Electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system

Abstract

The application belongs to the technical field of electrochemical water treatment and relates to an electrochemical water softening-crystallization induction-reverse osmosis coupled water treatment system, which comprises an electrochemical subsystem, a crystallization induction column, a buffer water tank and a reverse osmosis module, the water inlet of the electrochemical subsystem is connected to a polluted water source, the water outlet of the electrochemical subsystem is connected to the upper water inlet of the crystallization induction column, the lower water outlet of the crystallization induction column is arranged in the buffer water tank, the water outlet of the buffer water tank is connected to the water inlet of the reverse osmosis module, the clean water discharge port of the reverse osmosis module is connected to a clean water collecting device, the first electrode and the second electrode of the electrochemical subsystem are arranged in a staggered manner along the length direction of the electrolytic cell, the first electrode and the second electrode are respectively electrically connected to the positive electrode and the negative electrode of a direct current power supply, the crystallization induction column is in the shape of a vertical column, and the crystallization induction column is filled with a porous adsorbent; the application has multiple effects of long service life, multifunction, low cost, low energy consumption, high water recovery rate and high desalination rate.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water treatment technology and relates to an electrochemical water softening-induced crystallization-reverse osmosis coupled water treatment system. Background Technology

[0002] Reverse osmosis water treatment technology is a green water treatment technology. Its advantages are that membrane separation does not involve the addition of chemical reagents, the pollutant rejection rate is extremely high (the desalination rate can reach 99%), the effluent quality is good, and it has a small footprint, high treatment efficiency, simple operation and maintenance, and the treatment process is not limited by water quality and external conditions. It has been widely used in brackish water treatment, seawater desalination and deep wastewater treatment.

[0003] However, as the core of reverse osmosis water treatment technology, the reverse osmosis membrane has shown many shortcomings in engineering practice, such as:

[0004] Membrane fouling: While reverse osmosis membranes retain contaminants, these contaminants also adhere to the membrane. Interactions occur between contaminants and the membrane, and among contaminants themselves, forming a fouling layer on the membrane surface, leading to a rapid decrease in membrane flux.

[0005] Frequent membrane cleaning: Membrane cleaning can remove most reversible contaminants from the surface of reverse osmosis membranes, but it consumes a large amount of water, which contradicts the original intention of wastewater reduction. In addition, membrane cleaning may require the addition of extra chemical cleaning agents. Currently, the commonly used cleaning methods are acid + chelating agent or alkali + chelating agent, and the resulting acidic or alkaline wastewater may cause secondary pollution.

[0006] High water pollution leads to low water production rate: When the concentration of pollutants in the water is high, the water production rate of the reverse osmosis membrane drops sharply. Household reverse osmosis water purifiers using municipal tap water as feed water can achieve a water production rate of over 80%; in the deep treatment of municipal wastewater, the water production rate of reverse osmosis membranes is mostly between 50% and 65%; industrial-grade reverse osmosis membranes used for seawater desalination have a water production rate of around 35%; and some reverse osmosis membranes used directly for brackish water treatment have even lower water production rates.

[0007] High cost: The unit price of household reverse osmosis membranes is mostly several hundred yuan, while the unit price of domestic industrial-grade reverse osmosis membranes is mostly around 1,000-3,000 yuan, and the unit price of imported industrial-grade reverse osmosis membranes can be as high as 5,000 yuan or more. Frequent cleaning and replacement of membranes will result in extremely high material costs.

[0008] The aforementioned defects of reverse osmosis membranes also result in drawbacks such as the use of high-pressure pipelines, high energy consumption, and high costs associated with the reverse osmosis process. Meanwhile, industrial parks and businesses are increasingly demanding reductions in industrial wastewater.

[0009] Therefore, optimizing existing reverse osmosis water treatment systems, while minimizing the cost of reverse osmosis water purification and promoting wastewater reduction, can reduce sewage discharge costs and improve economic efficiency for enterprises. Summary of the Invention

[0010] To solve the above-mentioned technical problems, the present invention is implemented through the following technical solution.

[0011] An electrochemical water softening-induced crystallization-reverse osmosis coupled water treatment system includes: an electrochemical subsystem, an induced crystallization column, a buffer tank, and a reverse osmosis module;

[0012] The electrochemical subsystem is used to apply current and voltage to the polluted water within the electrochemical subsystem, thereby reducing water hardness, removing COD from the water, and inhibiting the growth and reproduction of microorganisms and algae in the water;

[0013] The induced crystallization column is used as an inducer to provide nucleation sites for the growth of scale crystals and induce scale particles generated in the electrochemical subsystem to crystallize.

[0014] The buffer tank is used to allow scale particles to settle further by gravity;

[0015] Reverse osmosis modules are used to remove dissolved solids, organic matter, inorganic matter, bacteria, viruses, salts, colloids and dissolved impurities from water through a semi-permeable membrane;

[0016] The inlet of the electrochemical subsystem is connected to the polluted water source, the outlet of the electrochemical subsystem is connected to the upper inlet of the induced crystallization column, the lower outlet of the induced crystallization column is set in the buffer tank, the outlet of the buffer tank is connected to the inlet of the reverse osmosis module, and the purified water outlet of the reverse osmosis module is connected to the purified water collection device.

