Chromium-containing wastewater treatment system and treatment method

Abstract

The present invention discloses a chromium-containing wastewater treatment system and treatment method, characterized in that the treatment system includes a reaction tank, a ceramic membrane filter tank and a clear water tank, a water inlet pump and a water inlet main pipe are connected between the reaction tank and the ceramic membrane filter tank, a plurality of parallel and spaced flat ceramic membranes are arranged in the ceramic membrane filter tank, the flat ceramic membrane has a plurality of water outlet holes arranged through along the length direction, one end of the water outlet hole is closed, and the other end is connected to a water collecting branch pipe; a water outlet main pipe is connected between the ceramic membrane filter tank and the clear water tank, and the water collecting branch pipes are all connected to the water outlet main pipe; a suction pump is arranged on the water outlet main pipe. The system of the present invention has the advantages of small footprint, short process flow, convenient operation and management, stable structure, long service life, etc. The method of the present invention has the advantages of fast response speed to water quality changes, good chromium removal effect, and is conducive to reducing treatment costs, etc.

Description

Technical Field

[0001] The invention relates to the technical field of environmental engineering, and in particular to a chromium-containing wastewater treatment system and a treatment method. Background Art

[0002] Chromium and its compounds are widely used in industry. A series of industries such as metallurgy, chemical industry, mineral engineering, electroplating, chromium production, pigments, pharmaceuticals, light industry and textiles, production of chromium salts and chromium compounds will produce a large amount of chromium-containing wastewater. Among them, chromium compounds are mainly trivalent (such as Cr2O3) and hexavalent (such as CrO4 2- or Cr2O7 2- ) forms, and hexavalent chromium is the most toxic, about one hundred times that of trivalent chromium.

[0003] At present, the main method for treating chromium-containing wastewater is chemical precipitation. The process flow is as follows: Figure 1 As shown, the method adopts a continuous reaction process, firstly, acid is added to the first pH adjustment tank to adjust the pH value of the chromium-containing wastewater raw water to acidic; then the wastewater flows into the reduction tank, and the hexavalent chromium is reduced to trivalent chromium by adding a reducing agent into the reduction tank; the wastewater then flows into the second pH adjustment tank, and alkali is added to the tank to adjust the pH value to alkaline; the wastewater then flows into the coagulation tank, and polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the coagulation tank to form larger, easy-to-precipitate flocs of chromium hydroxide; then, under slow water flow conditions, the wastewater enters the inclined tube sedimentation tank, and the chromium hydroxide is precipitated by gravity, and the supernatant flows into the sand filter tank, and is discharged after further filtration through quartz sand. It can be seen that the existing chemical precipitation method for treating chromium-containing wastewater has the following main shortcomings: using continuous reaction, the wastewater undergoes chemical or physical reactions in different treatment units, but due to the continuity of the reaction, it is difficult to make each treatment unit operate under the best working conditions, especially when the influent water quality fluctuates, it is difficult to quickly respond to the change in water quality by changing the reaction parameters, so that the treatment effect fluctuates, and even causes the treatment to fail to meet the standards; mainly using chemical methods to form precipitates for physical sedimentation, which is greatly affected by reaction conditions and water quality changes, and sometimes even does not precipitate or is difficult to precipitate, and chromium-containing compounds are discharged with wastewater, causing excessive emissions; using inclined tube sedimentation tanks for sedimentation, the inclined tubes are prone to scaling, and after long-term operation, the inclined tubes collapse and break; in order to ensure the sedimentation of chromium hydroxide and reduce the risk of excessive emissions, excessive dosage is often used, resulting in a large amount of heavy metal sludge precipitation, and the cost of hazardous waste disposal is high; the process is long, the area occupied is large, and the operation and management are relatively complicated. For electroplating and other enterprises that produce chromium-containing wastewater, due to the lack of professional and technical personnel, the phenomenon of substandard treatment due to human errors is more frequent. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is: how to provide a chromium-containing wastewater treatment system with a small footprint, a short process flow, convenient operation and management, a stable structure and a long service life, as well as a chromium-containing wastewater treatment method with a fast response speed to water quality changes, good chromium removal effect, and conducive to reducing treatment costs.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A chromium-containing wastewater treatment system, characterized in that it includes a reaction tank, a ceramic membrane filter tank and a clear water tank, wherein an inlet pump and a main water inlet pipe are connected between the reaction tank and the ceramic membrane filter tank, wherein a plurality of parallel and spaced flat ceramic membranes are provided in the ceramic membrane filter tank, wherein the flat ceramic membrane has a plurality of water outlet holes which are arranged through the length direction, wherein one end of the water outlet hole is closed, and the other end is connected to a water collecting branch pipe; an outlet main pipe is connected between the ceramic membrane filter tank and the clear water tank, and the water collecting branch pipes are all connected to the outlet main pipe; and a suction pump is provided on the outlet main pipe.

