Development Story: Powerful Antifouling pH Electrode

Water is indispensable to our daily life. 

Water treatment plants and other such facilities clean the wastewater produced from our daily lives and industry before it is returned to our rivers and oceans in order to protect our aquatic environments. 
pH control is essential to increase the efficiency of processes that clean this wastewater.

An activate sludge process using microorganism cleanses human grime, machine oil, and other organic contaminants found in wastewater. To ensure the high activity of functional microorganisms in the activated sludge, the wastewater must maintain a neutral pH level. However, contaminants in heavily polluted wastewater stick to the pH electrodes during the treatment processes, which lowers the sensitivity. The challenge for many years has been the tediousness of numerous daily cleanings, calibrations, and other maintenance.

In October 2022, the HORIBA Group released its new Gel-filled Self-cleaning pH Electrode. This is the first pH electrode in the world^*1 to apply photocatalyst and antifouling technologies.
The new self-cleaning pH electrode successfully reduces the maintenance burden up to 99%^*2 compared to conventional approaches thanks to its ability to continuously measure pH levels even when processing wastewater heavily polluted with organic contaminants.

We talked with Yuji Nishio about the difficulties and challenges that he had to overcome while developing this product for about 17 years. 

The words of Masao Horiba, the founder of HORIBA Ltd., who passed away in 2015, inspired the development of an antifouling electrode. 
I commercialized a cleaning solution for pH electrodes not long after joining the HORIBA Group. At the time, Founder Horiba said to me, “You’ve made a wonderful cleaning solution. I’d like you to develop an antifouling electrode next.” I remember his words really resonating with me because he had developed the first glass electrode pH meter in Japan himself while managing the company.
I was also surprised that the response to my cleaning solution surpassed expectations despite costing ten times as much as a household cleaner. Originally, this product was part of our lineup to improve the reliability of the electrodes. I was shocked that our customers were struggling this much with dirty pH electrodes. I become committed to developing an antifouling electrode through this experience.
 

I happened to reconnect with a mentor of mine from back in my school days at an association meeting in 2006. When I discussed the development of an antifouling pH electrode, he introduced me to Tadanori Hashimoto, professor at Mie University, who belonged to the Inorganic Materials Science Laboratory, a world-renowned laboratory in the glass industry. At the time, he was researching ecological glass with photocatalytic properties. This ecological glass realizes an antifouling function by breaking down contaminants on the glass and lowering adhesion when exposed to sunlight. In fact, this glass is used in some windows of airport passenger terminals to help reduce the need to clean the glass. 

Dr. Hashimoto and I agreed to take advantage of the photocatalytic properties of this self-cleaning glass in a pH electrode and started our collaborative research.

A uniform photocatalytic coating is difficult to do on glass pH electrodes because the tip that is vital for measurement of the electrode is round. We tried sprinkling titanium oxide powder (photocatalyst) into the melted glass of the pH electrode, but this did not provide the performance that we thought it would. The development took a lot of different trial and error.

I finally used a special dip-coating technique^*3 suitable for curved surfaces based on the advice of Dr. Hashimoto. This led to the successful development of the glass necessary for a self-cleaning electrode.

Experiments using pigments discovered the conditions necessary to sustain pH electrode performance while realizing photocatalytic antifouling around 2008. However, there was a huge pitfall between the research and commercialization stage.

Analyzers provide criteria to make specific decisions. Especially in industrial applications, a single mistake due to low stability or accuracy may cause accidents or product defects. Differentiating our pH meter from competitors is difficult by pursuing higher accuracy and stability alone because we must also consider the manufacturing process. Adoption of new components requires consideration of a variety of risks involved. This entails a different challenge from those faced during research.

That is why the next step started the trial and error necessary to overcome the obstacles standing in the way of commercialization.
Industrial pH electrodes must be able to be used continuously in applications to monitor and control water quality. An electrode that never gets dirty would be ideal. Our research efforts successfully irradiated an electrode tip coated in a photocatalyst to light from a xenon lamp^*4 to break down contaminants. However, xenon lamps are very expensive. I also consider running optical fiber through the inside of the electrode, but optical fiber costs about the same as the electrode. We tested to see if natural sunlight would be effective, but it wasn’t at all. Black light could not reach an electrode submerged under the water either. Unable to find a light source suitable for the harsh environment where industrial electrodes are used, our research and development met with a setback as we stumbled into the pitfalls of commercialization.
 

A blue light-emitting diode won the 2014 Noble Prize in Physics.
Fortunately for me, this small blue LED came onto the market as research blossomed. When I saw the news, I thought this might be the answer to make an antifouling electrode a reality. By then, however, the development project had been dissolved, and I had been transferred to the department for commercialization, not research.

