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CASE STORY
Denitrification
Denitrification – the solution for municipal
Waste Water Treatment Plant of Alingsås
How Purac provide a maximum flexible process, with optimum use of existing volumes,
at a minimum investment cost!
Background
Europe has recently set up rather stringent requirement for
the outlet of nitrogen compounds from municipal waste water
treatment plants in order to minimize the eutrophication of
our common water environment. In 2012, eight municipalities
in Sweden did still not reach the new standards, one of them
being Alingsås. The industrial city Alingsås is situated close to
Gothenburg. The city is famous for the honorary Jonas Ahlströmmer, the man whom introduced potatoes as stable food to
Sweden, built up the woolen based industry in the western part
of Sweden and established tanneries.
The Alingås municipal waste water treatment plant is situated
at the Säveån river and has the lake Mjörn as it’s recipient. The
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lake is used for fishing, sailing, and other leisure activities and it
is therefore vital to reach as low nitrogen outlets as possible to
prevent algea bloom. The Ahlströmmer castle Nolhaga is neighbour to the municipal Nolhaga waste water treatment plant.
The plant has a traditional municipal treatment process with
pre-treatment, biological treatment and chemical sedimentation.
The load is 30.000 pe including industries. The present total
Nitrogen outlet is 26 mg/l on a yearly average. For year 2014,
the yearly average must be lowered to 15 mg/l. The Nolhaga
Castle Park is used for the public nowadays as a recreation
area and thus the amount of trucks to and from the plant must
be minimized as the road to the plant passes straight through.
Post-denitrification is thus not considered to be the main process solution as this required Methanol transports.
Solution
As the nitrogen outlet is measured on a yearly basis, the existing aerated stone filters can be used for nitrification in the
traditional biological system as the sole nitrogen removal
stage part of the year.
Two of the existing sludge oxidation tanks where converted to
pre- and post-denitrification tanks by filling them with suspended
carriers on which the nitrification organisms thrive. Depending on
how much additional denitrification is required to reach the stipulated outlet on a yearly basis, the process can be run either with
predenitrification or with both pre- and postdenitrification. Carbon
source may be used in both the pre- and the postdenitrification
tanks, and thus the operator has full control of the denitrification
process on a daily basis no matter what levels of Carbon and
Nitrogen that comes into the denitrification plant.
If the Nitrogen load to the waste water treatment plant will
increase, or the outlet permit become even more stringent, more
carriers can be filled into the tanks to meet up the new conditions.
Sieves must be used to prevent the carriers to leave the plant.
New creative design for these where adopted to incorporate the
existing sloping walls into the plant design.
Result
The plant is able to bring the total Nitrogen outlet down to
below 13 mg/l on a yearly basis.
Facts
One of the obstacles where to accommodate the new pipelines in
the existing, already crowded, pump gallery in the basement of the
sludge oxidation plant.
• Plant load: 30.000 peq incl. industries
More or less the entire reconstruction of the existing plant could
be made without disturbance to the daily operation of the existing
process. The entire project time was 10 month.
• Total Nitrogen inlet: 490 kg/day
As existing volumes where reused, the price of the project was
only half the cost of build a new plant for the same purpose.
• Mechanical treatment; Max 4000 m3/h
• Biological/chemical treatment; Max 2.700 m3/h
• Organic Nitrogen inlet: 230 kg/day
• Total Nitrogen outlet before: 26 mg total Nitrogen /l
• Total Nitrogen outlet after: 13 mg total Nitrogen /l
• Pre-denitrification volume: 600m3 (1.5 basins)
• Post-denitrification volume: 200m3 (0.5 basin)
Purac AB
Emdalavägen 10, SE-223 69 Lund, Sweden
Box 1146, SE-221 05 Lund, Sweden
Phone: +46 46 19 19 00, Fax: +46 46 19 19 19
E-mail: [email protected]
www.purac.se