Environmental Engineering and Management Journal
September 2014, Vol.13, No. 9, 2211-2218
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
TOTAL AND DISSOLVED METALS OCCURRENCE
IN MUNICIPAL WASTEWATER TREATMENT PLANT EFFLUENTS
Elisabeta Chirila1, Camelia Draghici2, Adriana Puhacel1
1
“Ovidius” University of Constanta, Chemistry and Chemical Engineering Department, 124 Mamaia Blvd,
900527, Constanta, Romania
2
Transilvania University of Brasov, Department of Product Design, Mechatronics and Environment, 1 Colina Universitatii,
500068, Brasov, Romania
Abstract
Concentrations of seven heavy metals (Cd, Cr, Cu, Fe, Ni, Pb and Zn) in the discharged effluents of four wastewater treatment
plants located on the Romanian Black Seacoast, evaluated as average values for four seasons, during 2010-2011 are presented.
Total and dissolved metals occurrence was investigated from seasonal samples, to assess the bioavailability of the heavy metals
in the discharged effluents. The analytical measurements were performed by flame atomic absorption spectrometry (FAAS) for
Fe and Zn, and by graphite furnace atomic absorption spectrometry (GFAAS) for Cd, Cr, Cu, Ni and Pb, after appropriate sample
preparation. The obtained results show that the sum of total metals concentration in discharged effluents in the Black Sea was
below 2000 µg/L, for all investigated samples. Differences in metal concentrations in the effluent were site-specific and varied
with seasons, the maximum total metal concentrations being registered in autumn (900 – 1200 µg/L). Some of the metals were
occurring mostly in the dissolved forms, like Cd, Ni, and sometimes Cu or Fe. Due to the living organisms’ capacity to absorb or
assimilate dissolved heavy metals, they became more toxic to the flora and fauna present in the emissary. Even if the
concentrations of the individual or total heavy metals determined in the effluents from the studied wastewater treatment plants
were not exceeding the accepted values, they are exhibiting toxicity to the marine environment that underlines the need of
responsible decisions regarding pollution prevention and new technologies use, to ensure heavy metals removal from municipal
wastewater.
Key words: bioavailability, effluent, heavy metal concentration, municipal wastewater
Received: March, 2014; Revised final: August, 2014; Accepted: September, 2014
1. Introduction
Heavy metals exist in natural or wastewaters
in a large variety of inorganic and organic species, in
different concentrations. The biological availability,
and hence toxicity of heavy metals in aquatic
systems, is strongly dependent on the nature of the
metal species, especially of their dissolved forms.
Not all heavy metals are equally reactive, toxic, or
available to biota. The ionic forms of the metals are
considered to be the most available and toxic ones.
Regarding their reactivity, it is generally agreed that
different metal ions exhibit different affinities for the
surface binding sites of their substrates (Luoma,
1983). Most of the municipal wastewater treatment
plants (MWWTP) have primary treatment aiming the
physical removal of floatable and sedimentable
solids, followed by secondary treatment that ensures
mostly the removal of dissolved pollutants (Chirila et
al., 2006; Chirila et al., 2009; Meglei et al., 2006).
Despite significant efforts to reduce trace metals
loads in effluents, municipal wastewater still convey
important amounts of trace metals into the
environment (Buzier et al., 2006; Carletti et al., 2007;
Hope et al., 2012; Üstün, 2009). As a consequence,
heavy metals present in municipal wastewater
originated from domestic and industrial activities, as
well as from rain/storm water runoff, are still present
 Author to whom all correspondence should be addressed: e-mail: c.draghici@unitbv.ro; Phone/Fax: +40268473473
Chirila et al./Environmental Engineering and Management Journal 13 (2014), 9, 2211-2218
in the effluents and sludge (Chanpiwat et al., 2010;
Chen et al., 2008; Worms et al., 2010).
