Reclaimed water reuse system, backwashing control method and interlocked backwashing control method

Abstract

The invention relates to a reclaimed water recycling system, a backwashing control method and an interlocking backwashing control method. The reclaimed water reuse system comprises: a discharge treatment subsystem, which is used for treating paper mill sewage into wastewater meeting the discharge standard; the recycling treatment subsystem is arranged at the downstream of the discharging treatment subsystem, the recycling treatment subsystem comprises a fine filtering part section, and the fine filtering part section is used for filtering impurities exceeding a first preset size in the wastewater; and the water supply treatment subsystem selectively connects and disconnects the fine filtering part section and / or the clear water supply part through a valve at the downstream, the water supply treatment subsystem comprises a booster pump, and the booster pump is used for outputting treated waste water and / or clear water with preset pressure to the downstream paper mill paper machine shaft seal water system.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of reclaimed water reuse systems, for treating paper mill sewage, can realize the reuse of paper mill sewage station discharge wastewater after treatment, realize the reuse of reclaimed water after treatment, both save the consumption of clear water while also reduce wastewater discharge. BACKGROUND

[0002] Paper mill will produce a large amount of sewage during normal production operation, and the treatment of paper mill sewage is a complex process involving multiple steps, mainly including pretreatment, primary treatment, secondary treatment and advanced treatment stages.

[0003] To reduce wastewater discharge, many enterprises currently invest heavily in advanced treatment, such as membrane treatment technology, and the treated reclaimed water is reused, which saves the consumption of clear water and reduces wastewater discharge.

[0004] If the wastewater treated by the sewage treatment plant is to be reused, due to the high salt content of the wastewater, the discharge contains organic pollutants and refractory organic matter, as well as nitrogen and phosphorus nutrients, and also contains activated sludge and microorganisms, the effluent must be subjected to advanced treatment and disinfection to ensure that the water quality meets the standards; In addition, the water quality of the reclaimed water needs to be regularly detected to ensure that it meets the relevant standards; In addition, monitoring and maintenance are required, and a complete monitoring system needs to be established to monitor the operating status of the reclaimed water treatment equipment in real time, and timely maintenance and maintenance are required to ensure normal operation of the equipment.

[0005] The current advanced treatment generally has large investment costs and complex systems. For example, the membranes used in membrane treatment technology are easily clogged and contaminated by pollutants, and it is difficult to restore the membrane flux through conventional backwashing, and the service life of the membranes is short and the operation and maintenance costs are high.

[0006] There are many places in the paper machine industry where clear water is used, but the requirements for clear water vary. Although the wastewater is treated to a high degree, it can have a wider range of applications, but the cost is high and the time is long. For some places where the requirement for clear water is not high, a simple and fast method is needed to treat wastewater and realize the reuse of reclaimed water.

[0007] Based on the above reasons, the above-mentioned reclaimed water reuse treatment technology is limited in the advanced treatment and reuse of wastewater in the paper industry. SUMMARY

[0008] To achieve one or more of the above-mentioned purposes of the present application, the present application provides a reclaimed water reuse system for treating paper mill sewage.

[0009] In the first example of the reclaimed water reuse system, the reclaimed water reuse system comprises: a discharge treatment subsystem for treating the paper mill wastewater to meet the discharge standard; a reuse treatment subsystem arranged downstream of the discharge treatment subsystem, the reuse treatment subsystem comprising a fine filtration section for filtering the wastewater to remove the impurities larger than a first preset size; and a service water treatment subsystem selectively connected and disconnected to the fine filtration section and / or a clean water supply section downstream through a valve, the service water treatment subsystem comprising a booster pump for outputting the treated wastewater and / or clean water at a predetermined pressure to the paper machine shaft seal water system of the paper mill downstream.

[0010] According to the above configuration, the water treated by the self-cleaning filter has a filtration accuracy of 100 μm (the first preset size), which meets the use requirements of the shaft seal water of the paper machine of the paper mill.

[0011] In the second example of the reclaimed water reuse system, optionally comprising the first example, the fine filtration section of the reuse treatment subsystem comprises four fine filters connected in parallel.

