Ultra violet disinfecting plant
System: Magelis operator display and Modicon PLC
The effluent is directed through a channel of the UV system with ultrasonic level measurement used to maintain a specified level set point. Within the channel the treated effluent is exposed to UV Radiation in a series of UV Reactors (or UV Banks). Each Bank is composed of several Modules of UV discharge lamps (similar in general appearance to fluorescent lighting tubes) placed in the reactor parallel to the direction of flow. The treated water from the works travels past these tubes, during which time the bacteria within the water is sterilised and thus rendered inactive upon discharge. The intensity of the UV radiation, and the time that the effluent water is in contact with the radiation, determine the dose that is being given to the bacteria, and hence the effectiveness of the disinfecting process. Control is based on maintaining the UV Dose at a predetermined set point. Under normal circumstances the system is designed to be stand alone, and fully automatic, including automatic recovery from mains failure. There are however a range of diagnostic and manual facilities to allow the equipment to be investigated and maintained. The system includes comprehensive fault diagnosis via alarms generated at the Magelis display unit.The PLC controls the UV dose and automatic Bank switching as well as Bank wiping to keep the lamps clean. This is done by reading the effluent flow rate through the channel and the UV intensity measured by the sensors.
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