1. science
2. ecology
3. pollution

Wastewater
treatment in Sweden
Brief history of
wastewater disposal
From latrine to water closet. In Sweden’s larger towns
and cities, installation of an entirely novel system of
wastewater and sewage disposal began in the late 19th
century. Pipes were laid underground to conduct wastewater from kitchens and sewage from water closets
(WCs) to the nearest lakes or coastal waters. This
disposal system successively replaced the previous method, latrine management, whereby household waste
was collected in pits and barrels for subsequent use as
fertiliser by the local farmers and, where fertiliser use
was not possible, latrines were dug into the ground.
The main motive for introducing WCs was to improve
sanitary conditions in urban areas. From the 1920s,
waterborne systems predominated, first in major cities
and in time also in small towns and villages.
Growing pollution problems
Initially, urban and industrial wastewater was discharged in altogether untreated form. Over time, however,
problems of polluted lakes, watercourses and coastal areas in Sweden became increasingly severe. Discharged nutrients and oxygen-demanding substances caused hypoxia,
fish death and, in some cases, waterborne epidemics. Until the 1940s, water pollution
was regarded entirely as a municipal concern and the scope of remedial action was
small. Construction of municipal wastewater treatment plants (MWTPs) was slow: in
1940 there were only 15 plants in the country, and by 1955 the number had still only
doubled.
1960s a turning point
In the 1960s, eutrophication in the aquatic environment attracted a great deal of attention in Sweden. Many lakes and watercourses around major urban areas had, by then,
suffered for decades from the wastewater discharged into them. Lakes became overgrown and algae floated in towards beaches that had previously been ideal for bathing.
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The water was eutrophic; and in some lakes and watercourses heavy metals and other
chemicals were also found to be deposited in the sediments, often the legacy of previous
industrial activity. Environmental warning bells rang frequently, soon prompting greater
state efforts to combat water pollution. The Swedish Environmental Protection Agency
(EPA) was formed in 1967, new government grants for municipal wastewater treatment
were introduced in 1968 and an entirely new piece of legislation, the Environmental
Protection Act, came into force in 1969.
Extension of wastewater treatment in 1960s and ’70s
Between 1971 and 1979, the Swedish state invested some SEK 1.5 billion (corresponding
to approximately SEK 11 billion, i.e. EUR 1 billion, in present-day monetary value) in
MWTP construction. In the early 1970s certain industries also received government
grants for their environmental conservation measures. These grants were largely used to
improve wastewater treatment. Since then, industrial companies with their own wastewater disposal have taken major steps to reduce their effluents. Discharges from properties with on-site wastewater disposal, on the other hand, have shown no corresponding
decrease.
The extensive measures taken in the 1970s, in particular, made lakes and watercourses noticeably cleaner within just a few years. Bathing beaches reopened and the
fish returned.
The figure shows technological development
at Swedish wastewater
treatment works from the
1940s to the present day.
Source: Swedish EPA.
Treatment of urban wastewater, 1940–2006
Current situation
Today, virtually all households
in urban areas are connected
to municipal sewer networks,
and roughly 95% of urban
wastewater undergoes both
biological and chemical treatment. Major industrial facilities, mines, airports etc carry
out their own wastewater
treatment.
%
100
Chemical
treatment
90
80
70
Secondary chemical
treatment
No treatment
60
50
40
30
20
10
Sludge
removal
Primary
treatment
Supplementary
treatment
Tertiary biochemical
treatment
Tertiary
filtration treatment
Special
nitrogen removal
Secondary
biological
treatment
Tertiary treatment
0
1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
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Legislation in Sweden and the EU
In the Water Act of the early 1940s, Sweden introduced regulations on wastewater
discharge and made permits obligatory for certain industries. In 1956 a special Act on
supervision of lakes and other water areas was passed and a new agency known as the
Swedish Water Inspectorate was formed. With the 1969 Environmental Protection Act
and the 1999 Swedish Environmental Code, a collection of rules concerning all forms of
disturbance and degradation of the outdoor environment came into being.
After Sweden joined the European Union in 1995, EU water laws were successively
incorporated into Swedish legislation. At the time, there were various directives in the
EU covering different categories of water and application areas. In 2000, the decision
was taken to adopt a Water Framework Directive that, in the long term, will replace a
range of other water-related directives. During 2008, a corresponding directive for the
marine environment was adopted.
The key water directives are those on
•bathing waters (76/160/EEC and 2006/7/EC)
•drinking water (98/83/EC)
•urban waste water (91/271/EEC)
•nitrates (91/676/EEC)
•IPPC (Integrated Pollution Prevention and Control, 96/61/EC)
and also
•the Water Framework Directive (2000/60/EC)
•the Marine Strategy Framework Directive (2008/56/EC).
The Urban Waste Water Directive
The purpose of the EU Urban Waste Water Directive is to combat damage to the environment caused by wastewater discharges from urban areas and certain industrial
processes. The requirements imposed by the Directive include the following:
•All built-up areas (with reference to their size and location) must have collection systems for wastewater by year-end 1998, 2000 or 2005.
