|style="width:50%;"|{{santable_new|
sys1=[[Single Pit System |1]]|
sys2=[[Blackwater Treatment System with Infiltration|56]]|sys3=[[Blackwater Treatment System with SewerageEffluent Transport|67]]|sys4=[[Blackwater Transport to (Semi-) Centralized Treatment System |78]]|sys5=[[Sewerage System with Urine Diversion|9]]|
sys6=|
sys7=|
ManShared=XX|
ManPublic=XX|
Input1=Blackwater|Input2=Greywater |Input3= Brownwater | Input4= Effluent |Input5=|Output1= Effluent | Output2= Biomass | Output3= | Output4= | Output5=
|english_link=Horizontal_Subsurface_Flow_Constructed_Wetland
|french_link=Filtre_planté_à_écoulement_horizontal_sous-surface
[[Image:Icon_horizontal_subsurface_flow_constructed_wetland.png |right|80px]]
'''A Horizontal Subsurface Flow Constructed Wetland horizontal subsurface flow constructed wetland is a large gravel and sand-filled channel basin that is planted with aquatic wetland vegetation. As wastewater flows horizontally through the channelbasin, the filter material filters out particles and microorganisms degrade the organics.'''
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The water level in filter media acts as a filter for removing solids, a fixed surface upon which bacteria can attach, and a Horizontal Subsurface Flow Constructed Wetland is maintained at 5 to 15cm below base for the surface to ensure subsurface flowvegetation. The bed should be wide Although facultative and shallow so that anaerobic bacteria degrade most organics, the flow path vegetation transfers a small amount of oxygen to the water is maximized. A wide inlet root zone should be used to evenly distribute so that aerobic bacteria can colonize the flowarea and degrade organics as well. Pre-treatment is essential to prevent clogging and ensure efficient treatmentThe plant roots play an important role in maintaining the permeability of the filter.
===Design Considerations=== The design of a horizontal subsurface flow constructed wetland depends on the treatment target and the amount and quality of the influent. It includes decisions about the amount of parallel flow paths and compartmentation. The removal efficiency of the wetland is a function of the surface area (length multiplied by width), while the cross-sectional area (width multiplied by depth) determines the maximum possible flow. Generally, a surface area ofabout 5 to 10 m2 per person equivalent is required. Pre- and primary treatment is essential to prevent cloggingand ensure efficient treatment. The influent can be aerated by an inlet cascade to support oxygen-dependentprocesses, such as BOD reduction and nitrification. The bed should be lined with an impermeable liner (clay or geotextile) to prevent leaching. Small, round, evenly sized gravel (3–32mm It should be wide and shallow so that the flow path of the water in diameter) contact with vegetation roots is most commonly maximized. A wide inlet zone should be used to fill evenly distribute the bed to a depth of 0flow.5 A well-designed inlet that allows for even distribution is important to 1mprevent short-circuiting. To limit clogging, The outlet should be variable so that the gravel should water surface can be clean and free of fines. Sand is also acceptable, but is more prone adjusted to clogging. In recent years, alternative filter materials such as PET have been successfully usedoptimize treatment performance.
The removal efficiency of the wetland is a function of the surface area Small, round, evenly sized gravel (length multiplied by width3 to 32 mm in diameter), while is most commonly used to fill the cross-sectional area (width multiplied by bed to a depth) determines the maximum possible flowof 0. A well-designed inlet that allows for even distribution is important 5 to prevent short-circuiting1 m. The outlet To limit clogging, the gravel should be variable so that the water surface can be adjusted clean and free of fines. Sand is also acceptable, but is more prone to optimize treatment performanceclogging than gravel. The In recent years, alternative filter media acts materials, such as both a filter for removing solidsPET, a fixed surface upon which bacteria can attach, and a base for the vegetation. Although facultative and anaerobic bacteria degrade most organics, the vegetation transfers a small amount of oxygen to the root zone so that aerobic bacteria can colonize the area and degrade organics as wellhave been successfully used. The plant roots play an important role water level in maintaining the permeability of wetland is maintained at 5 to 15 cm below the filtersurface to ensure subsurface flow. Any native plant with deep, wide roots that can grow in the wet, nutrient-rich environment is appropriate. Phragmites australis (reed) is a common choice because it forms horizontal rhizomes that penetrate the entire filter depth. Pathogen removal is accomplished by natural decay, predation by higher organisms, and sedimentation.
