Backwashing multi-stage water treatment filtering and purifying method and system

Abstract

The invention provides a backwashing multi-stage water treatment filtering and purifying method and system, the method is used for filtering industrial sewage and then recollecting and reusing, and the method comprises the following steps: discharging gas in a filtering tank out of the tank and then closing an exhaust port; sewage to be filtered enters from the water inlet, is filtered by the multi-layer medium filtering layer and is discharged from the water outlet; various parameters in filtering are monitored, and under the condition that the remote control single chip microcomputer controls the pressure difference of each filtering tank to be within a pressure difference threshold value, it is guaranteed that filtered water discharged from a water outlet meets the turbidity requirement in the drainage standard; when the pressure difference in a certain filtering tank exceeds a pressure difference threshold value, backwashing the corresponding filtering tank; and after the back washing is finished, the forward filtering step is repeated again. The optimal flow velocity of the water inlet and the optimal flow velocity of the water outlet are obtained through learning optimization, and then it is guaranteed that sewage at the water outlet meets the turbidity requirement in the drainage standard. Meanwhile, when the pressure difference in a certain filtering tank exceeds a pressure difference threshold value, the filtering tank can be backwashed.

Description

Technical Field

[0001] The invention belongs to the technical field of intelligent filtration for sewage treatment, and in particular relates to a multi-stage water treatment filtration purification method and system capable of backwashing. Background Art

[0002] With the rapid development of cities, the amount of sewage discharged continues to increase, the overall water environment quality is not optimistic, and the pressure of reducing water pollutants is increasing. According to national requirements, it is necessary to increase the amount of urban sewage treatment and discharge standards to reduce pollutant emissions, thereby further improving the water environment. With the improvement of the quality of life, people's awareness of environmental protection and automation of sewage treatment plants has also begun to increase. For sewage treatment plants, it is not only required to ensure the quality of the water leaving the factory, but also to achieve unmanned operation of the entire plant, reduce energy consumption, and enhance sustainable and stable production, which is reflected in the following aspects;

[0003] (1) Improve the treatment efficiency of sewage discharge and reduce energy consumption. Through automated control, precise control of the sewage treatment plant process can be achieved, thereby improving the water quality standards of the discharged water, while also playing a role in energy conservation, emission reduction and cost reduction.

[0004] (2) Optimize structure and control rationally. In order to better meet the work of the entire system, each PLC control station automatically adjusts the working status of the equipment in the corresponding sewage treatment structure in the area.

[0005] (3) Reliable communication. Different levels can quickly transfer information up and down through different communication methods, which not only improves the reliability of control, but also saves the historical records of all equipment operation in the factory, facilitating regular maintenance and inspection in the future.

[0006] However, for the industrial sewage filtration system in the prior art, it is not possible to collect historical data, perform optimization learning, and then optimize and regulate the water flow rate of the water inlet and outlet in real time, so that the regulated inlet flow rate and outlet flow rate can ensure that the effluent through the filtration system meets the turbidity threshold requirements in the drainage standard, and further monitor in real time whether the pressure difference in the filter tank exceeds the threshold based on the regulated inlet and outlet flow rates, so as to further trigger the start of the backwash process, thereby ensuring the filtration efficiency in the filtration system while extending the service life of the filter material in the filtration system and the service life of the entire equipment system. In addition, it can also ensure that the turbidity of the effluent meets the emission standards. Summary of the invention

[0007] In view of the above-mentioned defects, the present invention provides a method and system which can remove pollutants in water, and when backwashing is detected, the filter material in the filter tank is cleaned by performing a process of single water flushing → single air flushing → air-water double flushing → secondary single water flushing in sequence. After cleaning, the filter tank can continue to perform forward sewage filtration.

[0008] The present invention provides the following technical solution: a multi-stage water treatment filtration and purification method capable of backwashing, wherein the method filters industrial wastewater and collects and reuses the industrial wastewater, comprising the following steps:

[0009] Step 1), control the water inlet on the filter tank of each filter combination unit to open, and control the exhaust port on the upper part of the filter tank of each filter combination unit to open, discharge the gas in the filter tank through the exhaust port, and close the exhaust port when the value of the exhaust pressure gauge drops to a specified value;

[0010] Step 2), opening the water outlet at the bottom of each filter tank, and each filter tank enters the state of sewage filtering; the sewage to be filtered enters from the water inlet, passes through the multi-layer medium filter layer from top to bottom, and is finally discharged through the water outlet;

[0011] Step 3), monitor the initial turbidity in the tank body and monitor the turbidity of the sewage discharged from the outlet, the water flow rate of the water inlet and the water flow rate of the water outlet in real time, and remotely control the single-chip microcomputer to control the pressure difference of each filter tank within the pressure difference threshold to ensure that the filtered water discharged from the outlet meets the turbidity requirements of the drainage standard;

[0012] Step 4), when the pressure difference in a filter tank exceeds the pressure difference threshold, the corresponding filter tank is backwashed;

[0013] Step 5) After the backwashing is completed, the steps 2) to 3) are repeated again to achieve continuous forward filtration of the industrial wastewater.

[0014] As a preferred embodiment of the present invention, in the step 3), the remote control microcontroller controls the pressure difference of each filter tank to be within the pressure difference threshold, thereby ensuring that the filtered water discharged from the water outlet meets the turbidity requirements in the drainage standard, including the following steps:

[0015] Step 31), calculate the total flow Q of the water inlet under normal filtration in step 2) i,in and the total outflow Q i,out :

[0016]

[0017] Among them, d i,in is the diameter of the water inlet of the ith filter tank, d i,outis the diameter of the water outlet of the i-th filter tank;

[0018] Step 32), calculate the pressure difference ΔP between the water inlet and the water outlet of the i-th filter tank i :

[0019]

[0020] Among them, P loss is the pressure loss, g is the gravitational acceleration, and ρ is the density of the filter material of the multi-layer medium filter layer in the filter tank;

[0021] Step 33), construct the optimal inlet flow rate and the optimal outlet flow rate within the turbidity range allowed by the drainage standard to solve the equation:

[0022]

[0023] Among them, T i,in is the initial turbidity in the i-th filter tank monitored in step 3), T i,out is the turbidity of the water outlet of the i-th filter tank; H a is the height of the multi-layer medium filter layer in the filter tank, k is the filter material coefficient, C1 is the first weight coefficient, C1 = 0.2, C2 is the second weight coefficient, C2 = 0.5; T out,max is the maximum turbidity threshold;

[0024] Step 34), using the LM method to solve the equation constructed in step 33), to obtain the optimal water inlet flow rate of the i-th filter tank and optimal outlet flow rate The remote control microcontroller controls the water inlet speed of the i-th filter tank to the optimal water inlet flow rate. Control the water outlet speed to the optimal outlet flow rate This ensures that the filtered sewage obtained at the outlet meets the turbidity requirements of the drainage standards.

[0025] As a preferred embodiment of the present invention, the calculation formula of the filter material coefficient k in step S33) is as follows:

[0026] Among them, k n is the permeability coefficient of the nth layer of filter material, H n is the thickness of the nth layer of filter material;

[0027] Among them, p n is the average particle size of the nth layer of filter material, ε n is the porosity of the nth layer of filter material.

