In wastewater treatment, industrial wastewater discharge, smart water management, circulating water control, and aquaculture engineering projects, water quality testing is no longer only a laboratory analysis process. It has become an important sensing layer for automation systems, data platforms, and process control loops. For system integrators, IoT solution providers, and environmental engineering companies, the correct selection of water quality monitoring parameters, sensor types, communication protocols, and installation methods directly affects project delivery efficiency, data stability, and long-term maintenance costs.
As an industrial water quality sensor manufacturer, YexSensor provides online water quality monitoring equipment and integration support for B2B project scenarios, helping engineering customers build stable, scalable, and easy-to-integrate water quality data acquisition systems. This article focuses on conventional water quality testing items such as COD, BOD, ammonia nitrogen, total nitrogen, turbidity, residual chlorine, and total phosphorus, and explains their engineering value, typical applications, and selection considerations.
1. Why Conventional Water Quality Testing Items Are the Core Sensing Layer of Engineering Systems
In water treatment projects, water quality parameters do not exist independently. COD, BOD, ammonia nitrogen, total nitrogen, and total phosphorus reflect pollution load and biological treatment status. Parameters such as turbidity, residual chlorine, pH, and dissolved oxygen directly affect process adjustment, disinfection control, and equipment operating safety.
For system integrators, a water quality online monitoring system usually needs to complete the following tasks:
Transmit on-site water quality data to PLC, SCADA, or cloud platforms in real time
Provide data support for aeration, dosing, discharge, reflux, alarm, and other control strategies
Reduce manual sampling frequency and improve project automation
Provide continuous data for environmental supervision, process optimization, and operation management
Support multi-parameter linkage analysis to improve system judgment accuracy
Therefore, at the project design stage, it is not enough to only compare the price of a single sensor. The measurement principle, installation environment, cleaning and maintenance, output signal, communication protocol, power supply method, and system compatibility should be evaluated comprehensively.
2. Conventional Water Quality Testing Items and Their Engineering Application Value
| Testing Item | Engineering Significance | Common Unit | Typical Application Scenario | System Integration Focus |
|---|---|---|---|---|
| COD | Reflects reducing substances and organic pollution load in water | mg/L | Industrial wastewater, municipal wastewater, discharge outlet monitoring | Range, anti-interference capability, cleaning maintenance, data compensation |
| BOD | Reflects the pollution level of biodegradable organic matter | mg/L | Biological treatment and wastewater treatment process evaluation | Linked analysis with COD; suitable for trend monitoring |
| Ammonia Nitrogen | Reflects NH3 and NH4+ pollution levels in water | mg/L | Wastewater treatment, aquaculture water, surface water | Temperature compensation, pH compensation, maintenance cycle |
| Total Nitrogen | Reflects the total amount of inorganic and organic nitrogen in water | mg/L | Nitrogen removal process and environmental discharge monitoring | Whether pretreatment or digestion system is required |
| Turbidity | Reflects the degree of water cloudiness caused by suspended solids, colloids, and microorganisms | NTU | Drinking water, circulating water, sedimentation tanks, filtration systems | Optical window cleaning, bubble prevention, sediment adhesion prevention |
| Residual Chlorine | Reflects the remaining effective chlorine level after disinfection | mg/L | Waterworks, pipeline network terminals, swimming pools, water treatment disinfection | Flow cell, constant flow conditions, pH influence |
| Total Phosphorus | Reflects the risk of eutrophication and phosphorus pollution level in water | mg/L | Rivers, lakes, wastewater treatment plants, discharge supervision | Digestion or analyzer system is usually required in many scenarios |
| pH | Reflects water acidity and alkalinity; a basic parameter for dosing and process control | pH | Industrial wastewater, neutralization tanks, reaction tanks | Electrode life, calibration cycle, temperature compensation |
| Dissolved Oxygen | Reflects the oxygen content in water; a key parameter for biological treatment and aquaculture systems | mg/L or %Sat | Aeration tanks, aquaculture water, river monitoring | Optical method is preferred; low maintenance; suitable for continuous monitoring |
3. COD and BOD: Core Indicators for Evaluating Organic Pollution Load
COD, or Chemical Oxygen Demand, is used to measure the amount of reducing substances in water that can be oxidized by a strong oxidant. In industrial wastewater and municipal wastewater projects, COD is commonly used to rapidly evaluate organic pollution load and is a core indicator in discharge monitoring and process control.
BOD, or Biochemical Oxygen Demand, reflects the amount of dissolved oxygen consumed when microorganisms decompose organic matter. BOD is closer to the actual operating logic of biological treatment systems and can be used to evaluate the biodegradability of wastewater. In engineering projects, the BOD/COD ratio is often used to judge the subsequent treatment route. When the BOD/COD ratio is relatively high, biological treatment is usually more feasible. When the ratio is low, pretreatment, chemical oxidation, or advanced treatment processes may be required.
