Electrode UV COD Sensors: A New Efficient Choice for Online Organic Pollution Monitoring

Chemical Oxygen Demand (COD), as one of the most critical comprehensive indicators of organic pollution in water environment monitoring, is like body temperature in human health—it quickly reflects the relative content of organic matter in water bodies. Rather than targeting a single substance, COD represents all reducing substances that can be oxidized by strong oxidants, mainly organic compounds, and is expressed as oxygen equivalent in mg/L. In river assessment, industrial wastewater treatment, and performance evaluation of wastewater treatment plants, COD is an indispensable parameter because it is directly linked to oxygen consumption potential, ecological balance, and discharge compliance.

Although the traditional potassium dichromate method is accurate, it requires chemical reagents, heating digestion, titration, and other complex steps. It is time-consuming and generates secondary pollution, making it unsuitable for real-time online monitoring. With advances in optical technology, the ultraviolet absorption-based electrode UV method (UV254 method) has gradually become mainstream. This method utilizes the characteristic absorption of most organic substances—especially compounds containing aromatic rings or unsaturated bonds—at the 254 nm ultraviolet wavelength. By measuring absorbance, COD values are estimated. In scenarios where water composition is relatively stable, it shows good correlation with chemical methods and has been widely applied in online instrument development. Nexisense UV COD sensors are a typical representative of this technology, gaining recognition in practical deployments for their stable performance and low maintenance requirements.

The Core Role of COD in Water Environment Monitoring

COD reflects the total amount of reducing substances in water, mainly originating from organic matter degradation processes. These organic substances are oxidized by microorganisms in natural cycles, consuming dissolved oxygen (DO). Once DO becomes insufficient, ecological balance is disrupted, leading to fish mortality, black and odorous water bodies, and degradation of self-purification capacity. The higher the COD value, the greater the organic load and the higher the potential risk. For example, domestic wastewater COD typically ranges from 200–500 mg/L, while industrial wastewater can reach several thousand mg/L. Timely COD monitoring helps assess treatment load, optimize aeration and chemical dosing, and achieve energy savings and emission reduction.

While traditional methods are reliable, their long laboratory analysis cycles and high costs cannot meet the needs of continuous online monitoring. UV-based methods fill this gap by offering second-level response times and long-term stability, making them the preferred choice for modern water quality monitoring.

Measurement Principle of Electrode UV COD Sensors

The UV254 method is based on the Beer–Lambert law: the intensity of ultraviolet light absorption by organic matter is proportional to its concentration. The sensor uses a 254 nm ultraviolet light source to irradiate the water sample and detects changes in transmitted or reflected light intensity. The absorbance coefficient (SAC254) is calculated and converted into COD values through empirical correlation models.

Most organic pollutants (such as humic acids, lignin, and aromatic compounds) exhibit strong absorption in the UV254 region, while inorganic interference is relatively small. Some sensors incorporate multi-wavelength or full-spectrum analysis to further eliminate background interference from turbidity, nitrates, and other factors. Nexisense sensors adopt an electrode-type optical design that integrates the light source, detector, and self-cleaning mechanism, ensuring a clean optical path and maintaining long-term accuracy.

The measurement process requires no chemical reagents and no sample pretreatment. Water samples directly contact the probe, providing fast response times and supporting continuous online operation. Typical detection ranges are 0–5000 mg/L with errors below 5%, suitable for various water bodies.

Key Advantages of UV COD Sensors

Compared with traditional chemical methods and electrochemical methods, UV-based COD sensors demonstrate multiple practical advantages in real-world applications.

• No reagents and no secondary pollution: Avoids the use of hazardous chemicals such as dichromate, making it more environmentally friendly and cost-effective.

• Real-time online monitoring: Second-level response captures dynamic water quality changes, enabling immediate process adjustments.

• Low maintenance requirements: Built-in automatic cleaning brushes prevent biofouling, bubbles, and dirt interference, extending maintenance intervals. Stability remains outstanding even under harsh conditions.

• Automatic turbidity compensation: Algorithms correct for suspended solids interference, improving accuracy in complex water samples.

• Factory calibration with no on-site adjustment: Plug-and-play operation simplifies deployment.

• Durable design: Scratch-resistant and easy-to-clean optical windows, RS485 digital interface, and MODBUS protocol enable easy integration with PLC or SCADA systems.

These characteristics make UV-based COD sensors particularly suitable for wastewater treatment plant aeration tanks, influent and effluent monitoring, surface water sections, marine aquaculture, and industrial discharge monitoring.

Application Scenarios and Practical Value

In wastewater treatment, UV COD sensors track influent load and effluent compliance in real time, reducing the risk of discharge violations. In river and lake monitoring, they provide early warnings of organic pollution and support ecological restoration. In industrial wastewater applications (such as textile, pharmaceutical, and food industries), they help evaluate biological treatment efficiency. Compared with offline sampling, continuous data supports refined management while reducing energy consumption and operating costs.

Nexisense UV COD sensors integrate multi-parameter capabilities (such as TOC, turbidity, and temperature), further enriching water quality profiles. In multiple projects, they have helped users shift from experience-based judgment to data-driven decision-making, achieving more efficient pollution control.

Frequently Asked Questions

How does the accuracy of UV COD measurement compare with chemical methods?
When water composition is stable, correlation is good (R² > 0.9). For high concentrations or special organic compounds, on-site validation of correlation curves is recommended.

Is measurement reliable at high turbidity?
Built-in compensation algorithms effectively eliminate interference, and the self-cleaning brush further reduces errors.

Are the sensors suitable for seawater or high-salinity environments?
The optical principle is not directly affected by salinity, and some models are optimized for seawater monitoring.

How often is maintenance required?
Maintenance frequency depends on water quality. With self-cleaning design, intervals are typically several months, far lower than traditional probes.

Conclusion: Embracing UV Technology to Drive Intelligent Water Quality Monitoring

As the “thermometer” of organic pollution, COD online monitoring is directly linked to water environmental safety and sustainable development. The electrode UV method, with its reagent-free, real-time, and low-maintenance advantages, represents a technological shift from chemical to optical methods. Through reliable optical design and intelligent compensation, Nexisense UV COD sensors help users obtain accurate data under complex conditions, enabling a transition from passive compliance to proactive optimization. In the future, with deeper integration of multi-parameter sensing and the Internet of Things, water quality monitoring will become more intelligent and efficient. Choosing the right technology ensures that every data point contributes to cleaner water bodies.