[0012] According to the above configuration, the filtration units of the reuse treatment subsystem can be maintained offline one by one without interrupting the filtration.

[0013] In the third example of the reclaimed water reuse system, optionally comprising one or more of the above examples, the fine filtration section comprises a plurality of fine filters, and the filter core of the fine filter is a stainless steel gap type filter core for filtering the impurities larger than 100 μm in the wastewater.

[0014] According to the above configuration, the filter core is convenient to take out and clean, and when stubborn impurities are filtered and need to be cleaned manually, manual operation is facilitated, and maintenance cost is saved.

[0015] In the fourth example of the reclaimed water reuse system, optionally comprising one or more of the above examples, the fine filtration section comprises a plurality of fine filters, and further comprises a plurality of pressure transmitters corresponding to the plurality of fine filters for measuring the pressure difference between the water inlet and the water outlet of the corresponding fine filter.

[0016] According to the above configuration, the pressure difference can be used to control the valve switching for backwashing, and there is no need for a complex mechanical structure for cleaning the filter, which is very easy to maintain.

[0017] In the fifth example of the reclaimed water reuse system, optionally comprising one or more of the above examples, the reuse treatment subsystem further comprises a coarse filtration section arranged upstream of the fine filtration section, the coarse filtration section being used for coarsely screening the impurities in the wastewater, wherein the coarse filtration section is internally provided with a screen, and the screen comprises at least a 10-mesh screen.

[0018] According to the above configuration, the coarse filter section and the screen provided in the basket filter and the filter element thereof ensure the strength of the filter element and the precision of the filtration.

[0019] In the sixth example of the reclaimed water reuse system, optionally including one or more of the above examples, the reuse treatment subsystem further comprises a sterilization section, the sterilization section is arranged upstream of the fine filter section, the sterilization section comprises a container containing wastewater and a sterilizing agent put therein, and the residual chlorine in the wastewater treated by the sterilization section is maintained at 1.5-3.0 mg / l.

[0020] According to the above configuration, the residual chlorine is maintained at 1.5-3.0 mg / l, which can kill bacteria and does not affect the normal operation of the downstream machine equipment.

[0021] In the seventh example of the reclaimed water reuse system, optionally including one or more of the above examples, the wastewater after passing through the sterilization section is optionally directly supplied to the downstream power plant cooling tower water system, the power plant cooling tower water system is optionally connected and disconnected to the sterilization section and / or the second clean water supply section downstream through a valve, the reuse treatment subsystem further comprises a sand filter downstream of the sterilization section, and the wastewater is optionally passed through the sand filter before being supplied to the downstream power plant cooling tower water system.

[0022] When the normal wastewater effluent online turbidity exceeds 5 NTU, the reclaimed water is directly supplied to the power plant cooling tower. According to the above configuration, when the paper machine produces coated paper, the loss of coating causes the color and turbidity of the wastewater effluent to increase, which will cause the color and turbidity of the cooling water to increase. At this time, the sand filter of the power plant cooling tower can improve the water quality and meet the requirements.

[0023] In the eighth example of the reclaimed water reuse system, optionally including one or more of the above examples, the water supply treatment subsystem further comprises a safety filter arranged downstream of the booster pump, wherein the safety filter is used to filter impurities greater than 60 μm in the wastewater.

[0024] According to the above configuration, the safety filter at the outlet of the booster pump increases the program interlocking, and after the backwashing of the inlet self-cleaning filter, the safety filter needs to be backwashed with a time delay to prevent synchronous backwashing from causing low shaft seal water pressure and affecting the normal production of the paper machine.

[0025] The present application provides a backwashing control method for a reclaimed water reuse system. The backwashing control method comprises: judging whether the fine filter needs backwashing according to the pressure difference between the inlet and outlet of each fine filter, wherein when the pressure difference is greater than a preset threshold, the fine filter is controlled to backwash.

[0026] Based on the configuration described above, the fine filter can be automatically backwashed when it is severely clogged.

[0027] In the second example of this backwash control method, it is determined whether each fine filter needs backwashing based on a preset time. When the fine filter has not undergone backwashing after the preset time, the fine filter is controlled to perform backwashing.