[0017] The electrochemical subsystem is equipped with a first electrode, a second electrode, and an electrolytic cell. The first electrode and the second electrode are arranged alternately along the length of the electrolytic cell. The first electrode and the second electrode are electrically connected to the positive and negative terminals of the DC power supply, respectively. The first electrode is a shape-stable anode, which includes a DSA electrode. Other anodes with good electrochemical stability can be used in this system.

[0018] The induced crystallization column is columnar and filled with a porous adsorbent.

[0019] Preferably, the first electrode is a ruthenium-iridium-titanium electrode, and the second electrode is a plate-shaped or mesh-shaped pure titanium or stainless steel electrode.

[0020] Preferably, the first electrode and the second electrode are arranged at equal intervals, and the first electrode and the second electrode are completely immersed in the polluted water in the electrolytic cell.

[0021] Preferably, the operating modes of the electrochemical subsystem include: constant current power supply mode, constant voltage power supply mode, and exponential decay power supply mode;

[0022] When the electrochemical subsystem operates in constant current power supply mode, the current value i remains unchanged when the electrochemical subsystem is energized, and the energization time is t1.

[0023] When the electrochemical subsystem operates in constant voltage power supply mode, the voltage value U remains unchanged when the electrochemical subsystem is energized, and the energization time is t2.

[0024] When the electrochemical subsystem operates in exponential decay power supply mode, the current flowing through the electrochemical subsystem varies with the polluted water flow rate and TDS as follows:

[0025]

[0026] In equation (9), i0 is the current, k1 is the hardness removal coefficient, TDS is the total dissolved solids content in the water, TDS0 is the standard total dissolved solids content, and q is the influent flow rate of polluted water; k1 and TDS0 are constants, and k1 is different under different operating conditions; TDS0 is different under different wastewater discharge standards.

[0027] Preferably, the processing methods of the electrochemical subsystem include: intermittent processing and continuous flow processing.

[0028] Preferably, the bottom of the electrolytic cell is provided with a funnel-shaped recessed scale collection chamber, and the bottom of the scale collection chamber is provided with a scale discharge outlet; the reverse osmosis module is provided with a concentrate return port, which is used to discharge the concentrate filtered by the reverse osmosis module, and the concentrate return port is connected to the water inlet of the electrochemical subsystem.

[0029] More preferably, a first water pump is provided at the inlet of the electrochemical subsystem, a second water pump is provided at the inlet of the reverse osmosis module, and integrated sensor modules are also provided at the inlet of the reverse osmosis module and the inlet of the electrochemical subsystem, respectively. The integrated sensor modules include: a flow meter, a TDS sensor, an electronic pH meter, and an electronic ORP meter.

[0030] More preferably, water valves are provided at the water inlet of the electrochemical subsystem, the water outlet of the electrochemical subsystem, the scale discharge outlet, and the water outlet of the buffer tank, and the water valves include solenoid valves.

[0031] Preferably, the voltage range of the DC power supply is 0V to 220V and the current range is 0A to 20A.

[0032] Preferably, the buffer tank is rectangular or cylindrical, and the height of the buffer tank is greater than the length and width of the rectangular prism or the diameter of the cylinder.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention provides a water softening-induced crystallization-reverse osmosis water treatment system with long lifespan, multifunctionality, low cost, low energy consumption, high water recovery rate, and high desalination rate. The first electrode of this invention has excellent catalytic oxidation activity, which can degrade organic matter in the water and reduce the organic pollutant load on the reverse osmosis module. The first electrode can oxidize chloride ions in the water into active chlorine products such as hypochlorite and chlorine free radicals. The increase in effective chlorine concentration and redox potential can kill algae and pathogens in the water. A hydrogen evolution reaction occurs on the surface of the second electrode, increasing the pH and causing hardness ions in the water to precipitate. These ions are then filtered out during the induced crystallization system, significantly reducing water hardness and decreasing the inorganic pollutant load on the reverse osmosis module.

[0035] 2. The first electrode of this invention uses a DSA electrode, which ensures the long-term safe and stable operation of the water softening-induced crystallization-reverse osmosis coupled water treatment system. The second electrode of this invention uses a mesh or plate-shaped pure titanium or stainless steel electrode, which is inexpensive, has strong mechanical and electrochemical stability, and the mesh electrode can provide more sites for hydrogen evolution reaction and scale crystallization.

[0036] 3. The heterogeneous inducing agent in the crystallization column of this invention can induce the formation of scale crystals, improve the hardness removal rate, and filter scale particles.

[0037] 4. The buffer tank of this invention can fully mix the pretreated wastewater, alleviate the flow difference caused by fluctuations in the treatment capacity of the electrochemical module and the reverse osmosis module, ensure the normal operation of the continuous flow reaction system, and reduce the hydraulic load of the reverse osmosis system. At the same time, the buffer tank can transform incompletely deposited scale particles in the induced crystallization system into large-sized crystals through Ostwald ripening, and then settle to the bottom of the tank by gravity.

