal effect, must be given special attention
(Knacker, 2003). It must be taken into account that hormone-active substances can be effective
even in the smallest concentrations. Furthermore, when estimating the concentrations in the
water body, the behavior of the substances in the sewage plant and the seasonal variation in the
consumption must be included in the calculation, which is not always a simple matter.
Separate treatment of hospital and industrial wastewater
Most hospital and specific industrial wastewater are heavily contaminated with medicaments and
EDCs. Moreover, it is also higher contaminated with antibiotic resisistant bacteria and it seems
that the development of bacterial resistances may especially occur in hospital waste water
because of its higher concentration of antibiotics compared to domestic waste water (Alder et al.,
2003). The separate treatment of the concentrated (not diluted with infiltration water) hospital
wastewater, for instance with a membrane bioreactor for separating the germs and by means of
ozonation of the discharge resulting in the oxidation of the dissolved persistent micro-pollutants
is therefore to be considered. The treated effluent could be recycled for toilet flushing and
gardening, which would reduce drinking and waste water fees and partly compensate the cost for
the separate wastewater treatment.
MEASURES IN MUNICIPAL WWTP TO IMPROVE EDC ELIMINATION
To be effective the introduction of the described measures to be taken at the source requires
(politically) coordinated action to be taken on a multitude of decentralized locations: a time
consuming effort. On the contrary, additional chemical or physical treatment steps may be
achieved on a shorter term at the municipal WWTP. Nevertheless for efficiency reasons (i.e. due
to the dilution in the sewer) centralized measures should not replace the measures at the source.
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Increasing the sludge age
Organic trace substances are significantly better decomposed when the age of the activated
sludge is around 10 days or more (Figure 9). But not all sewage plants in the EU satisfy these
requirements. Upgrading of medium sized and larger sewage plants to a total sludge age of 10-15
days – nitrification combined with denitrification (Figure 5) – is therefore beneficial. This would
have the additional advantage of efficiently eliminating the nitrogen so that the EU requirement
specifying 70-80 % nitrogen elimination for sewage plants in the catchments of sensitive water
bodies such as the Rhine could be achieved simultaneously. If the plants were also to be
extended with an upstream anaerobic zone for the biological phosphorus elimination (Figure 5),
chemicals for P-precipitation and sludge production and sludge disposal could be reduced.
Post Filtration
Flocculation filtration was installed for WWTP at sensitive freshwater lakes to reduce the
phosphate input due to suspended solids of biological treatment and two improve ortho-
phosphate precipitation with a two stage precipitant addition that reaches P-effluent
concentration smaller than 0.2 mgP L
-1
. Post filtration does also improve degradation of EDCs
due to biofilm growth on the filter material if sufficient oxygen is supplied (Goebel et al., 2005).
In the WWTP Kloten-Opfikon, consisting of mechanical treatment, activated sludge system with
total SRT of 11 days and 30% anoxic zone for denitrification, nonylphenolpolyethoxylate
elimination was improved from 88 to 96% with post filtration (Figure 13). Nonylphenol
concentration in the secondary clarifier was about 0.4 Pg L
-1
whereas in filter effluent it was
reduced to 0.12 Pg L
-1
. But post filtration would be to expensive in investment and operation
cost only for the aim of improving EDC degradation.
The estrogenicity of the other Nonylphenolpolyethoxylate metabolites are rather negligible since
no significant NPEO mixture effect are observed (Johnson and Sumpter, 2001) although the total
concentration in the secondary effluent and in the filtration effluent is in the range of 15’000 and
5’000 ng L
-1
, respectively
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Figure 13 – Degradation of nonylphenolpolyethoxylates in the municipal WWTP Kloten-
Opfikon (55’000 population equivalent, average inflow = 17’000 m
3
d
-1
) with sand filtration
(Wettstein, 2004).
