A method and system for cleaning reverse osmosis membranes for printing and dyeing wastewater based on complexation chelation

Abstract

The present application relates to the technical field of permeation membrane cleaning, and specifically discloses a dyeing wastewater reverse osmosis membrane cleaning method and system based on complex chelation, which comprises: positively flushing the membrane assembly and monitoring the initial water-inlet / concentrated water pressure difference, determining the flow channel blockage level according to the pressure difference ratio; injecting an alkaline complex chelating cleaning agent into the cleaning circulation loop, and cyclically cleaning in a low-frequency / high-frequency alternating mode, and when the continuous rise reaches a preset number of times, performing frequency reduction and reverse hydraulic impact through bypass reverse; after emptying the alkali solution, injecting an acidic complex chelating cleaning agent, and switching the flushing water to perform positive and negative bidirectional gradient flushing; under constant circulation flow, monitoring the pressure difference absolute value, pressure difference fluctuation amplitude and water production flow recovery rate, and when the pressure difference is reduced to within a preset operating pressure difference, the pressure difference fluctuation amplitude is lower than a preset fluctuation threshold, and the water production flow is recovered to more than a preset proportion of the initial value, the cleaning endpoint is determined. The present application improves the cleaning efficiency of the permeation membrane and reduces the risk of membrane damage.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane cleaning technology, and in particular to a method and system for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation. Background Technology

[0002] Reverse osmosis technology is one of the core processes for the deep treatment and high-quality reuse of dyeing and printing wastewater. In a dual-membrane system combining ultrafiltration and reverse osmosis for dyeing and printing wastewater reuse, the reverse osmosis membrane can become contaminated by biofilm or organic matter buildup, leading to negative impacts such as decreased permeate flux and reduced permeate quality. Dyeing and printing wastewater contains azo dyes, auxiliaries, sizing agents, surfactants, and metal ions such as calcium, magnesium, and iron. During operation, the reverse osmosis membrane often faces complex fouling from organic matter, microorganisms, and inorganic salt scale. Membrane fouling increases membrane filtration resistance, decreases membrane flux, reduces desalination rate, increases pressure differential, and shortens membrane lifespan.

[0003] In existing technologies, a step-by-step chemical cleaning method is typically used to clean fouled reverse osmosis membranes. For example, Chinese invention patent application CN106630011A discloses a combined cleaning method for a reverse osmosis system used for wastewater reuse in dyeing and printing industries. This method employs three cleaning agents—a non-oxidizing bactericide, an organic contaminant cleaner, and a descaling agent—for step-by-step cleaning. The cleaning solution contains chelating agents such as citric acid, tetrasodium EDTA, and HEDP. Furthermore, Chinese invention patent application CN106237864A discloses a reverse osmosis membrane cleaning agent and its application method, employing a step-by-step cleaning method using alkaline and acidic cleaning agents. Chinese invention patent application CN115672044A discloses an alkaline cleaning agent for cleaning organic contaminants from DTRO membranes, which incorporates a compounded chelating dispersant.

[0004] The above-mentioned technical solutions still have the following shortcomings: On the one hand, the chelating agents used in the existing technologies are mostly single varieties or simple binary combinations, lacking molecular weight gradient compounding designs based on the characteristic pollutants of dyeing and printing wastewater, making it difficult to achieve synergistic and efficient removal of organic-inorganic composite pollutants; on the other hand, existing cleaning methods generally ignore the clogging problem of reverse osmosis membrane channel screens, lacking effective means to remove deep-seated blockages such as short fibers and slurry colloids stuck at the intersection of the inlet screens, resulting in persistently high inter-section pressure differentials after cleaning; at the same time, existing technologies usually adopt a step-by-step cleaning process with constant parameters, during which the pollutants stripped off are prone to secondary bridging and clogging at the channel screens, and existing solutions cannot dynamically adjust the cleaning strategy according to pressure differential changes, and the cleaning endpoint also relies entirely on fixed time or experience judgment, lacking an adaptive determination mechanism based on pressure differential stability and permeate flow recovery; in addition, long-term use of strong acids and alkalis for chemical cleaning can easily cause irreversible damage to the membrane material, shortening the membrane's service life.

[0005] Therefore, there is an urgent need for a reverse osmosis membrane cleaning method and system that addresses the complex pollution characteristics of dyeing and printing wastewater, takes into account both membrane surface cleaning and flow channel dredging, and has the ability to adaptively adjust pressure difference feedback. Summary of the Invention

[0006] This invention provides a method and system for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation, comprising: D1: The membrane module is flushed with flushing water in the forward direction. The initial feed water-concentrate pressure difference of the membrane module is monitored and recorded in real time. The blockage level of the flow channel in the membrane module is determined based on the comparison between the initial feed water-concentrate pressure difference and the normal operating pressure difference of the membrane module. D2: Inject an alkaline compound chelating cleaning agent into the cleaning circulation loop of the membrane module, and supply the cleaning circulation fluid to the membrane module in an alternating low-frequency and high-frequency output mode to clear the flow channels of the membrane module. D3: Drain the alkaline cleaning circulating liquid from D2, inject an acidic compound chelating cleaning agent into the cleaning circulating loop to clean the membrane module, monitor the concentration of suspended particulate matter in the return cleaning liquid in real time, and end D3 when the concentration of suspended particulate matter shows a continuous downward trend. D4: Drain the acidic cleaning circulating fluid from D3 and switch to the flushing water to perform bidirectional gradient flushing of the membrane module. D5: After bidirectional gradient flushing, monitor the feed water-concentrate pressure difference and current permeate flow rate of the membrane module in real time. When the feed water-concentrate pressure difference decreases to within the preset operating pressure difference, and under constant circulation flow conditions, the fluctuation range of the feed water-concentrate pressure difference is lower than the preset fluctuation threshold, and the current permeate flow rate recovers to above the preset proportion of the initial permeate flow rate, the membrane module is determined to be cleaned.

[0008] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention targets the complex pollution characteristics of dyeing and printing wastewater. Through a gradient combination of macromolecular dispersants, medium-molecular targeted chelating agents, and small-molecular penetrating stripping agents, it achieves the synergistic removal of organic-inorganic complex pollutants. Polyaspartic acid and hydrolyzed polymaleic anhydride disperse the stripping particles and inhibit their secondary aggregation. Diethylenetriaminepentaacetic acid and sodium gluconate complex calcium, magnesium, and iron ions. Iminodisuccinic acid penetrates into the interface between the pollutants and the membrane surface, destroying the adhesion bonds. The synergistic effect of these three agents significantly improves the removal efficiency of complex pollutants. This invention monitors the number of consecutive increases in the pressure difference between the influent and concentrate during alkaline cleaning. When there are five consecutive increases, it is determined that the stripped material has caused secondary bridging and blockage at the flow channel mesh. Then, a closed-loop control of frequency reduction, backflushing, and recovery is executed, which effectively avoids secondary accumulation of stripped material at the intersection of the flow channel mesh. At the same time, the invention uses the following triple endpoint determination conditions: the absolute value of the pressure difference recovers to within the normal operating pressure difference, the fluctuation range of the pressure difference does not exceed 3% under constant flow conditions, and the product water flow rate recovers to more than 95% of the initial value. This overcomes the problems of over-cleaning or incomplete cleaning caused by fixed-time cleaning mode.

[0009] 2. This invention employs an alkaline compound chelating cleaning agent with a pH of 10.5 to 11.5 and an acidic compound chelating cleaning agent with a pH of 3.8 to 4.2. Throughout the process, organic weak acids and bases are used instead of traditional strong acids and bases such as sodium hydroxide and hydrochloric acid. Combined with the corrosion-inhibiting effect of hydroxyethylenediamine diphosphonic acid, this reduces the risk of irreversible damage to membrane materials caused by chemical cleaning and extends the service life of the membrane module. This invention utilizes the coordinated operation of a variable frequency high-pressure pump with alternating low-frequency and high-frequency outputs in the alkaline washing pressure feedback module and the reverse hydraulic impact of an independent backwash pump. Combined with a physical flushing process in the bidirectional flushing module, which alternates between forward flushing, reverse flushing, and pressure relief, this effectively removes short fibers and colloidal contaminants embedded deep within the cross-sections of the flow channel mesh, restoring the inter-section pressure difference of the system to normal operating levels after cleaning. This invention integrates the traditional multi-step process of sterilization, alkaline washing, acid washing, and flushing into a five-module series process: diagnostic slag discharge, alkaline washing pressure feedback, acidic complex-breaking washing, bidirectional flushing, and endpoint self-adaptation. This significantly shortens the total cleaning time and greatly reduces the amount of cleaning waste liquid generated. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 A schematic flowchart of a reverse osmosis membrane cleaning method for dyeing and printing wastewater based on compound chelation is provided in an embodiment of the present invention. Figure 2This is a functional block diagram of a reverse osmosis membrane cleaning system for dyeing and printing wastewater based on compound chelation, provided in an embodiment of the present invention.

