Best pH Sensors for Wastewater Treatment Plants

Do you know how much water is wasted without any treatment? According to UNESCO's 2023 report, more than 80% of wastewater is discharged without treatment, increasing environmental pollution. The sustainable development goals (SDGs) 6, 13, and 14 focus on clean water, the environment, and marine life, which can only be achieved when wastewater is treated before reusing or discharging it into rivers and seas.

In developed countries with strict environmental regulations and protection, the contaminated water from various sources like homes and industries is collected in a tank and sent to the wastewater treatment facilities, where it is processed before discharge. As per the EPA (Environmental Protection Agency), many parameters need to be monitored after wastewater processing and before its discharge into the environment, out of which the top 5 parameters are COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), TSS (Total Suspended Solids), ammonia, and pH.  

pH is a vital parameter measured at various points in the treatment facility, so monitoring it using a pH sensor is crucial. This article will step by step explain the pH sensor's working principle, types, and common uses and applications in wastewater treatment plants.

Introduction to pH Sensors for Wastewater Treatment

1.1 How pH Sensors Work

When using the word pH in our daily lives, do we think about what pH tells us? It's the hydrogen ion (H+) concentration in a solution. When pH=7, it means neutral/pure water. When pH<7, it means acidic (high concentration of H+ ions); pH>7 means basic (low concentration of H+ ions). In treatment plants, pH ranges from 5~9 at various stages.

The principle on which the pH water sensor works is electrochemical. A pH sensor has a reference electrode made of silver or silver chloride, which is coupled with a glass electrode (with a hydrated gel). The glass electrode acts as a sensing element, allowing hydrogen ions to interact with the gel when they enter the solution. This interaction develops a potential difference (PD) because of the difference in H+ ion concentration in the sample and between the reference and sensing element. This PD reflects the H+ ion concentration, translating into pH value using the Nernst Equation.

As one of the factors that tell the characteristics of water, pH is essential to monitor. In wastewater treatment plants, processes like coagulation and precipitation are pH dependent. Further, it affects the rate of microbial activity in biological treatment. Metal pipes and equipment in industries are affected by hydrogen ion concentration; low concentration increases the chances of scaling and clogging, while high concentration can cause corrosion.

1.2 Common Uses in Wastewater Monitoring

Sensors are used for monitoring purposes; pH sensors also have a wide use in various domains of wastewater, some of which are given below: 

• Sewage Treatment: pH is monitored and controlled within the treatment cycle at various steps. Monitoring is essentially to maintain a certain pH; for example, in the aeration tanks, microorganism growth relies heavily on pH values ranging from 6.5 to 8.5. Further, during aerobic digestion in sludge processing, pH is maintained from 6.8 to 7.5.

• Chemical Industry: Chemical industries' discharge is significantly contaminated; therefore, proper treatment and monitoring, especially pH, are part of the checklist before discharge.   

• Electroplating: pH sensors are placed near the discharge point to detect and manage acid or alkalinity. Since electroplating uses both acid and alkaline solutions, monitoring is necessary.

• Agriculture: Runoff from agricultural land contains fertilizers, pesticides, and other pollutants that must be monitored before discharge into nearby lakes or rivers. Depending on the use of chemicals and land fertility, runoff water is either acidic or alkaline, and pH monitors are placed to control it.   

Rika sensors are best suited for harsh environments and provide reliable results. The RK500-12 is a pH water sensor used to measure the pH of liquid solutions. It is designed with automatic temperature compensation (ATC) and protection against solid and liquid particles. It provides accurate results in any wastewater application. Rika sensors guarantee compliance with environmental standards with efficiency and durability.

Features of Top pH Sensors for Wastewater Treatment

♦ High Accuracy and Stability

In an environment where every bit counts, incorrect measurements might lead to serious problems. Mild variations in pH can disrupt the whole process in wastewater plants. Consequently, pH sensors must be highly stable and accurate to meet compliance.

The Rika Sensor (RK500-12) is the best quality available for pH measurement with an accuracy of ±0.05 and is stable for continuous monitoring with a change of ≤0.01 in 24 hrs. With this much accuracy and stability, the RK500-12 is recommended for every wastewater management plant.

♦ Temperature Compensation and Response Time

pH depends on temperature; unlike fixed calibration values, a pH sensor must adjust according to variation in temperature using automatic temperature compensation (ATC). This ATC feature is available in the RK500-12 liquid pH sensor (range: 0 to 80°C) but is optional and allows the user to opt in according to system requirements; it is especially recommended where there are high-temperature changes in wastewater systems.

Moreover, response time is essential for continuous monitoring applications, as conditions are dynamic. RK500-12 responds to changes in a flowing system in less than 8 seconds and 14 seconds in a static one.

♦ Rugged and Waterproof Design

The waterproof construction of a pH probe allows it to provide results in the long run in harsh conditions. The RK500-12 has an IP68 protection rating. IP stands for ingress protection, where the number 6 indicates that it protects against dust and particles, and the digit 8 means it's waterproof and allows for submersion during continuous operation up to 3 m. Further, the sensor casing comprises ABS or PPS plastic, which provides resistance against corrosion. Additionally, these sensors are designed to install in pipelines because of NPT3/4 threaded ends.

♦ Easy Output Integration

A sensor's output is either analog or digital, depending on system requirements; analog outputs are usually for field instrumentation, while digital outputs are used in control room monitoring. RK500-12 has dual outputs: 4–20mA analog and RS-485 digital (Modbus protocol). Both outputs are compatible with SCADA and PLC systems and are easy to install, acquire data from, and monitor.

