Reclaimed water reuse treatment process suitable for island high-chlorine tail water

Abstract

The invention relates to the technical field of water treatment, and discloses a reclaimed water reuse treatment process suitable for island high-chlorine tail water, which comprises the following steps: when the real-time chloride ion concentration value is not higher than the chloride ion concentration threshold value, introducing the pretreated water into a low-salinity treatment path, and carrying out first desalination treatment by adopting a capacitive deionization technology; and when the real-time chloride ion concentration value is higher than the chloride ion concentration threshold value, guiding the pretreated water into a high-salinity treatment path, and carrying out second desalination treatment by adopting a reverse osmosis technology. A parallel double-path deep desalination framework is constructed, an intelligent control system guides water flow into an MCD I path or an LPRO path, and frequent switching of the system at a critical point is avoided by setting a hysteresis interval, so that a treatment path with the lowest instantaneous operation cost is automatically selected according to real-time water quality, energy consumption optimization in a full working condition range is realized, and the energy consumption is reduced. And long-term stable and efficient operation of the system is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a reclaimed water reuse treatment process suitable for high-chloride tail water from an island. Background Art

[0002] With economic development and population growth in island regions, water shortages are becoming increasingly severe. Advanced treatment of wastewater treatment plant effluent (i.e., tailwater) for reuse has become a key technical approach to addressing this issue. Tailwater quality in island regions exhibits unique complexity. Its chloride ion concentration is not only generally high, but also, more critically, fluctuates erratically and significantly due to factors such as tides, seasonal rainfall, and tourist off-seasons. This poses significant challenges to the reuse and treatment technology of this high-chloride tailwater.

[0003] Currently, the mainstream technologies for deep desalination of saline wastewater include reverse osmosis (RO) technology driven by pressure and capacitive deionization (CDI) technology driven by an electric field. Reverse osmosis technology, especially low-pressure reverse osmosis (LPRO), can efficiently remove high concentrations of dissolved salts and is a mature and reliable option for treating high-salinity water. However, the core energy consumption of the reverse osmosis system is mainly used to overcome osmotic pressure. When it is used to treat water bodies with lower salinity, its inherent high-pressure operating mode will cause huge energy waste, and the operating efficiency is far from its optimal economic range.

[0004] On the other hand, membrane capacitive deionization (MCDI) technology, as an emerging desalination technology, has a core energy consumption proportional to the amount of salt removed from the water, demonstrating significant energy efficiency advantages when treating low-salinity water bodies. However, as the influent salinity increases, its unit water production energy consumption rises sharply, and the electrode adsorption capacity quickly saturates, resulting in a significant decrease in both treatment capacity and economic efficiency, making it unsuitable for treatment tasks in high-salinity conditions.

[0005] In existing technical practices, a single desalination technology path is usually selected to build the entire reuse treatment system. This design concept of using a fixed technical path is exposed to its inherent technical limitations when faced with high-chloride tail water from islands with a wide range of salinity fluctuations. If a reverse osmosis system is used, it must be designed according to the highest influent salinity, which results in high energy consumption and low efficiency during most operating periods with lower salinity. If a capacitive deionization system is used, it will be completely unable to operate stably during the peak salinity period, resulting in substandard water quality. Therefore, existing technologies generally have the fundamental defect of being unable to take into account both energy efficiency and treatment effects across the entire operating range. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides a reclaimed water reuse treatment process suitable for high-chloride tail water from islands, which solves the problem that the existing single desalination path process cannot adapt to large fluctuations in influent salinity, resulting in high energy consumption and unstable operation of the system under the full operating range.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: A water reuse treatment process suitable for high-chloride tail water on islands, comprising the following steps:

[0008] S1, pre-treating the high-chloride tail water to obtain pre-treated water;

[0009] S2. Real-time monitoring of the chloride ion concentration of the pretreated water to obtain a real-time chloride ion concentration value;

[0010] S3. Comparing the real-time chloride ion concentration value with a preset chloride ion concentration threshold;

[0011] S4. When the real-time chloride ion concentration value is not higher than the chloride ion concentration threshold, directing the pretreated water into a low-salinity treatment path and performing a first desalination treatment using capacitive deionization technology;

[0012] S5. When the real-time chloride ion concentration value is higher than the chloride ion concentration threshold, directing the pretreated water into a high-salinity treatment path and performing a second desalination treatment using reverse osmosis technology;

[0013] S6. Collect the produced water after the first desalination treatment or the second desalination treatment to obtain recycled water.

