What is a Wetland also known as Reed Beds?
In the natural world, they are known as ‘mangroves’, they improve the water quality by filtering polluted water, adding oxygen, improving and
stabilising the soil, the same natural process as occurs on river and creek banks.
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Constructed Wetland/Reed bed |
Mangroves |
WHEN IS A WETLAND/REED BED APPLICABLE?
(Secondary Treatment)
Secondary waste water treatment is required on environmentally sensitive and constrained sites, sites with limited space, no power, or if nutrients like nitrogen is an issue. The treated waste water can be disposed of via ETA Beds or Sub-Surface Irrigation. Wetlands can be used in domestic or commercial situations.
ADVANTAGES OF WETLANDS
Green treatment technology, does not require power and there are no mechanical parts, maintenance is minimal and can be done by anyone. Proven to be effective and robust with a constant discharge quality, long life expectancy with low running costs. Sizing can be adapted for small to large projects and has a lower capital cost than conventional aerated systems, extremely environ friendly as wetlands provide a wonderful wildlife habitat.CONSTRUCTING WETLANDS
(Copying Nature)
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Domestic Reed Bed system constructed with a series of pre-fab poly trays |
Small commercial project constructed with a EPDM rubber liner |
Large commecial wetland constructed into the ground and lined with clay |
Wetlands/Reed Beds usually contain a porous medium of gravel (Substrate) approximately 0.5m deep, supporting aquatic plants (Macrophytes) such as Reeds (hence the name Reed Bed). Water flows through the space between the media and the plants roots, which provides a large surface area for colonisation by friendly bacteria. Even though the sub-surface environment is largely devoid of oxygen, tiny oxygen rich microbes exist attached to the roots of the plants. The waste water is travelling through a sequence of oxygen-rich and oxygen-poor environments provided by the Wetland, thereby the waste water is subjected to conditions which enhance the removal of a number of damaging pollutants such as:
- Organic carbon – causes turbidity and odours in water
- Nitrogen – causes algae blooms in water
- Sulphate – causes acidity in water
- Ammonia – toxic to fresh water organisms
Wetlands also have the capacity to lower the concentration of disease causing pathogens and coli forms. Earthworms and Enzymes can also be introduced into the Wetlands/Reed Beds to further enhance their
filtering ability.
Wetlands under construction with the disposal field behind
SUBSTRATE
The choice of Wetland substrate will depend on the type and quality of the waste water stream and the desired treated outcome.Gravel of 10 – 20mm diameter is commonly used, as a rule media consisting of larger particles will have higher hydraulic conductivities and be less prone to clogging. On the other hand smaller particles will be more prone to clogging but will offer greater reactive surface area, hence providing better reatment. Because clogging is most likely to occur in the entrance zone of the Wetland substrate it is desirable to surround the inlet device with stones of about 30–50mm in diameter.
When treated effluent is being applied to soils with low nitrogen absorption capacity (eg sandy soils) it can be advantageous to use a Wetland substrate such as crushed brick which has a strong affinity for nitrogen. All commonly used media, including sands, gravels and soils have an initial porosity of between 35% and 45%, this can decrease with time as pore spaces become occupied by microphyte roots and effluent borne solids.
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3000L Septic Tank leading to a |
Poly Reed Bed tray with barrel |
The treated effluent from wetlands can be disposed of via ETA Beds or Sub-Surface Irrigation, it can also be treated further (tertiary treatment) for reuse.
MACROPHYTE SPECIES
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SPECIES: |
COMMON NAME: |
HEIGHT: |
Baumea Articula |
Jointed Twig Rush |
2.5m |
Baumea Rubiginosa |
1.0m |
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Bolboschoenus Fluviatiuis |
Marsh Club Rush |
2.0m |
Eleochanis Articulata |
Tall Spike Rush |
2.0m |
Leprionia Articulata |
Gray Rush |
4.0m |
Schoenoplectus Mucronatus |
Star Club Rush |
1.0m |
Schoenoplectus Validus |
River Club Rush |
3.0m |
Typha Orientalis |
Bull Rush or Lumbung |
4.0m |
Common Reed |
Phragmites Australis |
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Vetiver Grass |
(Click here for info) |
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Macrophytes should be planted at
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