[0007] By adopting the above structure, the wastewater to be treated can be put into the reaction tank, and the pretreatment of the wastewater is completed in the reaction tank to form tiny particles of metal hydroxide, which are then pumped into the ceramic membrane filter tank by the water inlet pump, and sucked by the suction pump to form a negative pressure in the water outlet hole of the flat ceramic membrane. The pretreated wastewater enters the water outlet hole after filtering through the flat ceramic membrane, and the tiny particles in the wastewater are blocked and retained in the ceramic membrane filter tank. The filtered clean water is sent to the clean water tank for storage, and the treatment of chromium-containing wastewater is completed. The above structure only requires a reaction tank, a ceramic membrane filter tank and a clean water tank, which occupies a small area, has a short process flow, and is easy to operate and manage. In addition, by using a flat ceramic membrane for filtration, there is no need to process the heavy metal substances to be treated into large particles that are easy to settle, which reduces the difficulty of pretreatment and improves the pretreatment efficiency. Moreover, the flat ceramic membrane has a stable structure, a long service life, and a high reuse rate.

[0008] Furthermore, it also includes a backwash pump arranged in parallel with the suction pump, the backwash pump is respectively connected to the water outlet main pipe and the clean water tank through a backwash pipe, and the water outlet direction of the backwash pump is toward the water collecting branch pipe; the suction pump and the backwash pump are each provided with a solenoid valve on one side facing the water collecting branch pipe.

[0009] In this way, the backwash pump can be used to extract clean water from the clean water tank to backwash the flat ceramic membrane, so that the sediment attached to the surface of the flat ceramic membrane falls off, avoiding the pores of the flat ceramic membrane from being blocked, affecting the filtration effect and filtration efficiency, and extending the service life of the flat ceramic membrane. The electromagnetic valve can control the on and off of the branch where the suction pump or backwash pump is located to prevent cross-flow.

[0010] Furthermore, a flushing device for flushing the surface of the flat ceramic membrane is also provided in the ceramic membrane filter tank.

[0011] In this way, flushing the surface of the flat ceramic membrane using a flushing device can prevent the deposition of tiny particles of chromium hydroxide on the surface of the flat ceramic membrane, which is beneficial to extending the service life of the flat ceramic membrane.

[0012] Furthermore, the flushing device includes aeration heads arranged in a matrix below the flat ceramic membrane, and an air pump connected to the aeration heads.

[0013] In this way, aeration can be performed while suction filtration is in progress, so that tiny particles of chromium hydroxide cannot adhere to the surface of the flat ceramic membrane under the scouring effect of the aeration gas, avoiding clogging of the filter pores of the flat ceramic membrane, which is beneficial to increasing the service life of the flat ceramic membrane.

[0014] Furthermore, the flushing device includes an air washing branch pipe arranged between two adjacent flat ceramic membranes, the air washing branch pipe is provided with a plurality of blowing holes arranged toward the flat ceramic membrane, and the air washing branch pipe is connected to the compressor through an air washing main pipe.

[0015] In this way, by utilizing the high-pressure air from the compressor, the surface of the flat ceramic membrane is subjected to high-pressure flushing through an air flushing branch pipe arranged between two adjacent flat ceramic membranes. This can wash away some of the tiny particles of chromium hydroxide deposited on the surface of the flat ceramic membrane. There is no need to disassemble the flat ceramic membrane for flushing and assembly, thereby extending the maintenance cycle of the flat ceramic membrane and improving its service life.