[0028] As a preferred embodiment of the present invention, the P in step S32) loss The calculation formula is as follows:

[0029] Among them, μ is the friction coefficient between sewage and filter material, and D is the diameter of the circular cross section of the filter tank.

[0030] As a preferred embodiment of the present invention, the LM method is used in step 34) to solve the equation constructed in step 33), including:

[0031] Step 341), construct the water flow velocity v of the water inlet of the i-th filter tank i,in (t) and the water velocity v at the outlet i,out (t) is the nonlinear equation system F(v i )=[f1(v i ),f2(v i ),…,f M (v i )] T , where f m (v i ) is the nonlinear equation system F(v i ) in the mth nonlinear equation, m=1,2,…,M; v i is the independent variable vector in the nonlinear equation system, v i =[v i,in (t),v i,out (t)] T , f m (v i )=f m (v i,in (t),v i,out (t));

[0032] Step 342), calculate the first-order derivative and second-order derivative of the m-th nonlinear equation with respect to all independent variables, and form the Jacobian ratio matrix J(v i ) and the Hessian matrix He(v i ):

[0033] Step 343), calculate the nonlinear equation system F(v i ) is the gradient function G(v i ):

[0034] G(v i )=J T (v i )·F(v i );J T (v i ) is the Jacobian ratio matrix J(v i )’s transposed matrix;

[0035] Step 344), calculate the independent variable vector v i The update result of the q+1th generation is:

[0036]

[0037] in, is the update result of the qth generation of the independent variable; q is the damping coefficient for continuing to update the qth generation update result; I is a 2×2 identity matrix;

[0038] Step 345), determine whether the obtained q+1th generation update result makes the nonlinear equation system F(v i ) decreases, that is, to judge whether Is it less than like Then reduce the damping coefficient λ for the update result of the q+1th generation q+1 , so that q+1 =λ q / 10; if Increase the damping absorption λ of the update result of the q+1th generation q+1 , so that q+1 =10λ q ;

[0039] Step 346), after repeating steps 342) to 345) for Q generations, determine the nonlinear equation system of the Qth generation The gradient function The norm of Whether the convergence is less than the stop iteration threshold θ, the stop iteration threshold θ = 0.8×10 -6 ~1×10 -6 ; If so, stop the iteration and output the independent variable vector of the Qth generation The elements in and As the optimal inlet flow rate of the i-th filter tank and optimal outlet flow rate Otherwise, continue to repeat steps 342)-345).

[0040] As a preferred embodiment of the present invention, in step 3), when the pressure difference in a filter tank exceeds the pressure difference threshold ΔP thr When the optimal water inlet flow rate calculated in step 34) is and optimal outlet flow rate Bring it into step 32) to calculate the pressure difference ΔP between the water inlet and the water outlet of the i-th filter tank i In the calculation formula, the calculated ΔP i >ΔPthr The pressure difference threshold ΔP thr It is 0.8bar.

[0041] As preferred embodiment of the present invention, the backwashing in step 4) comprises the following steps:

[0042] Step 41), control the water inlet of the corresponding filter tank to be fully closed, control the water outlet of the corresponding filter tank to be changed from a closed state to a partially open state, and then control the backwash drain outlet of the corresponding filter tank to be opened, and keep the single water flushing time period T1, T1 = 2min ~ 4min;

[0043] Step 42), continue to keep the water inlet of the corresponding filter tank closed, adjust the water outlet of each filter tank to a fully closed state, and simultaneously control the drive motor, butterfly valve, ball valve assembly, and the top of the filter tank to be backwashed and the diversion port of the air inlet diversion pipe to open, and perform single-gas flushing on the filter tank to be backwashed in the corresponding filter combination unit, and continue to keep the backwashing sewage outlet open; keep the single-gas flushing time period T2, T2 = 3min ~ 6min;

[0044] Step 43), control the ball valve assembly and the corresponding diversion port to continue to open, control the backwash drain port to be in an open state, control the water outlet to be in a partially open state, and control the cleaning cycle of the air-water double flushing stage to be T3, T3 = 5min to 8min;

[0045] Step 44), control the water outlet of the corresponding filter tank to be completely closed again, control the diversion port on the corresponding tank body to be closed, and then no gas enters the corresponding tank body, control the water outlet to be opened again to a partially open state, and control the duration of the secondary single water flushing cycle to be T4, T4 = 2min ~ 5min;

[0046] Step 45), control the backwash drain outlet to be adjusted from the open state to the closed state, then control the water outlet to be fully open in turn, control the water inlet to be fully open, and enter the normal filtering state of step 2).

[0047] As a preferred embodiment of the present invention, the partially opened state of the water outlet in step 41), step 43) and step 44) is controlled to be opened to 10% to 20% of the fully opened state.

[0048] The present invention also provides a backwashable multi-stage water treatment filtration and purification system using the method as described above, the system comprising a bottom frame, a plurality of rows of filter parallel units arranged in sequence from back to front arranged on the bottom frame, each filter parallel unit comprising two parallel filter combination units, each filter combination unit being a plurality of filter tanks arranged in sequence at equal intervals from left to right, a feed port being arranged on the upper side of each filter tank; each filter tank comprising a water inlet arranged on the upper rear side of the tank body, a backwashing outlet on the upper rear side of the tank body, a water outlet on the lower part of the tank body, an air inlet and an air outlet on the upper part of the tank body, and a plurality of media filter layers being arranged in each filter tank; and each filter parallel unit having front and rear corresponding filter tanks. The two filter tanks are connected to the same ball valve assembly through an air inlet diverter pipe, and each ball valve assembly is arranged on the same longitudinal air diverter pipe, the air outlet of the longitudinal air diverter pipe is connected to the air inlet of the air inlet diverter pipe, and the two air outlets of the air inlet diverter pipe are respectively connected to the air inlets on the upper parts of the two corresponding front and rear filter tanks of the corresponding filter combination unit; the bottom frame is also provided with a blower and a driving motor arranged on the right side thereof, the blower is connected to the transverse air supply pipe, and multiple longitudinal air diverter pipes are connected to the transverse air supply pipe, and a butterfly valve is arranged at the connection between the transverse air supply pipe and the blower; each exhaust port is connected to a horizontal exhaust pipe, and each horizontal exhaust pipe is sequentially provided with an exhaust valve and an exhaust pressure gauge;

[0049] The system also includes a remote control single chip microcomputer arranged on the bottom frame, a first water flow velocity monitoring sensor arranged at the water inlet of each filter tank, a second water flow velocity monitoring sensor and a sewage turbidity sensor arranged at the outlet of each filter tank; the remote control single chip microcomputer is used to control the system to execute steps 1) to 5) of the method described above.

[0050] As a preferred embodiment of the present invention, the multi-layer medium filter layer includes, from top to bottom, a first filter material layer with a height of 0.3m to 0.5m, a second filter material layer with a height of 0.2m to 0.4m, and a third filter material layer with a height of 0.5mm to 0.7mm, wherein the first filter material layer, the second filter material layer, and the third filter material layer are anthracite, manganese sand, and quartz sand, respectively;

[0051] The particle size and porosity of the anthracite used are 0.8mm~2.0mm and 0.45~0.55 respectively; the particle size and porosity of the manganese sand used are 1.0mm~2.0mm and 0.40~0.45 respectively, and the height of the third layer of filter material is; the particle size and porosity of the quartz sand used are 2.0mm~4.0mm and 0.38~0.42 respectively.

