The keyword of this article is "water quality sensor". With increasingly stringent environmental protection requirements, the treatment of industrial high-salinity wastewater has attracted more and more attention. Based on this, this article analyzes the sources and characteristics of high-salinity wastewater, focuses on introducing the current application status, advantages, and disadvantages of industrial high-salinity wastewater treatment technologies, and prospects the future development trends of high-salinity wastewater treatment technologies.

In recent years, the water pollution situation in China has become increasingly severe, and the research and application of water treatment technologies have become the focus of experts and scholars in related fields in China. Wastewater, especially industrial wastewater, mostly possesses the characteristics of high salinity. Direct discharge will bring great harm to the natural environment, causing pollution and increased salinity in natural water bodies, or leading to problems such as soil salinization and compaction. Since the salt content in high-salinity wastewater cannot be removed through natural biodegradation processes, the salt issue must be resolved during high-salinity wastewater treatment, or a solution must be sought after harmless treatment is conducted.

Analysis of Sources and Characteristics of Industrial High-Salinity Water

Industrial high-salinity water mainly originates from the coal chemical industry, pharmaceuticals, pesticides, and other industries, with salt content above 10,000 mg/L. There are many process nodes where industrial high-salinity water is generated, and it generally belongs to a class of wastewater characterized by high toxicity and refractory biodegradability. The main channels through which industrial wastewater is generated include: in industrial production, a large amount of water resources needs to be consumed. To reduce the consumption of water resources, recycling methods for water resources are commonly adopted within the industry, thereby forming high-salinity water; during the preparation of pharmaceuticals, pesticides, and their intermediates, processes such as the salting-out process, chemical synthesis, and acid-base neutralization will generate wastewater with relatively high salt content. Because this type of wastewater originates from product manufacturing, it usually carries along a large amount of raw materials, products, and impurities, so it also features high toxicity and refractory biodegradability. Overall, industrial high-salinity water has the characteristics of large discharge volume, wide range of sources, high salt content, and complex components, and the high-salinity water generated by different industries varies significantly.

For Engineering, Procurement, and Construction (EPC) contractors, system integrators, and automation control engineers, implementing an online water quality monitoring system is essential to accurately manage these complex streams and maintain continuous control loop reliability under harsh field conditions.

Analysis of Current Application Status, Advantages, and Disadvantages of High-Salinity Wastewater Treatment Technologies

Evaporation Technology

Evaporation technology for high-salinity water is generally targeted at high-salinity wastewater with a salt content above 40,000 mg/L. For low-concentration high-salinity water with a salt content of 1% to 4%, the salt removal efficiency of thermal evaporation is too low, making this technology unsuitable. Specifically, thermal evaporation technologies mainly include: multi-effect evaporation technology and mechanical vapor recompression technology. Multi-effect evaporation technology refers to the simultaneous use of multiple evaporation kettles connected in series, where hot steam passes through several evaporation kettles in sequence; the hot steam from the previous evaporation kettle then enters the next evaporation kettle to evaporate stage by stage, effectively utilizing the heat source to achieve the goal of high-salinity wastewater desalination. Mechanical vapor recompression technology, abbreviated as MVR technology, is a process that effectively utilizes heat sources with the help of a steam compressor. It obtains power through the recompression of steam and continuously reciprocates to improve the thermal efficiency of steam.

Evaporation technology can successfully separate the salt and water in wastewater, allowing them to be treated separately afterwards, which is a relatively thorough method for treating high-salinity wastewater. Therefore, this technology currently sees wide application in the coal chemical, pharmaceutical, and pesticide industries. However, for saline water with excessively high organic pollutant content, foaming is highly likely to occur during the evaporation process, causing material boil-over; at the same time, it may also affect the quality of the salt, resulting in the discharged salt carrying over too much organic matter, which still requires further treatment.

Membrane Treatment Technology

A membrane is a material with selective permeability that can achieve the purification, concentration, and separation of materials. Membrane pore sizes are generally on the micrometer scale, and are classified from largest to smallest into microfiltration, ultrafiltration, and nanofiltration. Membranes can be divided into pressure-driven and electrically-driven membranes based on differences in driving forces. Several types of membranes commonly used in industrial high-salinity wastewater treatment include: electrodialysis membranes and reverse osmosis membranes. Electrodialysis technology is currently relatively maturely developed; its traditional application modes are seawater desalination and industrial salt production, and its application in industrial wastewater is mainly concentrated in relatively clean coal chemical wastewater. Reverse osmosis technology was also originally applied to seawater desalination. Using it to treat industrial high-salinity wastewater incurs a relatively high cost, and since pollutants mostly exist in industrial high-salinity wastewater, it easily causes membrane fouling, which not only affects production efficiency but also leads to a reduction in membrane lifespan or even damage.

Biological Treatment Technology

The biological method treats pollutants contained in industrial high-salinity wastewater through microbial flora. The treatment cost is relatively low, but the conditions are strict; first of all, the salinity cannot be too high, otherwise it will exceed the tolerance range of the microorganisms, causing the treatment effect to be lost. Currently, biological treatment has been applied within a certain scope, and there are many salt-tolerant bacterial agents on the market; however, overall, biological methods still face certain problems in terms of microbial screening and stable engineering operation.

