CN114272761A - Deep cleaning method for unrecoverable pollution in micro/ultrafiltration membrane based on green solvent - Google Patents
Deep cleaning method for unrecoverable pollution in micro/ultrafiltration membrane based on green solvent Download PDFInfo
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- CN114272761A CN114272761A CN202111481991.6A CN202111481991A CN114272761A CN 114272761 A CN114272761 A CN 114272761A CN 202111481991 A CN202111481991 A CN 202111481991A CN 114272761 A CN114272761 A CN 114272761A
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Abstract
The invention provides a method for deep cleaning of unrecoverable pollution in a micro/ultrafiltration membrane based on a green solvent, which comprises the following steps: (1) pre-cleaning a polluted micro/ultrafiltration membrane, and removing reversible and irreversible pollution on the surface of the membrane and in the pores of the membrane; (2) slightly blowing the pre-cleaned polluted membrane by nitrogen, then soaking the polluted membrane in a green solvent to ensure that the membrane is fully contacted with the green solvent, and quickly transferring the membrane into deionized water after the treatment is finished; (3) and (3) backwashing the polluted membrane treated by the solvent by using deionized water, and fully washing out the green solvent remained in the membrane to obtain the deeply cleaned polluted micro/ultrafiltration membrane. The invention firstly removes reversible and irreversible pollution on the membrane surface/in the membrane pores by conventional chemical cleaning, then uses a specific solvent to wash out the irreversible pollution, and finally carries out post-treatment to restore the membrane flux to a new membrane level, thereby realizing the washing out of the irreversible pollutant and the restoration of the membrane flux on the premise of ensuring the effluent quality and not generating secondary pollution.
Description
Technical Field
The invention relates to the technical field of membrane separation, in particular to a pollution-unrecoverable deep cleaning method in a micro/ultrafiltration membrane based on a green solvent.
Background
A Membrane Bioreactor (MBR), which is a high-efficiency sewage treatment technology integrating biological treatment and membrane separation, has many advantages compared with the conventional activated sludge biological treatment process. The MBR performs solid-liquid separation by means of a micro/ultrafiltration membrane component, and has a good separation effect compared with a secondary sedimentation tank; the MBR has higher sludge concentration due to longer sludge age, high pollutant removal efficiency and good effluent quality, and has certain tolerance to water quality and water quantity fluctuation and more stable operation; the structure is highly integrated, the occupied area is small, and the device and the standardization are easy. Due to the complex quality of sewage, in actual operation, membrane pollution inevitably occurs due to deposition and adhesion of organic and inorganic pollutants on the membrane surface/membrane pores, and membrane cleaning is usually carried out regularly to maintain the water production capacity of MBR and ensure the stable operation of the system.
Membrane cleaning in Membrane bioreactors A review (Wang et al, Journal of Membrane Science,2014,468: 276-. Membrane fouling can be classified as recoverable and non-recoverable, depending on how easily the contaminants are cleaned off. Recoverable contamination is further subdivided into reversible contamination and irreversible contamination, wherein reversible contamination is referred to as being removable by physical cleaning mainly by hydraulic cleaning, and irreversible contamination is referred to as being removable only by conventional chemical cleaning such as acid cleaning, alkali cleaning, and oxidizing agent. Whereas the pollution that cannot be removed by conventional chemical cleaning is defined as "unrecoverable pollution", also known as "permanent pollution", the unrecoverable pollutants accumulate gradually and the water permeability of the membrane decreases gradually over a number of pollution-cleaning cycles until the water production demand cannot be met, and ultimately determines the service life of the membrane.
According to literature research, no method for effectively cleaning the micro/ultrafiltration membrane in the MBR to recover pollution is available at present. Although the unrecoverable contaminant components are generally unknown, they are characterized by strong binding force with the membrane, so that they are difficult to wash out by conventional chemical cleaning, i.e. the key problem is: conventional chemical cleaning is difficult to overcome the binding force between unrecoverable contaminants and the membrane.
In view of this, the solvent is primarily screened based on the hansen solubility parameter theory, and meanwhile, the early-stage molecular dynamics simulation theory calculation is combined, so that the green solvent with the affinity with the unrecoverable pollutants larger than that between the pollutants and the membrane is selected in a targeted manner, and the screening and optimization of the treatment conditions are performed, so that the unrecoverable pollutants are washed out on the premise of not damaging the membrane structure. In addition, due to the environment-friendly characteristic of the green solvent, the environment is not polluted secondarily while the washing-out of unrecoverable pollutants and the recovery of membrane flux are realized.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for deep cleaning of unrecoverable pollution in a micro/ultrafiltration membrane based on a green solvent. The invention firstly removes reversible and irreversible pollution on the membrane surface/in the membrane pores by conventional chemical cleaning, then uses a specific solvent to wash out the irreversible pollution, and finally carries out post-treatment to restore the membrane flux to a new membrane level, thereby realizing the washing out of the irreversible pollutant and the restoration of the membrane flux on the premise of ensuring the effluent quality and not generating secondary pollution.
