CN116328547A - External pressure type PVDF ultrafiltration membrane cleaning method - Google Patents

Abstract

The invention discloses an external pressure type PVDF ultrafiltration membrane cleaning method, which belongs to the technical field of membrane pollution cleaning, and can be used for cleaning a PVDF ultrafiltration membrane to better recover the membrane flux, and has the characteristics of simple operation, good cleaning effect and long service life of a membrane body; the method comprises the following steps: s1, pumping clear water into an ultrafiltration membrane cylinder by a pump to perform backwashing and forward washing, and discharging waste liquid after the washing is finished; s2, preparing an acidic washing solution containing citric acid and chlorine dioxide, pumping the acidic washing solution into an ultrafiltration membrane cylinder by using a pump, and discharging waste liquid after cyclic cleaning; s3, preparing alkaline washing liquid containing sodium hydroxide, pumping the alkaline washing liquid into an ultrafiltration membrane cylinder by using a pump, and discharging waste liquid after cyclic cleaning; and S4, pumping clear water into the ultrafiltration membrane cylinder by using a pump, and performing membrane flux test after washing off the residual waste liquid.

Description

A kind of external pressure type PVDF ultrafiltration membrane cleaning method

technical field

The invention relates to the technical field of membrane fouling cleaning, and more specifically, relates to an external pressure type PVDF ultrafiltration membrane cleaning method.

Background technique

Due to its superior separation performance, ultrafiltration membranes have been widely used in water treatment projects, but with the increase of filtration time, membrane fouling will occur in ultrafiltration membranes. Generally, ultrafiltration membrane pollution is divided into the following categories: in the early stage of filtration, macromolecular substances in the solvent are adsorbed on the surface of the membrane body, making the solute concentration on the membrane surface higher than that of the main solution, thus forming concentration polarization; It accumulates continuously on the surface of the membrane, and when its concentration reaches the saturation concentration, it precipitates out to form a gel layer. After the gel layer is formed, as the working pressure increases, the thickness of the gel layer also increases, and the increased pressure and coacervate resistance cancel each other out so that the membrane flux no longer increases. Finally, the solute molecules smaller than the membrane pore diameter enter the membrane pores under pressure to form membrane pore pollution, resulting in a gradual decrease in the number of membrane pores. When the above three types of membrane fouling seriously damage the separation characteristics of the membrane, the ultrafiltration membrane must be cleaned to restore the separation performance of the ultrafiltration membrane.

Clean and regenerate the PVDF ultrafiltration membrane by using a suitable cleaning method to clean the solute adsorbed on the surface of the ultrafiltration membrane and the contamination impurities in the membrane, so that the ultrafiltration membrane can be restored to the original flux value as much as possible. At present, the main cleaning method for PVDF ultrafiltration membrane is to use chemical solution immersion for cleaning, but the cleaning rate of these cleaning methods can only reach about 90%, the recovery effect of membrane flux is not good, and the corrosiveness of the chemical reagents used is relatively high. Strong, the cleaning process is easy to shorten the service life of the membrane body.

Therefore, it is urgent to design a cleaning method that can effectively clean the PVDF ultrafiltration membrane and prolong its service life.

Contents of the invention

The purpose of the present invention is to provide an external pressure type PVDF ultrafiltration membrane cleaning method, using this method to clean the PVDF ultrafiltration membrane, can better restore its membrane flux, has the advantages of simple operation, good cleaning effect, and long service life of the membrane body. long features.

Technical scheme of the present invention is as follows:

A method for cleaning an external pressure type PVDF ultrafiltration membrane, comprising the steps of:

S1 uses a pump to pump clean water into the ultrafiltration membrane cartridge for backwashing and forward washing, and discharges the waste liquid after cleaning;

S2 is equipped with acidic washing solution containing citric acid and chlorine dioxide, and pumps the acidic washing solution into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning;

S3 is equipped with alkaline lotion containing sodium hydroxide, and pumps the alkaline lotion into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning;

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Further, in the step S1, the time for backwashing is 3-5 minutes, and the time for forward washing is 3-5 minutes.