•The water piped into collection systems must undergo at least secondary treatment.
In general, this entails biological treatment or some other process whereby set quality
standards can be met.
•Treated wastewater must meet certain minimum water-quality standards.
•Wastewater discharges in ‘sensitive areas’ (waters vulnerable to the effects of nutrient
inputs) are subject to stringent requirements concerning effective treatment.
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Sweden has incorporated the Urban Waste Water Directive into Swedish legislation, both in the Environmental Code and in the Swedish
EPA’s Regulation on treatment of wastewater from urban areas (SNFS
1994:7). There are now, for example, general limit values for concentrations of nitrogen and oxygen-consuming substances in wastewater
outflows, and rules on inspection and sampling. Limit values for oxygen-demanding substances apply nationwide, while nitrogen controls
apply only to discharges that reach marine and coastal waters between
the Norwegian border to the west and Norrtälje (on the Baltic Sea
coast NE of Stockholm) to the east. Supplementary inspection rules are
contained in the Swedish EPA’s Regulation on inspection of discharges
to recipient water and land areas from installations for treating wastewater from urban areas (SNFS 1990:14).
Industrial on-site treatment facilities
Discharges from industrial installations with on-site treatment facilities
are regulated by means of conditions in permit decisions pursuant to
the Environmental Code. In the EU the IPPC Directive requires, for
environmental permitting purposes, coordinated assessment of the
impact of emissions to air and water from certain major activities in industry, waste management and agriculture. The norms imposed to date
are less stringent than those applied in Sweden. When it comes to emissions of certain particularly hazardous substances, there are special
limitations in regulations issued by the Swedish EPA (SNFS 1995:7).
Costs of municipal water supply and sanitation
In 2005, costs of running Sweden’s facilities for water supply and
sanitation totalled EUR 1.4 billion, including VAT at 25%. Costs of
sewerage, including collection and treatment, make up a somewhat
higher share than that represented by drinking-water production and
distribution costs. The replacement value of all facilities is an estimated
EUR 45 billion, of which infrastructure, i.e. sewerage, accounts for
EUR 27 billion (70%).
Source: Swedish Water & Wastewater Association, 2008
The 16 Swedish environmental
quality objectives
1. Reduced Climate Impact
2. Clean Air
3. Natural Acidification Only
4. A Non-Toxic Environment
5. A Protective Ozone Layer
6. A Safe Radiation Environment
7. Zero Eutrophication
8. Flourishing Lakes and Streams
9. Good-Quality Groundwater
10. A Balanced Marine Environment, Flourishing
Coastal Areas and Archipelagos
11. Thriving Wetlands
12. Sustainable Forests
13. A Varied Agricultural Landscape
14. A Magnificent Mountain Landscape
15. A Good Built Environment
16. A Rich Diversity of Plant and Animal Life
www.miljomal.se/Environmental-Objectives-Portal
The national environmental quality objectives describe the quality of the environment that characterises a sustainable society. Fifteen of the objectives were adopted by
Sweden’s Parliament (the Riksdag) in 1999 and the last (on biodiversity) was added in
2005.
Each environmental quality objective is specified in one or more interim targets,
which reveal whether Sweden is heading in the right direction. The Riksdag adopted
interim targets and action strategies in November 2001 (Govt. Bill 2000/01:130).
Several of the environmental quality objectives are connected with wastewater treatment. The following five are particularly important.
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4.
7.
8.
10.
15.
A Non-Toxic Environment
Zero Eutrophication
The environment must be
free from man-made or
extracted compounds and
metals that represent a
threat to human health or
biological diversity.
Nutrient levels in soil
and water must not be
such that they adversely
affect human health, the
conditions for biological
diversity or the possibility
of varied use of land and
water.
Flourishing Lakes and
Streams
A Balanced Marine
Environment, Flourishing Coastal Areas and
Archipelagos
A Good Built
Environment
The Riksdag has laid
down the following two
interim targets for emissions to water.
•2 By 2010 Swedish
waterborne anthropogenic
emissions of phosphorus
compounds into lakes,
streams and coastal waters will have decreased
by at least 20% from
1995 levels. The largest
reductions will be achieved in the most sensitive
areas.
•2 By 2010 Swedish
waterborne anthropogenic
emissions of nitrogen
compounds into sea areas
south of the Åland Sea
will have been reduced by
at least 30% compared
with 1995 levels.
Lakes and watercourses
must be ecologically
sustainable and that their
highly variable habitats
must be preserved.
The seas around Sweden
must have a sustainable
productive capacity and
their biological diversity
must be preserved.
Cities, towns and other
built-up areas must provide a good, healthy living
environment and contribute to a good regional
and global environment.
Natural and cultural
assets must be protected
and developed. Buildings
and amenities must be
located and designed in
accordance with sound
environmental principles
and in such a way as to
promote sustainable management of land, water
and other resources.
This environmental objective is supported by a
range of interim targets,
including the following on
phosphorus in wastewater:
•2 By 2015 at least
60% of phosphorus
compounds present
in wastewater will be
recovered for use on productive land. At least half
of this amount should be
returned to arable land.
