Reed Bed Systems
Reed Beds and Constructed Wetlands are two terms often used interchangeably. Although international terminology appears to be inconsistent, in Ireland the term Constructed Wetland (or Free Water Constructed Wetland) is usually used to describe a soil based marsh system in which the wastewater flows over the soil substrate; while a Reed Bed (or Gravel Reed Bed Treatment System) is usually a gravel based system in which the wastewater flows vertically or horizontally through the gravel substrate.
FH Wetland Systems offers a design service for both Constructed Wetlands and Reed Beds, and we will use the system which is most appropriate to the site conditions.
Other Features associated with reed beds and constructed wetlands:
- Ponds are often incorporated into the design of both soil based constructed wetland systems and gravel reed bed systems.
- Evapotranspiration areas are sometimes incorporated into the design of both soil based constructed wetland systems and gravel reed bed systems. These operate in a similar way to Zero Discharge Willow Facilities, but the storage volume is lower and a winter discharge is permitted during times of higher dilution in the receiving watercourse.
- Wet meadow areas are sometimes incorporated into the design of soil based constructed wetland systems for additional filtration. These operate on a similar basis to conventional Grass Plot Treatment Systems.
Advantages of Constructed Wetland Systems and Gravel Reed Bed Systems over alternative forms of effluent treatment:
- Low construction and running costs
- Easy management
- Excellent reduction of biochemical oxygen demand (BOD) and suspended solids (SS)
- Potential for efficient removal of a wide range of pollutants
- Secondary benefits in terms of potential wildlife habitat enhancement
- May be used in conjunction with old or overloaded systems to achieve high discharge standards
Principal Differences between Soil and Gravel Systems:
- Land area requirements are lower for gravel reed beds
- Capital cost are typically lower for soil based constructed wetlands
- Maintenance input is lower for constructed wetlands
- Preliminary settlement requirements are more stringent for reed beds
- Constructed wetlands are considerably easier to desludge in the event of excessive solids inputs
- Exposed water/effluent (to about 200mm depth, with tall plants growing in it) is present in soil based wetlands, but is covered with gravel in reed beds.
- Where a horizontal flow reed bed is used without a vertical flow component, the sewage effluent is completely covered, and thus there is less potential for disease transfer than with vertical flow gravel reed beds or for soil based constructed wetlands.
- Constructed wetlands more closely resemble natural habitats and provide exposed water and are thus more beneficial to wetland wildlife.
- While both systems have the potential to have zero energy requirements, constructed wetlands can achieve this with less site slope. Vertical flow reed beds usually require a pump for most sites.
- Constructed wetlands are more tolerant of variable loads; however both reed beds and wetlands are excellent for fitting in around treatment systems that suffer from seasonal overloads or under-use.
Principal Differences between Horizontal Flow and Vertical Flow Gravel Reed Beds:
- Vertical flow reed beds are top loaded, usually pump-fed systems, whereas Horizontal Flow reed beds do not require a pump if the falls on the site are favourable
- Oxygenation is typically better in Vertical Flow Reed Beds, leading to better ammonia and BOD removal per unit area
- The area requirements are typically smaller for Vertical Flow Reed Beds than for Horizontal Flow systems
- Although Vertical Flow and Horizontal Flow reed beds can be used in series, in either order, as secondary and tertiary treatment systems, typically the Vertical Flow reed beds come first.
Constructed Wetlands or Reed Beds? Choosing the Most Suitable Option for your Needs
The choice of system depends on site size and soil type, budget, degree of maintenance required, adjacent landuse. The above differences provide a basic background as to the factors to be considered when selecting which system to use. For additional information contact FH Wetland Systems to discuss a specific project.
Other Treatment Options
Click here if you want to see an updated list of treatment options based on Septic Tank Options and Alternatives - Your guide to conventional, natural and eco-friendly methods and technologies.
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© FH Wetland Systems, 2014