21 May 2008
Currently serving 300,000 people and processing 100,000 m³ of sewage, the plant will soon be able to provide a service for one million Parisians and return the purified waste to the river Seine.Les Grésillons differs from conventional sewage plants with biological purification stages in that it uses filter technology, rather than bacterial activation tanks. After the mechanical purification stage using sand filters and screening units, the pre-treated sewage passes three layers containing biofilters, where the nitrogen is removed from the sewage.The supply to the 28 biofilters, as well as the backwashing process, is controlled by process gates (shut-off or butterfly valves) using automated pneumatic actuators. Festo developed a Copac DLP linear actuator with a through-piston rod for the 28 Fontaine shut-off valves, which are not housed to facilitate the use of a handwheel in emergencies. Each shut-off valve is equipped with two proximity sensors for sensing the mechanical end stops and transmitting the information to the controller.Decentralised CPX/MPA valve terminals actuate the drives and record all data relating to the filtration tanks. Each tank communicates with the centralised Allen Bradley controller via the DeviceNet fieldbus interface of its CPX terminal. The CPX terminals also include Festo PLCs for managing the control circuits locally and ensuring safety positions. Diagnostic functionality enables the CPX terminals to quickly detect any faults in the plant. The CPX concept, plus the IP65/IP67 protection class, has kept electrical and pneumatic installation costs to a minimum.
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