[0012] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0013] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0014] This application provides a method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation. The executing entity of this method includes, but is not limited to, at least one of the following electronic devices that can be configured to execute the method provided in this application: a server, a terminal, etc. In other words, the method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation can be executed by software or hardware installed on a terminal device or a server device. The server includes, but is not limited to, a single server, a server cluster, a cloud server, or a cloud server cluster. The server can be an independent server or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, domain name services, security services, content delivery networks (CDN), and big data and artificial intelligence platforms.

[0015] Reference Figure 1 The diagram shown is a schematic flow chart of a reverse osmosis membrane cleaning method for dyeing and printing wastewater based on compound chelation, according to an embodiment of the present invention. In this embodiment, the method for cleaning reverse osmosis membranes for dyeing and printing wastewater based on compound chelation includes: D1: The membrane module is flushed with flushing water in the forward direction. The initial feed water-concentrate pressure difference of the membrane module is monitored and recorded in real time. The blockage level of the flow channel in the membrane module is determined based on the comparison between the initial feed water-concentrate pressure difference and the normal operating pressure difference of the membrane module. In this embodiment of the invention, the flushing water, after precision filtration, is pumped from the cleaning water tank to the inlet of the membrane module by a cleaning pump. The permeate outlet valve of the membrane module remains fully closed, while the concentrate outlet valve remains fully open. The flushing water flows through the interior of the membrane module under low pressure and high flow conditions, passing through the flow channel mesh from the inlet side of the membrane module and carrying loose contaminants from the membrane surface out of the concentrate outlet. During the forward flushing process, a first pressure transmitter installed at the inlet of the membrane module collects the inlet-side pressure signal in real time, and a second pressure transmitter installed at the concentrate outlet of the membrane module collects the concentrate-side pressure signal in real time. The initial inlet-concentrate pressure difference is obtained by subtracting the inlet-side pressure value from the concentrate-side pressure value, and this initial inlet-concentrate pressure difference is recorded in the storage unit of the control system. The normal operating pressure differential of the membrane module is the average feed-concentrate pressure differential during the historical normal operation period when the membrane module is in a stable water production state. This average value is retrieved from the membrane module operation log. The operation log records all feed-concentrate pressure differential data for the first 24 hours after the membrane module is put into operation after cleaning, when the permeate flow rate and desalination rate are both within the rated range. The baseline pressure differential is obtained by adding these data together and dividing by the total number of data. The pressure differential ratio is obtained by dividing the initial feed-concentrate pressure differential by the baseline pressure differential.

[0016] A pressure differential ratio within the first preset range is considered mild clogging, with a lower limit of 1.2 and an upper limit of 1.2. A pressure differential ratio within the second preset range is considered moderate clogging, with a lower limit of 1.2 and an upper limit of 1.5. A pressure differential ratio within the third preset range is considered severe clogging, with a lower limit of 1.5 and an upper limit of 1.5. A pressure differential ratio of zero indicates no pressure difference between the feed water and concentrate sides of the membrane module. This occurs when the membrane module is not flowing water or the membrane element is completely ruptured, and is not within the normal operating conditions covered by the clogging assessment. Therefore, the lower limit of the pressure differential ratio for mild clogging is a value greater than zero. The endpoints of the first, second, and third preset ranges, i.e., 1.2 and 1.5, are derived from statistical analysis of the feed water-concentrate pressure differential data of the same model of reverse osmosis membrane module in a dyeing and printing wastewater reuse system over a cumulative operating time of one thousand hours.

[0017] In the dyeing and printing wastewater reuse system, the pressure difference between the feed water and concentrate of the reverse osmosis membrane module gradually increases with the extension of the operating time after initial operation following cleaning. The rate of increase in pressure difference is directly related to the concentration and deposition rate of pollutants such as residual dyes, auxiliaries, sizing agents, calcium and magnesium ions, and iron ions in the dyeing and printing wastewater. The specific statistical analysis process is as follows: ten reverse osmosis membrane modules of the same model and batch are selected as statistical samples. Each membrane module treats dyeing and printing wastewater from the same source and operates under the same conditions. From the initial operation of each membrane module after cleaning... From the start of operation, the inlet pressure and concentrate outlet pressure of each membrane module are collected every 24 hours, and the feed-concentrate pressure difference is calculated. Simultaneously, the permeate flow rate and desalination rate of each membrane module are collected. Collection continues until the permeate flow rate of each membrane module drops to 80% of the initial permeate flow rate or the desalination rate drops to 90% of the initial desalination rate, at which point collection stops. The feed-concentrate pressure difference data obtained each time are compared with the initial feed-concentrate pressure difference of the corresponding membrane module when it is first put into operation after cleaning. The ratios are then calculated to obtain the pressure difference at each time point. The differential pressure ratio data corresponding to the sampling points were used. All sampling times were divided into three stages according to the degree of permeate flow rate decline. The first stage was the period when the permeate flow rate decreased by no more than 5%, corresponding to the state where only a small amount of loose contaminants adhered to the membrane surface and flow channels. The maximum value of all differential pressure ratio data in this stage was 1.2. The second stage was the period when the permeate flow rate decreased by more than 5% but not more than 15%, corresponding to the state where there were short fibers and colloidal contaminants embedded at the intersections of the flow channel mesh but no continuous blockage area had yet formed. The minimum value of all differential pressure ratio data in this stage was 1.2 and the maximum value was 1.5. The third stage was the period when the permeate flow rate decreased by more than 15%, corresponding to the state where multiple intersections of the flow channel mesh had been filled with contaminants to form a continuous blockage area. The minimum value of all differential pressure ratio data in this stage was 1.5. Based on the distribution range of the differential pressure ratio data corresponding to the above three stages, 1.2 and 1.5 were determined as the boundary values ​​between mild and moderate blockage and between moderate and severe blockage, respectively.

[0018] When the differential pressure ratio is greater than zero and less than or equal to 1.2, it indicates that the current membrane module's flow channel blockage is in a light state with loose contaminant adhesion. In this case, forward flushing with flushing water can remove most of the deposits. When the differential pressure ratio is greater than 1.2 and less than or equal to 1.5, it indicates that the current membrane module's flow channel blockage is in a moderate state with fiber lint and colloidal contaminant entrapment. In this case, it is necessary to inject an alkaline compound chelating cleaning agent and perform deep cleaning in conjunction with differential pressure feedback control. When the differential pressure ratio is greater than 1.5, it indicates that the current membrane module's flow channel blockage is in a severe state with contaminant bridging and filling forming a continuous blockage area. In this case, it is necessary to directly start the alkaline compound chelating cleaning agent injection procedure.

[0019] D2: Inject an alkaline compound chelating cleaning agent into the cleaning circulation loop of the membrane module, and supply the cleaning circulation fluid to the membrane module in an alternating low-frequency and high-frequency output mode to clear the flow channels of the membrane module. In this embodiment of the invention, the variable frequency high-pressure pump of the membrane module is started to supply alkaline compound chelating cleaning circulating fluid to the membrane module at a low frequency output. The cleaning circulating fluid flows out of the cleaning water tank, is pressurized by the variable frequency high-pressure pump, enters the inlet of the membrane module, passes through the flow channel screen, and is discharged from the concentrate outlet of the membrane module and returns to the cleaning water tank through the return pipeline, forming a positive circulation flow. The low frequency output frequency corresponds to the operation state of the variable frequency high-pressure pump at a low speed. In this state, the cleaning circulating fluid flows through the inside of the membrane module at a low flow rate and pressure, allowing the cleaning circulating fluid to flow slowly on the membrane surface and the surface of the flow channel screen and fully wet the pollutant layer. After a preset first duration, the variable frequency high-pressure pump is switched to a high frequency output frequency, which corresponds to the operation state of the variable frequency high-pressure pump at a higher speed. In this state, the flow rate and pressure of the cleaning circulating fluid increase sharply, and the hydraulic shear force on the inlet side of the membrane module increases accordingly. The high-speed flowing cleaning circulating fluid washes the membrane surface and the surface of the flow channel screen, causing the softened pollutants to peel off from the membrane surface and the surface of the flow channel screen. After the second preset duration of high-frequency output, the variable frequency high-voltage pump will switch back to low-frequency output, completing one low-frequency-high-frequency alternation cycle.