[0014] Preferably, the step of determining the chloride ion concentration threshold comprises:

[0015] Establishing comprehensive unit water production cost models for the low-salinity treatment path and the high-salinity treatment path respectively;

[0016] The influent chloride ion concentration when the two cost models are equal is solved and set as the chloride ion concentration threshold.

[0017] Preferably, the process further includes calibrating the unit water production comprehensive cost model and dynamically adjusting the chloride ion concentration threshold according to changes in electricity prices or reagent prices before or during system operation.

[0018] Preferably, steps S4 and S5 are implemented through a process of intelligent sensing and dynamic diversion control, which specifically includes: monitoring through an online chloride ion sensor connected to the water channel that transports the pretreated water, executing the comparison and judgment logic by a programmable logic controller, and controlling the electric regulating valve groups installed on the pipelines leading to the low-salinity treatment path and the high-salinity treatment path, respectively, to complete the introduction of the pretreated water.

[0019] Preferably, the pretreatment in step S1 specifically includes: sequentially performing high-density precipitation treatment, rapid filtration treatment and ultrafiltration treatment on the high-chloride tail water.

[0020] Preferably, the capacitive deionization technology used in the low-salinity treatment path is membrane capacitive deionization technology.

[0021] Preferably, the reverse osmosis technology used in the high-salinity treatment path is low-pressure reverse osmosis technology.

[0022] Preferably, a hysteresis interval is set near the chloride ion concentration threshold value. When the real-time chloride ion concentration value fluctuates within the hysteresis interval, the current processing path is kept unchanged to avoid frequent switching between the low-salinity processing path and the high-salinity processing path.

[0023] Preferably, the process further includes step S7: collecting the regenerated concentrated liquid generated when the low-salinity treatment path performs the first desalination treatment and the reverse osmosis concentrated water generated when the high-salinity treatment path performs the second desalination treatment, and returning them to the source sewage treatment plant of the high-chloride tail water for combined treatment.

[0024] Preferably, the execution of step S4 and step S5 is mutually exclusive, that is, at any time point, the pre-treated water is only introduced into one of the low-salinity treatment path or the high-salinity treatment path.

[0025] The present invention provides a water reuse treatment process suitable for high-chloride tail water from islands. It has the following beneficial effects:

[0026] 1. This invention monitors the chloride ion concentration of pretreated water in real time and makes judgments based on a preset chloride ion concentration threshold. When the chloride ion concentration is low, the process automatically switches to a capacitive deionization pathway, where energy consumption is proportional to the amount of salt removed. Only when the chloride ion concentration is high does the reverse osmosis pathway, designed for high-salinity conditions, become active. This intelligent selection mechanism avoids the energy waste caused by the long-term, low-load, high-pressure operation of traditional single reverse osmosis systems, significantly reducing the overall operating costs of the process over its entire lifecycle, particularly electricity consumption.

[0027] 2. The present invention combines two desalination paths - the capacitor deionization path and the reverse osmosis path, both of which operate within their respective optimal technical operating conditions. Capacitive deionization technology avoids the treatment of high-salinity wastewater, which it is not good at, while reverse osmosis technology also avoids instability problems such as operating pressure mismatch and excessive membrane flux that may occur under ultra-low salinity. This optimization of working conditions reduces the physical and chemical impact and loss on core equipment (such as reverse osmosis membrane elements and capacitor deionization electrode plates), thereby extending their effective service life and reducing the maintenance frequency and related costs of the system.

[0028] 3. This invention deeply integrates online water quality sensing, cost optimization models, and PLC logic control to create an intelligent treatment system that can proactively adapt to large fluctuations in source water salinity. The entire desalination path selection and switching process is fully automated, requiring no human intervention or judgment. This not only greatly reduces the reliance on the experience and skills of on-site operators, but also significantly improves the operational management efficiency and reliability of reclaimed water reuse facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the overall process flow of an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of control logic state transition according to an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the working principle of the membrane capacitor deionization unit in the adsorption stage according to an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the working principle of the high salinity treatment path according to an embodiment of the present invention;

[0033] Figure 5 This is a graph showing the monthly average concentration changes of chloride ion concentration and conductivity in tail water of a sewage treatment plant in the test example of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the specification of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Example:

[0036] Please see the attached Figure 1 -Attached Figure 4 The embodiment of the present invention provides a water reuse treatment process suitable for high-chloride tail water on an island, comprising the following steps:

[0037] S1. Pre-treating the high-chloride tail water to obtain pre-treated water; the pre-treatment in the step specifically includes: sequentially performing high-density precipitation treatment, rapid filtration treatment and ultrafiltration treatment on the high-chloride tail water.

