Difference between revisions of "Vertical Flow Constructed Wetland"
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|style="width:50%;"|{{santable_new| | |style="width:50%;"|{{santable_new| | ||
sys1=[[Single Pit System |1]]| | sys1=[[Single Pit System |1]]| | ||
| − | sys2=[[Blackwater Treatment System with Infiltration| | + | sys2=[[Blackwater Treatment System with Infiltration|6]]| |
| − | sys3=[[Blackwater Treatment System with | + | sys3=[[Blackwater Treatment System with Effluent Transport|7]]| |
| − | sys4=[[(Semi-) Centralized Treatment System | | + | sys4=[[Blackwater Transport to (Semi-) Centralized Treatment System |8]]| |
| − | sys5=[[Sewerage System with Urine Diversion | | + | sys5=[[Sewerage System with Urine Diversion|9]]| |
sys6=| | sys6=| | ||
sys7=| | sys7=| | ||
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ManShared=X| | ManShared=X| | ||
ManPublic=XX| | ManPublic=XX| | ||
| − | Input1=Blackwater|Input2=Greywater |Input3= | Input4= |Input5=| | + | Input1=Blackwater|Input2=Greywater |Input3=Brownwater | Input4=Effluent |Input5=| |
| − | Output1= Effluent | Output2= | Output3= | Output4= | Output5= | + | Output1= Effluent | Output2=Biomass | Output3= | Output4= | Output5= |
|english_link=Vertical_Flow_Constructed_Wetland | |english_link=Vertical_Flow_Constructed_Wetland | ||
|french_link=Filtre_planté_à_écoulement_vertical | |french_link=Filtre_planté_à_écoulement_vertical | ||
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[[Image:Icon_vertical_flow_constructed_wetland.png |right|80px]] | [[Image:Icon_vertical_flow_constructed_wetland.png |right|80px]] | ||
| − | '''A | + | |
| + | '''A vertical flow constructed wetland is a planted filter bed that is drained at the bottom. Wastewater is poured or dosed onto the surface from above using a mechanical dosing system. The water flows vertically down through the filter matrix to the bottom of the basin where it is collected in a drainage pipe. The important difference between a vertical and horizontal wetland is not simply the direction of the flow path, but rather the aerobic conditions.''' | ||
<br> | <br> | ||
| − | By dosing the wetland | + | By intermittently dosing the wetland (4 to 10 times a day), the filter goes through stages of being saturated and unsaturated, and, accordingly, different phases of aerobic and anaerobic conditions. During a flush phase, the wastewater percolates down through the unsaturated bed. As the bed drains, air is drawn into it and the oxygen has time to diffuse through the porous media. The filter media acts as a filter for removing solids, a fixed surface upon which bacteria can attach and a base for the vegetation. The top layer is planted and the vegetation is allowed to develop deep, wide roots, which permeate the filter media. The vegetation transfers a small amount of oxygen to the root zone so that aerobic bacteria can colonize the area and degrade organics. However, the primary role of vegetation is to maintain permeability in the filter and provide habitat for microorganisms. Nutrients and organic material are absorbed and degraded by the dense microbial populations. By forcing the organisms into a starvation phase between dosing phases, excessive biomass growth can be decreased and porosity increased. |
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| − | The filter media acts as | ||
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| − | + | ===Design Considerations=== | |
| + | The vertical flow constructed wetland can be designed as a shallow excavation or as an above ground construction. Clogging is a common problem. Therefore, the influent should be well settled in a primary treatment stage before flowing into the wetland. The design and size of the wetland is dependent on hydraulic and organic loads. Generally, a surface area of about 1 to 3 m2 per person equivalent is required. Each filter should have an impermeable liner and an effluent collection system. A ventilation pipe connected to the drainage system can contribute to aerobic conditions in the filter. Structurally, there is a layer of gravel for drainage (a minimum of 20 cm), followed by layers of sand and gravel. Depending on the climate, Phragmites australis (reed), Typha sp. (cattails) or Echinochloa pyramidalis are common plant options. Testing may be required to determine the suitability of locally available plants with the specific wastewater. | ||
