Käppala Association and the Käppala Wastewater Treatment Plant

Käppala Association and
the Käppala Wastewater
Treatment Plant
Connected area, but
not member of the
Käppala Association
Connected area
The red line shows the tunnel system for
wastewater transport.
Käppala wastewater treatment plant
The Käppala wastewater treatment plant is located in the
city of Lidingö, just east of Stockholm. Wastewater from
over half a million people is treated here. Eleven member
municipalities are connected to the plant. The Käppala
plant employs a very effective treatment process, and is
Sweden’s third-largest wastewater treatment plant.
Our goal is clean water in
lakes and the archipelago
The Käppala Association treats wastewater from over half a million people in
eleven municipalities located north and east of Stockholm. Our treatment plant,
the Käppala wastewater treatment plant, is Sweden’s third-largest, and employs
a very effective treatment process.
More than 40 years ago, before the Käppala plant
started operating, huge amounts of raw sewage
were discharged into local watercourses, lakes and
the Stockholm archipelago. This caused problems
involving disease transmission and environmental
pollution. So in 1957, several municipalities
north of Stockholm joined forces and formed the
Käppala Association, a local federation, to treat
their wastewater.
Twelve years later, in 1969, the Käppala wastewater treatment plant in Lidingö was completed
– including the 65 km long tunnel system that carries wastewater to the plant from the association’s
member municipalities. Following a major rebuilding
and extension project, the plant was re-inaugurated
in 2000.
Nowadays, you can swim and fish in clean water in
and around Stockholm, which is unusual compared
with many other major European cities. The Käppala
Association has been one of the key players behind
this positive development.
The Käppala plant more than meets the discharge
requirements stipulated by the regulatory authority,
the County Administrative Board. However, we are
not content with that. In accordance with our quality
and environmental management system, we strive for
continuous improvement and to be able to contribute
to a sustainable society. We are keen to test new technologies, partly to make our treatment process even
more efficient, partly to increase biogas production,
and to be able to produce high-quality sludge.
We treat wastewater in the Käppala plant every
day of the year, 24 hours a day, and always with a
combination of mechanical, biological and chemical
treatment. It takes about 1.5 days to treat the waste­
water before it is returned to nature at a depth of
45 m outside the island of Lidingö.
Wastewater treatment in Sweden
Approximately 85 percent of Sweden’s population live
in areas connected to municipal wastewater treatment
facilities. There has been an expansion in municipal sewage
treatment since the 1940s. Initially, mechanical treatment
was entirely dominant. Biological treatment was introduced
on a large scale in the 1960s, and chemical treatment in
the 1970s. Today approximately 95 percent of urban wastewater undergoes both biological and chemical treatment.
Since the late 1990s, the major treatment plants in
the southern part of Sweden have been augmented with
a special nitrogen removal step.
Source: The Swedish Environmental Protection Agency
The wastewater
treatment process
The treatment process at the Käppala wastewater
treatment plant includes five major steps:
Pre treatment
Primary sedimentation
Biological treatment
Final sedimentation
Sand filtration
1. Screens and grit removal
Toilet paper and debris are
removed from the sewage
with rotating step screens.
Sand and grit is settled on
the bottom of aerated grit
chambers. The removed sand
and grit is washed, dewatered
and then reused.
11. Fine screens
12. Odour control
13. Grit chamber
14. Primary sedimentation
15. Biological treatment
16. Final sedimentation
17. Sand filter
18. Chemical dosage
19. Digesters
10. Upgrading facility for vehicle fuel
11. Sludge dewatering (Kemicond)
12. Gas boiler
13. Heat pump
2. Odour control
The ventilation air from the
screens, grit chambers and the
primary sedimentation tanks
is collected and treated with
UV light and activated carbon
filters before it is released to
a 150 m tall chimney. The
treatment effect is more than
95 percent regarding odour units.
3. Primary sedimentation
Particulate matter is settled
to the bottom of the primary
sedimentation tanks. The
produced primary sludge is
collected with sludge scrapers
and thickened before it is
pumped to the digesters for
production of biogas.
4. Biological treatment
Micro-organisms consume
the organic material in the
water and produce a biological
sludge. By controlling the living
conditions for the microorganisms nutrients as nitrogen
and phosphorus are removed.
Nitrogen is transformed to
nitrogen gas and is released to
the atmosphere. Phosphorus is
bound to the biological sludge.
5. Final sedimentation
The produced biological
sludge is settled to the bottom
of the final sedimentation
tanks where it is collected
with sludge scrapers and
pumped back to the biological
treatment. A portion of the
biological sludge, excess sludge,
is pumped to the digesters for
production of biogas.
6. Chemical precipitation
Some of the phosphorus that is
not removed in the biological
treatment is precipitated with
ferrous iron sulphate.
7. Sand filters
The final treatment step is filtration where particulate matter
is removed from the water with
sand filters. The treated water is
released to the Stockholm archipelago at a depth of 45 m.
