wetparks

not a new way to purify water


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The name

The name 'wetpark' is chosen for a constructed wetland with ornamental qualities (wet-park). At the same time, they increase the biodiversity of the area by creating new habitats for plants and animals. Wetparks are used for the purification of grey water.

The function

The purification capacity of the shore zones in the pond system thus depends on the chain:

  1. Microbial and plant activity in the hyphoreic water flow
  2. Plant uptake of the decomposed material
  3. Continuous biomass removal by harvesting plant material (and fishing crayfish or fish).

Grey water usually have a rather low N/P ratio. This can restrict the phosphorus uptake by the plants (due to lack of nitrogen). In order to alleviate this problem, wetland plants (trees or shrubs) that are known to have a nitrogen fixating capacity are chosen.

In order to maintain a large and continuous flow of water in the wetpark, and to make up for evaporation during hot spells, rainwater is collected from roofs and put into the system. Normally, this constitutes an excess of purified water. This is rarely a problem. In the Kalmar wetpark, the calculated excess is about 700 m3 a year, In Rönås it is estimated to about 75 m3 per year. The purified water thus produced could be 'given away' to anybody needing it.

The method of using biological groundwater activities to purify water is definitively not a new one. It is the 'normal' way for water to be sufficiently clean to use. The difference in this case is that the system is created and consciously maintained by humans.

The construction

Figure 1. Schematic picture of a general wetpark.

The water flows very slowly from left to right. The turnover time is about one year. The total water volume of the wetpark is equal to the annual water flow. By that, the water entering the park will always spend a summer in the system, regardless of the time it is inserted.
Using some sort of back-pumping from the end of the park to the beginning, the actual size of the plant can be diminished in relation to the pumping capacity. This method is used in the smaller system, as well as in the larger Gudmundsparken storm water purification plant.

In order to contain the water in the system, the bottom of the wetpark is sealed.
This can be done by the use of puddled clay, and/or bentonite mats and/or an EPDM rubber mat, depending on available time and money during the construction. It must be done very careful, since a leaking wetpark will lose a lot of its capacity for water recycling.

The smaller wetpark

The small wetpark was originally thought of as integrated with the garden paths and a pond, to be fit into an average garden, using gravel under paths and planting alongside them as a part of the purification system. In Rönås, it wasn't possible to use the garden in this way, so the paths were excluded.

Figure 2 Schematic of a Small Wetpark

This is a smaller wetpark, adapted for installation in an ordinary garden. The plants along the paths absorb nutrients as well as the plants in the shore-zones of the pond. The water is slowly pumped back to the beginning of the system (with a very simple pump) to improve purification capacity. Click on the separate parts to see enlargements.

 

Wetpark projects:

Kalmar technical high school

Rönås household wetpark

Gudmundsparken stormwater purification

Source-separating toilets

Dry climates: The folkewall

Lecture on the wetparks



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Updated:
2013-01-06