[0038] The process for pretreatment of high-chloride tail water is as follows:

[0039] The high-chloride tail water from the island sewage treatment plant is first introduced into a high-density sedimentation tank. In the inlet mixing zone of the sedimentation tank, polyaluminum chloride (PAC) is added to the water flow as a coagulant to destabilize the tiny suspended particles and colloidal substances in the water. Subsequently, the water flows into the flocculation zone, where polyacrylamide (PAM) is added as a coagulant aid. Through slow stirring, the destabilized tiny particles are caused to collide and condense with each other, forming larger, higher-density, and easier-to-sediment alum flowers. Finally, the water flows into the inclined tube sedimentation zone. Through the huge sedimentation surface area provided by the large number of inclined tubes set up in this area, the alum flowers can be efficiently settled and separated, thereby removing most of the suspended solids (SS) in the raw water.

[0040] After high-density sedimentation, the supernatant flows by gravity or via a lift pump into a rapid filter. This rapid filter is layered with anthracite and quartz sand media from top to bottom. As water flows downward through these multi-media layers, the varying pore sizes between the media particles further trap and remove finer suspended particles that were not removed by the previous unit. This step significantly reduces water turbidity, ensuring excellent influent quality for the subsequent ultrafiltration unit.

[0041] The water treated by the rapid filter is then sent to the ultrafiltration (UF) system as a key protective barrier for the subsequent deep desalination unit. The ultrafiltration system uses an external pressure polyvinylidene fluoride (PVDF) hollow fiber membrane module. Its membrane fibers have a nominal pore size of 0.01 to 0.1 microns, which can effectively intercept bacteria, viruses, large molecular organic matter and any residual colloidal substances in the water. The operation of this step is strictly monitored to ensure that the water produced, that is, the pretreated water in this process, has a silt density index (SDI 15 ) remains consistently and stably below 3.0. Achieving this indicator is a prerequisite for ensuring that the membrane elements in the subsequent reverse osmosis path are not contaminated by suspended matter or colloids, thereby maintaining their long-term stable flux and desalination rate.

[0042] Through the above-mentioned high-density precipitation, rapid filtration and ultrafiltration treatment, the high-chloride tail water is prepared into pretreated water with clear and stable water quality, laying a solid foundation for the subsequent intelligent diversion and dual-path desalination treatment steps.

[0043] S2. Real-time monitoring of the chloride ion concentration of the pretreated water to obtain a real-time chloride ion concentration value;

[0044] The steps for determining the chloride ion concentration threshold include: establishing a comprehensive cost model for unit water production for the low-salinity treatment path and the high-salinity treatment path respectively; solving the influent chloride ion concentration when the two cost models are equal, and setting it as the chloride ion concentration threshold.

[0045] The process also includes calibrating the unit water production comprehensive cost model and dynamically adjusting the chloride ion concentration threshold according to changes in electricity prices or chemical prices before or during system operation.

[0046] In this step, the real-time monitoring and routing decision-making process for pretreated water is performed by an intelligent sensing and dynamic diversion control unit, which is the core of the intelligent operation of this process. In a specific embodiment, this unit consists of an online sensor, a programmable logic controller (PLC), and an electric control valve group.

[0047] After the pre-treated water flows out of the ultrafiltration system water pipeline, it first flows through an online, high-precision, four-electrode conductivity sensor installed in the pipeline. The sensor continuously measures the conductivity of the water flowing through it and converts the conductivity signal into an accurate chloride ion concentration value C in real time through a built-in temperature compensation algorithm. in The C in The value, as a key parameter reflecting the current water salinity condition, is continuously transmitted in the form of a standard electrical signal to the programmable logic controller (PLC) serving as the central control core.

[0048] The PLC (for example, Siemens S7-1200 series) is pre-programmed with a program containing the core control logic. The core task of the program is to receive and process real-time C signals from sensors. in signal and compare it with the internally stored chloride ion concentration threshold C calculated according to the cost model in the second part. th Perform uninterrupted comparison operations.

[0049] In order to avoid the chloride ion concentration in the influent reaching the threshold value C th The PLC control logic introduces a set of hysteresis interval control strategies to prevent small fluctuations near the threshold value C from causing frequent switching of the processing path, thereby protecting the electric regulating valve group and other equipment and ensuring the stable operation of the downstream processing unit. th A "non-reactive" buffer zone is formed above and below.

