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Case Story

Idre Waste Water Treatment PlantÄlvdalens Municipality, together with Purac AB, implemented during the years of 2010 to 2012 the planning and extension of the Waste Water Treatment Plant in Idre in order to satisfy a planned expansion of Idre tourist facilities. Up to 10 000 new beds are planned at the tourist facilities at Idre Fjäll and Himmelsfjäll.

BackgroundThe major challenge of the project was to dimension and expand the facility for the large required variations in loads and flows over the year. The facility will handle a load variation between 1500 pe in low season up to a maximum of 23 000 pe in high season. In connection with the expansion also biological treat-ment for BOD reduction where introduced.

Since the time schedule for the expansion of Himmelsfjäll is difficult to predict the design of the facility also required the possibility of a gradual capacity increase.

In the view of the complexity of the project and challenging design requirements the Municipality chose to implement the project as a ”Partnering” project, where Purac AB was responsible for process design and equipment deliveries.

For the Municipality a range of technical and environmental evaluation criteria were of great importance. The design had to put focus on the following:

• High flexibility and process stability.

• Minimised maintenance and care.

• Minimised odour sources.

• Expansion possibilities for future capacity increase and strengthened treatment requirements.

• Utilization of existing plant components.

SolutionAn extensive Feasibility Study was performed in close collabo-ration with the staff at the WWTP. Based on the report it was decided to design the facility as follows:

Waste Water Treatment Plant

Wastewater treatment• Pre Treatment in Rotosieve

• Primary Sedimentation

• MBBR (Moving Bed Bio Reactor)

• Chemical precipitation

• Final Sedimentation

Sludge treatment• Mechanical Pre Thickening

• Sludge storage

• Sludge dewatering in centrifuges

In order to meet the high demands flexibility of the design criteria the facility is designed two lines where all units are able to be turned off individually and bypassed.

Biological treatment – MBBR Selected biological treatment technology were MBBR (Moving Bed Biofilm Reactor) . MBBR technology is based on biofilm carriers of plastic which are maintained in suspension and in constant motion in the reactor. The microorganisms that grow as a biofilm inside the moving carriers break down the pollutants. The carriers are held suspended in the wastewater with aeration.

As the biofilm grows protected within the moving plastic carriers, which has a large specific sur-face, the MBBR system has a higher resistance to flow and load variations than a conventional activated sludge system.

The carriers design is impor-tant to get a good mass transport of substrates and oxygen to the biofilm. Excess biomass sludge continuously removed from the carriers in a natural pro-cess. The free biomass is separated and extracted as biological excess sludge in the subsequent sedimentation.

The oxygen is supported with aerators in the bottom of the reactor. The air supply also ensure the mixing of the carriers and wastewa-ter.

The plant was started up with a fill factor of 35% carrier but to secure a future increase in load is the maximum load factor on plant designed for a fill rate of 55%.

It is also possible to operate the plant with different filling ratio for each line in order to adapt the capacity of the plant for various seasonal loads.

ResultsThe plant was commissioned and tuned in during the first quar-ter of 2012. Following treatment results, as a yearly average, is for one year from July 2012 to August 2013.

• BOD7: 6,6 mg/l

• Total Phosphorus: 0,18 mg/l

Wastewater treatment data• Pre Treatment in Rotosieve

• Primary Sedimentation

• MBBR (Moving Bed Bio Reactor)

• Chemical precipitation

• Final Sedimentation

Sludge Treatment data• Mechanical Pre Thickening

• Sludge storage

• Sludge dewatering in centrifuges

Design data• Flow: 600 - 4 000 m3/d

• BOD7: 90 - 1 160 kg/d

• N-tot: 19 - 280 kg/d

• Total Phosphorus: 3 - 40 kg/d

Effluent requirements:• BOD7: 15 mg/l (Quarterly average)

• Total Phosphorus: 0,3 mg/l (Monthly avaerage)

Från vänster: Jan Spånberg (Operations Manager, Nodava), Jan-Åke Palmerand (Purac AB), P-O Brandt (Project Manager, Nodava), Simon Lundgren (Anjo Bygg AB), Carl-Otto Silfver (Purac AB)

”The biological part of the process worked even better than I had expected”Jan Spånberg, Operations Manager, Nodava

Purac AB Emdalavägen 10SE- 223 69 LundSweden

Phone: +46 46 19 19 00Fax: +46 46 19 19 19

e-mail: info@purac.sewww.purac.se

www.purac.sePurac ABEmdalavägen 10, SE-223 69 Lund, SwedenBox 1146, SE-221 05 Lund, SwedenPhone: +46 46 19 19 00, Fax: +46 46 19 19 19E-mail: info@purac.se

Customer facts:NODAVA AB (Northern Dalarna Water & Waste), is a municipal corporation that was formed July 1, 2010 jointly by Mora, Orsa and Älvdalens municipalities. NODAVA is responsible for the operations of water and wastewater, and waste and recycling.

This region is home to about 35 000 residents, and there are over 1 000 companies and a large number of homes and tourists, both in summer and winter, that needs to be provided with potable water, while their waste products should be disposed of in an environmentally sound manner, both sewage sludge as solid waste and recyclables .

Today, more than 70 people, including NODAVA waterworks, sewage treat-ment, recycling centers and repair and maintenance of approximately 145 mil, water, sewerage and stormwater pipes.

Secondary classifier

External sludge reception

Floating sludge

Flocculation

Flocculation

Flocculation

Primary classifier

Primary classifier

Primary classifier

Secondary classifier

Secondary classifier Chemical dosing

Idre Lake

MBBR Reactor

Air filter

Sludge storage Sludge storage

Sludge thickening

Pre-treatment

Pre-treatment

From Idre municipality

Inlet pumping station

MBBR Reactor

Blowers

Centrifuge

External sludge