The Danish action plan for promotion of eco-efficient technologies – Danish Lessons
The Danish action plan for promotion of eco-efficient technologies – Danish Lessons
The transformation of a Danish river system
A focused intervention to change a deteriorating state of the environment in and among the Lilleå river in
Aarhus in Denmark totally changed the river and the surroundings. Today the river hosts particular fish species
and it has become a popular area for the local population.
The story of the Lilleaa river system in
consisted of many, mostly very small and
Lilleaa, before it discharged into Gude-
Denmark is almost like the famous fairy
simple treatment plants among which
naa river, was slightly polluted and in an
tale by Danish writer Hans Christian An-
only some had mechanical treatment
acceptable state.
dersen about the ugly duckling, which
(see fig. 1), and very few had biologi-
turned into a beautiful swan.
cal treatment. As a result, not only the
But pollution was not the only problem
main river, but also many of the smaller
and the only reason for the deteriorated
In the 1970s, the Lilleaa river system
tributaries were polluted and unsuitable
river environment. Water courses had
was heavily polluted by domestic
for normal river fauna like trout.
been canalized to improve the drainage
wastewater, industrial wastewater (from
of the river valley for farming. In order
slaughterhouses and dairies) and direct
The result was that the environmental
to preserve drainage capacity, the river
discharge of liquid manure from farms.
status of the river system was very bad
was heavily maintained, including cut-
The wastewater treatment infrastructure
(see fig. 2), and only the last part of the
ting all plants and removing stones and
1974
2005
Randers
Fjord
Øster Tørslev Å
ing
All
nå
de
Bjerringbro Gu
nd
er
Julsø
Å
Salten Å
Salten
Langsø
Knud Sø
Ravn Sø
Ry
Mossø
nÅ
er
Gj
Å
Aarhus
Bay
Fu
nd
er
Salten Å
Skanderborg
Salten
Langsø
Ry
Mossø
up
ttr
Ma
Skanderborg Sø
Århus
Knud Sø
Ravn Sø
t
en
m
ch
at
åc
le
Lil
Julsø
Å
Hadsten
å
Hammel
Silkeborg Langsø
Aarhus
Å
lle
Å
Silkeborg
Aarhus
Bay
Skanderborg
Skanderborg Sø
Brædstrup
Hinnerup
Å
up
ttr
Ma
Brædstrup
Li
Tange Sø
Hinge
en
m
ch
at
åc
t
ing
All
enå
Gud
Bjerringbro
Kjellerup
le
Lil
Silkeborg Langsø
Fu
å
Hammel
nÅ
er
Gj
Silkeborg
Nørreå
ng
e
lle
Å
Grund Fjord
Viborg
Ta
Å
e
ng
Hinge
Å
Hald Sø
Tange Sø
Ta
Kjellerup
r
ve
Ri
d
Gu
Lilleaa
Grund Fjord
Li
aa
en
Langaa
Randers
Nørreå
Hald Sø
d
Gu
Øster Tørslev Å
Randers
Viborg
r
ve
Ri
Randers
Fjord
aa
en
Langaa
Å
Tørring
Langaa
0
Gu
a
na
de10 km
r
Waste water treatment plants:
ve
Large dots:
more than 5.000 persons
Ri
Medium dots:
1.000-5.000 persons
Small dots:
200-1.000 persons
Tørring
aa
Langaa
Mechanical treatments and basins
Biological treatment
Biological treatment and P-removal
u
rG
ve
Ri
n
de
1970's
Unpoluted or nearly unpoluted
Slightly poluted
Strong poluted
Very strong poluted
Fig 1: Wastewater treatment plants in the main catchment area of the Gudenaa river and its tributary, the
Fig 2: The environmental state (based on macro
Lilleaa.
fauna) of the Lilleaa before the introduction of efHadsten
200
ficient wastewater treatment.
Hadsten
1
charged into the river system dropped
dramatically as shown in fig 3. and at
the same time, the load of nutrients was
reduced significantly in order to protect
Randers Fjord downstream.
Socondly, the number of treatment
plants in the catchment area was reduced from approx. 25 in the 1970s to
five today.
The surrounding municipalities assessed that the advanced treatment
would be more stable and cheaper to
maintain if it was centralised at several larger plants. Many kilometres of
pipe line were constructed together
Photo: Jens Skriver Lindenborg.
with a number of pumping stations to
transport the wastewater from the more
gravel. The river was more or less like a
The first priority was to get clean water
than 25 small plants to the two to three
sand desert and only a few tributaries
in the river – i.e. to improve wastewa-
large new plants and still keep the water
were spared and could function as a
ter treatment and to prevent discharge
balance in the catchment area.
refuge for fauna, including fish like the
of liquid manure from the farms. The
sea trout.
management circle was travelled several
Fig. 4 shows the effect on river fauna
times before the water in the entire river
after introducing wastewater treatment
system was cleaned up.
plants. The fauna is used as an indica-
A final problem was the numerous
tor for the level of pollution in the river.
dams, which had been built for use as
watermills, but were no longer used
The treatment requirements were so
In 2001, the main part of the river was
for their original purpose. They made it
strict that the best and most advanced
only slightly polluted, and the objectives
nearly impossible for migrating species
technology had to be introduced. This
for the river system were fulfilled. In the
like eel and sea trout to move freely in
had two effects – first and foremost, the
last years monitoring results from the
the river system. The most important
amount of organic matter that was dis-
river around the fish farm have shown
dam was located by a fish farm in the
lower part of the Lilleaa (see fig. 6). This
dam made it very difficult for migrating fish like sea trout to reach the few
Organic matter BOD
(kg pr. year)
spawning areas left in the river system.