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{{procontable | pro=
- Requires less space than a Free-Water Surface Constructed Wetland. <br> - High reduction in of BOD, suspended solids and pathogens. <br> - Does not have the mosquito problems of the [[<br>- Free-Water Surface Constructed Wetland]]. <br> - Can be built and repaired with locally available materials. No electrical energy is required <br> - Construction can provide shortLow operating costs| con=-term employment to local labourers. Requires a large land area <br> - No electrical energy required. | con=- Requires expert design and supervision. Little nutrient removal <br> - Moderate capital cost Risk of clogging, depending on land, liner, fill, etc.; low operating costs. pre- and primary treatment <br>- PreLong startup time to work at full capacity <br>-treatment is required to prevent clogging.Requires expert design and construction
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===AdequacyAppropriateness=== Clogging is a common problem and , therefore , the influent should be well settled with primary treatment before flowing into the wetland. This technology is not appropriate for untreated domestic waste water wastewater (i.e. blackwater). This It is a good treatment for communities that have primary treatment (e.g. , [[Septic Tank|Septic Tanks]] or [[Waste Stabilization Pond|WSPs]], S.9) , but are looking to achieve a higher quality effluent. This is a good option where land is cheap and available, although the wetland will require maintenance for the duration of its life. Depending on the volume of water, and therefore the size, this type of wetland can be appropriate for small sections of urban areas, peri-urban and rural communities. They can also be designed for single households. Horizontal Subsurface Flow Constructed Wetlands are best suited for warm climates but they can be designed to tolerate some freezing and periods of low biological activity. ===Health Aspects/Acceptance===
The risk of mosquito breeding horizontal subsurface flow constructed wetland is reduced since there a good option where land is no standing cheap and available. Dependingon the volume of the water compared to and the corresponding area requirement of the risk associated with [[Freewetland, it can be appropriate for small sections of urban areas, as well as for peri-Water Surface Constructed Wetland|Free-Water Surface Constructed Wetlands]]urban and rural communities. It can also be designed for single households. The wetland This technology is aesthetically pleasing best suited for warm climates, but it can be designed to tolerate some freezing and can periods of low biological activity. If the effluent is to be reused, the losses due to high evapotranspiration rates could be integrated into wild areas or parklandsa drawback of this technology, depending on the climate.
===MaintenanceHealth Aspects/Acceptance===Significant pathogen removal is accomplished by natural decay, predation by higher organisms, and filtration. As the water flows below the surface, any contact of pathogenic organisms with humans and wildlife is minimized. The risk of mosquito breeding is reduced since there is no standing water compared to the risk associated with [[Free-Water Surface Constructed Wetland|Free-Water Surface Constructed Wetlands]] (T.7). The wetland is aesthetically pleasing and can be integrated into wild areas or parklands.
===Operation & Maintenance=== During the first growing season, it is important to remove weeds that can compete with the planted wetland vegetation. With time, the gravel will clog become clogged with accumulated solids and bacterial film. The filter material at the inlet zone will require replacement every 8 to 15 10 or more years. Maintenance activities should focus on ensuring that primary treatment is effective at reducing the concentration of solids in the wastewater before it enters the wetland. Maintenance should also ensure that trees do not grow in the area as the roots can harm the liner.
===References===
* Crites, R. and Tchobanoglous, G. (1998). Small and Decentralized Wastewater Management Systems. WCB and /McGraw-Hill, New York, USAUS. pp 599–609. 599-609. (Comprehensive summary chapter including solved problems.)
* MaraHoffmann, DDH., Platzer, C., Winker, M. and von Münch, E. (20032011). Technology Review of Constructed Wetlands. Subsurface Flow Constructed Wetlands for Greywater and Domestic wastewater treatment in developing countriesWastewater Treatment. EarthscanGesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, LondonEschborn, DE.:Available at: [http://www.susana. pp 85–187org/library susana.org/library]
* Poh-EngKadlec, LR. H. and PolprasertWallace, CS. D. (19982009). Constructed Treatment Wetlands for Wastewater Treatment and Resource Recovery, 2nd Ed. Environmental Sanitation Information CenterCRC Press, AITTaylor & Francis Group, BangkokBoca Raton, ThailandUS.
* Polprasert, C., et al. UN-HABITAT (20012008). Wastewater Treatment II, Natural Systems Constructed Wetlands Manual. UN-HABITAT Water for Wastewater ManagementAsian Cities Programme. Lectur NotesKathmandu, IHE Delft, The NetherlandsNP.:Available at: [http://www.unhabitat. Chapter 6org unhabitat.org]
* Reed, SCU.S. EPA (19932000). [http://water.epaConstructed Wetlands Treatment of Municipal Wastewaters.govEPA/type625/wetlandsR-99/restore/upload/2003_07_01_wetlands_pdf_sub010. U.pdf Subsurface Flow Constructed Wetlands For Wastewater Treatment, A Technology Assessment]S. United States Environmental Protection Agency, USAWashington, D. Comprehensive design manualC., US.:Available at: [http://www.epa.gov epa.gov]
===Acknowledgements===
{{:Acknowledgements Sanitation}}