What is ORP?

What is ORP?

ORP is an acronym for Oxygen Reduction Potential. It is a measurement that indicates the degree of oxidation or reduction of a liquid. For example, water may be moderately oxidizing (such as aerated water), strongly oxidizing (such as chlorinated water or hydrogen peroxide solutions), or reducing (such as an environment with active anaerobic microorganisms). In short, ORP is a measure of the cleanliness of water and its ability to break down contaminants.

ORP value is a measure of the REDOX capacity of an aqueous solution, and its unit is mV. It consists of ORP composite electrode and mV meter. An ORP electrode is an electrode that absorbs or releases electrons on the surface of its sensitive layer, an inert metal usually made of platinum and gold. The reference electrode is silver/silver chloride electrode as the pH electrode.

In natural water bodies, there are many kinds of base ions and dissolved oxygen, when some industrial wastewater discharged into the water, the water contains a large number of ions and organic material, due to the different nature between ions, REDOX reaction in water and tend to be balanced, so in the nature of water is not a single oxidation-reduction system, but a mixture of REDOX system. The measured electrode also reflects a mixed potential, which has a large experimental error. In addition, the pH value of the solution also affects the ORP value. Therefore, it makes no sense to emphasize the potential of the solution during actual measurements. We can say that the ORP value of a solution near a certain value indicates a reduction or oxidation state of the solution, or some property of the solution (such as sanitation, etc.), but this value is quite different and you cannot quantify it, which is the same concept as accuracy in pH tests. In addition, the temperature coefficient that affects the ORP value is also a variable and cannot be corrected, so ORP meters generally do not have temperature compensation.

Why ORP is important for water quality testing?

ORP is an integral part of water testing because it indicates how disinfected or contaminated the water is based on its oxidation and reduction properties. For safe drinking, recycling or contact with our skin, water is treated with disinfectants to have a higher oxidation potential, resulting in a higher ORP reading. By regularly monitoring ORP levels, you can monitor the effectiveness of disinfectants and adjust your water treatment program accordingly.

What is an ORP meter?

ORP meter is a device designed to measure the redox potential of water.ORP meters are also known in industry as redox probes. These chemical or microbial species form redox pairs that result in the loss of electrons. the ORP meter measures the number of electrons lost as an advantage to the redox potential of water.

How does an ORP meter work?

An ORP meter or redox meter works on a very simple principle. It is a measure of the electron transfer capacity of water, and an ORP meter consists of an electrode that is used as a probe or sensor to measure the redox potential of water. It works similar to pH measurement. Just as the pH of a solution is measured based on hydrogen ion activity, the ORP measurement is the result of the movement of electrons in water. Depending on the quality of the water, the ORP electrode acts as an electron donor or acceptor. If the contaminant in the water is a reducing agent, the ORP electrode acts as an acceptor. If the contaminant is oxidized, the ORP electrode acts as a donor. During this electron transfer, a potential difference is generated due to the electric potential. This potential difference is measured by an Apure-meter to give a reading based on the ORP scale. Therefore, the ORP meter is also called a differential ORP probe.

The ORP electrode is designed to read at 0mV, i.e., a null reading at 7pH. The ORP deflection can be seen when the pH deflection is above or below 7. The limit range of the ORP meter reading is maintained between -1500mV and 1500mV.

Common Uses of ORP Meters

There are many reasons why someone might be interested in knowing the ORP of a substance. Perhaps the most common application is water quality testing for chlorinated swimming pools. Because the ORP of a substance is affected by all the reagents present in the substance, ORP measurements are considered more informative than pH readings alone, which only recognize acids (hydrogen ions) and bases (hydroxide ions). Larger pools are often equipped with in-line ORP sensors, while backyard pools that lack built-in monitors may need to be tested with portable ORP monitors.