[0028] Based on the above configuration, considering that the fine filter has accumulated a certain amount of dirt, in order to prevent other fine filters from becoming clogged at the same time when the fine filter becomes severely clogged, thus affecting the normal operation of the entire fine filter section, the fine filter can be backwashed even if the differential pressure threshold is not reached at a preset time.

[0029] This invention provides a method for controlling interlocked backwashing in a greywater reuse system. It prevents the security filter from backwashing simultaneously when any filter in the fine filtration section is being backwashed.

[0030] As described above, this configuration can prevent low shaft seal water pressure caused by synchronous backwashing, which would affect the normal production of the paper machine.

[0031] The greywater reuse system of this invention allows power plants and paper mills to reuse treated wastewater discharged from paper mills. No advanced treatment is required; only simple filtration is needed, eliminating the need for expensive initial investments. Furthermore, the system boasts low operating costs and is simple and convenient to operate.

[0032] Compared with the currently widely used deep treatment (membrane treatment technology), the present invention has significant advantages in both investment and operating costs, and also has outstanding water-saving effects.

[0033] Currently, this filtration technology can meet the water quality and quantity requirements of power plant cooling towers and paper mill paper machine side shaft sealing water systems. The power plant cooling tower requires 1000 m³ of water replenishment per day. 3 The greywater reuse system of this invention can achieve 700m / day in terms of paper machine shaft seal water. 3 The reuse of greywater per day largely replaces the original clean water, saving 550,000 cubic meters of clean water annually. Attached Figure Description

[0034] To describe embodiments of the above and other features of the present invention, a more detailed description of the invention will be presented with reference to exemplary embodiments of the invention shown in the accompanying drawings. It is to be understood that these drawings depict only exemplary embodiments of the invention and should not be considered as limiting its scope; the invention will be described and explained using the drawings and with the aid of additional features and details. In the drawings:

[0035] Figure 1 This is a schematic diagram of a greywater reuse system according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the fine filtration section of the reuse treatment subsystem of a greywater reuse system according to an embodiment of the present invention.

[0037] Throughout this and all subsequent content, the same features appearing in different figures are indicated by the same or similar reference numerals.

[0038] List of reference numerals in the attached diagram:

[0039] 1. Greywater Reuse System

[0040] 2. Wastewater from paper mills

[0041] 3. Paper machine shaft sealing water system in paper mills

[0042] 4.4' Clean Water Supply Department

[0043] 5. Power Plant Cooling Tower Water System

[0044] 10. Emission Treatment Subsystem

[0045] 20 Reuse Processing Subsystem

[0046] 21 Fine filtration section

[0047] 211 Inlet

[0048] 212 Inlet header

[0049] 213 Inlet branch pipe

[0050] 214 Pressure Transmitter

[0051] 215 fine filter

[0052] 216 Outlet branch pipe

[0053] 217 Outlet header

[0054] 218 Outlet

[0055] 219 Sewage outlet

[0056] 22 Coarse Filtration Section

[0057] 23 Sterilization Section

[0058] 30 Water Treatment Subsystem Detailed Implementation

[0059] First, this invention relates to greywater reuse systems related to the treatment and reuse of compliant wastewater in any industrial sector. In particular, this invention relates to the reuse of wastewater from paper mills, but is not limited to this specific industrial sector. Determining whether wastewater should be further reused is outside the scope of this invention.

[0060] The terms “including,” “having,” “comprising,” and variations thereof, as used herein, are intended as open-ended transitional phrases, terms, or words that require the presence of a specified component / step, but also allow for the presence of other components / steps.

[0061] In this invention, unless explicitly stated otherwise, the terms “first,” “second,” etc., are not intended to indicate any difference in order, position, quantity, or importance, but are merely used as labels to distinguish different positions or components, to differentiate one element, component, region, and / or location from another element, component, region, and / or location.

[0062] In this invention, the term "backwashing" refers to the action of flushing away contaminants from the filter by reversing the flow direction of the fluid flowing through the filter.