[0038] 5. The reverse osmosis device of the present invention uses a commercially available industrial-grade reverse osmosis system, including a housing, a high-pressure pump, and a reverse osmosis membrane, to achieve a high desalination rate of over 96% and discharge reverse osmosis concentrate. The concentrate can be recirculated into the electrochemical unit or further treated or disposed of. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of an electrochemical water softening-induced crystallization-reverse osmosis coupled water treatment system according to the present invention;

[0040] Figure 2 This is a schematic diagram of the invention process;

[0041] Figure 3 This is a graph showing the decrease in inorganic pollutant levels in the water body compared to before treatment in Example 2 of the present invention;

[0042] Figure 4 This is a diagram showing the removal effect of organic pollutants in water in Example 3 of the present invention;

[0043] Figure 5 This is a diagram illustrating the algae removal and sterilization effect of the water body in Embodiment 4 of the present invention;

[0044] Figure 6 This is a graph showing the change in reverse osmosis membrane (water purification) flux over operating time in Example 5 of the present invention.

[0045] In the diagram, 1. Electrochemical subsystem; 2. Induced crystallization column; 3. Buffer tank; 4. Reverse osmosis module; 5. First electrode; 6. Second electrode; 7. Electrolytic cell; 8. DC power supply; 9. Scale collection chamber; 10. Scale outlet; 11. Concentrate return port; 12. First water pump; 13. Second water pump; 14. Integrated sensor module; 15. Water valve. Detailed Implementation

[0046] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] The purpose of this embodiment is to combine electrochemical technology, an induced crystallization water treatment system, and reverse osmosis technology to fully leverage the advantages of each while avoiding their disadvantages, thereby completing the target electrochemical water treatment process. This provides a coupled process that helps alleviate membrane fouling, reduces wastewater production, and lowers wastewater treatment costs, effectively addressing the limitations of current reverse osmosis technology due to membrane fouling and other defects. This embodiment applies electrochemical technology to reverse osmosis pretreatment; the coupled process has functions such as water softening, organic matter degradation, and algae removal and sterilization, demonstrating good effects on the degradation of organic matter, removal of inorganic pollutants, and inhibition of microbial growth in water.

[0048] To achieve the above objectives, this embodiment provides the following technical solution:

[0049] A water softening-induced crystallization-reverse osmosis coupled water treatment system combining electrochemical water treatment technology, an induced crystallization system, and a reverse osmosis process, comprising:

[0050] Electrochemical subsystem: includes a first electrode, a second electrode, a DC power supply, an electrolytic cell, etc., see details. Figure 2 ;

[0051] Induced crystallization column: consists of a shell and filler (commercial activated carbon, artificial zeolite, molecular sieves and other porous materials);

[0052] Buffer tank: Used to receive the effluent from the induced crystallization system. The water in the regulating tank is pumped into the reverse osmosis module by a constant pressure water pump.

[0053] Reverse osmosis module: includes housing, pressure pump and industrial-grade reverse osmosis membrane;

[0054] First electrode and second electrode: The first electrode and the second electrode are respectively connected to the positive and negative terminals of the DC power supply.

[0055] A further improvement in this embodiment is that the electrolytic cell has an inlet and an outlet. Several pairs of first and second electrodes are arranged in the electrolytic cell, dividing the water flow into several localized two-electrode electrochemical reaction systems.

[0056] A further improvement in this embodiment is that the bottom of the water outlet of the electrolytic cell is slightly inclined downwards and connected to a scale discharge port. This facilitates the deposition of water particles carried by the water flow in this area. When the deposited scale reaches a certain amount, the scale discharge port can be opened, and the scale flows out from the scale discharge port with the water flow under the action of gravity and the flow field.

[0057] A further improvement of this embodiment is that the first electrode is a size-stabilized anode (DSA electrode), preferably a ruthenium-iridium-titanium anode; the second electrode is a mesh or plate-shaped pure titanium or stainless steel cathode.

[0058] A further improvement in this embodiment is that an induced crystallization module is added to the back end of the electrochemical subsystem to induce crystallization and filter the scale particles generated by electrochemistry.

[0059] A further improvement in this embodiment is that porous materials such as activated carbon and zeolite are added to the induced crystallization module as inducing agents to provide nucleation sites for the growth of scale crystals such as calcium carbonate and magnesium hydroxide, thereby inducing scale crystallization. Simultaneously, the inducing agents can physically adsorb and filter the resulting scale crystals. The type and amount of inducing agent can be determined according to actual operating conditions.

[0060] A further improvement in this embodiment is that the lack of nucleation sites leads to a very slow crystal formation and growth process for scale crystals, while the porous structure of the inducer provides ample nucleation sites for crystal growth. In the induced crystallization module, the scale-laden water passes through the inducer under its own gravity or pump pressure. Simultaneously, the scale particles dispersed in the water rapidly mature and grow to a larger size under the action of the inducer, and are then removed through adsorption and filtration.