[0016] The air washing branch pipe is arranged along the length direction of the flat ceramic membrane, and multiple air washing branches are evenly distributed along the width direction of the flat ceramic membrane; in this way, the high-pressure gas flushing can cover the entire surface of the flat ceramic membrane, thereby improving the service life of the flat ceramic membrane. There are multiple groups of blowing holes evenly distributed along the length direction on each of the air washing branches, and each group of the blowing holes includes four blowing holes evenly distributed along the circumference of the air washing branch pipe; in this way, the gaps between the flat ceramic membranes can be fully utilized, and the surfaces of the flat ceramic membranes on both sides can be flushed at the same time using one air washing branch pipe. The angle between the direction of each of the air blowing holes and the flat ceramic membrane is 45 degrees; in this way, the blowing direction is blown toward the flat ceramic membrane at an angle of 45 degrees, so that the gas can form a tangential force on the surface of the ceramic membrane, which has a better flushing effect on the tiny particles of chromium hydroxide deposited on the surface of the peeling ceramic membrane. The blowing holes on two adjacent air-washing branches are staggered along the length direction of the air-washing branches; in this way, the airflows of the blowing holes on the two adjacent air-washing branches can be prevented from interfering with each other, which is convenient for shortening the distance between the two adjacent air-washing branches, so that the blowing holes on the air-washing branches can blow to the surface of the flat ceramic membrane in the area directly facing the adjacent air-washing branches, and the flushing effect is better. Furthermore, the surface of the flat ceramic membrane also has an arc-shaped groove arranged along the length direction of the air-washing branch, and the arc-shaped groove is arranged directly opposite to the air-washing branch one by one. In this way, the surface of the flat ceramic membrane is provided with an arc-shaped groove, which can increase the surface area of ​​the flat ceramic membrane and make the filtering area larger. After the gas from the blowing hole is flushed into the arc-shaped groove, a vortex can be formed along the arc-shaped groove, stirring the liquid on the surface of the flat ceramic membrane, and effectively preventing the washed-off chromium hydroxide tiny particles from being deposited again.

[0017] Furthermore, a flow meter is also provided on the water outlet main pipe.

[0018] In this way, the water outlet flux can be controlled to make the system operate in the best state.

[0019] Furthermore, a pressure gauge is provided on the water outlet main pipe.

[0020] A method for treating chromium-containing wastewater, characterized in that it comprises the following steps:

[0021] 1) Pretreatment of wastewater:

[0022] Lead the chromium-containing wastewater into the pre-reaction tank, stir continuously, and add dilute sulfuric acid to adjust the pH to 2-3. After stabilization, add sodium metabisulfite to control the redox potential below 250mV. After the reaction is completed, add alkali to raise the pH to 8-9.

[0023] 2) Deep treatment of wastewater:

[0024] The wastewater pretreated in step 1) is introduced into the ceramic membrane filter tank, and is sucked by a suction pump so that the chromium-containing wastewater enters the outlet holes of the inner cavity of the ceramic membrane through the micropores on the surface of the flat ceramic membrane under the action of negative pressure. The filtered clean water is introduced into the clear water tank through the outlet main pipe, and the dirt is retained in the ceramic membrane filter tank; the flat ceramic membrane is immersed in the wastewater.

[0025] Furthermore, the step 1) further comprises adding a coagulant, wherein the coagulant is one or more of polyaluminium chloride, aluminium sulfate, alum, ferrous sulfate, ferric chloride and polyferric sulfate, and the adding ratio is 10-20 mg / l.

[0026] Furthermore, the flat ceramic membrane in step 2) is made of a nanocomposite material with a pore size of 0.5-1.0 μm, and the nanocomposite material is synthesized from Al2O3, ZrO2 and TiO2 nanoparticles at a high temperature of 1600˚C.

[0027] In summary, the system of the present invention has the advantages of small footprint, short process flow, convenient operation and management, stable structure, long service life, etc. The method of the present invention has the advantages of fast response speed to water quality changes, good chromium removal effect, and is conducive to reducing treatment costs, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the process flow chart of the existing chromium-containing wastewater treatment process.

