The filter basins

In the context of the restoration to full operation of the Roubaix canal, part of the outflow from the Grimonpont wastewater treatment plant will be filtered through a series of basins then pumped into the canal, thus ensuring that the operating levels will be maintained.

Location of the wastewater treatment plant
and the filter basins, nearby the border.

Why are filter basins needed?

LMCU designed this new system using filter basins to guarantee sufficient water supply to the canal. This system will complement the back-pumping at each lock. In order to compensate for permanent water losses this water reservoir will feed the canal especially during peak periods.

How does the system work?

Water is taken from the outflow of the Grimonpont water treatment plant, and is discharged into a first basin planted with various natural pollution removal species: roses, irises and others. The water then descends by gravity from basin to basin and is naturally filtered in the process.

There are manual shut-off valves which allow each basin to be isolated in the case of accidental pollution.

After 7 days flowing slowly through the tortuous meandering path of successive filters the water finally arrives at the ninth basin, which acts as a reservoir. At this stage the water has been completely purified and is now of a very high quality.

The pumping of this water up into the Leers canal pound is automatic.

In addition to their "top-up" water supply function, these filter basins meet another objective : they provide an attractive natural area covering 8 ha, which will be open to the public and ideal for environmental education.

Particular care has been taken to maximise accessibility for the handicapped. LMCU is aiming for accreditation under the "tourism & handicap" label.

Layout plan of the future basins
What will these basins be like ?

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Hydraulic principle of the filter basins
Or how the water discharged from the treatment plant flows
through the channels and the filter basins.
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Hydraulic profile of the filter basins
At which end does the water flow out ?

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Landscaping of the basins
What are the preferences in landscaping, horticultural and
ecological terms that make such filtration possible ?
See this beautifully-illustrated document with pictures of all
the aquatic plants selected (zoom at 200% on the pdf file)
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Filter basins and eutrophication

The technique of filter basins is similar to that of aerated lagooning, but adds an extra dimension. In filter basins the oxygenation process is completed by natural filtration by microorganisms, algae and aquatic plants. It is a highly efficient method of wastewater treatment.

Eutrophication usually designates the imbalance resulting from an excessive supply of nutrients: nitrogen (nitrates for example), carbon...

Cf. the article in Wikipedia.

The filter basins

In the context of the restoration to full operation of the Roubaix canal, part of the outflow from the Grimonpont wastewater treatment plant will be filtered through a series of basins then pumped into the canal, thus ensuring that the operating levels will be maintained.

Filter basins and eutrophication

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