[0061] A further improvement in this embodiment is that the buffer tank is preferably a cuboid or cylinder, with a height greater than its length and width / diameter. No chemical reagents need to be added; gravity alone is sufficient for further sedimentation of scale particles. Furthermore, the large-volume buffer tank can buffer the differences in flow rates between the electrochemical subsystem, the induced crystallization system, and the reverse osmosis system, allowing the entire system to achieve a relatively stable operating state.

[0062] A further improvement in this embodiment is that the integrated sensor module connected to the computer includes an electronic flow meter, a TDS sensor, an electronic pH meter, and an electronic ORP meter, enabling in-situ real-time automatic monitoring of the feed water flow rate q, total dissolved solids (TDS), pH, and ORP of the electrochemical subsystem. The TDS sensor can be a commonly available model with an accuracy of at least 1 μS / cm. The flow sensor (i.e., the electronic flow meter) can be a commonly available model with an accuracy of at least 1 mL / min. The pH sensor (i.e., the electronic pH meter) can be a commonly available model with an accuracy of at least 0.01 pH. The ORP sensor (i.e., the electronic ORP meter) can be a commonly available model with an accuracy of at least 1 mV. A water pump delivers water from the equalization tank into the reverse osmosis system at a constant pressure; the pump flow rate (membrane flux) is denoted as Q.

[0063] A further improvement in this implementation is that, according to different operating conditions, corresponding ranges for influent flow rate, TDS, pH, and ORP can be set, including warning ranges and maintenance ranges. When any of the above water quality parameters exceeds the warning range, the computer will sound an alarm and remind the user to closely monitor changes in the influent water quality; when any of the above water quality parameters exceeds the maintenance range, the computer will sound an alarm and forcibly stop the system operation, reminding the user to perform maintenance.

[0064] A further improvement of this embodiment is that the components of the reverse osmosis system (pipes, connectors, water pumps, flow meters, sensors, reverse osmosis membranes, etc.) can be matched and adjusted according to actual needs without strict limitations.

[0065] A water softening-induced crystallization-reverse osmosis coupled water treatment process based on electrochemical technology includes the following steps:

[0066] A DC power supply applies an electric field to the first and second electrodes. When using a constant current power supply mode, the DC power supply applies current to the first and second electrodes. The key parameters for the applied current are: the current value *i* and the energizing time *t1*. When using a constant voltage power supply mode, the DC power supply applies voltage to the first and second electrodes. The key parameters for the applied voltage are: the voltage value *U* and the energizing time *t2*. When using an exponentially decaying power supply mode, the DC power supply applies current to the first and second electrodes. The key parameters for the applied current are: the current value *i* and the energizing time *t3*. Generally, for industrial wastewater treatment, a constant current or exponentially decaying power supply mode is preferred; for seawater desalination and brackish water treatment, a constant voltage or constant current power supply mode is preferred; and for municipal sewage treatment, a constant voltage or exponentially decaying mode is preferred.

[0067] Several pairs of electrode groups (each pair of electrode groups includes a first electrode and a second electrode) are used to electrochemically treat wastewater;

[0068] Under direct current, pollutant indicators such as COD, DOM, hardness, alkalinity, conductivity, and total bacterial count in water all decreased;

[0069] In exponential decay mode, the current efficiency for organic oxidation and hardness removal (hydrogen evolution reaction) is greatly improved, significantly reducing energy consumption.

[0070] A further improvement in this embodiment is that the first electrode can be obtained by methods such as coating, calcination, electrolysis, or electroreduction. Preferably, the DSA electrode can be formed on a titanium substrate by methods such as coating, calcination, or electrolysis to create an active layer. The second electrode can be directly fabricated into a mesh or plate cathode by methods such as metallurgy or electroreduction. The specific form and size of the electrodes can be determined according to actual needs.

[0071] A further improvement in this embodiment is that the power supply can be a single DC power supply unit, or a power supply or power supply combination capable of providing stable DC current or stable DC voltage. The power supply can provide a voltage range of 0V to 220V and a current range of 0A to 20A.

[0072] A further improvement in this embodiment lies in the following: the core of this embodiment is the use of a first electrode with catalytic oxidation activity for organic matter, a second electrode with electrochemical descaling capability, and a DC power supply system. Other components of the electrochemical subsystem (electrolytic cell, pipes, connectors, aeration equipment, etc.) can be matched and adjusted according to actual needs, without strict limitations.

[0073] A further improvement in this embodiment is that the current, voltage, and energizing time provided by the DC power supply can be optimized according to actual conditions; the flow rate Q provided by the water pump can be varied according to actual conditions. The feed water pump of the electrochemical subsystem can automatically adjust the feed water flow rate q to adapt to the flow rate Q of the reverse osmosis module. When the feed water flow rate q of the electrochemical subsystem is greater than the membrane flux Q, the feed water pump automatically reduces its speed until q matches Q; conversely, when q is less than Q, the feed water pump automatically increases its speed until q matches Q.

