General Cooling water Problem:

1. Scaling 2. Corrosion 3. Microbes 4. Fouling

With the proper treatment, a significant proportion of industrial on-site wastewater might be reusable. This can save money in three ways: lower charges for lower water consumption, lower charges for the smaller volume of effluent water discharged and lower energy costs due to the recovery of heat in recycled wastewater. Industrial water treatment and wastewater treatment will vary in cost.

Scaling can be mobile, like a fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because
it insulates and heat exchange becomes less efficient as the scale thickens,
which wastes energy. Scale also narrows pipe widths and therefore increases
the energy used in pumping the water through the pipes.

The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurised system can lead to catastrophic failures.

Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients, as wet cooling towers are very efficient air scrubbers. Dust, flies, grass, fungal spores and so on collect in the water and create a sort of "microbial soup" if not treated with biocides. Most outbreaks of the deadly Legionnaires' Disease have been traced to unmanaged cooling towers, and the UK has had stringent Health & Safety guidelines concerning cooling tower operations for many years as have had governmental agencies in other countries. Drinking water treatment

Fouling
The deposition of any undesired material on heat transfer surfaces is called fouling.  Fouling may significantly impact the thermal and mechanical performance of heat exchangers.  Fouling is a dynamic phenomenon which changes with time.
Fouling increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers.  Fouling also impedes fluid flow, accelerates corrosion and increases pressure drop across heat exchangers.
The most common fouling mechanisms are provided below:

Particulate/Sedimentation Fouling

• Scaling
• Corrosion
• Microbes
• Fouling

Corrosion Fouling: Metal oxides which are corrosion products exhibit quite a low thermal conductivity and even relatively thin coatings of oxides may significantly affect heat exchanger performance.	Scaling/Crystallization Fouling: Scaling is the most common type of fouling and is commonly associated with inverse solubility salts such as calcium carbonate (CaCO3) found in water.
Sedimentation Fouling Sedimentation occurs when particles (e.g. dirt, sand or rust) in the solution settle and deposit on the heat transfer surface.	Chemical Fouling: Fouling from chemical reactions in the fluid stream which result in the deposition of material on the heat exchanger surface.  This type of fouling is common for chemically sensitive materials when the fluid is heated to temperatures near its decomposition (degradation) temperature.  Coking of hydrocarbon material on the heat transfer surface is also a common chemical fouling problem.
	Biological Fouling Occurs when biological organisms grow on heat transfer surfaces.  It is a common fouling mechanism where untreated water is used as the coolant.  Problems range from algae to other microbes such as barnacles and zebra mussels.
Chemical Fouling: Fouling from chemical reactions in the fluid stream which result in the deposition of material on the heat exchanger surface.  This type of fouling is common for chemically sensitive materials when the fluid is heated to temperatures near its decomposition (degradation) temperature.  Coking of hydrocarbon material on the heat transfer surface is also a common chemical fouling problem.	Freezing Fouling: Occurs when a portion of the hot stream is cooled to near the freezing point of one of its components.  An example in refineries is when paraffin solidifies from a cooled petroleum product.  Another example is freezing of polymer products on the heat exchanger surface.