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Municipal Case Studies

Ile d'Yeu - France

The remarkable site of Ile d'Yeu required a high performance treatment plant. A new generation of treatment plant, unequalled water quality.

The chosen technology - odour and noise free - is compact, architecturally integrated, responsive to seasonal variations and outputs an exceptional quality of water. Thus protecting the natural environment of Ile d'Yeu for both residents and tourists. 

Technical Details

Effluents to be treated 






Flow (1) m3/d 1120 2260
  m3/h 91 183
COD Chemical oxygen demand kg/d 1080 3240
DBO5 Biological oxygen demand kg/d 390 1170
SS Suspended solids kg/d 480 1440
TKN Total Kjeldahl nitrogen kg/d 140 420
TP Total phosphorus kg/d 29.5 88.5

High-quality treated water


Maximum concentration over 24 h

COD 40 mg/l Total coliforms <1000/100 ml
DBO5 10 mg/l Heat tolerant coliforms <1000/100 ml
SS <5 mg/l Faecal streptococci D 500/100 ml
TKN 5 mg/l Phages ARN <10/ml

Water circuit

Effluents are screened through a rotating strainer before clarification. The water is then transferred to an aeration tank, where bacteria consume carbonaceous and nitrogenous pollutants. The treated water is then filtered using membranes to remove suspended matter before being discharged to the sea.

The sludge is extracted from the membranes, dewatered and dried by solar energy and recycled for agriculture use.


Ile d'Yeu Biosep
Biosep for wastewater biological treatment and re-use - Treatment capacity in population equivalent : Load variation : 3 500 / 7 000 / 19 000 PE....

Unequalled water quality

Operating principle  Biosep™ uses an aeration tank and a membrane system where membranes are located and grouped into modules. These modules are directly immersed in the aerated tank. The filtered water is extracted using two pipes and a third pipe is used in order to extract scouring air.

The membranes are hollow polymer fibres with a high mechanical resistance. Their break threshold is located between microfiltration and ultrafiltration (200 000 Daltons).

Filtering phase

The water is filtered from the outside to the inside because of a pressure difference generated by the height of water above the membranes. A draught pump completes this phase. 

Back washing phase

The prevention of clogging and caking is managed through the extensive use of membranes (with low pressure through the membranes) and by ensuring that operating conditions are adapted to the treatment process (agitation using air scouring and back washing).