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Mixed Oxidant Solution: Frequently Asked Questions

May 12, 2020 4:08:00 PM / by De Nora


There are many jobs and responsibilities in the field of water treatment. For many, knowing exactly what chemicals or procedures are used in the filtration process is not necessary. However, for those considering on-site water treatment understanding the makeup and uses of chemicals and their components is a vital step in the decision-making process. 

Q: What is a mixed oxidant solution? 

A. Mixed oxidant solution (MOS) is made from brine (salt) and energy. It is used for disinfecting, sanitizing and reducing the risk of infection brought on by pathogenic microorganisms in water and other applications. It is particularly useful for customers who have specific challenges, such as controlling biofilm or reducing disinfection byproducts exacerbated by biofilms.

The main components of MOS are chlorine and its derivatives hypochlorite and hypochlorous acid (ClO−, HClO). It also contains trace amounts of other chlor-oxygen species which work synergistically with the hypochlorite/hypochlorous acid to improve efficacy and performance. 

Q: How is MOS made?

A. MOS is produced by electrochlorination. Sodium chloride (NaCl) brine is streamed through a channel with a cathode and an anode. When a low voltage current is applied in the cell, sodium hypochlorite and hydrogen gas are produced. The hydrogen is removed, and the mixed oxidant solution is stored in a tank and used as needed. The only chemical required to generate MOS is ordinary salt (NaCl). The same process is also used to generate standard sodium hypochlorite. 

Although the chemical processes involved are complex, they are represented simply as NaCl + H2 O + ENERGY → NaOCl + H2. In short, energy is added to sodium chloride (table salt) in water, resulting in sodium hypochlorite and hydrogen gas.

Q: How is generating MOS different from generating standard sodium hypochlorite?

A. Both MOS and sodium hypochlorite are generated on-site and on-demand using the process of electrolysis. In fact, from the outside, there’s no discernible difference in the equipment. However, for advanced disinfection needs, the cell in the mixed oxidant generators are optimized for challenging applications. Basically, more power is applied to the solution, which is achieved via design modifications to the cell and operating conditions.

Q: If the generation process is the same, what’s the difference between sodium hypochlorite and MOS?

A. Chlorine-based mixed oxidant solution has all the oxidant power of sodium hypochlorite with additional treatment benefits, including biofilm removal, disinfection byproduct (DBP) reduction, improved taste, odor removal and water clarification. With a mixed oxidant solution, customers maintain more consistent control and residuals with a lower dose.

Q. What is MOS used for?

A. Mixed oxidant solution can be used for a variety of water treatment applications, including: 

  • Cooling water treatment
  • Industrial process water and wastewater treatment
  • Cooling tower water treatment
  • Aquatics (swimming pool disinfection)
  • Drinking water & beverage facilities
  • Municipal wastewater
  • Farm applications
  • Oil & gas water management

Q. How does the efficacy of MOS compare to standard sodium hypochlorite? 

A. Several peer-reviewed publications have published articles demonstrating the superior efficacy of MOS compared to sodium hypochlorite. MOS benefits were proven via extensive comparative studies using four microorganisms, two different temperatures and three separate pH values. 

The microorganism tested were Escherichia coli, Vibrio cholera, Clostridium perfringens spore and MS2. For each of these conditions, MOS performed better, even at low temperature and higher pH than chlorine. Years of compiled field data also show other varied differences in the efficacy of MOS.

Source: DNWT – Mixed Oxidant Solution: Frequently Asked Questions, 7/2019

Still Have Questions? 

Check out this FREE, easy-to-understand, technical overview of electrochemical generation, created by Chief Scientist, Andrew Boyle PhD. Click below for more information.


Tags: water treatment, sodium hypochlorite, MOS, mixed oxidant solution, biofilm, electrochlorination

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