Further, in the step S2, the percentage by weight of each substance in the obtained acid washing solution is: citric acid 1-5%, chlorine dioxide 0.1-0.5%, the rest is water, and the sum of each substance is 100% .

Further, in the step S2, the cleaning time is 7-10 hours.

Further, in the step S3, the content of sodium hydroxide in the obtained alkaline washing liquid is configured to be 0.05-0.1%, and the washing time is 7-10 hours.

Further, in the step S4, the time for performing the membrane flux test is 45 minutes.

Compared with prior art, the beneficial effect that the present invention has is:

An external pressure type PVDF ultrafiltration membrane cleaning method of the present invention adopts a combination of physical cleaning and cyclic chemical cleaning, and first uses clean water to backwash and positively wash the ultrafiltration membrane, so that the surface of the ultrafiltration membrane can be removed as much as possible. Loose and easy to shed pollutants, and then through citric acid and chlorine dioxide mixed solution, alkaline solution to carry out cyclic chemical cleaning on the ultrafiltration membrane, which can deeply remove the pollutants in the gel layer on the surface of the membrane and inside the membrane pores;

The cleaning method of the present invention can effectively clean inorganic substances such as calcium, magnesium, iron, aluminum complexes, inorganic silicon, organic substances such as colloids and suspended solids, and microorganisms such as bacteria and viruses that cause PVDF ultrafiltration membrane pollution. The cleaning process is simple to operate. Through the cooperation of these chemicals, the cleaning effect is good and the cleaning cost is low. The membrane flux recovery rate of the ultrafiltration membrane can reach 96%. frequency, which effectively solves the problem of poor recovery effect of immersion method and single chemical cleaning agent on ultrafiltration membrane flux;

The chemical reagents used in the cleaning method of the present invention are less corrosive, will not cause damage or loss to the PVDF ultrafiltration membrane and its modified substances, and prolong the service life of the ultrafiltration membrane.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention. In the attached picture:

Fig. 1 is a process flow diagram of the cleaning method of the present invention.

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments, but this does not constitute any limitation to the present invention.

Shown with reference to Fig. 1, a kind of external pressure type PVDF ultrafiltration membrane cleaning method of the present invention adopts the mode that physical cleaning combines with cyclic chemical cleaning, comprises the steps:

S1 uses a pump to pump clean water into the ultrafiltration membrane cartridge for backwashing and forward washing, and discharges the waste liquid after cleaning. Among them, the backwashing time is 3-5 minutes, and the forward washing time is 3-5 minutes. Through the front and back washing of the ultrafiltration membrane, the loose and easy-to-shed pollutants on the surface of the ultrafiltration membrane can be removed as much as possible.

S2 is equipped with acidic washing solution containing citric acid and chlorine dioxide, and pumps the acidic washing solution into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning.

Wherein, the percentage by weight of each substance in the acid washing solution obtained from the configuration is: citric acid 1-5%, chlorine dioxide 0.1-0.5%, the remainder is water, and the sum of each substance is 100%. The cleaning time is 7-10 hours.

S3 is equipped with alkaline washing solution containing sodium hydroxide, and pumps the alkaline washing solution into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning.

Wherein, the content of sodium hydroxide in the alkaline washing solution obtained from the configuration is 0.05-0.1%, and the cleaning time is 7-10 hours. Utilizing a mixed solution of citric acid, chlorine dioxide and alkaline solution to perform cyclic chemical cleaning on the ultrafiltration membrane can deeply remove the pollutants in the gel layer on the surface of the membrane and inside the pores of the membrane.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

The cleaning method of the present invention can effectively clean inorganic substances such as calcium, magnesium, iron, aluminum complexes, inorganic silicon, organic substances such as colloids and suspended solids, and microorganisms such as bacteria and viruses that cause PVDF ultrafiltration membrane pollution. The cleaning process is simple to operate. Through the cooperation of these chemicals, the cleaning effect is good and the cleaning cost is low. The membrane flux recovery rate of the ultrafiltration membrane can reach 96%. The frequency effectively solves the problem that the immersion method and a single chemical cleaning agent have a poor effect on the flux recovery of the ultrafiltration membrane.

