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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|89]]|
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Input1=BlackwaterEffluent|Input2=Greywater Stormwater |Input3= | Input4= |Input5=|Output1= Effluent | Output2= Biomass | Output3= | Output4= | Output5=
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[[Image:Icon_free-water_surface_constructed_wetland.png |right|80px]]
'''A free-water surface constructed wetland aims to replicate the naturally occurring processes of a
natural wetland, marsh or swamp. As water slowly flows through the wetland, particles settle, pathogens
are destroyed, and organisms and plants utilize the nutrients. This type of constructed wetland is commonly used as an advanced treatment after secondary or tertiary treatment processes.'''
The efficiency of the free-water surface constructed wetland also depends on how well the water is distributed at the inlet. Wastewater can be fed into the wetland, using weirs or by drilling holes in a distribution pipe, to allow it to enter at evenly spaced intervals.
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{{procontable | pro=
- Aesthetically pleasing and provides animal habitat. <br> - High reduction in of BOD and solids; moderate pathogen removal. <br> - Can be built and repaired with locally available materials. <br> - Construction can provide short-term employment to local labourers. <br> - No electrical energy is required. <br> - No real problems with flies or odours if used designed and maintained correctly. <br>- Low operating costs| con=- May facilitate mosquito breeding. <br> - Requires a large land area <br>- Long start up startup time to work at full capacity. <br> - Requires large land area. <br> - Requires expert design and supervision. <br> - Moderate capital cost depending on land, liner, etc.; low operating costs.construction
}}
===Appropriateness===
Free-water surface constructed wetlands can achieve a high removal of suspended solids and moderate removal of pathogens, nutrients and other pollutants, such as heavy metals. This technology is able to tolerate variable water levels and nutrient loads. Plants limit the dissolved oxygen in the water from their shade and their buffering of the wind; therefore, this type of wetland is only appropriate for low-strength
wastewater. This also makes it appropriate only when it follows some type of primary treatment to lower the BOD. Because of the potential for human exposure to pathogens, this technology is rarely used as secondary treatment. Typically, it is used for polishing effluent that has been through secondary treatment, or for stormwater retention and treatment.
===Health Aspects/Acceptance=== The open surface can act as a potential breeding ground for mosquitoes. However, good design and maintenance can prevent this. Free-Water Surface Constructed Wetlands water surface constructed wetlands are generally aesthetically pleasing, especially when they are integrated into pre-existing natural areas. Care should be taken to prevent people from coming in contact with the effluent because of the potential for disease transmission and the risk of drowning in deeper watersdeep water.
===Operation & Maintenance=== Regular maintenance should ensure that water is not short-circuiting, or backing up because of fallen branches, garbage, or beaver dams blocking the wetland outlet. Vegetation may have to be periodically cut back or thinned out.
* Kadlec, R. H., Knight, R. L., Vymazal, J., Brix, H., Cooper, P. and Haberl, R. (2000). Constructed Wetlands for Pollution Control. Processes, Performance, Design and Operation. Scientific and Technical Report No. 8. IWA Publishing, London, UK. (Book)
* Elizabeth Tilley etMerz, S.al (2008). [http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_highL.pdf Compendium of Sanitation Systems and Technologies] ([http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_low.pdf low res version]2000). Department of Guidelines for Using Free Water and Sanitation in Development Countries ([http://wwwSurface Constructed Wetlands to Treat Municipal Sewage.sandec.ch/ Sandec]) at the Swiss Federal Institute Queensland Department of Aquatic Science and Technology (Eawag)Natural Resources, Brisbane, AU. (Provides a full overview of sanitation systems.Book)
* CritesPoh-Eng, RL. and TchobanoglousPolprasert, GC. (1998). Small Constructed Wetlands for Wastewater Treatment and Decentralized Wastewater Management SystemsResource Recovery. WCB and McGraw-HillEnvironmental Sanitation Information Center, AIT, New YorkBangkok, USA. pp 582–599TH. (Comprehensive summary chapter including solved problems.Book)
* MaraPolprasert, DDC., Veenstra, S. and van der Steen, P. (20032001). Domestic wastewater treatment in developing countriesWastewater Treatment II. Natural Systems for Wastewater Management, Chapter 6. EarthscanUNESCO-IHE, LondonDelft, UK. pp 85–187NL.
* Poh-Eng, LU. and Polprasert, CS. EPA (19982000). [https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64144&Lab=NRMRL Constructed Wetlands for Wastewater Treatment and Resource Recoveryof Municipal Wastewaters]. EPA/625/R-99/010. U.S. Environmental Sanitation Information CenterProtection Agency, AITWashington, BangkokD.C., ThailandUS.
* PolprasertVymazal, C., et alJ. (20012008). [http://fos.darvodgeo.ru/CW_Vymazal_review_1.pdf Constructed Wetlands for Wastewater Treatment II: A Review]. In: Proceedings of Taal 2007: The 12th World Lake Conference, Natural Systems for Wastewater ManagementM. Sengupta and R. Dalwani (Eds.). IHE Delft, The Netherlandspp. Chapter 6965-980.