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Water Problems - Acidic Waters

Waters of the South Western Cape from the Coast to 200 km inland suffer from acidic and corrossive water caused in part from the fynbos and plant matter in the run-off of this area.
Ongoing research by various departments of the University of Cape Town in conjunction with the CSIR and often funded by the Water Research Commission have been studying this phenomena for over 7 years.

While solutions have been put forward and tested in the form of pilot projects the process is still not inexpensively available to the general public unless you are prepared to wade through research documents

Adjusting pH and alkalinity is the most common corrosion control method because it is simple and inexpensive. pH is a measure of the concentration of hydrogen ions present in water; alkalinity is a measure of water’s ability to neutralize acids.

Generally, water pH less than 6.5 is associated with uniform corrosion, while pHs between 6.5 and 8.0 can be associated with pitting corrosion. Some studies have suggested that systems using only pH to control corrosion should maintain a pH of at least 9.0 to reduce the availability of hydrogen ions as electron receptors.

However, pH is not the only factor in the corrosion equation; carbonate and alkalinity levels affect corrosion as well.
Generally, an increase in pH and alkalinity can decrease corrosion rates and help form a protective layer of scale on corrodible pipe material. Chemicals commonly used for pH and alkalinity adjustment are hydrated lime (CaOH2 or calcium hydroxide), caustic soda (NaOH or sodium hydroxide), soda ash (Na2CO3 or sodium carbonate), and sodium bicarbonate (NaHCO3, essentially baking soda).

Care must be taken, however, to maintain pH at a level that will control corrosion but not conflict with optimum pH levels for disinfection and control of disinfection by-products.

P&B Lime manufacturers of Bredasdorp are the only acredited Lime suppliers who are able to supply the correct grade and efficient product for this purpose. There product Aquastab+ is available in 25kg & 1 Ton bags to be used in the small scale system which was developed both by P&B and the CSIR. While this small scale system is not designed for the domestic residence and variation is available from some water solution providerfs at a hige price.

A simple method of suspending the contents in a hessian bag in your reservoir or dam does the job just as effectively and saves you many thousands in outlay.

Corrosion Inhibitors
Inhibitors reduce corrosion by forming protective coatings on pipes. The most common corrosion inhibitors are inorganic phosphates, sodium silicates and mixtures of phosphates and
silicates. These chemicals have proven successful in reducing corrosion in many water systems.

The phosphates used as corrosion inhibitors include polyphosphates, orthophosphates, glassy
phosphates and bimetallic phosphates. In some cases, zinc is added in conjunction with
orthophosphates or polyphosphates. ( Clarophos, Siliphos and Microphos to name a few brands)
Glassy phosphates, such as sodium hexametaphosphate, effectively reduce iron corrosion at
dosages of 20 to 40 mg/l. Glassy phosphate has an appearance of broken glass and can cut the operator. Sodium silicates have been used for over 50 years to inhibit corrosion. The effectiveness depends on the water pH and carbonate concentration.

Sodium silicates are particularly effective for systems with high water velocities, low hardness, low alkalinity and a pH of less than 8.4. Typical coating maintenance doses range from 2 to 12 mg/1. They offer advantages in hot water systems because of their chemical stability. For this reason, they are often used in boilers of steam heating systems.

Corrosion Control
Corrosion is the deterioration of a substance by chemical action. Lead, cadmium, zinc, copper and iron might be found in water when metals in water distribution systems corrode. Drinking water contaminated with certain metals (such as lead and cadmium) can harm human health.
Corrosion also reduces the useful life of water distribution systems and can promote the growth of microorganisms, resulting in disagreeable tastes, odors, slimes and further corrosion. Because it is widespread and highly toxic, lead is the corrosion product of greatest concern.

While the EPA has banned the use of lead solders, fluxes and pipes in the installation or repair of any public water system these products are still widely used in South Africa.It is common knowledge that EPA regulations are of a far higher standard than the South African Water Quality Guideline , otherwise referred to as SABS 241: Domestic Water.  In the past, solder used in plumbing has been 50% tin and 50% lead. Using lead-free solders, such as
silver-tin and antimony-tin is a key factor in lead corrosion control.

The highest level of lead in consumers’ tap water will be found in water that has been standing in the pipes after periods of nonuse (overnight or longer). This is because standing water tends to leach lead or copper out of the metals in the distribution system more readily than does moving water.
Therefore, the simplest short-term or immediate measure that can be taken to reduce exposure to lead in drinking water is to let the water run for two to three minutes before each use. Also, drinking water should not be taken from the hot water tap, as hot water tends to leach lead more readily than cold.

Long-term measures for addressing lead and other corrosion by-products include pH and alkalinity adjustment; corrosion inhibitors; coatings and linings; and Cathodic protection, all discussed below.

Cathodic Protection
Cathodic protection protects steel from corrosion which is the natural electrochemical process that results in the deterioration of a material because of its reaction with its environment.
Metallic structures, components and equipment exposed to aqueous environments, soil or seawater can be subject to corrosive attack and accelerated deterioration.

Therefore, it is often necessary to utilize either impressed current or sacrificial anode Cathodic protection (CP) in combination with coatings as a means of suppressing the natural degradation phenomenon to provide a long and useful service life. However, if proper considerations are not given, problems can arise which can produce unexpected, premature failure.

There are two types of Cathodic protection:
 Sacrificial Anodes (Galvanic Systems)
 Impressed (Induced) Current Systems

How Does Cathodic Protection Work ?
Sacrificial anodes are pieces of metal more electrically active than the steel piping system.
Because these anodes are more active, the corrosive current will exit from them rather than the piping system. Thus, the system is protected while the attached anode is “sacrificed.”
Sacrificial anodes can be attached to existing piping system or coated steel for a pre-engineered Cathodic protection system. An asphalt coating is not considered a suitable dielectric coating. Depleted anodes must be replaced for continued Cathodic protection of the system.