[0063] The greywater reuse system 1 of the present invention generally includes a discharge treatment subsystem 10, a reuse treatment subsystem 20, and a water supply treatment subsystem 30. In this invention, several different embodiments of the greywater reuse system 1 having the above structure will be provided.

[0064] First, refer to Figures 1 to 2 The wastewater reuse system 1 of the present invention will be illustrated herein, wherein, Figure 1 This is a schematic diagram of a greywater reuse system 1 according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the fine filtration section 21 of the reuse treatment subsystem 20 of the greywater reuse system 1.

[0065] In one embodiment of the present invention, the greywater reuse system 1 generally includes a discharge treatment subsystem 10, a reuse treatment subsystem 20, and a water supply treatment subsystem 30.

[0066] The discharge treatment subsystem 10 is used to treat the paper mill wastewater 2 into wastewater that meets relevant discharge standards. Subsequently, it can be optionally discharged directly into natural water bodies, or treated and reused by the rest of the greywater reuse system 1.

[0067] The reuse treatment subsystem 20 is located downstream of the discharge treatment subsystem 10. The reuse treatment subsystem 20 includes a fine filtration section 21, which filters impurities in the wastewater that exceed a first preset size. The first preset size can be set according to actual needs. In this embodiment, to meet the requirements of the downstream paper mill's paper machine shaft seal water system 3, the first preset size is 100 μm, meaning the treated water has a filtration precision of 100 μm, capable of removing residual algae, microorganisms, and activated sludge flocs from the wastewater, thus meeting the paper mill's requirements for shaft seal water.

[0068] The water treatment subsystem 30 can optionally connect and disconnect the fine filtration section 21 and / or the additional clean water supply section 4 of the reuse treatment subsystem 20 downstream via valves. Depending on water quality requirements and actual water quality conditions, clean water or filtered wastewater can optionally be supplied to the downstream paper mill paper machine shaft seal water system 3.

[0069] The paper mill's paper machine shaft seal water system primarily provides water for the shaft seals of all rotating machinery on the paper machine. It has high requirements for water quality, pressure, and quantity; a water shortage can cause equipment shutdowns, directly resulting in economic losses. The recycled water used in the paper machine must have guaranteed pressure and quantity. When using recycled water, if the recycled water pressure falls below the pressure required by the shaft seal water booster pump, the system will automatically switch to clean water immediately to ensure that the shaft seal water supply is not insufficient and thus does not affect paper machine production.

[0070] The water treatment subsystem 30 includes a booster pump 31, used to output treated wastewater and / or clean water at a predetermined pressure to the paper mill's paper machine shaft seal water system 3. In this embodiment, the booster pump 31 is set to a pressure of 3.0 bar. After being pumped through pipelines to the paper mill's paper machine shaft seal water system 3, the terminal pressure drops to 2.7 bar, meeting the requirements for shaft seal water. Preferably, two booster pumps are connected in parallel, allowing one to be used as a backup, ensuring normal system operation.

[0071] When a paper machine produces coated paper, the wastewater may contain latex or powdered activated carbon may be added in an emergency. In this case, the quality of the effluent is poor, and the online turbidity of the effluent may rise to 10 NTU. The fine filter 215, which is a self-cleaning filter, will backwash frequently according to the pressure difference (which will be described in detail below). If backwashing is not possible, the control system will automatically switch to clean water supply, or you can manually switch to clean water supply.

[0072] Preferably, a pressure transmitter can be installed on the valve on the pipeline from the clean water supply section 4 to the booster pump 41, and the pressure can be set to 2.0 bar. For example, when the pressure is lower than 2.0 bar, the automatic valve for clean water supply will open automatically after a delay of 5-10 seconds, while the water supply valve from the fine filtration section 21 of the reuse treatment subsystem 20 to the booster pump 41 will be closed.

[0073] Under normal circumstances, when using recycled water, the valve from the clean water supply unit 4 to the booster pump 41 is in the closed state in automatic mode. Only when the recycled water pressure is low or the water quality is poor and cannot meet the water pressure and water quality requirements of the shaft seal water will it be manually or automatically switched to the clean water supply unit 4 to ensure that the water pressure, water quality and water quantity of the shaft seal water meet the requirements of the shaft seal water.

