Constructed Wetlands Constructed Wetlands (CWs) 1 Beat Stauffer, international seecon gmbh.

Constructed Wetlands

Constructed Wetlands (CWs)

1

Beat Stauffer, international seecon gmbh


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Contents

1. Concept

2. How can Constructed Wetlands optimise SSWM

3. Design Principles

4. Treatment Efficiency

5. Operation and Maintenance

6. Applicability

7. Pros and Cons

8. References

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Introduction• Treatment step of DEWATS systems• Secondary treatment facilities for household (blackwater or

greywater, brownwater) and/or municipal or biodegredable industrial wastewater. (HOFFMANN et al. 2010)

• Tertiary treatment system for polishing (e.g. activated sludge, trickling filter plants) before safety disposal or reuse.

• Outflow of CW: groundwater recharge, fertigation, aquaculture

• Types of constructed wetlands. They are classified according to the water flow regime as:◦ Horizontal flow constructed wetlands◦ Vertical flow constructed wetlands◦ Free surface constructed wetlands

• Combined flow regimes are so called hybrid constructed wetlands and exploit the specific advantages of the different systems.

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1. Concept



Example 1: Onsite or Semi-centralised Treatment System

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2. How can Constructed Wetlands Optimise SSWM

Low-flush toilet, shower, kitchen sink, etc.

Horizontal (picture), vertical, free surface or a combined hybrid filter

Water for irrigation or aquaculture, etc.

Groundwater recharge

Source: UN-HABITAT (2008); STAUFFER (2012); MOREL & DIENER (2006); RUUESCH (2011); IPTRID (2008)

Compost filter (above), septic tank, imhoff tank, anaerobic baffled reactor (below), etc.



Example 2: Hybrid CW for a Community

CW’s can also act as a treatment system for a community up to 3400 people (e.g. Bayawan City):•Protecting coastal waters from pollution•Protect the health of local residents•Reuse of treated waste water for irrigation

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Source: LIPKOW and MUENCH (2010)

Wastewater is collected in septic tanks and transferred through a small bore sewer system to the hybrid constructed wetland. The treated water can be reused (irrigation), one part is recirculated or it could be disposed (optional).



Example 3: Greywater Treatment in Urban Areas (Norway)

CW’s can be embedded nicely in urban areas that greywater can be reused for irrigation or recharge groundwater.

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Source: JENSSEN (n.y)

The latest generation of constructed wetlands for cold climate with integrated aerobic biofilter in Norway.



Example 3: Greywater Treatment in Urban Areas (Norway)

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Source: JENSSEN (n.y)

Upper right: the wetland in the foreground the biofilter is underneath the playground behind the stonewall. UpperLeft: flowforms.

Lower left: the effluent is exposed in a shallow pond and can be discharged in a local stream (lower right).



Example 4: Stormwater Wetlands (also called Wet Ponds or Retention Ponds)

• Adapted design for stormwater management

• Microbiological breakdown of pollutants

• Plant uptake (nutrients)

• Retention, settling and adsorption

• Flood control

• Aesthetic design for rural areas (e.g. city parks)

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Source: METROCOUNCIL (n.y.); COASTAL WATER WATCH (2010)



Horizontal Flow (HF)

• Large gravel and sand-filled channel, planted with aquatic vegetation

• Wastewater flows horizontally through the channel

• Mainly anaerobic conditions

• The filter material filters out particles and microorganisms degrade organic matter

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3. Design Principals

Source: MOREL and DIENER (2006)



Vertical Flow (VF)

• Gravel and sand filter, aquatic vegetation

• Intermittent appliance (pump or syphon) of wastewater over the whole filter surface higher O2 injection

• Wastewater drains vertically through the filter layers towards a drainage system at the bottom

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Source: MOREL and DIENER (2006)

Source: HOFFMANN et al. (2010)



Free Water Surface Flow (FWS)

• Flooded and planted channels

• Imitate the naturally occurring processes of a natural wetland, marsh or swamp

• Water slowly flows through the wetland (on the surface), particles settle, pathogens are destroyed, and organisms and plants utilise the nutrients (TILLEY et al. 2008)

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Source: TILLEY et al (2008)



Hybrid Flow

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• Combined CWs, sequentially arranged (usually VF and HF)

• HF provide denitrification, VF nitrification

• Obviously the advantages of both systems can be combined

Source: UPC (n.y.)

Prototype of an integrated blackwater system (hybrid CW): UASB, followed by a vertical and then a horizontal flow wetland).



Pollution Removal

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Horizontal CW High reduction in BOD, suspended solids and pathogens. Provides mainly denitrification. (TILLEY et al. 2008)

Vertical CW High reduction in BOD, suspended solids and pathogens. Provides mainly nitrification.

Free-Surface CW • High removals of suspended solids• Moderate removal of pathogens, nutrients and

other pollutants such as heavy metals (TILLEY et al. 2008)

Hybrid CW Increased performance due to a combination of different methods (e.g. VF HF)



Health Aspect

• A CW system provides an adequate handling of wastewater and minimises health risks caused by pathogens and avoids contamination of the environment by untreated wastewater.

