Chlorination Process for Potable Water Treatment

For the potable water treatment we carry out chlorination at two different sites, using NaOCl.

 

The one site is the "Main Pump Station of Agia", where we chlorinate the water, through a metering pump and a standby one in case of an alarm, straight forward to a DN350 pipe which supplies water, at flow rate of 245 m3/h. This metering pump is been controlled by a PID controller, that takes into account the relevant water flow rate as a feedforward disturbance, the water PH (e.g. 7,95-8,05), the water temperature (e.g. 14oC) and , the residual HOCL measurement at a steady water flow sampling (e.g. 55l/h). The PID Controller evaluates, through the above measurements, the residual free chlorine that is HOCL + OCl-

The other site is the "Main water storage tanks of Vade" (3 water tanks of about 5500 m3 each) where we chlorinate the water, through a metering pump and a standby one in case of an alarm, in the inlet DN500 water pipe of water storage tanks, at a mean water flow rate of about 1050 m3/h. This metering pump is been controlled by a PID controller, adjusted at a 0,35 ppm set point, that takes into account the relevant water flow rate as a feedforward disturbance, the water PH (e.g. 7,95-8,05), the water temperature (e.g. 14oC) and the residual HOCL measurement at a steady water flow sampling (e.g. 55l/h). The PID Controller evaluates, through the above measurements, the residual free chlorine that is HOCL + OCl-.  The chlorination pumps work in the same way in Agia.

At the same site there is an other metering pump and a standby one in case of an alarm, which chlorinates the water straight forward to the outlet DN700 water pipe of water storage tanks, at a mean water flow rate of about 900 m3/h, only in the case that the residual free chlorine of the outlet water pipe of the water storage tanks is less than a desisted value at 0,25 ppm.

All the above chlorination process is been remotely monitored by a SCADA (Supervisory Control and Data Acquisition) Control System, which is located at the Supervisory Control Center at Agios Ioannis Water Tank Site. Through this Control system we can change remotely the set point of each PID controller and we can also be informed (by color change, horn and alarm message) on-line of any alarms that have to do with the chlorination processes. The SCADA Control System keeps a database of historical events and measurements and we can present, at any time, any of the residual free chlorine measurements in a form of a table or in a form of a curve.

In this way the chlorination process is fully automatic and the residual chlorine concentration in the water network is stable and there are no limit violations (lower limit set by Greek legislation (    0,2 ppm), higher limit is not set but we make sure that we never exceed 0,40 ppm in the network.)

Residual Free Chlorine Measurement Process for Potable Water Treatment

Residual free chlorine measurements take place at 17 different sites in the town's water pipe network, at the "leakage stations" which are located at the origins of the 30 "leakage zones".

Some more residual free chlorine measurements take place at 5 different sites in the outlet pipe of the storage water tanks that are located into several points of the water pipe network and supply water to several areas.

All the above residual free chlorine measurement process is been remotely monitored by a SCADA. The SCADA System keeps a database of historical events and measurements and we can present, at any time, any of the residual free chlorine measurements in a form of a table or a curve.