1. science
2. ecology
3. pollution

Air emissions at large municipal wastewater treatment plants in Finland for
national E-PRTR reporting register
T. Fred *, M. Heinonen **, L. Sundell***, and S. Toivikko****
*Helsinki Water, P.O. Box 1100, FIN-00099, The City of Helsinki, Finland (E-mail: [email protected])
**Helsinki Water, P.O. Box 1100, FIN-00099, The City of Helsinki, Finland (E-mail: [email protected])
***Helsinki Water, P.O. Box 1100, FIN-00099, The City of Helsinki, Finland (E-mail: [email protected])
****Finnish Water and Waste Water Works Association, Asemapäällikönkatu 7, FIN-00520, Helsinki,
Finland (E-mail: [email protected])
Abstract: EC regulation (166/2006) obligates all urban waste water treatment plants above 100.000 PE in European
Union area to report their water and air emissions by PRTR protocol from year 2007. There were no general rules or
correlations determined to calculate or measure air emissions of municipal wastewater plant. Due to fact that major part
of the treatment plants is uncovered, individual air emission study was demanding to implement. In Finland a group of
large wastewater treatment plants studied PRTR air emissions based on the samples of Viikinmäki WWTP (780.000
PE), the largest wastewater treatment plant in Finland. Since Viikinmäki WWTP is completely covered, underground
plant, ventilation air analyses were possible to implement in full scale. Based on this study, air emissions of Viikinmäki
WWTP has been determined and reported to fulfil the PRTR protocol demands. Air emission model was accepted by
Finnish Environmental Authorities and the air emission model of Viikinmäki WWTP was used by other, large Finnish
WWTPs.
Keywords: Air emissions, emission correlation factor, E-PRTR register, NMVOC, PRTR reporting, VOC emissions
INTRODUCTION
E-PRTR (European Pollutant Release and Transfer Register) regulation (166/2006) of the European
Commission obligates PRTR reporting of urban wastewater treatment plants when the capacity of
the plant exceeds 100.000 population equivalents, PE. This demand considers both water and air
emissions. Since there were no general rules or known methods to fulfil air emission reporting
demand of E-PRTR regulation, the group of large Finnish wastewater plants decided to make a
common study about this issue. Water and wastewater association of Finland (VVY) had an active
role as a co-ordinator of both water and air related emissions in Finland. However, Viikinmäki
WWTP of the Helsinki Water has had the leading role of the measuring, modelling and PRTRreporting of the air emissions for the group of large plants.
In Finland 13 urban wastewater treatment plants are required to participate E-PRTR reporting
system based on the PE size of the plant. Additionally two smaller plants have been involved in the
study of the group. Plants of the group have been listed in Table 1.
Air emissions at WWTP
Normal biological process is developing greenhouse gases like carbon dioxide, methane and N2O.
Volatile organic compounds – so called VOC compounds are easily released from the wastewater
unit processes were mixing or aeration occurs. Air emission level depends on the evaporation
characteristics and concentration of the compound. Carbon dioxide released from the biological
process (STOWA, 2007) is not part of PRTR register, since it has no fossil origin. However, so
called bio-origin CO2 is determined and shown in this paper.
Most of the major Finnish urban wastewater treatment plants have in some level their own power or
heat production, which means typically biogas for electricity production or oil usage for heating
purposes. Thus typical power production air emissions like SOX, NOX and CO have to be
considered what comes to PRTR reporting demands. When burning the biogas, some methane is
considered to be released as well due to incomplete burning process. Especially greenhouse gas
emissions are strongly depending on the process selection (Yasui et al., 2005; Keller et al.,
Water Practice & Technology Vol 4 No 2 © IWA Publishing 2009 doi: 10.2166/WPT.2009.029
2003).General background information about the power production of selected WWTP is given as
well in Table 1.