[0050] S3. Compare the real-time chloride ion concentration value with a preset chloride ion concentration threshold value. For a more intuitive explanation of the control logic, please refer to the attached Figure 2 , Figure 2 1 is a schematic diagram of control logic state transition according to an embodiment of the present invention. The specific control and switching logic is as follows:

[0051] 1. Path switching to high salinity treatment path: When PLC detects C in Continue to rise from the low concentration area and meet condition C in >(C th +ΔC), the PLC determines that the system should switch to high-salinity operation. At this point, the PLC issues a control command to open the electric control valve leading to the high-salinity treatment path (the reverse osmosis path) and simultaneously close the electric control valve leading to the low-salinity treatment path (the capacitive deionization path), redirecting the water flow entirely to the latter.

[0052] 2. Path switching to low salinity treatment path: When PLC detects C in Continuously decrease from the high concentration area and meet condition C in <(C th -ΔC), the PLC determines that the system should switch to low-salinity operation. At this time, the PLC will issue the opposite control command, opening the electric control valve leading to the low-salinity treatment path and closing the electric control valve leading to the high-salinity treatment path.

[0053] 3. State maintenance: When the real-time chloride ion concentration C in In the hysteresis range, that is, the condition (C th -ΔC)≤C in ≤(C th +ΔC), the PLC does not issue any new switching instructions, and the system will maintain its current processing path unchanged. For example, if the system is currently running in the low salinity processing path, even if C in Slightly above C th But it did not reach C th +ΔC, the system will continue to operate in the low-salinity treatment path until it breaks through the upper limit of the hysteresis range.

[0054] Through the above-mentioned refined control logic, this process ensures that each switch of the treatment path is based on clear and significant changes in water quality, realizing the intelligent, automated and stable operation of the entire system.

[0055] S4. When the real-time chloride ion concentration value is not higher than the chloride ion concentration threshold, the pretreated water is introduced into a low-salinity treatment path and a first desalination treatment is performed using capacitive deionization technology; the capacitive deionization technology used in the low-salinity treatment path is membrane capacitive deionization technology.

[0056] In this step, when the intelligent sensor and dynamic diversion control unit determines the influent chloride ion concentration C in Not higher than the preset chloride ion concentration threshold C th(and the switching conditions of the hysteresis interval control logic are met), the pretreated water will be automatically introduced into the low-salinity treatment path, and the membrane capacitive deionization (MCDI) technology will be used for the first desalination treatment in this path.

[0057] The core of this low-salinity treatment pathway is one or more membrane capacitive deionization modules. Each module is composed of multiple stacked pairs of electrodes, each consisting of an anode made of porous carbon material, a cathode made of porous carbon material, and an anion exchange membrane and a cation exchange membrane covering the electrode surfaces. The anion exchange membrane is adjacent to the anode, and the cation exchange membrane is adjacent to the cathode, forming a narrow flow channel between the two membranes for water to flow through.

[0058] To explain its working principle more clearly, refer to the attached Figure 3 , Figure 3 Schematic diagram of the working principle of a membrane capacitor deionization unit in the adsorption stage according to one embodiment of the present invention.

[0059] When the first desalination treatment is carried out, the PLC controls the DC power supply to apply a low DC voltage to the electrode stack (usually 1.2-1.6V to avoid water electrolysis). Under the action of this electric field, the electrode pair begins to charge like a capacitor, and the system enters the ion adsorption stage. Anions in the water flow (such as chloride ions Cl - 、Sulfate ion SO4 2- ) are attracted to move toward the positively charged anode. They can pass through the anion exchange membrane that only allows anions to pass through and are adsorbed and stored in the porous structure of the anode. At the same time, cations in the water flow (such as sodium ions Na + Calcium ion Ca 2+ ) are attracted to the negatively charged cathode, where they pass through the cation exchange membrane, which only allows cations to pass, and are adsorbed by the cathode's porous structure. Due to the membrane's selective permeability, ions that have already passed through the membrane are effectively "locked" to one side of the electrode, preventing reverse leakage, thereby significantly improving both desalination and charge efficiency. This process significantly removes a large amount of dissolved salt ions from the water flow, resulting in desalinated product water at the module's outlet.

