Sanitizing Using Salty Water

Using salt water chlorination to sanitize swimming pools is the most effective and most environmentally friendly method of all.

Let us consider chlorine as a sanitizer, how it is made, and how it can be used.


CHLORINE AS A SANITIZER

Chlorine is the most common swimming pool sanitizer in the world. It is produced in various forms.

Chlorine compounds:

1. Dry chlorine
   (calcium hypo-chlorite)
   65% Chlorine
   
2. Di-chlor
   (Sodium dichloro-isocyanurate)
   63% Chlorine
   
3. Tri-chlor
   (Sodium trichloro-isocyanurate)
   69% Chlorine
   
4. Liquid Chlorine
   (Sodium hypo-chlorite)
   12.5% Chlorine
   
5. Elemental Chlorine:
   Chlorine Gas
   100% Chlorine
   

When one of the chlorine compounds or chlorine gas is added to a swimming pool, the active constituent, chlorine, kills and oxidizes the various impurities in the water, thus making the water bacteria free. The oxidized impurities are removed from the water as the water passes through the swimming pool filtration system.

THE MANUFACTURE OF CHLORINE

Water is a compound of the gases hydrogen and oxygen. Common table salt is a compound of sodium and chloride. Common table salt has the chemical name Sodium Chloride. When salt is dissolved in water, the sodium and chloride break apart to form free sodium ions and chloride ions.

At a chlorine factory very large shallow containers of concentrated salt solution are constructed so that very powerful electrical currents are passed through the concentrated salt solution.

In simple terms, there are two major byproducts resulting from the electrolysis of salt water: Chlorine gas, and Hydrogen gas. The chlorine gas is formed at the positive electrode (anode) and the hydrogen gas is formed at the negative electrode (cathode). This technique is known as "electrolysis".

The chlorine gas dissolves in the water, and the hydrogen gas rises to the top of the salt water solution. Later in the process, at the chlorine factory, the dissolved chlorine gas is recovered from the salt water and compressed and stored, ready for sale. The hydrogen gas is released harmlessly. In practice, there are two major products of a chlorine production plant, chlorine gas and sodium hydroxide (NaOH). The chlorine gas may be combined with other chemicals to form the various chlorine compounds mentioned earlier.

THE ADDITION OF CHLORINE TO SWIMMING POOLS

It is generally recommended that home swimming pools are sanitized by the daily addition of a chlorine compound.

When using liquid chlorine or dry chlorine, it is customary that either the chlorine is added manually, on a daily basis, or perhaps may be fed into the swimming pool by some form of dosing pump.

When liquid or dry chlorine compounds are added to the swimming pool, there is usually a residue left over, after the active ingredient, chlorine, comes out of its compound to do the sanitizing work. In simple terms, the residue from liquid chlorine is salt (sodium chloride) and the residue from dry chlorine is calcium hydroxide. These residues stay in the pool water and build up over years.

Experimental work was conducted by several companies in a few countries in the early 1970s, whereby some primitive techniques were developed to produce chlorine in a miniature "chlorine factory" adjacent to the swimming pool filtration system. It was intended that the chlorine produced would somehow be injected under pressure, or otherwise added to the swimming pool water.

Two basic techniques were tried:

1. The addition of salt to the swimming pool water, and the electrolysis of this salty solution either by an electrode hanging in the water, or by electrodes fitted within the PVC pipework at the filtration system.
   
2. The generation of chlorine gas in a special vessel filled with concentrated salty water, and the collection of the chlorine gas for injection directly into the swimming pool water re-circulation system.
   

The first-mentioned technique became the dominant technique, being safer and easier to install.

These early salt water chlorinator designs were modified and improved to the extent that the salt water chlorinator is reliable, economical and effective. After 20 years of constant development, the technique has become standard practice for the Australian pool equipment industry. In the US, salt water chlorination is very quickly being adopted as the sanitation method of choice by pool builders and service professionals across the country.