Table 1: General information of the plants (based on year 2006 statistics)
WWTP
Helsinki
Qave
m3/d
PE
BOD7 Ninfluent Neffluent
t/d
t/d
t/d
Digestion
Y/N
Biogas
Mm3/a
Heating oil Heating oil
Y/N
t/a
260 000
820 000
57,4
11,5
1,3
Y
10,0
Y
85
Espoo
90 000
260 000
18,2
4,8
1,2
Y
2,9
Y
295
Turku
Jyväskylä
Tampere
Oulu
Lahti
Kuopio
Pori
Kotka
Seinäjoki
Rovaniemi
Lappeenranta
Riihimäki
Rauma
67 000
42 000
63 000
39 000
20 000
20 000
20 000
12 000
17 000
16 000
16 000
13 000
13 000
200 000
191 000
172 000
137 000
117 000
113 000
112 000
97 000
93 000
90 000
81 000
60 000
26 000
14,0
13,4
12,1
9,6
8,2
7,9
7,9
6,8
6,5
6,3
5,7
4,2
1,8
2,8
2,8
2,7
2,1
0,9
1,2
0,9
0,9
0,7
1,0
1,1
0,7
0,4
0,9
2,0
1,9
1,6
0,2
0,8
0,5
0,2
0,3
0,8
0,4
0,2
0,4
N
Y
Y
N
Y
Y
N
N
N
N
N
Y
N
1,2
1,7
1,5
1,2
0,5
N
N
N
N
N
Y
Y
Y
Y
Y
N
N
N
18
81
18
61
140
Viikinmäki WWTP
Viikinmäki WWTP treats the wastewater of 780,000 people in addition to the industry in the areas
of Helsinki and neighbouring municipalities. The average wastewater flow rate is 280 000 m3/d and
the peak flow as much as 800 000 m3/d. Treatment process is including primary settling, activated
sludge system and tertiary denitrification filter. All the sludge is unaerobically digested and
dewatered before transport. The process facilities for wastewater and sludge treatment have been
excavated into bedrock. Underground areas are 14 hectares and aboveground areas only 3 hectares.
Ventilation air flow is more than 100m3/s and all underground ventilation air of the plant is
collected into the one point. This makes measurement and calculation of air emissions more
accurate (Fred et al., 2008).
Figure 1: Viikinmäki WWTP
2
MATERIAL AND METHODS
Water phase concentrations of various VOC compounds are generally below detection limit at
sewage water (Fred et al., 2008; Wicht, 1996; Wild et al., 1995; Zheng et al., 1994). Therefore it
may be impossible to use models, which are based on water phase concentrations for air emission
estimation. Air emission mechanisms are divided in the pre-studies into five groups; power
production, biological formation in anaerobic conditions, combustion of gas or oil, denitrification
process and general volatilization from wastewater surface (Fred et al., submitted; Tchobanoglous
et al., 2003). All PRTR compounds were studied based on this emission mechanism idea. In some
cases only one phenomena could be found and in case of some other compounds, like methane, CO2
and NMVOC, more than one mechanism occurs simultaneously (Fred et al., submitted).
Most of the waste water treatment plants in Finland are uncovered, open-air plants, which makes air
emission studies very demanding. At the pre-study phase, most of the compounds had been
measured directly in the air phase at the chimney of Viikinmäki WWTP (Fred et al., 2008).
Analyses were made in the pre-phase of the project by accepted analyse methods, like
TD-GC/MSD-method and FT-IR-gas analyzer, for gases (Fred et al., 2008). Based on these
measurements at Viikinmäki WWTP, correlation factors for each compound have been determined
and used for estimation of the PRTR emissions of studied plants. Emission correlation factors have
been collected in Table 2.
