Composting of Sewage Sludge in Kirchbichl, Austria

The ARAB Kirchbichl plant in Tyrol, Austria uses the GORE® Cover Process Technology in order to compost sewage sludge whilst reducing odors and emissions. 6 GORE® Cover system units in the intensive rotting phase have been installed in 2009.

W. L. Gore & Associates GmbH

Site name: ARAB Kirchbichl GmbH (Abwasserreinigungsanlagenbetreibergesellschaft m.b.H.)
Ownership: Abwasserverband Wörgl-Kirchbichl
Location: Kirchbichl, Bichlwang, Austria
Inhabitants: 13 communities, for max. 100.000 people
Wastewater volume: 15.000 m³/day
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Start-Up: December 2009
Total Design Capacity: 15.000 t/y total (mixed material)
approx. 7.500 t/y of Biosolids + Digestate Foodwaste (DM of 24%)
approx. 7.000 t/y of Greenwaste
Site Size (Total Property Area): 12.000 m²
Compost Pad Area: 1.600 m²
Type of Sludge: Secondary sludge after centrifuge with a dry matter (DM) of 24%
(percentage of digestate is from ~ 1.500 t/y foodwaste)
Type of Structure Material: Green Waste (Yard/Garden Debris).
overscreen from Sieved Residue
Mix Ratio (by weight): 1:1
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Technology: GORE® Cover system / sidewall design
Design by: UTV AG, Germany
No. of Heaps: 6 Bunker w/sidewall design
Treatment time: 

- 3 weeks in phase 1 under GORE® Cover (high rate composting)
- 3 weeks in phase 2 under GORE® Cover (high rate composting)
- 6-8 weeks in phase 3, open windrow with Turner (maturation)

               
Process temperatures: up to 75°C
Aeration: In-Floor, positive aeration
Control Parameters: Oxygen Control Mode with Temperature Monitoring
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Regulatory Requirements: Ã–stereichisches Kompost-Gütesiegel des KGVÖ (Kompostgüteverband Österreich, Austrian Compost Quality Society )
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End Product: fraction < 10 mm into storage of finished products
different blendings before marketing
(> 10 mm back into composting process)

End Product/ Output Quality: Class A, Quality compost certificate issued by the State of Austria
(Austrian Compost Quality Society)
End Use: Agriculture, Country Scaping, Landscape Management

Description:

The plant ARAB Kirchbichl started in 1991 treating wastewater and producing roughly 5.000 tpy of sludge.

• In 2008 an expansion of the composting area was permitted
• Due to emission calculations for a larger amount of Biosolids to be treated, a decision was made for the use of 6 GORE® Cover system units in the intensive rotting phase.
• Installation in 2009. Odor reduction with this new technology was significant target
• Design for an input of 10.000 m³ of Biosolids + 20.000 m³ of structure material = 30.000 m³ in total

Due to the expansion in 2009 the site the requirement of treatment capacity was incrased from 5.000 tpy to 15.000 tpy. Open windrow composting was not allowed anymore at site due to emission. The chosen technology has been the GORE® Cover system for the intensive rotting phase.
Later also a Co-Fermentation was installed to also use food-waste to support the energy production. The additional output (digestate) from the Co-Fermentation had a positive impact on the compost quality.

Due to including the foodwaste-digestate into the following composting process there is no extra hygenisation step needed. Necessary hygenisation is insured for the complete batch of the biosolids/digestate during composting.

Following achievements with the implementation of the GORE® Cover technology:

• Odors had to be controlled to best possible manner due to odor complaints from neighbors odour reduction greater 90% no issues with neighbours anymore
• Capacity increase on the existing footprint. (Double capacity from former 5.000 tpy on 2.200 m² treatment surface to 10.000 tpy on 1.600 m² treatment surface)
• 2 operators needed from reception to marketing
• Energy consumption during composting phase : 2,0 kWh/t Input Material
• Reduction of disposal costs for plant is 32,- € per ton of sludge
•  Compost does fulfill the high quality standards for Austrian Compost Class A
• So far no problems with process under very rough winter conditions ( -20°C outside temperature possible)