Method and system for treating sewage of circulating water system

Abstract

The invention provides a method for treating sewage of a circulating water system, which comprises the following steps: (1) filtering the sewage of the circulating water system, and discharging first concentrated water to obtain first produced water; (2) carrying out ultrafiltration treatment on the obtained filtrate, and discharging ultrafiltration concentrated water to obtain ultrafiltration produced water; (3) carrying out special nanofiltration treatment on the obtained ultrafiltration produced water, and discharging special nanofiltration concentrated water to obtain special nanofiltration produced water; wherein the used nanofiltration membrane is a polyamide nanofiltration membrane; (4) carrying out nanofiltration treatment on the obtained special nanofiltration produced water, and discharging nanofiltration concentrated water of which the solute is mainly sodium sulfate to obtain nanofiltration produced water of which the solute is mainly sodium chloride; (5) carrying out reverse osmosis treatment on the obtained nanofiltration produced water, and discharging reverse osmosis concentrated water to obtain reverse osmosis produced water; wherein the obtained nanofiltration concentrated water and / or reverse osmosis produced water are / is returned to a circulating water system. The invention further provides a corresponding system. According to the method and the system, the sewage of the circulating water system can be partially recycled, and the sewage discharge amount is reduced.

Description

Technical Field

[0001] The invention belongs to the field of sewage treatment, and in particular relates to a method and a system for treating sewage discharged from a circulating water system. Background Art

[0002] At present, many domestic enterprises need circulating water as cooling water. The circulating water cooling towers configured in the factory have high water consumption and large sewage discharge, becoming a major water consumer in the factory. At present, the treatment method for sewage discharged from the circulating water system is basically to send it to the sewage treatment plant for pretreatment such as sedimentation and filtration, and then enter the ultrafiltration and reverse osmosis system. The reverse osmosis water is supplemented to the circulating water system for recycling. The reverse osmosis desalination rate is very high, and the salt content in the produced water is very low. Although adding it to the circulating water system can effectively increase the concentration multiple, due to the low salt content, there are not enough ions that can passivate steel or produce insoluble precipitates to cover the metal surface, and the corrosion of the steel surface cannot be suppressed. It is extremely corrosive and easily causes the corrosion rate of the circulating water to exceed the standard. In addition, the circulating water system requires a certain amount of alkalinity and hardness. Since the replenishment water is reverse osmosis water, its alkalinity and hardness are very low. The circulating water system needs to supplement alkalinity and hardness agents, and the operating cost is very high.

[0003] The current treatment process for wastewater from circulating water systems cannot effectively solve the aforementioned technical problems. Summary of the invention

[0004] The first object of the present invention is to provide a method for treating wastewater from a circulating water system, which method can solve at least one of the above-mentioned technical problems;

[0005] A second object of the present invention is to provide a system for use in the aforementioned method.

[0006] To achieve the first object of the present invention, the following technical solutions are adopted:

[0007] A method for treating wastewater from a circulating water system, the method comprising:

[0008] (1) Filtering the wastewater from the circulating water system to remove suspended solids, discharging the first concentrated water and obtaining the first produced water;

[0009] (2) subjecting the filtrate obtained in step (1) to ultrafiltration to remove organic matter and particulate matter therein, discharging ultrafiltration concentrated water, and obtaining ultrafiltration product water;

[0010] (3) performing special nanofiltration treatment on the ultrafiltration product water obtained in step (2) to remove COD pollutants therein, discharging special nanofiltration concentrated water, and obtaining special nanofiltration product water; wherein the nanofiltration membrane used for the special nanofiltration treatment is a polyamide nanofiltration membrane;

[0011] (4) subjecting the special nanofiltration produced water obtained in step (3) to nanofiltration treatment to separate the salt, separate the sulfate ions and chloride ions therein, discharge the nanofiltration concentrated water whose solute is mainly sodium sulfate, and obtain the nanofiltration produced water whose solute is mainly sodium chloride;

[0012] (5) performing reverse osmosis treatment on the nanofiltration product water obtained in step (4) to desalinate, discharge the reverse osmosis concentrated water, and obtain reverse osmosis product water; wherein,

[0013] The nanofiltration concentrated water obtained in step (4) and / or the reverse osmosis produced water obtained in step (5) are returned to the circulating water system.

[0014] The method of the present invention preferably further comprises step (6), subjecting at least part of the reverse osmosis concentrated water obtained in step (5) to an electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution;

[0015] Preferably, the sodium hypochlorite solution obtained in step (6) is returned to the circulating water system as a bactericide; and / or,

[0016] The concentration of the sodium hypochlorite solution obtained in step (6) is 0.5-0.8 wt %; and / or,

[0017] In step (6), the conditions for the electrochemical reaction include: a current of 50 to 70 A, and / or a voltage of 220 to 380 V.

[0018] In the method of the present invention, preferably, in step (4), the nanofiltration treatment includes a primary nanofiltration treatment and a secondary nanofiltration treatment;

[0019] In step (4), the special nanofiltration product water obtained in step (3) is first subjected to a primary nanofiltration treatment, and the primary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the primary nanofiltration product water with sodium chloride as the main solute is obtained; then the primary nanofiltration product water is subjected to a secondary nanofiltration treatment, and the secondary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the secondary nanofiltration product water with sodium chloride as the main solute is obtained as the nanofiltration product water;

[0020] The primary nanofiltration concentrate and / or the secondary nanofiltration concentrate are returned to the circulating water system.