Major urban inputs of sewage wastewater
include households, drainage water, industrial
activities, atmospheric deposition, pipe sediment and
traffic. Moreover, heavy metals concentration in
wastewater can be affected by people's lifestyles and
their lack of awareness about the impacts on the
environment. As a consequence, the municipal
wastewater discharges could cause toxicity to
organisms in receiving waters (Gagnon and Saulnier,
2003; Nayek et al., 2010; Peijnenburg et al., 2007).
Analytical determinations of trace metals after
the appropriate sampling stage give important
information regarding the impact of MWWTP
effluents (Benetto at al., 2009; Chirila and Draghici,
2011). Atomic absorption spectrometry (AAS) is the
mostly used technique for traces of heavy metal
determination in environmental samples, due to the
availability of instrumentation, simplicity of
procedure, sensitivity, accuracy, time of analysis
(Draghici et al., 2007; Draghici et al., 2011; Ghaedi
et al., 2009). Table 1 is sumarizing total heavy metal
concentrations measured in influents (I) or effluents
(E) of some MWWTP reported in literature during
the last years. The variation in influent metal content
being site-specific and possible related to the
economic activities of small-scale companies was
observed (Chanpiwat et al., 2010).
The study aims to present data on seven heavy
metals concentrations in the discharged effluents of
four wastewater treatment plants form the Romanian
Black Seacoast. After the appropriate sample
preparation, flame atomic absorption spectrometry
(for Fe and Zn) and graphite furnace techniques (for
Cd, Cr, Cu, Ni and Pb) were used for the
measurements of the total and dissolved metals
concentrations. The bioavailability of the heavy
metals of interest in the discharged effluents was
alaso assess, based on the total and dissolved metals
occurrence in the seasonal samples.
2. Experimental
2.1. Sampling and sample pretreatment
Wastewater effluents samples were collected
from different MWWTP located on the Romanian
Black Seacoast: A – Constanta North, B – Constanta
South, C – Eforie South, and D – Mangalia, situated
as presented in Fig. 1. During the monitored period
(summer 2010 – spring 2011), volumes of 800 mL
effluent samples were collected each 2 hours, daily.
400 mL of them were further used for total (t) heavy
metals concentrations, and 400 mL for dissolved (d)
heavy metals concentrations, respectively, following
a sampling procedure presented in Fig. 2. For the
total heavy metals concentration measurements, 400
mL of effluent samples collected each 2 hours, daily,
were adjusted with nitric acid 65% (from Merck) to
pH 1-2, obtaining the daily acidulated sample (t), and
stored at 1-5ºC.
2212
Fig. 1. The location of the studied MWWTP from
Constanta County, Romania
At the end of each month, 20 mL of daily
acidulated sample (t) were mixed to form the
monthly samples (t). Seasonal sample (t) was
obtained by mixing the monthly samples (t), still
stored as stock solutions at 1-5ºC, until their use for
measurements. Seasonal samples were mixed as
follows: June-August (summer), SeptemberNovember (autumn), December-February (winter),
and March-May (spring).
For the dissolved heavy metals concentration
measurements, the rest of 400 mL of effluent samples
collected each 2 hours, daily, were firstly filtered on
0.45 µm pores membrane, than adjusted with 0.5%
nitric acid at pH 1-2, obtaining the daily acidulated
sample (d), and stored at 1-5ºC. In order to obtain the
seasonal sample (d) the same procedure was followed
as for the seasonal samples (t). The differences in
sampling the two different types of samples were
marked in Fig. 2 in italic.
Before the measurements, the seasonal
samples (t) were subject of sample pretreatment, as
follows: in 40 mL of sample were added 5 mL of
HNO3 65%, refluxed 90 min at 120ºC, cooled, than
made up to 50 mL with deionized water in calibrated
flasks. The seasonal samples (d) were used as such,
with no pretreatment.