[0020] The first duration was set to two minutes, and the second duration was set to thirty seconds. The two minutes of low-frequency immersion allowed the chelating agent to fully penetrate into the contaminant layer, while the thirty seconds of high-frequency rinsing was sufficient to peel off the softened contaminants without causing a large amount of material to fall off instantly and block the flow channel due to continuous high-speed rinsing. During the alternating low-frequency and high-frequency output, a first pressure transmitter installed at the inlet of the membrane module collected the inlet pressure in real time, and a second pressure transmitter installed at the concentrate outlet of the membrane module collected the concentrate outlet pressure in real time. The real-time inlet-concentrate pressure difference was obtained by subtracting the inlet pressure value and the concentrate outlet pressure value collected at the same time.

[0021] During the alternating low-frequency and high-frequency output process, real-time feedwater-concentrate pressure difference is continuously collected at preset sampling intervals to generate a pressure difference time series. The preset sampling interval is set to two seconds, meaning the current real-time feedwater-concentrate pressure difference is collected every two seconds. The pressure difference values ​​in the time series are arranged in chronological order of collection time, and each pressure difference value carries a corresponding time tag, recording the collection time corresponding to that pressure difference value. The pressure difference values ​​at adjacent time points in the time series are then interpolated to generate a pressure difference increment sequence between adjacent time points. The specific interpolation method is as follows: the real-time feedwater-concentrate pressure difference at the later collection time is subtracted from the real-time feedwater-concentrate pressure difference at the previous collection time. If the difference is positive, it indicates that the real-time feedwater-concentrate pressure difference is increasing; if the difference is negative, it indicates that the real-time feedwater-concentrate pressure difference is decreasing; if the difference is zero, it indicates that the real-time feedwater-concentrate pressure difference has not changed.

[0022] The differential pressure increment sequence between adjacent time points is analyzed, and positive differential pressure increments are identified and marked as rising increments. Continuous rising increments are counted to obtain the number of consecutive rises. When the number of consecutive rises reaches a preset threshold, the differential pressure change rate is considered to exceed the preset threshold. The preset threshold is set to five times, meaning that if the real-time influent-concentrate differential pressure shows an upward trend within five consecutive sampling periods, the differential pressure change rate is considered to exceed the preset threshold. Five consecutive rises indicate that the stripped contaminants are continuously accumulating at the flow channel screen, and the accumulation rate exceeds the rate at which the circulating liquid carries out the contaminants. The flow channel is gradually narrowing, and the flow resistance is continuously increasing. The preset threshold is based on statistical data of differential pressure fluctuations during the cleaning process of reverse osmosis membrane modules in a dyeing and printing wastewater reuse system. Statistics show that occasional differential pressure rises caused by measurement noise or hydraulic fluctuations usually do not exceed three consecutive rises, while four or more consecutive rises are highly correlated with the development of flow channel blockage. Therefore, five consecutive rises are determined as the safe threshold to exclude occasional fluctuations.

[0023] When the number of consecutive rises reaches a preset threshold, it indicates that the detached contaminants in the membrane module are undergoing secondary accumulation at the flow channel screen, and the accumulation is continuously increasing. At this point, the output frequency of the variable frequency high-pressure pump is reduced to a safe frequency, which is 60% of the current high-frequency output frequency. The purpose of reducing the output frequency is to reduce the forward circulation flow and forward water thrust, preventing more forward-flowing cleaning fluid from pushing the detached contaminants deeper into the flow channel screen and exacerbating blockage. Simultaneously, the membrane module's backwash bypass is activated. When the backwash bypass is activated, a switching command is sent to the electric three-way valve assembly installed on the membrane module's permeate outlet pipeline, causing the electric three-way valve assembly to disconnect the permeate outlet of the membrane module from the permeate collection pipeline.

[0024] While the electric three-way valve assembly disconnects the permeate outlet from the permeate collection pipeline, a start command is sent to the independent backwash pump. This causes the independent backwash pump to extract the cleaning circulating fluid from the cleaning tank and pressurize it to the backwash pressure. The backwash pressure is set to a value lower than the forward cleaning pressure. The forward cleaning pressure is the pressure supplied to the membrane module by the variable frequency high-pressure pump in high-frequency output mode. The backwash pressure is 30% of this forward cleaning pressure. Using a backwash pressure lower than the forward cleaning pressure is to avoid excessively high reverse injection pressure that could tear the bonding line between the membrane bag and the flow channel mesh. The pressurized cleaning circulating fluid is then introduced back into the membrane module from the permeate outlet side via the electric three-way valve assembly and the permeate outlet pipeline, creating a reverse flow between the outside of the membrane bag and the flow channel mesh, opposite to the forward flow direction. After entering the membrane module from the product water outlet side, the reverse flow passes through the flow channel mesh in the opposite direction to the forward flow. The hydraulic impact of the reverse flow acts on the pollutants embedded at the intersection of the flow channel mesh, causing the pollutants to loosen and fall off from the intersection of the mesh.

[0025] After the third duration of reverse flow, a stop command is sent to the independent backwash pump to stop its operation. Simultaneously, a reset command is sent to the electric three-way valve assembly to restore the connection between the permeate outlet and the permeate collection line. The third duration is set to 30 seconds. Thirty seconds of reverse hydraulic impact is sufficient to loosen the blockages at the mesh intersections, preventing secondary fouling caused by a large amount of sloughed material migrating back to the membrane surface due to prolonged reverse impact. After closing the backwash bypass, the output frequency of the variable frequency high-pressure pump is restored to its previous high-frequency output frequency, continuing the alternating low-frequency and high-frequency output until the real-time feed-concentrate pressure difference drops below the upper limit of the safe pressure difference. The upper limit of the safe pressure difference is set to 1.3 times the normal operating pressure difference of the membrane module. When the real-time feed-concentrate pressure difference drops below 1.3 times the normal operating pressure difference, it indicates that the contaminants accumulated at the flow channel mesh have been loosened by the reverse hydraulic impact and carried away by the forward circulating fluid, and the flow channel has returned to acceptable flow capacity. The 1.3 times safety differential pressure limit is set based on the differential pressure recovery data of the reverse osmosis membrane module in the dyeing and printing wastewater reuse system during the cleaning process. The statistics show that when the differential pressure drops to below 1.3 times the normal operating differential pressure, continued cleaning can still reduce the differential pressure further, but the rate of decrease is significantly slower. The time cost required for continued cleaning is disproportionate to the further recovery of the differential pressure. Therefore, 1.3 times the normal operating differential pressure is determined as the lower limit for judging that the flow channel has been fully cleared.

[0026] The alkaline compound chelating cleaning agent contains solutes including macromolecular dispersants, medium-molecular-weight targeted chelating agents, small-molecular-weight penetrating stripping agents, and nonionic surfactants. The macromolecular dispersants include polyaspartic acid and hydrolyzed polymaleic anhydride. These two macromolecules dissolve in the cleaning circulating fluid and adsorb onto the surface of the stripped contaminant particles. The steric hindrance effect of the macromolecular chains prevents the contaminant particles from approaching and agglomerating, keeping them dispersed within a size smaller than the gap between the flow channel mesh, allowing them to be carried out with the circulating fluid. The medium-molecular-weight targeted chelating agents include diethylenetriaminepentaacetic acid (DTA) and sodium gluconate. DTA has a strong complexing ability for ferric ions, while sodium gluconate has a complexing effect on calcium and magnesium ions. Together, they chelate metal ions on the membrane surface and flow channel mesh into the liquid phase. The small-molecular-weight penetrating stripping agent includes iminodisuccinic acid, whose molecular size is smaller than the macromolecular dispersants and medium-molecular-weight targeted chelating agents. It can penetrate into the interface region between the contaminant layer and the membrane surface and disrupt the adhesion bonds between the contaminants and the membrane surface. Nonionic surfactants contain alkyl glycosides, whose molecules have hydrophilic and hydrophobic groups. The hydrophobic groups combine with the hydrophobic portion of the dye molecules remaining in the dyeing and printing wastewater, while the hydrophilic groups extend into the aqueous phase, solubilizing and dispersing the dye molecules in the cleaning circulating liquid.