♦ Simple Maintenance and Long Life

Sensor maintenance is simple, and with regular upkeep, the operational life of sensors can be prolonged. Calibration is an essential part of sensor maintenance. pH sensors used for clean water require calibration in 6 months, while calibration is due within 3 months for polluted water. Cleaning also lies in the domain of maintenance; sensors can be cleaned using alcohol (for organic contamination), potassium chloride solution (for removal of fouling), or diluted HCl or sodium hydroxide solution (for inorganic or acid removal).

Suggested pH Sensors for Wastewater Plants

3.1 RK500-12 Liquid pH Sensor 

When focusing on sustainability and building advanced, robust systems to cater to water waste, the equipment installed in the system needs to be smart with advanced technology. Rika Sensor is focused on the future and providing reliable and adaptable sensors. The RK500-12 liquid pH sensor is a one-of-a-kind pH sensor designed for modern technological use with advanced characteristics. It has a wide range from 0 to 14, covering basic, acidic, and neutral solutions. It is waterproof, submersible, and designed for harsh environmental conditions, meeting the IP68 protection rating criteria. Additionally, the ATC operates effectively from 0 to 80°C and adjusts pH accordingly to reflect actual values that change with temperature.

The RK500-12 is simple to install, clean, and maintain, and it is highly precise and accurate. Because of its wide applications, it can be used in sewage treatment plants, papermaking industries, pharmaceuticals, and agriculture.

3.2 RK500-09 Multi-parameter Water Quality Sensor 

For an all-in-one solution, Rika Sensor introduced the RK500-09 multi-parameter sensor that measures eight quality parameters of water: conductivity, turbidity, dissolved oxygen, chemical oxygen demand, oxygen reduction potential, ammonia, temperature, and pH. This sensor records all the essential parameters simultaneously, reducing the need for individual sensors. The RK500-09 also has an automatic cleaning unit that inhibits biofouling and ultimately saves time for maintenance. This sensor is the ideal choice for industries looking for a one-stop solution.

3.3 SE555 All-Purpose pH Sensor

Knick designed the SE555 all-purpose pH sensor to withstand harsh environments with high temperatures up to 135°C and pressures up to 6 bar, making it a perfect choice for chemical, food, and beverage industries and wastewater treatment plants. Unlike the RK500-12, the sensor has a wide measuring range from 0 to 14 and is made of durable construction. Also, it supports both PLC and SCADA, supporting effective data acquisition and process control. The SE555 uses memosens technology, eliminating issues at connection points related to corrosion. Additionally, these sensors are certified to be installed in hazardous areas.  

3.4  CPS11E Digital pH sensor Memosens

The Endress+Hauser CPS11E is a premier choice for a pH sensor with high reliability, precision, and longevity in harsh industrial conditions. This sensor uses Memosens 2.0, minimizing the effect of corrosion and moisture at the connection plates. Similarly, like all other sensors, it ranges from 0 to 14. It operates at a high temperature of 135°C and can withstand a high pressure of 17 bar. This pH sensor can store data related to calibration and processing for a prolonged period, which helps in predictive maintenance. These sensors are used in chemical processing plants, power-generating industries, and water purification systems.

3.5 InPro 3253i

To solve a problem with the pH sensor, Mettler Toledo brings in the InPro 3253i pH sensor, which is smart and specially designed for the pharmaceutical, food, and chemical industries. It shares almost similar specs with other sensors, having a range of 0 to 12, operational at 140 °C, and working well up to 4 bar pressure. The ISM function (Intelligent Sensor Management) makes this sensor smart and unique by providing real-time information about the sensor's health that helps in predictive maintenance. Just like the sensor, if you are smart, make a move to opt for this robust and intelligent sensor.

Conclusion

To compete in the fourth industrial revolution, where automation, innovation, and digitalization are at their peak, manufactured products must not just be good but exceptional. pH sensors for water with features like high accuracy, temperature compensation, IP rating, rugged design, longevity, and compatibility can help operate wastewater treatment plants efficiently. Moreover, they can help meet sustainability goals as per environmental standards.

If you are looking for high-end pH sensors, then consider Rika. Their goal is to ensure thoughtful products that are highly compatible. Their Rika RK500-12 and RK500-09 pH sensors are two great examples of combining accuracy and comprehensiveness. Both these sensors are reliable and used for various industrial applications. RK500-09 is a complete package measuring 8 parameters simultaneously with an automatic cleaning system, while the RK500-12 has a high accuracy of ±0.05 pH, an IP68 waterproof rating, and an optional automatic temperature compensation feature.  Rika has a variety of industrial application-based modern and innovative sensors. Visit the website https://www.rikasensor.com/ to explore its complete range.

pH sensors are vital for wastewater treatment.

FAQs

Q1: How often should I calibrate my pH sensor?
Calibration is performed to ensure reliable and accurate results from the equipment. When used in clean water, pH sensors require calibration within 6 months, and for typical wastewater, every 3–6 months. Sensors like the RK500-12 support easy calibration, with no professional tool needed.

Q2: What is the lifespan of a pH sensor?
Lifespan is a relative term depending on the equipment's usage and care. Typical sensors like the Rika RK500-12 will last 12–24 months, depending on water quality and maintenance frequency. The lifespan also depends on the type of sensor.

Q3: Can pH sensors measure in non-aqueous solutions?
pH sensor probes are designed for aqueous environments like water or wastewater. They provide unstable, drifting, and fluctuating values in alcohols, oils, and organic solvents. pH water sensors with traditional electrodes rely on measuring hydrogen activity in aqueous solutions.

Q4: Can pH sensors be used in high-temperature environments?
Yes, most pH sensors are designed for extreme environments up to 135°C. Sensors like RK500-12 are effective from 0 to 80°C and include optional temperature compensation for stable readings.