Sludge Drying Beds
Dorothee Spuhler, seecon gmbh
Sludge Drying Beds
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Depending on the initial situations and respective local circumstances, there is no guarantee that single measures described in the toolbox
will make the local water and sanitation system more sustainable. The main aim of the SSWM Toolbox is to be a reference tool to provide
ideas for improving the local water and sanitation situation in a sustainable manner. Results depend largely on the respective situation
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Sludge Drying Beds
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Contents
1. Concept
2. How can Drying Beds Optimise SSWM
3. Design Principals
4. Treatment Efficiency
5. Operation and Maintenance
6. Applicability
7. Pros’ and Cons’
8. References
Sludge Drying Beds
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1. Concept
Background
All organic degradation process produce sludge. (SASSE 1998)
Sludge has a total solid content of 2 to 10 % and can not be
transported easily with simple equipment. (SASSE 1998)
Apart from this, sludge is contaminated and occupies large volumes
for storage. (SASSE 1998)
Therefore it is better to dry or sludge (dewatering) before further use
or dumping. (SASSE 1998)
Anaerobic sanitation systems (e.g. latrines, septic tanks, aqua privies,
anaerobic baffled reactors, biogas reactors) produce less sludge than
aerobic treatments (e.g. from trickling filters, activated sludge) and
anaerobic sludge also dries better and results in less odour as it is more
stabilised.
Sludge Drying Beds
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1. Concept
What is a Sludge Drying Bed ?
Sludge drying beds are one of the simplest and oldest techniques for
sludge dewatering. (SANIMAS 2005)
They are impermeable beds filled with different layers of gravel and
sand.
Draining pipes are in incorporated in the bottom of the beds.
Sludge is applied in layers on the top gravel beds.
Drying is achieved by evaporation and gravity percolation. In planted
drynge bed, the removal of humidity is enhanced by evapotranspiration.
Dried sludge is not stabilised, but additional composting (e.g. cocomposting) will allow to recycle nutrients and organic matter into
agriculture.
The effluent (percolate) that is collected in the drainage pipes must be
treated correctly.
Sludge Drying Beds
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1. Concept
What is a Sludge Drying Bed ?
Faecal Sludge
Conveyance
Septic tank
Sludge drying beds
Biogas plants
Latrines
Source: adapted from EAWAG/SANDC
(2008); TILLEY et al. (2008); WAaF (2002
); SANIMAS (2005); BALASUBRAMANIYAM
(2008); www.Clker.com and
http://whrefresh.com/wpcontent/uploads/2010/01/potato_field.j
pg [Accessed: 10.06.2010]
Trickling filters
gas
manholes
inflow
scum
Co-composting
outflow
sludge
sedimentation
Aqua priviy
Sludge Drying Beds
inoculation of fresh wastewater with active sludge
final settler
Anaerobic baffled
reactor
Fertiliser for
agriculture
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1. Concept
The Role of Sludge Drying Bed in Faecal Sludge Management
Source: STRAUSS & MONTANGERO (2002)
Source: STRAUSS & MONTANEGRO 2004
Sludge Drying Beds
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1. Concept
What is a Sludge Drying Bed ?
Planted
Unplanted
Sludge drying beds can be
• Unplanted
• Planted
Unplanted sludge drying beds
Source: STRAUSS & MONTANEGRO 2004
• Design similar to unplanted filters sand/gravel filters
• Require desludging after every cycle of drying (manpower required)
Planted sludge drying beds
• Design similar to reed beds or vertical constructed wetlands
• Do not need desludging after every cycle: (STRAUSS & MONTANGERO 2002; SASSE 1998; TILLEY et al.
2008)
◦ Porosity is maintained by the root systems of the plants.
◦ Sludge is transformed into biomass (plants) and can be
harvested.
Sludge Drying Beds
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1. Concept
Examples: Unplanted Drying Bed
Source: SASSE (1998)
Sludge Drying Beds
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1. Concept
Examples: Planted Drying Bed
Source: TILLEY et al. (2008)
Sludge Drying Beds
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1. Concept
Examples
Covered
sludge drying
bed at the
Arcata
wastewater
treatment
plant (USA)
Unplanted
drying bed at
a waste
stabil- isation
pond (WSP)
site in
Colombia.
http://www.humboldt.edu/arcatamarsh/compost.html
Source: IRC (2004)
Source: EAWAG/SANDC (2008)
Unplanted drying beds in Ghana (Sandec)
Sludge Drying Beds
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1. Concept
Examples
Source: EAWAG/SANDC (2008)
Source: MUENCH, E.,von 2009)
Primary sludge drying
bed and reed bed (in the
background).
