pH & ORP Electrodes

One of the most labor intensive maintenance efforts in a plant relates to the figurative care and feeding of pH and ORP probes and other electrochemical sensors. While many such probes are touted as “rugged,” they are actually quite delicate. Advertisements tout their rugged build quality, often suggesting that they have been “beefed up” by wrapping a “tougher” pH measurement element in a strong, protective housing.

While this may help with handling in transit and on site, the measurement method is still identical, but the supposedly tougher pH measurement elements often result in reduced sensitivity and slower response to parameter changes.

Toughness aside, no electrochemical sensor can report accurate measurements if it is covered in gunk and grime, but traditional cleaning approaches are time intensive and costly.

It’s a common task to remove and clean probes in industrial installations. This may be done on a preventative schedule basis, or only when the measurement is “acting up,” but the cleaning process is largely the same.

First, the plant control room must be informed that the measurement point is going offline. The process flow, or sample line from the main flow, is then shut off and isolated so the technician can physically remove the probe and carefully clean it.

In hazardous applications, protective clothing is needed, often including disposable gloves. Once cleaned, the probe is reinstalled and the measurement brought back on line by reinsertion into the process. But this takes time, and the process of uninstallation, cleaning and reinstallation can cause damage to the probe itself.

A safer and more efficient method of keeping the measurement on line is to install an automatic retractor and cleaning system.

Retracting and cleaning a probe by hand must be performed as infrequently as possible, due to downtime and the potential for equipment damage. However, a retractor can operate frequently—as often as every 15 minutes, if necessary!—to keep the probe clean and in operating condition.

Automatic retraction systems can work in conjunction with a probe’s electronic unit to provide seamless measurement to a remote control system. In addition to providing a more reliable measurement, the useful measuring life of the probe is extended, and the probe is protected from potential handling damage.

At the very least, a manual extractor can provide a safe and efficient means to pull the probe out of the process.

Exner Process Equipment manufactures a wide range of automatic and manual probe retractors that can be used in process conditions both benign and aggressive.

Typically installed directly on process vessels or into piping, the Exner EXtract series use either a pneumatic or manual rotary action actuator to insert the sensor into the process medium and retract it back into an integral cleaning chamber within the assembly. When retracted, the mechanism isolates the probe from the process fluid. In manual retractors, a safety interlock engages at each end of its travel to prevent further movement without depression of an “insert” or “retract” button on the housing. On automatic units, there are pneumatic and optional electrical feedback switches to indicate position. Whether automatic or manual, the insertion mechanism cannot be operated when no sensor is installed, and it is impossible to uninstall any probe while in the inserted position.

All EXtract housings have inlet/outlet fittings for cleaning and rinsing of the installed sensor when retracted from the process. Calibration solutions can also be introduced to the housing while the probe is retracted, allowing for in situ calibration and standardization of the sensor, all without interrupting process flow.

Advantages of Exner Extract Retractable Housings

Greater reliability and confidence in the measurement
Protects technicians from process material contact, with no need for additional PPE
Dramatically reduces maintenance time
Prolongs sensor life
Manual or automatic operation versions
Operate without process line shut down
Integrated process scraper cleans probe as it is retracted
Manual unit has position locking system with indicators
No way to uninstall probe when inserted into process
Automatic safety lock while sensor is removed
Optional electrical position feedback switches
Operates safely under high process pressures
Immersion lengths up to 107mm
Suitable for use in hazardous areas
Wide variety of process connections
Up to 16 bar / 230 psi and 140°C / 285°F

In the United States there are many regulatory requirements at both the state and federal levels regarding the discharge of wastewater from industrial manufacturing facilities. Any company that discharges any sort of effluent into sewer systems, lakes, streams or the ocean is required to neutralize this effluent before discharge.

