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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.'''
Unlike the [[Horizontal Subsurface Flow Constructed Wetland |Horizontal Subsurface Flow Constructed Wetland]] (T.8), the free-water surface constructed wetland allows water to flow above ground exposed to the atmosphere and to direct sunlight. As the water slowly flows through the wetland, simultaneous physical, chemical and biological processes filter solids, degrade organics and remove nutrients from the wastewater. Raw blackwater should be pre-treated to prevent the excess accumulation of solids and garbage. Once in the pond, the heavier sediment particles settle out, and this also removes the nutrients attached to them. Plants, and the communities of microorganisms that they support (on the stems and roots), take up nutrients like nitrogen and phosphorus. Chemical reactions may cause other elements to precipitate out of the wastewater.
Pathogens are removed from the water by natural decay, predation from higher organisms, sedimentation and UV irradiation. Although the soil layer below the water is anaerobic, the plant roots exude (release) oxygen into the area immediately surrounding the root hairs, thus, creating an environment for complex biological and chemical activity.
===References===
* Crites, R. and Tchobanoglous, G. (1998). Small and Decentralized Wastewater Management Systems. WCB/McGraw- Hill, New York, US. pp. 582-599. (Book; Comprehensive summary chapter including solved problems)
* 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.:Available at: [http://www.iwawaterwiki.org iwawaterwiki.org](Book)
* Kadlec, R. H. and Wallace, S. D. (2009). [https://sswm.info/sites/default/files/reference_attachments/KADLEC%20WALLACE%202009%20Treatment%20Wetlands%202nd%20Edition_0.pdf Treatment Wetlands, 2nd Ed. ] CRC Press, Taylor & Francis Group, Boca Raton, US.
* Merz, S. L. (2000). Guidelines for Using Free Water Surface Constructed Wetlands to Treat Municipal Sewage. Queensland Department of Natural Resources, Brisbane, AU.(Book)
* Poh-Eng, L. and Polprasert, C. (1998). Constructed Wetlands for Wastewater Treatment and Resource Recovery. Environmental Sanitation Information Center, AIT, Bangkok, TH.(Book)
* Polprasert, C., Veenstra, S. and van der Steen, P. (2001). Wastewater Treatment II. Natural Systems for Wastewater Management, Chapter 6. UNESCO-IHE, Delft, NL.
* U.S. EPA (2000). [https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64144&Lab=NRMRL Constructed Wetlands Treatment of Municipal Wastewaters]. EPA/625/R-99/010. U.S.Environmental Protection Agency, Washington, D.C., US.:Available at: [http://www.epa.gov epa.gov]
* Vymazal, J. (2008). [http://fos.darvodgeo.ru/CW_Vymazal_review_1.pdf Constructed Wetlands for Wastewater Treatment: A Review]. In: Proceedings of Taal 2007: The 12th World Lake Conference, M. Sengupta and R. Dalwani (Eds.). pp. 965-980.:Available at: [http://www.moef.nic.in moef.nic.in]
===Acknowledgements===
{{:Acknowledgements Sanitation}}