[0029] Figure 2 This is a schematic diagram of the structure of the chromium-containing wastewater treatment system of the present application.

[0030] Figure 3 for Figure 2 Schematic diagram of the structure of the air washing main pipe and air washing branch pipe of the middle flushing device.

[0031] Figure 4 This is a schematic diagram of the positional relationship between the gas washing branch pipe and the flat ceramic membrane. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with embodiments.

[0033] When implementing: Figure 2 to Figure 4As shown, a chromium-containing wastewater treatment system includes a reaction tank, a ceramic membrane filter 2 and a clear water tank 8, wherein an inlet pump and a main inlet pipe are connected between the reaction tank and the ceramic membrane filter 2, wherein a plurality of parallel and spaced flat ceramic membranes 3 are provided in the ceramic membrane filter 2, wherein the flat ceramic membrane 3 has a plurality of water outlet holes which are arranged through the length direction, wherein one end of the water outlet hole is closed, and the other end is connected to a water collecting branch pipe 4; a main outlet pipe 5 is connected between the ceramic membrane filter 2 and the clear water tank 8, and the water collecting branch pipes 4 are all connected to the main outlet pipe 5; and a suction pump 6 is provided on the main outlet pipe 5.

[0034] By adopting the above structure, the wastewater to be treated can be put into the reaction tank, and the pretreatment of the wastewater is completed in the reaction tank to form tiny particles of metal hydroxide, which are then pumped into the ceramic membrane filter tank by the water inlet pump, and sucked by the suction pump to form a negative pressure in the water outlet hole of the flat ceramic membrane. The pretreated wastewater enters the water outlet hole after filtering through the flat ceramic membrane, and the tiny particles in the wastewater are blocked and retained in the ceramic membrane filter tank. The filtered clean water is sent to the clean water tank for storage, and the treatment of chromium-containing wastewater is completed. The above structure only requires a reaction tank, a ceramic membrane filter tank and a clean water tank, which occupies a small area, has a short process flow, and is easy to operate and manage. In addition, by using a flat ceramic membrane for filtration, there is no need to process the heavy metal substances to be treated into large particles that are easy to settle, which reduces the difficulty of pretreatment and improves the pretreatment efficiency. Moreover, the flat ceramic membrane has a stable structure, a long service life, and a high reuse rate.

[0035] During implementation, it also includes a backwash pump 7 arranged in parallel with the suction pump 6, and the backwash pump 7 is respectively connected to the water outlet main pipe 5 and the clean water tank 8 through a backwash pipe, and the water outlet direction of the backwash pump 7 is toward the water collecting branch pipe 4; the suction pump 6 and the backwash pump 7 are each provided with a solenoid valve on one side facing the water collecting branch pipe 4.

[0036] In this way, the backwash pump can be used to extract clean water from the clean water tank to backwash the flat ceramic membrane, so that the sediment attached to the surface of the flat ceramic membrane falls off, avoiding the pores of the flat ceramic membrane from being blocked, affecting the filtration effect and filtration efficiency, and extending the service life of the flat ceramic membrane. The electromagnetic valve can control the on and off of the branch where the suction pump or backwash pump is located to prevent cross-flow.

[0037] During implementation, a flushing device 10 for flushing the surface of the flat ceramic membrane 3 is also provided in the ceramic membrane filter 2 .

[0038] In this way, flushing the surface of the flat ceramic membrane using a flushing device can prevent the deposition of tiny particles of chromium hydroxide on the surface of the flat ceramic membrane, which is beneficial to extending the service life of the flat ceramic membrane.

[0039] During implementation, the flushing device 10 includes aeration heads arranged in a matrix below the flat ceramic membrane 3 and an air pump connected to the aeration heads.

[0040] In this way, aeration can be performed while suction filtration is in progress, so that tiny particles of chromium hydroxide cannot adhere to the surface of the flat ceramic membrane under the scouring effect of the aeration gas, avoiding clogging of the filter pores of the flat ceramic membrane, which is beneficial to increasing the service life of the flat ceramic membrane.

