Chlorine or Hydrogen Peroxide – Which is Better for Treating Water?

Chlorine or Hydrogen Peroxide – Which is Better for Treating Water?

The water treatment industry has used Chlorine (Cl2) for well over a hundred years. Chlorine gas was used in Belgium in 1903 to disinfect drinking water. In 1908, Jersey City, New Jersey, used the first liquid chlorine to disinfect water (sodium hypochlorite). In the 1950s, Eastern Europe was the first to use hydrogen peroxide (H2O2) for drinking water disinfection. H2O2 is known for its high oxidative and biocidal efficiency. Hydrogen peroxide has not been used often for drinking water disinfection, but its popularity seems to increase each year.

The use of chlorine in drinking water has always been prevalent since it first being introduced, and it remains popular. The linchpin for chlorine is that it is an excellent disinfectant. Chlorine is toxic to pathogens and very effective, but chlorine can be harmful not only for microorganisms but also for humans. Chlorine is an eye irritant to humans and an irritant to nasal passages and the human respiratory system. Chlorine is an excellent disinfectant but not a strong oxidizer, which is where H2O2 breaks from chlorine.

Hydrogen Peroxide

Hydrogen peroxide is a strong oxidizer. In fact, it is more potent than chlorine (Cl2), chlorine dioxide (ClO2), and potassium permanganate (KMnO4). Also, through catalysis, hydrogen peroxide can be converted into hydroxyl radicals (OH). This blog is not to say that one technology is better than the other, but rather to make you aware of what chlorine can and cannot do and understand what role the use of hydrogen peroxide can play in water treatment.

On major advantage that H2O2 has over chlorine is that it does not form Disinfection By-Products (DBP’s) like trihalomethanes (THM) which are known carcinogens. Whenever chlorine is used, you must follow it with the correct amount of granular activated carbon (GAC) to remove the DBP’s effectively. Hydrogen Peroxide, on the other hand, does not seem to produce such DBP’s.

Water treatment professionals may have to change their thinking when comparing hydrogen peroxide to chlorine because they are two different animals. One is an excellent disinfectant (chlorine), but the other is a great oxidizer (hydrogen peroxide) and how they are utilized is dramatically different.

Chlorine requires contact time, which is typically 20 minutes for every gallon per minute of flow. Therefore, if you are flowing 10 GPM, you need 200 gallons of contact time (10 GPM x 20 minutes = 200 GPM). On the other hand, hydrogen peroxide is not a good disinfectant but rather an excellent oxidizer. It does not require contact time. Contact time only dilutes its ability to oxidize. Therefore, you do not want to use hydrogen peroxide with a retention tank.

Hydrogen Peroxide VS Chlorine

If you haven’t already figured it out – hydrogen peroxide is not a good idea for disinfection; the same as chlorine is not a good idea for oxidation. If you have surface water and need to disinfect it, especially if there is algae, then chlorine is dramatically superior to hydrogen peroxide. However, if you have incredibly high iron or sulfur, chlorine is not a good choice, but hydrogen peroxide is. Removing iron and sulfur is best accomplished with oxidation, and H2O2 is an excellent oxidizer.

Just do not confuse oxidation and disinfection. The definition of disinfection is “the process of cleaning something, especially with a chemical, to destroy bacteria.” Oxidation, on the other hand, is different. The terms oxidation and reduction can be defined by adding or removing oxygen to a compound. Both reduction and oxidation coincide, so we call that a “redox reaction.”

As stated, hydrogen peroxide has the chemical formula H2O2 and is an oxidizing agent similar to oxygen in effect but is significantly more robust. The oxidizing activity of hydrogen peroxide results from the presence of the extra oxygen atom compared with the structure of water. I like to say that “Hydrogen peroxide is very forgiving.” What I mean by that is that (when applied correctly) extreme amounts of iron and hydrogen sulfide can be removed from the water supply effectively and consistently.

Many water treatment specialists have been involved in the pioneering of hydrogen peroxide technology… even before me. Still, in my 25+ years of using H2O2, I doubt that anyone has sold the vast number of systems that we have. I will be the first to admit that we made a lot of mistakes in the beginning. Among them are the following:

  • We used to use a contact tank or inject H2O2 ahead of a pressure tank – all that did was slow the oxidation process. Now we inject it just ahead of a catalytic carbon tank.
  • We used to use a static mixer – all that did was knock out some of the air bubbles and weaken the reaction. No static mixer is needed. In fact, a static mixer is counter-productive.
  • We used to use a flow switch to activate the H2O2 pump (or hook it up to the pressure switch so that it ran when the pump ran – now we use a meter and proportional injection system that injects the “precise amount” of H2O2 regardless of whether the flow is 1 GPM or 18 GPM.
  • We used to use regular hydrogen peroxide, which “decomposes” quickly – now we have it “stabilized” so that it does not decompose and remains at maximum strength for over a year.

We Still Have Love For Chlorine

It’s not that we hate chlorine – it is necessary in many cases – but we prefer hydrogen peroxide for iron and sulfur eradication. The only drawback to a H2O2 system is that you will have an annual peroxide bill of $200 to $600/year, but that is insignificant to having amazing iron and sulfur-free water.

What about maintenance? Of course, all water is different, and water chemistry is vitally important. “Competing contaminants” can affect the efficacy of H2O2 as an oxidizer. Therefore, a detailed laboratory water analysis is paramount with H2O2, chlorine, or any other type of water treatment.

If you inject chlorine, I would advise you to become intimately acquainted with your chemical injection pump (or have someone on speed dial to service it) because chemical injection pumps typically have issues with chlorine. It degrades the rubber parts or tubes, necessitating repair and maintenance (typically a couple of times a year… if you are lucky). Additionally, chlorine frequently crystallizes at the “injection point,” also necessitating disassembly and cleaning of the injection fitting.

When injecting hydrogen peroxide, we always use a Stenner Peristaltic Pump because this type of pump injects much more consistently. The H2O2 does not cause issues with degrading the rubber parts or tubes. Additionally, it does not crystalize at the injection point. We have been using these pumps for 25+ years,

and it is not unusual for a pump to go 5 to 10 years without any maintenance. Zero!

Typically, the catalytic carbon in the tank needs replaced about every five years, but it could be more or less frequent… depending upon the water analysis and daily usage. Since we sell systems all over the United States, we need a technology that is very forgiving and nearly foolproof! Hydrogen Peroxide is generally the best solution for sulfur and high levels of iron. It’s not perfect, but it is closer than any other technology found at a price that you can afford.

Overall, hydrogen peroxide is more expensive than chlorine and works best when iron and sulfur are present in the water supply. Since it works faster than chlorine, no contact tank is required. Additionally, H2O2 is effective at a more comprehensive pH range, meaning that it is more effective on more types of water.

June 9, 2021
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