ORP is a frequently used term in the water treatment and food processing industry. ORP means ”Oxidation Reduction Potential OR. So what is this? The ORP can best be defined as follows; ORP is a measure of the ability to clean water and to break down contaminants. It is measured in mV (millivolt) from -2000 to +2000 measuring range. Since ozone is also an oxidant, it is the positive ORP levels (above 0 mV) that we need to address.

Sensors

ORP sensors work by measuring dissolved oxygen levels. The higher the level of oxygen in water, the lower the oxygen level because the organics in the water consume oxygen and the low ORP level is observed. The higher the ORP level, the better the ability to remove microbes or carbon-based contaminants in the water. The left column of the table below defines ORP levels for various applications.

The ORP level can also be used to monitor bacterial activity in water because there is a direct link between the ORP level in the water and the Coliform count.

Drawbacks
ORP does not directly show the dissolved ozone residue, except for very clean water.

Benefits
ORP measures the ability of ozone to fulfill a chemical task. The ORP operates at almost any pH level and the ORP probes are as robust as can be measured in-house measurements. These probes are very comfortable to measure up to 2 Bar.

Relationship with ozone
Using ORP to measure ozone in a clean water system gives very clear results. However, despite the high oxidation power of ozone, an ORP level in medium turbidity may be lower than expected or even negative. In general, measuring ozone from a location close to the production source gives clearer results, while measurement in contaminated water may not yield the expected result. In addition to ORP, ozone measurement kits can also be used to measure desired concentrations for the application.