[0041] During implementation, the flushing device 10 includes an air washing branch pipe 11 arranged between two adjacent flat ceramic membranes 3, and the air washing branch pipe 11 is provided with a plurality of blowing holes 12 arranged toward the flat ceramic membrane 3. The air washing branch pipe 11 is connected to the compressor through an air washing main pipe 13.

[0042] In this way, by utilizing the high-pressure air from the compressor, the surface of the flat ceramic membrane is subjected to high-pressure flushing through an air flushing branch pipe arranged between two adjacent flat ceramic membranes. This can wash away some of the tiny particles of chromium hydroxide deposited on the surface of the flat ceramic membrane. There is no need to disassemble the flat ceramic membrane for flushing and assembly, thereby extending the maintenance cycle of the flat ceramic membrane and improving its service life.

[0043] The air washing branch pipe is arranged along the length direction of the flat ceramic membrane 3, and multiple air washing branches are evenly distributed along the width direction of the flat ceramic membrane 3; in this way, the high-pressure gas flushing can cover the entire surface of the flat ceramic membrane, thereby improving the service life of the flat ceramic membrane. There are multiple groups of blowing holes evenly distributed along the length direction on each of the air washing branches, and each group of the blowing holes includes four blowing holes evenly distributed along the circumference of the air washing branch pipe; in this way, the gaps between the flat ceramic membranes can be fully utilized, and the surfaces of the flat ceramic membranes on both sides can be flushed at the same time using one air washing branch pipe. The angle between the orientation of each of the air blowing holes and the flat ceramic membrane 3 is 45 degrees; in this way, the blowing direction is blown toward the flat ceramic membrane at an angle of 45 degrees, so that the gas can form a tangential force on the surface of the ceramic membrane, which has a better flushing effect on the tiny particles of chromium hydroxide deposited on the surface of the peeling ceramic membrane. The blowing holes on two adjacent air-washing branches are staggered along the length direction of the air-washing branches; in this way, the airflows of the blowing holes on the two adjacent air-washing branches can be prevented from interfering with each other, which is convenient for shortening the distance between the two adjacent air-washing branches, so that the blowing holes on the air-washing branches can blow to the surface of the flat ceramic membrane in the area directly facing the adjacent air-washing branches, and the flushing effect is better. Furthermore, the surface of the flat ceramic membrane also has an arc-shaped groove arranged along the length direction of the air-washing branch, and the arc-shaped groove is arranged directly opposite to the air-washing branch one by one. In this way, the surface of the flat ceramic membrane is provided with an arc-shaped groove, which can increase the surface area of ​​the flat ceramic membrane and make the filtering area larger. After the gas from the blowing hole is flushed into the arc-shaped groove, a vortex can be formed along the arc-shaped groove, stirring the liquid on the surface of the flat ceramic membrane, and effectively preventing the washed-off chromium hydroxide tiny particles from being deposited again.

[0044] During implementation, a flow meter is also provided on the water outlet main pipe 5 .

[0045] In this way, the water outlet flux can be controlled to make the system operate in the best state.

[0046] During implementation, a pressure gauge is also provided on the water outlet main pipe 5 .

[0047] The flat ceramic membrane is made of a nanocomposite material with a micropore diameter of 0.5-1.0 μm, and the nanocomposite material is synthesized from Al2O3, ZrO2 and TiO2 nanoparticles at a high temperature of 1600°C.

[0048] The clean water tank 8 also has an overflow tank 9 separated by a partition, and the height of the partition is lower than the depth of the clean water tank; the outlet of the main water outlet pipe 5 is connected to the overflow tank 9.

[0049] In this way, the filtered clean water can be further precipitated in the overflow tank, and the clean water on the upper layer can flow into the clean water tank, which is beneficial to further improve the treatment effect.

