PPM and ORP - now you can have both! - CHEMTROL Australia
Relationships between Oxidation-Reduction Potential, Oxidant, and pH in Drinking . established in the plant and correlations from ORP, pH, residual chlorine. Download scientific diagram | Relation between free chlorine concentration, ORP , and pH (Source: Santa from publication: Towards Identifying Disinfectants and. ORP sensor response as a function of pH was studied for chlorine concentrations between ppm (mg/l) and. 10 ppm (mg/l) and pH values between . ppm of free chlorine showed a very good correlation between the values obtained by.
This has both advantageous environmental and economic impacts. It allows for reduced discharge of potential environmental pollutants and a more cost effective control program for diverse industrial systems.
Monitoring Mortality of Pythium Zoospores in Chlorinated Water Using Oxidation Reduction Potential
Chlorine is used as an oxidizing biocide to control this biological growth in most industrial cooling towers. For Chlorine Cl2 to function properly in the cooling towers it must be present in the oxidizing forms of hypochlorous acid HOCl or hypochorite ion OCl.
The equilibrium between the three species is pH dependent and can be monitored by using oxidation-reduction potential ORP electrodes. ORP is a measure of a solutions oxidizing or reducing strength.
The chemical way to look at redox processes is that the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized and the oxidant or oxidizing agent gains electrons and is reduced. When electrons are transferred from one species to another in a chemical reaction, the reaction is called an oxidation-reduction reaction; where the oxidizing and reducing agents are called a redox pair.
Oxidation and reduction reactions occur together, the electrons generated by a reduction reaction must be acquired by an oxidation reaction. The electron transfer between the two species continues until equilibrium is reached. ORP measure the ratio of the activities of the oxidizing and reducing species in a solution. This indicates the solutions electron activity, i. The speed of response varies with the concentration of the redox system, high concentrations are fast and low concentrations are slow.
Activity and Measurement of Chlorine Figure 1: As the pH increases above 1. Thus, for optimum effectiveness it is desirable to control the pH of the cooling tower between pH.
It is also necessary to control the quantity of chlorine in the tower to insure there is enough to control the biological growth, but not so much that it causes corrosion of equipment or creates an excessive load on the water treatment facility.
An ORP measurement system can be used to indicate both the quantity and activity of the chlorine in cooling water.
Since addition of chlorine increases the oxidizing capability of water, measurement of the ORP provides a useful indicator of the quantity and effectiveness of the chlorine present in the water.
However, as we have seen, the pH affects the oxidizing potential of the available chlorine so the ORP will vary with pH changes as well as changes in the chlorine levels. The higher the millivolt reading, the more powerfully the swimming pool water is able to oxidise and disinfect.
Oxidisers cause the millivolt value to increase and therefore increase disinfection. Typical oxidisers are hypochlorous acid a component of free chlorineozone, hydrogen peroxide, and potassium monopersulphate. Reductants cause the millivolt value to decrease and therefore decrease disinfection. Typical reductants are the hypochlorite ion a component of free chlorinechloramines, cyanuric acid, organic matter dust and dirturine, perspiration, sputum, micro-organisms, cosmetics, and faecal material.
A drop in the ORP indicates an increase in chlorine demand caused by reducing agents or contaminants entering the water. A decrease in ORP indicates that chemical reactions are about to occur.
Compared to amperometric control, ORP is considered to be a more accurate measure of disinfection rate. Also, ORP controllers can automatically add disinfectant according to demand. They therefore anticipate the disinfecting and oxidising chemical reactions that are about to occur.
ORP is an indicator of micro-organism inactivation. Studies on specific micro-organisms have found a direct correlation between increasing ORP and micro-organism inactivation as shown in Graph 6. Drinking water is adequately disinfected at an ORP of mV. In swimming pools, an ORP of to mV allows for both a quick disinfection and for breakpoint chlorination destruction of chloramines where conditions permit. Eutech Instruments Pty Ltd The ORP value required in swimming pools is higher than that required for water supplies because contamination is constantly being added to swimming pools.
An increasing pH decreases the concentration of HOCl and hence its disinfection power. Similarly a decreasing pH increases ORP because the oxidative power of free chlorine increases. ORP measurement correlates weakly with free chlorine measurement because they measure two different entities. ORP measures oxidative disinfection power not the concentration of free residual chlorine. Free chlorine measures the concentrations of hypochlorous acid HOCl and the hypochlorite ion OCl- not the oxidation disinfection power.
Free chlorine is a variable component of ORP. Oxidative disinfection does not correlate well to free chlorine for two reasons: This will occur when the pH is high.
- Cooling Tower: ORP Control of Chlorine
- PPM and ORP – now you can have both!