[0074] The fine filtration section 21 includes a self-cleaning fine filter 215, which will be described in detail below. Figure 2 As shown, in the wastewater filtration mode of the fine filtration section 21, wastewater from upstream enters the inlet 211 of the fine filtration section 21 and flows through the inlet main pipe 212, the corresponding inlet branch pipe 213, the corresponding fine filter 215, the corresponding outlet branch pipe 216, the outlet main pipe 217 and the outlet 218, and is supplied to the downstream water supply treatment subsystem 30.

[0075] The fine filtration section 21 of the wastewater treatment subsystem 20 includes multiple fine filters 215 connected in parallel. In this embodiment, the fine filtration section 21 includes four fine filters 215. These multiple fine filters serve as backups for the entire system, minimizing the risk of downtime. Each fine filter can be maintained offline individually without interrupting wastewater filtration.

[0076] Preferably, the filter element of the fine filter 215 in the fine filtration section 21 is a stainless steel slit filter element, thus it is a self-cleaning filter with a filtration accuracy of 100μm. The stainless steel slit filter element is easy to remove and clean, facilitating manual operation and saving maintenance costs when filtering stubborn impurities and requiring regular manual cleaning.

[0077] When the fine filter 215 needs backwashing, it can be switched to backwash mode by closing the valve of the corresponding inlet branch pipe 213 and opening the valve of the corresponding drain pipe leading to the drain outlet 219. Switching between filtration and backwashing modes by opening and closing the corresponding valves involves no complex mechanical structure, ensuring high reliability and easy maintenance.

[0078] Preferably, the fine filtration section 21 further includes a plurality of pressure transmitters P corresponding to the plurality of fine filters 215, for measuring the pressure difference between the inlet and outlet of the corresponding fine filter 215. Preferably, the pressure transmitters P can be installed on the inlet branch pipe of the corresponding fine filter 215. In this example, the pressure transmitters P can be installed on the valve of the corresponding inlet branch pipe.

[0079] Preferably, this application also includes a backwash control method for a greywater reuse system for the fine filtration section 21, which can determine whether each fine filter needs backwashing and control the fine filters to perform backwashing. In this example, the backwash controller can be integrated into the control system and prompted to the operator via the control panel.

[0080] Preferably, the backwash control method determines whether the fine filter 215 needs backwashing based on the pressure difference between the inlet and outlet of the fine filter 215. For example, when the pressure difference is greater than a preset threshold, it indicates that the fine filter 215 is severely clogged, and the fine filter can be automatically controlled to backwash, and the operator can be prompted to manually perform backwashing.

[0081] Preferably, the backwash control method also determines whether the fine filter 215 needs backwashing based on a preset time. When a fine filter 215 has not undergone backwashing after a preset time, it indicates that the fine filter 215 has accumulated a certain amount of dirt. In order to prevent other fine filters 215 from becoming clogged at the same time when the fine filter 215 becomes severely clogged, thus affecting the normal operation of the fine filtration section 21 as a whole, the fine filter 215 can be backwashed even if the differential pressure threshold is not reached after a preset time.

[0082] In one embodiment of the invention, now reversed Figure 1 The reuse treatment subsystem 20 also includes a coarse filtration section 22, which is located upstream of the fine filtration section 21. The coarse filtration section 22 is used to coarsely screen impurities in the wastewater and to preliminarily remove large mechanical impurities, including moss, biofilm, algae, algal blooms, mosquitoes, red worms, and silt.

[0083] Preferably, the coarse filtration section 22 has an internal screen, which includes a screen with at least 10 mesh. In this embodiment, the screen is a 20-mesh steel wire screen with a filtration accuracy of approximately 770 μm, or it can be a 40-mesh screen with a filtration accuracy of approximately 425 μm. The steel wire screen is easy to clean, ensuring the water flow from the greywater to the greywater tank and not affecting the water supply capacity to the greywater tank.

