A plate-and-frame filtration assembly for a membrane bioreactor and a method of using the same

Abstract

The application discloses a plate-and-frame type filtering assembly applicable to a membrane bioreactor and an application method thereof, and belongs to the field of membrane bioreactors, which comprises a plate frame; filter cloths are arranged on both side end faces of the plate frame, the filter cloths adopt modified hydrophilic polyester filter cloths; reinforcing component assemblies for supporting the filter cloths are arranged on both sides of the filter cloths; and a water outlet pipe is connected to the lower end of the plate frame. In application, the working period of the filtering stage is 1-3 days; and the backwashing stage is processed through the process of air flushing-soaking-air flushing-water flushing. The solid-liquid separation effect before and after backwashing is very stable, the operation is simple, and the filtering assembly applicable to the membrane bioreactor and provided by the application is low in price and very stable in water quality; and in the optimization scheme, the special arrangement design of the reinforcing components on the inner and outer sides of the filter cloths can promote the cleaning work of the mud cake layer on the outer side of the filter cloth.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane bioreactor, in particular to a plate-and-frame filter assembly for membrane bioreactor and a method for using the same. BACKGROUND

[0002] A membrane bioreactor (MBR) for wastewater treatment mainly consists of two parts: an aeration tank in which activated sludge is cultivated to biodegrade wastewater, and a microfiltration or ultrafiltration membrane assembly (usually microfiltration membrane) for solid-liquid separation (sludge-water separation). However, membrane fouling requires the membrane assembly to be operated intermittently and to be backwashed frequently to restore the membrane flux, which is an extremely complicated operation procedure. When the irreversible fouling reaches a certain degree, chemical cleaning must be performed to restore the membrane filtration performance, but this will accelerate the aging of the membrane material and shorten the service life of the membrane assembly. The high price of the membrane assembly makes the operation cost of the MBR very high, which is the fundamental reason why the MBR is difficult to be rapidly promoted.

[0003] Therefore, some researchers have attempted to use some inexpensive coarse-pore materials (such as filter cloth, non-woven fabric, nylon mesh, stainless steel, etc.) to replace expensive microfiltration / ultrafiltration membranes. Due to the larger pores of the filter medium, the effluent quality of the coarse-pore filter assembly is generally poor at the beginning of operation; after a period of operation, a mud cake layer will form on the surface of the coarse-pore material, which is equivalent to forming a "secondary membrane", at this time the filtration performance of the coarse-pore filter assembly is enhanced, and good effluent quality can be achieved; as the operation time continues to extend, the filtration resistance of the mud cake layer continues to increase, and the flux decreases accordingly; when it decreases to a certain degree, the filtration performance must be restored by backwashing; but backwashing will destroy the structure of the mud cake layer, causing the effluent quality of the coarse-pore filter assembly to drop sharply, and the effluent quality can only be restored after the mud cake layer is reformed and matured. Therefore, the effluent quality of such coarse-pore filter assemblies is very unstable.

[0004] In addition, the filter cloth of the existing plate-and-frame filter assembly is basically in a flat state, and its structure needs to be improved. SUMMARY

[0005] The technical solution of the present application provides a significantly different solution from the prior art to solve the technical problems of high price of microfiltration membranes and unstable effluent quality of inexpensive coarse-pore filter assemblies.

[0006] The technical solution adopted by the present application to solve the above technical problems is:

[0007] A kind of plate and frame filter assembly that can be used in membrane bioreactor, including plate and frame;Filter cloth is arranged on the both side end faces of the plate and frame, the filter cloth uses modified hydrophilic polyester filter cloth;The both sides of the filter cloth are equipped with reinforcement assembly for supporting filter cloth;The lower end of the plate and frame is connected with water outlet pipe.

[0008] Further, the both sides of the bottom of the plate and frame are equipped with support, and the water outlet pipe is connected at the center of the bottom surface of the plate and frame.

