CN102773022A - Cross-flow ultrafiltration membrane backwashing method - Google Patents

Abstract

The invention relates to a cross-flow ultrafiltration membrane backwashing method, which belongs to the field of water treatment. In the present invention, on the basis that the cross-flow ultrafiltration membrane enhanced backwash method adopts a single addition of sodium hypochlorite to strengthen the backwash, based on the ultrafiltration membrane device material having strong oxidation resistance and the characteristics of being able to resist acid and alkali, it is supplemented by hydrochloric acid and hydrogen oxidation Sodium chemical enhanced backwashing, that is, ultrafiltration enhanced backwashing methods are backwashing with hydrochloric acid, sodium hypochlorite and sodium hydroxide to strengthen backwashing. It ensures the effluent water quality and membrane flux during the operation of the membrane system, keeps the transmembrane pressure difference within a small range, reduces energy consumption, and ensures the long-term stable, economical and safe operation of the ultrafiltration device.

Description

Cross-flow ultrafiltration membrane backwash method

technical field

The invention belongs to the field of water treatment.

Background technique

Ultrafiltration membranes are widely used in raw water pretreatment systems in the fields of seawater desalination, thermal power, nuclear power, medicine, petroleum, and chemical industry. As an advanced and economical water treatment technology, membrane technology has increasingly prominent social and economic benefits. Ultrafiltration enhanced backwashing is the most important performance recovery method for ultrafiltration membranes, and the choice of the enhanced backwashing method is crucial to the long-term stable operation of ultrafiltration membranes. For the most widely used cross-flow ultrafiltration membrane, its enhanced backwashing method often uses a single addition of sodium hypochlorite to strengthen backwashing. This enhanced backwashing method is conducive to removing the deposition and growth of microorganisms on the surface of the membrane, but it cannot remove the influent water. The deposition of slime and scale on the surface of the membrane, especially when the influent is treated with flocculant, improper adjustment of the dosage will cause the deposition of flocculant on the surface of the membrane, and the deposition of slime, scale and flocculant will be greatly reduced. Reduce the membrane flux of the system operation, resulting in an increase in the transmembrane pressure difference and energy consumption. In severe cases, the membrane filaments are completely blocked, making the ultrafiltration device unable to operate. Although it is equipped with a chemical cleaning system that is used regularly, when the amount of deposition on the membrane surface reaches a certain level, the system still cannot restore the normal water flux of the membrane after chemical cleaning.

Usually, the maximum water inlet pressure of the cross-flow ultrafiltration membrane is 400-500kPa, the normal water inlet pressure is 30-80kPa, the maximum transmembrane pressure difference is 200kPa, and the normal transmembrane pressure difference is between 30kPa and 60kPa. When the water production cycle of ultrafiltration operation reaches the set value or the inlet water pressure increases by more than 30% or the transmembrane pressure difference reaches 80-100kPa or the water flow rate drops by 15% while the inlet water pressure remains constant (deducting the influence of temperature), the Chemically enhanced backwash CEB. The conventional enhanced backwash CEB of the cross-flow ultrafiltration membrane adopts several water production cycles and then adds sodium hypochlorite backwash. The ultrafiltration operation steps are as follows:

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 to 3 minutes;

The second step of the first water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, and the time is 30 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 to 3 minutes;

The second step of the sixth water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, and the time is 30 minutes;

The third step of the sixth water production cycle: ultrafiltration to strengthen backwashing, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hypochlorite dosing pump, dosing amount of sodium hypochlorite in backwash water 50 ~ 100mg/L, time 2 minutes;

After reaching the sixth cycle, it will automatically enter the first water production cycle and cycle.

However, the above-mentioned operations cannot effectively remove deposits such as slime and scale on the ultrafiltration membrane.

Contents of the invention

The invention provides a cross-flow ultrafiltration membrane backwashing method to solve the problem that deposits such as slime and scale on the ultrafiltration membrane cannot be effectively removed in the current cross-flow ultrafiltration membrane backwashing method.

The technical scheme that the present invention takes is, comprises the following steps:

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 to 3 minutes;

The second step of the first water production cycle: Ultrafiltration runs to produce water, open the water inlet valve and water production valve, and the time is 45 to 50 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 to 3 minutes;

The second step of the sixth water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, the time is 45 to 50 minutes;

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwashing water inlet valve, backwashing drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, and the dosage of hydrochloric acid in backwashing water is 50-100mg/L Or the pH value is 1.8~2.2, and the time is 2~3 minutes;

The fourth step of the sixth water production cycle: ultrafiltration and acid soaking, close all valves, and soak for 10 to 15 minutes;

Step 5 of the sixth water production cycle: flushing with ultrafiltration and acid backwash, open the backwash inlet valve and backwash drain valve for flushing, and the flushing time is 2 to 3 minutes;

The seventh water control cycle to the eleventh water control cycle are the same as the first water control cycle to the fifth water control cycle above;

The first step of the twelfth water production cycle: the ultrafiltration is exhausted and filled with water, and the exhaust valve on the water inlet side, the produced water exhaust valve side, and the water inlet valve are opened for 2 to 3 minutes;

The second step of the twelfth water production cycle: Ultrafiltration runs to produce water, open the water inlet valve and water production valve, and the time is 45 to 50 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite in the backwash water is 50-100mg/L, the dosage of sodium hydroxide is 50-100mg/L or the pH value is 9.8-10.2, and the time is 2-3 minutes;

The fourth step of the twelfth water production cycle: Ultrafiltration strengthens backwashing, closes all valves and soaks for 10 to 15 minutes,

The fifth step of the twelfth water production cycle: Ultrafiltration strengthens backwash flushing, open the backwash inlet valve and backwash drain valve for flushing, and the flushing time is 2 to 3 minutes;

After reaching the twelfth water-making cycle, it will automatically enter the first water-making cycle and cycle.