[0060] As the adsorption process continues, the ions adsorbed on the electrode surface gradually reach a saturated state, and its desalination efficiency decreases accordingly. At this time, the PLC will automatically control the system to enter the regeneration stage. During the regeneration stage, the DC voltage applied to the electrode is removed (short-circuiting the electrode) or a reverse low voltage is applied. The disappearance or reversal of the electric field will destroy the electrostatic adsorption force of the electrode on the ions, causing the anions and cations previously adsorbed in the porous structures of the anode and cathode to be released again and enter a small stream of water flowing through the module, forming a high-concentration regeneration concentrate and being discharged from the system. In the ion release process, anion exchange membranes and cation exchange membranes also play a key role. They prevent ions from entering the opposite electrode and avoid ineffective circulation of ions.

[0061] A complete treatment cycle consists of an adsorption phase and a regeneration phase. A PLC automatically controls the switching between these two phases based on a preset time schedule or online monitoring of product water conductivity, ensuring continuous and efficient system operation. By executing these steps, this process achieves efficient primary desalination of pretreated water under low-salinity conditions with extremely low energy consumption.

[0062] S5. When the real-time chloride ion concentration value is higher than the chloride ion concentration threshold, the pretreated water is introduced into a high-salinity treatment path and reverse osmosis technology is used for a second desalination treatment; the reverse osmosis technology used in the high-salinity treatment path is a low-pressure reverse osmosis technology.

[0063] A hysteresis interval is set near the chloride ion concentration threshold. When the real-time chloride ion concentration value fluctuates within the hysteresis interval, the current processing path is kept unchanged to avoid frequent switching between the low-salinity processing path and the high-salinity processing path.

[0064] In this step, when the intelligent sensor and dynamic diversion control unit determines the influent chloride ion concentration C in Higher than the preset chloride ion concentration threshold C th When the pre-treated water is automatically diverted to the high-salinity treatment path (and the switching conditions of the hysteresis control logic are met), it will undergo secondary desalination using low-pressure reverse osmosis (LPRO) technology. This path is optimized for treating high-salinity influent water.

[0065] To explain its working principle more clearly, refer to the attached Figure 4 , Figure 4 Schematic diagram of the working principle of a high-salinity treatment path according to an embodiment of the present invention.

[0066] After switching to this route, pretreated water first flows through the chemical dosing unit. Here, a metering pump precisely doses the appropriate amount of scale inhibitor based on the influent flow rate and water quality. This step aims to inhibit the precipitation and crystallization of scaling ions, such as calcium and magnesium, on the reverse osmosis membrane surface due to increased concentrations. This prevents membrane fouling and performance degradation, ensuring long-term stable system operation.

[0067] The water after the addition of the reagent is sent to the inlet of the high-pressure pump. The high-pressure pump is the core power equipment of the reverse osmosis system, which provides an operating pressure P for the water flow that is much higher than its own osmotic pressure. op The setting of the operating pressure is related to the real-time influent chloride ion concentration C in There is a positive correlation, that is, the higher the inlet water salinity, the higher the required operating pressure.

[0068] Driven by sufficient pressure, water is sent into one or more pressure vessels connected in series and parallel. Each pressure vessel is equipped with one or more low-pressure reverse osmosis membrane elements. Low-pressure reverse osmosis membrane is a semi-permeable membrane with highly selective permeability. Its surface is covered with micropores that only allow water molecules and other solvent molecules to pass through. When the pressurized water flows through the membrane surface, due to the applied operating pressure P op The osmotic pressure is much greater than that of water. Water molecules will overcome the natural osmotic tendency and actively pass through the reverse osmosis membrane to form a pure water flow with almost no salt. This is osmotic water, which is also the desalination water in this step. At the same time, most of the soluble salt ions (such as Na + 、Cl - etc.), organic matter and other solutes are effectively retained by the reverse osmosis membrane because their molecular or ionic size is larger than the membrane pore size and cannot pass through the membrane.

[0069] These trapped solutes remain on the inlet side of the membrane and are gradually enriched as the water continues to pass through it, forming a high-salinity concentrated water flow, which is the reverse osmosis concentrate. This reverse osmosis concentrate is eventually discharged from the concentrate outlet of the pressure vessel.

[0070] Through this low-pressure reverse osmosis process, the high-salinity influent is successfully separated into two streams: one is pure permeate water that meets reuse standards, and the other is a smaller volume of reverse osmosis concentrate with a significantly higher salt ion concentration. This completes the secondary desalination process under high-salinity conditions.

[0071] Steps S4 and S5 are implemented through a process of intelligent sensing and dynamic diversion control, specifically including: monitoring through an online chloride ion sensor connected to the water channel that transports pretreated water, executing comparison and judgment logic by a programmable logic controller, and controlling the electric regulating valve groups installed on the pipelines leading to the low-salinity treatment path and the high-salinity treatment path, respectively, to complete the introduction of pretreated water.