The chemical reagents used in the cleaning method of the present invention are less corrosive, will not cause damage or loss to the PVDF ultrafiltration membrane and its modified substances, and prolong the service life of the ultrafiltration membrane.

Example 1

Take 7 pieces of PVDF ultrafiltration membranes of the same size and specifications that need to be cleaned in the same wastewater filtration system, and after checking the membrane body and its support, they are randomly divided into membranes No. 1 to No. 7.

Take the PVDF ultrafiltration membrane numbered 1 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 3% citric acid and 0.3% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body. After 7 hours of circular cleaning, discharge the waste liquid.

S3 is equipped with an alkaline lotion containing 0.1% sodium hydroxide, pump the alkaline lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after 8 hours of circular cleaning.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Example 2

Take the PVDF ultrafiltration membrane numbered 2 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 2% citric acid and 0.2% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body. After 7 hours of circular cleaning, discharge the waste liquid.

S3 is equipped with an alkaline lotion containing 0.05% sodium hydroxide, pump the alkaline lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after 8 hours of circular cleaning.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Example 3

Take the PVDF ultrafiltration membrane numbered 3 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 1% citric acid and 0.1% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after circular cleaning for 7 hours.

S3 is equipped with an alkaline lotion containing 0.05% sodium hydroxide, pump the alkaline lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after 8 hours of circular cleaning.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Comparative example 1

Take the PVDF ultrafiltration membrane numbered 4 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 3% citric acid and 0% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after circular cleaning for 7 hours.

S3 is equipped with alkaline washing solution containing 0% sodium hydroxide, and the alkaline washing solution is pumped into the ultrafiltration membrane cartridge until it completely covers the membrane body, and the waste liquid is discharged after cyclic cleaning for 8 hours.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Comparative example 2

Take the PVDF ultrafiltration membrane numbered 5 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 0% citric acid and 0.3% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body. After 7 hours of circular cleaning, discharge the waste liquid.

S3 is equipped with an acid washing solution containing chlorine dioxide with a concentration of 0%. The acid washing solution is pumped into the ultrafiltration membrane cartridge until it completely covers the membrane body, and the waste liquid is discharged after circulating and cleaning for 8 hours.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Comparative example 3

Take the PVDF ultrafiltration membrane numbered 6 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 0% citric acid and 0% chlorine dioxide. Use a pump to pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body. After 7 hours of circular cleaning, discharge the waste liquid.

S3 is equipped with an alkaline lotion containing 0.1% sodium hydroxide, pump the alkaline lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharge the waste liquid after 8 hours of circular cleaning.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Comparative example 4

Take the PVDF ultrafiltration membrane numbered 7 for cleaning, the specific steps are:

S1 Use a pump to pump clean water into the ultrafiltration membrane cartridge to completely cover the membrane body, backwash for 5 minutes, and wash for 5 minutes. After cleaning, discharge the waste liquid.

S2 is equipped with an acidic lotion containing 3% citric acid and 0.3% chlorine dioxide. Pump the acidic lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body. After soaking for 7 hours, discharge the waste liquid.

S3 is equipped with an alkaline lotion containing 0.1% sodium hydroxide, and pumps the alkaline lotion into the ultrafiltration membrane cartridge until it completely covers the membrane body, and discharges the waste liquid after soaking for 8 hours.

S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test.

Comparative Experiment

Record the membrane fluxes measured from 1 to 7, and calculate the membrane flux recovery rate of each PVDF ultrafiltration membrane according to the factory membrane fluxes of these ultrafiltration membranes. The details are shown in Table 1.

