neutralisation – remineralisation

pH correction treatment that consists in adjusting the pH of a water to a specific figure and often wrongly covered under the general term ‘neutralisation’, can be involved in the following areas of utilisation:

• neutralising various types of effluent before they are discharged into the natural environment: acid or alkaline industrial effluent, acid mine drainage water, etc…;
• pH correction before a biological or physical chemical treatment stage (e.g. flocculation pH adjustment);
• acidification upstream from a desalination membrane, industrial circuit vaccination (see chapter treatment and conditioning of industrial water);
• correcting the calcium-carbonate balance to protect structures and distribution pipelines against corrosion (by encouraging the formation of a protective pipeline carbonaceous lining) or scaling.

The last point alone will be addressed in greater detail in this subsection because it constitutes one of the major steps in drinking water treatment.

All treatment and distribution structures are concerned and there are a number of stakes involved:

• consumer health protection:
  • eliminating the danger of toxic metals dissolution, e.g. lead and copper;
  • eliminating the risk of "red water" at the tap (corroded cast iron or steel pipelines);
  • maintaining residual chlorine in the systems (any deterioration to structures will result in increased consumption of residual disinfectant);
  • maintaining network "integrity" (no leaks) and thus ensuring that it is less vulnerable to incoming soiled water;

• safeguarding assets:
  • protecting against corrosion that creates leakages and fractures;
  • protecting against scaling that creates increased head losses and, therefore, additional energy costs, jammed hydraulic units (e.g. valves…).

In the absence of conditions encouraging the formation of a protective carbonaceous layer (see section treatment objectives), distribution pipelines can also be protected:

• against corrosion by applying a treatment based on corrosion inhibitors and which forms a film (see chapter corrosion in metal and concrete);
• against scaling, especially caused by salts other than calcium carbonate, by chemical treatment of the water. These treatments are usually applicable to industrial circuits where the presence of ions that are "harmful" to the consumer is less critical (see sections industrial water or treatment and conditioning of industrial water).