wsew:willow_sewage_treatment

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wsew:willow_sewage_treatment [2026/03/10 12:45] – external edit 127.0.0.1wsew:willow_sewage_treatment [2026/03/26 18:33] (current) – external edit 127.0.0.1
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-# Willow sewage treatment systems+This topic is part of [[gt:water|Water & sewage]]. 
 +====== Willow sewage treatment systems ======
  
  
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-## What are willow sewage treatment systems?+===== What are willow sewage treatment systems? =====
  
 They're an increasingly popular method for managing domestic wastewater. Far from being simple plantings, they're engineered ecosystems that leverage the natural capabilities of specific willow varieties (Salix species), in conjunction with soil and microbial action, to purify effluent. They're an increasingly popular method for managing domestic wastewater. Far from being simple plantings, they're engineered ecosystems that leverage the natural capabilities of specific willow varieties (Salix species), in conjunction with soil and microbial action, to purify effluent.
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 </WRAP> </WRAP>
  
-### Willow filters+==== Willow filters ====
  
 Typically unlined systems where willows are planted over a percolation pipe layout or drainage field (with modified piping to prevent blockage), through which effluent flows after primary treatment in a [septic tank](/sept/septic_tanks). Typically unlined systems where willows are planted over a percolation pipe layout or drainage field (with modified piping to prevent blockage), through which effluent flows after primary treatment in a [septic tank](/sept/septic_tanks).
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-### Zero discharge willow facilities+==== Zero discharge willow facilities ====
  
 Also known as willow evapotranspiration (ET) beds, these are designed for complete containment and on-site processing of effluent, with no liquid discharge to the surrounding environment. Also known as willow evapotranspiration (ET) beds, these are designed for complete containment and on-site processing of effluent, with no liquid discharge to the surrounding environment.
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 Effluent is pumped into a lined, soil-filled, planted basin for 100% evapotranspiration to air in summer and full storage in winter. This is typically lined with plastic (or indigenous marl clay where suitable impermeable subsoil exists) and backfilled with loose subsoil or top-soil to _c_.1.5m deep. This approach is typically used in areas of impermeable subsoil where a surface discharge is prohibited or impractical and where a guaranteed zero discharge is required all year round. However it can also be an excellent system for sites where zero environmental impact is required. Effluent is pumped into a lined, soil-filled, planted basin for 100% evapotranspiration to air in summer and full storage in winter. This is typically lined with plastic (or indigenous marl clay where suitable impermeable subsoil exists) and backfilled with loose subsoil or top-soil to _c_.1.5m deep. This approach is typically used in areas of impermeable subsoil where a surface discharge is prohibited or impractical and where a guaranteed zero discharge is required all year round. However it can also be an excellent system for sites where zero environmental impact is required.
  
-### History+==== History ====
  
 Willows have long been employed for a wide variety of uses, including basketry, furniture, erosion control, fencing and hurdles. Although willow wood is slow to dry for burning as logs, willows have been increasingly grown in recent decades as a short rotation coppice crop to produce biomass fuel for municipal power plants and district heating systems. Willows have long been employed for a wide variety of uses, including basketry, furniture, erosion control, fencing and hurdles. Although willow wood is slow to dry for burning as logs, willows have been increasingly grown in recent decades as a short rotation coppice crop to produce biomass fuel for municipal power plants and district heating systems.
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-## What are the benefits of willow treatment systems?+===== What are the benefits of willow treatment systems? =====
  
-### Self-provisioning / personal+==== Self-provisioning / personal ====
  
 Provides households with a tangible means of self-reliance and responsible resource management. Provides households with a tangible means of self-reliance and responsible resource management.
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-### Decentralising power away from corporations+==== Decentralising power away from corporations ====
  
 - The adoption of on-site, nature-based solutions represents a shift away from centralized, often corporate-controlled, infrastructure, which has gone horribly wrong in recent years, discharging raw sewage into seas and rivers. - The adoption of on-site, nature-based solutions represents a shift away from centralized, often corporate-controlled, infrastructure, which has gone horribly wrong in recent years, discharging raw sewage into seas and rivers.
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 - Keeps money in communities, that would otherwise have gone to corporate shareholders. - Keeps money in communities, that would otherwise have gone to corporate shareholders.
  