2.2. Materials and methods
Certipure multielement standard solutions
from Merck (1 mg/mL of each metal) were used for
calibration. Measurements were performed with a
spectrometer ContrAA® 700 using flame (for Fe and
Zn) or graphite furnace technique (for Cd, Cr, Cu, Ni
and Pb).
In order to ensure the quality of analytical
data, the following performance parameters have
been determined: concentration domain (µg/L),
correlation coefficients of the calibration curves (R2),
limits of detection (LOD) and limits of quantitation
(LOQ), as given in Table 2.
Total and dissolved metals occurrence in municipal wastewater treatment plant effluents
Table 1. Total metal concentration in the influents and effluents of some MWWTP.
Cd
Cr
Total concentration of metals, µg/L
Cu
Fe
Ni
I
E
I
E
I
E
Pb
I
Reference
Zn
I
E
I
E
E
I
E
0.6
0.3
9.0
3.0
65
18
650
180
12
8
18
4
na
na
nd
nd
46
12.7
265
26.3
5795
613
40.9
11.4
78
20.7
1698
545
137
6
2120
54
179
17
3580
338
202
53
358
30
982
150
(1)
Buzier et
al., 2006
(2)
Carletti et
al., 2007 (*)
(3)
Üstün, 2009
(**)
(4)
2.3
0.4
18.5
4.8
455
95.9
1727
396
(1)
32.2
22.6
13.9
4.8
311
101
Chanpiwat
et al., 2010
(***)
(2)
na – not analyzed, nd – not detectable; Seine-Aval, France, 2004; four MWWTPs from center-north of Italy, 2005 – 2006, * values for one
plant; (3) Bursa, Turkey, 2002 and 2007, ** maximum influent values for 2007, and effluents downstream of the activated sludge process; (4)
Bangkok, Thailand, 2007 – 2008, *** mean values.
Fig. 2. Sampling scheme of the wastewaters collected from the four MWWTP
Table 2. Performance parameters for AAS measurements.
Metal
concentration domain (µg/L)
R2
LOD (µg/L)
LOQ (µg/L)
Cd
0.25-3
0.9839
0.14
0.42
Cr
3.5-50
0.9984
0.20
0.61
The measurements on seasonal samples for
total and dissolved heavy metals were performed in
the same day, using 5 replicates for each seasonal
sample.
According to the Romanian regulation,
Governmental Decision (GD, 2005) for the heavy
metals total content in wastewaters discharged in
natural receptors (effluents), the accepted values are
Cu
1-20
0.9973
0.21
0.64
Fe
50-2000
0.9954
-
Ni
5-50
0.9907
0.97
2.9
Pb
2.5-50
0.9962
4.03
12.12
Zn
30-1000
0.9780
-
given in Table 3. These limits were further used to
compare the results obtained in the present study.
3. Results and discussions
3.1. Total metal concentration in MWWTP effluents
For the seasonal
concentrations of heavy
distribution of total
metals in MWWTP
2213
Chirila et al./Environmental Engineering and Management Journal 13 (2014), 9, 2211-2218
The annual report on the quality of the marine
coastal waters during 2011 (Nicolaev and Zaharia,
2012) published the range of the metals
concentrations determined in different monitoring
sites along the Black Seacoast (Table 4). Comparing
the reported results with the concentrations accepted
according to the Romanian regulation (MO, 2006), it
was observed that the concentrations of Cd, Ni and
Cr ware within the accepted limits, while Cu and Pb
exceeded them. The report also relieved differences
in the spatial distribution of the studied metals.
Higher concentration values were also
registered for Cu at Constanta North, Constanta
South and Eforie South monitoring sites, where the
effluents from the related MWWTP might have
considerable contribution.
effluents, the obtained results are presented in Fig. 3
(a–d). All investigated effluents contain metals in
concentration below the accepted limits, and
comparable with the concentrations in different
effluents worldwide (Table 1). The maximal
concentration values differ with the seasons: Cd is
higher in autumn and winter, Cr in spring and
summer, Cu and Ni in autumn, Zn in autumn (except
MWWTP of Constanta North with higner
concentrations in spring) and Pb concentration is
higher in summer (except MWWTP of Eforie South
with higner concentrations in autumn).
