How Industry and Municipalities Can Measure and Control pH and ORP of Water, Wastewater and Manage Expenses

Demands for meeting and maintaining water quality standards from local, state and federal agencies are a continuing challenge for industry and municipalities of all sizes. This case study will provide a generic example of how a typical industrial or municipal user keeps up with the demands of managing the measuring and controlling process and staying within shrinking operational budgets.

Municipalities and Industry face a variety of regulatory as well as practical requirements when managing pH or ORP measurement and control with respect to water and wastewater. Not only is the cost of capital equipment a consideration, but the on-going cost of ownership relating to maintenance, labor and replacement components is involved. The importance that sensor selection and versatility plays in overall system cost of ownership and performance is often overlooked. At the heart of any pH or ORP measurement or control system is the sensor itself. pH and ORP electrodes provide the data to effectively analyze and control the measurement. System performance can be directly correlated to the performance of the sensor.

pH and ORP sensors are available in a wide range of shapes and construction styles. Sensor selection and mounting considerations are a vital part of the system design process and are far too often just an afterthought. pH and ORP electrodes are similar to batteries. They have a finite use and shelf life. They will require some cleaning and calibration to maintain performance. Installation requirements need to be a primary consideration to ensure that a system is reliable, serviceable and operates at an optimum level of performance with minimal maintenance, costs and system down time. When, not if, a user has to calibrate the system, are provisions made to isolate the sensor for removal from pressurized flowing lines to avoid system shutdown? Can the user lift a sensor from a tank for calibration with having to maneuver a 10 foot long assembly while standing atop an open tank?

These are some of the questions which should be addressed when selecting a sensor or even when replacing a current sensor. A difficult situation will not improve unless there is a change made. The following are key installation concerns in order to save user’s time, costs and labor: 

Location and Mounting requirement- Will the sensors be installed in-line or submersed in an open vessel?

Accessibility- The electrodes will require periodic cleaning, calibration or replacement, can they be accessed easily?

Distance- How far is the instrumentation from the sensor? This will dictate if you need any additional signal transmission or amplification capabilities.

Location and Mounting – Since pH and ORP electrodes will require some cleaning and calibration as well as eventual replacement, decide how best to mount and where to mount the sensor. A flat surface style sensor can provide improved performance when used in areas with good flow or agitation. The flat measuring surface is easier to clean and very durable. It also can resist fouling and coatings to increase intervals between service. If you have multiple installations such as in-line, submersion as well as a variety of instrument brands, the same electrode which can be used for in-line or submersion applications will reduce the number of spares on hand required. Mounting hardware which allows sensor replacement with no tools or having to re-route cables and re-tape threads is a further opportunity to reduce costs thru labor savings. Lastly, a cartridge type sensor will save time and cost of ownership expense. Users can quickly change a non-functional electrode cartridge in seconds; or replace it to perform cleaning later at a more convenient time.

Accessibility – We have identified the best location and mounting installation, now we must ensure we can get to it readily. If one has to crawl over pipes and needs tools, there are probably better options. A cartridge style design of the electrode itself ensures users can quickly and easily replace a sensor in seconds with no tools to minimize labor and down time. Ensure the location has easy access. If installed in-line, consider installing a by-pass line with ball valves to facilitate sensor removal without system shutdown.

Distance - The design of the instrumentation package location to senor distance is a consideration. Many instruments can accept a pH electrode input directly. Others require an amplified signal or 4-20mA input. A modular system would allow users to add only when necessary the electronics required. Additionally, long cable runs would not have to be disturbed with the modular approach. When sending sensor signal over 25 feet, even if an instrument is designed for direct sensor input, an amplifier is generally recommended after this distance to ensure signal integrity.

When selecting a pH or ORP electrode, these three simple considerations can save you time, substantial expenses and improved system performance. Let’s look at a few case studies to see how to apply some practicality to this process.

