ORP

ORP stands for oxidation-reduction potential, a parameter used to quantify the tendency of a chemical solution to either acquire electrons (be reduced) or lose electrons (be oxidized). It is measured with a redox probe that typically includes a sensing electrode (often platinum) and a reference electrode, with the result expressed in millivolts (mV) relative to the reference. The sign and magnitude indicate the oxidative strength of the environment: higher positive values indicate stronger oxidizing conditions, while negative values indicate reducing conditions. ORP provides a real-time sense of a solution’s overall oxidizing power and is influenced by temperature, pH, and the presence of oxidants and reductants such as chlorine, ozone, hydrogen peroxide, and organic matter.

Common applications include water treatment, swimming pools, aquaculture, and the food and beverage industry, where ORP is used to monitor disinfection potential and oxidative capacity. It is often read alongside other measures such as free or combined chlorine, pH, and temperature. However, ORP is not a direct measure of the concentration of any particular oxidant; different oxidants can produce the same ORP, and the reading can lag behind changes in oxidant levels. Calibration and electrode maintenance are important for reliable results.

Limitations and interpretation: ORP readings depend on electrode condition and solution composition. Fouling, low oxygen, high salinity, very high or low pH, or strong reducing agents can distort measurements. For disinfection control, ORP is best used as a supplementary indicator, not a sole basis for setting chemical doses. In practice, operators use ORP together with targeted disinfectant residuals and process knowledge.