The lower concentrations were registered
mostly in winter times (except Cd), possible due to
the biogeochemical processes involved in the metal
compounds separation to low temperatures.
Table 3. Accepted values for heavy metals content in wastewaters discharged in effluents.
Cd
200
Cr
1000
Cu
100
Fe
5000
Ni
500
Pb
200
Zn
500
150
100
50
300
200
100
0
Cd Cr Jun‐Aug
Cu Ni Sept‐Nov
Pb Dec‐Feb 0
Zn Cd Cr Cu Jun‐Aug
Mar‐May
Ni Sept‐Nov
a
Dec‐Feb Pb Zn Mar‐May
b
400
total conc., (µg/L)
200
total conc., (µg/L )
Total metals
2000
400
200
total conc., (µg/L)
t o t al co n c., (µg/ L ) Metal
Accepted limits (µg/L)
150
100
50
300
200
100
0
0
Cd Jun‐Aug
Cr Cu Sept‐Nov
Ni Dec‐Feb Pb Cd Zn Mar‐May
Jun‐Aug
c
Cr Cu Sept‐Nov
Ni Dec‐Feb
Pb Zn Mar‐May
d
Fig. 3. Seasonal metals concentrations in the effluents from MWWTPs: Constanta North (a); Constanta South (b); Eforie South
(c); Mangalia (d)
Table 4. Heavy metals concentration determined in Black Seacoast during 2011
Metal
Cadmium
Chromium
Copper
Lead
Nickel
Reported heavy metals concentration, µg/L
0.02 – 1.35
0.01 – 22.94
0.24 – 68.70
0.01 – 51.97
0.01 – 30.59
*Accepted values for marine coastal waters according to the MO, 2006
2214
Heavy metals concentration, µg/L*
5.0
100
30
10
100
Total and dissolved metals occurrence in municipal wastewater treatment plant effluents
3.2. Dissolved metal concentrations in MWWTP
effluents
The seasonal distribution of the dissolved
fraction of individual metals is illustrated in Table 5,
while their site-specific differences are given in
Table 6, all data being expressed as mean values.
The seasonal distributions of the dissolved
fraction of individual metal have the similar
characteristics with the total concentrations, being
less discharged during the winter (except Cd), some
metals less than half registered in summer, while the
site-specific differences shows that MWWTP
Mangalia contributed less to the discharge of all the
metals in their dissolved forms, in the marine aquatic
environment. The results revealed that differences in
metal concentrations in the investigated MWWTPs
effluent were site-specific and varied with seasons,
for both total and dissolved forms (Fig. 4).
The sum of heavy metals total concentration
in discharged effluents in the Black sea was below
2000 µg/L in all investigated samples. The maximum
values have been registered in autumn (except
Mangalia WWTP), with values ranged between 900
– 1200 µg/L. The seasonal distribution of the sum of
dissolved metals concentrations reveals higher
concentration in the effluents during spring and
summer, and lower discharges during winter (except
Eforie South WWTP).
3.3. Bioavailability of studied metals in MWWTP
effluents
The term bioavailability denotes heavy metals
in a water-soluble form that plants and animals can
uptake and assimilate (Sreedhara Nayaka et al.,
2009). The bioavailability of the metals partially
depends on the concentration of anions and chelating
ligands present in the water, pH and redox status of
the metal, as well as on the presence of particulate
matter. Treated municipal wastewater discharges
should be carefully considered as a possible source of
bioavailable trace metals (Buzier et al., 2006).
Figs. 5 and 6 present the bioavailability of the
heavy metals content in effluents from different
MWWTPs., that were calculated as the ratio between
dissolved and total metal concentration, expressed in
percentage (Sreedhara Nayaka et al., 2009).