Excess sludge
Degradation
Back wash filter sludge
822 mmol/d
2 %
166 mmol/d
4%, 257 mmol/d
Activated
sludge system
SRT ~ 11 d
Sand filter
7140 mmol/d
Effluent
0.5 %
31 mmol/d
12 %
86 %
6152 mmol/d
7.5 %
534 mmol/d
NPnEO 85%
NP1EC 5%
NP 3%
NP1EO 4%
NP2EO 3%
Influent
NP1EC 21%
NP2EC 1%
NP 14%
NP1EO 2%
NP2EO 24%
NP1EC 53%
NP2EC 37%
NP 4%
NP1EO 3%
NP2EO 3%
NP1EC 52%
NP2EC 0%
NP 14%
NP1EO 17%
NP2EO 17%
NP1EC 53%
NP2EC 36%
NP 4%
NP1EO 4%
NP2EO 3%
Degradation
Membrane bioreactor
More stringent effluent requirements (extensive P-reduction at sensitive freshwater lakes, particle
free effluent, wastewater disinfection) and small footprint makes membrane bioreactor (MBR)
systems interesting although energy consumption of the WWTP is significantly increased (0.7 to 1
kWh m
-3
instead of 0.2-0.4 kWh m
-3
for a nutrient removal plant with activated sludge system). But
MBR allow operating with substantially higher SRT due to higher activated sludge concentrations
(8-10 kg
SS
m
-3
). From Figure 14 it is seen that the elimination efficiency of
nonyphenolpolyethoxylate (effluent nonylphenol concentration <0.2 Pg L
-1
) is similar to the
combined system composed of activated sludge treatment and post filtration
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Figure 14 – Degradation of nonylphenolpolyethoxylates in the MBR pilot plant (100 population
equivalent, average inflow = 30 m
3
d
-1
) of WWTP Kloten-Opfikon (Wettstein, 2004).
NPnEO 87%
NP1EC 3%
NP 3%
NP1EO 4%
NP2EO 3%
Excess sludge
Degradation
3 %
0.43 mmol/d
2 %
0.26 mmol/d
Membrane
Bioreactor
SRT ~ 30 d
Influent
14.1 mmol/d
Effluent
95 %
13.4 mmol/d
NP1EC 23%
NP2EC 61%
NP 8%
NP1EO 4%
NP2EO 4%
NP1EC 52%
NP2EC 9%
NP 7%
NP1EO 16%
NP2EO 16%
Ozonation of the biologically treated discharge
In the case of insufficient dilution of the treated effluent in the receiving water body, high sensitivity
of the receiving water or direct infiltration of the treated effluent into the underground partial
ozonation of the biologically purified waste water before discharge should be considered. After
treatment with 5-10 mg ozone per m
3
waste water, most pharmaceuticals are removed below
detection limit (Ternes et al., 2003). Only the iodinated radiological contrast agents (mostly
originating from hospital wastewater) were still present in appreciable quantities (Figure 15).
The effectiveness of ozone is dependent on the background level of dissolved organic carbon and
the chemical properties of the residual substances (Huber et al., 2002; Huber et al., 2005). Due to
the low background loads, for Swiss WWTP it could be shown that an ozone amount of 5 g m
-
3
wastewater,treated
is sufficient for complete removal of most compounds (including all EDCs
discussed so far). Although the price is only a few cents per m
3
of waste water, the energy
expenditure is about 0.1-0.2 kWh/m
3
, and is therefore significant in comparison with the total
energy consumption of a plant. Thus, the application of the process ought to be limited to
sensitive locations. In any case, the fate of the metabolites occurring with the ozonation is to be
investigated prior to any large-scale application: since the amount of ozone used achieves only a
partial oxidation of the parent compounds and only little information is presently available to
confirm the ecotoxicologic meaning of the products formed.
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Figure 15 - Ozonation of a municipal WWTP effluent with a pilot plant (Ternes et al., 2003).
Trimethopr.
Sulfamethox
Erythromy.
Eryth-H2O
Clarithromy.
Roxithromy.
Atenolol
Sotalol
Metoprolol
Propranolol
Carbamazep.
Clofibric ac.