When you add chlorine to a pool, the chlorine gives up its own excess of electrons to neutralize or oxidize potentially harmful bacteria. Activated chlorine electrons increase the ORP level of the water, thereby neutralizing contaminants. For chlorinated pools and spas, safe ORP readings are typically between 650 millivolts (mV) and 750 mV. Over time, the chlorine breaks down and loses its oxidation potential, and the overall ORP reading of the water gradually decreases. Although ORP levels are typically correlated with the proportion of disinfectant in the water, ORP does not measure disinfectant levels; instead, it measures the net oxidation and reduction characteristics of all reagents present.

In addition to being used to monitor water quality in chlorination ponds, ORP meters are widely used in the food processing and water treatment industries to ensure that water is free of contaminants and can be safely recycled or used. Contaminant-free bottled water or tap water will have a positive ORP value.

Adjustment of ORP levels

For swimming pools, ORP levels can often be adjusted by adding more active chlorine to the water to increase its antioxidant potential. More complex water purification systems may involve a more complex balance of total dissolved solids (TDS) in the water to achieve a more favorable redox potential.

For more information on how to interpret ORP readings and use ORP meters, please research your choice of ORP meter and its unique features.

Interested in purchasing an online ORP meter? Click the button below to learn about the different models and features.

Scope of application

ORP meters are used when water quality is to be measured in terms of disinfection or contamination. ORP meters measure redox potential by measuring the electric potential of electrons passing from reducing substances to oxidizing substances. These ORP meters cannot be used for all types of water testing. factors such as pH have a significant effect on the ORP reading. If the pH of the water is higher than 9.5, then the ORP meter becomes an ineffective method of measuring water quality.

Therefore, the answer to the question of when to use an ORP meter becomes somewhat complicated. Although, a simplified answer to this question could be to use it when the water is being treated or processed. Below are a few examples of applications where ORP meters can be used to identify water quality.

• Chlorinated swimming pool water quality testing
• Oxidized or disinfected water storage
• Potable water distribution units
• Wastewater treatment plants

Industrial sewage treatment

REDOX systems used in water treatment are mainly the reduction of chromic acid and the oxidation of cyanide. If the addition of sodium disulfide or sulfur dioxide to wastewater can make hexavalent chromium ions into trivalent chromium. The addition of chlorine or sodium hypochlorite can be used to oxidize cyanide, followed by the hydrolysis of cyanide chloride to form cyanate. This chemical reaction is called a REDOX reaction system. REDOX potential is a measure of electron activity, similar to how hydrogen ion activity is measured.

Water disinfection and application

REDOX electrode can measure the disinfection effect of swimming pool water, mineral water and tap water. Because the bactericidal effect of coliforms in water is affected by REDOX potential, REDOX potential is a reliable indicator of water quality. If the REDOX potential value in the pool water and mineral water is equal to or higher than 650mV, it means that the bacteria content is acceptable.

Installation and inspection of electrodes

1. ORP electrode can be used on any pH/ mV meter.
2. ORP meter can be used directly without calibration. Only when there is doubt about the quality of ORP electrode or test results, ORP standard solution can be used to check whether the potential is between 200-275mV to judge the quality of ORP electrode or instrument. REDOX electrode Operation Manual REDOX electrode operation manual
3. ORP measurement electrodes (platinum or gold) should have a bright surface, rough or contaminated surface will affect the potential (mV) of the electrode. Can be cleaned and activated by the following methods.(1) For inorganic pollution, the electrode can be immersed in 0.1mol/L dilute hydrochloric acid for 30 minutes, cleaned with pure water, and then immersed in 3.5mol /L potassium chloride solution for 6 hours before use.(2) For organic oil stains and oil film pollution, detergent can be used to clean the surface of platinum or gold with pure water, and then immersed in 3.5MOL/L potassium chloride solution for 6 hours before use.(3) The surface of platinum is severely polluted to form an oxide film. The surface of platinum or gold can be polished with toothpaste, cleaned with pure water, and then immersed in 3.5mol /L potassium chloride solution for 6 hours before use.

Read more about water quality:

Water quality sensors for water treatments
What is pH sensor & How does it work?
Main water quality indicators
Why is water quality important?