[0052] The beneficial effects of the present invention are:

[0053] 1. The present invention realizes efficient filtration of the multi-stage water treatment filtration and purification method and the timing and process of backwashing start-up through reasonable water flow velocity of the water inlet and the water outlet, and finally achieves the technical effect of optimizing resource utilization and improving filtration effect.

[0054] 2. The present invention constructs a model to solve the optimal water inlet flow rate and the optimal water outlet flow rate when the drainage turbidity meets the standard requirements, and establishes a relationship formula between pressure difference, flow rate and turbidity, so as to better control the operation of the filtration system. The real-time monitoring and feedback control strategy can ensure the quality of the filtered water while extending the service life of the multi-layer medium filter layer and reducing the frequency of starting the backwashing program, providing a feasible control method and a programmable logic that can be manipulated and implemented for the optimal operation of the system.

[0055] 3. The method and system provided by the present invention can remove pollutants in water, and when backwashing is detected, the filter material in the filter tank is cleaned by performing a process of single water flushing → single air flushing → air-water double flushing → secondary single water flushing in sequence. After cleaning, the filter tank can continue to perform forward sewage filtration.

[0056] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0058] Figure 1 A schematic diagram of the method provided by the present invention;

[0059] Figure 2 The method provided by the present invention controls the sewage turbulence distribution diagram at the 20th minute and the 35th minute after the system is filtered;

[0060] Figure 3 The method provided by the present invention controls the sewage turbulence distribution diagram at the 60th minute and the 90th minute after filtration;

[0061] Figure 4 The method control system provided by the present invention is a sewage turbulence distribution diagram at the 120th minute and the 300th minute after filtration;

[0062] Figure 5The method provided by the present invention optimizes the equation constructed in step 33) in step 34) based on the LM method to obtain the optimal water inlet flow rate of the i-th filter tank. and optimal outlet flow rate Three-dimensional graph of turbidity changes;

[0063] Figure 6 A schematic diagram of turbidity changes during backwashing of a system during forward flushing using the method provided by the present invention;

[0064] Figure 7 It is a schematic diagram of the Cartesian coordinate system structure that conforms to the right-hand rule of the system;

[0065] Figure 8 This is a structural diagram of the system from another perspective;

[0066] Fig. 9 for Figure 7 Enlarged view of part A. DETAILED DESCRIPTION

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] The present invention provides a multi-stage water treatment, filtration and purification method capable of backwashing, the method adopts Figure 7-Figure 8 The system of the partial structure shown is used to filter industrial wastewater and then collect and reuse it. Figure 1 As shown, the following steps are included:

[0069] Step 1), control the water inlet 21 on the filter tank 2 of each filter assembly unit to open, and control the exhaust port 25 on the upper part of the filter tank of each filter assembly unit to open, so that the sewage to be filtered enters the filter tank 2 of each filter assembly unit, and the gas in the filter tank 2 is discharged from the tank through the exhaust port 25. When the value of the exhaust pressure gauge 251 decreases to a specified value, close the exhaust port 25, and the exhaust ends;

[0070] Before step 1) begins, it is an initial state. In the initial state, all valves (water inlet valve, water outlet valve, exhaust valve, backwashing drain valve, and the diverter valve of the diverter port connecting the air inlet diverter pipe with the upper part of the filter tank) are in a closed state;

[0071] Step 2), opening the water outlet 23 at the bottom of each filter tank 2, and each filter tank 23 enters a state of filtering sewage; the sewage to be filtered enters from the water inlet 21 at the top of each filter tank 2, and is filtered through the multiple layers of medium filter layers from top to bottom, and finally discharged through the water outlet 23;

[0072] Step 3), monitor the initial turbidity T in the tank i,in (t) and monitor the turbidity T′ of the sewage discharged from the outlet in real time i,out (t), water flow velocity v at the water inlet i,in (t), water flow velocity v at the outlet i,out (t), the remote control microcontroller (6) controls the pressure difference of each filter tank 2 to be within the pressure difference threshold, thereby ensuring that the filtered water discharged from the water outlet 23 meets the turbidity requirements of the drainage standard;

[0073] Step 4) When the pressure difference in a filter tank exceeds the pressure difference threshold ΔP thr When , the corresponding filter tank 2 is backwashed;

[0074] Step 5) After the backwashing is completed, steps 2) to 3) are repeated again to achieve continuous forward filtration of industrial wastewater.

[0075] Sand filtration is an advanced treatment step in sewage treatment, usually after secondary treatment, also known as tertiary treatment or advanced treatment. In this step, sand filtration is mainly used to remove suspended solids (SS), partially soluble organic matter, phosphorus, etc. in water to further purify water quality and meet higher discharge standards or reuse requirements. Figure 7-Figure 8 The system of the partial structure shown can be operated automatically and continuously for 24 hours. In the process of filtering the sewage after secondary treatment, on the one hand, by first monitoring the water flow rate v through the water inlet 21 of each filter tank 2 i,in (t) and the water flow velocity v at the water outlet 23 i,out (t), and then the optimal water inlet flow rate is obtained through remote control of the single chip microcomputer 6 after learning and optimization and optimal outlet flow rate The calculated results are used to control the water flow rate at the water inlet and the water flow rate at the water outlet in real time, thereby ensuring that the filtered sewage obtained at the outlet meets the turbidity requirements of the drainage standard: 0 <T i,out <T out,max On the other hand, real-time monitoring of the turbidity T' of the sewage discharged from each filter tank outlet 23 i,out (t) Whether it exceeds the T specified in the emission standards out,max , and can find that the pressure difference in a filter tank exceeds the pressure difference threshold ΔP under the condition of normal filtration of the system with the optimal inlet and outlet flow ratesthr The method and system provided by the present invention can remove pollutants in water, and when a backwash is detected, the filter material in the filter tank is cleaned by a process of single water flushing → single gas flushing → double gas and water flushing → secondary single water flushing. After cleaning, the filter tank can continue to filter sewage in the forward direction.

[0076] In the upgrading and transformation of sewage treatment plants, the method and system provided by the present invention can be used as a filtering unit for deep treatment to meet more stringent emission standards.

