ORP Control in Cooling Towers

Combat Microbiological Fouling in Cooling Systems

ORP is an important factor in water testing and treatment quality. ORP, also known as Oxidation Reduction Potential, is a useful tool in measuring and combating microbial fouling in open loop cooling tower systems, which provide the ideal environment for the growth of microbial organisms. The circulating system water gains microbes from the air as it passes through the tower and evaporation causes bacteria in the make-up water to become more concentrated.  Left unchecked, algae, fungi and bacteria will proliferate, and biofilm will develop on pipe walls, condenser tubes and cooling tower surfaces.  This causes reduced flow and heat transfer capability, resulting in increased equipment runtime and water usage.

Oxidation Reduction Process

The standard method to combat microbial growth is to add an oxidizing biocide such as chlorine, bromine or ozone.

The interaction produces an electrochemical process where the microbial organism (Reducing agent) loses an electron to the biocide (Oxidizing agent).  This destroys the organism’s cell walls, killing it.

How Much Biocide do you Need?

The appropriate amount of oxidizing biocide depends on the amount and type of microbial organisms in the system.  Ideally, the determined concentration will kill the existing microbial organisms and prevent further growth.  The concentration level can be increased to maintain a residual amount, to proactively combat any new organisms introduced to the system.

55 Gallon Chemical Drums

Determining and maintaining the proper biocide concentration level requires regular water testing and associated biocide dosing level adjustments.  Even with an intensive testing/adjusting program, there is always a risk of underfeeding or overfeeding biocide.  Underfeeding can result in biofouling and overfeeding is a waste of money and can potentially damage the system piping and components.

Oxidation Reduction Potential Sensors

NexSys ORP Sensor

Despite the measured biocide concentration level of system water, any microbial organism’s survivability, overall, depends on the ORP of the water.  An ORP sensor contains a platinum sensing electrode that generates a millivolt potential due to the electron transfer that occurs during the oxidizing/reducing process.  The millivolt potential is created on the sensing electrode with respect to a silver chloride reference electrode.  The measured ORP value directly corresponds to the biocide’s lethality to organisms in the system.  As such, with an accurately determined ORP setpoint, biocide dosing can be controlled to prevent microbiological growth at the minimal required level.

NexSys Chemical Feed ORP Setpoint

Our NexSys controller allows the option to use an ORP setpoint during any scheduled feed event.

If you would like more information on ORP Control in Cooling Towers, contact us today, or feel free to call us at 800-228-0839.


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