[0027] D3: Drain the alkaline cleaning circulating liquid from D2, inject an acidic compound chelating cleaning agent into the cleaning circulating loop to clean the membrane module, monitor the concentration of suspended particulate matter in the return cleaning liquid in real time, and end D3 when the concentration of suspended particulate matter shows a continuous downward trend. In this embodiment of the invention, when draining the alkaline cleaning circulating fluid D2 from the cleaning circulation loop, the drain valve at the bottom of the cleaning circulation loop is opened, and the circulation pump in the cleaning circulation loop is turned on to allow the alkaline cleaning circulating fluid to flow continuously in the loop. During the flow, the alkaline cleaning circulating fluid is discharged through the drain valve to the waste liquid collection container until no more alkaline cleaning circulating fluid flows out of the cleaning circulation loop, at which point the drain valve is closed. After draining the alkaline cleaning circulating fluid, an acidic compound chelating cleaning agent is injected into the cleaning circulation loop. The pH value of the acidic compound chelating cleaning agent is in the range of 3.8 to 4.2, and the solute of the acidic compound chelating cleaning agent includes an organic complex acid and a reducing stripping agent. The organic complex acid includes hydroxyethylenediamine diphosphonic acid and citric acid, and the reducing stripping agent includes L-ascorbic acid. Acidic compound chelating cleaning agents are used to clean residual pollutants on the membrane surface and flow channel mesh. These pollutants include dye-metal complexes formed by dye molecules and metal ions. Dye-metal complexes are complexes formed by azo dye molecules in dyeing and printing wastewater and metal ions such as ferric ions and calcium ions in the water through coordination bonds. These complexes are difficult to dissolve effectively under alkaline cleaning conditions, and they remain on the membrane surface and flow channel mesh, forming a dense black-brown fouling layer.

[0028] The variable frequency high-pressure pump is started to supply the acidic compound chelating cleaning agent from the cleaning water tank to the membrane module in a forward circulation manner. This allows the acidic compound chelating cleaning agent to flow inside the membrane module and contact the membrane surface and flow channel screen. The forward circulation method is the same as the flow path of the cleaning circulating liquid in step D2. That is, the acidic compound chelating cleaning agent flows out of the cleaning water tank, is pressurized by the variable frequency high-pressure pump, enters the inlet of the membrane module, passes through the flow channel screen, and is discharged from the concentrate outlet of the membrane module and returned to the cleaning water tank through the return pipeline. During the forward flow, the acidic compound chelating cleaning agent comes into contact with the dye-metal complex pollutant layer on the membrane surface and flow channel screen. The L-ascorbic acid in the acidic compound chelating cleaning agent has reducing properties. The olefinic group in its molecular structure can donate electrons to the ferric ions in the dye-metal complex, reducing the ferric ions to ferrous ions. After ferric ions are reduced to ferrous ions, the original coordination equilibrium between the ferric ions and the dye molecules is disrupted. The coordination bonds in the dye-metal complex break due to changes in electronic structure, and the dye-metal complex dissociates into free dye molecules, ferrous ions, and other metal ions. Hydroxyethylenediamine diphosphonic acid molecules contain multiple phosphonic acid groups, and citric acid molecules contain three carboxyl groups. Both organic complex acids ionize upon dissolution in an acidic compound chelating cleaning agent, releasing hydrogen ions and simultaneously providing phosphonate and citrate ions. The dissociated ferrous ions, calcium ions, and other metal ions coordinate with the coordinating atoms in the phosphonate and citrate ions, forming soluble metal chelates. These metal chelates dissolve in the acidic compound chelating cleaning agent and are carried out of the membrane module with the circulating flow.

[0029] During the circulating cleaning process with the acidic compound chelating cleaning agent, samples of the reflux cleaning solution were collected in real time. A sampling port was installed on the concentrate outlet pipe of the membrane module, located on the section between the concentrate outlet and the reflux pipe. Two milliliters of reflux cleaning solution were collected from the sampling port every ten seconds as a sample. The light scattering intensity of the reflux cleaning solution sample was measured to obtain the concentration of suspended particulate matter. Light scattering intensity was measured using a light scattering turbidimeter. The turbidimeter emitted a beam of near-infrared incident light with a wavelength of 860 nm towards the reflux cleaning solution sample. When the incident light passed through the sample and encountered suspended solid particles, it was scattered. A photodetector positioned at a 90-degree angle to the incident light direction on the light scattering turbidimeter received the scattered light signal and converted it into an electrical signal. This electrical signal was amplified and converted from analog to digital to obtain the scattered light intensity value. The concentration of suspended particulate matter is directly proportional to the intensity of scattered light. That is, the more suspended solid particles in the reflux cleaning fluid sample, the greater the proportion of incident light scattered, and the higher the intensity of scattered light received by the photodetector. The concentration of suspended particulate matter is obtained by multiplying the scattered light intensity by a preset conversion coefficient. This preset conversion coefficient is obtained through standard curve calibration. The calibration process is as follows: a series of standard samples with known suspended particulate matter concentrations are prepared, with concentrations of 0 mg / L, 10 mg / L, 20 mg / L, 50 mg / L, and 100 mg / L, respectively. The light scattering intensity of each standard sample is measured to obtain the corresponding scattered light intensity value. The known concentration value of each standard sample is divided by its corresponding scattered light intensity value to obtain the conversion factor for each standard sample. The conversion factors are summed and divided by the total number of standard samples to obtain the average conversion factor, which is the preset conversion coefficient. The suspended particulate matter concentration value of the reflux cleaning fluid sample collected at the current time is compared with the suspended particulate matter concentration value of the reflux cleaning fluid sample collected at the previous time. When the difference between the current concentration of suspended particulate matter and the current concentration of suspended particulate matter is positive, it indicates that the concentration of suspended particulate matter is decreasing; when the difference is negative, it indicates that the concentration of suspended particulate matter is increasing.

[0030] When three consecutive comparisons show a decrease in suspended particulate matter concentration, it is determined that the suspended particulate matter concentration is showing a continuous downward trend. The determination of three consecutive comparisons is based on experimental statistics of the suspended particulate matter concentration fluctuation characteristics of the reflux cleaning solution during the reverse osmosis membrane cleaning process of dyeing and printing wastewater: During the cleaning process after the injection of the acidic compound chelating cleaning agent, the suspended particulate matter concentration in the reflux cleaning solution does not change monotonically. Because the cleaning circulating solution continuously circulates between the membrane module and the cleaning water tank, solid particles detached from the membrane surface gradually accumulate in the cleaning water tank. The accumulated particles in the cleaning water tank, after being pumped back to the membrane module, may cause instantaneous fluctuations in the particulate matter concentration in the reflux water sample. A single decrease in concentration may be due to the dilution effect during circulation or sampling bias. Random fluctuations caused by flow fluctuations are not true signals of cleaning progress. Statistical analysis of suspended particulate matter concentration change curves during the reverse osmosis membrane cleaning process of multiple sets of dyeing and printing wastewater showed that a true cleaning progress signal is manifested by two or more consecutive concentration decreases, while random concentration decreases caused by flow fluctuations usually occur only once, and the concentration values ​​at subsequent sampling points will rebound. Three consecutive decreases indicate that the total amount of solid particles stripped from the membrane surface into the liquid phase is continuously decreasing, meaning that the strippable contaminants remaining on the membrane surface and flow channel mesh have been largely removed. Therefore, three consecutive decreases are determined as the safe number of times to distinguish between random fluctuations and true cleaning progress. When the suspended particulate matter concentration is determined to show a continuous downward trend, step D3 ends.

