General operation of the water supply

1. Coagulation and Flocculation

In these stages, the impurities present in the water are grouped by the action of the coagulant into larger particles (flocs) that can be removed by the decantation process. The reagents used are called coagulants, which are usually Aluminum Sulfate and Ferric Chloride.

Afterwards, it goes through a strong agitation with the objective of facilitating the agglomeration of the particles.

At this stage it may also be necessary to use an alkalinizer (hydrated lime or virgin lime), which will make the necessary pH correction for a more effective coagulant action.

In coagulation occurs the phenomenon of grouping of impurities present in the water and, in flocculation, the effective production of flocs.

2. Decantation

This stage consists of the moment when the flakes, formed in the previous stage, are deposited at the bottom of the tank. The flakes formed are separated from the water by the action of gravity.

3. Filtration

The decanted water is forwarded to the filtering units where the filtration process is carried out. A filter consists of a porous granular medium, usually sand, of one or more layers, installed over a drainage system, capable of retaining and removing impurities still present in the water. A final pH correction of the water can be performed to prevent corrosion of the pipes.

4. Disinfection

To disinfect water supplies, a physical or chemical agent (disinfectant) is used, whose purpose is the destruction of pathogenic microorganisms that can transmit diseases through them.

Normally the following disinfecting agents are used in public supplies, in order of frequency: chlorine, ozone, ultraviolet light, and silver ions.

Chlorine in its gaseous form can be used as a disinfectant agent, which is dosed into the water through equipment that allows for a systematic control of its application.

5. Fluoridation

Fluoridation of water supplies is carried out using fluoride-based compounds. The application of these compounds in public water supplies contributes to reducing the incidence of dental caries by up to 60%, if children ingest adequate amounts of fluoride ion from birth.

Distribution of the treated water

In the distribution of treated water the most numerous types of stations in the municipal water supply system are involved. The following figure gives an idea of the different seasons.

Treated water pumping station

Popularly called pump house or pumping station, this type of installation has the function of pumping water from a lower point to a higher point, usually a reservoir that in turn will supply a region of the municipality by gravity.

The treated water lift usually consists of motor-pump groups, one or more, driven by MCC (motor control center) panels, consisting of star delta circuits, compensator switches, soft starters, or frequency inverters.

The elevators can also contain check valves, manual valves, and motorized valves.
The main variables of interest in controlling a treated water lift are:

• Suction pressure;
• Back pressure;
• Electric currents, grid voltages and power factor;
• Feedback from the motors (ON/OFF status, trip, temperature and vibration alarms).

Treated water reservoir

Usually, reservoirs are built on high points and supply a neighborhood or region by gravity.

The main variables of interest in the control of treated water reservoirs are:

• Level;
• Flow;
• Stored volume;
• Chlorine level.

Booster

The booster’s function is to reinforce and guarantee pressure in the network. They are normally built at points in the network where the pressure is low, mainly due to the pressure drop in the piping. Generally, the pressure at these points is lower during the day and at times of higher consumption, and higher at night, when consumption is higher. To keep the pressure constant, frequency in verters are used to control the motors and the back pressure is monitored. The speed is controlled so as to keep the pressure constant.

The main variables of interest in controlling a booster are:

• Suction pressure;
• Back pressure;
• Electric currents, grid voltages and power factor;
• Feedback from the motors (ON/OFF status, trip, temperature and vibration alarms).

Macro Flow Meter

Macro flow meters are installed at starting points in a sector. Sectorization is fundamental in loss control. When the network is sectored it is possible to compare the total water supplied to that sector(macro measurement), which can be a neighborhood, with the total water sold to that population, counted as the sum of all consumption registered in the hydrometers (micro measurement).

The main variables of interest in macro meter monitoring are:

• Instantaneous flow rate (usually and liters per second);
• Accumulated volume (usually in cubic meters per hour);
• Pressure.

VRP – Pressure Regulating Valve

The VRPs are installed at points in the network that need limitation to prevent pipeline rupture due to excess pressure. These are electromechanical devices that can be controlled by pressure feedback downstream, i.e. at the valve outlet. VRPs can also be remote-controlled motorized valves.

The main variables of interest in the control and monitoring of VRPs are:

• Upstream pressure;
• Downstream pressure;
• Valve opening ( 0 to 100% );
• Command to open and close the valve.

Read more