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Discharges from municipal
treatment plants
Nutrient discharges in Sweden increased sharply up to the 1960s
owing to the extension of municipal sewer networks. The late
1960s and ’70s therefore saw the construction of a system of
modern treatment plants for removal of phosphorus and organic
substances. A major fall in such discharges then ensued. Since the
mid-1980s, the plants have been supplemented with new removal
methods involving nitrogen reduction as well. These maps show
discharges of the substances from MWTPs, per sea basin, in 2006.
The largest quantities of nitrogen and organic substances are
discharged in the Baltic Proper basin, while phosphorus discharges
are roughly equal in the Kattegat and the Baltic Proper. Quantities
entering the Skagerrak, being small, hardly show on the figure.
The removal rate for phosphorus and the biological oxygen
demand (BOD) load has been around 95% for the past decade. For
nitrogen, the removal rate is considerably lower but has improved
during this period for the larger treatment plants with recipients
vulnerable to nitrogen. On average, for the whole of Sweden, this
rate was just under 60% in 2006.
Nitrogen
in 2006,
tonnes
Nitrogen
in 2006,
tonnes
Nitrogen in 2006, tonnes
Nitrogen (Ntot)
tonnes
30 000
4 6734 673
4 673
20 000
338 338
338
Skagerrak
Skagerrak
Skagerrak
Kattegat
Kattegat
992 992
Kattegat
992
15 000
10 000
5 000
0
1940
3 5443 544
3 544
7 6847 684
7 684
25 000
50
60
70
80
90 95 00 05 10
Öresund
Öresund
Öresund
Bothnian
Bay Bay
Bothnian
Bothnian Bay
Bothnian
Sea Sea
Bothnian
Bothnian Sea
BalticBaltic
ProperProper
Baltic Proper
Phosphorus
in 2006,
tonnes
Phosphorus
in 2006,
tonnes
Phosphorus in 2006, tonnes
Phosphorus (Ptot)
113 113
113
125 125
125
tonnes
8 000
7 000
53
53
53
6 000
9
5 000
9
9
Skagerrak
Skagerrak
Skagerrak
38 38
Kattegat
38Kattegat
Kattegat
4 000
3 000
2 000
1 000
0
1940
Öresund
Öresund
Öresund
50
60
70
80
Bothnian
Bay Bay
Bothnian
Bothnian Bay
BalticBaltic
ProperProper
Baltic Proper
2 7192 719
2 719
2 5332 533
2 533
60 000
158 158
158
Skagerrak
Skagerrak
Skagerrak
661 661
Kattegatt
Kattegatt
661
Kattegatt
40 000
20 000
Öresund
Öresund
Öresund
60
16
16
BODBOD
tonnes
in 2006,
tonnes
7 in 2006,
BOD77 in 2006, tonnes
80 000
50
Bothnian
Sea Sea
Bothnian
Bothnian Sea
16
90 95 00 05 10
Organic substances (BOD7)
tonnes
100 000
0
1940
1 1661 166
1 166
70
80
90 95 00 05 10
1 5771 577
1 577
Bothnian
Sea Sea
Bothnian
Bothnian Sea
651 651
651
Bothnian
Bay Bay
Bothnian
Bothnian Bay
BalticBaltic
ProperProper
Baltic Proper
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Treatment plants as emission sources
Swedish wastewater treatment plants currently achieve a good and steadily rising
removal rate of nutrients. However, discharges from wastewater disposal systems are
still a substantial source of eutrophying substances (phosphorus, nitrogen and organic
matter) in Swedish waters. Discharges of these substances have decreased considerably
over the past few decades. The diagrams below, summarising anthropogenic nitrogen
and phosphorus emissions in 2006, show that agriculture is the largest source while the
share derived from treatment plants is just under 25% for both nitrogen and phosphorus.
Municipal wastewater treatment plants (MWTPs) receive mainly wastewater from
urban areas, while permanent or holiday homes in rural areas often have their own
stand-alone (‘local’ or ‘on-site’) installations for wastewater disposal. In Sweden some
750,000 properties are not connected to MWTPs. Disposal standards in these areas are
highly variable and only some 60% of installations are estimated as meeting standards
complying with the Environmental Code’s requirements. Today, the amount of phosphorus released from local wastewater disposal is more than half that of the total amount
discharged by MWTPs.
To deal with these discharges, the Swedish EPA has drawn up general recommendations concerning small-scale local installations for wastewater disposal. Many municipalities are currently engaged in systematic work to bring about improvements and devise
action strategies.
Metals and other contaminants
Many chemicals in use today end up in sewers and are found in wastewater and sewage
sludge (see page 14). Metals mostly remain in sludge, and quantities of metals in water
outflows are therefore relatively small. The total amount of cadmium discharged to water from treatment plants annually is some 100 kg; the corresponding figure for mercury
is 60 kg. The heaviest discharges of mercury are those previously emitted to air and
accumulated in forest land. The heaviest cadmium discharges come from atmospheric
deposition and fertilisers in farmland.
