Evaluation of properties of fly ash stabilized sewage sludge (FSS) as
liner on landfills
Märta Ländell, Swedish Geotechnical Institute Karsten Håkansson, Vectura Consulting AB
Josef Mácsik, Ecoloop AB
Background
• Several hundred Swedish landfills will soon be closed
• The purpose of the cover is to minimize leachate
• Usually exhaustible natural materials are used
• Alternatives?
Waste products?
Layer for vegetation
Top soil cover
Drainage layer Liner (FSS) Terrace layer
Waste
FSS
(Fly ash Stabilized sewage Sludge )
• Sewage sludge
– Low hydraulic conductivity – Low shear strength
– Organic content
• Fly ash
– From combustion of mainly wood and coal – High shear strength
– Hardening, high pH and salinity → prevent degradation
• FSS mixture
– 40-60 % fly ash
– Dry solid content 40-45 %
– Low hydraulic conductivity and high shear strength
Field work
• Test areas built starting 2004
• Some landfills are using the material as final covering
Sofielund 0,1 hectares Summer 2005 Blåberget
0,06 hectares Autumn 2004
Dragmossen 1,2 hectares Spring 2004
Gärstad 0,55 hectares Autumn 2004
Lilla Nyby
>8 hectares
Autumn 2005 - Atleverket
3 hectares Autumn 2006 -
Salvatore Vuono
Follow-up project
• Results up to spring 2011
• Monitoring of hydraulic conductivity
– Percolate volume
– Samples of solid FSS material
• Drainage water quality
– Metals
– Organic substances – Nutrients
• Durability (FSS as liner)
– Leaching and transport of material – Biological degradation
– Drying and deformation
– Compression (packing) http://www.varmeforsk.se/rapporter?action=show&id=2777
Hydraulic conductivity
Hydraulic conductivity (l/(m²×year)) for FSS-liner measured 0.3, 1, 2 and 6 years after installation
Drainage water quality
• Some sites: initially high levels of metals, nutrients, DOC
• Reduced over time to acceptable levels
0 10 20 30 40 50 60
aug-04 dec-05 apr-07 sep-08 jan-10 jun-11
Copper (µg/l)
Drain 1 Drain 2 Drain 3 Drain 4 Sw. EPA Ref.
Drainage water quality
• Some sites: initially high levels are not
decreasing
Drainage water quality –
Reasons for high levels of contaminants
• Compression → pore water → high levels initially
• No separation between FSA and drainage material
(gravel) → rough surface → large contact area for run off water → high levels
• Deformation → ”ponds” on the FSA liner → long contact time → high levels
Durability
• Durability (in this study) = the ability for the liner material to maintain its function
• Threatened by three factors:
– Transport of material – Biological degradation – Drying and deformation
WASCON, 1 June 2012 11
Transport of material
• Field and laboratory tests show low percolation → limited possibilities for particulate transport by water
• Biological degradation can cause transport of gas or dissolved matter in water
Biological degradation
• Limited by high pH and salinity, high content of ash
• Methane and carbon dioxide in pore gas
• No measurable decrease of organic matter
Durability
Durability - Drying and deformation
Sampling over a period of six years
• No drying, constant water content
• Increasing shear strength
• Decreasing hydraulic conductivity
Conclusions
• Hydraulic conductivity: very low after compression of the FSS liner
• Drainage water quality: at some test sites acceptable, at some test sites high contaminant levels probably due to insufficient separation of layers
• Durability: the function (as a dense layer) is maintained during the test period
The FSS material is well suited for the use as liner on landfills!
Recommendations for use
• Use the instruction manual (SVU 2007-10*, Värmeforsk Report 1010**)
• High content of fly ash (~ 50 %, DW)
• Mixing and building cycle, avoid heavy rain and very cold weather
• Separation between FSS layer and drainage layer
*
Receiving Premixing Storing Mixing Mixing and construction
Thank you…
• …for your attention
• Acknowledgements for the financial support
– Thermal Engineering Research Association (Värmeforsk) – Swedish Waste Management (Avfall Sverige)
– The Swedish Water & Wastewater Association (Svenskt Vatten) – Landfill owners in Eskilstuna, Örebro, Linköping, Huddinge,
Sundsvall, Älvkarleby
– Geo Innova/Vectura, Ecoloop, SGI
