intake - recirculation system - treatment
of reject water
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The water intake occurs at high tide in the Douhet Canal which runs along the side of the hatchery, in collaboration with the Commune of St Georges, which administers the Douhet salt-flats.
The water is stored in two large ponds of 60 000 cubic metres from which it is then pumped to a settling tank of 450 cubic metres, before being divided between the various production units.
The incoming water is filtered mechanically to remove suspended matter, sterilized by exposure to UV, and treated to get rid of any gaseous supersaturation.
A daily check of the numerous physico-chemical parameters of the incoming water, of the water used for rearing and the reject water is part of the framework of internal quality control.
The water recirculation circuits, apart from their zootechnical interest, allow us to minimise the volumes of water used, and to eliminate practically all suspended matter in the reject water.
Thanks to the intensive use of these systems, the daily needs for new water are a maximum of 4 800 cubic metres for a circulation flow-rate of 50 000 cubic metres per day. This represents a greater than 90 % economy in water taken from the sea and it also leads to a substantial energy saving in heating the water.
For the sake of preservation and protection of the environment, all of the reject waters from the rearing are purged in a decantation canal and are then regenerated in a ponding unit of twelve tanks. The presence of planktonic algae in these tanks allows the transformation of the rejects from the rearing (nitrates, phosphates) into substances which can be used by the aquatic fauna of the salt marshes. The Ferme Marine de Douhet is thus perfectly integrated with its surrounding environment.