[0084] In this embodiment, the coarse filtration section 22 adopts a basket-type filter, with the filter element housed in the basket for easy and quick disassembly by the operator. Cleaning can typically be completed independently within 30 minutes. The filter is periodically cleaned and inspected, with a bypass pipe used to ensure uninterrupted operation of the greywater supply system during cleaning. The filter element is lined with a steel wire mesh to ensure both the strength of the filter element and the accuracy of filtration.

[0085] In one embodiment of the invention, the reuse treatment subsystem 20 further includes a sterilization section 23, which is located upstream of the fine filtration section 21. Since the proliferation of bacteria and microorganisms produces biological sludge, which can easily cause microbial corrosion and sediment corrosion in the wastewater reuse process system, it is necessary to control bacteria and microorganisms.

[0086] The sterilization section 23 may include a container for containing wastewater and a sterilizing agent added therein. The residual chlorine in the wastewater treated by the sterilization section 23 is maintained at 1.5 mg / L-3.0 mg / L, which can kill microorganisms and bacteria without affecting the normal operation of downstream machinery and equipment.

[0087] In one embodiment of the invention, the reuse treatment subsystem 20 further includes a sand filter 24 downstream of the sterilization section 23, and the wastewater optionally passes through the sand filter 24 after passing through the sterilization section 23 and before being supplied to the downstream power plant cooling tower water system 5.

[0088] Preferably, the sand particle size in the sand filter can be 0.5-1.2mm, and / or the filtration accuracy is approximately 30µm. Because air-cooled cooling towers introduce a lot of dust and power plant fly ash into the air, considering operating costs and actual water quality requirements, 1-2% of the circulating water volume is filtered through a sand filter.

[0089] The power plant cooling tower water system 5 can optionally connect and disconnect the sterilization section 23 and / or the second clean water supply section 4' downstream via valves. Depending on water quality requirements and actual water quality conditions, clean water or filtered wastewater can optionally be supplied to the downstream power plant cooling tower water system 5.

[0090] In this embodiment, the operator sets the reclaimed water replenishment flow rate, which is normally 42 m³ / h. The pneumatic valve adjusts its opening according to the replenishment flow rate. The cooling tower's original replenishment water, clean water, automatically adjusts its opening to replenish the water. The normal cooling tower water level is controlled at 1.1 meters. Clean water replenishment is automatically adjusted according to the liquid level via PID control. When the paper machine produces coated paper, coating loss causes an increase in the color and turbidity of the wastewater effluent. When the online turbidity of the wastewater effluent exceeds 5 NTU, directly replenishing the power plant cooling tower with reclaimed water will cause an increase in the color and turbidity of the cooling water. Reclaimed water can be filtered first using the cooling tower sand filter 24 before being replenished to the power plant cooling tower. This will improve the water quality of the power plant cooling water and will not negatively affect the power plant heat exchanger.

[0091] In one embodiment of the present invention, the water treatment subsystem 30 further includes a security filter 32, which is disposed downstream of the booster pump 31, wherein the security filter 32 is used to filter impurities larger than 60 μm in the wastewater.

[0092] Preferably, the water treatment subsystem 30 includes two security filters 32 connected in parallel. In this example, the filter element of the security filter 32 is a PP filter bag, and the filtration accuracy is 60μm, further ensuring the removal of impurities. This security filter is a self-cleaning filter, which is backwashed manually based on the pressure difference between the inlet and outlet of the security filter 32, currently being cleaned every two days.

[0093] Preferably, this application also includes an interlocking backwash control method for a greywater reuse system for the water treatment subsystem 30, which can determine whether each security filter 32 needs backwashing and control the security filter 32 to perform backwashing. In this example, the interlocking backwash controller can be integrated into the control system and prompted to the operator via the control panel.

[0094] Preferably, in this interlocking backwash control method, when any filter in the fine filtration section 21 is backwashed, it is determined that the security filter 32 cannot be backwashed, and the backwashing of the security filter 32 is delayed. This interlocking backwash control method can prevent the security filter 32 and any filter in the fine filtration section 21 from being backwashed simultaneously, which can prevent low shaft seal water pressure caused by synchronous backwashing and avoid affecting the normal production of the paper machine.