[0021] In the method of the present invention, preferably, in step (5), the reverse osmosis treatment includes a primary reverse osmosis treatment and a secondary reverse osmosis treatment;

[0022] In step (5), the nanofiltration product water obtained in step (4) is first subjected to a primary reverse osmosis treatment, and the primary reverse osmosis concentrated water is discharged to obtain the primary reverse osmosis product water as the reverse osmosis product water; then the primary reverse osmosis concentrated water is subjected to a secondary reverse osmosis treatment, and the secondary reverse osmosis concentrated water is discharged as the reverse osmosis concentrated water to obtain the secondary reverse osmosis product water;

[0023] The primary reverse osmosis water is returned to the circulating water system as reverse osmosis water;

[0024] Preferably, the secondary reverse osmosis produced water is returned to the primary reverse osmosis treatment.

[0025] In the method of the present invention, preferably, in step (1), the operating pressure difference of the filtration device is 0.05-0.1 MPa, and / or the inlet turbidity is ≤30NTU, and / or the outlet turbidity is ≤2NTU, and / or the operating backwash pressure difference is ≤0.05MPa, and / or the filter pore size is 80-100μm.

[0026] In the method of the present invention, preferably, in step (2), the pore size of the ultrafiltration device is 0.005 to 0.1 mm.

[0027] In the method of the present invention, preferably, in step (3), the influent COD of the special nanofiltration device is less than 300 mg / l, and / or the salt content is greater than 1000 mg / l, and / or the membrane flux is 10 to 30 LMH, and / or the operating pressure is 0.7 to 2.0 MPa, and / or the operating pH range is 2 to 12, and / or the influent turbidity is less than 3 NTU.

[0028] In the method of the present invention, preferably, in step (4), the membrane flux of the nanofiltration device is 15-25LMH, and / or the operating pressure is 1.5-3.0MPa, and / or the operating pH range is 2-12, and / or the inlet turbidity is <5NTU.

[0029] In the method of the present invention, preferably, in step (5), the pore size of the membrane of the reverse osmosis device is 0.1 to 10 nm.

[0030] To achieve the second object of the present invention, a system for the above method is provided.

[0031] The beneficial effects of the present invention are:

[0032] (1) The method for treating wastewater from a circulating water system of the present invention comprises the following steps: subjecting the wastewater from the circulating water system to filtration + ultrafiltration + special nanofiltration + nanofiltration in sequence, returning the nanofiltration concentrate to the circulating water system for use, subjecting the nanofiltration product water to reverse osmosis + electrochemical reaction in sequence to produce sodium hypochlorite, and returning the produced sodium hypochlorite solution to the circulating water system as a bactericide; and adjusting the amount of reverse osmosis concentrate subjected to electrochemical reaction according to the demand for bactericide in the circulating water system, thereby adjusting the discharge amount of reverse osmosis concentrate, and discharging the remaining small amount of reverse osmosis concentrate to a sewage treatment plant for treatment; the method of the present invention can partially recycle the wastewater from the circulating water system and reduce the amount of wastewater discharged.

[0033] (2) The method for treating wastewater from a circulating water system of the present invention uses a special nanofiltration treatment to intercept suspended matter and organic matter, and uses a nanofiltration treatment to separate sulfate ions and chloride ions therefrom, so that the solute of the obtained nanofiltration concentrated water is mainly sodium sulfate, and the obtained nanofiltration concentrated water contains beneficial components such as alkalinity, hardness, and zinc ions, and is returned to the circulating water system for continued use, which helps to reduce or avoid additional supplementation of alkalinity and hardness agents and reduce operating costs; the obtained nanofiltration produced water contains chloride ions and sodium ions, and the reverse osmosis concentrated water obtained by reverse osmosis desalination has a high sodium chloride content. The reverse osmosis concentrated water undergoes an electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution, which is an oxidizing bactericide and can be returned to the circulating water system as a bactericide for repeated use.

[0034] (3) The method for treating wastewater from a circulating water system of the present invention can effectively reduce the output of wastewater from circulating water, reasonably recover beneficial components, ensure the stable operation of the circulating water system, reduce the discharge of wastewater, and reduce the cost of wastewater disposal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic flow chart of a method for treating wastewater from a circulating water system according to the present invention in one embodiment. DETAILED DESCRIPTION

[0036] The technical scheme and its effects of the present invention are further described below in conjunction with specific implementation modes / examples and drawings. The following implementation modes / examples are only used to illustrate the contents of the present invention, and the invention is not limited to the following implementation modes or examples. Simple changes made to the present invention by applying the concept of the present invention are within the scope of protection claimed by the present invention.