• High risk of infection if contact with the liquid filter influent or the settled sludge in the pre-treatment facility

• Low risk of mosquito breeding (could be a problem of free-surface CW due to open water surface)

• Settled sludge must be disposed safe and correctly

• Correct handling of treated water if used for irrigation

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• CWs constantly require basic maintenance throughout the duration of its life but its relatively simple (no high-tech appliances or chemical additives). (GAUSS 2008)

• It is important to ensure that primary treatment effectively lowers organics and solids concentrations. (TILLEY et al. 2008)

• The pre-treatment facility (e.g. septic tank) should be emptied periodically and sludge discharged in a safe way properly (see photo – ABR in Pune, India).

• Filter material has to be replaced every 8 to 15 years. (TILLEY et al. 2008)

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5. Operation and Maintenance

Source: SPUHLER (2010)



• Secondary or tertiary treatment process for black, brown and greywater

• Adequate strategy if land is no limiting factor (space and costs)

• Constructed wetlands are natural systems and do not require electrical energy (unless for pumps) or chemicals

• Best suited for warm climates, but can be designed to tolerate freezing periods

• CW’s can be combined with many other techniques such as aquaculture, irrigation and several pre-treatment options.

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6. Applicability



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Advantages:•Simple O&M due to high

process stability•No chemicals required•Can be built and repaired

with locally available materials

•Utilisation of natural processes

•Efficient removal of suspended and dissolved organic matter, nutrients and pathogens

Disadvantages:•Permanent land required•Requires expert design and

supervision•Moderate capital cost

depending on land, liner, fill, etc.; low operating costs

•Pre-treatment is required to prevent clogging

•Low tolerance to durable cold climates

•Electricity may be required

7. Pros’ and Cons’



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8. References

COASTAL WATER WATCH (Editor) (2010): Rain Garden and Ponds. URL: http://www.coastalwaterwatch.com/product2121.htm [Accessed: 21.02.2012]

GAUSS, M.; WSP (Editor) (2008): Constructed Wetlands: A Promising Wastewater Treatment system for Small Localities. Experiences from Latin America. Washington D.C.: The World Bank. URL: http://www.wsp.org/wsp/sites/wsp.org/files/publications/ConstructedWetlands.pdf [Accessed: 12.12.2011]

HOFFMANN, H.; PLATZER, C.; WINKER, M.; MUENCH, E., v.; GTZ (Editor) (2011): Technology Review of Constructed Wetlands. Subsurface Flow Constructed Wetlands for Greywater and Domestic Wastewater Treatment. Eschborn: Deutsche Gesellschaft für Technische Zusammenarbeit GmbH (GTZ) Sustainable sanitation - ecosan program. URL: http://www.gtz.de/en/dokumente/giz2011-en-technology-review-constructed-wetlands.pdf [Accessed: 14.11.2011]

IPTRID (Editor) (2008): Grid – IPTRID Network Magazine. February 2008. Rome: International Programme for Technology and Research in Irrigation and Drainage (IPTRID). URL: http://www.fao.org/landandwater/iptrid/docs/GRID28eng.pdf [Accessed: 27.06.2011]

JENSSEN, P. (n.y.): Decentralized Urban Greywater Treatment at Klosterenga Oslo. In: Ecological Engineering-Bridging between Ecology and Civil Engineering, 84-86. URL: http://www.umb.no/statisk/ecosan/publications/Klosterenga.pdf [Accessed: 21.02.2012].

LIPKOW, U.; MUENCH, E. von (2010): Constructed Wetland for a Peri-urban Housing Area Bayawan City, Philippines. Eschborn: Sustainable Sanitation Alliance (SuSanA). URL: http://www.susana.org/docs_ccbk/susana_download/2-51-en-susana-cs-philippines-bayawan-constr-wetlands-2009.pdf [Accessed: 10.01.2011]

METROCOUNCIL (n.y.): Constructed Wetlands: Stormwater Wetlands. Saint Paul: Metropolitan Council. URL: http://www.metrocouncil.org/environment/water/bmp/CH3_STConstWLSwWetland.pdf [Accessed: 21.02.2012]

MOREL, A.; DIENER, S. (2006): Greywater Management in Low and Middle-Income Countries, Review of different treatment systems for households or neighbourhoods. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL: http://www.eawag.ch/forschung/sandec/publikationen/ewm/dl/Morel_Diener_Greywater_2006.pdf [Accessed: 19.05.2010]

TILLEY, E.; LUETHY, C.; MOREL, A.; ZURBRUEGG, C.; SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and Technologies. Duebendorf and Geneva: Swiss Federal Institute of Aquatic Science and Technology (EAWAG). URL: http://www.eawag.ch/forschung/sandec/publikationen/index [Accessed: 15.02.2010]

UN-HABITAT (Editor) (2008): Constructed Wetlands Manual. Kathmandu: UN-HABITAT, Water for Asian Cities Program. URL: http://www.un.org.np/sites/default/files/CWManual.pdf [Accessed: 15.02.2012]

UPC (n.y.): Prototype of an Integrated Blackwater System. Barcelona: Universitat Politecnica de Catalunya.

VYMAZAL, J. (2005): Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment. Durham: Duke University Wetland Center. URL: http://www.uvm.edu/~atuttle/john%20todd%20copy/zanzibar/HSF%20and%20hybrid%20CW%20for%20WW%20treatment%20Vymazal.pdf [Accessed: 22.08.2011]

Constructed Wetlands 20

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