[0095] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention have been clearly and completely described above in conjunction with the specific embodiments and accompanying drawings.

[0096] Although various embodiments have been described above, it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of them, and are presented by way of example rather than limitation. It will be apparent to those skilled in the art that the disclosed subject matter may be implemented in other specific forms without departing from its spirit and essential characteristics.

Claims

1. A greywater reuse system for treating wastewater (2) from a paper mill, the greywater reuse system (1) comprising: The discharge treatment subsystem (10) is used to treat the paper mill wastewater (2) into wastewater that meets the discharge standards; A reuse treatment subsystem (20) is located downstream of the discharge treatment subsystem (10). The reuse treatment subsystem (20) includes a fine filtration section (21) for filtering impurities in the wastewater that exceed a first preset size. as well as A water treatment subsystem (30) is provided downstream, which selectively connects and disconnects the fine filtration section (21) and / or the clean water supply section (4) via valves. The water treatment subsystem (30) includes a booster pump (31) for outputting treated wastewater and / or clean water at a predetermined pressure to the downstream paper mill paper machine shaft seal water system (3).

2. The greywater reuse system according to claim 1, characterized in that, The fine filtration section (21) of the reuse processing subsystem (20) includes four fine filters connected in parallel.

3. The greywater reuse system according to claim 1, characterized in that, The fine filtration section (21) includes multiple fine filters, the filter element of which is a stainless steel slit filter element, used to filter impurities larger than 100μm in wastewater.

4. The greywater reuse system according to claim 1, characterized in that, The fine filtration section (21) includes multiple fine filters and multiple pressure transmitters (P) corresponding to the multiple fine filters, used to measure the pressure difference between the inlet and outlet of the corresponding fine filter.

5. The greywater reuse system according to claim 1, characterized in that, The reuse treatment subsystem (20) further includes a coarse filtration section (22), which is located upstream of the fine filtration section (21). The coarse filtration section (22) is used to coarsely screen impurities in the wastewater. The coarse filtration section (22) has a screen inside, which includes a screen with a mesh size of at least 10 mesh.

6. The greywater reuse system according to claim 1, characterized in that, The reuse treatment subsystem (20) further includes a sterilization section (23), which is located upstream of the fine filtration section (21). The sterilization section (23) includes a container for containing wastewater and a sterilizing agent added therein, and the residual chlorine in the wastewater treated by the sterilization section (23) is maintained at 1.5 mg / l-3.0 mg / l.

7. The greywater reuse system according to claim 6, characterized in that, After passing through the sterilization section (23), the wastewater may optionally be directly supplied to the downstream power plant cooling tower water system (5), which may optionally connect and disconnect the sterilization section (23) and / or the second clean water supply section (4') downstream via a valve. The reuse treatment subsystem (20) further includes a sand filter (24) downstream of the sterilization section (23), and the wastewater may optionally pass through the sand filter (24) before being supplied to the downstream power plant cooling tower water system (5).

8. The greywater reuse system according to claim 1, characterized in that, The water treatment subsystem (30) also includes a security filter (32) located downstream of the booster pump (31), wherein the security filter (32) is used to filter impurities larger than 60 μm in the wastewater.

9. A backwashing control method for a greywater reuse system, wherein the greywater reuse system is the greywater reuse system (1) according to claim 4, characterized in that, The backwash control method includes: The need for backwashing of each fine filter is determined based on the pressure difference between its inlet and outlet. When the pressure difference exceeds a preset threshold, the fine filter is controlled to perform backwashing.

10. The backwash control method according to claim 9, characterized in that, The backwash control method further includes: The system determines whether each fine filter needs backwashing based on a preset time, wherein if the fine filter has not undergone backwashing after the preset time, the system controls the fine filter to undergo backwashing.

11. A method for interlocking backwash control in a greywater reuse system, wherein the greywater reuse system is the greywater reuse system (1) according to claim 8, characterized in that, The chain backwash control method includes: When any filter in the fine filtration section (21) is backwashed, the security filter (32) is prevented from being backwashed at the same time.

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