[0037] The present invention provides a method for treating wastewater from a circulating water system, such as Figure 1 As shown, the method includes:

[0038] (1) Filtering the wastewater from the circulating water system to remove suspended solids, discharging the first concentrated water and obtaining the first produced water;

[0039] (2) subjecting the filtrate obtained in step (1) to ultrafiltration to remove organic matter and particulate matter therein, discharging ultrafiltration concentrated water, and obtaining ultrafiltration product water;

[0040] (3) performing special nanofiltration treatment on the ultrafiltration product water obtained in step (2) to remove COD pollutants therein, discharging special nanofiltration concentrated water, and obtaining special nanofiltration product water; wherein the nanofiltration membrane used for the special nanofiltration treatment is a polyamide nanofiltration membrane;

[0041] (4) subjecting the special nanofiltration produced water obtained in step (3) to nanofiltration treatment to separate the salt, separate the sulfate ions and chloride ions therein, discharge the nanofiltration concentrated water whose solute is mainly sodium sulfate, and obtain the nanofiltration produced water whose solute is mainly sodium chloride;

[0042] (5) performing reverse osmosis treatment on the nanofiltration product water obtained in step (4) to desalinate, discharge the reverse osmosis concentrated water, and obtain reverse osmosis product water; wherein,

[0043] The nanofiltration concentrated water obtained in step (4) and / or the reverse osmosis produced water obtained in step (5) are returned to the circulating water system.

[0044] Those skilled in the art will appreciate that, in the present invention, the devices used in each step are commonly used devices in the art. For example, the filtering device used in step (1) can be a commonly used filter, including a self-cleaning filter.

[0045] The nanofiltration membrane used in the special nanofiltration treatment of the present invention is a polyamide nanofiltration membrane, the surface of which is strongly negatively charged, and the surface charge is 4 times that of an ordinary nanofiltration membrane. It can intercept non-charged organic matter with a molecular weight of more than 300 (Daltons), and can also partially intercept negatively charged organic matter with a molecular weight of more than 150 (Daltons). The inorganic salt interception is relatively low, and the salt permeability is 10-30%. The COD interception rate is generally 60-70%, the maximum tolerance pressure of the nanofiltration membrane is ≤4.5MPa, which is three times that of an ordinary nanofiltration membrane, and the thickness of the support layer of the nanofiltration membrane is twice that of an ordinary nanofiltration membrane. Such a structure enables the nanofiltration membrane to exhibit excellent performance.

[0046] Those skilled in the art understand that the wastewater from a circulating water system refers to the wastewater from a circulating water system, i.e., the backwash water from the bypass filtration of circulating water.

[0047] The method for treating wastewater from a circulating water system of the present invention sequentially performs filtration + ultrafiltration + special nanofiltration + nanofiltration on the wastewater from the circulating water system, returns the nanofiltration concentrated water to the circulating water system for use, sequentially performs reverse osmosis + electrochemical reaction on the nanofiltration produced water to produce sodium hypochlorite, and returns the produced sodium hypochlorite solution to the circulating water system as a bactericide, thereby partially recycling the wastewater from the circulating water system and reducing the amount of wastewater discharged.

[0048] In one embodiment, if Figure 1 As shown, the method further includes step (6), subjecting at least part of the reverse osmosis concentrated water obtained in step (5) to an electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution.

[0049] Those skilled in the art will appreciate that sodium hypochlorite solution can be used as a bactericide in a circulating water system.

[0050] Those skilled in the art will understand that the electrochemical reaction of NaCl and H2O can be carried out in a sodium hypochlorite generator, which is a device that generates sodium hypochlorite solution by electrochemical reaction of low-concentration salt water through energized electrodes. The overall reaction is as follows:

[0051] NaCl+H2O→NaClO+H2.

[0052] In one embodiment, the sodium hypochlorite solution obtained in step (6) is returned to the circulating water system as a bactericide.

[0053] In one embodiment, the concentration of the sodium hypochlorite solution obtained in step (6) is 0.5-0.8wt%, such as 0.5wt%, 0.6wt%, 0.7wt% and 0.8wt% and any value and range of values ​​within the range, so that when it is returned to the circulating water system as a bactericide, it is very safe, stable and cost-effective.

[0054] In one embodiment, in step (6), the conditions of the electrochemical reaction include: a current of 50 to 70 A, such as 50 A, 60 A, 70 A and any value and range of values ​​within the range, and / or a voltage of 220 to 380 V, such as 220 V, 240 V, 260 V, 280 V, 300 V, 320 V, 340 V, 360 V, 380 V and any value and range of values ​​within the range.

[0055] In one embodiment, in step (1), the operating pressure difference of the filtration device is 0.05-0.1MPa, such as 0.06MPa, 0.07MPa, 0.08MPa, 0.09MPa and 0.1MPa and any value and numerical range within this range; and / or the inlet turbidity is ≤30NTU, such as 29MPa, 28MPa and any value and numerical range within this range; and / or the outlet turbidity is ≤2NTU, such as 2MPa, 1MPa and any value and numerical range within this range; and / or the operating backwash pressure difference is ≤0.05MPa, such as 0.04MPa, 0.04MPa and any value and numerical range within this range; and / or the filter pore size is 80-100μm, such as 80μm, 90μm, 100μm and any value and numerical range within this range, thereby retaining suspended matter larger than the filter pore size.

[0056] The present invention can intercept suspended matter of 100 μm through the filtration in step (1).

[0057] In one embodiment, in step (2), the pore size of the ultrafiltration device is 0.005-0.1 mm, such as 0.005 mm, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm and 0.1 mm and any value and range of values ​​within this range, so as to separate and remove particles with a molecular weight greater than 500 Daltons (atomic mass units) and a particle size greater than 10 nanometers, and retain organic matter with a molecular weight of approximately 200-400.