The technical scheme of the invention is as follows:
a method for deep cleaning unrecoverable pollution in a micro/ultrafiltration membrane based on a green solvent comprises the following steps:
(1) pre-cleaning of the contaminated micro/ultrafiltration membrane: soaking and cleaning the polluted membrane for 1.0-2.0 h by using a sodium hypochlorite solution with the concentration of 0.2-1.0 wt%, and then soaking and cleaning for 1.0-2.0 h by using oxalic acid with the concentration of 0.5-3.0 wt%, so as to remove reversible and irreversible pollution on the surface of the membrane and in the pores of the membrane;
(2) deep cleaning of the polluted micro/ultrafiltration membrane by using a green solvent: slightly blowing the pre-cleaned polluted membrane for 2.0-5.0 min by using nitrogen, then soaking the polluted membrane in a green solvent, placing the soaked polluted membrane in a constant-temperature oscillation table at the temperature of 20-60 ℃ for 1.0-10.0 h, wherein the oscillation frequency is 50-200 rpm, fully contacting the membrane with the green solvent, and after the treatment is finished, quickly transferring the membrane into deionized water;
(3) post-treatment of contaminated micro/ultrafiltration membranes: and (3) backwashing the polluted membrane treated by the solvent for 2.0-4.0 hours by using deionized water, and sufficiently washing out the green solvent remained in the membrane to obtain the deeply cleaned polluted micro/ultrafiltration membrane.
The polluted micro/ultrafiltration membrane to be cleaned is a micro/ultrafiltration membrane which is not capable of meeting the requirement of engineering water production and is difficult to recover by conventional cleaning after long-term operation and the membrane flux is reduced to a lower level.
Further, the to-be-cleaned polluted micro/ultrafiltration membrane is a membrane used for 5-7 years.
Further, the forms of the contaminated micro/ultra-filtration membrane module to be cleaned include flat membrane, hollow fiber membrane and roll membrane.
Further, the material of the polluted micro/ultra-filtration membrane to be cleaned comprises polyvinylidene fluoride (PVDF), polyether sulfone (PES), Polysulfone (PS), Polyacrylonitrile (PAN), polypropylene (PP), Polytetrafluoroethylene (PTFE) and polyvinyl chloride (PVC).
Further, the green solvent in the step (2) refers to
And isosorbide dimethyl ether DMI or a mixture of two solvents.
Furthermore, the green solvent in the step (2) can be reused for 5-10 times.
The beneficial technical effects of the invention are as follows:
1. firstly, pre-cleaning a polluted membrane by using sodium hypochlorite and oxalic acid to remove reversible pollution and irreversible pollution in the membrane; then according to the Hansen solubility parameter theory, a green solvent with affinity with unrecoverable pollutants larger than that between the pollutants and the membrane is selected in a targeted manner, and the green solvent is used for deeply cleaning the membrane, so that the unrecoverable pollutants in the membrane body can be effectively washed out; and finally, backwashing the membrane by using deionized water, cleaning redundant green solvent, wherein the flux of the deeply cleaned polluted membrane can reach the level of a new membrane, and the pollutant interception capability is not obviously reduced.
The method can remove the unrecoverable pollution which is difficult to solve by the existing membrane cleaning technology, thereby obviously prolonging the service life of the micro/ultrafiltration membrane in the MBR, effectively reducing the carbon footprint of the MBR technology, and saving the transportation cost and the membrane replacement cost for related enterprises.
2. The green solvent used in the invention belongs to a bio-based environment-friendly solvent, has short half-life period, is non-toxic, is biodegradable and recyclable, does not generate the problem of secondary pollution in the using process, and gives consideration to both reaction rate and safety.
3. The deep cleaning method for the polluted micro/ultrafiltration membrane, provided by the invention, has the advantages of simple operation, easy implementation, wide application range and strong popularization, is an important technical breakthrough in the field of MBR membrane cleaning, and has important innovative significance and practical application value for sustainable utilization of membrane materials and green development of membrane sewage treatment technology.
Drawings
FIG. 1 is a scanning electron microscopy characterization of new films, contaminated films, and repair films obtained in examples 1-2 of the invention.
FIG. 2 is a three-dimensional fluorescence spectrum of the green solvent recovered after deep cleaning of the contaminated film in example 2.
FIG. 3 is a graph comparing water flux and rejection after cleaning of the new membrane, the fouled membrane, and the membranes of examples 1-3 and comparative examples 1-3.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
pre-cleaning of the contaminated micro/ultrafiltration membrane: the contaminated PVDF ultrafiltration membrane was rinsed by 0.5% sodium hypochlorite for 1.5h, then 2.0% oxalic acid for 1.5h, followed by rinsing with deionized water to remove excess chemicals on the surface.