Noncompliance can result in financial penalties, at a minimum, and may also include other consequences such as being required to remediate any resulting environmental damage. It is in the best interests of any company—and depending upon local rules, it may be compulsory—to record discharged effluent characteristics such as pH at the point where it leaves their facility.

pH Monitoring and Neutralization Systems

Many plants operate an automatic pH neutralization system that monitors and controls effluent pH by chemical addition. A simple pH neutralization system consists of four basic components:

Instrumentation for monitoring, controlling, and recording, including pH and ORP electrodes
Effluent holding tank
Chemical reagent storage tanks and addition pumps
Agitator(s)

In such a system, effluent flows into the holding tank where a pH sensor (also known as a pH electrode or pH probe) measures the pH of the solution. The pH controller has a preset pH set point for the effluent and uses this measured value to determine whether the effluent is within compliance with that set point. If not, chemical pump(s) are operated to inject acidic or caustic solutions as required to bring the effluent in the holding tank to the correct level. The agitator(s) keep the contents of the holding tank adequately mixed, so that the pH probe is always measuring a representative sample of the effluent and any chemicals added are properly and quickly distributed within the tank.

The pH Neutralization Process

pH neutralization can be accomplished in a batch or continuous mode. Batch systems operate by filling an effluent holding tank and carefully treating the contents with a variety of chemicals to remove metals and other contaminants before finally setting the pH level before discharge. Continuous systems operate by flowing effluent through a series of tanks or basins where measurements are taken and treatment chemicals added. Whichever treatment mode is used, it is of primary importance that measurements can be relied upon and chemical addition equipment is in good condition if the final effluent is to be safe to discharge.

After the neutralization process is completed, the effluent is discharged to waste. At the point of discharge, a pH sensor should be installed dedicated to monitoring and recording the effluent’s pH level. This provides a record of the discharge pH level that can be produced for inspection by external agencies while also providing valuable data for internal use.

In many industrial plants, maintenance of wastewater treatment equipment can be a key challenge. In these plants, wastewater is often a cost center rather than a revenue generating center within the business, and therefore does not enjoy the maintenance resources of the rest of the facility. Poorly operating pH measurement systems can lead to off spec neutralization. In these cases, manual override of dosing systems is a common practice, and costly overdosing with correction chemicals can occur.

Common Problems for pH Neutralization Systems

Many of the operational problems encountered in a pH neutralization system are related to pH sensor performance, with incorrect choice of electrode technology and placement being common causes. pH sensor selection is therefore a key element in problem-free operation.

Sensor Selection

Choosing the best pH (and ORP) sensor for your needs is essential to proper system operation. There are a variety of different electrodes on the market. Here is a quick rundown of a few of the most common:

Single junction combination sensors combine a pH glass electrode with an Ag/AgCl electrode-in-KCl reference cell in a single convenient package, and are available in a variety of sizes. The reference junction in these electrodes is porous and allows the KCl salt solution to come into direct contact with the effluent, thus completing the sensor electrical circuit. These electrodes are depleting, in that the internal KCl reservoir will become diluted over time and is susceptible to poisoning when the measured effluent contains heavy metals, sulfides, proteins, or other materials that interact with silver. Dilution causes measurement drift, while poisoning causes measurement error and eventual electrode “death.” Furthermore, should the porous junction become blocked, proper measurement is not possible. A sign of junction blockage is sluggish sensor response, which can lead to expensive overdosing of pH correction chemicals. Without proper maintenance, pH measurement systems using this type of electrode will soon provide unreliable readings.

Double junction combination sensors are similar to single junction electrodes, except that they have two porous junctions in series instead of one. They typically have a longer lifetime than single junction sensors because they generally have better resistance to poisoning. They still require frequent maintenance and standardization if the pH values they produce are to be reliable.

Differential pH electrodes were designed to combat the poisoning of the Ag/AgCl electrode in standard reference cells. In a differential electrode, two pH glass electrodes are used, one in contact with the effluent and the other immersed in KCl within the probe body (the reference junction). While this combats the problem of poisoning, there is still a porous junction, and the KCl within is diluted over time. Differential electrodes still require maintenance to keep their measurement correct.

Non-porous reference junction pH electrodes (such as the REFEX brand) have a glass pH sensor just like all others. The difference is that they do not have a porous reference junction, so poisoning and dilution of the reference junction electrolyte is prevented. The lifespan of non-porous junction electrodes in wastewater neutralization systems is much, much longer than those with porous junctions, and maintenance requirements are almost zero. Typically, non-porous junction electrodes require only periodic cleaning as a maintenance requirement, and this can be easily automated for “hands-free” operation.