[0009] As optimization to the above scheme, the reinforcement assembly includes outer transverse reinforcement, outer longitudinal reinforcement located outside the filter cloth and inner transverse reinforcement, inner longitudinal reinforcement located inside the filter cloth, the outer transverse reinforcement and the inner transverse reinforcement are arranged in an alternating intermittent staggered manner, and the outer transverse reinforcement is close to the inner longitudinal reinforcement, and the inner transverse reinforcement is close to the outer longitudinal reinforcement, so that the filter cloth is in a wave shape in the longitudinal direction.

[0010] Further, the outer longitudinal reinforcement and the inner longitudinal reinforcement are arranged in rows respectively, the outer transverse reinforcement is connected with the outer longitudinal reinforcement through the connecting members arranged along the length direction of the outer transverse reinforcement, and the inner transverse reinforcement is connected with the inner longitudinal reinforcement through the connecting members arranged along the length direction of the inner transverse reinforcement.

[0011] Further, the connecting members between the outer transverse reinforcement and the outer longitudinal reinforcement are elastic expansion members, and the connecting members between the inner transverse reinforcement and the inner longitudinal reinforcement are fixed connecting rods.

[0012] The application also provides an application method of the plate and frame filter assembly, including two stages of filtration and backwashing, specifically:

[0013] A. Filtration: submerge the plate and frame filter assembly in the aeration tank, start the self-priming pump, under the suction of the self-priming pump, relatively clean water passes through the filter cloth on both sides from outside to inside to enter the inside of the plate and frame filter assembly, and then flows out from the water outlet pipe, and the activated sludge is intercepted by the filter cloth in the aeration tank; the working period of the plate and frame filter assembly is 1-3 days, and the maximum transmembrane pressure difference is ≤0.06 MPa;

[0014] B. Backwashing: first air flushing to remove the sludge blocked in the pores of the filter cloth, the air flushing intensity is 1.0-1.5 L / (m 2 ·s), and the air flushing time is 1-3 min; then stop air flushing, immerse the plate and frame filter assembly in the aeration tank to make the sludge adhered to the inner wall of the pores of the filter cloth soft, the immersion time is 1-2 h; air flushing again to remove part of the sludge adhered to the inner wall of the pores of the filter cloth, the air flushing intensity is 1.0-1.5 L / (m 2 ·s), and the air flushing time is 5-10 min; finally water flushing to rinse the filter cloth and discharge the air in the inside of the assembly, the water flushing intensity is 0.5-1.0 L / (m 2 ·s), and the water flushing time is 30-60 s.

[0015] Further, in the backwashing stage, the air flushing is intermittent.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) In the present application, the filter cloth is modified hydrophilic polyester filter cloth, and the pore size is much smaller than that of the coarse pore filter assembly. After continuous pressure filtration for a long time, a layer of sludge will adhere to the inner wall of the filter cloth pores, greatly reducing the filter cloth pore size, so that the retention effect of the filter cloth pores plays a dominant role in removing suspended solids in water, and the retention effect of the sludge cake layer formed on the outside of the filter cloth is in the secondary position. Because the adhesion of sludge on the inner wall of the filter cloth pores is very strong, the combination between the filter cloth and the sludge is very tight, and backwashing cannot destroy its structure, so the solid-liquid separation effect of the plate-and-frame filter assembly before and after backwashing is very stable, and the turbidity and suspended solids concentration of the effluent can be stabilized at 4.2-6.4 NTU and 43-78 mg / L, respectively, and the effluent quality is very stable. Thus, the problem of unstable effluent quality of the coarse pore filter assembly can be solved. In addition, the market price of the present application is expected to be no more than 20 yuan / m 2 , which is much lower than that of the traditional hollow fiber microfiltration membrane assembly. Therefore, the present application provides a filter assembly with low price and stable effluent quality for membrane bioreactor.