| − | + | Due to good oxygen transfer, vertical flow wetlands have the ability to nitrify, but denitrification is limited. In order to create a nitrification-denitrification treatment train, this technology can be combined with a [[Free-Water Surface Constructed Wetland|Free-Water Surface]] or [[Horizontal Subsurface Flow Constructed Wetland|Horizontal Flow Wetland]] (T.7 and T.8). | |
<br> | <br> | ||
{{procontable | pro= | {{procontable | pro= | ||
| − | - Does not have the mosquito problems of the [[Free-Water Surface Constructed Wetland]]. <br> - Less clogging than in a [[Horizontal Subsurface Flow Constructed Wetland|Horizontal Flow Constructed Wetland]]. <br> - Requires less space than a Free-Water Surface Constructed Wetland. <br> - High reduction in BOD, suspended solids and pathogens. <br> - Construction can provide short-term employment to local labourers. | con= | + | - Does not have the mosquito problems of the [[Free-Water Surface Constructed Wetland]]. <br> - Less clogging than in a [[Horizontal Subsurface Flow Constructed Wetland|Horizontal Flow Constructed Wetland]]. <br> - Requires less space than a Free-Water Surface Constructed Wetland. <br> - High reduction in BOD, suspended solids and pathogens. <br> - Construction can provide short-term employment to local labourers. |
| + | | con= | ||
- Constant source of electrical energy required. <br> - Not all parts and materials may be available locally. <br> - Requires expert design and supervision. <br> - Moderate capital cost depending on land, liner, etc.; low operating costs. <br> - Pre-treatment is required to prevent clogging. <br> - Dosing system requires more complex engineering. | - Constant source of electrical energy required. <br> - Not all parts and materials may be available locally. <br> - Requires expert design and supervision. <br> - Moderate capital cost depending on land, liner, etc.; low operating costs. <br> - Pre-treatment is required to prevent clogging. <br> - Dosing system requires more complex engineering. | ||
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Revision as of 02:31, 29 October 2014
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A vertical flow constructed wetland is a planted filter bed that is drained at the bottom. Wastewater is poured or dosed onto the surface from above using a mechanical dosing system. The water flows vertically down through the filter matrix to the bottom of the basin where it is collected in a drainage pipe. The important difference between a vertical and horizontal wetland is not simply the direction of the flow path, but rather the aerobic conditions.
By intermittently dosing the wetland (4 to 10 times a day), the filter goes through stages of being saturated and unsaturated, and, accordingly, different phases of aerobic and anaerobic conditions. During a flush phase, the wastewater percolates down through the unsaturated bed. As the bed drains, air is drawn into it and the oxygen has time to diffuse through the porous media. The filter media acts as a filter for removing solids, a fixed surface upon which bacteria can attach and a base for the vegetation. The top layer is planted and the vegetation is allowed to develop deep, wide roots, which permeate the filter media. The vegetation transfers a small amount of oxygen to the root zone so that aerobic bacteria can colonize the area and degrade organics. However, the primary role of vegetation is to maintain permeability in the filter and provide habitat for microorganisms. Nutrients and organic material are absorbed and degraded by the dense microbial populations. By forcing the organisms into a starvation phase between dosing phases, excessive biomass growth can be decreased and porosity increased.
Contents
Design Considerations
The vertical flow constructed wetland can be designed as a shallow excavation or as an above ground construction. Clogging is a common problem. Therefore, the influent should be well settled in a primary treatment stage before flowing into the wetland. The design and size of the wetland is dependent on hydraulic and organic loads. Generally, a surface area of about 1 to 3 m2 per person equivalent is required. Each filter should have an impermeable liner and an effluent collection system. A ventilation pipe connected to the drainage system can contribute to aerobic conditions in the filter. Structurally, there is a layer of gravel for drainage (a minimum of 20 cm), followed by layers of sand and gravel. Depending on the climate, Phragmites australis (reed), Typha sp. (cattails) or Echinochloa pyramidalis are common plant options. Testing may be required to determine the suitability of locally available plants with the specific wastewater.