[0077] The control and optimization of flow fluctuations during water treatment is a key issue in process control, and flow fluctuations may affect the stability and efficiency of the overall system. By reasonably controlling and optimizing the speed of water inlet and outlet, thereby affecting the flow of water inlet and outlet, the flow fluctuations of the multi-layer medium filter layer in the entire tank body during the sewage filtration process can be reduced, and the filtration performance of the system can be improved. Therefore, as another preferred embodiment of the present invention, in step 3), the remote control microcontroller 6 controls the pressure difference of each filter tank 2 within the pressure difference threshold to ensure that the filtered water discharged from the outlet 23 meets the turbidity requirements in the drainage standard, including the following steps:

[0078] Step 31), calculate the total flow Q of the water inlet under normal filtration in step 2) i,in and the total outflow Q i,out :

[0079]

[0080] Among them, d i,in is the diameter of the water inlet 21 of the i-th filter tank, d i,out is the diameter of the water outlet 23 of the i-th filter tank;

[0081] Step 32), calculate the pressure difference ΔP between the water inlet 21 and the water outlet 23 of the i-th filter tank 2 i :

[0082]

[0083] Among them, P loss is the pressure loss, that is, the pressure loss of the water inlet during the sewage filtration until the water outlet flows out, g is the acceleration of gravity, g = 9.81m / s 2 , ρ is the density of the filter material in the multi-layer medium filter layer in the filter tank 2;

[0084] P lossThe calculation formula is as follows:

[0085] Where μ is the friction coefficient between sewage and filter media, D is the diameter of the circular cross section of the filter tank, and H is a is the height of the multi-layer medium filter layer in the filter tank 2; D is 1.0m to 2.5m according to different filtering requirements; H a The total height of the filter tank is 1.0m~1.6m according to different filtering requirements, and the total height of the filter tank is 2.6m~3.0m according to the requirements; the sewage filtration flow rate of each filter tank is about 10m 3 / h~50m 3 / h;

[0086] Step 33), construct the optimal inlet flow rate and the optimal outlet flow rate within the turbidity range allowed by the drainage standard to solve the equation:

[0087]

[0088] Among them, T i,in is the initial turbidity in the i-th filter tank monitored in step 3), T i,out is the turbidity of the water discharged from the outlet of the i-th filter tank; k is the filter material coefficient, C1 is the first weight coefficient, and C2 is the second weight coefficient. Preferably, in the method provided by the present invention, C1=2, C2=0.5; T out,max is the maximum turbidity threshold of the filtered sewage that can be discharged as defined in the drainage standard; preferably, T out,max =0.5NTU; NTU is the turbidity unit; where, To solve the calculation formula for the optimal inlet flow rate and the optimal outlet flow rate, st 0 <T i,out <T out,max It represents the limiting condition of the solution calculation formula, that is, limiting the above solution calculation formula to the turbidity range allowed by the drainage standard;

[0089] The calculation formula of filter material coefficient k is as follows:

[0090] Among them, k n is the permeability coefficient of the nth layer of filter material, H n is the thickness of the nth layer of filter material (i.e. the height of the nth layer of filter material in the tank body of the filter tank 2),

[0091] Among them, p n is the average particle size of the nth layer of filter material, ε n is the porosity of the nth layer of filter material. n When ε is larger, the permeability of the nth layer of filter material is higher (the filtered sewage is easier to pass through).n When it is larger, the permeability is also higher.

[0092] In the process of multi-stage water treatment and filtration, the pressure difference ΔP of the pressure loss during the sewage filtration process is calculated based on the fluid mechanics analysis of the Fluent simulation in step 31) and the Poiseuille pressure difference formula in step 32) combined with the height change of the water inlet and outlet. i Combined with the above, the optimal flow rate of the water inlet and outlet can be precisely controlled. With the help of CFD simulation, the inlet and outlet flow rates in the multi-stage water treatment filtration process can be optimized to ensure that the sewage is fully filtered out of suspended solids and solid particles of different particle sizes in the i-th filter tank, and the turbidity of the outlet water is within the drainage standard range; on the other hand, the fluid flow mode in the system can be accurately and dynamically evaluated and optimized in real time to achieve precise and stable flow control.

[0093] Figure 2-Figure 4 In order to use the method of the present invention to monitor the flow rate of the water inlet and the water outlet at different times, Figure 2 As shown, Figure 2 (a) Figure 2 (b) are CFD simulation diagrams of the fluid-solid coupling state in the monitored filter tank at the 20th minute and the 35th minute from the start of filtration (i.e., the moment when both the water inlet and the water outlet are opened). The left side of the figure shows the suspended matter and solid particles in the sewage with different particle sizes and their corresponding colors from top to bottom. The figure shows the CFD simulation of the xz plane section of the filter tank. Figure 3 (a) Figure 3 (b) are the simulated turbulence distribution diagrams of the sewage flowing from the inlet to the outlet at the 60th minute (1st hour) and the 90th minute (1.5th hour) in the monitored filter tank from the start time, respectively. Figure 4 (a) Figure 4 (b) Dynamic CFD simulation diagrams of sewage turbulence at 120 minutes (2 hours) and 300 minutes (5 hours) from the start time;

[0094] like Figure 2-Figure 4It can be seen that, using the method of the present invention, from the beginning of filtration, after 20 minutes of filtration, suspended matter with large molecular size begins to gradually enter the middle layer where the filter material is located from the water inlet, and suspended matter with smaller particle size and pollutant particles with larger particle size enter the multi-layer medium filter layer faster. Therefore, particles with smaller molecular size arrive at the lower part of the multi-layer medium filter layer earlier. After about 35 minutes, particles with smaller molecular size are about to reach the bottom of the filter tank. After about 1 hour, due to the concave bottom of the filter tank and the structural characteristics of the middle water outlet, medium molecular size pollutant particles form turbulent reflux at the bottom of the filter tank, and at this time, large molecular pollution particles finally reach the bottom layer of the multi-layer medium filter layer. At this time, small molecular size pollutant particles are again carried up due to the turbulent reflux and filtered again from top to bottom by the multi-layer medium filter layer. At 1.5h-2h, most of the pollutant particles have been adsorbed and processed by the multi-layer medium filter layer, and the filtered sewage is gradually discharged from the filter tank through the water outlet. After 5 hours, the sewage entering from the water inlet has basically been filtered clean.

[0095] Step 34), use the LM method to solve the equation constructed in step 33), and obtain the optimal water inlet flow rate of the i-th filter tank and optimal outlet flow rate The remote control microcontroller 6 controls the water inlet speed of the i-th filter tank to the optimal water inlet flow rate. Control the water outlet speed to the optimal outlet flow rate This ensures that the filtered sewage obtained at the outlet meets the turbidity requirements of the drainage standards.

[0096] The LM method is an iterative update method that combines the optimization calculation results of the gradient descent method and the Newton method, which can achieve a balance between the stability of the gradient descent method and the rapid convergence of the Newton method. In order to obtain an accurate optimal water inlet flow rate and an optimal water outlet flow rate, as another preferred embodiment of the present invention, the LM method is used in step 34) to solve the equation constructed in step 33), including:

[0097] Step 341), construct the water flow velocity v of the water inlet of the i-th filter tank i,in (t) and the water velocity v at the outlet i,out (t) is the nonlinear equation system F(v i )=[f1(v i ),f2(v i ),…,f M (v i )] T , where f m (v i ) is the nonlinear equation system F(v i) has the water flow velocity v at the water inlet of the i-th filter tank i,in (t) and the water velocity v at the outlet i,out (t) is the mth nonlinear equation, m = 1, 2, ..., M; v i is the independent variable vector in the nonlinear equation system, v i =[v i,in (t),v i,out (t)] T , f m (v i ) = f m (v i,in (t),v i,out (t));

[0098] Step 342), calculate the first-order derivative and second-order derivative of the m-th nonlinear equation with respect to all independent variables, and form the Jacobian ratio matrix J(v i ) and the Hessian matrix He(v i ):

[0099]