[0018] (2) In the application, the working cycle of the filtration stage is 1-3 days, which is different from the intermittent operation filtration mode of the traditional microfiltration or ultrafiltration membrane assembly. The working cycle of the present application is significantly longer, and the self-priming pump does not need to be started frequently, and the operation is very simple.

[0019] (3) The backwashing process of air flushing-soaking-air flushing-water flushing in the present application can meet the cleaning requirements, and chemical cleaning is not required, which can save a large amount of chemical agents and labor cost, and the service life of the plate-and-frame filter assembly is greatly extended.

[0020] (4) In the optimization scheme of the present application, the filter cloth is arranged in a special wave shape in the longitudinal direction by special arrangement of the reinforcing bars on the inside and outside of the filter cloth, which can increase the contact area between the filter cloth and the sewage and improve the filtration efficiency. The elastic members are arranged on the reinforcing bars on the outside of the filter cloth, and the intermittent air flushing during backwashing can make the elastic members be compressed when air is blown, and the elastic members return to their original position when the air flushing is paused. In this way, the filter cloth can be deformed, and the effect of shaking can be achieved, which can promote the cleaning of the sludge cake layer on the outside of the filter cloth.

[0021] The present application will be explained in detail in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1Structure diagram of plate and frame filter assembly provided in the present application;

[0023] Figure 2 Structure diagram of monolithic filter cloth and its reinforcing assembly in the present application;

[0024] Figure 3 Side view of monolithic filter cloth and its reinforcing assembly in the present application;

[0025] Reference signs:

[0026] 1, plate and frame; 2, filter cloth; 3, reinforcing assembly; 31, outer transverse reinforcing; 32, outer longitudinal reinforcing; 33, inner transverse reinforcing; 34, inner longitudinal reinforcing; 35, elastic expansion piece; 36, fixed connecting rod; 4, support; 5, water outlet pipe. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings, in which several embodiments of the present application are given, but the present application can be realized in different forms and is not limited to the embodiments described herein, on the contrary, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0028] It should be noted that when an element is referred to as being "fixedly attached" to another element, it can be directly on the other element or intervening elements can also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements can also be present. The terms "vertical", "horizontal", "left", "right" and similar expressions as used herein are for illustrative purposes only.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The use of the terms "and / or" includes a combination of one or more of the associated listed items.

[0030] Embodiment one: please refer to the accompanying drawings Figure 1 A plate and frame filter assembly for a membrane bioreactor, comprising:

[0031] The plate and frame 1 is used for installing the filter cloth 2 as the basic component of the plate and frame filter assembly.

[0032] The filter cloth 2 is provided with two pieces, which are respectively arranged on the two opposite side end faces of the plate and frame 1; the filter cloth 2 is a modified hydrophilic polyester filter cloth, and the modified hydrophilic polyester filter cloth has a gas permeability ≤25L / (m 2Polyvinyl alcohol and polyvinyl amine are blended and coated on the terylene filter cloth of s) to enhance the hydrophilic property and anti-pollution property of the filter cloth;

[0033] The reinforcing assembly 3 is arranged on both sides of the filter cloth 2 to support the filter cloth 2 during filtration and backwashing;

[0034] The support 4 is installed at the bottom of the plate frame 1 to support the whole assembly;

[0035] The water outlet pipe 5 is installed at the bottom of the plate frame 1 and is connected with the inside of the plate frame 1 and is externally connected with the self-suction pump. The water outlet pipe 5 is installed at the bottom of the plate frame 1 mainly to prevent the air bubbles in the water from entering the inside of the plate frame 1 and being sucked out by the self-suction pump.

[0036] The preparation method of the modified hydrophilic terylene filter cloth is as follows: the filter cloth is soaked in ethanol to remove impurities and then is dried for standby; polyvinyl alcohol and polyvinyl amine are mixed in a certain proportion to prepare a casting solution, and then a pore former polyethylene glycol is added into the casting solution and is stirred; the casting solution is uniformly coated on the filter cloth, and then is blow-dried at a certain temperature; the dried filter cloth is placed in a glutaraldehyde aqueous solution for constant-temperature crosslinking for a certain time, and then is blow-dried; and the filter cloth is soaked in deionized water to remove the polyethylene glycol.