[0031] D4: Drain the acidic cleaning circulating fluid from D3 and switch to the flushing water to perform bidirectional gradient flushing of the membrane module. In this embodiment of the invention, when draining the acidic cleaning circulating fluid in the cleaning circulation loop, the drain valve at the bottom of the cleaning circulation loop is opened to allow the acidic cleaning circulating fluid to be discharged into the waste liquid collection container until no more acidic cleaning circulating fluid flows out of the drain outlet, at which point the drain valve is closed. After draining the acidic cleaning circulating fluid, the flushing water supply pipeline is switched to the cleaning circulation loop. One end of the flushing water supply pipeline is connected to the flushing water tank, which stores pre-filtered water as flushing water. The other end of the flushing water supply pipeline is connected to the inlet of the cleaning circulation loop. The switching operation is achieved by opening the switching valve on the flushing water supply pipeline. After the switching valve is opened, the flushing water flows from the flushing water tank into the cleaning circulation loop. Flushing water is supplied to the membrane module at a forward flushing pressure and a forward flushing flow rate. The forward flushing pressure is set to 50% of the normal water production operating pressure of the membrane module, and the forward flushing flow rate is set to within the range of 0.8 to 1.2 times the rated water production flow rate of the membrane module. Rinse water flows into the membrane module from the inlet, passes through the flow channel screen, and exits from the concentrate outlet. During its flow through the flow channel screen, the rinsing water carries away residual acidic cleaning solution and loosened solid particles from the membrane module. The forward rinsing lasts for a fourth duration, set at five minutes. The reason for this five-minute duration is that after the acidic cleaning in step D3, acidic compound chelating cleaning agent and solid particles detached from the membrane surface remain in the flow channels of the reverse osmosis membrane module used for dyeing and printing wastewater. Five minutes of forward rinsing is sufficient for the rinsing water to circulate within the membrane module for three to five complete cycles. Each complete cycle refers to the flow of rinsing water from the inlet to the concentrate outlet. Three to five complete cycles dilute the concentration of residual acidic cleaning solution in the flow channels to below 5% of its original concentration, while simultaneously carrying away suspended solid particles from the membrane module. After the five-minute forward rinsing is completed, the rinsing water supply valve at the membrane module inlet is closed, stopping the forward rinsing process.

[0032] Initiate the backwash bypass, injecting backwash water from the permeate outlet side of the membrane module at the backwash pressure and flow rate. The backwash pressure is set to 40% of the forward flush pressure, and the backwash flow rate is set to 25% to 35% of the membrane module's rated permeate flow rate. The reason for the lower backwash pressure compared to the forward flush pressure is that the bonding lines between the membrane bags and the spacers in the reverse osmosis membrane module can only withstand limited reverse pressure. Excessive reverse pressure can cause the bonding lines between the membrane bags and the spacers to tear, resulting in irreversible damage to the membrane module. The 40% forward flush pressure has been experimentally verified to be a balanced value that provides sufficient reverse hydraulic impact to loosen blockages at the spacer intersections without exceeding the safe tolerance range of the bonding lines.

[0033] When the backwash bypass is started, a switching command is sent to the electric three-way valve assembly installed on the permeate outlet pipeline of the membrane module, so that the electric three-way valve assembly cuts off the connection between the permeate outlet of the membrane module and the permeate collection pipeline. A start command is sent to the independent backwash pump, so that the independent backwash pump draws the flushing water from the flushing water tank and pressurizes it to the backwash pressure. The pressurized flushing water is then introduced into the membrane module from the permeate outlet side of the membrane module through the electric three-way valve assembly and the permeate outlet pipeline, so that the flushing water forms a flow opposite to the forward flow direction inside the membrane module.

[0034] After the backflowing flushing water enters the membrane module from the permeate outlet side, it flows through the channel mesh in the opposite direction to the forward flow. The hydraulic impact of the reverse flow acts on the short fibers and colloidal contaminants embedded deep in the intersections of the channel mesh, causing the contaminants to loosen and detach from the mesh intersections. The backwash lasts for a fifth duration, which is set to ten seconds. The reason for the ten-second backwash is that the main purpose of backwashing is to use the instantaneous reverse hydraulic impact to loosen the contaminants embedded deep in the mesh intersections. Ten seconds of reverse water flow impact is sufficient to loosen and displace the contaminants at the mesh intersections. After ten seconds, the reverse water flow can only dilute and flush without further loosening. Continuing to extend the backwash time would only increase the accumulation time of reverse pressure on the membrane bag bonding lines.

[0035] After ten seconds of backwashing, the independent backwash pump is shut down, and a reset command is sent to the electric three-way valve assembly to restore the connection between the permeate outlet and the permeate collection pipeline, thus closing the backwash bypass. Simultaneously, the pressure relief valve located on the membrane module inlet pipeline is opened. Upon opening, the pressure inside the membrane module is released to the atmospheric environment outside the cleaning circulation loop. The internal pressure of the membrane module decreases to atmospheric pressure within the duration of the pressure relief. The pressure relief duration is set to three seconds, which is sufficient to reduce the residual pressure inside the membrane module from the backwash pressure value to atmospheric pressure equal to the external atmospheric pressure.

[0036] The alternating flushing process of forward flushing, reverse flushing, and depressurization was repeated. During each alternating flush, the duration of forward flushing was fixed at five minutes, the duration of reverse flushing at ten seconds, and the duration of depressurization at three seconds. After each alternating flush, a flushing wastewater sample was collected from the concentrate outlet of the membrane module, and the suspended solids content of the sample was determined. The suspended solids content was determined using a gravimetric method: the flushing wastewater sample was vacuum filtered through a pre-dried and weighed glass fiber membrane. The membrane and precipitates were then dried in a constant-temperature drying oven at 105°C until constant weight. The total weight of the dried membrane and precipitates was subtracted from the weight of the membrane before drying to obtain the suspended solids mass. The suspended solids mass was divided by the sample volume to obtain the suspended solids content. The measured suspended solids content was compared with an emission threshold set at 20 mg / L. The emission threshold of 20 mg per liter is based on the suspended solids concentration limit of the influent water quality when the reverse osmosis membrane module is cleaned and put into normal operation in the dyeing and printing wastewater reuse system. The limit is 20 mg per liter. When the suspended solids content in the flushing discharge is lower than the limit, it indicates that the cleanliness of the flushing discharge meets the influent water quality requirements when the system is operating normally, and there are no large amounts of detachable pollutants in the membrane module flow channel.

[0037] When the suspended solids content in the flushing drain falls below 20 mg / L, stop the alternating flushing. If the suspended solids content in the flushing drain remains above 20 mg / L, continue the alternating process of forward flushing, reverse flushing, and depressurization. During the repeated alternating flushing, the duration of forward flushing, reverse flushing, and depressurization remains constant. After each alternating flush, collect a new sample of the flushing drain and retest the suspended solids content until the test results show that the suspended solids content in the flushing drain is below 20 mg / L.

[0038] D5: After bidirectional gradient flushing, monitor the feed water-concentrate pressure difference and current permeate flow rate of the membrane module in real time. When the feed water-concentrate pressure difference decreases to within the preset operating pressure difference, and under constant circulation flow conditions, the fluctuation range of the feed water-concentrate pressure difference is lower than the preset fluctuation threshold, and the current permeate flow rate recovers to above the preset proportion of the initial permeate flow rate, the membrane module is determined to be cleaned.

[0039] In this embodiment of the invention, after the forward and reverse gradient flushing is completed, the backflushing bypass is closed and the cleaning circulation loop is restored to the forward circulation state. Flushing water is supplied to the membrane module at a constant circulation flow rate, which is set to 90% of the rated permeate flow rate of the membrane module. The reason for setting the constant circulation flow rate to 90% of the rated permeate flow rate is that the rated permeate flow rate is the design flow rate of the membrane module under normal water production conditions, at which the hydraulic flow state inside the membrane module is most stable. However, the cleaning judgment stage requires continuous circulating flushing for a certain period of time. If the flow rate is too low, the flow velocity of the flushing water in the channel is insufficient to fully carry away the residual trace particles in the channel. If the flow rate is too high, the flushing water generates turbulent disturbances in the channel, which will increase the noise of the differential pressure reading and thus interfere with the accuracy of the judgment. Experimentally verified, 90% of the rated permeate flow rate is the optimal balance point that is sufficient to maintain a stable laminar flow state in the channel without generating significant turbulent noise.

[0040] Under constant circulation flow conditions, the inlet pressure and concentrate outlet pressure of the membrane module are continuously collected at a preset judgment period of two seconds, meaning that the inlet pressure and concentrate outlet pressure are collected synchronously every two seconds. This process is repeated for twenty consecutive collection times, resulting in twenty sets of pressure data. Based on the inlet pressure and corresponding concentrate outlet pressure values ​​at the same collection time in each set of pressure data, the real-time inlet-concentrate pressure difference is calculated for each collection time. The real-time inlet-concentrate pressure difference at that collection time is obtained by subtracting the concentrate outlet pressure value from the inlet pressure value at the same collection time. Twenty real-time inlet-concentrate pressure difference values ​​are obtained from the twenty collection times. These twenty real-time inlet-concentrate pressure difference values ​​are then arranged in chronological order of collection time to generate a judgment pressure difference sequence. The average judgment pressure difference is generated by averaging the twenty real-time inlet-concentrate pressure difference values ​​in the judgment pressure difference sequence. The specific method for averaging is to add all twenty real-time inlet-concentrate pressure difference values ​​in the judgment pressure difference sequence and then divide by twenty to obtain the judgment average pressure difference.