MWTPs also receive minor quantities of solvents and small amounts of more or less
persistent organic pollutants (POPs), such as nonylphenol, brominated flame retardants,
polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), hexachlorobenzene and dioxins. Several POPs are used in industry or found in household products. Nonylphenol, for example, is banned in the EU but reaches us in imported textiles. Drugs
flushed into sewers cause several types of problem; many are not readily degraded and,
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despite their low levels, affect aquatic organisms. This problem is discussed in the Swedish EPA’s Report 5794 (‘Wastewater Treatment Plants’ Capacity to Dispose of Pharmaceutical Residues and Other Hazardous Substances’, in Swedish, Avloppsreningsverkens
förmåga att ta hand om läkemedelsrester och andra farliga ämnen, with a summary in
English). At the Pharmaceutical Specialities in Sweden (FASS) drug portal www.fass.se,
a tentative environmental pharmaceutical classification is available for patients, doctors
and interested members of the public.
Nitrogen discharges (tonnes/year) in 2006
On-site
wastewater
disposal 2 %
Forestry 4 %
Storm water from
urban areas 1 %
Industry 6 %
Athmospheric
deposition
19 %
Agriculture
44 %
Municipal
wastewater
treatment
plants 24 %
Phosphorus discharges (tonnes/year) in 2006
Storm water
from urban
areas 5 %
Forestry
4%
On-site wastewater disposal
12 %
Total: 85,800 tonnes/year
Agriculture
45 %
Industry
17 %
Municipal
wastewater
treatment
plants 20 %
Source: Swedish EPA Report 5815.
Total: 2,080 tonnes/year
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Discharges from municipal wastewater treatment
plants with loads exceeding 10,000 population
equivalents (pe) in 2006.
Compliant: meets Urban Waste Water
Directive (91/271/EEC) requirements.
Non-compliant: does not meet Urban
Waste Water Directive (91/271/EEC)
requirements.
Organic matter (BOD7)
Phosphorus (Ptot)
Greater
Stockholm
Greater
Gothenburg
Greater
Malmö
Greater
Gothenburg
Quantity of BOD7
discharged, tonnes, 2006
1
10
100
1,000
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Greater
Malmö
Greater
Stockholm
Quantity of phosphorus
discharged, tonnes, 2006
0.01
1
100
Compliant: affects sensitive marine areas
(nitrogen) and meets Urban Waste Water
Directive (91/271/EEC) requirements.
Non-compliant: affects sensitive marine
areas (nitrogen) and does not meet Urban
Waste Water Directive (91/271/EEC)
requirements.
Nitrogen (Ntot)
Not relevant: does not affect sensitive
marine areas. These are: (a) treatment
plants that drain into the Bothnian Bay or
Bothnian Sea, and (b) other, small inland
plants where, because of retention, the
quantity of nitrogen reaching a sensitive
marine area does not exceed 20 tonnes.
Nitrogen limits for discharges into
sensitive marine areas
The maximum allowable concentrations
of nitrogen (Ntot) in effluents are:
Greater
Gothenburg
•210 mg/l for wastewater treat-
ment plants with loads exceeding
100,000 pe
Greater
Stockholm
•215 mg/l for wastewater treatment plants
with loads of 10,000–100,000 pe.
Alternatively, a removal rate of at least
70% is required for nitrogen. In exceptional cases the requirements are applied
collectively to a few geographically close
plants.
Greater
Malmö
Quantity of nitrogen
discharged, tonnes,
2006
10
100
1,000
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Number of plants, amounts (tonnes)
and concentrations
No of treatment plants
2,000– 10,000– 100,000–
10,000 100,000
Treatment method
Biological
3
2
0
Chemical
39
9
0
Biochemical
215
101
6
Supplementary
14
11
1
Nitrogen removal
13
49
12
Inland
217
113
8
Bothnian Bay
12
3
0
Bothnian Sea
57
16
1
Baltic Proper
75
49
5
Öresund
5
5
1
Kattegat
66
40
1
Skagerrak
2
0
0
Coast
67
59
11
Bothnian Bay
6
5
0
Bothnian Sea
20
13
1
Baltic Proper
21
24
5
Öresund
1
3
2
Kattegat
4
8
3
Skagerrak
15
6
0
Total 2006 284
172
19
Total 2004
289
170
20
Total 2002
289
170
20
Total 2000 289
169
20
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Number of plants, amounts (tonnes) and concentrations (mg/l) of BOD7,
phosphorus and nitrogen and in outflow from municipal waste ater treatment plants designed for more than 2 000 persons. Data from 2006,
distributed by plant size, treatment method, position and catchment area.