[0058] In one embodiment, in step (3), the inlet COD of the special nanofiltration device is less than 300 mg / l, such as 290 mg / l, 280 mg / l, 250 mg / l, etc.; and / or the salt content is greater than 1000 mg / l, such as 1100 mg / l, 1200 mg / l, 1300 mg / l, etc.; and / or the membrane flux is 10 to 30 LMH, such as 10 LMH, 15 LMH, 20 LMH, 25 LMH, 30 LMH and any value within the range. and numerical range; and / or operating pressure 0.7-2.0MPa, such as 0.7MPa, 1.0MPa, 1.2MPa, 1.5MPa, 1.7MPa, 2.0MPa and any numerical value and numerical range within the range; and / or operating pH range 2-12, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and any numerical value and numerical range within the range; and / or inlet turbidity <3NTU, such as 2.5NTU, 3NTU, etc.

[0059] The present invention can remove most of the COD pollutants and retain a small amount of inorganic salts through the special nanofiltration in step (3). The obtained special nanofiltration concentrated water contains most of the COD but has a low salt content and can be sent to the sewage biochemical system for COD reduction treatment.

[0060] In one embodiment, in step (4), the membrane flux of the nanofiltration device is 15-25LMH, such as 15LMH, 20LMH, 25LMH and any value and numerical range within the range; and / or the operating pressure is 1.5-3.0MPa, such as 1.5MPa, 2MPa, 2.5MPa, 3.0MPa and any value and numerical range within the range; and / or the operating pH range is 2-12, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and any value and numerical range within the range; and / or the inlet turbidity is less than 5NTU, such as 2.5NTU, 3NTU, 3.5NTU, 4NTU, 4.5NTU, 5NTU, etc.

[0061] Those skilled in the art understand that nanofiltration membrane is a mature separation membrane. The pore size range of nanofiltration membrane is between that of reverse osmosis membrane and ultrafiltration membrane. Nanofiltration membrane is a composite membrane whose surface separation layer is composed of polyelectrolytes, and thus has a certain retention rate for inorganic salts.

[0062] The most notable feature of nanofiltration is that it has a high removal performance (i.e., retention performance) for divalent and multivalent ions and organic matter with a molecular weight between 200 and 1000 (Daltons), and has a good penetration effect on monovalent ions.

[0063] In the present invention, the COD pollutants have been intercepted and removed by special nanofiltration in step (3). The main function of the nanofiltration treatment in step (4) is to separate the salt, that is, to separate the sulfate ions and chloride ions in the water. The solute of the obtained nanofiltration water is mainly sodium chloride, and the solute of the obtained nanofiltration concentrated water is mainly sodium sulfate.

[0064] In one embodiment, in step (4), the maximum tolerable pressure of the nanofiltration membrane used in the nanofiltration treatment is ≤4.2 MPa.

[0065] In one embodiment, in step (4), the nanofiltration treatment includes a primary nanofiltration treatment and a secondary nanofiltration treatment;

[0066] In step (4), the special nanofiltration product water obtained in step (3) is first subjected to a primary nanofiltration treatment, and the primary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the primary nanofiltration product water with sodium chloride as the main solute is obtained; then the primary nanofiltration product water is subjected to a secondary nanofiltration treatment, and the secondary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the secondary nanofiltration product water with sodium chloride as the main solute is obtained as the nanofiltration product water;

[0067] The primary nanofiltration concentrate and / or the secondary nanofiltration concentrate are returned to the circulating water system.

[0068] Step (4) of the present invention can achieve SO4 removal by performing two-stage nanofiltration treatment on the special nanofiltration produced water obtained in step (3). 2- The retention rate of Cl - The interception rate is less than 1% and the overall recovery rate is greater than 85%.

[0069] In one embodiment, in step (5), the pore size of the membrane of the reverse osmosis device is 0.1 to 10 nm, such as 0.1 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm and any value and range of values ​​within this range, so that substances larger than 0.0001 microns can be retained.

[0070] Those skilled in the art understand that reverse osmosis is the core part of desalination and is the most sophisticated membrane separation process. It can effectively intercept all dissolved salts and organic matter with a molecular weight greater than 100 (Daltons), while allowing water molecules to pass through, and can remove more than 97% of salt. The resulting reverse osmosis water can be reused as high-quality recycled water.

[0071] In one embodiment, in step (5), the reverse osmosis treatment includes a primary reverse osmosis treatment and a secondary reverse osmosis treatment;

[0072] In step (5), the nanofiltration product water obtained in step (4) is first subjected to a primary reverse osmosis treatment, and the primary reverse osmosis concentrated water is discharged to obtain the primary reverse osmosis product water as the reverse osmosis product water; then the primary reverse osmosis concentrated water is subjected to a secondary reverse osmosis treatment, and the secondary reverse osmosis concentrated water is discharged as the reverse osmosis concentrated water to obtain the secondary reverse osmosis product water;

[0073] The primary reverse osmosis product water is returned to the circulating water system as reverse osmosis product water.

[0074] In a preferred embodiment, the secondary reverse osmosis produced water is returned to the primary reverse osmosis treatment, that is, the secondary reverse osmosis produced water is circulated as the inlet water of the primary reverse osmosis treatment for the primary reverse osmosis treatment.