-### Building community and preparing for any potential collapse scenarios+==== Building community and preparing for any potential collapse scenarios ====
  
 While often designed for individual households, willow treatment can scale to the community level. While often designed for individual households, willow treatment can scale to the community level.
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-### Environmental+==== Environmental ====
  
 The environmental credentials of well-designed willow treatment systems are arguably their most significant benefit. The environmental credentials of well-designed willow treatment systems are arguably their most significant benefit.
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-## What can I do?+===== What can I do? =====
  
 Willow filters and zero discharge willow facilities have two very different design protocols, construction input and budget. Zero discharge facilities are best designed by a specialist and then constructed with careful attention to detail to ensure that the system size and layout are correct. Willow filters are more straightforward and can be DIY or excavated by a local machine contractor. Willow filters and zero discharge willow facilities have two very different design protocols, construction input and budget. Zero discharge facilities are best designed by a specialist and then constructed with careful attention to detail to ensure that the system size and layout are correct. Willow filters are more straightforward and can be DIY or excavated by a local machine contractor.
  
-### Willow filters+==== Willow filters ====
  
 Laid out as a drainage field (aka leachfield, infiltration area or percolation area), but with a modified pipe layout. Dig the drainage field trenches as [set out in the standard guidance](/sept/septic_tanks) (having followed the correct procedures to determine the size needed to satisfy local legislation and to protect the groundwater and adjacent surface waters). Then, instead of using standard perforated piping, use a trench infiltrator unit to ensure that the willow roots won't clog the pipe perforations and block the system. This is essentially an upside down gutter, placed on the trench base and covered with soil. The higher up this can be in the ground, the easier it will be for the effluent to be accessed by tree roots. Too shallow will risk effluent exposure at surface level in times of heavy rain, and too deep will risk being beyond the easy reach of the roots of the trees. That said, due to the deep reach of willow roots, the bigger risk of having the trench base too low down is that the effluent will be introduced closer to bedrock or ground water. Laid out as a drainage field (aka leachfield, infiltration area or percolation area), but with a modified pipe layout. Dig the drainage field trenches as [set out in the standard guidance](/sept/septic_tanks) (having followed the correct procedures to determine the size needed to satisfy local legislation and to protect the groundwater and adjacent surface waters). Then, instead of using standard perforated piping, use a trench infiltrator unit to ensure that the willow roots won't clog the pipe perforations and block the system. This is essentially an upside down gutter, placed on the trench base and covered with soil. The higher up this can be in the ground, the easier it will be for the effluent to be accessed by tree roots. Too shallow will risk effluent exposure at surface level in times of heavy rain, and too deep will risk being beyond the easy reach of the roots of the trees. That said, due to the deep reach of willow roots, the bigger risk of having the trench base too low down is that the effluent will be introduced closer to bedrock or ground water.
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 </WRAP> </WRAP>
  
-### Zero discharge facilities+==== Zero discharge facilities ====
  
 First determine the effluent volumes likely to be produced, the evapotranspiration rate from local meteorological data, and soil type and depth. With this data, it's possible to determine the required facility size. A typical system size is _c_.6m x 35m for drier parts of the UK, but wetter locations can be as much as double this length (where careful design is employed to exclude a large proportion of the rainfall landing on the system). Keep the width relatively narrow to avoid a build-up of humidity in the centre of the basin. Here's the order of work: First determine the effluent volumes likely to be produced, the evapotranspiration rate from local meteorological data, and soil type and depth. With this data, it's possible to determine the required facility size. A typical system size is _c_.6m x 35m for drier parts of the UK, but wetter locations can be as much as double this length (where careful design is employed to exclude a large proportion of the rainfall landing on the system). Keep the width relatively narrow to avoid a build-up of humidity in the centre of the basin. Here's the order of work:
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 </WRAP> </WRAP>
  