[0050] The specific processing steps are as follows:

[0051] First, the wastewater flows into the reaction tank, and dilute sulfuric acid is added to the reaction tank to adjust the pH value to between 2 and 3. After stabilization, sodium metabisulfite is added to control the redox potential below 250mV, and the reaction time is controlled to be not less than 30min. After the reaction is completed, NaOH is added to raise the pH value to between 8 and 9, and the pre-reaction is completed after stabilization. A trace amount of polyaluminium chloride (PAC) solution can also be added to the reaction tank at a rate of 10 to 20mg / l to promote the formation of tiny particles of metal hydroxide. A stirring blade is set in the pre-reaction tank to ensure that the reaction is complete. The entire pre-reaction time is 1 to 1.5h.

[0052] Then pump the wastewater into the ceramic membrane filter tank, start the suction pump for suction, control the working pressure of the suction pump to be less than 30kPa, and the water flux is 40~60L / (m 2 ∙h) to prevent the flat ceramic membrane from being quickly blocked; the suction time of wastewater in the ceramic membrane filter is 1.5~2.0h.

[0053] During the suction process, the surface of the flat ceramic membrane is continuously aerated and flushed by an air pump to prevent the deposition of chromium hydroxide particles on the surface of the flat ceramic membrane. The air pump can be a fan or an air compressor. The aeration volume flow rate is controlled to be 10 to 15 times the amount of water treated per hour. For example, 10m3 is treated in 1 hour. 3 For wastewater, the aeration volume during treatment should be 100~150m 3 .

[0054] At the same time, during the suction process, the suction is stopped for 1 minute every 5 minutes, and the compressor is used to pump high-pressure air into the air washing main pipe, and sprayed toward the surface of the flat ceramic membrane through the blowing holes on the air washing branch pipe, producing a purge effect on the surface of the flat ceramic membrane, and blowing off the sediment accumulated on the surface of the flat ceramic membrane. The designed pressure of compressed air for blowing off is 1Mpa.

[0055] The filtered water enters the clean water tank, and clean water is regularly drawn from the clean water tank to backwash the flat ceramic membrane to restore the membrane flux. The backwash cycle is 2 hours, and the backwash intensity is 80~100L / (m 2 ∙h), backwash time ≤5min.

[0056] After each filtration treatment cycle, the chromium-containing sludge is discharged. The discharge cycle is determined by the amount of sludge produced by the reaction, and the maximum is generally not more than 24 hours.

[0057] Compared with the traditional treatment process, the above treatment process has the following advantages:

[0058] 1. Solve the fuzzy operation defects caused by continuous reaction (it is difficult for each processing unit to reach the optimal working condition), accurately control the reaction parameters of each link, achieve optimal operation conditions, and ensure the efficiency and effect of the reaction.

[0059] 2. Use other methods to separate chromium hydroxide from the system to avoid the phenomenon of unstable chemical precipitation effect.

[0060] 3. Reduce the output of chromium hydroxide sludge (under the same water inlet conditions, the heavy metal sludge produced is only 1 / 3~1 / 2 of the traditional precipitation method), and reduce the cost of hazardous waste disposal. In addition, when the total chromium concentration in the wastewater is ≥1000mg / l, since the sludge does not contain coagulants, it has a higher purity and is economical for heavy metal recovery.

[0061] 4. Simplify the processing links to make the system easier to operate and manage; solve the problem of collapse caused by accumulation of metal hydroxides on the inclined tube, and reduce the complexity and cost of system maintenance.

[0062] 5. Ensure that wastewater meets discharge standards after treatment (the total chromium concentration in the effluent can be below 0.1 mg / l, far lower than the national standard of 1.0 mg / l).