[0100] Step 343), calculate the nonlinear equation system F(v i )’s gradient function G(v i ):

[0101] G(v i )=J T (v i )·F(v i );J T (v i ) is the Jacobian ratio matrix J(v i )’s transposed matrix;

[0102] Step 344), calculate the independent variable vector v i The update result of the q+1th generation is:

[0103]

[0104] in, is the update result of the qth generation of the independent variable; q is the damping coefficient for continuing to update the qth generation update result; I is a 2×2 identity matrix; is the water flow velocity at the water inlet obtained by the qth generation update, is the water flow velocity at the outlet updated in the qth generation;

[0105] Step 345), determine whether the obtained q+1th generation update result makes the nonlinear equation system F(v i ) decreases, that is, to judge whether Is it less than like Then reduce the damping coefficient λ for the update result of the q+1th generation q+1 , so that q+1 =λ q / 10; if Increase the damping absorption λ of the update result of the q+1th generation q+1 , so that q+1 =10λ q ;

[0106] The LM method adjusts the damping coefficient of each generation in the iterative update process. For example, when updating the q+1th generation, adjust λ according to the update result of the qth generation. q+1 , so that when the qth generation update result is far away from the target result, q+1 =10λ q , and then the optimization method is closer to the gradient descent method; when the qth generation update result is close to the target result, make λ q+1 =λ q / 10, and then the optimization method is closer to Newton's method. Its goal is to correct the qth generation update result by constructing the first-order Jacobian matrix and the second-order Hessian matrix, and then minimize the residual square sum of the nonlinear function;

[0107] Step 346), after repeating steps 342)-345) for Q generations, determine the nonlinear equation system of the Qth generation The gradient function The norm of Whether the convergence is less than the stop iteration threshold θ, the stop iteration threshold θ = 0.8×10 -6 ~1×10 -6 ; If so, stop the iteration and output the independent variable vector of the Qth generation The elements in and As the optimal inlet flow rate of the i-th filter tank and optimal outlet flow rate Otherwise, continue to repeat steps 342)-345).

[0108] like Figure 5 As shown, the water flow velocity v of the real-time water inlet is obtained by solving step 33) based on the LM method to ensure that the turbidity of the water outlet 23 of the i-th filter tank 2 meets the discharge standard threshold. i,in (t) and the real-time water flow velocity v at the outlet i,out(t) Turbidity changes in the optimized filter tank 2. The colors in the figure represent different turbidity values. The red dotted contour line at the bottom represents the st 0 of the solution calculation formula constructed in step 33). <T i,out <T out,max The turbidity threshold T in this constraint out,max =0.5NTU height position, v i,in (t) and v i,out The (t) axis represents the water flow rate at the inlet and outlet when optimization is required. Figure 5 It can be seen that under the optimization of the LM method, the optimal inlet flow rate below the turbidity threshold represented by the red dotted contour line can be solved more accurately. and optimal outlet flow rate

[0109] In step 3), when the pressure difference in a filter tank exceeds the pressure difference threshold ΔP thr When the optimal water inlet flow rate calculated in step 34) is and optimal outlet flow rate Bring it into step 32) to calculate the pressure difference ΔP between the water inlet 21 and the water outlet 23 of the i-th filter tank 2 i In the calculation formula, the calculated ΔP i >ΔP thr situation;

[0110] The optimal water inlet flow rate calculated based on the LM method in step 34) and optimal outlet flow rate Substitute into step 32) ΔP i Calculation formula, ΔP at this time i as follows:

[0111]

[0112] Determine the ΔP calculated according to this formula i Is it greater than the pressure difference threshold ΔP? thr ; Pressure difference threshold ΔP thr It is 0.8bar.

[0113] After the filter tank has been working for a period of time, a layer of small particles has been covered on the filter sand layer. If it is not washed in time, the filtering effect will be affected. Usually, the filter tank needs to be backwashed after being used for a few hours. In order to optimize the cleaning effect of the multi-layer medium filter layer, as another preferred embodiment of the present invention, the backwashing of step 4) includes the following steps:

[0114] Step 41), in the single water flushing stage, the water inlet 21 of the corresponding filter tank 2 is controlled to be fully closed, the water outlet 23 of the corresponding filter tank is controlled to be changed from a closed state to a partially open state, and then the backwashing drain port 22 of the corresponding filter tank 2 is controlled to be opened, and the single water flushing period is maintained at T1, T1 = 2min~4min; due to the closure of the water inlet 21 and the partial opening of the water outlet 23, a negative pressure appears in the backwashed filter tank, and then after the backwashing drain port 22 is opened, the sewage containing the particles and other pollutants that block the filter layer in the backwashing pipe flows out from the backwashing drain port 22; the purpose of this stage is to flush the surface of the filter layer with a low-speed water flow to remove the loose particles attached thereto, so as to reduce the interference of large particle blockages or attachments on the subsequent air flow flushing and the mud pollution raised during the backwashing process, thereby avoiding the poor single-gas flushing effect caused by the obstruction of the flow of compressed air during the subsequent single-gas flushing.

[0115] Step 42), after the single water flushing is completed, continue to keep the water inlet 21 of the corresponding filter tank 2 closed, adjust the water outlet 23 of each filter tank to a fully closed state, and simultaneously control the drive motor 51, the butterfly valve 53, the ball valve assembly 4, and the top of the backwashed filter tank 2 and the diversion port 31 of the air inlet diversion pipe 3 to be opened, so as to drive the blower 5 to enter the blowing state. After the butterfly valve 53 is controlled to open, the air blown out by the blower 5 can be transported from the horizontal air supply pipe 52 to the longitudinal air distribution pipe 41 connected with it from left to right in sequence, and the ball valve assembly 4 on the longitudinal air distribution pipe 41 where the corresponding tank body is located is opened, so that the gas output by the blower 5 passes through the butterfly valve 53 and then is sent to the corresponding filter combination unit of the filter parallel unit through the horizontal air supply pipe 52. At the filter tank 2 that needs to be backwashed, after controlling the corresponding ball valve assembly 4 to open, the wind blown out by the blower 5 further enters the air inlet diversion pipe 3 through the longitudinal air diversion pipe 41, and since the diversion port 31 on the filter tank 2 that needs to be backwashed is opened, the gas enters the corresponding filter tank 2, and the filter tank 2 that needs to be backwashed in the corresponding filter combination unit is flushed with a single gas. At this time, the backwashing sewage outlet 22 continues to be opened; the single gas flushing time period is maintained at T2, T2 = 3min~6min; the purpose of single gas flushing is to input compressed gas, stir the particles inside the filter layer through airflow counteraction, and then break the adhesion between the particles, remove the accumulated bacteria and biofilm inside the filter layer, and restore the permeability of the filter layer.

[0116] Step 43), in the air-water double flushing stage, the ball valve assembly 4 and the corresponding diversion port 31 are controlled to continue to be opened, the backwashing drain port 22 is controlled to be in an open state, and the water outlet 23 is in a partially open state. The cleaning cycle of the air-water double flushing stage is controlled to be T3, T3 = 5min ~ 8min; in this stage, the gas flow rate is preferably controlled at 30m 3 / (h·m 2 )~60m 3 / (h·m2 ), the gas pressure entering the corresponding filter tank 2 from the diversion port 31 is between 2 bar and 5 bar, and the multi-layer medium filter layer in the filter tank is cleaned by the gas-water combination in step 43), and the multi-layer medium filter material is simultaneously flushed by gas and water flow to prevent particulate matter from re-entering the filter layer, so as to achieve the purpose of thorough cleaning and better impurity removal effect.

