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Floating Islands
(Synonyma: Floating rafts, floating treatment wetlands, floating
vegetated islands, floating wetland systems, buoyant mats with emergent
aquatic plants, rafts of vegetation, prevegetated floating plant
carriers, preplanted mats, les îles flottantes, islas
flotantes,
insulis natantibus)
We use floating islands in our engineered wetlands since 1995. Some
examples from our realized projects:
- Nesting
and refuge area for waterfowl and wastewater treatment by submerged
(microbiological active) biofilms:
Stormwater treatment biotope
Gadenstedt, Germany
- Odour
control and bacterial metabolism of high strength silage effluent:
Sedimentation pond at Dittmannsdorf, Germany
- Filterponds
covered with floating islands for sedimentation of secondary sewage
sludge from a trickling filter (3.500 person equivalents):
- Filterponds covered with floating islands
for
sedimentation of secondary sewage sludge from a rotating biological
contactor (5.000 person equivalents):
- Floating islands for tertiary treatment
of activated sludge treatment systems:
Renquishausen,
Germany
Groß-Lafferde,
Germany
- Floating islands as a barrier for oil and
floating rubbish at a wastewater lagoon system:
Berel,
Germany
- Floating islands at different stormwater
treatment wetlands:
Oberg,
Germany
Münstedt
- Floating islands for high strength (COD
>
10.000 mg/l) industrial wastewater treatment in a tropical country, as
fish breeding habitat and for odour control:
Tay
Ninh, Vietnam
- Sedimentation ponds with floating islands
for polluted effluent of the construction material recycling industry:
Gunzgen,
Switzerland
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World Map
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Artificial
and natural floating islands are characterized by buoyant
dense mats of roots and rhizomes of marsh
plants (helophytes). There
are natural self-buoyant floating root mats and artificial ones growing
on rafts.
Natural
floating islands gain their self-buoyancy either from the
occurrence of air spaces within the aerenchyma
tissue of the rhizomes
or from gases (such as methane) released by decaying plant material.
Natural floating
islands occur, for example, in the Danube Delta, where
they are called plaur. The plaur consists of a combination
of reed
rhizomes, other organic materials and soil which breaks away from river
banks and lake bottoms to form
floating islands of different size and
shape. These floating marsh ecosystems provide valuable habitat for
many,
often very rare, species of birds.
Common genera of marsh plants (emergent aquatic macrophytes) forming
floating islands are Phragmites, Typha,
Phalaris, Glyceria, Cyperus,
Eichhornia among others with air filled aerenchyma tissues.
Under moderate climatic conditions, e.g. in Germany and other European
countries, we preferably use plant
genera as Lythrum, Carex, Juncus,
Iris, Scirpus, Mimulus, Caltha, Glyceria among others.
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In
tropical regions like South-Vietnam we tested different species like
Persicaria, Neptunia, Ipomoea, Limnocharis, Hydrocotyle, Cyperus,
Colocasia successfully, even under conditions of high strength starch
production wastewater in a pretreatment pond.
Colocasia esculenta
Impomoea aquatica
In most
applications
we use a special textile plant carrier as a platform structure to
support the buoyancy of the wetland plants (helophytes).
The plant roots growing in the water take up nutrients and provide
large surfaces on their root and rhizome mats for active biofilms
(microbes improving water quality). By shading the water surface
floating root mats suppress the proliferation of algae. Floating rafts
provide wildlife habitats for waterfowl above the water surface and
breeding areas for young fishes in the root network below.
We use floating islands (floating rafts) in our treatment wetland
projects for the removal of pollutants in water bodies1
and for different other purposes alongside with constructed wetlands
for nearly 25 years.
- Our floating islands precultivation ponds
at Habichtswald, Germany:
- Our floating islands precultivation ponds
at Rosdorf, Germany:
For purchase of floating islands look at www.rhizotech.de or at
similar websites.
1 Removal
of
-nutrients like phosphorus and nitrogen (direct plant uptake from the
water through the plant roots and microbial metabolism)
-suspended solids (particulate organic matter) by filtration and
sedimentation
-organic matter (BOD, COD) and volatile organic compounds like MTBE and
benzene by biodegradation and direct plant uptake of contaminants and
metabolism within the marsh plants (AFIFI, S., (1991): Biochemische
Umwandlung von Halogenphenolen 2. Mitteilung: Das Verhalten
von
Halogenphenolen in bepflanzten Bodenkörpern. In:
Berichte
zur Ökotechnik, Arbeitsgruppe Ökotechnik
(Hrsg.)).
-heavy metals by precipitation as insoluble salts and binding to
particulate matter and uptake by plants and root mat biofilm microbes
and following sedimentation processes.
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civil
engineering