[0072] It should be noted that the execution of step S4 and step S5 is mutually exclusive, that is, at any time point, the pre-treated water is only introduced into one of the low-salinity treatment path or the high-salinity treatment path.

[0073] S6, collect the water produced after the first desalination treatment or the second desalination treatment to obtain recycled water; in this step, the water produced after the desalination treatment is collected and regulated. Figure 1 As shown in the overall process flow, no matter whether the system is currently operating in the low-salinity treatment path or the high-salinity treatment path, the desalinated water produced by each is directed to a unified water collection and regulation unit to form the final qualified recycled water.

[0074] Specifically, the membrane capacitor deionization water production line from step S4 and the low-pressure reverse osmosis water production (i.e., permeate water) production line from step S5 are combined into a total water production line at a confluence point through a pipe connector (such as a tee). The total water production line discharges the collected water flow into a reclaimed water production tank. The main function of the water production tank is to serve as a buffer container for the system's water production, to balance the slight flow or water quality differences that may exist between different paths or different operating batches, and to provide a stable water supply for subsequent water use points.

[0075] In a preferred embodiment of the present invention, in order to ensure that the final recycled water quality meets specific reuse standards (for example, equipment cooling water or landscape water has requirements on pH value and microbial indicators), this step may also include subsequent adjustment treatment of the produced water.

[0076] One type of adjustment treatment is the adjustment of pH value. In particular, when the system is operated under high salinity conditions and the permeate water is produced by the reverse osmosis path of step S4, the carbon dioxide molecules in the water can pass through the reverse osmosis membrane, which may cause the produced water to be weakly acidic. For this reason, an online pH sensor is set in the reclaimed water tank or on its outlet pipe. The sensor feeds back the pH value monitored in real time to the PLC. If the pH value is lower than the preset lower limit of the qualified range (for example, pH 6.5), the PLC will automatically start a metering pump connected to the alkali solution storage tank to add a trace amount of alkaline solution (such as sodium hydroxide solution) into the produced water tank until the pH value is adjusted to neutral or within the set target range (for example, pH 6.5-8.5), and then stop adding.

[0077] Another optional conditioning treatment is final disinfection to prevent secondary microbial growth in the reclaimed water during storage or transportation. In this embodiment, an ultraviolet (UV) sterilizer can be installed on the main outlet pipe of the reclaimed water production tank. All water discharged from the production tank for reuse must flow through this UV sterilizer. The high-intensity ultraviolet light it produces effectively inactivates any bacteria and viruses that may remain in the water, thereby ensuring the biosafety of the reclaimed water without introducing any chemical residues.

[0078] Through the collection and adjustment in this step, the system finally obtains recycled water with stable water quality that meets various reuse indicators. The recycled water is stored in the recycled water production tank and is ready to be transported to the water use point at any time.

[0079] S7: The regenerated concentrated liquid generated by the first desalination treatment in the low-salinity treatment path and the reverse osmosis concentrated water generated by the second desalination treatment in the high-salinity treatment path are collected and returned to the source sewage treatment plant of the high-chloride tail water for combined treatment.

[0080] The by-products generated during the desalination process of this process are uniformly collected and disposed of to achieve closed-loop management of all water flows in the system and environmental friendliness.

[0081] Refer to the attached Figure 1 As shown in the overall process flow, the by-products produced by this process mainly include two parts: one part is the regeneration concentrate with a small water volume but a high salt ion concentration produced by the membrane capacitor deionization module in step S4 during the regeneration stage when the system operates in the low salinity treatment path; the other part is the reverse osmosis concentrated water with a high salt ion concentration produced by the low-pressure reverse osmosis unit in step S5 when the system operates in the high salinity treatment path.

[0082] In a specific embodiment of the present invention, the two high-salinity concentrates are not discharged directly to avoid impacting the local water environment of the island. Instead, they are directed through separate discharge pipelines to a shared concentrate collection pipeline. This collection pipeline combines the concentrates from the low-salinity treatment path and the high-salinity treatment path.

[0083] Subsequently, the collecting pipeline will eventually return the combined concentrate to the source of the process water through a concentrate return pump, that is, the front-end water inlet or regulating tank of the sewage treatment plant, the source of the high-chloride tail water.