[0075] In step (5) of the present invention, the nanofiltration water obtained in step (4) is treated with two-stage reverse osmosis to concentrate the solution to 7-8% (i.e., the concentration of the obtained reverse osmosis concentrated water is 7-8%). Considering that the conductivity of the secondary reverse osmosis water is relatively high, the secondary reverse osmosis water is refluxed to the primary reverse osmosis water inlet to achieve self-circulation treatment.

[0076] The present invention also provides a system for the above method, Figure 1 shown.

[0077] In one embodiment, if Figure 1 As shown, the system includes a filtration unit 1, an ultrafiltration unit 2, a special nanofiltration unit 3, a nanofiltration unit 4 and a reverse osmosis unit 5 which are connected in sequence through pipelines, the water inlet of the filtration unit 1 is connected to the sewage outlet of the circulating water system 8, the nanofiltration concentrate outlet of the nanofiltration unit 4 and / or the reverse osmosis produced water outlet of the reverse osmosis unit 5 are connected to the circulating water system 8, for feeding the sewage from the circulating water system 8 and performing filtration treatment, ultrafiltration treatment, special nanofiltration treatment, nanofiltration treatment and reverse osmosis treatment on it in sequence, and returning the nanofiltration concentrate discharged from the nanofiltration unit 4 and / or the reverse osmosis produced water obtained by the reverse osmosis unit 5 to the circulating water system 8.

[0078] Those skilled in the art will appreciate that the filtering device used in the filtering unit 1 is a commonly used filtering device in the art. In one embodiment, the filtering device used in the filtering unit 1 is a self-cleaning filtering device.

[0079] In one embodiment, the system further comprises a sodium hypochlorite generating unit 6, and a water inlet thereof is connected to the reverse osmosis concentrated water outlet of the reverse osmosis unit 5, for performing an electrochemical reaction of NaCl and H2O on the reverse osmosis concentrated water from the reverse osmosis unit 5 to generate a sodium hypochlorite solution.

[0080] The sodium hypochlorite generating unit 6 is carried out using a sodium hypochlorite generator.

[0081] In one embodiment, the system further includes a bactericide pipeline, the feed inlet of the bactericide pipeline is connected to the sodium hypochlorite solution outlet of the sodium hypochlorite generating unit 6, and the discharge port is connected to the circulating water system 8, for returning the sodium hypochlorite solution from the sodium hypochlorite generating unit 6 to the circulating water system 8 as a bactericide.

[0082] In one embodiment, the nanofiltration unit 4 includes a primary nanofiltration device 41 and a secondary nanofiltration device 42 connected in sequence, and the primary nanofiltration concentrate outlet of the primary nanofiltration device 41 and / or the secondary nanofiltration concentrate outlet of the secondary nanofiltration device 42 are connected to the circulating water system 8, and the secondary nanofiltration product water outlet of the secondary nanofiltration device 42 is connected to the reverse osmosis unit 5, which is used to perform two-stage nanofiltration treatment on the special nanofiltration product water from the special nanofiltration unit, and return the obtained primary nanofiltration concentrate and / or secondary nanofiltration concentrate to the circulating water system 8, and send the obtained secondary nanofiltration product to the reverse osmosis unit 5.

[0083] In one embodiment, the reverse osmosis unit 5 includes a primary reverse osmosis device 51 and a secondary reverse osmosis device 52 connected in sequence, and the primary reverse osmosis product water outlet of the primary reverse osmosis device 51 is connected to the circulating water system 8, and the secondary reverse osmosis concentrated water outlet of the secondary reverse osmosis device 52 is connected to a discharge pipe, which is used to perform two-stage reverse osmosis treatment on the nanofiltration product water from the nanofiltration unit, and return the obtained primary reverse osmosis product water to the circulating water system 8, and discharge the secondary reverse osmosis concentrated water of the secondary reverse osmosis device 52;

[0084] Preferably, the secondary reverse osmosis water outlet of the secondary reverse osmosis device 52 is connected to the inlet of the primary reverse osmosis device 51, so as to return the secondary reverse osmosis water of the secondary reverse osmosis device 52 to the primary reverse osmosis device 51 for circulation treatment;

[0085] Preferably, the secondary reverse osmosis concentrated water outlet of the secondary reverse osmosis device 52 is connected to the sodium hypochlorite generating unit 6 for performing an electrochemical reaction of NaCl and H2O on the secondary reverse osmosis concentrated water from the secondary reverse osmosis device 52 to generate a sodium hypochlorite solution.