Future Development Trends of High-Salinity Wastewater Treatment Technologies

Application of Pretreatment Technologies

High-salinity water comes from numerous sources and has complex compositions; direct desalination or biological treatment cannot thoroughly resolve the problems. Therefore, many pretreatment technologies have been developed in recent years. Currently, harmless treatment technologies targeted at high-salinity water mainly include: physical adsorption, precision filtration, coagulation-flocculation, air flotation, catalytic wet oxidation, electrochemical oxidation, and supercritical water oxidation. For high-salinity wastewater containing refractory, toxic, and harmful substances, adopting the aforementioned methods can achieve the harmlessness of saline water, after which continuous desalination or diluted discharge can be performed to achieve the goal of thorough saline water treatment.

For high-salinity water containing only sodium chloride and sodium sulfate, after being processed by pretreatment technologies, the salt components become similar to seawater composition; those meeting the conditions can be discharged into the sea, or naturally discharged after dilution reaches emission standards. Pretreatment technology only treats toxic and harmful substances in the salt and does not affect the inorganic salt content, making direct discharge very promising. However, there are currently no very clear regulations, mainly considering that the removal of pollutants by this method is not completely thorough, and direct discharge still poses certain environmental risks, so it should be used with caution; but with the development of environmental protection treatment technologies and the gradual improvement of related regulations, it is believed that the destination problem of harmlessly treated saline water will be properly resolved in the future.

New Membrane Technologies

In addition to the previously mentioned membrane technologies, many new membrane technologies have emerged in environmental protection treatment in recent years, such as membrane distillation technology, which has now begun to be applied in high-salinity wastewater treatment. The application of new membrane technologies can not only achieve saline water treatment but also recover useful raw materials, intermediates, or products, showing a very promising future. In addition, due to the high production cost of membranes, its use in the high-salinity wastewater treatment industry is greatly limited; therefore, in the future, new membrane technologies will move towards directions with more and stronger functions, lower membrane production costs, and stronger anti-pollution capabilities.

Bioaugmentation Technology

Currently, biological treatment technologies are also applied, but because of problems with the strains themselves and insufficient process maturity, the application scope of biological treatment is localized. In the future, besides screening out salt-tolerant bacteria, it is also necessary to domesticate them to possess pollutant-degrading properties to enhance their treatment effects and expand their treatment scope.

In summary, industrial high-salinity wastewater treatment technology is currently developing very rapidly, and many technologies have already begun to be applied on a large scale with very good utilization effects. However, these technologies still have many shortcomings, such as: harmless treatment technologies and regulations are not yet complete, evaporation technology has not thoroughly resolved pollutant issues, the usage cost of the membrane method remains high, and the use of the biological method still faces large limitations. In future development, these technologies will become more and more complete, and the problem of high-salinity wastewater will surely be properly resolved.

Industrial Online Monitoring System Architecture

To ensure process optimization and data closed-loop control in automated sewage treatment plants, system integrators require an integrated architectural solution. Below is the multi-layer industrial IoT monitoring topology designed for continuous deployment:

[ Cloud Platform Layer: Smart Wastewater Management Platform / SCADA Center ]
                         ▲
                         │ (Secure MQTT Stream via 4G LTE Gateway)
                         ▼
[ Edge Control Layer: Local PLC (e.g., S7-1200) / Dosing Control Valves ]
                         ▲
                         │ (RS485 Modbus RTU Protocol / Isolated Daisy-Chain)
                         ▼
[ Field Sensor Layer: YexSensor Online Water Quality Sensors (IP68, 316L/Titanium) ]

By utilizing RS485 Modbus RTU networking, a single PLC communication module can poll multiple field digital sensors simultaneously, including industrial pH sensors, industrial dissolved oxygen sensors, and online COD monitoring instruments. This architecture replaces vulnerable analog loops with highly reliable, real-time data acquisition, delivering direct 4-20mA compatibility when legacy hardwired interlocks are required.

Product Parameters Section

Industrial Project Selection Guide

When procuring instruments for high-fouling, high-salinity environmental engineering installations, procurement departments and engineering contractors must align the sensor specifications with the chemical background of the water type to minimize operational expenditure (OPEX):

• Corrosive Ion Backgrounds: In chemical wastewater and desulfurization wastewater containing extreme $Cl^-$ levels, standard stainless steel is prone to pitting. Integrators should opt for a Titanium Alloy or POM housing from YexSensor's product range.

• Fouling and Scaling Conditions: For biological treatment stages like MBR systems or aeration basins where biological films grow rapidly, selecting an automatic cleaning water quality sensor configuration is vital. The motorized wiper minimizes calibration frequency and extends the maintenance cycle from days to months.

• System SCADA Wastewater Monitoring Compatibility: Ensure proper matching of PLC compatibility. For new telemetry remote water monitoring systems, select direct Modbus water quality sensor configurations to utilize full digital status register reporting, allowing remote diagnostic platform integration.