Fortunately, a small stock of original sea
80000
trout was able to maintain the population during the time of deteriorated
60000
environmental state.
40000
So the problems piled up –
but where to start?
Planning was a very important tool –
planning for water quality on a regional
level, as well as planning for wastewater
20000
0
1982
85
88
91
94
97
00
2003
treatment on a local level.
Fig. 3: Discharge of organic matter into the Lilleaa river system.
2
that the state of the river has improved
doing so, they are able to use less water
even more since 2001, and probably this
from the river. The aim of the project
is also valid for much of the rest of the
was to document that production could
river system.
increase without increasing the pollution
load, or maybe even reduce the pollu-
The fish farm situated in the lower part
tion load compared to the previous situ-
of the Lilleaa river system was another
ation. The pilot projects did succeed in
important source of organic matter
this, but the investment in this new type
and nutrients polluting the river. In the
of production is large and, in general,
1970s, when the production was based
possible only for larger fish farms.
Fig 5: Restored tributary to the Lilleaa.
on raw, chopped fish and without any
pollution abatement, it was this produc-
The next step was to create a more
tion that, in particular, put pressure on
natural habitat in the river, while simul-
the river. In the late 1980s, it became
taneously securing drainage of the river
compulsory for fish farmers to feed the
valley. In the main river, this was done
fish dry pellets instead and to construct
by constructing a double profile, with
ponds or small lagoons for simple treat-
a narrow profile for the small summer
ment of the effluent water. However,
flow and a much wider one for the
this regulation reduced the discharge
winter flow.
only to a certain level. Moreover, fish
farmers had no possibility to increase
In some places, it was necessary to
production. A number of Danish fish
restore the river with new meanders and
farmers, including the owner of the
layout of gravel and stones, as shown
farm at Lilleaa, joined in a pilot project
in fig 5. In these cases, the land owners
concerning the use of other produc-
were subsidised because the higher
tion methods and new technology for,
water level made it impossible to use
Fig 6: The dam at the fish farm – top: before the
e.g., physical and biological treatment
the valley for normal farming.
construction of the by-pass, bottom: the recon-
of the effluent. With the high level of
structed part of the river (by-pass) around the fish
farm.
purification of the water, it is possible
The last step was to secure the free
for farmers to re-circulate water. By
migration of fish and other fauna in the
have been fulfilled. The habitat for the
river system. Therefore, with the help of
fauna has been improved and there
new designs by-passes were constructed
are no significant obstacles left for the
at the dams, and especially at the larg-
migrating fauna, including fish. Today,
est dam as shown in fig 6. The cost of
the Lilleaa is the most productive river
these projects was paid by the regional
system for natural self-reproducing sea
authority (the county).
trout in Denmark – and some say maybe
a
na
e
Langaa
ud
rG
ve
Ri
Unpoluted or nearly unpoluted
Slightly poluted
Strong poluted
Very strong poluted
Hadsten
Hadsten
among the best in Europe.
Lilleaa
Lilleaa
A number of different parties like mu-
Hinnerup
Hinnerup
aa
n
de
gaa
R
r
ive
Gu
2001
nicipalities, water consumers, industry
The story of the Lilleaa shows the neces-
and fish farmers have contributed to
sity of a holistic approach and planning
reaching these results. The total cost
to restore river habitats. Advanced
for wastewater treatment and physical
technology has to be applied, and it
restoration of the Lilleaa is not known.
is important to be aware of the fact
that entities have to be large to ensure
Unpoluted or nearly unpoluted
Slightly poluted
Strong poluted
Very strong poluted
Fig 4: The environmental state (based on macro
What does the beautiful
swan look like today?
stable results (whether it is wastewater
Today, the general state of the Lilleaa
time be cost-effective.
fauna) of the Lilleaa river after introduction of ef-
river system is very good and the water
ficient wastewater treatment.
Hadsten
is clean. The environmental objectives
treatment or fish farms) and at the same
3
Photo: Jørgen Kjems.
Many Danish river systems have similar
•
New technologies used on fish
background stories, but they have not
farms ensure higher produc-
yet reached the same state as the Lil-
tion with the same or even lower
leaa. The pollution with wastewater is
pollution impact, which allows a
reduced to an acceptable level in most
reduction in the demand for water
rivers, but a lot of rivers are still physi-
and thus “gives back” the water to
cally deteriorated and measures need to
the river.
be taken before they can live up to the
standards in the EU regulation.
•
Clean water is not enough to restore the river habitat – the physical
habitat must also be improved.
Fig 7: A happy man.
Lessons learnt:
•
The story also shows that it is not
destroyed rivers can be restored – if
enough to ensure clean water. The recreation of at least more natural habitats
Even heavily polluted and physically
•
is necessary to secure a good ecological
the potential is still there.
Contact:
Planning is crucial – both for water
Poul Nordemann Jensen, Senior Adviser
National Environmental Research Institute
University of Aarhus
[email protected]
quality and for wastewater treat-
status in our rivers.
ment.
•
Advanced and stable wastewater
By doing so, nature responds in a posi-
treatment changes infrastructure
tive manner.
dramatically.
Read more:
www.ecoinnovation.dk/english
– choose Danish Lessons
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