For system integrators, COD and BOD are more suitable as trend monitoring and process evaluation parameters connected to data platforms. YexSensor can provide COD and BOD-related sensors or water quality analysis solutions according to project requirements, suitable for wastewater treatment plant influent and effluent, industrial discharge outlets, river sections, and smart environmental monitoring platforms.
4. Ammonia Nitrogen, Total Nitrogen, and Total Phosphorus: Data Foundation for Nitrogen and Phosphorus Removal Processes
Ammonia nitrogen mainly includes free ammonia NH3 and ammonium ion NH4+ in water. In wastewater treatment, biological filters, aquaculture, and surface water monitoring, an increase in ammonia nitrogen concentration usually indicates organic nitrogen decomposition, insufficient nitrification, or abnormal system load. For fish and aquatic organisms, high ammonia nitrogen levels may create toxicity risks.
Total nitrogen includes nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, and organic nitrogen. It is an important indicator for evaluating nitrogen pollution and nitrogen removal efficiency. Total phosphorus is closely related to water eutrophication. Excessive phosphorus content may cause massive algae growth, water blooms, or red tides.
In engineering applications, ammonia nitrogen can be used for continuous online monitoring. Total nitrogen and total phosphorus may require supporting analyzers, digestion units, or sampling pretreatment systems in some projects. For projects that need to connect to PLC or SCADA systems, it is recommended to clarify whether the data is required for continuous online monitoring, regulatory compliance, trend analysis, or process control at the solution design stage, so that the appropriate equipment type can be selected.
5. Turbidity and Residual Chlorine: Key Parameters for Water Supply, Disinfection, and Filtration Systems
Turbidity reflects the influence of suspended solids, colloids, organic matter, and microorganisms in water on light transmission. The commonly used unit is NTU. Turbidity is an important parameter in drinking water, filtration systems, circulating cooling water, and sedimentation tank operation. For system integration projects, the installation position of the turbidity sensor, optical window cleaning, bubble prevention design, and anti-fouling capability are very important.
Residual chlorine refers to the remaining effective chlorine content in water after disinfection. It is an important indicator for water supply safety, pipeline network terminal disinfection performance, and water treatment system control. In waterworks, secondary water supply, swimming pool water treatment, and industrial circulating water disinfection projects, online residual chlorine monitoring usually requires stable flow, a suitable flow cell, and pH compensation conditions. If the on-site water quality fluctuates significantly, the measurement method, installation method, and maintenance cycle should be confirmed in advance.
6. YexSensor Water Quality Online Monitoring System Integration Solution
YexSensor provides multiple types of industrial water quality sensors for B2B engineering projects, suitable for single-parameter monitoring, multi-parameter integration, data acquisition, remote transmission, and automated control scenarios. A typical system architecture is as follows:
Field Sensor Layer: COD, BOD, ammonia nitrogen, turbidity, residual chlorine, pH, dissolved oxygen, conductivity, ORP, and other sensors
Data Acquisition Layer: RS485 acquisition devices, data loggers, 4G gateways, IoT modules
Control System Layer: PLC, SCADA, HMI, dosing control cabinet, aeration control system
Platform Application Layer: Cloud platform, data dashboard, alarm system, reporting system, remote operation and maintenance platform
In actual projects, YexSensor can provide RS485 Modbus RTU, 4-20mA, and other output methods according to the needs of system integrators, making it easier to connect with mainstream PLCs, RTUs, DTUs, gateways, and SCADA systems. For unattended sites, 4G data transmission, solar power supply, and cloud platforms can also be combined to realize remote monitoring.
7. Product Selection Guide: Reverse Configuration from Project Objectives
7.1 Wastewater Treatment Plant Process Monitoring
Recommended configuration: COD, BOD, ammonia nitrogen, pH, dissolved oxygen, turbidity, ORP
Key focus: Aeration control, influent and effluent load variation, nitrification and denitrification status, effluent stability.
7.2 Industrial Wastewater Discharge Monitoring
Recommended configuration: COD, pH, turbidity, conductivity, ammonia nitrogen, flow
Key focus: High pollution load, corrosive media, on-site installation environment, data upload, and alarm linkage.
7.3 Drinking Water and Secondary Water Supply
Recommended configuration: Residual chlorine, turbidity, pH, conductivity, temperature
Key focus: Disinfection performance, pipeline network terminal safety, flow cell design, and low-range measurement stability.
7.4 Aquaculture and Recirculating Aquaculture Systems
Recommended configuration: Dissolved oxygen, pH, ammonia nitrogen, nitrite, temperature, turbidity
Key focus: Fish safety, aeration linkage, filtration efficiency, and real-time data alarms.
