Under the framework of the Industrial Internet of Things (IIoT) and green manufacturing, the centralized treatment of wastewater in industrial parks has become a core indicator to measure the smart and ecological construction of the parks. The high density of enterprises and significant variations in production processes within industrial parks result in discharged wastewater characterized by highly complex compositions, high toxicity, numerous refractory substances, and severe fluctuations in water quality. The interweaving of inorganic wastewater, organic wastewater, heavy metal wastewater, and chemical wastewater poses immense process challenges to the centralized wastewater treatment plants (WWTP) of the parks.

For system integrators, IoT solution providers, and environmental engineering contractors, building a water quality monitoring and automated treatment system with high stability, high compatibility, and anti-interference capabilities is the key to ensuring that the park's drainage fully meets discharge standards and achieves water reclamation (such as meeting boiler feed water standards).

Multi-stage Wastewater Treatment Processes and System Integration Architecture in Industrial Parks

Standard centralized sewage treatment systems in industrial parks generally adopt a dual-control mode of "decentralized pre-treatment at the enterprise end + centralized deep treatment at the park end." Based on the wastewater characteristics of different industrial sectors (such as the chemical industry, coal chemical industry, and metallurgical industry), integrators need to configure corresponding monitoring and control units according to different process nodes.

Biochemical Treatment Integration for Mixed Chemical Wastewater

Biochemical treatment is the core of wastewater treatment in the park, mainly including anaerobic treatment (complete anaerobic and incomplete anaerobic processes) and aerobic treatment (activated sludge process, SBR sequence batch activated sludge process, and BAF biological aerated filter).

• Integration Points: In the biochemical reaction tanks, the system needs to monitor dissolved oxygen (DO), pH value, oxidation-reduction potential (ORP), and mixed liquor suspended solids (MLSS) in real time. Through the closed-loop control of these physical and chemical parameters, the variable frequency of the aerator and the flow rate of the reflux pump are adjusted to prevent biofilm poisoning or sludge bulking caused by excessively high concentrations of incoming organic matter.

Gravity Sedimentation and Coagulation Flotation Control

For industrial wastewater containing high concentrations of suspended particles from industries such as cement and metallurgy, gravity sedimentation is widely used, supplemented by coagulant aids such as polyacrylamide (PAM) or polyaluminum chloride (PAC).

• Integration Points: Integrators need to integrate online turbidity meters or suspended solids (SS) sensors at the front end of the sedimentation tank. The measured data directly links with the metering pumps of the chemical dosing system to realize automatic adjustment of the PAM dosing ratio based on the incoming turbidity, ensuring that the removal rate of suspended particles remains stable at above 80% to 90%.

Multi-stage Combined Advanced Oxidation Process (A/O + Ozone + Biological Filter)

For refractory and complex wastewater such as coal chemical wastewater, the mainstream engineering solution currently adopts a multi-stage combined process consisting of "hydrolysis acidification + A/O (Anoxic/Oxic) + ozone oxidation + submerged aerobic biological filter + cloth media filter."

• Integration Points: The degradation efficiency of organic compounds in the ozone advanced oxidation stage relies heavily on the ozone dosing amount and residual concentration. The system must integrate high-precision UV absorption (UV254) online COD monitors and residual ozone-in-water analyzers at the outlet of the ozone contact tank to evaluate the effect of organic decomplexation and degradation, thereby preventing excessive ozone from entering the subsequent submerged biological filter and destroying the microbial flora.

Membrane Separation and Freeze Concentration System Monitoring

In specialized wastewater treatment and resource recovery (such as food raw material trapping and heavy metal reclaimed water reuse), membrane treatment technologies like ultrafiltration (UF) and reverse osmosis (RO), along with freeze concentration technologies, are widely applied.

• Integration Points: The core of membrane system integration lies in anti-fouling and pressure monitoring. Integrators must configure differential pressure transmitters at both the front and rear ends of the membrane modules, and monitor conductivity and total dissolved solids (TDS) online. When the desalination rate drops or the differential pressure exceeds the set threshold, the PLC control system automatically triggers the clean-in-place (CIP) process.

Industrial Water Quality Sensor Selection Guide

In highly harsh and complex industrial park wastewater environments, ordinary consumer-grade or laboratory-grade sensors can easily fail due to chemical corrosion, electrode contamination, and electromagnetic interference. Tailored for industrial-grade system integration, YexSensor provides water quality hardware support featuring high durability and digital output.