Mounting Considerations

pH sensors used in wastewater neutralization systems should be suitable for the use. As many systems are open tank, pH sensors are often installed as dip tubes, with a plastic pipe connected to the back of the pH sensor over the sensor wire. A holding bracket of some kind is used to secure the dip tube in place. For closed top effluent tanks, sensors can be installed through entry ports either in the top of the tank or through the side. When mounting, it is recommended that the following be considered:

The sensor dip tube must be properly supported to prevent the sensor from moving around in the tank. Excessive movement may cause impact of the sensor on the tank wall or agitator, leading to damage.
Ensure the electrode is installed with a moving, turbulent flow around it. This will help minimize coating and therefore reduce maintenance overhead.
Make sure the electrode is not mounted where chemical addition takes place, as this will unduly influence or bias the measurement. It can take a while for mixing and reaction to occur in a tank.
In applications with heavy coating, consider an automated sensor cleaning system. For dip tube installations, a spray head attachment fed with a cleaning agent suitable for the process—often clean water, but other materials such as detergent are sometimes used—is a good option. For closed tank mounted probes, an automatic retractor and cleaning system like the examples from Exner Process Equipment below can be used.

Electrode Maintenance

Common problems experienced with pH electrodes (and recommended solutions) are:

Buildup of oils and/or solids on pH electrodes, necessitating frequent cleaning: The lifespan of electrodes in these applications tends to be quite short. Use sensors with non-porous reference junctions, as these have much greater resilience to this kind of problem than porous junction electrodes. The addition of an automated cleaning system will reduce maintenance requirements further.
pH bulb breakage or failure as a result of abrasives or heavy solids in the effluent: Fit probes with a bulb guard or house in a stilling well to slow the flow of material over the pH electrode and protect it from abrasion or impact from large objects.
Reference junction fouling or plugging: Use non-porous reference junction electrodes to prevent reference junction blockage.
Short electrode life caused by reference poisoning due to interaction between silver ions in the electrode and material in the effluent: Use non-porous reference junction electrodes to completely remove the possibility of reference junction poisoning.

Electrode Care and Cleaning

Whenever handling pH electrodes and any associated solutions, always wear gloves and safety glasses. Safety first.

Keep all electrodes wetted when not in use. Electrodes will become useless if allowed to dry out. Electrodes will typically be supplied fitted with a “boot” or bottle filled with a salt solution from the manufacturer and this should not be removed until the electrode is placed into use. A good tip is to keep the boot or bottle to one side so it is available should the electrode be taken out of service. Fill with a pH 7.0 buffer when putting back on the probe if storage solution is not to hand.

A common way to clean electrodes is to immerse it in a mild (2% to 5%) solution of hydrochloric acid (HCl). This will dissolve most coatings. Always make sure the solution used for cleaning is compatible with the process—sometimes other solutions are more effective. Soak the sensor for 5 minutes then rinse with water. For heavy coatings, it may be necessary to repeat several times, carefully wiping with a soft, non-abrasive cloth between immersions. Never use abrasive materials or brushes to clean pH sensors, as this can damage the measuring surface and render the electrode useless.

Conclusion

pH neutralization is a critical wastewater treatment process in many industrial manufacturing environments. Through proper choice of sensor components, ongoing operation of the system can be optimized resulting in minimal maintenance and significantly lowering costs and risk of accidental discharge.

Images used by kind permission from:

REFEX Sensors Ltd

Exner Process Equipment GmbH

People often take for granted the water they drink. Whether it’s from the tap of your sink or purchased from the local grocery store, water is vital to human life.

Potable water is everywhere but be careful of what your drink. Water with a positive oxygen reduction potential (ORP) can be dangerous as can water with a high or low pH. ORP and pH levels are generally taken care of in processed and filtered water.

What happens if you’re at a water source that isn’t filtered? Do you dare drink to satiate your thirst or do you pass it in favor of the next water fountain? You’ve probably never thought about ORP and pH levels in what you drink.

What Are ORP and pH?

Pure water has an equal amount of H and OH ions, making it neutral on the pH scale. pH is the measurement of acidity and alkalinity in a substance with 0-6 acidic and 8-14 alkaline or basic. Pure water is at a 7.