Sludge dewatering
Heat pump
Sludge silo
Heat pump
Gas boiler
Upgrading facility
District heating
for vehicle fuel
Sludge treatment
The sludge is pumped into the
digesters, where biogas is formed.
The biogas is upgraded to vehicle
fuel quality, and used as fuel for
public transport buses. The digested
sludge is treated with chemicals,
dewatered, quality checked and
then used as an agricultural fertilizer and for production of soil and
soil amendment products.
We contribute to clean water in our region
and recycle nutrients and energy to the
Every year, we treat 50 million cubic metres of
The Käppala plant is an underground facility.
Wastewater is treated in large chambers blasted
into the rock. Every year, we treat approximately
50 million cubic metres of wastewater. This represents
approximately 900,000 bathfuls per day.
Treating wastewater is our main task. But we also
exploit the nutrients and energy contained in the
wastewater, and produce sludge and biogas that are
recycled to the community.
Our sludge is used as fertilizer by farmers in our
Our sludge is certified annually in accordance with
the Swedish Water & Wastewater Association’s (our
industry organisation) certification system REVAQ,
and can be used on arable land as an alternative to
chemical fertilizers. The sludge is rich in nutrients,
among them phosphorus and nitrogen. It undergoes
continuous quality control. In recent years, we have
been able to improve the quality of the sludge to
such an extent that most of the nutrients can now be
returned to the ecological cycle and used on arable
land in the Stockholm region. The rest is used for
production of soil and soil amendment products.
... and we process the biogas into environmentally
friendly fuel for public transport buses
We produce the biogas in the Käppala plant’s digesters.
We upgrade the biogas to vehicle fuel quality in our
upgrading facility. The gas is used as an environmentally
friendly fuel for public transport buses. In this way, we
help reduce the emissions of fossil carbon dioxide in the
Stockholm region.
Environmentally certified
The Käppala Association is environmentally certified
in accordance with ISO 14001. Our own laboratory is
accredited by SWEDAC in accordance with ISO 17025.
Technical data1
People equivalents
Average flow
Maximum flow
Total nitrogen
Total phosphorus
570,000 p e
160,000 m3/d
520,000 m3/d
35 tonnes/d
6 tonnes/d
0.9 tonnes/d
Total nitrogen
Total phosphorus
8 mg/L
10 mg/L
0.3 mg/L
3 mg/L (July–October)
Treatment results
< 3 mg/L
9 mg/L
0.2 mg/L
< 1 mg/L
Ferrous iron
sulphate (18 % Fe)
Sulphuric acid
(98%) 2
Hydrogen peroxide
(100%) 2
2,300 tonnes/yr
50 tonnes/yr
2,000 tonnes/yr
200 tonnes/yr
32 m3/yr
Biogas production3
Biogas for vehicle
fuel production3
Gas to boilers3
Heat production of
Heat production for
district heating3
31 GWh/yr
6.5 million m3/yr
2 million m3/yr
4.3 million m3/yr
21,100 MWh/yr
14,000 MWh/yr
Chemical consumption
Biogas and energy
Sludge dewatering
TS concentration of dewatered sludge
Sludge production
39 %
19,000 tonnes/yr
Data from 2010.
Used for chemical conditioning in Kemicond.
3 All produced biogas will be upgraded to vehicle fuel quality in the coming years.
1 2 • At the Käppala plant, 99 percent of the organic
pollutants and 97 percent of the phosphorus are
removed. Nitrogen in the wastewater is reduced by
80 percent.
• The Käppala plant’s two digesters produce about
6.5 million cubic metres of biogas each year. The gas
is used as vehicle fuel and is sufficient to run about
100 buses.
• The Käppala plant started operating in 1969.
Between 1994 and 2000, the plant was modernised
and a new section was built. Today, the plant has the
capacity to treat wastewater from 700,000 people.
• The Käppala Association owns and maintains a
65 km long tunnel system with pumping stations that
transport waste­water from the member communities’
own sewer systems to the Käppala plant in Lidingö.
The Käppala Association is a local federation consisting of eleven munici­
palities that have joined forces to solve a shared problem: managing and
treating the member municipalities’ wastewater. We work in accordance with
the cost price principle, on a non-profit basis. The Käppala Association’s
board consists of politicians from the member municipalities. We have
approximately 40 employees.
If you would like to know more about our activities, please visit our website
at www.kappala.se.
Käppala Association Postal Address Box 3095, SE-181 03 Lidingö Visiting Address Södra Kungsvägen 315, Lidingö
Phone +46 8 766 67 00 Fax +46 8 766 67 01 E-mail [email protected] Website www.kappala.se
Photo: Rikkard Häggbom, Johnér Bildbyrå and iStockphoto. Illustrations: Mario Salutskij. Print: Davidsons Tryckeri, september 2011.
Eleven municipalities are behind the Käppala Association