CHLORINE AS A SANITIZER

SANITIZING USING SALT 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 pipe work 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 and Canada, salt water chlorination is very quickly being adopted as the sanitation method of choice by pool builders and service professionals.

ZODIAC SALT WATER CHLORINATION COMPARED WITH CHEMICAL TREATMENT

Zodiac is often asked to explain how a salt system works, how the chlorine is produced, and how it is different from the chlorine which is available in the form of granular chlorine, liquid chlorine, or chlorine tablets. The following information is presented in a question/answer format to cover the most frequently asked questions by engineers, swimming pool operators, or perhaps swimming pool owners.

All the commercial production of chlorine gas throughout the world uses the same basic technology as used by Zodiac Salt Systems.



IS THE CHLORINE PRODUCED BY A SALT WATER CHLORINATOR DIFFERENT TO THE CHLORINE IN GRANULAR CHLORINE OR LIQUID CHLORINE?

Sanitizing a pool with a Zodiac Salt System uses a similar technique as sanitizing the same pool in other chlorine forms. The most common form of chlorine used for manually sanitizing pools is either granular chlorine, or sodium hypochlorite (sometimes called liquid chlorine). Commercial pools which do not use a salt system use a variety of forms of chlorine, including chlorine gas.

Note that calcium hypochlorate contains 65% chlorine, sodium hypochlorite contains approximately 12.5% chlorine, but the chlorine produced by a Zodiac Salt System is 100% chlorine.

The chlorine produced by a Zodiac Salt System is exactly the same element (chlorine) as is contained within sodium hypochlorite and calcium hypochlorate. In other words, the active sanitizing agent for all of these methods is the same....chlorine.



DOES A ZODIAC SALT SYSTEM PRODUCE CHLORINE IN ANY DIFFERENT WAY TO THE PRODUCTION OF GRANULAR CHLORINE OR LIQUID CHLORINE?

Mass chlorine production in huge chlorine factories uses exactly the same basic technique as is used by a Zodiac Salt System. This technique involves the passage of electric current through salty water to produce chlorine gas at the positive electrode (anode).



WHAT IS THE CHEMICAL REACTION AND FORMULA?

The chlorine produced by a Zodiac Salt System is a product of salt water. The process may be explained in chemical terms by the formula below.



(Salt + Water + Electricity produces Hypochlorous acid and Hypochlorite ions + Sodium Hydroxide.)

The formula does not mention chlorine gas, because the chlorine dissolves immediately as part of the reaction. (The elemental chlorine gas produced at the anodes in the electrolysis process dissolves immediately into the water to form hypochlorous acid and hypochlorite ions.)

This is the same chemical reaction as occurs at commercial chlorine manufacturing facilities.

It is the hypochlorous acid and to a lesser extent, the hypochlorite ions that perform the sanitizing function in the swimming pool.



HOW DOES THE ZODIAC SALT SYSTEM PUT THE CHLORINE INTO THE WATER?

The Zodiac cell produces elemental chlorine gas in the water, and the chlorine produced is exactly the same as other types of chlorine used for swimming pool sanitization.

Regardless of whether the chlorine comes from the electrolytic action of a Zodiac cell, or from the chlorine contained in granular chlorine or liquid chlorine, the chlorine dissolves into the water to form hypochlorous acid and hypochlorite ions.

It is actually these two components which are the active sanitizers in pool water. Hypochlorous acid is a strong sanitizer and hypochlorite ions are a weak sanitizer. It is important that the pH of the water is correct to ensure a high proportion of hypochlorite acid, and therefore, the most effective sanitizing of the pool.



WHY IS ZODIAC SALT SYSTEM BETTER THAN TRADITIONAL METHODS?

The reasons why sanitizing using a Zodiac Salt System is better than other techniques are as follows:

a) Zodiac Salt Systems manufacture and deliver chlorine to the swimming pool automatically. The pool owner no longer needs to purchase, transport, store or manually add chlorine as part of their routine maintenance.

b) Not only is the water passing through the cell subjected to the sanitizing effect of the chlorine being introduced into the water, but as the water passes between the positive and negative electrodes, the bacteria, and algae are subjected to a very strong electric field which oxidizes these contaminants. These contaminants and others, including sunscreen, lotion, and body oils, etc are doubly attacked when using a Zodiac cell. They are destroyed not only by the chlorine in the water, but also by the electric field within the electrodes.

c) Zodiac manufactures and delivers chlorine to the pool in a constant and controlled manner. Because a Zodiac salt system is part of the filtration system, the sanitizing takes place every time the filtration system is switched on. There is less reliance on the human factor.

d) Say good-bye to red stinging eyes, skin irritation and harsh chemical odors. In general, whenever swimmers enter chlorinated water, chloramines are formed. This occurs because the body wastes, perspiration and skin oils all contain amine compounds which react with the chlorine in the water. If the chlorine only partly oxidizes (destroys) the amine compounds, "chloramines" are formed.

Chloramines are unpleasant smelling substances which sting the skin, cause eyes to become red and sore, and in extreme cases (high concentrations and allergic individuals), can cause skin rashes.

The major scientific benefit offered by salt water chlorination in the sanitizing process is that not only is there a sanitizing action in the swimming pool resulting from the free chlorine residual in the water, but there is a far more powerful sanitizing action which takes place in the cell itself.

As the water passes between the electrodes, the chloramines in the water are destroyed as they pass through the cell. Only a salt water chlorinator can destroy chloramines in this way.



WHY IS THE ADDITION OF CHLORINE STABILIZER (CYANURIC ACID) NECESSARY WHEN USING A ZODIAC (OR ANY OTHER) SALT SYSTEM?

This chemical acts as a sunscreen for chlorine and prevents it from being too quickly destroyed by the sun. Chlorine stabilizer is essential to prolong the life of chlorine in the pool water. Although some types of chlorine (dichlor and trichlor) already contain stabilizer, the chlorine gas produced by a Zodiac salt system does not. Chlorine stabilizer cyanuric acid must therefore be added to the pool water when using any salt system.