[0037] The application process of the plate-and-frame filter assembly includes two stages of filtration and backwashing:

[0038] (1) Filtration: the plate-and-frame filter assembly is submerged in the aeration tank, and the self-suction pump is started. Under the suction of the self-suction pump, relatively clean water passes through the filter cloth 2 on both sides from outside to inside to enter the inside of the plate-and-frame filter assembly, and then flows out through the water outlet pipe 5. The activated sludge is intercepted by the filter cloth 2 in the aeration tank. In order to prevent concentration polarization and slow down membrane pollution, the filtration mode of the traditional microfiltration or ultrafiltration membrane assembly is generally intermittent operation, for example, "on" for 8 min and "off" for 2 min. The present application must be continuously filtered for a long time, and the working cycle is 1-3 days, without intermittent stop during the period, and the maximum transmembrane pressure difference is ≤0.06 MPa.

[0039] (2) Backwashing: stop the self-suction pump, connect the air supply equipment to the water outlet pipe 5, first air flush to remove the blocked sludge in the pores of the filter cloth 2, the air flushing intensity is 1.5 L / (m 2 ·s), and the air flushing time is 1 min; then stop the air flushing, immerse the plate-and-frame filter assembly in the aeration tank, so that the sludge adhered to the inner wall of the pores of the filter cloth 2 is soft, the immersion time is 2 h; air flush again to remove part of the sludge adhered to the inner wall of the pores of the filter cloth 2, the air flushing intensity is 1.5 L / (m 2 ·s), and the air flushing time is 5 min; finally, water flush to rinse the filter cloth 2 and discharge the air in the inside of the assembly, the water flushing intensity is 0.5 L / (m 2 ·s), and the water flushing time is 60 s.

[0040] The advantages of the present application are analyzed by comparing the present application with common filter cloth assemblies and conventional hollow fiber microfiltration membrane assemblies.

[0041] 1) The water quality of the common filter cloth assembly is very unstable, especially after backwashing, the water quality is very poor, and there is a big gap before and after backwashing. Compared with other coarse pore filtration assemblies, the pores of the filter cloth 2 in the present application are much smaller. After a long time of continuous pressure filtration, a layer of sludge will adhere to the inner wall of the filter cloth 2 pores, which will greatly reduce the filter cloth 2 pores, so that the retention effect of the filter cloth 2 pores plays a dominant role in removing suspended solids in water, and the retention effect of the mud cake layer formed on the outside of the filter cloth 2 is in the secondary position. Because the adhesion of the sludge on the inner wall of the filter cloth 2 pores is very strong, the combination between the filter cloth 2 is very tight, and the backwashing cannot destroy its structure (after backwashing, the pore resistance of the filter cloth is slightly reduced, the filter cloth pore is slightly increased, but it is far from the initial state of the clean filter cloth, and the thickness of the sludge layer adhered to the inner wall of the filter cloth pore is slightly reduced, so it is believed that backwashing cannot fundamentally destroy the structure of this layer of sludge, only slightly affects the thickness), therefore the solid-liquid separation effect of the plate and frame filter assembly before and after backwashing is very stable, the water turbidity and suspended solids concentration can be stabilized at 4.2-6.4 NTU (scattering turbidity unit) and 43-78 mg / L, and the water quality is very stable.

[0042] 2) The market price of the conventional hollow fiber microfiltration membrane assembly is about 100 yuan / m 2 , and the flux when treating domestic sewage should not be higher than 10 L / (m 2 ·h). The market price of the present application is expected to be no more than 20 yuan / m 2 , and the flux can be stabilized at 100 L / (m 2 ·h). Therefore, compared with the conventional microfiltration membrane assembly, the present application has a strong competitive advantage.

