The Operation of Backwash Pumps and Air Scour Blowers

1.1.        Control Philosophy

1.1.1.        General

The major equipment such as low-lift pumps, high-lift pumps, and power generating sets will be automatically controlled with manual override.  In addition, the operation of backwash pumps and air scour blowers during the filter backwash cycle of the rapid sand filters are also activated and controlled automatically, when each filter reach its preset clogged position.

Furthermore, alum and lime dosing units as well as chlorinator booster pumps will be automatically shut down soon after the low-lift pumps are shut off with a preset timer delay.  The cut-in and cut-out operation of backwash recovery pumps and thickener supernatant recycle pumps will also be carried out automatically according to the preset high levels and low levels of the backwash recovery tank and the thickener respectively.  Similarly, the sludge pumps used to remove accumulated sludge from thickener to the sludge drying beds will also be carried out automatically through level sensing.

A comprehensive SCADA system is provided and installed at the treatment plant site office for monitoring and controlling the vital equipment associated with water supply project.

Dedicated radio link systems will be installed in all four locations namely, intake pump house, treatment plant, X tower and Y tower.  The encoding and decoding of radio signals will be carried out using dedicated PLC installed at those locations.  In addition to the PLC installed at treatment plant site office, separate PLCs will be installed at generator house, chemical house, chlorinator house, filter house, high-lift pump house and backwash water recovery tank, as indicated in table-1.

All the PLCs within the treatment plant including centralized server at the site office will be interconnected through optical fiber cable.  All the signals received from radio communication systems from distant locations such as intake location, X tower and Y tower are coordinated through the centralized server at site office and send to the corresponding PLC at the desired location within the treatment plant and vice versa.  The centralized server will be connected to the display and the control desk of the SCADA system.

The summery of locations where the PLCs are installed together with the electrical control panels are shown in table-1.  The corresponding equipment controlled by each panel is also shown therein.  In addition, the locations where radio link equipment to be installed which consist of both receiver and transmitter are also indicated separately.  However, at X tower and Y tower locations, only the function of transmitter is used for normal operational purposes.

Table-1