Precision Meters: Effective use of Water (Part C)

System Users – Residential, Industry and Agriculture:

c) Reuse & Recycle:

These recommendations involve changing water usage habits and can be applied both indoors in the kitchen, bathroom, and laundry room and outdoors so that water is used more efficiently, thus reducing the overall water consumption.

Water Reuse:

This is the re-use of waste / reclaimed water from an operation such as a municipal waster water treatment facility for another use such as landscape watering. The reused water has to benefit a specific purpose and will need to comply to applicable regulations / rules such as local ordinances that govern the quality of reused water for that purpose.

The use of re-used water is furthermore beneficial as it reduces the demands on potable water supply and treatment and delays the need to expand these facilities.

The following factors determine need to be considered wherever possible to maximise the use of re-used water.

• Identify opportunities for water re-use.
• Determine the applicable water quality requirements for any give use of re-used water.
• Sources of waster water, that are able to meet the water quality requirements, need to be then identified.
• Determine how to transport the re-used water to the proposed usage area.
• Measure the amount of water that is being re-used.

Some potential applications that reused water would be considered for:

1) Landscape Irrigation:

These would typically be areas such as golf courses, playing fields, road reserves and roundabouts, refuse dump rehabilitation etc.

2) Agricultural Irrigation:

We are fast approaching the stage where agriculture resulting in vegetable crops being closer to market is needed to feed growing populations and so in city opportunities need to be identified for this purpose.

3) Fountains / decorative:

Re-use water in fountains, reflective pools or just simply as a bubbling stream within an urban context leads to a calming and soothing atmosphere against the hustle and bustle of city life.

4) Fire Protection:

Although re-used water would require a separate water reticulation system, this should be considered when new industrial developments are planned. as a future scenario to save water.

Water Recycling:

Complimentary to using re-used water is the practice of water recycling that is the use of water for the same application for which it was originally used. Under certain circumstances water used for recycling might require treatment before recycling.

Similar factors to the above should be considered in a water recycling program include (Brown and Caldwell, 1990):

• Identify opportunities for water re-use.
• Determine the applicable water quality requirements for any give use of re-used water.
• Evaluation of any water quality degradation that may result from the recycling.
• Determine treatment steps, if any, required to ensure that the water is suitable for recycling.

Cooling Water Re-circulation:

One of the largest water usage applications is the use of water for cooling heat generating equipment or to condense gases in a thermodynamic cycle and the most intensive of these is when the water is used as a once-off when the water contacts and lowers the temperature of the heat source and is then discharged. By recycling water under these circumstances, to perform several cooling operations, water usage is greatly reduced and represents a substantial savings to industry.

There are three distinct water conserving approaches that may be deployed to reduce water:

• Evaporative cooling:

These systems ‘loose’ water when a portion of the cooling water evaporates as it reaches boiling point from being in contact with the hot surface that has to be cooled. Some evaporation will will drift away and also because of blowdown which is the practice of reducing some of the poor quality water, that has high levels of dissolved solids, by discharging this from the whole. Water loss savings can be achieved by reducing blowdown or water discharge from cooling towers.

• Ozonation:

The use of ozone treatment in the cooling tower water system is able to result in a 5 fold reduction in water loss as compared to other chemical treatments and so should be top of the list for implementation.

• Heat exchange:

Cooling that is achieved as a result of using a heat exchange method results in almost zero water loss as the water is in a closed system and is thus not subjected to external influences. Heat exchangers are however more expensive to implement as compared to cooling towers.

Of importance in considering the above is to be able to know just how much water is being introduced into the cooling system.

To achieve this, accurate metering is required that will provide feedback to management and enable decisions to be made as to how to optimise the system to achieve the degree of cooling as well as to minimised the loss of water which will result in an overall saving and improve the environmental footprint of the installation.

Precision Meters: Effective use of Water (Part C)

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