Organic substances (BOD7)
Quantity Conc Quantity Conc Quantity Conc
(tonnes) (mg/l) (tonnes) (mg/l) (tonnes) (mg/l)
Treatment method
Biological
24 17.9
38 7.6
–
–
Chemical
482 28.4
392 12.4
–
–
Biochemical
899 7.4
2,043 7.5
612
7
Supplementary
51 8.2
72 4.3
60 2.4
Nitrogen removal
56
7
710 3.8
2,861 6.2
Inland
Bothnian Bay
Bothnian Sea
Baltic Proper
Öresund
Kattegat
Skagerrak
Coast
Bothnian Bay Bothnian Sea
Baltic Proper
Öresund
Kattegat
Skagerrak
Total,2006,
Total,2004,
Total,2002
Total,2000,
1,196 10.3
173 31.1
482 16.8
285 7.3
7 2.9
243 6.2
5 4.1
2,004 6.4
136 12.4
410 11.9
687 4.9
43 2.5
728 6.5
–
–
521
–
36
391
19
76
–
4.8
–
4.7
4.9
3.8
4.6
–
316
8.4
57 27.6
85 7.9
76
6
2
3
27 8.9
69 8.2
1,251
285
412
355
53
62
84
6.3
1.3
8.2
5.1
3.4
2.7
5.1
3,011
6.5
–
–
152 11.6
740 3.1
536 8.4
1 583 10.4
–
–
1,512
9.8
1,480 10.0
1,784 11.3
1,674 9.5
3,254
3,127
3,128
4,605
6.4
7.0
6.4
8.3
3,533
3,081
3,247
3,505
6.1
5.4
5.6
5.6
Phosphorus (Ptot)
Nitrogen (Ntot)
2,000–10,000 10,001–100,000 100,001–
2,000–10,000 10,001–100,000
100,001–
Quantity Conc Quantity Conc Quantity Conc
Quantity Conc Quantity Conc Quantity Conc
(tonnes) (mg/l) (tonnes) (mg/l) (tonnes) (mg/l)
(tonnes) (mg/l) (tonnes) (mg/l) (tonnes) (mg/l)
Treatment method
Biological
0.3
0.2
2.4
0.5
–
–
26
20
63 12.8
–
–
Chemical
5.2
0.3
7.2
0.2
–
395 23.3
732 23.1
–
–
Biochemical
35.3
0.3
85.4
0.3
23.6
0.3
2,178 17.9
5,511 20.2
1,930
22
Supplementary
2.5
0.4
3.2
0.2
17
0.7
155 24.8
343 20.7
201 8.2
Nitrogen removal
2.6
0.3
45.1
0.2
132.1
0.3
102 12.8
2,295 12.4
4,466 9.7
Inland (total)
34.5
0.3
75.5
0.2
21.6
0.2
2,189
18.8
5,684
18.1
1,847
Bothnian Bay
2
0.4
4.1
0.4
–
–
123
22
236 21.5
.
Bothnian Sea
9.9
0.3
10.3
0.3
2.4
0.3
604
21
928
27
199
Baltic Proper
11.9
0.3
26.2
0.2
15.1
0.2
736 18.8
2,340 16.8
1,355
Öresund
0.4
0.1
3
0.2
0.4
0.1
49 19.3
181 10.3
59
Kattegat
10.1
0.3
32
0.3
3.8
0.2
660 16.8
1,999 17.9
233
Skagerrak
0.3
0.2
–
–
–
–
17 13.5
–
–
–
Coast (total)
11.4
0.3
67.8
0.3
151.1
0.3
667
17.8
3,260
16.5
4,751
Bothnian Bay
0.6
0.3
9.1
0.4
–
–
62 29.6
747 34.2
–
Bothnian Sea
2.6
0.2
21.5
0.4
6.4
0.5
165 15.2
1,097 21.8
551
Baltic Proper
2.7
0.2
19.9
0.3
49.2
0.2
232 18.6
909 12.9
2,110
Öresund
0.2
0.3
4.7
0.3
29.2
0.5
6
7.8
118
7.5
579
Kattegat
1.3
0.4
7.8
0.3
66.3
0.4
60 20.1
211
9.2
1,511
Skagerrak
4
0.5
4.8
0.3
–
–
142
17
178 10.9
–
Total 2006
46
0.3
143.3
0.3
172.7
0.3
2,855
18.5
8,944
17.5
6,598
Total 2004 45
0.3
126
0.3
147
0.3
2,794 18.9
8,521 18.1
6,464
Total 2002 47
0.3
141
0.3
163
0.3
2,711 17.1
8,595 17.5
6,730
Total,2000
57
0.3
178
0.3
188
0.3
2,796 15.9
9,283 16.6
6,898
Biological = secondary biological treatment
Chemical = secondary chemical treatment
Biological-chemical = tertiary treatment
Supplementary = tertiary filtration treatment
Nitrogen removal = tertiary nitrogen-removal
treatment
17
.
26
17
11.9
14.
10.2
–
41.9
8.9
9.1
9.9
–
11.5
11.4
11.6
11.0
Treatment methods
wastewater tre atment in sweden
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Treatment methods
Wastewater treatment plants in Sweden usually combine various means of mechanical,
biological and chemical treatment. The process invariably begins with some form of
mechanical removal of solids. Thereafter, the most frequent combinations in treatment
plants are:
•biological treatment
•chemical treatment
•biological-chemical treatment (conventional three-stage treatment)
•biological-chemical treatment with a special nitrogen removal stage
•biological-chemical treatment with supplementary treatment (e.g. filtering).
