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Many users ask during consultation: "Is an online wastewater monitoring instrument a single instrument or multiple instruments?" In fact, an online wastewater monitoring instrument usually refers to an integrated monitoring system composed of various online analytical instruments and sensors with different functions. The system configuration depends on the specific wastewater monitoring items required by the user, including core indicators such as COD, ammonia nitrogen, total phosphorus, total nitrogen, total phenol, PH, and dissolved oxygen. For system integrators, understanding the measurement principles and integration logic of each device is the key to project delivery.
Working Principles of Mainstream Wastewater Online Monitoring Equipment
1. COD Online Monitoring Equipment
The instrument uses the potassium dichromate high-temperature digestion and colorimetric method. In a high-temperature and high-pressure environment, water samples, potassium dichromate, silver sulfate (catalyst), and concentrated sulfuric acid are mixed, and the reducing substances in the water sample reduce hexavalent chromium (Cr VI) to trivalent chromium (Cr III). By measuring the degree of change in the color of the solution through photoelectric colorimetry, the chemical oxygen demand (COD) concentration can be directly calculated. For chloride ion interference in water samples, the COD online analyzer can eliminate it by adding mercury chloride for complexation.
2. Total Phosphorus Online Monitoring Equipment
The instrument uses the ammonium phosphomolybdate colorimetric method. Under high-temperature, high-pressure acidic conditions, polyphosphates and other phosphorus-containing compounds in the water sample are hydrolyzed to generate phosphate radicals; other difficult-to-oxidize phosphorus compounds are oxidized to phosphate radicals by the strong oxidant sodium persulfate. In an acidic medium, orthophosphate reacts with ammonium molybdate and potassium antimonyl tartrate to generate phosphomolybdenum heteropoly acid compounds, which are reduced to blue phosphomolybdate by ascorbic acid. The instrument obtains the total phosphorus content in the water sample by measuring the absorbance.
3. Total Nitrogen Online Monitoring Equipment
The instrument uses the ultraviolet colorimetric method. Under high-temperature and high-pressure conditions, the potassium persulfate oxidant digests various nitrogen-containing compounds in the water sample and converts them into nitrates. After adjusting the acidity and alkalinity of the solution, under ultraviolet light irradiation, the depth of the solution color is proportional to the total nitrogen content in the water sample, and the final concentration is calculated by measuring the absorbance value.
Sensor Technology and System Integration Selection Table
| Monitoring Index | Recommended Model | Measurement Principle | Application Logic |
|---|---|---|---|
| pH Value | YEX-S1-PH | Glass Electrode Method | Real-time Acid-Base Monitoring |
| Oil-in-Water | YEX-S2-OIL-8 | Fluorescence Method | Industrial Wastewater Oil Content Monitoring |
| COD | YEX-S2-COD-8 | Dual-wavelength UV Absorption Method | Organic Pollution Total Control |
| Ammonia Nitrogen | YEX-S2-NHN | Ion Selective Electrode Method | Sewage Ammonia Nitrogen Warning |
| Automatic Cleaning | Clean-200 | Physical Cleaning | Reduce On-site Electrode Maintenance Cycle |
| Flow Installation | Cell-100A | 3/4" NPT Thread | Pipeline Network Sampling Monitoring |
| Integrated Control | YEX-S2-MPS-A | Multi-parameter Integration | System Integration Central Node |
System Integrator Application Scenarios and Precautions
For integrators, wastewater monitoring is not just a combination of instruments, but involves on-site environmental adaptability. When building a wastewater online monitoring system, be sure to pay attention to the following points:
Sampling System Stability: 70% of the accuracy of online monitoring depends on the sampling system. Select sampling devices with anti-blocking and automatic backwashing functions, such as the recommended Cell-100A.
System Compatibility: All analytical instruments should support the standard Modbus RTU protocol to ensure that they can be uniformly uploaded to the environmental protection platform through YEX series controllers.
Anti-interference Design: The on-site power environment is complex. Signal transmission should use shielded twisted-pair cables, and sensors should be physically isolated from high-voltage power lines to avoid electromagnetic interference affecting measurement accuracy.
Frequently Asked Questions (FAQ)
Q1: Does the wastewater online monitoring system require regular maintenance?
A1: Yes, the system includes reagent consumables and sensor probes, which usually require calibration and reagent replenishment every quarter to ensure the continuity and accuracy of the data.
Q2: Why is there a large deviation between my online monitoring COD data and laboratory data?
A2: It may be caused by insufficient water sample pretreatment, unrepresentative sampling points, or incomplete elimination of chloride ion interference. Recalibration and inspection of the sampling logic are required.
Q3: How does Clean-200 link with the upper-level machine?
A3: This bracket supports Modbus instruction triggering. Integrators only need to write timer logic in the PLC and send instructions through the bus to realize automatic cleaning.
Q4: How far can the system support data transmission?
A4: Basic equipment supports RS485 bus, and with IoT gateways, it can realize remote cloud transmission of data worldwide.
Q5: Can the equipment be installed directly in strong acid and alkali wastewater?
A5: Direct immersion is not recommended. It is necessary to be equipped with a Cell-100A flow cell and perform PH adjustment or dilution treatment on the sample to protect the service life of the sensor.
Q6: How to judge whether the monitoring data meets the standards?
A6: The system can set threshold alarms in the background. Once the indicators exceed the emission limits stipulated by local environmental protection departments, the system will trigger an automatic alarm function.
Q7: Does integration need to consider explosion-proof requirements?
A7: If the monitoring point is located inside the production workshop of a chemical zone, all monitoring equipment must have explosion-proof certification.
Q8: Does YexSensor provide sensor installation accessories?
A8: We provide a variety of installation interfaces, including 3/4" NPT thread adapters, supporting immersion installation or pipeline installation, which greatly simplifies construction difficulty.
Summary
The wastewater online monitoring instrument is not a single device, but a comprehensive monitoring system composed of a series of precision instruments. For system integrators, reasonable equipment configuration according to on-site working conditions, optimization of pretreatment schemes (such as using Cell-100A and Clean-200), and the establishment of standardized integration processes are the keys to ensuring stable project operation and data compliance. Through scientific selection and rigorous system integration, the environmental management efficiency of enterprises can be greatly improved, realizing visualized and intelligent management and control of wastewater discharge.