Due to good oxygen transfer, vertical flow wetlands have the ability to nitrify, but denitrification is limited. In order to create a nitrification-denitrification treatment train, this technology can be combined with a Free-Water Surface or Horizontal Flow Wetland (T.7 and T.8).
| Advantages | Disadvantages/limitations |
|---|---|
| - Does not have the mosquito problems of the Free-Water Surface Constructed Wetland. - Less clogging than in a Horizontal Flow Constructed Wetland. - Requires less space than a Free-Water Surface Constructed Wetland. - High reduction in BOD, suspended solids and pathogens. - Construction can provide short-term employment to local labourers. |
- Constant source of electrical energy required. - Not all parts and materials may be available locally. - Requires expert design and supervision. - Moderate capital cost depending on land, liner, etc.; low operating costs. - Pre-treatment is required to prevent clogging. - Dosing system requires more complex engineering. |
Adequacy
Clogging is a common problem. Therefore, the influent should be well settled with primary treatment before flowing into the wetland. This technology is not appropriate for untreated domestic wastewater (i.e. blackwater).
This is a good treatment for communities that have primary treatment (e.g. Septic Tanks or WSPs 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.
There are many complex processes at work, and accordingly, there is a significant reduction in BOD, solids and pathogens. In many cases, the effluent will be adequate for discharge without further treatment. Because of the mechanical dosing system, this technology is most appropriate for communities with trained maintenance staff, constant power supply, and spare parts.
Vertical Flow Constructed Wetlands are best suited to warm climates but can be designed to tolerate some freezing and periods of low biological activity.
Health Aspects/Acceptance
The risk of mosquito breeding is low since there is no standing water. The system is generally aesthetic and can be integrated into wild areas or parklands. Care should be taken to ensure that people do not come in contact with the influent because of the risk of infection.
Maintenance
With time, the gravel will become clogged with accumulated solids and bacterial film. The material may have to be replaced every 8 to 15 or more years. Maintenance activities should focus on ensuring that primary treatment effectively lowers organics and solids concentrations before entering the wetland. Testing may be required to determine the suitability of locally available plants with the specific wastewater. The vertical system requires more maintenance and technical expertise than other wetland technologies.
References
- Crites, R. and Tchobanoglous, G. (1998). Small and Decentralized Wastewater Management Systems. WCB and McGraw-Hill, New York, USA. pp 599–609. Comprehensive summary chapter including solved problems.
- Mara, DD. (2003). Domestic wastewater treatment in developing countries. London, Earthscan, pp 85–187.
- Poh-Eng, L. and Polprasert, C. (1998). Constructed Wetlands for Wastewater Treatment and Resource Recovery. Environmental Sanitation Information Center, AIT, Bangkok, Thailand.
- Polprasert, C., et al. (2001). Wastewater Treatment II, Natural Systems for Wastewater Management. Lecture Notes. IHE Delft, The Netherlands. Chapter 6.
- Reed, SC. (1993). Subsurface Flow Constructed Wetlands For Wastewater Treatment, A Technology Assessment. United States Environmental Protection Agency, USA. Comprehensive design manual.
Acknowledgements
The material on this page was adapted from:
Elizabeth Tilley, Lukas Ulrich, Christoph Lüthi, Philippe Reymond and Christian Zurbrügg (2014). Compendium of Sanitation Systems and Technologies, published by Sandec, the Department of Water and Sanitation in Developing Countries of Eawag, the Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
The 2nd edition publication is available in English. French and Spanish are yet to come.