Mechanical treatment
In this stage of treatment, large solids are removed: grit (stones, sand and
gravel), pieces of wood, paper, hair, textiles and plastic. This takes place
by means of screening, the use of sand catchers and presedimentation:
• The screens catch rags and other coarse debris that would otherwise
clog up pumps or cause problems in the rest of the treatment process.
• A sand catcher consists of a basin-like chamber with a ‘pocket’ to
collect grit and other particles that, owing to their weight, easily sink to
the bottom. The particles that settle on the bottom are extracted with
pumps and the solids from the sand catcher are transported to a landfill.
• In presedimentation, particles that have not been caught in the screen
or sand catcher and need removing before the subsequent biochemical
treatment are extracted. The heavier particles sink to the bottom, where
scrapers collect them and push them into a ‘sludge pocket’, from where
the sludge is pumped for sludge treatment.
Chemical treatment
The chemical stage mainly involves removing phosphorus from the wastewater. This is done by adding precipitating chemicals based on aluminium or iron that cause the dissolved phosphorus to precipitate. After
flocculation (see below) the sludge is separated by means, for example, of
sedimentation. Some 90% of the phosphorus is thus removed.
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Biological treatment
Biological treatment makes use of microorganisms, mainly bacteria, which feed on the
organic matter left in the wastewater after the mechanical treatment. Some 90% of this
organic matter, which is largely dissolved in the wastewater, is removed from the water.
Approximately 20% of the nitrogen is consumed by the microorganisms, which undergo
flocculation, i.e. form clumps or ‘flocs’, which are then separated in sedimentation basins
(the activated sludge process).
Nitrogen removal
In certain wastewater treatment plants nitrogen, too, can be removed in the biological
stage. Nitrogen removal is a relatively complicated process and is therefore more common
in large wastewater treatment plants (>10,000 pe) discharging into sensitive recipients.
Transporting the water between different basins, some with oxygen and others without,
generates favourable environments for various kinds of microorganisms. Nitrifying bacteria convert ammonia into nitrate if oxygen is present. Thereafter, in anoxic conditions,
denitrifying bacteria can convert nitrate into nitrogen gas. Normally, the whole process
of nitrogen removal is expected to involve removing some 50–75% of the nitrogen.
Filtration
Screens
Sandcatcher
Presedimentation
Biological treatment
Stirring and
aeration
Sedimentation
Wastewater
Removal of
large solids
Sand
Sludge
Sludge
Sludge
Precipitating
Mechanical treatment
agents
Filtration, a final stage of treatment, is carried out to boost the degree of purification in
wastewater treatment plants with particularly stringent treatment requirements. It involves the removal of sludge and particles that have not previously sunk to the bottom in the
sedimentation basins.
Chemical treatment
Flocculation
Sedimentation
Treated
water
Sludge
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Restoring wastewater
nutrients to the soil
In a sustainable society, the nutrients contained in wastewater should be reused. Presentday agriculture is not self-supporting when it comes to plant nutrients and, accordingly,
has a large annual requirement of raw phosphate and other substances in commercial
fertiliser. If the plant nutrients found in wastewater can be returned to farmland, they
can form part of a natural cycle, enabling money to be saved and the environment
spared. If nutrients end up in the wrong place, one risk is substantial eutrophication. In
wastewater treatment plants the phosphorus in sewage sludge, in particular, is collected
and can be used to fertilise fields or other land in need of fertilisation. For sewage sludge
to be restored to the land, it must not contain such substances as heavy metals or organic contaminants in excess.
Sweden’s wastewater treatment plants are built to remove plant nutrients from the
water phase and bind them in sludge, but the removal methods are not intended to dispose of hazardous substances. The latter generally pass through the system and reach lakes and seas; there they may affect the benthic fauna and fish, for example. Sometimes,
toxic substances also kill the organisms contained in the basins at wastewater treatment
plants causing problems in the removal. Some substances may also remain in the sludge
and thus be spread on farmland.
poluttants in sewage sludge
Undesired substances may also reach wastewater treatment plants via storm water.
Much of the heavy metals that enter these plants comes from road transport — tyres,
brakes and carwash facilities, for example. Work is therefore under way to separate
storm water from other wastewater or purify it before it is allowed to enter the flow.
Researchers consider that the risks entailed by undesired substances in sludge are
small for human beings, animals and plants. Nevertheless, there is concern about the
effects that more or less unknown substances may have. Perfluorooctane sulphonates
(PFOS), which belong to the category of substances that are resistant to biodegradation,
are an example of substances alien to nature that have been detected in the environment
relatively recently.
The figures show that the quality of sewage sludge in Sweden has improved in the
past few decades. Nonetheless, a great deal of work remains to be done before the sludge
is free from undesired substances. Silver and triclosan are substances increasingly used
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for antibacterial purposes, and this means that high levels in sludge
pose risks. Alongside the continued improvement in sludge quality, there
is scope for restoring nutrients by separating urine and WC water from
solid matter, and also for recovering the nutrients in and extracting contaminants from sludge. Since pathogens may occur in various fractions
of sewage, there is a need for hygienisation to take place before sludge is
used on land.