Field Deployment and Integration Best Practices

Based on real-world commissioning experience in industrial sewage treatment plants, proper electrical installation is essential to safeguard data stability and eliminate field bus disruptions:

• Grounding and Shielding: The cable shield must be single-point grounded exclusively at the local PLC control cabinet end to prevent ground potential loop currents from destabilizing sensor microprocessors.

• Anti-Interference Wiring: Maintain a minimum safety distance of 30cm between weak-signal RS485 lines and heavy 380VAC power cables running to recirculation or dosing pumps.

• RS485 Termination Resistor: In long-distance field loops exceeding 100 meters, bridge a $120\ \Omega$ termination resistor across the A(+) and B(-) terminals at the furthest device node to avoid high-frequency signal reflections.

Process and Automation Interface FAQ

Q1. How does the high salinity of industrial effluent affect the readings of an industrial dissolved oxygen sensor for aeration control, and how does the system compensate?
   High ionic strength physically decreases oxygen solubility. YexSensor's digital fluorescence dissolved oxygen sensors feature an internal salinity compensation register. Integrators simply write the fixed background TDS value into the sensor via Modbus commands, and the internal DSP automatically corrects the calculation matrix to ensure precise aeration basin PID control loop feedback without manual scaling offsets.

Q2. Can the automatic cleaning brush assembly handle the crystallized salt crusts formed during MVR evaporation plant failures?
   The built-in motorized wiper features an overcurrent safety cutoff logic. If extreme crystallization jams the wiper blade, the sensor shuts down the motor drive and triggers a "wiper block" fault status code in its Modbus diagnostic register. For systems integrating a SCADA wastewater monitoring layout, this instantly alerts operators to run a flush cycle before mechanical damage can occur.

Q3. Why are the floating-point values from the online COD monitoring sensor read out by our Siemens PLC completely inverted or garbled?
   This is a routine byte order mismatch issue common to multi-vendor Modbus water quality sensor integration. Different automation platforms interpret Big-Endian and Little-Endian byte sequences differently. YexSensor instruments provide user-configurable word swap settings (e.g., AB-CD vs. CD-AB options) directly within the holding registers, which can be toggled using standard PLC programming software to immediately restore proper telemetry data representation.

Q4. In high-turbidity activated sludge processes, how does the system prevent optical window occlusion on the MLSS-8S-Online-Sludge-Concentration-Sensor.html">sludge concentration sensor?
   YexSensor's sludge concentration monitoring solution relies on a dual-beam near-infrared optical paths architecture ($180^\circ$ transmission combined with backscattering). The ratio logic calculates concentrations relative to baseline transmission, meaning slight, uniform window shading is mathematically canceled out, ensuring data stability between scheduled preventative manual cleanings.

Q5. What is the recommended calibration frequency for an industrial pH sensor deployed in chemical wastewater neutralization tanks?
   Because high salt concentrations stress the reference junction potential, we recommend an automated two-point buffer calibration sequence every 14 to 30 days. The digital sensor stores its calibration slope matrix internally, allowing maintenance teams to pre-calibrate sensors in a clean workshop and swap them into the field immersion brackets via quick-disconnect waterproof connectors, minimizing field downtime.

Q6. How do we prevent micro-bubbles from the aeration basin from skewing the data of the industrial turbidity monitoring system?
   Micro-bubbles mirror the scattering behavior of suspended solids, causing falsely inflated readings. The industry-proven solution involves avoiding direct immersion near aeration heads and instead routing the sample stream through a stainless steel bypass flow cell with an integrated de-foaming baffle system, allowing entrained gas to escape before the water passes the turbidity sensor path.

Q7. Can the RS485 water sensor survive extreme lightning surges common to outdoor municipal water projects and remote environmental monitoring stations?
   Yes. YexSensor industrial-grade online water quality sensors feature 1500VDC galvanic power-to-signal isolation alongside built-in TVS surge protection diodes capable of absorbing high-voltage transients. For remote field stations, external DIN-rail lightning surge arrestors should still be installed inside the junction control box to shield the entire local RS485 network.

Q8. What happens to the automated chemical dosing control loop when a sensor goes offline or undergoes an internal automatic cleaning cycle?
   When the automatic brush cleaning sequence is active, the sensor sets an internal status register flag and locks its last valid measurement output. The master PLC ladder logic must be programmed to read this status bit: whenever the cleaning or fault flag is active, the PLC must freeze its PID algorithm calculation and hold the chemical dosing pump at its pre-existing speed, preventing false chemical overdosing during the 30-second maintenance window.

Conclusion

Managing industrial high-salinity wastewater requires robust physical treatment infrastructure combined with intelligent, continuous data oversight. Utilizing premium, industrial-grade online water quality monitoring instruments engineered for high-fouling, heavy-salinity environments allows EPC contractors and plant system integrators to secure seamless PLC/SCADA integration. These steps protect membrane components from premature scaling, streamline aeration energy efficiency, and ensure verifiable environmental compliance, significantly reducing the project's long-term operational expenditures (OPEX) and unlocking true smart water management capabilities.