[0063] At the same time, compared with some processes that use flat ceramic membranes to treat heavy metal wastewater, the dual membrane pollution control measures used in the present invention can effectively remove pollutants attached to the membrane surface and maintain membrane flux. The high-intensity compressed air generated by the pulse air pipe arranged along the membrane surface will disperse or peel off the relatively heavy pollutants deposited on the membrane surface, and the backwash water will further wash away the residual sediments. And with a stronger backwash intensity, the cleaning is more thorough.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A chromium-containing wastewater treatment system, characterized in that: The invention comprises a reaction tank, a ceramic membrane filter tank (2) and a clean water tank (8), wherein a water inlet pump and a water inlet main pipe are connected between the reaction tank and the ceramic membrane filter tank (2), wherein a plurality of parallel and spaced flat ceramic membranes (3) are provided in the ceramic membrane filter tank (2), wherein the flat ceramic membrane (3) has a plurality of water outlet holes which are arranged through the length direction, wherein one end of the water outlet hole is closed and the other end is connected to a water collecting branch pipe (4); a water outlet main pipe (5) is connected between the ceramic membrane filter tank (2) and the clean water tank (8), wherein the water collecting branch pipes (4) are all connected to the water outlet main pipe (5); and a suction pump (6) is provided on the water outlet main pipe (5); The ceramic membrane filter tank (2) is also provided with a flushing device (10) for flushing the surface of the flat ceramic membrane (3); The flushing device (10) comprises an air washing branch pipe arranged between two adjacent flat ceramic membranes (3), the air washing branch pipe being provided with a plurality of blowing holes arranged toward the flat ceramic membranes (3), and the air washing branch pipe being connected to a compressor via an air washing main pipe; The surface of the flat ceramic membrane (3) also has an arc-shaped groove arranged along the length direction of the gas washing branch pipe, and the arc-shaped groove is arranged opposite to the gas washing branch pipe one by one.

2. The chromium-containing wastewater treatment system according to claim 1, characterized in that: It also includes a backwash pump (7) arranged in parallel with the suction pump (6); the backwash pump (7) is connected to the water outlet main pipe (5) and the clean water tank (8) respectively through a backwash pipe, and the water outlet direction of the backwash pump (7) is toward the water collecting branch pipe (4); and a solenoid valve is respectively arranged on one side of the suction pump (6) and the backwash pump (7) facing the water collecting branch pipe (4).

3. The chromium-containing wastewater treatment system according to claim 1, characterized in that: The flushing device (10) comprises aeration heads arranged in a matrix below the flat ceramic membrane (3), and an air pump connected to the aeration heads.

4. The chromium-containing wastewater treatment system according to claim 1, characterized in that: The water outlet main pipe (5) is also provided with a flow meter.

5. The chromium-containing wastewater treatment system according to claim 1, characterized in that: The water outlet main pipe (5) is also provided with a pressure gauge.

6. A method for treating chromium-containing wastewater, characterized in that: This method is based on the chromium-containing wastewater treatment system according to claim 1 and comprises the following steps: 1) Pretreatment of wastewater: Lead the chromium-containing wastewater into the pre-reaction tank, stir continuously, and add dilute sulfuric acid to adjust the pH to 2-3. After stabilization, add sodium metabisulfite to control the redox potential below 250mV. After the reaction is completed, add alkali to raise the pH to 8-9. 2) Deep treatment of wastewater: The wastewater pretreated in step 1) is introduced into the ceramic membrane filter tank, and is sucked by a suction pump so that the chromium-containing wastewater passes through the micropores on the surface of the flat ceramic membrane and enters the water outlet holes in the inner cavity of the ceramic membrane under the action of negative pressure. The filtered clean water is introduced into the clean water tank through the outlet main pipe, and the dirt is retained in the ceramic membrane filter tank; the flat ceramic membrane is immersed in the wastewater; During the suction process, stop suction for 1 minute every 5 minutes, and use the compressor to pump high-pressure air into the air washing main pipe, and spray it toward the surface of the flat ceramic membrane through the blowing holes on the air washing branch pipe, thereby producing a purge effect on the surface of the flat ceramic membrane and blowing off the sediment accumulated on the surface of the flat ceramic membrane; the designed stripping pressure of compressed air is 1Mpa.

7. The method for treating chromium-containing wastewater according to claim 6, characterized in that: The step 1) further comprises adding a coagulant, wherein the coagulant is one or more of polyaluminium chloride, aluminium sulfate, alum, ferrous sulfate, ferric chloride and polyferric sulfate, and the adding ratio is 10-20 mg / l.

8. The method for treating chromium-containing wastewater according to claim 6, characterized in that: The flat ceramic membrane in step 2) is made of a nanocomposite material with a micropore size of 0.5-1.0 μm, wherein the nanocomposite material is composed of Al2O3, ZrO2 and TiO2 The nanoparticles were synthesized at a high temperature of 1600°C.

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