Sludge Drying Beds
New installation of a constructed wetland with
ventilation pipes at the Asian Institute of
Technology (AIT) in Bangkok, Thailand
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2. How it can optimize SSWM
Faecal sludge collected from on-site
sanitation installations are commonly
dumped untreated, because it is
difficult to transport and treatment
facilities lye often far away or are not
available at all.
This causes heavy environmental
pollution and major risk for the
transmittance of diseases.
Sludge drying beds are a simple mean to
reduce the volume of the sludge and
prepare them for co-composing, which
transform them to a safe and valuable
fertiliser.
Sludge Drying Beds
Source: EAWAG/SANDEC (2008)
Indiscriminate disposal of faecal sludge,
Ouagadougou. (Photo: Eawag/Sandec)
Source: ERIKSEN-HAMEL & DANSO (2002)
Lettuce farm fertilised with compost
at Gyenyasi farmers association in
Kumasi.
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3. Design Principals
Basics
Treatment objective:
Separation of solid from the liquid fraction of faecal sludge.
Similar treatment options: sedimentation/thickening ponds
Pre-treatments: Latrines, septic tanks, aqua privies, anaerobic baffled
reactors, biogas reactors, trickling filters, activated sludge, etc.
Post-treatment: Co-composting in order to transform it into fertiliser
Main-components:
• Impermeable shallow pond
• Drainage pipes in the bottom (perforated PVC pipes or hollow
blocks)
• Different layers of coarse gravel, gravel, sand
• Slightly sloped surface for drainage (1:20) (STRAUSS & MONTANEGRO 2004)
Sludge Drying Beds
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3. Design Principals
Unplanted Sludge Drying Bed
Sludge application depth: about 20 cm (STRAUSS & MONTANGERO 2002; WSP 2007)
Loadings: 100 to 200 KgTS/m2/year (STRAUSS & MONTANGERO 2002)
Percolation: 50 to 80 % of initial Volume
Time required for drying: 10 to 20 days
(STRAUSS & MONTANGERO 2002)
(STRAUSS & MONTANGERO 2002)
Achieved drying: 40 to 70 % TS (STRAUSS & MONTANGERO 2002)
Sludge
Percolate
Sludge Drying Beds
Drainage
(STRAUSS & MONTANGERO 2002)
Source: STRAUSS & MONTANEGRO (2004)
Land requirements: 0.05 m2 per capita for a 10 days cycle
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3. Design Principals
Filter bed (EAWAG/SANDEC 2008)
Large gravel (d=20mm):25 cm
Fine gravel (d=5mm): 25 cm
Sand: 10 cm
Source: STRAUSS & MONTANEGRO (2004)
Planted Sludge Drying Bed
Sludge
Drainage
Sludge application depth: about 20 cm (STRAUSS & MONTANGERO 2002 WSP 2007)
Loadings: 250 KgTS/m2/year (STRAUSS & MONTANGERO 2002)
Percolation: 50 to 80 % of initial Volume
(STRAUSS & MONTANGERO 2002)
Application: Once a week; Desludging: every 5 to 6 years (STRAUSS & MONTANGERO 2002
Achieved drying: 40 to 70 % TS
Sludge Drying Beds
(STRAUSS & MONTANGERO 2002)
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3. Design Principals
Treatment Efficiency (STRAUSS & MONTAGERO 2002)
Suspended solids: >= 95 %
COD 70 to 90 %
Helminth eggs 100 %
NH4 40 to 60 %
Health aspects
Dewatered sludge is still infectious; Additional composting of dried
sludge in heaps or wind-rows will further stabilise recycled organic
materials. (SANIMAS 2005)
Operation and Maintenance
A splash spate should be used for application of the sludge.
In the case of unplanted beds, sludge must be removed frequently.
Checking of drainage capacities.
Sludge Drying Beds
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6. Applicability
Any kind of sludge can be treated in drying beds.
It is best combined with co-composting in order to produce fertiliser.
The method is simple but requires professional design and trained
manpower for the operation.
However, large land areas are required for the construction.