[0074] In the electrochemical process of this embodiment, the electrochemical reactions occurring in both the anode and cathode regions can reduce the concentration of certain water pollutants. The hydrogen evolution reaction on the cathode surface can generate hydroxide ions, shifting the precipitation-dissolution equilibrium of calcium and magnesium ions in the water to the right, resulting in a decrease in water hardness. The reaction equations are shown in formulas (1)-(4):

[0075] 2H2O+2e - →2OH - +H2↑ (1)

[0076]

[0077] Mg 2+ +2OH - →Mg(OH)2↓ (4)

[0078] Furthermore, the anode zone can catalytically generate free radicals to oxidize organic matter in the water, thereby removing COD (Equations 5 and 6). Chloride ions in the water are oxidized near the anode into oxidizing disinfectants such as hypochlorous acid, increasing the water's oxidation-reduction potential (ORP) and inhibiting the growth and reproduction of microorganisms and algae (Equations 7 and 8). The reaction equations are as follows:

[0079] H2O-e - →·OH+H + (5)

[0080] ·OH + Organics → H₂O + CO₂ (6)

[0081] Cl - -e - →·Cl (7)

[0082] Cl - +H₂O-2e - →HClO + H+ + (8)

[0083] A further improvement in this embodiment is that, in exponential decay mode, the current of the electrochemical subsystem can be automatically adjusted according to the influent flow rate q and the TDS fed back by the sensor. The change of current with flow rate and TDS in exponential decay mode is shown in formula (9):

[0084]

[0085] Where i0 is the standard current, k1 is the hardness removal coefficient (which varies depending on the application scenario), TDS is the total dissolved solids content in the water, TDS0 is the standard total dissolved solids content, and q is the influent flow rate.

[0086] A further improvement of this embodiment is that the system can be used in scenarios including but not limited to: circulating cooling water, seawater desalination, surface brackish water treatment, industrial wastewater treatment, and advanced municipal sewage treatment. The treatment method used is not limited; both intermittent and continuous treatment methods can be used.

[0087] A further improvement of this implementation method is that, in different application scenarios, if other processing technologies are required, different processing modules can be combined according to actual needs.

[0088] Example

[0089] Electrocatalytic oxidation, also known as anodic oxidation, is a process in which hydroxyl radicals generated on the anode surface under the influence of an electric field oxidize and degrade organic matter. DSA anodes are made from TiO2, one of the most abundant raw materials on Earth, and possess excellent mechanical strength and electrochemical stability. They exhibit good catalytic degradation activity for organic matter, making them ideal anode materials.

[0090] Under the influence of an electric field, chloride ions in the water can be oxidized on the anode surface, and the oxidation products (hypochlorous acid, hypochlorite, chlorine free radicals, etc.) have bactericidal properties. At the same time, the low pH and high redox potential of the anode area can kill microorganisms and inhibit the growth of pathogens and algae.

[0091] Electrochemical descaling, also known as electrochemical water softening, is an active descaling technology. Under the influence of an electric field, anions such as hydroxide ions and carbonate ions are generated on the cathode surface. These anions react with hardness ions such as calcium and magnesium ions in the water to form precipitates. The titanium-based cathode surface provides excellent sites for the growth of scale crystals, which is beneficial for scale deposition and removal.

[0092] In the electrochemical-induced crystallization-reverse osmosis process described in this embodiment, the three electrochemical reactions mentioned above occur simultaneously in the electrochemical subsystem, leading to a decrease in water pollutant indicators such as COD, DOM, hardness, conductivity, and total bacterial count. However, existing technologies lack effective means of using electrochemical methods as RO pretreatment. Titanium-based electrodes possess good conductivity and strong corrosion resistance, and can be used as a substrate for diverse modifications, making them a promising electrode material and an ideal electrode material for the electrochemical subsystem described in this embodiment.

[0093] This embodiment uses a water softening-induced crystallization device as a pretreatment process for the reverse osmosis module. It was found that water softening-induced crystallization significantly improves the feed water quality of the reverse osmosis module, alleviates membrane fouling, reduces reverse osmosis concentrate production, and greatly extends the lifespan and cleaning cycle of the reverse osmosis membrane, thereby reducing reverse osmosis energy consumption and operating costs. This embodiment employs a DC power supply mode with constant current density for electrolysis, and the energizing time and hydraulic residence time can be manually controlled.

[0094] In this embodiment, the electrochemical-induced crystallization method for mitigating inorganic fouling of the reverse osmosis membrane differs from the traditional addition of chemical scale inhibitors. Traditional chemical scale inhibitors suppress the precipitation of hardness ions in water through physicochemical processes such as chelation, dispersion, complexation, and coordination, but they do not effectively remove hardness ions. The electrochemical subsystem used in this embodiment generates a large number of hydroxide ions on the surface layer of the second electrode (cathode). The high pH in the cathode region increases the supersaturation of calcium carbonate and other scale deposits in the solution, causing scale to precipitate in the bulk solution or on the cathode surface. The subsequent induced crystallization system further induces scale deposition, improving the hardness removal effect.

[0095] In this embodiment, the mitigation of organic fouling in the reverse osmosis membrane by electrochemical-induced crystallization stems from advanced oxidation technology based on free radical reactions. The electrochemical subsystem used in this embodiment can generate hydroxyl radicals on the surface of the first electrode (anode), thereby non-selectively oxidizing and degrading organic pollutants in the water.

