Microbial fouling on a heat exchanger versus a well-maintained unit

Unveiling the Connection: Does pH Affect ORP?

Does pH affect ORP?

Does pH affect ORP? The simple answer is “yes”, pH can affect ORP. However, understanding the answer is not all that simple. pH and ORP are two separate water quality measurements that are somewhat inversely related (in terms of their scales). ORP will increase as pH decreases and vice versa. To understand how pH and ORP affect each other, one must understand what pH and ORP are and the interrelationships that exist between the two, as well as the importance of maintaining good water quality.

Why is maintaining water quality so important?

The presence of impurities in the water can cause scaling and corrosion, which in turn reduces how effectively heat is transferred. This greatly impacts the efficiency and performance of the system. Corrosion can also shorten the life of key components within the system, shortening the equipment’s  life expectancy and increasing maintenance and operational costs. 

Microbial fouling on a heat exchanger versus a well-maintained unit

Microbial fouling on a heat exchanger versus a well-maintained unit.

Results of corrosion within a heat exchanger

Results of corrosion within a heat exchanger.

Understanding ORP and pH

What is pH?

pH is a quantitative measurement that defines the concentration of hydrogen ions in a water-based solution.  This measurement indicates whether the solution is acidic (an acid) or alkaline (a base). The pH scale ranges from 0 to 14. As the hydrogen ion concentration increases, an acid is formed and produces pH values below 7. As the hydrogen ion concentration decreases, a base is formed and produces pH values greater than 7. The pH scale is not linear, but rather logarithmic. This means that when the pH increases or decreases by a unit of 1.0pH, the hydrogen ion concentration level changes by a factor of ten. As an example, a solution with a pH of 8.0 is ten times more alkaline than a solution with a pH of 7.0.  A solution with a pH of 5.0 is 100 times more acidic than a solution with a pH of 7.0.

What is ORP?

Oxidation Reduction Potential, or ORP, is a measurement of a substance’s ability to either oxidize or reduce another substance. If a substance does not have enough electrons, it will attempt to acquire them through a process known as oxidation. Oxidation is a chemical reaction whereby one substance loses electrons to another substance. Conversely, a substance that has too many electrons, that can afford to lose electrons to an oxidizing substance without becoming destabilized themselves are called anti-oxidizing or reducing agents. Substances with higher (positive) ORP readings are looking to acquire electrons and are referred to as oxidizing agents. Conversely, lower (negative) ORP readings indicate a substance with excess electrons and are called an antioxidizing (reducing) agents. 

OPR is integral to water testing because it indicates how sanitized or contaminated water is based on its oxidization or reduction properties. It is a useful tool in measuring and combating microbial fouling in open loop cooling tower systems which provides the ideal environment for the growth of microbial organisms. It also can help monitor the corrosion potential of the metal in the equipment. Corrosion  reduces the efficiency and ultimately causes mechanical problems. Substances like dissolved oxygen, bromine and chlorine will contribute to higher oxidation and higher ORP. These substances have higher oxidizing agents and will pull electrons from other substances like unwanted contaminants and bacteria. However, ORP is susceptible to other active ions and total dissolved solids that do not contribute to sanitation. As such, ORP is not the cure for all water quality measurements. 

ORP vs pH Chart

On a pH scale, an acid is defined as a substance that is capable of liberating hydrogen ions and a base is a substance capable of absorbing hydrogen ions. Every acid has a complementary base. When pH equals 7.0, the substance is neutral. An ORP system can be defined in much the same manner as pH. Similarly, the ORP scale range is typically +1500mV to -1500 mV. Just like pH, the ORP electrode is designed to produce 0 mV at pH of 7.0. Unlike pH, ORP values are affected by all oxidizing agents, including acids and bases. Only the acids and bases affect pH. While pH is a specific measure of the hydrogen ion concentration in a solution, ORP only provides relative measures of chemicals and cannot discriminate one chemical from another.