[0117] Step 44), in the secondary single water flushing stage, the water outlet 23 of the corresponding filter tank 2 is controlled to be completely closed again, the diversion port 31 on the corresponding tank body is controlled to be closed, and then no gas enters the corresponding tank body, the water outlet (23) is controlled to be opened again to a partially open state, and the duration of the secondary single water flushing is controlled to be T4, T4 = 2min~5min; after the air-water double flushing, the single water flushing is performed again to remove the residual pollutant particles and bubbles in the filter layer, restore the initial normal result of the filter layer, avoid bubbles from forming gaps in the filter layer, and provide a stable filter layer for subsequent normal filtration.

[0118] Step 45), after the backwashing is finished, the backwashing sewage outlet 22 is controlled to be adjusted from the open state to the closed state, and then the water outlet 23 is controlled to be in the fully open state in turn, and the water inlet 21 is controlled to be in the fully open state, and the normal filtering state of step 2) is entered.

[0119] The partially open state of the water outlet 23 in the above-mentioned steps 41), 43) and 44) ​​is to control it to be opened to 10% to 20% of the full opening; preferably, in step 41) it is opened to 10% of the full opening, in step 43) it is opened to 20% of the full opening, and in step 44) it is opened to 13% of the full opening. During backwashing, the water inlet valve is closed and the water outlet valve maintains a small opening. Due to the pressure difference, the function of the water outlet valve becomes to allow water in, and the air inlet valve is opened intermittently for pneumatic backwashing. The backwash drain valve is kept in an open state, and the multi-layer medium is cleaned with water flow or air flow, which can effectively improve the cleaning effect of the multi-layer medium filter material in the filter tank. Figure 6 As shown in FIG. 1 , the turbidity variation trend diagram of the effluent from the method provided by the present invention using a backwashable multi-stage water treatment filtration and purification system to filter sewage within 0h-6h is shown in FIG. Figure 6 It can be seen that Figure 6 The partial opening state of the water outlet 23 in each step is the above-mentioned preferred limit value; at the 1.75h and 3.75h moments, the turbidity exceeds the turbidity threshold value of the drainage standard of 0.5NTU, and the system is controlled to be backwashed. At the 1.75h moment, T1=2min, T2=6min, T3=7min, T4=2min are controlled. In step 43), the gas flow rate is controlled to be 30m 3 / (h·m 2), the gas pressure entering the corresponding filter tank 2 from the diversion port 31 is 5 bar; at 3.75 h, T1 = 4 min, T2 = 3 min, T3 = 8 min, T4 = 5 min are controlled, and the gas flow rate in step 43) is controlled to be 45 m 3 / (h·m 2 ), the gas pressure entering the corresponding filter tank 2 from the diversion port 31 is 2 bar; after backwashing for about 20 minutes at the 1.75h and 3.75h time, the turbidity gradually decreases to 0.1NTU, indicating that the cleaning has achieved the expected effect, and then the system continues to filter the sewage forward. You can also choose the flushing time of each step of the backwashing process to be T1=4min, T2=5min, T3=5min, T4=4min, and control the gas flow rate to 60m in step 43). 3 / (h·m 2 ), the gas pressure entering the corresponding filter tank 2 from the diversion port 31 is 3.5 bar.

[0120] The present invention also provides a multi-stage water treatment, filtration and purification system capable of backwashing using the above method, such as Figure 7-Figure 8 As shown, Figure 7 The system is a schematic diagram of a Cartesian coordinate system structure that conforms to the right-hand rule. The system includes a bottom frame 1 arranged in the xy plane, a plurality of rows of coordinates arranged on the bottom frame 1 from back to front ( Figure 7 The filter parallel units are arranged in sequence (in the y-axis direction in the figure), each filter parallel unit includes two parallel filter combination units, each filter combination unit is a plurality of filter tanks 2 arranged in sequence with equal spacing from left to right (in the x-axis direction in the figure), and a feed port 20 is arranged on the upper side of each filter tank 2; it is characterized in that each filter tank 2 includes a water inlet 21 arranged at the upper rear side of the tank body, a backwash drain port 22 at the upper rear side of the tank body, a water outlet 23 at the lower part of the tank body, an air inlet 24 and an air outlet 25 at the upper part of the tank body, and each filter tank 2 is provided with multiple layers of medium filter layers; each filter parallel unit has corresponding front and rear parts. The two filter tanks are connected to the same ball valve assembly 4 through an air inlet manifold 3, and each ball valve assembly 4 is arranged on the same longitudinal air distribution pipe 41. The air outlet of the longitudinal air distribution pipe 41 is connected to the air inlet of the air inlet manifold 3, and the two air outlets of the air inlet manifold 3 are respectively connected to the air inlets 24 on the upper parts of the two corresponding filter tanks 2 at the front and rear of the corresponding filter combination unit; the bottom frame 1 is also provided with a blower 5 and a drive motor 51 arranged on the right side thereof, the blower 5 is connected to the transverse air supply pipe 52, and multiple longitudinal air distribution pipes 41 are connected to the transverse air supply pipe 52, and a butterfly valve 53 is provided at the connection between the transverse air supply pipe 52 and the blower 5; Fig. 9As shown, each exhaust port 25 is connected to a horizontal exhaust pipe, and each horizontal exhaust pipe is sequentially provided with an exhaust valve 251 and an exhaust pressure gauge 252; each water inlet 21 is provided with a water inlet valve, each water outlet 23 is provided with a water outlet valve, and each backwash drain port 22 is provided with a backwash drain valve. The water inlet valve, water outlet valve, backwash drain valve, ball valve assembly 4, exhaust valve and the diverter valve at the diverter port of the air inlet diverter pipe connected to the tank body are all communicated with the remote control microcontroller 6, and are opened or closed by receiving instructions from the remote control microcontroller 6.

[0121] The system further comprises a remote control single chip microcomputer 6 arranged on the bottom frame 1, a first water flow velocity monitoring sensor arranged at the water inlet 21 of each filter tank 2, a second water flow velocity monitoring sensor and a sewage turbidity sensor arranged at the outlet of each filter tank 2; the remote control single chip microcomputer is used to control the system to execute steps 1) to 5) in the above method;

[0122] The first water flow velocity monitoring sensor is used to monitor the water flow velocity v of the water inlet in real time i,in (t), the second water flow velocity monitoring sensor is used to monitor the water flow velocity v at the water outlet in real time i,out (t), the sewage turbidity sensor is used to monitor the turbidity T′ of the sewage discharged from the outlet in real time i,out (t). Figure 7-Figure 8 The number of filter tanks 2 shown in the figure is only part of the filter tanks. According to the flow rate per unit time required for filtration, multiple filter tanks 2 can be arranged at equal intervals horizontally along the x-axis and longitudinally along the y-axis. Every two filter tanks 2 correspond to each other along the front-to-back direction of the y-axis and are connected to the two air outlets of the same air inlet diverter pipe 3, and then connected to the same longitudinal air diverter pipe 41. The water inlets 21 of the multiple filter tanks 2 arranged at equal intervals along the x-axis are connected to the same water inlet diverter pipe, and the water inlet diverter pipe is connected to the sewage discharge end to be filtered. The backwash sewage outlet 22 is also connected to the same sewage outlet pipe, and then finally discharged out of the system and flows into the same backwash sewage collection pool. The lower part of the water outlet 23 of each filter tank is finally recovered to the same filtered recovered water collection pool through the setting of a pipeline for use.

