Electrolyzed Oxidizing Water (EOW)

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Electrolyzed Oxidizing Water (EOW) is a Japanese invention, developed to inactivate a variety of microorganisms. Major advantages of using EOW for the inactivation of microorganisms are less adverse impact on the environment and no need for storage and transport of potentially hazardous chemicals.

Contents

Description

EOW is obtained by passing a dilute salt solution (NaCl) through a cell, which has on each side a cathode or an anode, respectively. This cell is separated by a membrane in the middle. By applying a direct current voltage on both electrodes, negatively charged ions (OH- and Cl-) will move to the anode side and give up electrons. This will result in the formation of oxygen gas, chlorine gas, hypochlorite ion, hypochlorous acid and hydrochloric acid. The positively charged ions (H+) will move to the cathode side to take up electrons and become hydrogen gas and sodium hydroxide. This shift will result in two types of water: an Electrolyzed Basic Solution (EBS) from the cathode side and Electrolyzed Acid Solution (EAS) from the anode side. EBS (pH=11.4; low ORP; -795 mV) has a strong reducing power and can be used as a cleaning agent, while EAS has a great oxidation potential and can be used as a disinfectant (pH<3; high ORP; 1,150 mV, HOCl).

The following table provides an overview of the components formed. The amount of free chlorine components is dependent of:

Component Concentration (mg/L)
Sodium chloride (NaCl) 4237
Sodium hypchloride (NaOCl) 148
Sodium chlorate (NaOCl3) 6.4
Sodium perchlorate (NaOCl4) 32.7
Chlorine dioxide (ClO2) <0.4
Ozone (O3) 0.7
Hydrogen peroxide (H2O2) 0.03

During storage of EOW, the redox potential will reduce. This is the result of the reduction of the active chlorine components. This is mainly due to the operation of UV light and less due to the temperature during storage (higher temperature, faster reduction). UV light results in photo decomposition of the chlorine components and next to this evaporation of chlorine will take place.

There is also a possibility to produce Neutral Electrolyzed Oxidation Water (NEOW). This is made, by removing the membrane, so that the components mix. Another option is to add produced cathode water to the anode side. Advantages of this type of water are that it is less corrosive for equipment and less irritating for hands than EAS. It is also more stable, because the higher pH results in less loss of chloride. However there are signs of less antimicrobial activity.

Scope

The formed components in EOW production each have an antimicrobial effect. HOCl, present in the EAS (acid solution from the anode side), is a disinfectant. NaOH is also a disinfectant (less strong), present in the EBS (basic solution from the cathode side). There are only a few MO’s able to survive acid conditions, thence is why EAS is a good disinfectant. EBS can also be used, but works at a smaller range of MO’s. This is partly due its lower redox potential. Another reason for the inactivating effect of EOW is the presence of hypochlorite acid. This component penetrates the cell wall of the bacteria and disrupts the membrane transport proteins and the energy production of the bacteria. EOW has a larger impact on the inactivation of MO’s than the individual components at the same concentration. Only gaseous COCl2 has a larger log reduction than an equivalent amount of EOW. EOW is also able to inactivate spores, when the concentration chlorine and contact time is high enough. The components in EOW do not react with MO’s only, but also with organic matter. The amount of organic matter has a large impact on the level of inactivation. This is also demonstrated in sewer water. So for applying EOW in the inactivation of MO’s in for example process water, a filtering step should be added to remove organic matter.

Medical sector

Water treatment

Food technology

Agricultural sector

Other

Pros and cons

Pros

Cons

Available equipment

Some companies that are selling EOW equipment are:

Costs

Investment costs for EOW equipment are relatively low and require furthermore only water, salt and electricity.

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