Heavy metals (mercury, cadmium, lead, chromium, nickel, zinc and copper) in sludge from
municipal wastewater treatment plants, 1987–2006. Median values for plants dimensioned
for 20,001–100,000 pe. Limit values for heavy metal content in sludge are indicated by
dotted lines.
mg/kg dry matter
mg/kg dry matter
mg/kg dry matter
3,0
100
800
700
2,5
80
600
Zinc
2,0
500
60
Mercury
Lead
1,5
Cadmium
400
40
300
1,0
Copper
20
0,5
200
Chromium
100
Nickel
0,0
´87 ´90 ´92 ´95 ´98 ´00 ´02
´06
0
´87 ´90 ´92
´95
´98 ´00 ´02
´06
0
´87
´90 ´92
´95
wastewater tre atment in sweden
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Monitoring environmental status
Discharges from MWTPs and industrial facilities affect the environment on varying
scales, from the local watercourse to the whole Baltic or North Sea. To determine where
a load originates, all discharges affecting a particular body of water (the ‘recipient’) can
be quantified. Pollution in small lakes, sea inlets or bays can commonly be linked to specific sources, but the larger the recipient, the harder it is to specify the sources. Winds,
currents and atmospheric deposition have a major bearing on the distribution of various
substances in the marine environment.
Recipient monitoring
All activities with permits under the Swedish Environmental Code, including treatment
plants, carry out ‘operator self-monitoring’. This usually involves inspecting the facilities
themselves; their handling of chemicals and management of waste; and their emissions
to water and air. In some cases, it also involves carrying out measurements in the recipient. All these data are reported in annual environmental reports, such as those available at www.stockholmvatten.se (in Swedish). Stockholm Vatten, a municipal limited
company (which produces Stockholm’s drinking water, treats wastewater and operates
sewer networks), is the principal for several treatment plants in the Stockholm area.
Since the early 1980s, jointly with other municipalities with discharges into the Stockholm archipelago, it has run a recipient monitoring programme.
In many cases, monitoring of major watercourses, lakes and coastal areas is conducted through the agency of local water conservation associations. These associations’
members are usually municipalities, industrial companies and trade organisations. The
Lake Vänern water quality association is an example of one engaged in coordinated
operator self-monitoring; see www.vanern.se (in Swedish).
Environmental monitoring
In Sweden, state-funded environmental monitoring is in progress to document the overall state of, and changes in, the environment. Results show whether the environmental
protection measures implemented are bringing about the desired improvements, and
whether Sweden is attaining its set environmental quality objectives. The Swedish EPA
is responsible for nationwide environmental monitoring, which is divided into various
programme areas, Freshwater being one and Seas and Coastal Areas another; see www.
naturvardsverket.se/en/In-English/Menu/State-of-the-environment/Environmentalmonitoring/. The EPA is also in charge of coordinating the regional environmental
monitoring that is otherwise organised by the county administrative boards. Regional
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monitoring of surface water has been partly changed: since 2007, monitoring of water status has been
at the water-district level, pursuant to the Water
Framework Directive and the Swedish Ordinance on
Water Quality Management.
EPA screening programme
Many of the chemical substances found in society
at large end up in sewers and treatment plants. The
amounts of heavy metals discharged, at least, are
regularly monitored within the obligatory inspection programmes. The numerous organic contaminants, on the other hand, are not analysed regularly
because doing so would be both difficult and costly.
In addition, new chemical substances are appearing all the time. The Swedish EPA therefore has a
special programme with campaign-type sampling
and analysis of new environmental pollutants and
pharmaceutical residues, in particular. This ‘screening programme’ makes it possible to carry out spot
checks to see how far these substances occur in the environment, what their sources
are and whether human beings are at risk of exposure to them. Sludge, sediments and
wastewater from industry and MWTPs are usually sampled, since they collect pollutants
from many sources.
Bathing water
Discharges can affect bathing-water quality. For the treatment plants, it may be a matter
of overflows, when untreated water is released in conjunction with heavy inflows. Under
the Bathing Water Directive, Sweden is obliged to monitor all the major bathing waters
nationwide. The Swedish EPA bears overall responsibility for this monitoring, and since
2001 the Swedish Institute for Infectious Disease Control has, on the EPA’s behalf, provided advice and information for sampling agencies, municipalities, the public and the
media, and supervised the reporting of results. For more information (in Swedish) about
water quality in Sweden’s bathing waters, see the Institute’s portal, http://badplatsen.
smittskyddsinstitutet.se
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Eutrophication – a key issue
Eutrophication is due to inputs of nitrogen and phosphorus that are excessive in relation to natural status. There are two primary causes of eutrophication of lakes and
watercourses: leaching of phosphorus from arable land and discharges from wastewater
treatment and industrial facilities. Storm water and rural on-site wastewater disposal
also account for substantial shares of phosphorus emissions (see figure on page 8). Both
phosphorus and nitrogen can affect the marine environment, depending on which substance is in relatively short supply for algal production.