The following table outlines the core hardware selection parameters for system integrators when designing water quality monitoring chains for industrial parks:

Engineering Practices and Scenario Applications from a System Integrator's Perspective

From the perspective of field deployment and IoT system architecture, system integration for industrial park wastewater treatment typically encounters three major technical bottlenecks: high background chemical interference, complex onsite electromagnetic environments, and physical structural fouling.

Data Bus Design and Electrical Isolation

In large-scale industrial parks, monitoring points are distributed across various structures, with transmission distances often reaching hundreds or even thousands of meters.

• Communication Protocol Standard: The solution should utilize RS-485 buses across the board, running the standard Modbus RTU protocol. Compared to traditional 4-20mA analog signals, a digital bus allows multiple YexSensor probes with different parameters (pH, DO, conductivity, turbidity) to be daisy-chained on a single shielded twisted pair, greatly reducing field wiring and PLC analog module procurement costs.

• Anti-interference and Lightning Protection Design: Addressing the common-mode interference generated by the start and stop of large pumps and mixers in sewage plants, the bus integration must employ optoelectronic isolation devices to ensure that the communication interface of each sensor possesses an electrical isolation capacity of no less than 2KV. Meanwhile, for outdoor cable tray routing, surge protective devices (SPD) must be configured to prevent transient overvoltages from lightning strikes from burning out the bus equipment.

Bypass Flow Cell and Submerged Deployment

Depending on the flow velocity and physical characteristics of the water body, integration deployment is divided into two formats:

[Main Process Pipeline] ---> (Manual Valve) ---> [Bypass Flow Cell (Configured with Self-cleaning YexSensor)] ---> [Return / Discharge]
                                                    ^
                                                    |--- (PLC Linkage Compressed Air / Automatic Brush)

• Bypass Flow Cell Architecture: For inlet ends or high-pressure pipelines with high corrosion and high suspended solids, bypass installation is recommended. By introducing wastewater into a dedicated bypass flow cell via an induction pipe, the water flow velocity is controlled between 0.5m/s and 1.0m/s. This ensures measurement real-time accuracy and allows technical personnel to close the valves at both ends to calibrate and maintain the sensor without interrupting the main process line.

• Self-cleaning Mechanism Integration: Oil fouling adhesion and biofilm growth easily occur in coal chemical or food wastewater. When choosing equipment, integrators should prioritize probes equipped with an integrated mechanical wiper or those that support external compressed air/water spray cleaning interfaces. The PLC can be set to trigger a self-cleaning sequence every 4 to 12 hours, effectively preventing data drift caused by sensor window contamination.

Technical QA in Environmental Engineering Projects (FAQ)

Q1. Industrial park wastewater has a complex composition, and ordinary glass pH electrodes easily suffer from poisoning and failure in chemical wastewater. How can this be resolved?
   Traditional pH electrodes easily face contamination of their internal reference system (known as "electrode poisoning") in chemical wastewater containing strong acids, strong bases, organic solvents, or heavy metal complexes. In integrated system designs, an industrial pH sensor with a double junction featuring a polytetrafluoroethylene (PTFE) large annular ring or solid gel electrolyte should be selected. This structure significantly extends the diffusion path of harmful ions to the internal reference electrode, thereby greatly increasing the sensor's lifespan in harsh chemical water quality.

Q2. Why is an optical dissolved oxygen sensor recommended instead of a membrane (polarographic) method in A/O processes and biochemical reaction tanks?
   Polarographic dissolved oxygen sensors rely on a Teflon breathable membrane and require electrolyte consumption. In industrial park sewage, residual gases such as hydrogen sulfide (H2S) and ammonia penetrating the membrane will directly corrode the internal precious metal electrodes. Moreover, high-concentration sludge easily blocks the breathable membrane, causing high-frequency system shutdowns for maintenance.
   The optical dissolved oxygen sensor is based on the principle of fluorescence quenching, does not consume oxygen, requires no specific flow velocity limitations during measurement, and has no breathable membrane or electrolyte on the sensor surface. It exhibits strong resistance to sulfides and interfering ions, immensely reducing the long-term operation and maintenance costs of integrated systems.

Q3. How can the Modbus RTU protocol be utilized to integrate multiple water quality probes with different parameters onto a single PLC serial port?
   Modbus RTU allows different devices to be distinguished via a Slave ID. Integrators can use host computer software before factory shipment or during onsite configuration to modify the slave addresses of the pH, conductivity, and turbidity sensors within the same network to unique values (for example: 01 for pH, 02 for conductivity, and 03 for turbidity). When writing the PLC or RTU acquisition program, a polling mechanism is adopted to sequentially send Modbus 03 commands to read registers from each address, leaving a bus idle interval of 50ms to 100ms between them to achieve stable acquisition of multiple parameters via a single serial port.