[0086] Use Figure 1 The system shown treats the wastewater from the circulating water system, and its process includes:

[0087] (1) The wastewater from the circulating water system 8 is sent to the filtration unit 1 for filtration to remove suspended matter therein, discharge the first concentrated water, and obtain the first produced water;

[0088] (2) sending the filtrate obtained in step (1) to ultrafiltration unit 2 for ultrafiltration treatment to remove organic matter and particulate matter therein, discharging ultrafiltration concentrated water and obtaining ultrafiltration product water;

[0089] (3) sending the ultrafiltration product water obtained in step (2) to the special nanofiltration unit 3 for special nanofiltration treatment to remove COD pollutants therein, discharging the special nanofiltration concentrated water, and obtaining special nanofiltration product water; wherein the nanofiltration membrane used for the special nanofiltration treatment is a polyamide nanofiltration membrane;

[0090] (4) sending the special nanofiltration product water obtained in step (3) to the nanofiltration unit 4 for nanofiltration treatment to separate the salt, separate the sulfate ions and chloride ions therein, discharge the nanofiltration concentrated water with sodium sulfate as the main solute, and obtain the nanofiltration product water with sodium chloride as the main solute;

[0091] Further, the special nanofiltration product water obtained in step (3) is first sent to the first-level nanofiltration device 41 for first-level nanofiltration treatment, and the first-level nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the first-level nanofiltration product water with sodium chloride as the main solute is obtained; then the first-level nanofiltration product water is sent to the second-level nanofiltration device 42 for second-level nanofiltration treatment, and the second-level nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the second-level nanofiltration product water with sodium chloride as the main solute is obtained as the nanofiltration product water; and the first-level nanofiltration concentrated water and / or the second-level nanofiltration concentrated water are returned to the circulating water system as nanofiltration concentrated water;

[0092] (5) sending the nanofiltration product water obtained in step (4) to the reverse osmosis unit 5 for reverse osmosis treatment to desalinate, discharging the reverse osmosis concentrated water, and obtaining reverse osmosis product water; wherein,

[0093] Further, the nanofiltration product water obtained in step (4) is first sent to the primary reverse osmosis device 51 for primary reverse osmosis treatment, the primary reverse osmosis concentrated water is discharged, and the primary reverse osmosis product water is obtained as the reverse osmosis product water; then the primary reverse osmosis concentrated water is sent to the secondary reverse osmosis device 52 for secondary reverse osmosis treatment, the secondary reverse osmosis concentrated water is discharged as the reverse osmosis concentrated water, and the secondary reverse osmosis product water is obtained; and the primary reverse osmosis product water is returned to the circulating water system as the reverse osmosis product water, and the secondary reverse osmosis product water is returned to the primary reverse osmosis device 51 for circulation treatment;

[0094] (6) sending at least part of the reverse osmosis concentrated water obtained in step (5) to a sodium hypochlorite generating unit 6 for electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution, and discharging the remaining reverse osmosis concentrated water to a sewage treatment plant;

[0095] Furthermore, the secondary reverse osmosis concentrated water obtained in step (5) is sent to the sodium hypochlorite generating unit 6 for electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution.

[0096] The recovery rate of the present invention refers to the recovery rate of water.

[0097] The method for treating the wastewater of a circulating water system of the present invention comprises the following steps: filtering the wastewater of the circulating water system in sequence, performing ultrafiltration, special nanofiltration and nanofiltration, returning the nanofiltration concentrated water to the circulating water system for use, performing reverse osmosis and electrochemical reaction on the nanofiltration produced water in sequence to produce sodium hypochlorite, and returning the produced sodium hypochlorite solution to the circulating water system as a bactericide; and adjusting the amount of electrochemical reaction of the reverse osmosis concentrated water according to the demand for bactericides in the circulating water system, thereby adjusting the discharge amount of the reverse osmosis concentrated water, and discharging the remaining small amount of the reverse osmosis concentrated water to a sewage field for treatment; the method of the present invention can partially recycle the wastewater of the circulating water system and reduce the discharge amount; the method for treating the wastewater of the circulating water system of the present invention intercepts suspended matter and organic matter through special nanofiltration treatment, and separates sulfuric acid therein through nanofiltration treatment. Root ions and chloride ions, so that the solute of the obtained nanofiltration concentrated water is mainly sodium sulfate, and the obtained nanofiltration concentrated water contains beneficial components such as alkalinity, hardness, zinc ions, etc., which are returned to the circulating water system for continued use, which helps to reduce or avoid additional supplementation of alkalinity and hardness agents and reduce operating costs; the obtained nanofiltration produced water contains chloride ions and sodium ions, and the reverse osmosis concentrated water obtained by reverse osmosis desalination has a high sodium chloride content. The reverse osmosis concentrated water undergoes an electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution, which is an oxidizing bactericide and can be used as a bactericide back in the circulating water system for repeated use; the method for treating wastewater from a circulating water system of the present invention can effectively reduce the output of circulating water wastewater, reasonably recover beneficial components, ensure the stable operation of the circulating water system, reduce the discharge of sewage, and reduce the cost of sewage disposal.

[0098] Raw materials used in the following examples / comparative examples:

[0099] Unless otherwise specified, the raw materials and reagents used in the present invention were purchased from commercial sources and used directly without treatment.

[0100] In the embodiment of the present invention, the wastewater of the circulating water system is the backwash water of the circulating water bypass filter, and the water volume is 100m 3 / h; indicators include: turbidity is 30NTU, COD is 50mg / l, salt content is 1500mg / l, chloride is 800mg / l, and sulfate is 600mg / l.