[0043] 3) The working cycle of the present application is obviously longer, the self-priming pump does not need to be started frequently, and the operation is very simple.

[0044] 4) The present application can meet the cleaning requirements through air flushing-soaking-air flushing-water flushing backwashing treatment, without chemical cleaning, which can save a lot of chemical agents and labor cost, and the service life of the plate and frame filter assembly is greatly prolonged.

[0045] Example 2: The difference between this example and example 1 is:

[0046] Please refer to the attached Figure 2 and the attached Figure 3The reinforcing assembly 3 comprises outer transverse reinforcing bars 31 on the outside of the filter cloth 2, outer longitudinal reinforcing bars 32, inner transverse reinforcing bars 33 on the inside of the filter cloth 2, and inner longitudinal reinforcing bars 34. The outer longitudinal reinforcing bars 32 and the inner longitudinal reinforcing bars 34 are arranged oppositely, the outer transverse reinforcing bars 31 and the inner transverse reinforcing bars 33 are arranged alternately and intermittently in the space between the outer longitudinal reinforcing bars 32 and the inner longitudinal reinforcing bars 34, the outer transverse reinforcing bars 31 are close to the inner longitudinal reinforcing bars 34, and the inner transverse reinforcing bars 33 are close to the outer longitudinal reinforcing bars 32. The outer transverse reinforcing bars 31 are connected with the outer longitudinal reinforcing bars 32 through elastic expansion pieces 35, and the inner transverse reinforcing bars 33 are fixedly connected with the inner longitudinal reinforcing bars 34 through fixed connecting rods 36. The filter cloth 2 passes the outer transverse reinforcing bars 31 and the inner transverse reinforcing bars 33 in turn, and forms a filter cloth 2 in a wave shape in the longitudinal direction. The elastic expansion piece 35 comprises a telescopic sleeve rod and a spring arranged in the telescopic sleeve rod. The spring is arranged in an outer sleeve tube and connected with an inner telescopic rod. The outer transverse reinforcing bars 31, the outer longitudinal reinforcing bars 32, the inner transverse reinforcing bars 33, and the inner longitudinal reinforcing bars 34 are all in contact with the filter cloth 2. Each of the two filter cloths 2 is provided with a set of reinforcing assembly 3.

[0047] In the application process, when filtering, water enters the plate-and-frame filter assembly from the outside to the inside through the filter cloth 2 on both sides. Since the fixed connecting rod 36 cannot change in length, the elastic expansion piece 35 has a tendency to stretch under the action of water flow, and the existence of the inner longitudinal reinforcing bars 34 restricts the displacement of the outer transverse reinforcing bars 31, indirectly restricting the stretching of the elastic expansion piece 35, so that the filter cloth 2 remains in a wave shape. Compared with a flat filter cloth, the wave-shaped filter cloth 2 has a larger contact area with water, which can improve the filtering efficiency.

[0048] In the backwashing stage, air flushing is first performed to remove the sludge blocking the pores of the filter cloth 2, the air flushing intensity is 1.0 L / (m 2 ·s), and the air flushing time is 1 min. Then, air flushing is stopped, and the plate-and-frame filter assembly is immersed in the aeration tank to make the sludge adhering to the inner wall of the pores of the filter cloth 2 soft, the immersion time is 1 h. Air flushing is performed again to remove part of the sludge adhering to the inner wall of the pores of the filter cloth 2, the air flushing intensity is 1.0 L / (m 2 ·s), and the air flushing time is 10 min. Finally, water flushing is performed to rinse the filter cloth 2 and discharge the air in the inside of the assembly, the water flushing intensity is 1.0 L / (m 2 ·s), and the water flushing time is 30 s.

[0049] The air flushing is controlled to be intermittent (for example, “on” for 10 s and “off” for 3 s). When air flushing, the filter cloth 2 drives the elastic expansion piece 35 to contract under the action of wind; when paused, the elastic expansion piece 35 resets. In this way, the filter cloth 2 can have a deformation process, producing an effect similar to shaking, thereby promoting the cleaning work of the sludge cake layer on the outside of the filter cloth 2.