Table 2: Emission correlation factors (Fred et al., 2008)
Compound
CASnumber
Methane
74-82-8
Carbon monoxide
630-08-0
Carbon dioxide (bio)
124-38-9
Carbon dioxide (fossil)
124-38-9
Nitrous oxide (N2O)
10024-97-2
Ammonia (NH3)
7664-41-7
Waste
water
kg/m3
BOD7
kg/kg
Nitrogen
kg/kg
1,31E-02
Biogas
kg/m3
Heating oil
kg/kg
7,31E-03
7,33E-03
8,78E-01
1,70E-02
1,79
3,13
1,62E-02
2,47E-5
NMVOC
3,23E-05
Nitrogen oxides (NOx)
6,72E-05
4,35E-03
6,72E-08
Sulphuric oxides (SOx)
5,28E-08
8,76E-05
1,12E-04
1,2-dichloroethane (EDC)
107-06-2
6,77E-09
Dichloromethane (DCM)
75-09-2
2,68E-08
Hexachlorobentzene
(HCB)
Pentachlorobentzene
118-74-1
8,33E-11
608-93-5
8,38E-11
Tetrachloroethylene
(PER)
Tetrachloromethane
(TCM)
1,1,1-trichloroethane
127-18-4
2,09E-07
56-23-5
6,76E-09
71-55-6
7,88E-09
Trichlorothene
79-01-6
1,78E-07
Trichloromethane
67-66-3
2,18E-08
Benzene
71-55-6
1,15E-07
2,03E-02
3
Data collection
After the preliminary phase of measurements and laboratory tests, operational data of each plant
was collected and processed by a common data collection sheets. Common and simple data sheet
ensures equal data format. Common calculation sheet is also easy to revise when future studies
increase the accuracy of the method. Based on correlation factors represented in Table 2, emissions
of each wastewater treatment plant have been calculated.
RESULTS AND DISCUSSION
Wastewater quality at Finnish municipal wastewater treatment plants is very similar as it is shown
by some examples in Table 3. Level of PRTR compounds is also generally relatively low in Finnish
municipal wastewaters. In most of the cases concentrations were below analyze limit accuracy.
Table 3: Wastewater effluent quality of PRTR compounds in Finnish urban WWTPs (2006)
Compound
1,2-dichloroethane (EDC)
Dichloromethane (DCM)
Hexachlorobenzene (HCB)
Pentachlorophenol (PCP)
Tetrachloroethylene (PER)
Trichloroethylene
Trichloromethane
Benzene
Median, µg/l
< 0,30
< 0,3
< 0,05
< 0,1
< 0,5
< 0,5
< 0,3
< 0,5
Max,µg/l Environmental Quality Environmental Quality WHO limitation for
Standard*, Sea water, drinking water, µg/l
Standard*, Surface
µg/l
water, µg/l
<1
10
10
30
2
20
< 0,25
0.03
0.03
< 0,1
2
2
9
<1
10
10
40
<1
10
10
20
< 0,5
12
12
300
<1
10
* Government Decree 1022/2006
Based on this fact the method of one large reference plant, Viikinmäki, was selected for air
emission calculations and statistical quality of the correlation factors shown in Table 2 is considered
acceptable by Finnish Environmental Authorities.
Based on described pre-studies correlation factors were used for all 13 wastewater treatment plants
operational data to be able to check the reporting obligation. Modelling of the greenhouse gases and
ammonia emissions shows that methane and nitrous oxide exceed the reporting limits what comes
to the case of three large wastewater treatment plants of the group. On the other hand carbon
dioxide and ammonia emission levels were far below of the reporting limits. Figure 2 shows as an
example calculated greenhouse gas and ammonia emissions of the studied plants.
NMVOC emissions are based on either usage of heating oil (Tata et al. 2003) or normal release of
the VOC from the waste water. Figure 3 shows the emissions of the power production. Nitrous
oxide (NOX) emission of the Viikinmäki WWTP is 50 % of the reporting limit and other WWTP
has approximately 10 % emissions of the reporting limit. All other NMVOC emissions are marginal
compared to limits given by PRTR guidance of EU regulation. In case of CVOC compounds and
benzenes calculation shows similar results giving approximately 0 - 10 % fraction of the reported
emission level.