[0101] Example 1 (S1)

[0102] Use Figure 1 The system shown treats the wastewater from the circulating water system, and the specific methods include:

[0103] (1) The wastewater from the circulating water system 8 is sent to the filter unit 1 for filtration through a self-cleaning filter to remove suspended solids, discharge the first concentrated water, and obtain the first produced water; wherein,

[0104] The operating pressure difference of filter unit 1 is 0.06MPa, and automatic backwashing is performed after overpressure;

[0105] The turbidity of the first produced water obtained was 1 NTU;

[0106] (2) sending the filtrate obtained in step (1) to ultrafiltration unit 2 for ultrafiltration treatment to remove organic matter and particulate matter therein, discharging ultrafiltration concentrated water, and obtaining ultrafiltration product water; wherein,

[0107] The pore size of the ultrafiltration unit 2 is 0.015 mm;

[0108] The COD of the ultrafiltration water obtained was 156 mg / l and the salt content was 1500 mg / l;

[0109] (3) sending the ultrafiltration product water obtained in step (2) to the special nanofiltration unit 3 for special nanofiltration treatment to remove COD pollutants therein, discharging the special nanofiltration concentrated water, and obtaining special nanofiltration product water; wherein,

[0110] The nanofiltration membrane used in special nanofiltration treatment is a polyamide nanofiltration membrane;

[0111] The operating pressure is 0.7MPa, the operating pH is 7.5, and the membrane flux is 28LMH;

[0112] The obtained special nanofiltration concentrated water has a COD of 320 mg / l, a salt content of 300 mg / l, a chloride content of 160 mg / l, and a sulfate content of 120 mg / l;

[0113] The obtained special nanofiltration produced water has a COD of 20 mg / l, a salt content of 1633 mg / l, a chloride of 871 mg / l, a sulfate of 653 mg / l, and a turbidity of 4 NTU;

[0114] The recovery rate of the special nanofiltration unit 3 (i.e., special nanofiltration produced water / special nanofiltration influent) is 95%, and the other 5% (i.e., special nanofiltration concentrated water) is discharged through sewage treatment;

[0115] The total water recovery rate of steps (1) to (3) is 90%, and the other 10% (including the intercepted sewage of the filtration unit 1 in step (1), the intercepted sewage of the ultrafiltration unit 2 in step (2), and the special nanofiltration concentrated water of the special nanofiltration unit 3 in step (3)) is discharged through sewage treatment and sent to the biochemical system for treatment, that is, a total of 10m3 / h sewage is discharged and sent to the biochemical system for treatment, and the remaining 90m 3 / h enters the nanofiltration unit 4 for treatment in the form of special nanofiltration produced water;

[0116] (4) The special nanofiltration product water obtained in step (3) is sent to the nanofiltration unit 4 and sequentially passed through the primary nanofiltration device 41 and the secondary nanofiltration device 42 for two-stage nanofiltration treatment to separate the salt, and the sulfate ions and chloride ions therein are separated. The primary nanofiltration product water obtained is sent to the secondary nanofiltration device 42, and the primary nanofiltration concentrated water and the secondary nanofiltration concentrated water with the solute mainly composed of sodium sulfate are discharged as the nanofiltration concentrated water and returned to the circulating water system, and the secondary nanofiltration product water with the solute mainly composed of sodium chloride is obtained as the nanofiltration product water; wherein,

[0117] The membrane flux of nanofiltration unit 4 is 22LMH, the operating pressure is 1.7MPa, and the operating pH range is 7.6;

[0118] The obtained nanofiltration concentrate (i.e., mixed water of primary nanofiltration concentrate and secondary nanofiltration concentrate) had a COD of 45 mg / l, a salt content of 2577 mg / l, a chloride content of 17 mg / l, and a sulfate content of 1529 mg / l;

[0119] The COD of the nanofiltration product water obtained was 2 mg / l, the salt content was 943 mg / l, the chloride was 1495 mg / l, and the sulfate was 13 mg / l;

[0120] The recovery rate of nanofiltration unit 4 (i.e., nanofiltration produced water / nanofiltration influent water) was 58%;

[0121] The amount of nanofiltration water produced is 52m 3 / h;

[0122] (5) sending the nanofiltration product water obtained in step (4) to the reverse osmosis unit 5 and sequentially passing through the primary reverse osmosis device 51 and the secondary reverse osmosis device 52 for two-stage reverse osmosis treatment to desalinate, sending the primary reverse osmosis concentrated water to the secondary reverse osmosis device 52, outputting the primary reverse osmosis product water as reverse osmosis product water and returning it to the circulating water system, outputting the secondary reverse osmosis product water and returning it to the primary reverse osmosis device 51 for circulation treatment, and discharging the secondary reverse osmosis concentrated water as reverse osmosis concentrated water; wherein,

[0123] The membrane pore size of the reverse osmosis unit 5 is 0.15 nm;

[0124] The water return rate is 60%;

[0125] The amount of reverse osmosis water produced is 31.2m 3 / h;

[0126] The amount of reverse osmosis concentrated water obtained is 20.8m 3 / h, concentration is 7.5%;

[0127] (6) After calculation, 20.8 m3 of the reverse osmosis concentrated water obtained in step (5) 3 / h is sent to the sodium hypochlorite generating unit 6 for electrochemical reaction between NaCl and H2O in the sodium hypochlorite generator to generate a sodium hypochlorite solution with a concentration of 0.72, wherein the conditions of the electrochemical reaction include a current of 60A and a voltage of 300V, and the obtained sodium hypochlorite solution is returned to the circulating water system as a bactericide, that is, all the reverse osmosis concentrated water is reused without sewage discharge.