[0096] In this embodiment, electrochemical-induced crystallization alleviates microbial fouling of reverse osmosis membranes based on electrochemical disinfection technology. Without the addition of additional disinfectant, chloride ions present in the wastewater are oxidized in the anodic region, producing active chloride species (hypochlorous acid, hypochlorite, chlorine free radicals, etc.) and hydrogen ions with oxidizing and disinfecting properties, thus increasing the redox potential of the water body. It is generally believed that a redox potential above 600 mV is sufficient to effectively kill most pathogenic microorganisms. The redox potential of the solution after electrolysis can reach as high as 600–1100 mV, exhibiting a certain killing effect on pathogenic microorganisms and algae in the water.

[0097] Example 1

[0098] Please see Figure 1 As shown, this embodiment provides an electrochemical-induced crystallization-reverse osmosis water treatment system with long life, multifunctionality, low cost, low energy consumption, high water recovery rate, and high desalination rate, including: an electrochemical subsystem, a ball valve, an induced crystallization column, a buffer tank, a pressure pump, an integrated sensor module (including an electronic flow meter, a TDS sensor, an electronic pH meter, an electronic ORP meter, etc.), and a reverse osmosis module.

[0099] Please see Figure 2 As shown, the electrochemical subsystem provided in this embodiment includes a pressure water pump, an integrated sensor module (including an electronic flow meter, a TDS sensor, an electronic pH meter, an electronic ORP meter, etc.), a second electrode, a first electrode, an electrolytic cell, a DC power supply, a reactor base, a ball valve, and another ball valve. The first electrode and the second electrode are respectively connected to the positive and negative terminals of the DC power supply. The first electrode is a DSA electrode, preferably a ruthenium-iridium titanium electrode. The second electrode is a pure titanium electrode, preferably a mesh titanium electrode. The DC power supply can provide three modes: constant current, constant voltage, and exponentially decaying current.

[0100] In this embodiment, by inputting core parameters (current value i and energizing time t in constant current mode; voltage value U and duration t in constant potential mode; current value i and electrochemical subsystem flow rate q in exponential decay current mode), a DC power supply applies DC current to the first and second electrodes. The ball valve is closed, and raw water enters the reactor via a pressure pump. Once the electrolytic cell is full, power is supplied to the first and second electrodes according to preset power supply conditions, thus completing the electrochemical reaction process. The treated water flows out from the upper outlet by opening the ball valve, and the scale produced by electrolysis is discharged from the lower outlet by periodically opening the ball valve.

[0101] The first electrode and the second electrode can each be one or more; each pair forms an electrode group.

[0102] The reaction method of this embodiment will be further described below with reference to specific examples.

[0103] Example 2

[0104] Inorganic pollutant removal: See Figure 2 The electrochemical subsystem uses a pair of electrode sets (including a plate-shaped DSA first electrode and a plate-shaped titanium second electrode), with each electrode measuring 80mm*80mm*2mm. Each electrode set is connected to one pole of the DC power supply. When the electrolyzer is filled with raw water (using a batch processing mode), a constant current mode is used, with the core input current parameter (current value i = 3.200A, corresponding to a current density of 50mA / cm³)... 2 (Power-on time t is 120 min), powered by DC power supply at room temperature.

[0105] Please see Figure 3 As shown, the simulated wastewater had a total hardness of 360 mg / L, including 300 mg / L calcium hardness and 60 mg / L magnesium hardness; bicarbonate alkalinity was 300 mg / L, and the solution conductivity was approximately 1100 μS / cm. After a 120-minute electrolysis process, the total hardness of the system effluent decreased to 134 mg / L, calcium hardness to 77 mg / L, magnesium hardness to 57 mg / L, bicarbonate alkalinity to 69 mg / L, and conductivity to 574 μS / cm. The removal rates for total hardness, calcium hardness, and alkalinity reached 62.8%, 76.7%, and 77.0%, respectively.

[0106] Example 3

[0107] Organic pollutant removal: The electrochemical subsystem uses five electrode pairs (each pair includes one plate-shaped DSA first electrode and one plate-shaped titanium second electrode), with each electrode measuring 200mm*100mm*2.5mm. Each electrode pair is connected to one pole of the DC power supply. When the electrolyzer is filled with raw water (using continuous flow treatment mode), a constant voltage mode is used, with the core input voltage parameters (voltage value U = 6.00V, electrochemical subsystem flow rate q), powered by a DC power supply at room temperature. The water quality parameters of the simulated wastewater are shown in Table 1 below.

[0108]

[0109]

[0110] Table 1

[0111] Please see Figure 4 As shown, within 30 hours of operation of the electrochemical subsystem, the TOC removal rate of the simulated wastewater fluctuated between 13.5% and 31.3%, with an average TOC removal rate of 19.71%, demonstrating that in addition to water softening, the electrochemical process also has a good oxidative degradation effect on organic matter in water.

