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Measure ORP in Ozone System Monitoring?

Measure ORP in Ozone System Monitoring?

2021-03-12

What is ORP?

ORP is a term used frequently in the water treatment and food processing industry. ORP stands for "Oxidation-Reduction Potential." So what does that mean a good working definition is that "ORP is a measure of the cleanliness of the water and its ability to break down contaminants." ORP has a range of -2,000 to +2,000, and units are in "mV" (millivolts). Since ozone is an oxidizer, we are only concerned with positive ORP levels (above 0 mV).


ORP sensor work by measuring the dissolved oxygen. More contaminants in the water result in less dissolved oxygen because the organics are consuming the oxygen and therefore lower the ORP level. The higher the ORP level, the more ability the water has to destroy foreign contaminants such as microbes or carbon-based contaminants. The chart below identifies ORP levels for various applications.


ORP LEVEL (mV)APPLICATION
0-150No practical use
150-250Aquaculture
250-350Cooling Towers
400-475Swimming Pools
450-600Hot Tubs
600Water Disinfection
800Water Sterilization


ORP level can also be viewed as the level of bacterial activity of the water because a direct link occurs between ORP level and Coliform count in water. The chart below lists ORP levels and relative Coliform counts.

ORP LEVEL (mv)COLIFORM COUNT IN 100 ML OF WATER
200300
30036
4003
6000


How does an ORP meter work?

An ORP probe works by creating a small voltaic cell (battery) between the fluid it contains and the solution it is immersed in. The measured voltage is then converted into pH or oxidation/reduction potential. Modern probes have the following components:

The body of the electrode, typically made from non-conductive glass or impact-resistant plastics.

The reference electrode, usually comprised of the same metals as the main electrode.

The junction zone between the studied solution and the reference solution, usually made from ceramics or a capillary with asbestos or quartz fiber.

The reference solution, usually 0.1 mol/L KCI.

The internal electrode, usually made of silver chloride or calomel (Mercury(l) chloride).

The internal reference solution, neutral buffered solution of 0.1 mol/L KCI.

The sensing part of the electrode, a bulb made from a special type of glass.

When using a silver chloride electrode, a small amount of AgCI can precipitate inside the glass bulb.

An ORP meter measures very small voltages generated with a probe placed in ozonated water. The ORP electrode is made of platinum or gold, which reversibly loses its electrons to the oxidizer. A voltage is generated which is compared to a silver (reference) electrode in a silver salt solution, similar to a pH probe. The more oxidizer available, the greater the voltage difference between the solutions.


What's the Ozone?

Ozone, also known as trioxygen, is an elemental molecule consisting of three oxygen atoms. Commonly and naturally occurring in a level of the atmosphere called the stratosphere, the ozone layer is instrumental in protecting Earth from harmful UV light rays and solar radiation. However ozone also has applications beyond atmospheric protection and that is in the water purifying industry, through a process called ozonation.


How does the Ozone generator work?

Ozonation works when water purifiers create and raise ozone concentrations in water to a specified level. This process of creating ozone comes around from an ozone generator, a device which pushes compressed air through a powerful UV light source that creates a chemical reaction much in the same way that the sun is able to. Some of this air is then converted into ozone and the entire gaseous mixture is then sent through a diffuser that mixes ozone-saturated bubbles with water, thus increasing the dissolved ozone concentration. Ozone has been proven to increase water quality by reducing and neutralizing dangerous bacteria and other organisms that are increasingly found in water, by “oxidizing” the bacteria much the same way iron is turned to rust. This oxidation kills harmful microbes that can cause diarrheal diseases and other sicknesses.


What's Relationship between ORP and Dissolved Ozone?

ORP meters are instrumental in the application of ozone and ozone system monitoring. Oxidation-Reduction Potential (ORP) can be used to measure the level of ozone concentrations due to the chemical properties of how ozone reacts with contaminants and oxidizes them. Ozone is negative in nature because of its elemental composition and thus its third oxygen atom is prone to break its covalent bond to the other two oxygen atoms and bind to other bodies, such as bacteria. This binding is called oxidation and it breaks down the bacteria and other contaminants and transforms them into another material that can be sifted out (cleaned) by other filter systems that would normally be unable to cleanse the water of those organisms. ORP meters measure the electric potential, or the level and ability of these negative ozone molecules to break apart and oxidize in water. There exists a correlation between the level of negative electric potential in the water and the level of ozone concentration.

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