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Sludge digesters
The raw and thickened sludge is sent to sludge digesters for treatment. The sludge is treated in eight sealed anaerobic digesters in which the temperature is kept at a constant 35°C. The sludge is treated in an anaerobic biological process, i.e., the organic material is decomposed with microbes in the absence of oxygen.
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Sludge dewatering
[At this stage,] the sludge is too thin to transport to composting sites. The sludge is therefore dewatered in order to make it more concentrated. Water is removed from the sludge with centrifuges that significantly reduce sludge volume.
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External composting
The treated sludge is then transferred by special trucks to an external composting site at which a composting process takes place. During this process, the sludge is placed in piles together with municipal crushed plants where a natural fermentation process then takes place, at the end of which organic material is obtained – compost, which is used as an agricultural fertilizer.
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Organic fertilizer
The compost that is produced in the composting process contains numerous nutrients such as nitrogen and phosphorus, and is used as a superb fertilizer for field crops.
- Step 1
Sludge digesters
- Step 2
Sludge dewatering
- Step 3
External composting
- Step 4
Organic fertilizer