[0112] Example 4

[0113] Microbial contaminant removal: The electrochemical subsystem uses a pair of electrode groups (including a plate-shaped DSA first electrode 3 and a plate-shaped titanium second electrode 2), with each electrode measuring 80mm*80mm*2mm. Each electrode group is connected to one pole of the power supply 6. When the electrolyzer is filled with raw water (using a batch processing mode), a constant current mode is adopted, with the core input current parameter (current value i is 1.280A, corresponding to a current density of 20mA / cm³)... 2 (Power-on time t is 120 min), powered by DC power supply at room temperature.

[0114] Please see Figure 5As shown, the simulated wastewater theoretically has a chloride ion content of 19.2 mmol / L, a total hardness of 960 mg / L, a bicarbonate alkalinity of 200 mg / L, and a solution conductivity of approximately 1900 μS / cm. Different microorganisms require different oxidation-reduction potentials (ORP) for survival. For example, methanogens thrive at an ORP of approximately -400 mV to -300 mV, most anaerobic bacteria at approximately -250 mV to -200 mV, most facultative anaerobic bacteria at approximately -330 mV to +400 mV, and most aerobic bacteria at approximately +200 mV to +600 mV. In this embodiment, after 120 minutes of electrolysis, the water's ORP increased from +508 mV before electrolysis to +828 mV, reaching the standard for inhibiting the growth and reproduction of most microorganisms.

[0115] Example 5

[0116] Electrochemical-induced crystallization-reverse osmosis application scenarios: See [link / reference] Figure 2 The electrochemical subsystem uses five electrode pairs (five plate-shaped DSA first electrodes and five plate-shaped titanium second electrodes), with each electrode measuring 20cm*10cm*2.5mm. Each electrode pair is connected to one pole of the DC power supply. When the electrolyzer is filled with raw water (using continuous flow treatment mode), an exponential decay mode is adopted, with the input current core parameters (current value i, electrochemical subsystem flow rate q) and DC power supply at room temperature. Activated carbon is filled in the induced crystallization column as an adsorbent. The water quality parameters of the simulated wastewater are shown in Table 2 below.

[0117] Total Hardness ~400mg / L nitrates ~20mg / L Calcium hardness ~360mg / L ammonia nitrogen ~20mg / L magnesium hardness ~40mg / L pH ～7 Total alkalinity ~400mg / L Total bacterial count <![CDATA[~10 5 -10 6 CFU / L]]> chloride ions ~350mg / L COD ~100mg / L sulfates ~20mg / L water temperature ～20℃

[0118] Table 2

[0119] After the wastewater flows through the electrochemical subsystem and the induced crystallization module, the contents of inorganic pollutants such as total hardness, calcium hardness, magnesium hardness, and alkalinity in the effluent all decrease significantly, while the concentrations of organic pollutants such as TOC, ammonia nitrogen, and total nitrogen all decrease significantly. ORP increases significantly, indicating that the growth and reproduction of aquatic microorganisms and algae are inhibited. Through the hardness removal, oxidative degradation of organic matter, algae removal and sterilization effects of the electrochemical subsystem, and the induced crystallization effect of the induced crystallization module, most organic, inorganic, and microbial pollutants are removed, and the quality of the influent to the reverse osmosis module is greatly improved.

[0120] Please see Figure 6As shown, compared to the standalone reverse osmosis process (control group), the water softening-induced crystallization-reverse osmosis coupling process described in this patent (experimental group) can significantly alleviate the decrease in membrane flux caused by membrane fouling, with an average increase in permeate flux of over 50% over the same operating time. To better compare the improvement effects of different processes on reverse osmosis membrane performance, a specific flux (i.e., the ratio of permeate flux to the maximum membrane flux measured using pure water) below 0.3 is considered as the reverse osmosis membrane reaching its membrane life limit. Without any pretreatment process, the reverse osmosis membrane will reach its membrane life limit in 390–420 minutes, while the water softening-induced crystallization-reverse osmosis coupling process described in this patent has not reached its membrane life limit even after 15 hours of operation. Linear fitting results show that using the water softening-induced crystallization-reverse osmosis coupling process described in this patent can extend the reverse osmosis membrane life to approximately 1153 minutes. Compared to the standalone reverse osmosis process, the water softening-induced crystallization-reverse osmosis coupling process described in this patent extends the membrane life by at least 100%.

[0121] In summary, this invention provides a water softening-induced crystallization-reverse osmosis water treatment system with long lifespan, multifunctionality, low cost, low energy consumption, high water recovery rate, and high desalination rate. The first electrode exhibits excellent catalytic oxidation activity, degrading organic matter in the water and reducing the organic pollutant load on the reverse osmosis module. The first electrode oxidizes chloride ions in the water into active chlorine products such as hypochlorite and chlorine free radicals. The increased effective chlorine concentration and redox potential kill algae and pathogens in the water. A hydrogen evolution reaction occurs on the surface of the second electrode, raising the pH and causing hardness ions in the water to precipitate. These ions are then filtered out during the induced crystallization system, significantly reducing water hardness and decreasing the inorganic pollutant load on the reverse osmosis module.