Ibuprofen
Naproxen
Ketoprofen
Diclofenac
Tonalide
Galaxolide
Iopamidol
Iopromide
Diatrizoate
Concentration in µg/L
0.01
0.10
1.00
10.00
effluent
5 mg/L ozone
10 mg/L ozone
15 mg/L ozone
effluent
5 mg/L ozone
10 mg/L ozone
15 mg/L ozone
Iodinated
contrast media
Iodinated
contrast media
MusksMusks
Lipid regulators,
Antiphlogistics
Lipid regulators,
Antiphlogistics
BetablockersBetablockers
AntiepilepticAntiepileptic
AntibioticsAntibiotics
Advanced processes, such as nanofiltration and active carbon adsorption, are too costly and only
of interest if the waste water is used for groundwater recharging or directly reused as drinking
water.
EU PERSPECTIVE ON EDC REGULATION
In the EU currently none of the environmental regulations are specifically dealing with
endocrine disrupting compounds although compounds, with endocrine related functions are
mentioned in the EU Water Framework Directive. In the substance priority list of the EU only
alkylphenols, phthalates and triazines are mentioned as hazardous compounds. However, they
are included not due to their endocrine properties, but due to their overall toxicity. Within the
registration of pesticides, endocrine effects are covered in chronic effect studies. However,
EDCs are included in many current research projects. After the results of these projects are
available, it is expected that most EDCs will be covered by environmental regulations.
Endocrine effects have been included in the criteria to define possible hazardous substances by
Annex VIII of the Water Framework Directive (EU, 2000) and by OSPAR’s “Safety Net
Procedure for the Inclusion of Substances in the List of Substances of Possible Concern”, which
is related to “OSPAR Strategy with regards to Hazardous Substances”. In both cases EDCs can
be listed as priority substance even if the so called PBT (persistent, bioaccumulative and toxic)
selection criteria are not fulfilled (OSPAR, 2003).
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CONCLUSIONS
Treated effluents from WWTP contain a cocktail of endocrine disrupting chemicals (EDCs) at
concentrations which are high enough to cause adverse effects in aquatic wildlife. Hormones
enter the waste water after being excreted in urine, ingredients of cleaning, washing and day care
product enter it via grey water and hormone active chemicals used in industrial products
(plastics, tubes, paintings, etc.) getting in contact with drinking water, rainwater and infiltration
water are entering indirectly the water cycle. In the sewage plant, partial removal of the
substances is occurring through sorption and biological degradation. The remaining part enters
the water bodies with the treated wastewater. This article describes possible measures with
which the residual substances can be reduced. These include on the one hand, permanent
measures implemented at the source such as reducing the consumption by ban or replacement
with compounds without endocrine disrupting effects (characterised by ecolabel) or the
separation and separate treatment of strongly polluted wastewater e.g. hospital and industrial
wastewater. However, it is expedient to also consider technical measures such as increasing the
solid retention time of bacteria in the biological step of WWTPs and for critical cases (low
dilution in the receiving water and direct infiltration) the ozonation of the purified wastewater or
other polishing processes have to be considered.
Most ecotoxicological studies analysed estrogenic effects in fish although these represent only a
minor, though economically important part of the aquatic biodiversity. Consequently, the strong
focus on fish as the dominating sentinel group for aquatic ecotoxicity testing and monitoring
bears the risk of underestimating the potential impact on other aquatic wildlife groups,
particularly invertebrates. The existing evidence points to an almost equal toxicological potential
of estrogenic industrial chemicals (i.e. as compared to estrogens) particularly in mollusks.
Because the concentrations of xenoestrogens such as BPA, phthalates, alkylphenols and their
ethoxylates in WWTP effluents exceed those of natural and synthetic steroids it can be expected
that they are more important in terms of environmental endocrine disruption at least for
particular invertebrate groups.
In the EU currently none of the environmental regulations are specifically dealing with
endocrine disrupting compounds although compounds with endocrine related functions are
mentioned in the EU Water Framework Directive.
ACKNOWLEDGMENTS
This study was part of the EU project Poseidon (EVK1-CT-2000-00047), which was financially
supported by grants obtained from the European Commission within the Program Energy,
Environment and Sustainable Development of the Fifth Framework Program. Further funding
was obtained from the Swiss Federal Environmental Protection Agency.
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