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t/a
Methane, CH4
t/a
400
70
350
60
300
50
250
40
Reporting limit 100 t/a
100
50
0
Carbon dioxide, CO2
Reporting limit 100 000 t/a
100 000
90 000
80 000
70 000
60 000
50 000
40 000
30 000
20 000
10 000
0
Reporting limit 100 t/a
100
90
80
70
60
50
40
30
20
10
0
t/a
Reporting limit 500 t/a
0
5
Nitrous oxide, N2O
30
20
10
Reporting limit 10 t/a
0
t/a
Ammonia, NH3
10,0
Reporting limit 10 t/a
1,0
0,1
0,0
Figure 2: Calculated greenhouse gas and ammonia emissions
Nitrogen oxides, NOX
t/a
Sulphuric oxides, SOX
1000,000
Carbon monoxide, CO
Reporting limit 150 t/a
100,000
10,000
1,000
0,100
0,010
0,001
0,000
kg/a
NMVOC
100
Figure 3: Calculated emissions of power production and NMVOC emissions
Reporting limit 100 t/a
100
10
10
1
1
0
Modeling of the PRTR emissions shows that three largest municipal wastewater plants – Helsinki,
Espoo and Turku, exceed reporting level in case of methane and nitrous oxide. All other WWTP are
far behind and probability to achieve reporting limit in any compounds is very small. However the
future improvements in nitrogen removal level might cause reporting responsibility of nitrous oxide
in case of Tampere and Jyväskylä. Reported compounds and treatment plants in Finland are
collected in Table 4.
Table 4: Reported PRTR compounds in Finland, reporting year 2007
WWTP
Reported
WWTP
compound
compound
Helsinki
CH4, N2O
Pori
Espoo
CH4, N2O
Kotka
Turku
Jyväskylä
Tampere
Oulu
Lahti
Kuopio
N2O
-
Reported
-
-
Seinäjoki
Rovaniemi
Lappeenranta
Riihimäki
Rauma
-
CONCLUSIONS
The study shows that the reliable measurements for air emissions for complete ventilated WWTP
can be conducted. Possibility to make measurements in ventilation air stream at a single point
makes emission estimations very accurate compared to the other estimation methods. Accuracy is
high enough if the results are used for the evaluation whether the reporting limits of the PRTR
compounds are exceeded or not at some other WWTP’s. By using generated simplified model, the
demands of the reporting of the PRTR can be fulfilled also in the uncovered urban waste water
treatment plants, where the air emission analysing is very difficult to arrange in a proper way.
From the perspective of the PRTR reporting limits, it seems that the greenhouse gas emissions of
urban wastewater treatment plant can be significant at reporting point of view. In case of Finland
reporting limit is exceeded with nitrous oxide (N2O) and methane (CH4) emissions in Helsinki and
Espoo. Nitrous oxide emissions caused reporting responsibilities at the Turku WWTP. Volatile
organic compounds (VOC) emissions are low due to very strict control of industrial discharges to
municipal sewer based on the measurements and models made for this study.
References
European Commission (2006) Guidance document for the implementation of the European PRTR
Fred T., Heinonen M., Sundell L. and Toivikko S. (2008) E-PRTR reporting of air emissions at
urban wastewater treatment plants – case Viikinmäki WWTP, IWA World Water Congress and
Exhibition 7-12 September 2008 ,Vienna, Austria, Proceedings
Fred T., Heinonen M., Sundell L. and Toivikko S. (2008) Modelling total air emissions at large
municipal wastewater treatment plant, WEFTEC 2008, Chicago, poster presentation,
Proceedings
Keller J. & Hartley K. (2003) Greenhouse gas production in wastewater treatment: process
selection is the major factor, Water Science and Technology 47(12), 43-48
STOWA (2007) E-PRTR voor rwzi’s: deelproject van STOWA: ‘Wm en rwzi’s’, version
07-02-2007
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