[0128] According to the relevant data of Example 1, the original 100m 3 / h of sewage from the circulating water system 8. After being treated by the present invention, the overall sewage discharge is only 10m 3 / h, and the rest are all reused, reducing the discharge volume by 90%, effectively reducing the subsequent sewage treatment volume and sewage treatment difficulty, and reducing the sewage treatment cost; and all divalent salts are recovered to supplement the system's alkalinity, hardness and other indicators, and part of the monovalent salt is recovered to ensure the stable operation of the circulating water system.

Claims

1. A method for treating wastewater from a circulating water system, characterized in that: The method comprises: (1) Filtering the wastewater from the circulating water system to remove suspended solids, discharging the first concentrated water and obtaining the first produced water; (2) subjecting the filtrate obtained in step (1) to ultrafiltration to remove organic matter and particulate matter therein, discharging ultrafiltration concentrated water, and obtaining ultrafiltration product water; (3) performing special nanofiltration treatment on the ultrafiltration product water obtained in step (2) to remove COD pollutants therein, discharging special nanofiltration concentrated water, and obtaining special nanofiltration product water; wherein the nanofiltration membrane used for the special nanofiltration treatment is a polyamide nanofiltration membrane; (4) subjecting the special nanofiltration produced water obtained in step (3) to nanofiltration treatment to separate the salt, separate the sulfate ions and chloride ions therein, discharge the nanofiltration concentrated water whose solute is mainly sodium sulfate, and obtain the nanofiltration produced water whose solute is mainly sodium chloride; (5) performing reverse osmosis treatment on the nanofiltration product water obtained in step (4) to desalinate, discharge the reverse osmosis concentrated water, and obtain reverse osmosis product water; wherein, The nanofiltration concentrated water obtained in step (4) and / or the reverse osmosis produced water obtained in step (5) are returned to the circulating water system.

2. The method according to claim 1, characterized in that The method further comprises step (6), subjecting at least part of the reverse osmosis concentrated water obtained in step (5) to an electrochemical reaction of NaCl and H2O to generate a sodium hypochlorite solution; Preferably, the sodium hypochlorite solution obtained in step (6) is returned to the circulating water system as a bactericide; and / or, The concentration of the sodium hypochlorite solution obtained in step (6) is 0.5-0.8 wt %; and / or, In step (6), the conditions for the electrochemical reaction include: a current of 50 to 70 A, and / or a voltage of 220 to 380 V.

3. The method according to claim 1 or 2, characterized in that: In step (4), the nanofiltration treatment includes a primary nanofiltration treatment and a secondary nanofiltration treatment; In step (4), the special nanofiltration product water obtained in step (3) is first subjected to a primary nanofiltration treatment, and the primary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the primary nanofiltration product water with sodium chloride as the main solute is obtained; then the primary nanofiltration product water is subjected to a secondary nanofiltration treatment, and the secondary nanofiltration concentrated water with sodium sulfate as the main solute is discharged, and the secondary nanofiltration product water with sodium chloride as the main solute is obtained as the nanofiltration product water; The primary nanofiltration concentrate and / or the secondary nanofiltration concentrate are returned to the circulating water system.

4. The method according to any one of claims 1 to 3, characterized in that In step (5), the reverse osmosis treatment includes a primary reverse osmosis treatment and a secondary reverse osmosis treatment; In step (5), the nanofiltration product water obtained in step (4) is first subjected to a primary reverse osmosis treatment, and the primary reverse osmosis concentrated water is discharged to obtain the primary reverse osmosis product water as the reverse osmosis product water; then the primary reverse osmosis concentrated water is subjected to a secondary reverse osmosis treatment, and the secondary reverse osmosis concentrated water is discharged as the reverse osmosis concentrated water to obtain the secondary reverse osmosis product water; The primary reverse osmosis water is returned to the circulating water system as reverse osmosis water; Preferably, the secondary reverse osmosis produced water is returned to the primary reverse osmosis treatment.

5. The method according to any one of claims 1 to 4, characterized in that In step (1), the operating pressure difference of the filtration device is 0.05-0.1 MPa, and / or the inlet turbidity is ≤30 NTU, and / or the outlet turbidity is ≤2 NTU, and / or the operating backwash pressure difference is ≤0.05 MPa, and / or the filter pore size is 80-100 μm.

6. The method according to any one of claims 1 to 5, characterized in that In step (2), the pore size of the ultrafiltration device is 0.005-0.1 mm.

7. The method according to any one of claims 1 to 6, characterized in that In step (3), the influent COD of the special nanofiltration device is less than 300 mg / l, and / or the salt content is greater than 1000 mg / l, and / or the membrane flux is 10 to 30 LMH, and / or the operating pressure is 0.7 to 2.0 MPa, and / or the operating pH range is 2 to 12, and / or the influent turbidity is less than 3 NTU.

8. The method according to any one of claims 1 to 7, characterized in that In step (4), the membrane flux of the nanofiltration device is 15-25LMH, and / or the operating pressure is 1.5-3.0MPa, and / or the operating pH range is 2-12, and / or the inlet turbidity is <5NTU.

9. The method according to any one of claims 1 to 8, characterized in that In step (5), the pore size of the membrane of the reverse osmosis device is 0.1 to 10 nm.

10. A system for use in the method according to any one of claims 1 to 9.

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