Most water isn’t pure and can be either on the acidic or basic side. Water used in a pool, for instance is slightly basic as this acts as a buffer against rapid pH change. Many times, people place chlorine into the water because it has a high ORP value. When added to water, it increases the water’s ORP value and can damage the DNA and proteins of bacteria.

ORP is a measurement of ion exchange. Substances with a negative ORP value can donate extra ions, but positive ORP values lead to ion absorption. All substances look for a state of stability either through shedding electronics or grabbing them.

Without the ability to calculate ORP and pH, people could drink waters with varying levels of acidity and alkalinity. The human body needs to have a negative ORP and be on the alkaline side to function. If a person had acidic blood, they would likely die.

Luckily, the likelihood of that happening is low thanks to the body’s natural defenses.

Measuring pH and ORP

ORP is the amount of energy in water in terms of electrons. Since the movement of electrons is electricity, ORP is measured in millivolts.

Drinking water should have a rating of least -50 millivolts, but it’s not often the case. Filtered water can have ORP values ranging from 357 to -25, depending on the brand and type of water. It’s most often measured using an ORP meter.

pH is the measurement of molar concentration of hydrogen ions in a liquid, pH stands for “power of Hydrogen” and it’s value relates to negative of the power of 10 of the molar
concentration. The pH level of water (and hence how acidic or basic it is) can be measured using an electronic meter or determined using an indicator like the color on strips of litmus
paper. The meter is the most accurate.

A pH of 0 is extremely acidic, 14 is extremely basic and 7 is neutral. For context, stomach acid has an acidity of 2, soda and vinegar are 4. On the opposite end, Bicarbonate of soda is 12, oven cleaner is 13 and seawater is 8.

Drinking Water and ORP

If a person were to take an ORP meter to tap water, it will likely have a positive value. Why? Water isn’t made of just hydrogen and oxygen. It also has metal ions like copper, zinc, and chlorides. In fact, some filtration systems add salt to the water too.

A person’s saliva and many other body fluids have a negative ORP value as do many fresh fruit juices. In fact, its ORP value rises the longer it is in a juice state. It’s been suggested that you can test the freshness of fruit juice by its ORP level.

When you bring in other drinks like soft drinks they have even higher positive ORP levels. Scientists suggest that drinking water should have a negative ORP value and balanced pH because it’s better for the body and its fluids.

Something to keep in mind is what is more important than the ORP value itself is what in the water is causing the positive value. It could be toxic.

For example, minerals like iron may taste bad, but it won’t hurt you. If the ORP level is changed because of lead or mercury, then you need to take steps to remove them.

Importance of Anti-Oxidant Water

When your water has a negative ORP value, it has anti-oxidant properties. This is associated with anti-aging and cellular health. Positive ORP values are oxidative and have the opposite effect. As we said before, most water you drink, both in the tap and filtered, have oxidative properties.

If you’re able to get negative ORP value drinking water, then it can donate electrons to neutralize free radicals. Water with positive ORP values cannot. Free radicals are unstable ions in the body. They’re generated by the body and can cause problems with lipids, proteins, and DNA.

There needs to be a balance of free radicals in the body. Without it, the body can be overrun and become ill. In addition to the natural body’s defenses, you can decrease free radicals by drinking anti-oxidant water with negative ORP values.

The body is made up of oxidative and antioxidative substances. We mentioned earlier how important negative ORP values were in a healthy body. When you drink anti-oxidant water, it can neutralize excess acids in the body. It helps regulate the body and keeps it healthy.

ORP and You

Water surrounds us. It’s in our bodies, comes out faucets and runs throughout rivers, lakes, and oceans. While water seems similar, each source has its own set of ORP and pH values.

If you’re concerned about the health of your body, then pay attention to ORP and pH in what you drink. While soft drinks won’t reach pH levels of hydrochloric acid, they’re not so good for the body. They can contribute to free radicals because of their acidic nature.

ORP meters and litmus paper can tell you all you need to know about water or other liquid you’re drinking. If you want to know if the water is potable, then make sure it’s got a low ORP level. If you want to know more about ORP and pH, water clarity, turbidity and more then feel free to explore the rest of our website.