Wherein, the PVDF membranes cleaned in the examples and the comparative examples are micro/ultra-filtration membranes (usually membranes used for 5-7 years) which have membrane flux reduced to a lower level after long-term operation, cannot meet the requirement of engineering water production and are difficult to recover by conventional chemical cleaning
As can be seen from the scanning electron microscope shown in fig. 1, after the pre-cleaning, part of the contaminants adhered to the surface of the film were removed from the surface of the film.
Example 2:
deep cleaning of the polluted micro/ultrafiltration membrane by using a green solvent: slightly blowing the precleaned PVDF ultrafiltration membrane with nitrogen for 3.0min, and soaking in green solvent
And placing the membrane in a constant-temperature shaking table (100rpm) at 40 ℃ for 4.0h to ensure that the membrane is fully contacted with a green solvent, backwashing the polluted membrane treated by the solvent for 3.0h by using deionized water after the treatment is finished, and fully washing out the green solvent remained in the membrane to obtain the deeply cleaned PVDF ultrafiltration membrane.
The film surface is further cleaned and the film surface is relatively more flat as observed by the scanning electron microscope shown in figure 1.
The three-dimensional fluorescence spectrogram shown in figure 2 shows that unrecoverable pollutants in the membrane are washed out, and the peak value of the pollutants appears in the humic acid-like fluorescence spectrum region.
Example 3:
deep cleaning of the polluted micro/ultrafiltration membrane by using a green solvent: and (2) blowing the precleaned PVDF ultrafiltration membrane with nitrogen for 3.0min, soaking the precleaned PVDF ultrafiltration membrane in a green solvent, namely isosorbide dimethyl ether (DMI), placing the membrane in a constant-temperature shaking table (100rpm) at 60 ℃ for 6.0h to ensure that the membrane is fully contacted with the green solvent, backwashing the polluted membrane treated by the solvent for 3.0h by using deionized water after the treatment is finished, and fully washing out the green solvent remained in the membrane to obtain the deeply cleaned PVDF ultrafiltration membrane.
Test example:
laboratory performance testing of repair films: the membrane component is connected with a hose with matched size and a reducing straight-through to form a small-sized membrane component convenient for performance test. The assembly is placed in a beaker filled with a certain solution, the upper end of the assembly is connected with a vacuum meter and a peristaltic pump, a constant pressure pumping mode is adopted for testing (the pressure is constant at 30kPa), a balance monitors the water outlet quality in real time, and the water flux can be obtained according to the change of the quality.
Preparing 0.1g/L sodium alginate solution as water inlet, and measuring inlet and outletThe retention rate of the membrane to the sodium alginate can be obtained by changing the water concentration. The water flux of the new membrane, the contaminated membrane and the washed membranes obtained in examples 1 to 3 (FIG. 3) was tested to be 376.2L/(m)2 h bar)、47.6L/(m2 h bar)、94.7L/(m2 h bar)、390.9L/(m2h bar) and 250.4L/(m)2h bar), the retention rates for sodium alginate were 95.9%, 96.4%, 91.7%, 93.7% and 94.2%, respectively. From the above data, it is clear that both examples 2 and 3 have significantly improved water flux compared to example 1, and that example 2 has comparable water flux and rejection to the new membrane.
Comparative example 1:
the contaminated PVDF ultrafiltration membrane was rinsed by 0.5% sodium hypochlorite for 1.5h, then 2.0% oxalic acid for 1.5h, followed by rinsing with deionized water to remove excess chemicals on the surface. And (2) blowing the precleaned PVDF ultrafiltration membrane by nitrogen for 3.0min, soaking the precleaned PVDF ultrafiltration membrane in N, N-dimethylformamide DMF, placing the membrane in a constant-temperature shaking table (100rpm) at 40 ℃ for 4.0h to ensure that the membrane is fully contacted with a green solvent, backwashing the polluted membrane treated by the solvent for 3.0h by using deionized water after the treatment is finished, and fully washing out the solvent remained in the membrane to obtain the PVDF ultrafiltration membrane after the solvent cleaning.
As shown in fig. 3, the membrane flux was not significantly changed before and after solvent cleaning, i.e. N, N-dimethylformamide DMF did not achieve deep cleaning of the contaminated membrane.
Comparative example 2:
the contaminated PVDF ultrafiltration membrane was rinsed by 0.5% sodium hypochlorite for 1.5h, then 2.0% oxalic acid for 1.5h, followed by rinsing with deionized water to remove excess chemicals on the surface. And (2) blowing the pre-cleaned PVDF ultrafiltration membrane by nitrogen for 3.0min, then soaking the membrane in dichloromethane, placing the dichloromethane in a constant-temperature shaking table (100rpm) at 40 ℃ for 4.0h to ensure that the membrane is fully contacted with a green solvent, after the treatment is finished, backwashing the polluted membrane treated by the solvent for 3.0h by using deionized water, and fully washing out the solvent remained in the membrane to obtain the PVDF ultrafiltration membrane cleaned by the solvent.