7.5 Rivers, Lakes, and Smart Water Management
Recommended configuration: COD, ammonia nitrogen, total phosphorus, total nitrogen, turbidity, dissolved oxygen, pH, conductivity
Key focus: Long-term stability, low power consumption, remote communication, protection rating, and anti-fouling design.
8. System Integration Considerations
First, confirm the characteristics of the water sample. Industrial wastewater may contain oil, suspended solids, strong acids, strong alkalis, oxidants, or corrosive substances. Material compatibility and cleaning methods must be confirmed in advance.
Second, confirm the communication protocol. For PLC and SCADA systems, RS485 Modbus RTU is a common choice. For traditional control cabinets, 4-20mA signals can be selected. For IoT platforms, data can be uploaded through data loggers or 4G gateways.
Third, confirm power supply and wiring. The site should be evaluated for power supply conditions, cable distance, anti-interference requirements, grounding methods, and lightning protection measures to avoid data instability caused by the electrical environment.
Fourth, confirm the installation method. Immersion, pipeline, flow cell, and bypass sampling installations are suitable for different operating conditions. Parameters such as residual chlorine and turbidity require special attention to flow rate, bubbles, and sedimentation.
Fifth, confirm the maintenance cycle. Online sensors are not completely maintenance-free. Calibration, cleaning, consumable replacement, and data comparison should be included in the project operation and maintenance plan.
Sixth, confirm the data usage. If the data is used for process optimization, trend stability is the main focus. If it is used for regulatory compliance, local regulations, certification requirements, and sampling analysis methods should be further confirmed.
9. FAQ
Q1: How should conventional water quality testing items be combined?
They should be selected according to the project type. Wastewater treatment projects should prioritize COD, BOD, ammonia nitrogen, pH, dissolved oxygen, and turbidity. Water supply projects should prioritize residual chlorine, turbidity, pH, and conductivity. Aquaculture projects should focus on dissolved oxygen, pH, ammonia nitrogen, nitrite, and temperature.
Q2: Do COD and BOD both need to be monitored online?
Not necessarily. COD is more suitable for quickly reflecting changes in pollution load, while BOD is more suitable for evaluating biodegradability. In engineering projects, one of them or a combined configuration can be selected according to control objectives, budget, and data usage.
Q3: Is RS485 Modbus RTU suitable for PLC integration?
Yes. RS485 Modbus RTU is a commonly used industrial field communication method, suitable for integration with PLC, RTU, data acquisition devices, and SCADA systems. Before project implementation, the register address, baud rate, data format, and power supply requirements should be confirmed.
Q4: How should 4-20mA and RS485 be selected?
If the system only requires a single analog signal, 4-20mA is simple and stable. If multiple parameters, digital transmission, device address management, and remote reading are required, RS485 Modbus is more suitable for system integration projects.
Q5: Must a residual chlorine sensor be equipped with a flow cell?
For most continuous online residual chlorine monitoring scenarios, a flow cell is recommended to maintain a stable flow rate and reduce the influence of bubbles and pressure fluctuation on measurement. The specific configuration should be determined according to the on-site pipeline, water pressure, and installation method.
Q6: Can total nitrogen and total phosphorus be directly measured by ordinary sensors?
In some projects, total nitrogen and total phosphorus usually require digestion, reagent reaction, or analyzer systems, and they are not exactly the same as ordinary immersion sensors. During selection, it should be clarified whether the application is for trend monitoring, process control, or compliance monitoring.
Q7: Can sensor data be uploaded to a cloud platform?
Yes. YexSensor devices can be connected to cloud platforms through RS485 acquisition devices, 4G gateways, or data loggers to achieve remote viewing, alarms, reports, and data management. They can also be integrated with customers' own IoT platforms.
Q8: What should system integrators focus on most when purchasing water quality sensors?
They should focus on measurement parameters, range, accuracy, output signal, communication protocol, installation method, protection rating, maintenance cycle, adaptability to on-site water quality, and supplier technical support capability, rather than only the price of a single device.
10. Conclusion
Conventional water quality testing items are the foundation of water treatment automation and smart environmental protection systems. For system integrators, IoT solution providers, and engineering companies, the value of COD, BOD, ammonia nitrogen, total nitrogen, turbidity, residual chlorine, and total phosphorus is not limited to single-point testing results. Their greater value lies in whether they can be stably connected to PLC, SCADA, cloud platforms, and automated control systems to form a reliable data loop.
YexSensor provides sensors, communication interfaces, and system integration support for industrial water quality online monitoring projects, suitable for wastewater treatment, industrial wastewater, water supply disinfection, aquaculture, river monitoring, and smart water management applications. Through reasonable parameter combination, reliable communication protocols, and engineering-based installation design, project parties can improve monitoring efficiency, reduce operation and maintenance difficulty, and lay a foundation for subsequent automatic control and data management.