[0050] Other same as example one.

[0051] The application is described above by way of example with reference to the accompanying drawings without thereby limiting the application to the described embodiments. Any modifications of the application that are not essential to the application's concept and technical solution are deemed to be within the scope of the application.

Claims

1. A plate-and-frame filtration assembly for a membrane bioreactor, comprising a plate-and-frame (1); characterized in that: The filter cloth (2) is arranged on both side end faces of the plate frame (1), and the filter cloth (2) is modified hydrophilic polyester filter cloth; both sides of the filter cloth (2) are provided with a reinforcing component (3) for supporting the filter cloth (2); and the plate frame (1) is connected with a water outlet pipe (5) at the lower end; The reinforcing component (3) comprises outer transverse reinforcing bars (31), outer longitudinal reinforcing bars (32) on the outer side of the filter cloth (2), and inner transverse reinforcing bars (33), inner longitudinal reinforcing bars (34) on the inner side of the filter cloth (2), the outer transverse reinforcing bars (31) and the inner transverse reinforcing bars (33) are arranged in an alternating intermittent staggered manner, and the outer transverse reinforcing bars (31) are close to the inner longitudinal reinforcing bars (34), and the inner transverse reinforcing bars (33) are close to the outer longitudinal reinforcing bars (32), so that the filter cloth (2) is in a wave shape in the longitudinal direction; The outer longitudinal reinforcing bars (32) and the inner longitudinal reinforcing bars (34) are arranged in rows respectively, the outer transverse reinforcing bars (31) are connected with the outer longitudinal reinforcing bars (32) through the connecting members arranged along the length direction of the outer transverse reinforcing bars (31), and the inner transverse reinforcing bars (33) are connected with the inner longitudinal reinforcing bars (34) through the connecting members arranged along the length direction of the inner transverse reinforcing bars (33); The connecting members between the outer transverse reinforcing bars (31) and the outer longitudinal reinforcing bars (32) are elastic expansion members (35), and the connecting members between the inner transverse reinforcing bars (33) and the inner longitudinal reinforcing bars (34) are fixed connecting rods (36).

2. A plate-and-frame filtration module for a membrane bioreactor according to claim 1, characterized in that: Both sides of the bottom of the plate frame (1) are provided with supports (4), and the water outlet pipe (5) is connected at the center of the bottom surface of the plate frame (1).

3. A method of using a plate-and-frame filter assembly according to any one of claims 1-2, characterized in that: The method comprises two stages of filtration and backwashing, and specifically comprises: A. Filtration: the plate frame filter assembly is submerged in the aeration tank, and the self-priming pump is started, under the suction of the self-priming pump, relatively clean water passes through the filter cloth (2) on both sides from outside to inside into the plate frame filter assembly, and then flows out from the water outlet pipe (5), and the activated sludge is intercepted in the aeration tank by the filter cloth (2); the working period of the plate frame filter assembly is 1-3 days, and the maximum transmembrane pressure difference is ≤0.06 MPa; B. Backwashing: first air scouring to remove the clogged sludge in the pores of the filter cloth (2), air scouring intensity is 1.0-1.5 L / (m 2 ·s), air scouring time is 1-3 min; then stop air scouring, immerse the plate-and-frame filter assembly in the aeration tank to make the sludge adhered to the inner wall of the pores of the filter cloth (2) soft, soaking time is 1-2 h; air scouring again to remove the part of the sludge adhered to the inner wall of the pores of the filter cloth (2), air scouring intensity is 1.0-1.5 L / (m 2 ·s), air scouring time is 5-10 min; finally water scouring to rinse the filter cloth (2) and discharge the air inside the assembly, water scouring intensity is 0.5-1.0 L / (m 2 ·s), water scouring time is 30-60 s.

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