ORP scale range

Factors Influencing ORP

Managing and controlling industrial water treatment can be challenging when based on ORP readings. Oxidizing agents, such as chlorine, increases ORP while reducing agents such as sulfite reduces ORP. There are a few other factors that affect ORP readings. ORP has an inverse relationship with temperature. The higher the temperature, the lower the ORP reading. Higher pH levels will render a smaller ORP response to an oxidizer feed. When the ORP value is high, there is a lot of oxygen present in the water. Bacteria that decompose contaminants can work more efficiently. There has not been an ORP value that has been determined to be too high. However, when the ORP value is low, the bacteria that decomposes contaminants work less effectively. Low ORP readings indicate that there are high amounts of contaminants in the water. 

A basic understanding of the relationship between pH and ORP is particularly important in cooling water treatment. The higher the pH, the lower the ORP response due to the higher concentration of the less active hypochlorite/hypobromite to hypochlorous/hypobromous acid. Free and total chlorine residuals do not vary with pH, only the ORP response changes. When the pH in a system varies due to changes in makeup water quality, inconsistent cycles, extended pre-bleed, bleed lockout times, or high pH chemical additions, the ORP setpoint required to maintain a particular oxidizer residual also varies, and the oxidizer residual associated with a particular ORP setpoint can vary even within the same system. Due to these factors, the same oxidizing biocide dosage added to two different water systems can give very different oxidizer residuals and ORP readings.

pH and ORP Controller Options from Lakewood Instruments

Model 1520e pH Controller

The Model 1520e Controller precisely controls pH in a simple, easy to set up package, minimizing time and costs. The 1520e Controller uses four relays to add acid or base, control valves and additional chemicals. Up to twelve user defined chemical feed schedules are available allowing you to set the feed precisely to match the system performance you seek. The chemical feed relays can be configured for setpoint control, based on water meter, percent blowdown, percent of time or on a scheduled feed basis. An additional 4-20 mA output is standard to send the system pH to an external monitor (BMS or another system).

Process inputs include up to two water meter inputs, two drum switch inputs, pH, flow switch input and a 4-20 mA input which can be used for a remote pH or other input. Lakewood Instruments has all the pH probes for your system. From sample line locations to remotely located probes using signal transmitters, we can get the information from your system to the controller. With pH probes for cooling water, condensate and process/waste water applications, we can help with all your pH control needs. Visit our 1520e pH Controller product page to learn more and place an order today.

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Model 1530e ORP Controller

The Model 1530e ORP Controller uses reliable ORP sensors to deliver the performance you need. The controller is designed to ensure your biocide program is doing just what you want it to by keeping biofilms under control. The 1530e Controller uses four relays to control valves and add additional chemicals. Up to twelve user defined chemical feed schedules are available allowing you to set the feed precisely to match the system performance you seek. An additional 4-20 mA output is standard to send the system ORP to an external monitor (BMS or another system).

Process inputs include up to two water meter inputs, two drum switch inputs, ORP, flow switch input and a 4-20 mA input which can be used for a remote ORP or other input. Lakewood Instruments has all the ORP probes for your system. From sample line locations to remotely located probes using signal transmitters, we can get the information from your system to the controller.  With ORP probes for cooling water, condensate and process/waste water applications, we can help with all your ORP control needs. Learn more about our Model 1530e ORP Controller and place an order today. 

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The Lakewood pH ORP Controller products can be taken to the next level with Lakewood’s OnSight Remote Access System. The OnSight Remote Access System converts most existing water treatment controllers into smart controllers with remote monitoring, system graphs and accessible data logs. These features can be accessed via smartphone, tablet or pc and provide a secure data link without actual control access to the controller. 

Our system’s communications module can handle four 4-20mA analog signals, and our controllers just happen to have system conductivity as that type of output signal. The other 4-20 mA channels can be used for other system parameters – we suggest level transmitters (Echopods) that will let you know your chemical tank levels. In addition, the OnSight system handles up to four dry-contact digital inputs which can log blowdown valve activation (with the right valve!) or pump operation history.

We pair the communications module with a 4G router so that you can access the OnSight data directly from your pc, tablet, or phone. Through the built-in web interface, you can download system logs, system graphs over time, and set up alarm emails or text alerts to keep you apprised of any unplanned circumstances. Setup is easy – allowing you to convert a site-only controller to a true remote data logged system.  Learn more about our OnSightRemote Access System and place an order today. 

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Contact us to discuss how we can help with your ORP and pH control needs. 

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