When water treatment is mentioned, the first thing comes to your mind should be chlorine. Chlorine has been widely used for tap water disinfection and purification for decades. But today, chlorine’s dominance in water treatment field is under challenge. The challenge comes from ozone. Ozone water treatment with ozone water generators has become more and more popular for home, business, and industrial use. In this blog, we will compare the use of chlorine and ozone in water treatment from several aspects.
Chlorine is a nonmetallic element. Chlorine gas at room temperature and pressure is a yellow-green gas with a strong pungent smell. It is chemically active and toxic. The earliest use of chlorine to disinfect water appeared in Britain at the end of the 19th century. Today, tap water is disinfected by adding sodium hypochlorite to the water as a disinfectant. When sodium hypochlorite is hydrolyzed, it forms hypochlorous acid, which is effective in killing bacteria, viruses, and microorganisms in water.
Ozone is a bluish gas at room temperature and pressure. As an allotrope of oxygen, each ozone molecule consists of three oxygen atoms instead of two in an oxygen molecule. With this kind of structure, ozone has a strong oxidizing effect and becomes a very good disinfectant. In ozone water treatment, firstly, ozone gas will be generated by the generating equipment. Ozone gas will then be dissolved into water. With ozone gas dissolved, the ozone water will kill various kinds of organic and inorganic compounds and microorganisms in water with its strong oxidation property. For more knowledge of ozone, you can refer to our previous blog An Introduction of Ozone.
Ozone has been used in water treatment since the late 1800s. The world’s first drinking water plant using ozone for water treatment emerged in France in 1906. But for years, ozone has not been widely used for some misunderstandings. As a matter of fact, ozone is safe to clean and disinfect in both home and business environments as long as it is safely applied. Furthermore, compared with chlorine and other chemical disinfectants, ozone has the advantage of being non-toxic in water treatment process.
Ozone Water Treatment vs. Chlorine Water Treatment
Ozone is the most powerful oxidizer than can be used in water treatment. By comparison, ozone disinfects and purifies water thousands of times faster than chlorine. The disinfection effect of 1 ppm ozone water will be equal to that of 50 ppm chlorine solution.
Ozone is effective in treating both organic and inorganic pollutants, including bacteria, viruses, and protozoa that cause water pollution. Ozone can also be used to solve odor problems caused by microbial reproduction. Chlorine is also used to kill bacteria and viruses. But for protozoa, chlorine can do nothing. Moreover, appropriate dose of ozone can kill pathogens that either cannot be killed by chlorine.
One problem in water disinfection and purification with chlorine is that there will be certain amount of chlorine and by-product such as trihalomethanes left in water after treatment. When ozone is used, there will be no residues or any by-products left in water after treatment. If there is excess amount of ozone dissolved in water in the treatment process, it will turn itself into oxygen and thus produce no harmful substances. Ozone can even be used to treat residues and by-products in chlorinated water. Furthermore, with its flocculation function, ozone also makes it easier to remove minerals such as iron and manganese which are sometimes present in water.
Unlike chlorine, which is less effective in purifying water with higher pH values, ozone works regardless of the pH value of water. And at the same time, the original pH value of water will remain after the treatment. The effectiveness of ozone water treatment can simply be measured by a commonly used OPR meter.
When corrosivity is mentioned, ozone is also less corrosive than chlorine. As a result, ozone dissolved in water will not cause irritation to nose, ears or skin. Ozone also does better than chlorine in keeping the original taste of water. Chlorinated water often contains bleach smell while ozone-treated water doesn’t.
In addition, there is no need to consider ozone storage when it is used for water treatment. Reason 1 is that when ozone is used, it will be generated on spot. Reason 2 is that ozone’s highly oxidizing property makes it hardly possible for storage.
One thing that we probably know most about tap water is that it is not suitable for fish to live in. If tap water needs to be used for fish, it needs to be kept for two or three days for chlorine element to evaporate from water.
Well, that is a common sense in our daily life. For our health, what is believed is that people who drink chlorinated water over long period of time will have a higher risk of developing cancer than those who don’t. According to a study, women with breast cancer in the United States have been found to have around 50% more chlorine compounds in their breast tissue than average. Not only that, people who drink too much chlorinated water over a long period of time are at a greater risk of arteriosclerosis, heart disease and stroke. This is why there is a growing tendency to replace conventional chlorine with ozone in water treatment field. Today, in some cattle breeding sites, more and more dechlorinated water is used for drinking needs.
Ozone Represents the Future
For what we have talked above, ozone is becoming a better choice for water treatment application. Ozone today is increasingly used in industrial water treatment, large swimming pools, aquariums, and municipal wastewater treatment projects, etc. In recent years, with the ongoing technical progress in ozone generating equipment, the cost of investment of ozone water treatment has declined. Ozone water treatment will be more cost-efficient in the long run. Therefore, ozone represents the future trend of the water treatment industry no matter for financial investment or health concerns.