-### Planning permission+==== Planning permission ====
  
 Planning permission is generally needed for any new sewage treatment system, so if you're building a new house and new zero discharge willow facility then apply for planning for everything together. To carry out a major upgrade of a sewage treatment system usually requires planning, even for an existing house, but ask your local planning authority anyway since there may be exemptions. Planning permission is generally needed for any new sewage treatment system, so if you're building a new house and new zero discharge willow facility then apply for planning for everything together. To carry out a major upgrade of a sewage treatment system usually requires planning, even for an existing house, but ask your local planning authority anyway since there may be exemptions.
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-### Species+==== Species ====
  
 There are _c_.526 species of willow in the world, mostly native to the Northern Hemisphere. Although there are many different willow species native to the UK and Europe, the osier, _Salix viminalis_ is the main species used for breeding biomass willow cultivars. This is also the willow used for sewage treatment applications due to the high growth rates and consequent high uptake of liquid and nutrients. If you're planting a willow filter yourself, be sure to use only hybrid biomass willows and not basket willows or locally-growing willows. Find a farmer who grows them for biomass and ask for some if you like. The difference in growth rates is striking. There are _c_.526 species of willow in the world, mostly native to the Northern Hemisphere. Although there are many different willow species native to the UK and Europe, the osier, _Salix viminalis_ is the main species used for breeding biomass willow cultivars. This is also the willow used for sewage treatment applications due to the high growth rates and consequent high uptake of liquid and nutrients. If you're planting a willow filter yourself, be sure to use only hybrid biomass willows and not basket willows or locally-growing willows. Find a farmer who grows them for biomass and ask for some if you like. The difference in growth rates is striking.
  
-### Establishment time+==== Establishment time ====
  
 Danish willow systems are often put into first use immediately following planting in March or April (the end of the dormant season for willows). As the growing trees in a willow system become more mature, the volume of effluent evapotranspired into the air will increase, so some local authorities prefer to have 1 year of willow growth prior to first connection to the septic tank for new properties. Note that this may necessitate watering in the first year to ensure that adequate moisture and nutrients are available for the growing trees. Every 3 years the willows will reach their full height (for filter purposes anyway), and are ready to coppice. As the years go by, the willow roots will become more established and the number of willow poles per stem will increase, further increasing the uptake of effluent and generation of biomass. Danish willow systems are often put into first use immediately following planting in March or April (the end of the dormant season for willows). As the growing trees in a willow system become more mature, the volume of effluent evapotranspired into the air will increase, so some local authorities prefer to have 1 year of willow growth prior to first connection to the septic tank for new properties. Note that this may necessitate watering in the first year to ensure that adequate moisture and nutrients are available for the growing trees. Every 3 years the willows will reach their full height (for filter purposes anyway), and are ready to coppice. As the years go by, the willow roots will become more established and the number of willow poles per stem will increase, further increasing the uptake of effluent and generation of biomass.
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-### Maintenance+==== Maintenance ====
  
 - Ensure that the septic tank is desludged on an annual basis. This will avoid carry-over of solids to the willow facility. - Ensure that the septic tank is desludged on an annual basis. This will avoid carry-over of solids to the willow facility.
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-## Further resources+===== Forum ===== 
 + 
 +This topic belongs to the section [[gt:water|Water & sewage]]. You can ask questions or add information on the corresponding [Forum section](https://forum.growingthecommons.org/t/water). 
 + 
 +===== Further resources =====
  
 - [Septic Tank Options and Alternatives](https://wetlandsystems.ie/bookshop/) - [Septic Tank Options and Alternatives](https://wetlandsystems.ie/bookshop/)
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 +===== Related topics =====
  
-## Related topics +- [[bask:basketmaking|Basketmaking]] 
 +- [[wodl:woodland_management|Tree / woodland management]] 
 +- [[sewg:sewage|Low-impact sewage treatment]] 
 +- [[hrdl:hurdles|Hurdles]] 
 +- [[reed:reed_beds|Reed beds]] 
 +- [[sept:septic_tanks|Septic tanks & drainage fields]] 
 +- [[livw:living_willow_structures|Living willow structures]] 
 +- [[cptt:compost_toilets|Compost toilets]]
  
-## Specialist curators of this topic+===== Specialist curators of this topic =====
  
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