[0084] By executing this step, the process returns the low-flow, high-concentration desalination byproduct to the source sewage treatment plant with full treatment capacity and a flow rate far exceeding the process's capacity for dilution and reprocessing. This disposal method not only avoids the need for high-cost and energy-intensive concentrate disposal facilities such as terminal evaporation or crystallization for the reclaimed water reuse system, but also enables material circulation between the reclaimed water reuse system and the source sewage treatment plant, synergistically optimizing the entire water treatment process as a whole. It is a systematic solution that is responsible for the island's limited resources and fragile environment.

[0085] Test example:

[0086] Take a municipal sewage treatment plant in Shengsi as an example:

[0087] Basic information: The effluent from the disinfection tank of the domestic sewage treatment plant (referred to as "tail water") is used as the influent for the reclaimed water reuse process. The tail water quality meets the Class A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002). The main indicators are detailed in Table 1:

[0088] Table 1 GB18918-2002 Level A standard and GB / T19923-2024 water quality standard unit mg / L:

[0089]

[0090]

[0091] Outlet water quality requirements:

[0092] To meet the demand for industrial water reuse, the effluent design quality of the reclaimed water reuse system refers to the "Urban Recycling - Industrial Water Quality" standard (GB / T19923-2024). Key indicators are detailed in Table 1. The reverse osmosis concentrate meets the "Integrated Wastewater Discharge Standard" (GB8798-1996) and is returned to the original domestic sewage treatment plant for treatment.

[0093] Analytical methods:

[0094] The pH of the water was determined by Mettler-Toledo FE28, the conductivity was determined by Mettler-Toledo F3-Standard, the COD was determined by the dichromate method, the ammonia nitrogen and total nitrogen were determined by spectrophotometry, the suspended solids SS was determined by weight, the chloride ion and sulfate ion were determined by ion chromatography, and the heavy metals were determined by atomic absorption spectrometry.

[0095] From Table 1, the tail water of urban sewage treatment plant meets the limited value requirements of COD, BOD, ammonia nitrogen, total nitrogen, total phosphorus, SS and other indicators. These indicators can basically meet the water quality requirements of industrial recycled water, urban miscellaneous water and the like. However, the tail water does not have limited value requirements for indicators such as chloride, sulfate and total hardness. For island areas, seawater level, astronomical spring tide and the like can affect the sewage treatment plant pump station and cause seawater backflow phenomenon, resulting in chloride and conductivity concentrations in the tail water being much higher than those of sewage treatment plants in inland areas. Therefore, long-term monitoring of chloride and conductivity in the tail water is needed to explore the variation law thereof. The tail water chloride and conductivity monitoring results are shown in Table 2. Figure 5 As shown in Table 2, the tail water conductivity and chloride concentration vary greatly throughout the year. In terms of months, the average chloride concentrations in the tail water in January, December, November, October, September, August, July, June, May, April and March are 2430, 1143, 724, 632, 202, 119, 220, 337, 1081, 1134, 1263 and 2052 mg / L respectively. The chloride concentration is the highest in January and the lowest in June. In terms of seasons, the chloride concentration is higher in autumn and winter and lower in spring and summer. The variation law of the tail water conductivity is the same as that of the chloride. The conductivity is the highest in January, reaching 7154 us / cm, and the lowest in June, being close to 643 us / cm. The fluctuations of the chloride concentration and the conductivity are mainly affected by factors such as weather, hydrology, residents' living habits and the like. In winter, there are fewer tourists in the island area, the residents' water consumption is low, the water level of the sewage treatment station is relatively low, the daily treatment capacity is only 6000 m 3 , the seawater backflow phenomenon is relatively serious, and therefore the chloride concentration and the conductivity are relatively high. In May to July, it is the plum rain season and there are many typhoons, and the rainfall can reach 200-400 mm per day. Due to historical problems, the rainwater and sewage pipes have not been separated, and therefore a large amount of rainwater flows into the sewage treatment station. In addition, there are many tourists in the island area in May to July, and the residents' water consumption also increases significantly, and the daily treatment capacity of the sewage treatment station is as high as 12000 m 3 . Most of the water is rainwater, the water level is high, and there is basically no seawater backflow phenomenon, and therefore the chloride concentration and the conductivity are low. It can be seen that the tail water quality and quantity fluctuate greatly, especially the chloride concentration.

[0096] Treatment step: The reclaimed water is treated according to the treatment mode provided in the examples, and the treatment effect is shown in Table 2.