[0041] The average differential pressure is compared with the preset operating differential pressure, which is set as the feed-concentrate differential pressure value when the membrane module is first put into normal operation after cleaning. This differential pressure value is retrieved from the membrane module's operation log. This differential pressure value represents the standard flow resistance of the membrane module in a foul-free state. When the average differential pressure decreases to within this standard value, it indicates that cleaning has restored the flow resistance of the membrane module to the foul-free state level. The absolute value condition of the differential pressure is met when the average differential pressure is less than or equal to the preset operating differential pressure. The deviation of each differential pressure value in the differential pressure sequence from the average differential pressure is statistically analyzed to obtain the differential pressure fluctuation amplitude value. The maximum and minimum values ​​are found from the twenty real-time feed-concentrate differential pressure values ​​in the differential pressure sequence. The first difference between the maximum value and the average differential pressure, and the second difference between the average differential pressure and the minimum value are calculated. The magnitudes of the first and second differences are compared, and the larger of the two values ​​is divided by the average differential pressure and then multiplied by 100% to obtain the differential pressure fluctuation amplitude value. The differential pressure fluctuation amplitude value characterizes the degree of dispersion of the real-time influent-concentrate pressure difference around the determination average pressure difference under constant circulation flow conditions. The larger the differential pressure fluctuation amplitude value, the more likely there is unstable blockage migration or local flow resistance changes in the flow channel. The smaller the differential pressure fluctuation amplitude value, the more likely the flow state in the flow channel is stable.

[0042] The differential pressure fluctuation amplitude was compared with a preset fluctuation threshold, which was set at 3%. The 3% threshold was based on statistical analysis of the normal fluctuation range of the feed-concentrate pressure difference of reverse osmosis membrane modules in a dyeing and printing wastewater reuse system under stable operating conditions. Ten reverse osmosis membrane modules of the same model and batch were selected and put into normal operation for the first time after cleaning, with the permeate flow rate constant at 90% of the rated flow. The inlet pressure and concentrate outlet pressure of each membrane module were continuously collected over 24 hours, and the real-time feed-concentrate pressure difference was calculated at each collection point. The fluctuation amplitude was calculated for each membrane module's 24-hour pressure difference data, and the maximum value of all fluctuation amplitudes was found to be no more than 2.5%. Considering the potential for additional measurement noise due to differences in water quality and temperature between the flushing water during the cleaning judgment stage and the normal operation stage, a safety margin of 0.5% was set. Therefore, the preset fluctuation threshold was determined to be 3%. When the differential pressure fluctuation amplitude is less than or equal to 3%, the differential pressure stability condition is considered met.

[0043] While meeting the absolute pressure difference and pressure difference stability conditions, the current permeate flow rate of the membrane module is acquired in real time via an electromagnetic flowmeter installed on the permeate outlet pipeline of the membrane module. The current permeate flow rate is then compared to the initial permeate flow rate to generate the permeate flow rate recovery rate. Specifically, the ratio is calculated by dividing the current permeate flow rate by the initial permeate flow rate and multiplying by 100%. The initial permeate flow rate is the flow rate value obtained from the membrane module's operation log when it is first put into normal operation after cleaning and is in a stable water production state. When the permeate flow rate recovery rate reaches a preset recovery rate threshold, the permeate flow rate recovery condition is considered met. The preset recovery rate threshold is set to 95%. The preset recovery rate threshold of 95% is based on the engineering operation experience of reverse osmosis membrane modules in dyeing and printing wastewater reuse systems: even after thorough cleaning, reverse osmosis membrane modules cannot recover to 100% of their initial operating flow rate due to the residual traces of irreversible pollutants on the membrane surface and the degradation of the membrane material itself. The industry considers a recovery of the permeate flow rate to more than 95% of the initial value as a standard for qualified cleaning. This standard value is derived from the statistics of permeate flow rate recovery rates after cleaning of multiple sets of reverse osmosis membrane modules for dyeing and printing wastewater. The statistics show that the upper limit of the permeate flow rate recovery rate that can be stably achieved after thorough cleaning is 95% to 97%. Using 95% as the judgment threshold ensures that the cleaning effect meets the standard without leading to endless cleaning due to setting it too high.

[0044] When the absolute pressure difference condition, the pressure difference stability condition, and the permeate flow rate recovery condition are all met simultaneously, the cleaning endpoint is reached, and the membrane module cleaning is complete. The absolute pressure difference condition reflects the degree of recovery of the overall flow resistance of the membrane module; the pressure difference stability condition reflects the stability of the flow state within the channel, i.e., the absence of migrating blockages; and the permeate flow rate recovery condition reflects the degree of recovery of the membrane surface filtration performance. If only the absolute pressure difference condition is met but the pressure difference stability condition is not, suspended particles may still be migrating within the channel, potentially causing secondary blockage. If only the permeate flow rate recovery condition is met but the absolute pressure difference condition is not, the membrane surface filtration performance may have recovered, but residual pollutants may still remain within the channel. These three conditions correspond to the three dimensions of membrane surface recovery, channel unobstructed flow, and flow stability, respectively. Only when all three dimensions are met simultaneously can the membrane module be safely put into normal operation.

[0045] During actual operation, due to the continuous circulation of the cleaning fluid between the membrane module and the cleaning tank, the timing of the fulfillment of the three conditions—absolute pressure difference, pressure difference stability, and permeate flow recovery—may not be completely synchronized. Typically, the pressure difference stability condition is met last. Therefore, if the absolute pressure difference and permeate flow recovery conditions are met, but the pressure difference stability condition is not, constant circulation flow is maintained for flushing. A new set of pressure difference data is collected every two seconds, and the pressure difference fluctuation amplitude is recalculated. After each recalculation, the new pressure difference fluctuation amplitude is compared with the preset fluctuation threshold until all three conditions are met simultaneously. At this point, flushing is stopped, and the cleaning endpoint is determined. If constant circulation flow flushing lasts for more than thirty minutes and the three conditions are still not met simultaneously, it indicates that the membrane module may have irreversible damage or fouling. In this case, flushing is stopped, and a cleaning failure warning signal is issued, awaiting the operator's decision on whether to replace the membrane module or adopt other enhanced cleaning measures.

[0046] The cleaning time of hundreds of reverse osmosis membrane modules with different levels of fouling was statistically analyzed. More than 95% of the modules could meet the three conditions simultaneously within 30 minutes of continuous rinsing. The modules that did not meet the conditions after more than 30 minutes were found to have irreversible membrane surface oxidation or structural damage to the flow channel mesh after subsequent disassembly and inspection. Continuing to rinse would not improve the judgment indicators but would waste water resources and energy. Therefore, 30 minutes was determined as the upper limit of the time for judging cleaning failure.

[0047] like Figure 2 The diagram shown is a functional block diagram of a reverse osmosis membrane cleaning system for dyeing and printing wastewater based on compound chelation, provided by an embodiment of the present invention.

[0048] The reverse osmosis membrane cleaning system 100 for dyeing and printing wastewater based on compound chelation, as described in this invention, can be installed in an electronic device. Depending on the functions implemented, the reverse osmosis membrane cleaning system 100 may include a diagnostic sludge discharge module 101, an alkaline washing pressure feedback module 102, an acidic complex-breaking washing module 103, a bidirectional flushing module 104, and an endpoint adaptive module 105. The module described in this invention can also be referred to as a unit, which refers to a series of computer program segments that can be executed by the processor of an electronic device and can perform a fixed function, stored in the memory of the electronic device.

[0049] In this embodiment, the functions of each module / unit are as follows: The diagnostic sludge removal module 101 is connected to the inlet and concentrate outlet of the reverse osmosis membrane module. It is used to perform forward flushing of the membrane module with flushing water, monitor and record the initial feed-concentrate pressure difference in real time, and determine the clogging level of the flow channels in the membrane module based on a comparison between the initial feed-concentrate pressure difference and the normal operating pressure difference of the membrane module. The output of the diagnostic sludge removal module 101 is connected to the input of the alkaline washing pressure feedback module 102, and the diagnostic sludge removal module 101 sends the determined clogging level signal to the alkaline washing pressure feedback module 102.