Drying beds are centralised treatment options and thus adapted for
larger areas. The operation and maintenance requires an efficient
community organization.
As odour could be an issue, they should be constructed far away from
households.
The bottom needs to be sealed to prevent groundwater pollution and
the percolate must be treated.
Therefore, drying beds are not adapted for areas prone to flooding.
At places with frequent rain must be roofed.
Sludge Drying Beds
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7. Pros’ and Cons’
Advantages:
Disadvantages:
• Easy to operate
• Requires large land area
• Dried sludge can be composted
and used as fertiliser
• Re-use or treatment of seepage
water required
• Simple operation, no skilled
personnel required
• Only applicable during dry
seasons or needs a roof
• Results in much reduced volume
of sludge
• Manual labour or specialised
equipment is required to remove
dried sludge from beds
• Can achieve pathogen removal
• Can cause odour problems
• Can be built with local materials
Sources: adapted form SANIMAS (2005);
http://www.training.gpa.unep.org/content.html?id=215&ln=6 [Accessed: 10.07.2010]
Sludge Drying Beds
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8. References
BALASUBRAMANIYAM, U., ZISENGWE, L.S., MERIGGI, N., BUYSMAN, E. (2008): Biogas Production in Climates with long cold
Winters. Wageningen: Wageningen University Available at: http://www.wecf.eu/english/publications/2008/biogascoldclimates.php [Accessed: 20.04.2010]
EAWAG/SANDEC (2008): Fecal Sludge Management. Lecture notes. (=Sandec Training Tool 1.0, Module 5). Duebendorf: Swiss
Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC)
EAWAG/SANDEC (2008): Fecal Sludge Management. Presentation. (=Sandec Training Tool 1.0, Module 5). Duebendorf: Swiss
Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC)
ERIKSEN-HAMEL, N.S., DANSO, G. (2008): Urban Compost: A Socio-economic and Agronomic Evaluation in Kumasi, Ghana in
REDWOOD, M. (ed) (2008): Agriculture in Urban Planning: Generating Livelihoods and Food Security. Earthscan/IDRC.
Available
at: http://www.idrc.ca/en/ev-135127-201-1-DO_TOPIC.html
SANIMAS (2005): Informed Choice Catalogue. PPT-Presentation. remen Overseas Research and Development Agency (BORDA) and
United States Agency for International Development (USAID)
SASSE, L. (1998): DEWATS Decentralised Wastewater Treatment in Developing Countries. Bremen: Bremen Overseas Research and
Development Association (BORDA) Available at: http://www.bordanet.org/modules/wfdownloads/uploads/062%20BORDA_Dewats-Handbook.pdf [Accessed: 27.05.2010]
STRAUSS, M., MONTANEGRO, A. (2002): FS Management – Review of Practices, Problems and Initiatives. London and Duebendorf:
DFID Project R8056, Capacity Building for Effective Decentralised Wastewater Management, Swiss Federal Institute of Aquatic
Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). Available at:
http://www.eawag.ch/organisation/abteilungen/sandec/schwerpunkte/ewm/fsm/index_EN [Accessed: 10.06.2010]
STRAUSS, M., MONTANEGRO, A. (2004): Fecal Sludge Treatment, Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG),
Department of Water and Sanitation in Developing Countries (SANDEC). Available at:
http://www.eawag.ch/organisation/abteilungen/sandec/schwerpunkte/ewm/fsm/index_EN [Accessed: 10.06.2010]
TILLEY, E., LUETHI, C., MOREL, A., ZURBRUEGG, C., SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and
Technologies. Duebendorf and Geneva: Swiss Federal Institute of Aquatic Science (EAWAG) & Water Supply and Sanitation
Collaborative Council (WSSCC) Available at:
http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/compendium_e/index_EN Accessed: 09.04.2010]
WAaF (2002) Sanitation Technology Options. Pretoria: Department of Water Affairs and Forestry (WAaF) Available at:
http://www.bvsde.paho.org/bvsacd/cd66/Technical.pdf [Accessed: 27.05.2010]
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“Linking up Sustainable Sanitation
and Water Management”
Main Funding Partners:
Further Funding, Content & Dissemination Partners
Compiled by:
Sludge Drying Beds
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“Linking up Sustainable Sanitation,
Water Management & Agriculture”
SSWM is an initiative
supported by:
Compiled by:
Sludge Drying Beds
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