[0122] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An electrochemical water softening-crystallization induction-reverse osmosis coupled water treatment system, characterized in that, The water treatment system comprises an electrochemical subsystem (1), an induced crystallization column (2), a buffer tank (3), and a reverse osmosis module (4). The electrochemical subsystem (1) is used to apply current voltage to the contaminated water in the electrochemical subsystem (1) to reduce water hardness, remove COD in the water, and inhibit the growth and reproduction of microorganisms and algae in the water. The induced crystallization column (2) is used as an inducer to provide nucleation sites for the growth of scale crystals and induce scale crystallization of scale particles generated in the electrochemical subsystem (1). The buffer tank (3) is used to allow the scale particles to settle by gravity. The reverse osmosis module (4) is used to remove dissolved solids, organic matter, inorganic matter, bacteria, viruses, salts, colloids, and soluble impurities in the water through a semi-permeable membrane. The water inlet of the electrochemical subsystem (1) is connected to a contaminated water source, the water outlet of the electrochemical subsystem (1) is connected to the upper water inlet of the induced crystallization column (2), the lower water outlet of the induced crystallization column (2) is arranged in the buffer tank (3), the water outlet of the buffer tank (3) is connected to the water inlet of the reverse osmosis module (4), and the clean water discharge outlet of the reverse osmosis module (4) is connected to a clean water collection device. The electrochemical subsystem (1) is provided with a first electrode (5), a second electrode (6), and an electrolytic tank (7), the first electrode (5) and the second electrode (6) are arranged in an alternating manner along the length direction of the electrolytic tank (7), the first electrode (5) and the second electrode (6) are respectively electrically connected to the positive electrode and the negative electrode of a direct current power supply (8), and the first electrode (5) is a shape-stable anode. The induced crystallization column (2) is in the shape of a vertical column, and the induced crystallization column (2) is filled with a porous adsorbent. The second electrode (6) is a plate-shaped or net-shaped pure titanium or stainless steel electrode. The first electrode (5) and the second electrode (6) are arranged at equal intervals, and the first electrode (5) and the second electrode (6) are completely immersed in the contaminated water in the electrolytic tank (7). The working mode of the electrochemical subsystem (1) includes a constant current power supply mode, a constant voltage power supply mode, and an exponential decay power supply mode; when the working mode of the electrochemical subsystem (1) is the constant current power supply mode, the current value i is constant and the power-on time is t1. When the working mode of the electrochemical subsystem (1) is the constant voltage power supply mode, the voltage value U is constant and the power-on time is t2. When the working mode of the electrochemical subsystem (1) is the exponential decay power supply mode, the current of the electrochemical subsystem is automatically adjusted according to the water inflow q and the TDS feedback of the sensor. The treatment process of the water treatment system comprises the following steps: The direct current power supply applies an electric field to the first electrode and the second electrode; when the constant current power supply mode is used, the direct current power supply applies a current to the first electrode and the second electrode, and the core parameters of the applied current are the current value i and the power-on time t1. When the constant voltage power supply mode is used, the direct current power supply applies a voltage to the first electrode and the second electrode, and the core parameters of the applied voltage are the voltage value U and the power-on time t2. ​ When the exponential decay power supply mode is used, the direct current power supply applies current to the first electrode and the second electrode, and the core parameters of the applied current are: current value i when energized, energized time t3; For industrial wastewater treatment, constant current or exponential decay power supply mode is selected;For seawater desalination and brackish water treatment, constant voltage or constant current power supply mode is selected;For municipal sewage treatment, constant voltage or exponential decay mode is selected.

2. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 1, characterized in that, The processing mode of the electrochemical subsystem (1) includes intermittent processing and continuous flow processing.

3. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 1, characterized in that, The electrolytic cell (7) is provided with a funnel-shaped concave scale collection bin (9) at the bottom, and the bottom of the scale collection bin (9) is provided with a scale discharge port (10); the reverse osmosis module (4) is provided with a concentrated water backflow port (11) for discharging concentrated water filtered by the reverse osmosis module (4), and the concentrated water backflow port (11) is communicated to the water inlet of the electrochemical subsystem (1), and the backflow ratio can be adjusted.

4. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 3, characterized in that, The water inlet of the electrochemical subsystem (1) is provided with a first water pump (12), and the water inlet of the reverse osmosis module (4) is provided with a second water pump (13); the water inlets of the reverse osmosis module (4) and the electrochemical subsystem (1) are also respectively provided with integrated sensor modules (14), and the integrated sensor modules (14) include: electronic flow meter, TDS sensor, electronic pH meter and electronic ORP meter.

5. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 3, characterized in that, The water inlets of the electrochemical subsystem (1), the water outlets of the electrochemical subsystem (1), the scale discharge port (10) and the water outlet of the buffer tank (3) are respectively provided with water valves (15), and the water valves (15) include electromagnetic valves.

6. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 1, characterized in that, The voltage range of the direct current power supply (8) is 0V-220V, and the current range is 0A-20A.

7. The electrochemical water softening-inducing crystallization-reverse osmosis coupled water treatment system according to claim 1, characterized in that, The buffer tank (3) is in the shape of a rectangular parallelepiped or a cylinder, and the height of the buffer tank (3) is greater than the length, width or diameter of the rectangular parallelepiped or the cylinder.

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