Sensitive areas
Within the Urban Waste Water Directive Sweden has identified as ‘sensitive’ those areas
that are affected by, or at risk of, eutrophication in the absence of remedial action. Every
water area in Sweden (including coastal areas) has been identified as vulnerable to the
impact of phosphorus emissions; and the coastal areas from the municipality of Norrtälje to the Norwegian border, i.e. the Baltic Proper and the straits of Öresund, Kattegat
and Skagerrak, have been assessed as vulnerable to the impact of nitrogen emissions.
Throughout Sweden, particularly strict requirements concerning removal of phosphorus
in treatment plants apply. Improved nitrogen removal is required in South Sweden, for
MWTPs with coastal discharges corresponding to more than 10,000 person equivalents. For the purposes of environmental permitting or supervision of treatment plants,
requirements concerning nitrogen removal at small MWTPs or in other recipients can be
imposed pursuant to Chapter 2, Section 3 of the Environmental Code.
Marine environment
A great deal of attention has been paid to the environmental status of the seas surrounding Sweden in recent years. For the Baltic Sea, eutrophication is regarded as perhaps
the biggest problem. Levels of both nitrogen and phosphorus in seawater are higher than
they were 50–60 years ago and the problem of anoxic sea bottoms in non-coastal Baltic
areas has become not less but more severe, despite substantial measures to date.
Attitudes concerning the implications of reducing nitrogen and phosphorus discharges have also changed. Some researchers have questioned the usefulness of nitrogen
removal in the wastewater treatment plants along the Baltic coasts, since natural inputs
due to nitrogen fixation from the atmosphere are massive. Nitrogen fixation is carried out by cyanobacteria (blue-green algae), which are favoured by an ample supply of
phosphorus in the water, a high temperature and a low water turnover. Where nitroISBN 978-91-620-8416-5.
Print: CM Gruppen, Stockholm, 09-09.
Production: Swedish EPA. Design and
coverphoto: P. Hönig. Photo: Page 1, 2, 16
T. Kyrklund, p 5 U. Nylén/BLR-fotograferna,
p 8 SYVAB, Himmerfjärdsverket, p 21 M.
Nedinge, p 22 B. Ekberg/Megapix.
Graphics: A. Orrgård/SCB (p 6-7 T. Flygar
and p 23 SMHI).
gen levels are low, cyanobacteria also have a competitive
advantage in relation to non-nitrogen fixing algae. Reducing
nitrogen in relation to phosphorus inputs could thus encourage cyanobacteria even more since, at worst, their nitrogen
fixation may eliminate the benefits of reducing nitrogen
emissions. The complex connection between algal blooms
and emissions of eutrophying substances is analysed in
various publications, including the Swedish EPA’s Monitor
19 (Change Beneath the Surface — An In-Depth Look at
Sweden’s Marine Environment) and the 2005 report (in
Swedish) on the environmental status of the Baltic Proper
(Miljötillståndet i Egentliga Östersjön 2005, including
English summaries) from the Stockholm Marine Research
Centre (www.smf.su.se).
In 2005, the Swedish EPA commissioned a panel of
foreign researchers to evaluate the current eutrophication
status of the seas surrounding Sweden. This expert panel
concluded in its report that the connections between the
measures under way and changes in marine environmental
status are complex. The panel’s main recommendation was
to step up efforts to reduce phosphorus inputs to the Baltic
Proper, given the conditions both out at sea and along the
coast. However, the panel members disagreed on whether
nitrogen removal was worthwhile. For the Skagerrak and
Kattegat, their recommendation was to focus on reducing
nitrogen inputs, given that cyanobacteria problems were less
widespread in those areas. Regarding phosphorus emissions,
the panel noted that Sweden had already taken major steps
to reduce releases from point sources and that it is, in the
long term, inputs from land use that must be reduced. The
Swedish EPA has analysed the expert panel’s conclusions in
a report of its own (No. 5587, ‘Eutrophication of Sweden’s
Coasts and Seas’ [Övergödning av Sveriges kuster och hav,
with a summary in English]).
Bothnian Bay
Bothnian Sea
Skagerrak
Kattegat
Baltic Proper
Öresund
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ISBN 978-91-620-8416-5
Wastewater disposal has metamorphosed from a solution to
a local sanitary problem into an international environmental
issue. This publication describes how treatment of wastewater
from urban areas has evolved in Sweden.
The report is issued pursuant to Article 16 of Council Directive
91/271/EEC concerning urban wastewater treatment, often
known as ‘the Urban Waste Water Directive’. This Directive
covers all wastewater collected in sewer networks, but quantitative controls are imposed only on the treatment plants that
serve more than 2,000 people. In Sweden, this corresponds
to some 450 installations.
Swedish EPA SE-106 48 Stockholm. Visiting address: Stockholm - Valhallavägen 195, Östersund - Forskarens väg 5 hus Ub, Kiruna - Kaserngatan 14.
Tel: +46 8-698 10 00, fax: +46 8-20 29 25, e-mail: [email protected] Internet: www.naturvardsverket.se Orders Ordertel: +46 8-505 933 40,
orderfax: +46 8-505 933 99, e-mail: [email protected] Address: CM Gruppen, Box 110 93, SE-161 11 Bromma. Internet: www.naturvardsverket.se/bokhandeln