What This Requirement Covers
Reed bed systems (constructed wetlands) provide a natural, low-energy method of treating foul water in rural properties where connection to the public sewer is not practicable. They are used as secondary treatment after a septic tank or as tertiary treatment (polishing) after a package treatment plant.
Key Requirements
System Design
- Horizontal flow reed beds: Wastewater flows horizontally through a gravel bed planted with common reed (Phragmites australis); the most common domestic design
- Vertical flow reed beds: Wastewater is intermittently dosed onto the surface and flows vertically through the gravel bed; more compact and effective but requires dosing equipment
- Hybrid systems: Combine horizontal and vertical flow stages for higher treatment standards
Sizing
- Typical sizing for a horizontal flow reed bed: 5 m2 per person (based on a standard household of 4-6 persons)
- The bed depth is typically 600-800 mm with a gravel substrate
- A pre-treatment stage (septic tank or primary settlement tank) is essential to remove solids before the reed bed
Regulatory Requirements
- Discharge from a reed bed to a watercourse or ground requires an environmental permit from the Environment Agency (or compliance with general binding rules for discharges under 2000 litres per day)
- The treated effluent must meet the quality standards specified in the permit
- Reed bed systems must be designed by a specialist and should follow the guidance in the Constructed Wetland Association design manual
Maintenance
- Reed beds require minimal but regular maintenance: annual cutting of reeds, removal of accumulated sludge from the septic tank (every 1-2 years), and monitoring of effluent quality
- The reeds must be allowed to establish for 1-2 growing seasons before reaching full treatment capacity
Practical Compliance Tips
- Commission a specialist to design the reed bed system based on the specific site conditions and discharge requirements
- Ensure adequate land area is available; reed beds are space-intensive compared to package treatment plants
- Locate the reed bed downhill from the property if possible to allow gravity flow
- Plant the reeds in spring for the best establishment; protect new plantings from grazing animals
- Monitor effluent quality annually to verify compliance with the environmental permit
- Maintain the septic tank to prevent solids reaching the reed bed and blocking the gravel substrate
- Keep maintenance records and permit documentation for regulatory inspection