As shown in fig. 3, the membrane flux after solvent cleaning was tested to decrease, i.e. methylene chloride did not achieve deep cleaning of the fouled membranes, but instead could cause a loss of membrane flux.
Comparative example 3:
CN102145258A is adopted as a cleaning method of a membrane module polluted by heavy oil sludge for membrane cleaning.
Continuously injecting clean water into the membrane modules through a backwashing system by using the polluted PVDF ultrafiltration membrane, wherein the injection amount is 2L of clean water into each membrane module, and simultaneously carrying out full high-strength aeration on the membrane modules, wherein the gas-water ratio is maintained at 30:1 for 3 hours; then, injecting 300ppm acidic hydrogen peroxide solution into the membrane modules through a backwashing system for backwashing, wherein the injection amount is 0.5L acidic hydrogen peroxide solution for each membrane module, and standing and soaking for 12 h; after soaking, high-strength aeration is carried out on the membrane component, and the gas-water ratio is maintained at 45: 1. And (4) after the aeration is finished, obtaining the PVDF ultrafiltration membrane cleaned by the solvent.
As shown in FIG. 3, the membrane flux was found to be 103.6L/(m)2h bar), it can be seen that the technology only uses a back washing method to strengthen chemical cleaning, still belongs to the category of conventional chemical cleaning, and has no effect of removing unrecoverable pollution.
While the embodiments of the present invention have been disclosed above, it is not limited to the applications listed in the description and embodiments, but is fully applicable to various fields suitable for the present invention, and it will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in the embodiments without departing from the principle and spirit of the present invention, and therefore the present invention is not limited to the specific details without departing from the general concept defined in the claims and the scope of equivalents thereof.
Claims (7)
1. A method for deeply cleaning unrecoverable pollution in a micro/ultrafiltration membrane based on a green solvent is characterized by comprising the following steps of:
(1) pre-cleaning of the contaminated micro/ultrafiltration membrane: soaking and cleaning the polluted membrane for 1.0-2.0 h by using a sodium hypochlorite solution with the concentration of 0.2-1.0 wt%, and then soaking and cleaning for 1.0-2.0 h by using oxalic acid with the concentration of 0.5-3.0 wt%, so as to remove reversible and irreversible pollution on the surface of the membrane and in the pores of the membrane;
(2) deep cleaning of the polluted micro/ultrafiltration membrane by using a green solvent: slightly blowing the pre-cleaned polluted membrane for 2.0-5.0 min by using nitrogen, then soaking the polluted membrane in a green solvent, placing the soaked polluted membrane in a constant-temperature oscillation table at the temperature of 20-60 ℃ for 1.0-10.0 h, wherein the oscillation frequency is 50-200 rpm, fully contacting the membrane with the green solvent, and after the treatment is finished, quickly transferring the membrane into deionized water;
(3) post-treatment of contaminated micro/ultrafiltration membranes: and (3) backwashing the polluted membrane treated by the solvent for 2.0-4.0 hours by using deionized water, and sufficiently washing out the green solvent remained in the membrane to obtain the deeply cleaned polluted micro/ultrafiltration membrane.
2. The method of claim 1, wherein the contaminated micro/ultrafiltration membrane to be cleaned is a micro/ultrafiltration membrane that has a membrane flux that decreases to a low level after long-term operation, fails to meet engineering water production requirements, and is difficult to recover from conventional chemical cleaning.
3. The method of claim 2, wherein the contaminated micro/ultrafiltration membrane to be cleaned is a membrane used for 5-7 years.
4. The method of claim 1, wherein the contaminated micro/ultrafiltration membrane module form to be cleaned comprises a flat sheet membrane, a hollow fiber membrane and a roll-up membrane.
5. The method of claim 1, wherein the contaminated micro/ultrafiltration membrane material to be cleaned comprises polyvinylidene fluoride (PVDF), Polyethersulfone (PES), Polysulfone (PS), Polyacrylonitrile (PAN), polypropylene (PP), Polytetrafluoroethylene (PTFE) and polyvinyl chloride (PVC).
6. The method for deep cleaning of unrecoverable contaminants on micro/ultrafiltration membrane based on green solvent as claimed in claim 1, wherein the green solvent in the step (2) is
And isosorbide dimethyl ether DMI or a mixture of two solvents.
7. The method for deep cleaning of unrecoverable contamination on a green solvent-based micro/ultrafiltration membrane according to claim 1, wherein the green solvent in the step (2) can be reused for 5-10 times.
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