Table 1 The situation table of each ultrafiltration membrane

serial number membrane flux Membrane flux recovery rate 1 96L/(m ² ·h) 96.2% 2 89L/(m ² ·h) 89.4% 3 81L/(m ² ·h) 80.7% 4 51L/(m ² ·h) 50.6% 5 60L/(m ² ·h) 60.2% 6 45L/(m ² ·h) 45% 7 71L/(m ² ·h) 71.4%

According to Table 1, the membrane flux recovery rate of the PVDF ultrafiltration membrane cleaned by the cleaning method of Example 1 is the highest. The membrane flux recovery rate of the PVDF ultrafiltration membrane cleaned by the cleaning method of Examples 2 and 3 is lower than that of the cleaning method of Example 1 due to the added chemical reagent concentration, so that its membrane flux recovery rate is not as good as that of Example 1. The cleaning method of Comparative Examples 1 to 3 is similar to that of Example 1, but the chemical reagents added are incomplete, so that the membrane flux recovery rate of the PVDF ultrafiltration membrane that it cleans out is not as good as the cleaning method of Example 1, especially the comparison In the cleaning method of Example 3, because the cleaning process does not use the configuration solution of citric acid and chlorine dioxide for cleaning, the membrane flux recovery rate is very low among so many cleaning processes. The cleaning method of Comparative Example 4 is also similar to that of Example 1, but the cleaning process does not apply cyclic cleaning, but only soaks in acidic lotion and alkaline lotion, so that the membrane flux recovery rate is not as good as that of Example 1. method. It can be seen that the cleaning method of an external pressure type PVDF ultrafiltration membrane of the present invention can deeply remove the PVDF ultrafiltration membrane by applying pressure to the membrane body during the cleaning process and using citric acid in the pickling process. Contaminated calcium, magnesium, iron, aluminum complexes, inorganic silicon and other inorganic substances, organic substances such as colloids and suspended solids, and microorganisms such as bacteria and viruses have the best cleaning effect and the highest membrane flux recovery rate.

The above descriptions are only preferred embodiments of the present invention, and any modifications, equivalent replacements and improvements made within the spirit and scope of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. an external pressure type PVDF ultrafiltration membrane cleaning method is characterized in that, comprises the steps: S1 uses a pump to pump clean water into the ultrafiltration membrane cartridge for backwashing and forward washing, and discharges the waste liquid after cleaning; S2 is equipped with acidic washing solution containing citric acid and chlorine dioxide, and pumps the acidic washing solution into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning; S3 is equipped with alkaline lotion containing sodium hydroxide, and pumps the alkaline lotion into the ultrafiltration membrane cartridge, and discharges the waste liquid after circular cleaning; S4 Use a pump to pump clean water into the ultrafiltration membrane cartridge, wash off the remaining waste liquid, and conduct a membrane flux test. 2 . The method for cleaning an external pressure type PVDF ultrafiltration membrane according to claim 1 , wherein, in the step S1 , the time for backwashing is 3 to 5 minutes, and the time for forward washing is 3 to 5 minutes. 3. A kind of external pressure type PVDF ultrafiltration membrane cleaning method according to claim 1, is characterized in that, in described step S2, the percentage by weight of each substance in the acid lotion that configures gained is: citric acid 1～ 5%, chlorine dioxide 0.1-0.5%, the rest is water, and the sum of all substances is 100%. 4 . The method for cleaning an external pressure PVDF ultrafiltration membrane according to claim 3 , wherein, in the step S2, the cleaning time is 7 to 10 hours. 5. A kind of external pressure type PVDF ultrafiltration membrane cleaning method according to claim 1, is characterized in that, in described step S3, the content of sodium hydroxide in the alkaline lotion that configures gained is 0.05～0.1% , The cleaning time is 7-10 hours. 6. A kind of external pressure type PVDF ultrafiltration membrane cleaning method according to claim 1, is characterized in that, in described step S4, the time for carrying out membrane flux test is 45min.

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