I still was not ready to give up commercializing an antifouling pH electrode. I continued my research while working in commercialization despite objections from people around me. Although this was a lonely pursuit, I aimed to get the data that would highlight how to commercialize an antifouling electrode. 
During this time in my life, I was blessed with twins. I was overjoyed but also overwhelmed with days of sleepless nights while raising children, conducting this research, and working to heighten my expertise by earning a Ph.D.  in engineering. I was gradually becoming both physically and mentally exhausted, but I pushed onward motivated by a desire as an engineer to not only help customers overcome this problem but also advance research in this field.

HORIBA has Blackjack Projects, which act as an internal improvement program. Once I had the geometry for the pH electrode, I took advantage of the Blackjack Project to launch a development team in order to collaborate with my colleagues at HORIBA. I also asked Professor Satoshi Kaneco from Mie University if I could use his aeration tank (microbial chamber) as a practical testing space to evaluate my electrode design. Our partner companies got involved as well. Thanks to all of this help, we finally completed a pH electrode equipped with an internal ultraviolet light emitting diode (UV-LED) and could start practical experiments in the aeration tank.
Founder Masao Horiba was overjoyed when I showed him my prototype. “If you can successfully commercialize this, I will commemorate your success not with our 

The results of the actual test showed the UV light intensity was weak and could only achieve antifouling on a portion of the response glass membrane. The speed with which contaminants broke down was slower than that with which contaminants adhered to the glass.

I was shocked when I saw the electrode. I knew the laboratory differed a lot from the actual usage environment, but it was a moment when everything I had worked so hard to build up was shattered in an instant.

In my despair, I just happened to hear from an LED manufacturer that they had just released a new UV-LED. The price was almost the same as the conventional LED, but this UV-LED offered about ten times the UV intensity. This was a stroke of good fortune. Cleaning functions for air-conditioners and other devices had made products using UV-LED commonplace, driving up the UV-LED demand while propelling new product development forward.
 

In 2017, we finally realized a self-cleaning electrode that lasted between one and two months in an aeration tank.
There were still some hurdles to overcome for commercialization though, such as performance, stability, and durability. Every obstacle caused worry, but I steadily made progress by using new materials developed together with our partner companies and a lot of other trial and error. 
A customer at a food product plant who helped us in the proof-of-concept testing encouraged me with kind words, saying, “Please don’t worry. I told my supervisor that I would take responsibility so you can use our plant however you see fit. It would be great if this becomes a product soon.” Day or night, rain or shine, this plant manually cleaned and maintained its electrodes every day. I could really feel once again how much companies like this wanted us to succeed in commercializing this product.

We finally completed a self-cleaning electrode thanks to the help of so many people. Many of the customers who had helped us with implementation tests before the release praised our new product: “We’ve tried so many different cleaning functions, but none work.” “It’s unbelievable.” “The prototype was so good that I want to buy it.” I finally felt all those years of hard work had paid off as I heard these kind words praising the developers.

Looking back on the last 17 years, I completed this product thanks to wonderful people, including our customers, the professors, and my colleagues at HORIBA, as well as their unified passion, tenaciousness, and search for discovery as engineers. I must also say that there are not many companies who take on the challenge of such a long research and development project. I believe that this success is due to the love for glass electrodes given to me by my mentors as well as a fun environment that enables employees to pursue their own research themes, praises people for taking on challenges, and celebrates one little success after another.
The world tends to believe we have already learned all we can about glass pH electrodes, but I am confident these electrodes have much more potential. My challenge is still not over.

*1 First in the world as a glass electrode-type pH meter (based on internal research as of October 2022).
*2 99% compared to conventional HORIBA products. The effectiveness differs according to the usage methods and conditions.
*3 The dip-coating technique applies a gel film by immersing a base material in a low viscosity solution, and then gradually raising the base material out of that solution at a consistent speed. The solvent evaporates from the solution to create a gel film on the surface of the base material. Dip coatings are uniquely suitable for coating large areas or curved surfaces.
*4 A xenon lamp uses a light source that discharges electricity in xenon gas for a strong light intensity similar to natural light.

Yuji Nishio, Dr.Eng.
Senior Meister,
Advenced Technology Research and Development Department,
HORIBA Advanced Techno, Co., Ltd.

[Awards]
・Paper Encouragement Award 2018, Outstanding Paper Award 2019 and 2023 (Co-author), the Society of Environmental Instrumentation Control and Automation
・Encouragement Award 2019, Advanced Analysis Technology Award JAIMA Equipment Development Award, the Japan Society for Analytical Chemistry
・Kyoto Prefecture Invention Merit Award 2024
・Kinki Regional Invention Awards, Minister of Education, Culture, Sports, Science and Technology Award 2024
 

Gel-filled Self-Cleaning pH Electrode Using Antifouling Technology