[0050] The alkaline wash pressure feedback module 102 is connected to the cleaning circulation loop of the membrane module. It injects an alkaline compound chelating cleaning agent into the cleaning circulation loop based on the clogging level signal sent by the diagnostic sludge discharge module 101. It supplies the cleaning circulation fluid to the membrane module using alternating low-frequency and high-frequency output to clear the flow channels. The alkaline wash pressure feedback module 102 includes a variable frequency high-pressure pump, a first pressure transmitter, a second pressure transmitter, an electric three-way valve assembly, and an independent backwash pump. The variable frequency high-pressure pump is located in the cleaning circulation loop between the cleaning water tank and the membrane module inlet. The first pressure transmitter is located at the membrane module inlet, the second pressure transmitter is located at the membrane module concentrate outlet, the electric three-way valve assembly is located on the membrane module permeate outlet pipeline, and the independent backwash pump's inlet is connected to the cleaning water tank, and its outlet is connected to the electric three-way valve assembly. The output of the alkaline washing pressure feedback module 102 is connected to the input of the acidic complex-breaking washing module 103. After completing the flow channel dredging, the alkaline washing pressure feedback module 102 sends a cleaning switching signal to the acidic complex-breaking washing module 103.

[0051] The acidic complex-breaking washing module 103 is connected to the cleaning cycle loop of the membrane module. After receiving the cleaning switching signal from the alkaline washing pressure feedback module 102, it drains the alkaline cleaning circulating liquid from the cleaning cycle loop, injects an acidic compound chelating cleaning agent into the cleaning cycle loop to clean the membrane module, and monitors the concentration of suspended particulate matter in the reflux cleaning liquid in real time. Acidic cleaning ends when the concentration of suspended particulate matter shows a continuous decreasing trend. The output of the acidic complex-breaking washing module 103 is connected to the input of the bidirectional flushing module 104. After completing acidic cleaning, the acidic complex-breaking washing module 103 sends a flushing switching signal to the bidirectional flushing module 104.

[0052] The bidirectional flushing module 104 is connected between the cleaning circulation loop and the flushing water supply line of the membrane module. After receiving the flushing switching signal from the acidic complex-breaking flushing module 103, it drains the acidic cleaning circulating fluid from the cleaning circulation loop, switches the flushing water supply line to the cleaning circulation loop, and performs bidirectional gradient flushing of the membrane module. The output of the bidirectional flushing module 104 is connected to the input of the endpoint adaptive module 105. After completing the bidirectional gradient flushing, the bidirectional flushing module 104 sends an endpoint determination signal to the endpoint adaptive module 105.

[0053] The endpoint adaptive module 105 is connected to the inlet, concentrate outlet, and permeate outlet of the membrane module. It is used to receive the endpoint determination signal sent by the bidirectional flushing module 104 and monitor the current feed-concentrate pressure difference and current permeate flow rate of the membrane module in real time. When the feed-concentrate pressure difference decreases to within the preset operating pressure difference, and the fluctuation amplitude of the feed-concentrate pressure difference is lower than the preset fluctuation threshold under constant circulation flow conditions, and the current permeate flow rate recovers to above the preset proportion of the initial permeate flow rate, the membrane module is determined to be cleaned and a cleaning completion signal is output.

[0054] In the connection between the modules, the rinsing water is filtered through a precision filter and then pumped from the rinsing water tank to the diagnostic slag discharge module 101 and the bidirectional rinsing module 104. The alkaline compound chelating cleaning agent and the acidic compound chelating cleaning agent are stored in the cleaning water tank respectively and are called in sequence by the alkaline washing pressure feedback module 102 and the acidic complex breaking washing module 103. The cleaning waste liquid generated during the entire cleaning process is discharged to the waste liquid collection container through the discharge valve.

[0055] In the several embodiments provided by this invention, it should be understood that the disclosed methods and systems can be implemented in other ways. For example, the system embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and other division methods may be used in actual implementation.

[0056] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional modules.

[0057] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation, characterized in that, The method includes: D1: The membrane module is flushed with flushing water in the forward direction. The initial feed water-concentrate pressure difference of the membrane module is monitored and recorded in real time. The blockage level of the flow channel in the membrane module is determined based on the comparison between the initial feed water-concentrate pressure difference and the normal operating pressure difference of the membrane module. D2: Inject an alkaline compound chelating cleaning agent into the cleaning circulation loop of the membrane module, and supply the cleaning circulation fluid to the membrane module in an alternating low-frequency and high-frequency output mode to clear the flow channels of the membrane module. D3: Drain the alkaline cleaning circulating liquid from D2, inject an acidic compound chelating cleaning agent into the cleaning circulating loop to clean the membrane module, monitor the concentration of suspended particulate matter in the return cleaning liquid in real time, and end D3 when the concentration of suspended particulate matter shows a continuous downward trend. D4: Drain the acidic cleaning circulating fluid from D3 and switch to the flushing water to perform bidirectional gradient flushing of the membrane module. D5: After bidirectional gradient flushing, monitor the feed water-concentrate pressure difference and current permeate flow rate of the membrane module in real time. When the feed water-concentrate pressure difference decreases to within the preset operating pressure difference, and under constant circulation flow conditions, the fluctuation range of the feed water-concentrate pressure difference is lower than the preset fluctuation threshold, and the current permeate flow rate recovers to above the preset proportion of the initial permeate flow rate, the membrane module is determined to be cleaned.

2. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, The determination of the clogging level of the flow channels in the membrane module based on the comparison result of the initial feed-concentrate pressure difference and the normal operating pressure difference of the membrane module includes: The average feed-concentrate pressure difference during the historical normal operation of the membrane module is used as the baseline pressure difference. The pressure difference ratio is generated by calculating the ratio between the initial feed water-concentrate pressure difference and the reference pressure difference. When the pressure differential ratio is in the first preset range, it is determined to be a mild blockage; when the pressure differential ratio is in the second preset range, it is determined to be a moderate blockage; and when the pressure differential ratio is in the third preset range, it is determined to be a severe blockage.

3. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, The method of supplying cleaning circulating fluid to the membrane module using alternating low-frequency and high-frequency output to clear the flow channels of the membrane module includes: The variable frequency high-pressure pump of the membrane module is started to supply cleaning circulating fluid to the membrane module at a low frequency output frequency, so that the cleaning circulating fluid forms a positive circulation flow between the feed water side and the concentrate side of the membrane module. After a preset first duration, the variable frequency high-pressure pump is switched to a high frequency output frequency to strip contaminants from the membrane surface and flow channel mesh of the membrane module. After the high-frequency output continues for a preset second duration, the variable frequency high-voltage pump is switched back to the low-frequency output frequency to complete a low-high frequency alternation cycle. During the alternating low and high frequency cycle, the inlet pressure and concentrate outlet pressure of the membrane module are collected in real time to generate a real-time inlet-concentrate pressure difference. The pressure difference change rate is calculated based on the real-time feed water-concentrate pressure difference. When the pressure difference change rate exceeds the preset change rate threshold, the pollutants stripped from the membrane module will accumulate again at the flow channel partition. At this time, the output frequency of the variable frequency high-pressure pump will be reduced to a safe frequency, and the backwash bypass of the membrane module will be started. The cleaning circulating liquid will be injected into the membrane module from the permeate outlet side of the membrane module in reverse to apply reverse hydraulic impact to the membrane bag and flow channel partition of the membrane module. After the reverse injection continues for the third duration, the backflush bypass is closed, the output frequency of the variable frequency high-pressure pump is restored to the frequency before the reduction, and the alternating output of low and high frequencies continues until the real-time feed water-concentrate pressure difference drops below the upper limit of the safe pressure difference.

4. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 3, characterized in that, The calculation of the pressure difference change rate based on the real-time influent-concentrate pressure difference includes: Real-time pressure difference between influent and concentrate is continuously collected at preset sampling intervals to generate a pressure difference time series. The pressure difference values ​​in the pressure difference time series are arranged in chronological order of collection time, and each pressure difference value carries a corresponding time tag. The pressure difference values ​​at adjacent time points in the pressure difference time series are calculated by performing a difference operation to generate a pressure difference increment sequence between each adjacent time point; The pressure difference increment sequence between each adjacent time point is determined, and the pressure difference increment with positive value in the pressure difference increment sequence is identified and marked as an upward increment. The consecutive increases are accumulated and counted to obtain the number of consecutive increases; When the number of consecutive increases reaches a preset threshold, it is determined that the differential pressure change rate exceeds a preset change rate threshold.

5. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 3, characterized in that, The backwash bypass of the membrane module is activated by injecting the cleaning circulating fluid into the membrane module from the permeate outlet side, applying reverse hydraulic impact to the membrane bag and flow channel screen of the membrane module, including: The connection status between the permeate outlet of the membrane module and the permeate collection pipeline; At the same time, the independent backflush pump of the membrane module draws the cleaning circulating fluid from the cleaning water tank of the membrane module and pressurizes it to the backflush pressure. The pressurized cleaning circulating fluid is introduced into the membrane module from the permeate outlet side, so that the cleaning circulating fluid forms a reverse flow opposite to the forward flow direction between the outside of the membrane bag and the flow channel mesh. After the reverse flow has continued for a third duration, a stop command is sent to the independent backwash pump, and the connection between the product water outlet and the product water collection pipeline is restored.

6. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, The process of injecting an acidic compound chelating cleaning agent into the cleaning circulation loop to clean the membrane module, and real-time monitoring of the suspended particulate matter concentration in the return cleaning solution, includes: After draining the alkaline cleaning circulating fluid D2 from the cleaning circulation loop, an acidic compound chelating cleaning agent is injected into the cleaning circulation loop. The acidic compound chelating cleaning agent contains an organic compound acid and a reducing stripping agent. The acidic compound chelating cleaning agent is used to clean residual contaminants on the membrane surface and flow channel mesh, wherein the contaminants include dye-metal complexes formed by dye molecules and metal ions. The variable frequency high-pressure pump is started to supply the acidic compound chelating cleaning agent to the membrane module in a positive circulation mode, so that the acidic compound chelating cleaning agent flows inside the membrane module and contacts the membrane surface and the flow channel mesh. The reducing agent is used to attack the coordination bonds in the dye-metal complex, causing the dye-metal complex to dissociate into dye molecules and metal ions. The hydrogen ions provided by the organic composite acid undergo a chelation reaction with the dissociated metal ions to generate a soluble metal chelate. The metal chelate is then dissolved in the acidic compound chelating cleaning agent and carried out of the membrane module with the circulating flow. Real-time collection of reflux cleaning fluid samples; light scattering intensity detection of the reflux cleaning fluid samples to obtain the concentration value of suspended particulate matter. The concentration of suspended particulate matter at the current moment is compared with the concentration of suspended particulate matter at the previous moment. When the continuous comparison results show that the concentration of suspended particulate matter is decreasing, it is determined that the concentration of suspended particulate matter is showing a continuous downward trend.

7. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, The bidirectional gradient rinsing of the membrane module includes: After draining the acidic cleaning fluid from the cleaning circulation loop, switch the flushing water supply line to the cleaning circulation loop so that the flushing water enters the cleaning circulation loop. The flushing water is supplied to the membrane module with forward flushing pressure and forward flushing flow rate, so that the flushing water flows in from the inlet of the membrane module and passes through the flow channel screen and is discharged from the concentrate outlet to perform forward flushing. After the fourth continuous duration of forward flushing, stop forward flushing and shut off the flushing water supply to the membrane module inlet; The backwash bypass is activated, and the backwash water is injected in reverse from the permeate outlet side of the membrane module with backwash pressure and backwash flow rate, so that the backwash water forms a flow opposite to the forward flow direction inside the membrane module, and applies a reverse peeling force to the contaminants embedded at the intersection of the flow channel mesh. After the fifth duration of backflushing, the backflushing bypass is closed, and the pressure relief valve is opened at the same time to release the internal pressure of the membrane module to atmospheric pressure during the pressure relief duration. Repeatedly perform forward and reverse alternating flushing, and monitor the suspended solids content in the flushing drain after each alternation until the suspended solids content in the flushing drain is lower than the discharge threshold.

8. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, After bidirectional gradient flushing, the feed-concentrate pressure difference and current permeate flow rate of the membrane module are monitored in real time. When the feed-concentrate pressure difference decreases to within a preset operating pressure difference, and under constant circulation flow conditions, the fluctuation amplitude of the feed-concentrate pressure difference is lower than a preset fluctuation threshold, and the current permeate flow rate recovers to or exceeds a preset proportion of the initial permeate flow rate, the membrane module is determined to be cleaned, including: After the forward and reverse gradient flushing is completed, flushing water is supplied to the membrane module at a constant circulation flow rate so that the membrane module operates under constant circulation flow rate conditions. Under the constant circulation flow condition, the inlet pressure value and concentrate outlet pressure value of the membrane module are continuously collected at a preset judgment period. The real-time inlet-concentrate pressure difference at each collection time is calculated based on the inlet pressure value and the corresponding concentrate outlet pressure value, and a judgment pressure difference sequence is generated. The average value of each pressure difference in the determination pressure difference sequence is calculated to generate the determination average pressure difference; The average pressure difference is compared with the preset operating pressure difference. When the average pressure difference is less than or equal to the preset operating pressure difference, the absolute value condition of the pressure difference is met. The deviation of each pressure difference value in the determined pressure difference sequence from the determined average pressure difference is statistically analyzed to obtain the pressure difference fluctuation amplitude value; The differential pressure fluctuation amplitude value is compared with a preset fluctuation threshold. When the differential pressure fluctuation amplitude value is less than or equal to the preset fluctuation threshold, the differential pressure stability condition is determined to be met. While satisfying the absolute value of pressure difference and the stability of pressure difference, the current permeate flow rate of the membrane module is obtained, and the ratio of the current permeate flow rate to the initial permeate flow rate is calculated to generate the permeate flow rate recovery rate. When the water production flow recovery rate reaches the preset recovery rate threshold, it is determined that the water production flow recovery condition is met. When the absolute value of the differential pressure, the stability of the differential pressure, and the recovery of the permeate flow rate are all met simultaneously, the cleaning endpoint is determined to have been reached, and the membrane module cleaning is completed.

9. The method for cleaning reverse osmosis membranes in dyeing and printing wastewater based on compound chelation as described in claim 1, characterized in that, The alkaline compound chelating cleaning agent and the acidic compound chelating cleaning agent comprise: The solute in the alkaline compound chelating cleaning agent includes macromolecular dispersants, medium-molecular-weight targeted chelating agents, small-molecular-weight penetrating stripping agents, and nonionic surfactants. The pH value of the acidic compound chelating cleaning agent is in the acidic range, and the solute of the acidic compound chelating cleaning agent includes an organic complex acid and a reducing stripping agent.

10. A reverse osmosis membrane cleaning system for dyeing and printing wastewater based on compound chelation, characterized in that, For implementing the reverse osmosis membrane cleaning method for dyeing and printing wastewater based on compound chelation as described in claim 1, the system comprises: The diagnostic sludge removal module is used to perform forward flushing of the membrane module with flushing water, monitor and record the initial feed water-concentrate pressure difference of the membrane module in real time, and determine the blockage level of the flow channel in the membrane module based on the comparison result of the initial feed water-concentrate pressure difference and the normal operating pressure difference of the membrane module. The alkaline washing pressure feedback module is used to inject alkaline compound chelating cleaning agent into the cleaning circulation loop of the membrane module, and to supply cleaning circulation fluid to the membrane module in an alternating low-frequency and high-frequency output mode to clear the flow channel of the membrane module. The acidic complex-breaking washing module is used to drain the alkaline cleaning circulating liquid of D2, inject acidic compound chelating cleaning agent into the cleaning circulation loop to clean the membrane module, monitor the concentration of suspended particulate matter in the return cleaning liquid in real time, and end D3 when the concentration of suspended particulate matter shows a continuous downward trend. The bidirectional flushing module is used to drain the acidic cleaning circulating fluid of D3 and switch to the flushing water to perform bidirectional gradient flushing of the membrane module. The endpoint adaptive module is used to determine that the membrane module cleaning is complete when the pressure difference between the feed water and concentrate decreases to within the preset operating pressure difference, and under constant circulation flow conditions, the fluctuation amplitude of the pressure difference between the feed water and concentrate is lower than the preset fluctuation threshold, and the current product water flow rate recovers to above the preset proportion of the initial product water flow rate.

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