[0097] Table 2: Water quality of the reclaimed water reuse system

[0098]

[0099] From Table 2, under the condition of constant water recovery rate, with the increase of the influent chloride ion concentration, the effluent chloride ion concentration also increases. Under the condition of water recovery rate of about 70%, when the influent chloride ion concentration is 1081 mg / L (conductivity 2724 us / cm), the effluent chloride ion concentration is only 24 mg / L (conductivity 77 us / cm); when the influent chloride ion concentration increases to 1704 mg / L (conductivity 5432 us / cm), the effluent chloride ion concentration rises to 44 mg / L (conductivity 133 us / cm); when the influent chloride ion concentration further increases to 2052 mg / L (conductivity 6015 us / cm), the effluent chloride ion concentration rises to 58 mg / L (conductivity 202 us / cm), and the effluent water quality can meet the tap water quality standard, indicating that the "combination of two desalination paths, capacitive deionization path and reverse osmosis path" can effectively remove chlorides in tail water of a sewage treatment plant in an island area, and the treated effluent can be reused as iron ore sand flushing water, cement mixing water and the like.

[0100] Combined with the cost of reagents and power consumption, the operation cost is about 1.6 yuan / ton of water, and the investment cost is about 1.4 yuan / ton of water in 10 years. The industrial water price in an island area is as high as 10 yuan / ton of water, and with a daily water consumption of 6000 tons, 42,000 yuan of water cost can be saved every day. It can be seen that water reuse not only can promote the sustainable development of an island area, but also has certain economic value.

[0101] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A water reuse treatment process suitable for high-chloride tail water on islands, characterized in that: The following steps are involved: S1, pre-treating the high-chloride tail water to obtain pre-treated water; S2. Real-time monitoring of the chloride ion concentration of the pretreated water to obtain a real-time chloride ion concentration value; S3. Comparing the real-time chloride ion concentration value with a preset chloride ion concentration threshold; S4. When the real-time chloride ion concentration value is not higher than the chloride ion concentration threshold, directing the pretreated water into a low-salinity treatment path and performing a first desalination treatment using capacitive deionization technology; S5. When the real-time chloride ion concentration value is higher than the chloride ion concentration threshold, directing the pretreated water into a high-salinity treatment path and performing a second desalination treatment using reverse osmosis technology; S6. Collect the produced water after the first desalination treatment or the second desalination treatment to obtain recycled water.

2. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that, The step of determining the chloride ion concentration threshold comprises: Establishing comprehensive unit water production cost models for the low-salinity treatment path and the high-salinity treatment path respectively; The influent chloride ion concentration when the two cost models are equal is solved and set as the chloride ion concentration threshold.

3. A water reuse treatment process suitable for island high-chloride tail water according to claim 2, characterized in that, The process also includes calibrating the unit water production comprehensive cost model and dynamically adjusting the chloride ion concentration threshold according to changes in electricity prices or reagent prices before or during system operation.

4. A water reuse treatment process suitable for high-chloride tail water on an island according to claim 1, characterized in that: Steps S4 and S5 are implemented through a process of intelligent sensing and dynamic diversion control, which specifically includes: monitoring through an online chloride ion sensor connected to the water channel that transports the pretreated water, executing the comparison and judgment logic by a programmable logic controller, and controlling the electric regulating valve groups installed on the pipelines leading to the low-salinity treatment path and the high-salinity treatment path, respectively, to complete the introduction of the pretreated water.

5. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that, The pretreatment in step S1 specifically includes: sequentially performing high-density precipitation treatment, rapid filtration treatment, and ultrafiltration treatment on the high-chloride tail water.

6. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that, The capacitive deionization technology used in the low-salinity treatment path is membrane capacitive deionization technology.

7. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that: The reverse osmosis technology used in the high salinity treatment path is a low-pressure reverse osmosis technology.

8. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that: A hysteresis interval is set near the chloride ion concentration threshold. When the real-time chloride ion concentration value fluctuates within the hysteresis interval, the current processing path is kept unchanged to avoid frequent switching between the low-salinity processing path and the high-salinity processing path.

9. A water reuse treatment process suitable for island high-chloride tail water according to claim 1, characterized in that: The process also includes step S7: collecting the regenerated concentrated liquid generated by the first desalination treatment in the low-salinity treatment path and the reverse osmosis concentrated water generated by the second desalination treatment in the high-salinity treatment path, and returning them to the source sewage treatment plant of the high-chloride tail water for combined treatment.

10. A water reuse treatment process suitable for high-chloride tail water on an island according to claim 1, characterized in that: The execution of step S4 and step S5 is mutually exclusive, that is, at any time point, the pre-treated water is only introduced into one of the low-salinity treatment path or the high-salinity treatment path.

Images