Q4. After coal chemical wastewater undergoes ozone oxidation, how can the degradation effect of advanced oxidation be accurately evaluated and linked for control?
   Ozone oxidation is primarily used to cleave conjugated bonds of large, refractory organic molecules. In system integration, online monitoring of UV254 (UV light absorption rate at 254 nm wavelength) can be implemented to replace or supplement traditional chemical-method COD monitoring. Since organic compounds containing aromatic rings or conjugated double bonds exhibit strong absorption at 254nm, variations in UV254 correlate highly with COD. Furthermore, this measurement uses a physical method, providing second-level responses. The PLC system can dynamically adjust the output power of the ozone generator or the dosing rate of ozone gas based on the real-time drop in UV254.

Q5. In gravity sedimentation methods, how can sensors achieve efficient closed-loop linkage control with chemical dosing pumps (PAC/PAM)?
   To achieve accurate chemical dosing, the integrated system should be configured with a feed-forward or feedback control loop. The data from the suspended solids (SS) sensor installed at the inlet of the sedimentation tank serves as the feed-forward input, calculating the theoretical chemical dosage according to the inlet load (flow rate × SS concentration). Concurrently, the turbidity sensor at the outlet of the sedimentation tank serves as the feedback correction. Through the internal PID control algorithm of the PLC, 4-20mA signals or Modbus commands are output to adjust the stroke frequency of the chemical dosing metering pump, ensuring that chemical consumption is minimized while output compliance is met.

Q6. In reverse osmosis (RO) membrane treatment processes, what specific requirements does high-salinity wastewater place on sensors?
   High-salinity wastewater possesses extremely high conductivity. When traditional two-electrode conductivity sensors face high-conductivity media, a severe electrode polarization effect occurs on the electrode surface, resulting in poor linearity in high-range segments and vulnerability to scaling effects.
   The integrated system should configure a four-electrode conductivity meter or an electromagnetic induction (inductive) conductivity meter at the RO inlet end and brine end. Four-electrode technology completely eliminates polarization errors and lead resistance impacts by separating the current and voltage electrodes. Meanwhile, because the inductive sensor is fully encapsulated in plastic and does not come into direct electrical contact with the water body, it fundamentally eradicates electrochemical corrosion and scaling interference under high-salt conditions.

Q7. How can water quality sensors in industrial park wastewater treatment systems be prevented from exhibiting data distortion in winter or low-temperature environments?
   The physical and electrochemical characteristics of water bodies (especially pH and conductivity) are significantly influenced by temperature variations. For instance, the ionization constant of aqueous solutions increases with rising temperatures. If uncorrected, the pH measured for the same sewage composition at different temperatures will differ vastly.
   Consequently, the selected water quality sensors for integrators must feature integrated high-precision temperature sensors (such as PT100 or PT1000) internally, and enable hardware-level or software-level automatic temperature compensation (Automatic Temperature Compensation) algorithms to convert all measurement results uniformly to standard values based on a 25-degree Celsius reference.

Q8. For industrial park factory outlets that frequently experience flow interruptions or intermittent discharges, how should the monitoring point deployment solution be designed?
   If a sensor is directly submerged in an open channel that frequently dries up, prolonged exposure of the electrode (especially the pH electrode) to air will cause the sensitive membrane to dry out and deteriorate, severely reducing its lifespan.
   To address such scenarios, a "U-shaped water traps" or a flow cell configured with isolation valves should be engineered. When the factory stops discharging, the U-shaped bend or flow cell can still maintain a filled state, keeping the sensor constantly in a wet, submerged environment. When the next discharge arrives, the new water flow will naturally flush and replace the stagnant water body, thereby ensuring sensor safety and measurement continuity.

Conclusion

Industrial park wastewater treatment is a highly sophisticated system engineering task. Addressing diverse pollution components such as inorganic, organic, and heavy metal compounds, the stable operation of every process node—from biochemical treatment and gravity sedimentation to advanced oxidation and membrane separation—deeply depends on the real-time accuracy of underlying monitoring data. For system integrators and project contractors, selecting industrial-grade water quality sensors with high anti-interference capabilities, digital outputs, and high physical durability is not only the hardware foundation to satisfy strict environmental audits, but also the key to optimizing chemical dosing and achieving automated, low-carbon operations in industrial parks. YexSensor is dedicated to providing highly adaptable sensor closed-loop solutions for global industrial IoT and environmental water treatment projects, helping integrators build a more robust and intelligent industrial wastewater treatment ecosystem.