[0123] The multi-layer media filter layer includes the first layer of filter material, the second layer of filter material and the third layer of filter material from top to bottom. The first layer of filter material, the second layer of filter material and the third layer of filter material are anthracite (used to intercept large particles and adsorb part of suspended matter), manganese sand (further remove iron and manganese elements in sewage through the principle of chemical and physical dual adsorption) and quartz sand (provide support for the first layer of filter material and the second layer of filter material, and further filter and adsorb suspended matter that is not intercepted and adsorbed by anthracite and manganese sand).

[0124] The particle size of the anthracite used is 0.8mm-2.0mm, the porosity of the anthracite used is 0.45-0.55, and the height of the first layer of filter material is 0.3m-0.5m;

[0125] The particle size of the manganese sand used is 1.0 mm to 2.0 mm, the porosity of the manganese sand used is 0.40 to 0.45, and the height of the second layer of filter material is 0.2 m to 0.4 m;

[0126] The particle size of the quartz sand used is 2.0 mm to 4.0 mm, the porosity of the quartz sand used is 0.38 to 0.42, and the height of the third layer of filter material is 0.5 mm to 0.7 mm.

[0127] Therefore, when using the above-mentioned multi-layer medium filter layer composed of filter materials of different types and parameters, when the filter material coefficient k is calculated in step 33) of the sewage filtration process using the control system of the present invention, the permeability absorption coefficient of the first layer of filter material is first calculated based on the various parameters of the anthracite. The permeability absorption coefficients k2 and k3 of the second and third filter materials can also be calculated in the same way;

[0128] H1, H2 and H3 are pre-arranged in the filter tank in different situations. The height of the first filter layer is within the range of 0.3m to 0.5m, the height of the second filter layer is within the range of 0.2 to 0.4m, and the height of the first filter layer is within the range of 0.5 to 0.7m. The calculation is performed and the filter coefficient k is finally obtained.

[0129] At this time, the pressure difference ΔP between the water inlet 21 and the water outlet 23 is i When calculating, the pressure loss P loss The friction coefficient μ in: Among them, μ1, μ2 and μ3 are the friction coefficients when anthracite, manganese sand and quartz sand are used to filter sewage separately. According to the empirical value or the table, μ1 = 0.26, μ2 = 0.375, and μ3 = 0.32. This combination can effectively remove pollutants of different particle sizes, ensure the filtration efficiency and service life of the system, and adjust it within the above range according to the actual drainage quality requirements.

[0130] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A multi-stage water treatment, filtration and purification method capable of backwashing, wherein the industrial wastewater is filtered, collected and reused, and characterized in that: The following steps are involved: Step 1), controlling the water inlet (21) on the filter tank (2) of each filter assembly unit to open, and controlling the exhaust port (25) on the upper part of the filter tank (2) of each filter assembly unit to open, so that the gas in the filter tank (2) is discharged from the tank through the exhaust port (25), and when the value of the exhaust pressure gauge (251) drops to a specified value, the exhaust port (25) is closed; Step 2), opening the water outlet (23) at the bottom of each filter tank (2), so that each filter tank (23) enters a state of filtering sewage; The sewage to be filtered enters from the water inlet (21), is filtered through the multiple layers of medium filter layers from top to bottom, and is finally discharged through the water outlet (23); Step 3), monitoring the initial turbidity in the tank body and monitoring the turbidity of the sewage discharged from the outlet, the water flow rate of the water inlet and the water flow rate of the water outlet in real time, and remotely controlling the single chip microcomputer (6) to control the pressure difference of each filter tank (2) within the pressure difference threshold, so as to ensure that the filtered water discharged from the outlet (23) meets the turbidity requirements of the drainage standard; Step 4), when the pressure difference in a certain filter tank exceeds the pressure difference threshold, the corresponding filter tank (2) is backwashed; Step 5) After the backwashing is completed, the steps 2) to 3) are repeated again to achieve continuous forward filtration of the industrial wastewater.

2. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 1, characterized in that: In the step 3), the remote control microcontroller (6) controls the pressure difference of each filter tank (2) to be within the pressure difference threshold, thereby ensuring that the filtered water discharged from the water outlet (23) meets the turbidity requirements of the drainage standard, including the following steps: Step 31), calculate the total flow Q of the water inlet under normal filtration in step 2) i,in and the total outflow Q i,out : Among them, d i,in is the diameter of the water inlet (21) of the i-th filter tank, d i,out is the diameter of the water outlet (23) of the i-th filter tank; Step 32), calculate the pressure difference ΔP between the water inlet (21) and the water outlet (23) of the i-th filter tank (2) i : Among them, P loss is the pressure loss, g is the gravitational acceleration, and ρ is the density of the filter material of the multi-layer medium filter layer in the filter tank (2); Step 33), construct the optimal inlet flow rate and the optimal outlet flow rate within the turbidity range allowed by the drainage standard to solve the equation: Among them, T i,in is the initial turbidity in the i-th filter tank monitored in step 3), T i,out is the turbidity of the water outlet of the i-th filter tank; H a is the height of the multi-layer medium filter layer in the filter tank (2), k is the filter material coefficient, C1 is the first weight coefficient, C1=0.2, C2 is the second weight coefficient, C2=0.5; T out,max is the maximum turbidity threshold; Step 34), using the LM method to solve the equation constructed in step 33), to obtain the optimal water inlet flow rate of the i-th filter tank and optimal outlet flow rate The remote control single chip computer (6) controls the water inlet speed of the water inlet of the i-th filter tank to be the optimal water inlet flow rate. Control the water outlet speed to the optimal outlet flow rate This ensures that the filtered sewage obtained at the outlet meets the turbidity requirements of the drainage standards.

3. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 2, characterized in that: The calculation formula of the filter material coefficient k in step S33) is as follows: Among them, k n is the permeability coefficient of the nth layer of filter material, H n is the thickness of the nth layer of filter material; Among them, p n is the average particle size of the nth layer of filter material, ε n is the porosity of the nth layer of filter material.

4. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 2, characterized in that: The P in step S32) loss The calculation formula is as follows: Among them, μ is the friction coefficient between sewage and filter material, and D is the diameter of the circular cross section of the filter tank.

5. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 2, characterized in that: The step 34) uses the LM method to solve the equation constructed in the step 33), including: Step 341), construct the water flow velocity v of the water inlet of the i-th filter tank i,in (t) and the water velocity v at the outlet i,out (t) is the nonlinear equation system F(v i )=[f1(v i ),f2(v i ),....,f M (v i )] T , where f m (v i ) is the nonlinear equation system F(v i ) in the mth nonlinear equation, m=1,2,…,M; v i is the independent variable vector in the nonlinear equation system, v i =[v i,in (t),v i,out (t)] T , f m (v i ) = f m (v i,in (t),v i,out (t)); Step 342), calculate the first-order derivative and second-order derivative of the m-th nonlinear equation with respect to all independent variables, and form the Jacobian ratio matrix J(v i ) and the Hessian matrix He(v i ): Step 343), calculate the nonlinear equation system F(v i )’s gradient function G(v i ): G(v i )=J T (v i )·F(v i );J T (v i ) is the Jacobian ratio matrix J(v i )’s transposed matrix; Step 344), calculate the independent variable vector v i The update result of the q+1th generation is: in, is the update result of the qth generation of the independent variable; q is the damping coefficient for continuing to update the qth generation update result; I is a 2×2 identity matrix; Step 345), determine whether the obtained q+1th generation update result makes the nonlinear equation system F(v i ) decreases, that is, to judge whether Is it less than like Then reduce the damping coefficient λ for the update result of the q+1th generation q+1 , so that q+1 =λ q / 10; if Increase the damping absorption λ of the update result of the q+1th generation q+1 , so that q+1 =10λ q ; Step 346), after repeating steps 342) to 345) for Q generations, determine the nonlinear equation system of the Qth generation The gradient function The norm of Whether the convergence is less than the stop iteration threshold θ, the stop iteration threshold θ = 0.8×10 -6 ~1×10 -6 ; If so, stop the iteration and output the independent variable vector of the Qth generation The elements in and As the optimal inlet flow rate of the i-th filter tank and optimal outlet flow rate Otherwise, continue to repeat steps 342)-345).

6. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 2, characterized in that: In step 4), when the pressure difference in a filter tank exceeds the pressure difference threshold ΔP thr When the optimal water inlet flow rate calculated in step 34) is and optimal outlet flow rate Bring it into the step 32) to calculate the pressure difference ΔP between the water inlet (21) and the water outlet (23) of the i-th filter tank (2) i In the calculation formula, the calculated ΔP i >ΔP thr The pressure difference threshold ΔP thr It is 0.8bar.

7. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 1, characterized in that: The backwashing of step 4) comprises the following steps: Step 41), control the water inlet (21) of the corresponding filter tank (2) to be fully closed, control the water outlet (23) of the corresponding filter tank to be changed from a closed state to a partially open state, and then control the backwashing outlet (22) of the corresponding filter tank (2) to be opened, and maintain the single water flushing time period T1, T1 = 2min to 4min; Step 42), continue to keep the water inlet (21) of the corresponding filter tank (2) closed, adjust the water outlet (23) of each filter tank to a fully closed state, and simultaneously control the drive motor (51), the butterfly valve (53), the ball valve assembly (4), and the top of the filter tank (2) to be backwashed and the diversion port (31) of the air inlet diversion pipe (3) to be opened, and perform single-gas flushing on the filter tank (2) to be backwashed in the corresponding filter combination unit, and at this time continue to keep the backwashing sewage outlet (22) open; keep the single-gas flushing time period T2, T2 = 3min to 6min; Step 43), control the ball valve assembly (4) and the corresponding diversion port (31) to continue to open, control the backwash drain port (22) to be in an open state, and the water outlet (23) to be in a partially open state, and control the cleaning cycle of the air-water double flushing stage to be T3, T3 = 5min to 8min; Step 44), control the water outlet (23) of the corresponding filter tank (2) to be completely closed again, control the diversion port (31) on the corresponding tank body to be closed, and then no gas enters the corresponding tank body, control the water outlet (23) to be opened again to a partially open state, and control the duration of the secondary single water flushing cycle to be T4, T4 = 2min to 5min; Step 45), control the backwash drain outlet (22) to be adjusted from the open state to the closed state, then control the water outlet (23) to be in the fully open state, control the water inlet (21) to be in the fully open state, and enter the normal filtering state of step 2).

8. The multi-stage water treatment, filtration and purification method capable of backwashing according to claim 3, characterized in that: The partially open state of the water outlet (23) in step 41), step 43) and step 44) is to control the water outlet (23) to be opened to 10% to 20% of the fully open state.

9. A backwashable multi-stage water treatment filtration and purification system using the method as claimed in any one of claims 1 to 8, the system comprising a bottom frame (1), a plurality of rows of filter parallel units arranged in sequence from back to front arranged on the bottom frame (1), each filter parallel unit comprising two parallel arranged filter combination units, each filter combination unit being a plurality of filter tanks (2) arranged in sequence at equal intervals from left to right, each filter tank (2) being provided with a feed inlet (20) on the upper side thereof; characterized in that: Each filter tank (2) comprises a water inlet (21) arranged at the upper rear side of the tank body, a backwashing outlet (22) at the upper rear side of the tank body, a water outlet (23) at the lower part of the tank body, an air inlet (24) and an air outlet (25) at the upper part of the tank body, and each filter tank (2) is provided with a plurality of medium filter layers; two corresponding filter tanks at the front and rear of each parallel filtering unit are connected to the same ball valve assembly (4) via an air inlet manifold (3), and each ball valve assembly (4) is arranged on the same longitudinal manifold (41), and the air outlet of the longitudinal manifold (41) is communicated with the air inlet of the air inlet manifold (3), and the air inlet manifold (3) is connected to the air inlet of the air inlet manifold (3). The two air outlets are respectively connected to the air inlets (24) on the upper parts of the two corresponding filter tanks (2) at the front and rear of the corresponding filter combination unit; the bottom frame (1) is also provided with a blower (5) and a drive motor (51) arranged on the right side thereof; the blower (5) is connected to a transverse air supply pipe (52); a plurality of longitudinal air distribution pipes (41) are connected to the transverse air supply pipe (52); a butterfly valve (53) is provided at the connection between the transverse air supply pipe (52) and the blower (5); each exhaust port (25) is connected to a horizontal exhaust pipe; each horizontal exhaust pipe is provided with an exhaust valve (251) and an exhaust pressure gauge (252) in sequence; The system further comprises a remote control single chip microcomputer (6) arranged on the bottom frame (1), a first water flow velocity monitoring sensor arranged at the water inlet (21) of each filter tank (2), a second water flow velocity monitoring sensor and a sewage turbidity sensor arranged at the outlet of each filter tank (2); the remote control single chip microcomputer is used to control the system to execute steps 1) to 5) of the method as claimed in any one of claims 1 to 8.

10. The backwashable multi-stage water treatment, filtration and purification system according to claim 9, characterized in that: The multi-layer media filter layer includes, from top to bottom, a first filter material layer of 0.3m to 0.5m in height, a second filter material layer of 0.2m to 0.4m in height, and a third filter material layer of 0.5mm to 0.7mm in height, wherein the first filter material layer, the second filter material layer, and the third filter material layer are anthracite, manganese sand, and quartz sand, respectively; The particle size and porosity of the anthracite used are 0.8mm~2.0mm and 0.45~0.55 respectively; the particle size and porosity of the manganese sand used are 1.0mm~2.0mm and 0.40~0.45 respectively, and the height of the third layer of filter material is; the particle size and porosity of the quartz sand used are 2.0mm~4.0mm and 0.38~0.42 respectively.

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