There are some heavy metals occurring
mostly in dissolved form, sometimes Cu or Fe,
mostly Cd, Ni, similar with results presented in other
studies (Buzier et al., 2006), highlighting the
increased bioavailability of these trace metals to flora
and fauna present in the emissary. The metals from
the effluents of three MWWTPs, situated in the
northern part of the Black Seacoast, have the highest
bioavailability during summer and the lowest during
spring.
The differences registered on seasonal
distribution of the dissolved metals is also relieving
the influence of the anthropogenic activities and of
temperature to the mechanisms involved in the
metals release from particles or in metal aggregation.
4. Conclusions
Heavy metals concentrations in the discharged
effluents of four municipal wastewater treatment
plants located on the Black Seacoast were determined
by AAS, and their bioavailability was determined.
Even if the individual and total concentrations of the
metals present in the effluents of the MWWTP were
not exceeding the accepted values, they are
exhibiting toxicity to the marine environment.
Table 5. Seasonal variation of the dissolved metal concentrations in MWWTP
Season
Metal
Summer
2.75
77.03
17.42
171.05
9.11
9.71
37.55
324.62
Cd
Cr
Cu
Fe
Ni
Pb
Zn
Sum of metals
Heavy metals concentrations (µg/L) in different seasons
Autumn
Winter
3.89
7.66
18.79
6.29
25.20
6.70
147.68
115.18
14.27
4.54
9.91
1.28
52.98
10.50
272.72
152.15
Spring
5.25
77.70
14.92
146.05
6.38
9.71
13.00
273.01
Table 6. Site-specific differences of the dissolved metal concentrations in MWWTP effluents
MWWTP
Metal
Cd
Cr
Cu
Fe
Ni
Pb
Zn
Sum of metals
Constanta North
3.34
38.45
10.33
171.36
10.61
7.94
20.97
263
Heavy metals concentrations (µg/L) in different MWWTPs
Constanta South
Eforie South
5.41
4.98
67.76
27.38
27.61
13.55
144.10
172.60
10.58
8.63
8.50
5.84
47.70
24.98
311.66
257.96
Mangalia
5.81
46.22
12.75
91.90
4.47
8.24
22.34
191.73
2215
Chirila et al./Environmental Engineering and Management Journal 13 (2014), 9, 2211-2218
Fig. 4. Seasonal distribution of all heavy metals in MWWTP effluents evaluated as total concentrations (a) and as dissolved
concentrations (b).
Summer (Jun-Aug)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
0%
100%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Autumn (Sept- Nov)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
0%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Winter (Dec-Feb)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
0%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Spring (Mar-May)
Zn
Pb Ni Fe Cu Cr
Cd 0%
Zn
Pb Ni Fe Cu Cr
Cd 20%
40%
60%
Particulated
80%
Dissolved
a
100%
0%
20%
40%
60%
Particulated
80%
100%
Dissolved
b
Fig. 5. Bioavailability of heavy metals content in the effluents from MWWTP Constanta North (a) and Constanta South (b)
2216
Total and dissolved metals occurrence in municipal wastewater treatment plant effluents
Summer (Jun –Aug)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
0%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Autumn (Sept – Nov)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
0%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Winter (Dec – Feb)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
0%
Dissolved
20%
40%
60%
Particulated
80%
100%
Dissolved
Spring (Mar – May)
Zn
Pb Ni Fe Cu Cr
Cd Zn
Pb Ni Fe Cu Cr
Cd 0%
20%
40%
60%
Particulated
80%
100%
Dissolved
0%
20%
40%
60%
Particulated
a
80%
100%
Dissolved
b
Fig. 6. Bioavailability of heavy metals content in the effluents from MWWTP Eforie South (a) and Mangalia (b)
This underlines the need of responsible
decisions regarding pollution prevent, of new
technologies, to ensure metals removal from
municipal wastewater as well as of studies on the
metals release in the environment and on their toxic
effects on marine flora and fauna.
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