CASE STUDY 1

Issue

Scott Mann of Hawkins Associates in Georgia was challenged with an application for a waste water treatment solution for Jim Lewis of Complete Water Services located in Marietta Georgia. A primary concern was the serviceability and ownership costs relative to the pH and ORP sensors. The sensors ideally would be provisioned for in-line as well as submersion installations to simplify inventory logistics. A differential amplifier was also required to ensure ground loop problems were avoided as well as the electrode signal needed to be sent 100 feet back to the control panel. The use of a front end cartridge style electrode would be desirable as it was not practical to re-run 100 feet of cable when sensor replacement was required.

Solution

Hawkins Associates chose to offer CWS the Sensorex S8000 modular solution. The base cartridge style flat surface pH and ORP sensors were combined with a dual use in-line or submersion mounting holder with solution ground, interconnect cap cables with 100 feet of cable, flow cells were added for the in line configurations and the optional differential amplifier modules were plugged in between the cables and mounting holders. All parts are re-useable and only the sensor cartridges would periodically need to be replaced.

Result

After the project installation, Jim Lewis of Complete Water Services reported to Hawkins Associates: “The installation was for the control of pH and ORP in Industrial Waste Water. The key item he liked the most was having one style S8000 cartridge probe to use for both the submersion and in-line installations. This minimized the number of on-hand spares needed and reduced costs and the confusion factor for the customer when installing replacements. Also, the installation required the cable lengths to be 100ft or longer. He was able to use the same parts and add the optional EM801 differential pre-amp on both the pH and ORP probes to boost the signal back to the controllers. Using the external optional EM801 pre-amp will help reduce probe replacement cost as compared to the probes with the amplifier built in which cost substantially more.”

CASE STUDY 2

Issue

Danny Smith of NE PUMP of Lunenburg MA, had a plating customer who was only getting a service life of about 5-6 weeks from the sensors he was using. The installation was a basic simple submersion installation, but the application was aggressive toward the reference of the pH electrodes. The customer wanted to use the existing BNC cables and submersion pipes they had in place.

Solution

NE Pump decided to retrofit the installation with a Sensorex S8000CD electrode. The electrode cartridge incorporates an ERP reference path to protect the electrode in the presence of aggressive solutions. They provided a simple S8000 to BNR mounting adapter to connect to the existing assembly and coax cabling.

Result

NE PUMP reports: “The customer is now getting 8-9 months out of the S8000CD electrode. He is extremely pleased with the results. The retro-fit was quite simple and the cartridge is a solid electrode holding up extremely well in the aggressive solutions. Choosing the right electrode made all the difference and the versatility only required us to purchase minimal hardware.”

CASE STUDY 3

Issue

Bill Giglio of Facility Care outside of Cleveland OH had a challenge to improve service life of sensors and adapt these to multiple brands of instrumentation. His customer was a full Service Waste Water System Designer, Fabricator and Service Company with a Certified Laboratory.

Solution

Bill needed to address the issue of several different brands of controls used by his customer. The customer was looking for improved service life and help reducing the complexity of spare sensor logistics for multiple brands. Bill chose to offer the Sensorex S8000 solution to his customer. By utilizing the modular design and offering the hardware as needed to retrofit each specific brand and installation, he was able to provide them a cost effective electrode with dependability and dramatically simplify logistics of replacement electrodes for multiple brands of instrumentation.

Result

Facility Care reports: “My customer is achieving outstanding performance and service life. They only have to deal with a single replacement pH electrode for all the different brands and mounting configurations saving time, money and complexity. They have successfully retrofitted the S8000 to multiple brands of control instrumentation and they now use the S8000 pH electrodes for all their new installations, replacements and conversions whenever needed. The flexibility of the S8000 platform made the retrofits simple. The ERP reference system makes the cartridge the right choice for simple and difficult applications. The plug and play feature allowing the addition of a 4-20mA module for data logging”.

Conclusion

Hopefully this article has stimulated users to not overlook the importance of sensor considerations when purchasing, installing or retrofitting a pH or ORP measurement and control system. A small amount of thought on the front end will save time and expenses over the life of an installation. Existing installations can make changes to improve the current system as required. One should not feel they are boxed in by an off the shelf solution if it does not fit the requirement.