ORP stands for Oxidation Reduction Potential – a measure in millivolts of the potential for oxidation or reduction chemical reactions to take place. Oxidation is the loss of electrons by an atom, molecule or ion. The process may or may not involve the addition of oxygen, which is where the term originated from.
Reduction is the net gain of electrons by an atom, molecule or ion. Oxidation reactions always go hand in hand with reduction reactions. The electrons lost in oxidation must have a destination, and the electrons gained in reduction reactions must have come from a source. In an oxidation reduction reaction between iron and chlorine, iron is called a reductant or reducing agent because it reduces chlorine, whereas chlorine oxidises iron so is called an oxidant or oxidising agent.
ORP is a standard parameter included on Aquaprobes AP-7000, AP-5000 and AP-2000. The AP-7000 is a groundbreaking device that is specifically designed for long term water quality monitoring when the system will be unmanned. The AP-5000 and AP-2000 are designed to be portable to offer maximum flexibility. The oxidation reduction potential of water is measured in the range of +/- 2000mV and is accurate to +/- 5mV. The pH and ORP sensor is combined due to the fact that they work similarly. This ORP meter is easily recognisable from the others because it's the only one that is not black. To maintain the maximum accuracy, ORP electrodes should be calibrated at least once a month.
ORP meters have an ORP electrode and a reference electrode. The ORP electrode is designed to either give up electrons to an oxidant or accept electrons from a reductant. These chemical reactions will continue until the electrode develops a potential, caused by the build up in charge, which is equal to the ORP of the solution. The reference electrode is encased in a stable gel. The measurement is referenced from the voltage of each electrode.
When the ORP probe is placed in the water sample the measurement of water oxidation reduction potential will be recorded by the Aqualogger or Aquameter being used, in conjunction with the Aquaprobe. The ORP water testing measurements are particularly useful when considered in collaboration with the other measurements that our multiparameter water quality testing equipment provide. It is vital to follow the instructions for usage in the manual for your ORP sensor to ensure that you maintain the meter properly and prevent damage.
ORP water testing measurements can be taken in the field to directly measure bodies of water. The pH and temperature of the water has an effect of the ORP measurement, so ORP should not be used as a direct indicator of the concentration of the oxidiser. ORP data can be collected over time to identify patterns or the normal range of ORP for this water body. By understanding the normal levels it is easier to identify when there has been an alteration that could affect the aquatic ecosystem.
ORP water testing equipment can also be used to measure the effectiveness of swimming pool sanitiser. Chlorine is an oxidiser, and helps to clean water by killing unwanted organisms through altering their chemical makeup. Continual or regular monitoring with ORP water testing equipment will ensure the correct levels of water cleanliness is maintained.
ORP monitoring is additionally used in the waste water treatment process, and can measure the performance of the treatment plant. The higher the ORP at the end of the process the cleaner the water. Monitoring the ORP at different stages of the treatment process can also help the operators to gain a more thorough understanding of the process' performance in detail.