Measure Ozone in water with ORP Meters
ORP Meters Defined
ORP stands for oxidation-reduction potential. It is a measure of the ability of a solution to oxidize or reduce other substances. ORP may also be referred to as redox Potential.
ORP levels in water can be measured with an electronic ORP meter. ORP meters use electrodes in water that measure the voltage difference between the two electrodes. Water with a higher potential to lose electrons (oxidize) will create a higher ORP reading, measured in Millivolts (mv). Lower, (potentially negative) ORP values indicate the water is more reducing.
ORP is an important parameter in water treatment, as it can be used to monitor the effectiveness of disinfectants and to prevent corrosion. For example, ORP is used to monitor the chlorine levels in swimming pools to ensure that the water is properly disinfected.
ORP can also assess drinking water quality; higher ORP generally indicates better water quality. than water with a low ORP value.
Here are some of the factors that can affect ORP in water:
- Dissolved oxygen: water with greater levels of dissolved oxygen will have a higher ORP value,
- pH: pH also affects ORP. In general, ORP decreases as pH increases.
- Other oxidizers or reducers: Other oxidizers, such as chlorine and ozone, will increase the ORP of water. Other reducers, such as sulfides and iron, will decrease the ORP of water.
ORP meters are generally very reliable, easy to use, and respond quickly to changes in water quality. Therefore, ORP meters are commonly used in water treatment processes as a tool to verify water quality.
Using ORP to measure Dissolved Ozone
ORP meters can also be used to measure dissolved ozone levels in water. ORP is a measure of the oxidation-reduction potential of a solution, which is a measure of its ability to oxidize or reduce other substances. Ozone is a strong oxidizer, so it will increase the ORP of water.
However, there are a number of other factors that can also affect ORP, such as pH, dissolved oxygen level, and the presence of other oxidizers or reducers in the water. This means there is no direct correlation between ORP values and dissolved ozone levels in water.
ORP meters can be calibrated, or correlated to a known dissolved ozone levels in a specific water source. Provided other water quality parameters remain stable, this correlation between dissolved ozone and ORP can remain stable and consistant. In addition, ORP is extremely valuable as a tool to indicate general water quality, and an increase, or decrease of dissolved ozone levels in water.
These tools can be used to measure ozone in water for correlation purposes:
Some advantages of ORP Meters
Due to the measurement principle of simple electrodes in water ORP meters are generally very reliable, and provide very stable measurements. Calibration of ORP meters is fairly simple with readily available buffer solutions. In addition, ORP sensors can be very low cost and simply replaced on a schedule to eliminate any calibration requirements.
In some application with poor water quality, a dissolved ozone sensor may not be a reliable option due to the sensitive membrane and electrolyte that are used to measure dissolved ozone. As ORP uses simple electrodes in water it may offer reliability, and stability of ORP (and therefore ozone) levels in this water. In essence, ORP meters can be used where dissolved ozone meters may not be an option.
ORP meters can also be used in conjunction with a dissolved ozone meter to provide an additional reference. For example, if 1.0 ppm of ozone in water normally indicates 900-950 mV of ORP in this application, when a great disparity to these values is indicated a potential issue with the water treatment system can be detected, and corrected faster, and potentially with automation.
Due to the simplicity of the measurement principle ORP meters implement, water quality changes will be indicated quickly with an ORP meter. Overall response times of dissolved ozone levels in water will typically be detected faster with an ORP meter than with a dissolved ozone meter.
Dissolved ozone meters are very pressure dependent. Many dissolved ozone meters require specialized flow-cells to flow water past the sensor at a specific flow-rate and pressure for accurate measurement of dissolved ozone. Conversely, ORP sensors operate across a much wider pressure range and can be inserted directly into water the water stream itself with much less concern for water pressure changes, and specific water flows over the sensor.
Some disadvantages of ORP Meters
There is no reliable correlation of ORP values to dissolved ozone values. As ORP values are affected by dissolved oxygen levels in water, PH values, and many other water chemistry components a correlation between ORP and dissolved ozone must be created with the specific water source in question. In addition, as water chemistry changes, the correlation between ORP and dissolved ozone may also change.
Due to the fact ORP is not a direct indication of ozone levels in water it does not offer the same accuracy of an actual dissolved ozone meter. If accuracy is required, a high quality dissolved ozone meter should be implemented.
Ozone is a potent oxidizer. When dissolved in water, ozone significantly increases the ORP due to It’s strong oxidation potential. Due to this fact an ORP meters maximum detection limits will be reached quickly as ozone levels in water increase. Measuring dissolved ozone levels greater than ~1.0 ppm with repeatability with an ORP meter can be challenging. Ozone levels above ~1.0 ppm in water may create very little (if any) change to the value an ORP meter detects.
When the same source water is treated with ozone, such as water in a holding tank, as ozone levels decrease, ORP values will not decrease linearly with dissolved ozone. Ozone in water will decompose to oxygen and create very high dissolved oxygen levels in this water. This elevated level of dissolved oxygen will increase the ORP value to water. Therefore, one might assume there is ozone in this water due to the previously indicated values while this is no longer true as all ozone has reverted to oxygen and is crating an elevated ORP value on the ORP meter.
Summary
In summary, if you need to measure ozone concentration in clean water, it is best to use a dedicated ozone meter. Ozone meters are specifically designed to measure ozone concentration and are much more accurate than ORP meters. However, if precise accuracy is not required but a general indication to an increase or decrease of dissolved ozone levels is sufficient, ORP is a great measurement option. In addition, when dissolved ozone meters are not a reliable option due to poor water quality, ORP meters may offer a viable alternative and provide an electronic meter to measure dissolved ozone in water.