In the present invention, on the basis that the cross-flow ultrafiltration membrane enhanced backwash method adopts a single addition of sodium hypochlorite to strengthen the backwash, the material of the ultrafiltration membrane device has the characteristics of strong oxidation resistance and can resist acid and alkali, supplemented by hydrochloric acid and hydrogen oxidation Sodium chemical enhanced backwashing, that is, ultrafiltration enhanced backwashing methods are backwashing with hydrochloric acid, sodium hypochlorite and sodium hydroxide to strengthen backwashing.

Advantages of the present invention:

Although "cross-flow" ultrafiltration is less likely to cause severe fouling on the membrane surface than "dead-end filtration", the actual operation is affected by factors such as changes in water sources, adjustments in dosage, and changes in water temperature. After a certain operation period of "flow type" ultrafiltration, the membrane surface still generally has serious deposition fouling phenomenon. The present invention not only helps to remove the deposition and growth of microorganisms on the membrane surface, but also effectively removes slime, The deposition of scales and flocculants on the surface of the membrane depends on the efficient removal ability of hydrochloric acid for inorganic scales and sodium hydroxide plus sodium hypochlorite for organic scales, microorganisms and bacteria, ensuring the effluent water quality and membrane flux during the operation of the membrane system. The transmembrane pressure difference is maintained in a small range, and the energy consumption is also reduced, which ensures the long-term stable, economical and safe operation of the ultrafiltration device, and avoids the influent water quality of the lower-level water treatment equipment.

On the basis of the original equipment and system, the transformation cost is very low and the transformation difficulty is small. The whole operation adopts automatic control. At the same time, because sodium hypochlorite and sodium hydroxide are compatible and no chemical reaction occurs, when adding sodium hypochlorite and sodium hydroxide, use a pipe.

In addition, by modifying the "hydrochloric acid backwashing cycle", "sodium hypochlorite + sodium hydroxide backwashing cycle" and the backwashing discharge time, soaking time, and flushing time of each drug-dosing backwashing can be changed, which is beneficial to the passing time Adjust to ensure that the influent water adopts different water quality to enhance the effect of backwashing. At the same time, the discharge of hydrochloric acid and sodium hydroxide during operation will not change the pH value of wastewater.

At the same time, the ultrafiltration device can be regularly protected by adding protective drugs through the acid-base storage tank.

Detailed ways

Example 1

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 minutes;

The second step of the first water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, the time is 45 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 minutes;

The second step of the sixth water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, and the time is 45 minutes;

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwashing water inlet valve, backwashing drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, and the dosage of hydrochloric acid in the backwashing water is 50mg/L Time 3 minute;

The fourth step of the sixth water production cycle: ultrafiltration and acid soaking, close all valves, and soak for 15 minutes;

The fifth step of the sixth water production cycle: flushing with ultrafiltration and acid backwash, open the backwash water inlet valve and backwash drain valve for flushing, and the flushing time is 3 minutes;

The seventh water control cycle to the eleventh water control cycle are the same as the first water control cycle to the fifth water control cycle above;

The first step of the twelfth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2 minutes;

The second step of the twelfth water production cycle: Ultrafiltration runs to produce water, open the water inlet valve and water production valve, and the time is 45 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite in the backwash water is 50mg/L, the dosage of sodium hydroxide is 50mg/L, and the time is 3 minutes;

The fourth step of the twelfth water production cycle: Ultrafiltration strengthens backwashing, closes all valves and soaks for 15 minutes,

The fifth step of the twelfth water production cycle: Ultrafiltration strengthens the backwashing flushing, and the backwashing water inlet valve and the backwashing drain valve are opened for flushing, and the flushing time is 3 minutes;

After reaching the twelfth water-making cycle, it will automatically enter the first water-making cycle and cycle.

Example 2

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2.5 minutes;

The second step of the first water production cycle: Ultrafiltration runs to produce water, open the water inlet valve and water production valve, and the time is 47.5 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 2.5 minutes;

The second step of the sixth water production cycle: Ultrafiltration runs to produce water, open the water inlet valve and water production valve, and the time is 47.5 minutes;

The third step of the sixth water production cycle: ultrafiltration and acid backwash, open the backwash water inlet valve, backwash drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, and the dosage of hydrochloric acid in the backwash water is 75mg/L;

The fourth step of the sixth water production cycle: ultrafiltration and acid soaking, close all valves, and soak for 12.5 minutes;

The fifth step of the sixth water production cycle: flushing with ultrafiltration and acid backwash, open the backwash water inlet valve and backwash drain valve for flushing, and the flushing time is 2.5 minutes;

The seventh water control cycle to the eleventh water control cycle are the same as the first water control cycle to the fifth water control cycle above;

The first step of the twelfth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the produced water exhaust valve side, and the water inlet valve are opened for 2.5 minutes;

The second step of the twelfth water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, the time is 47.5 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite and sodium hydroxide in the backwash water is 75mg/L, and the dosage of sodium hydroxide is 75mg/L, and the time is 2.5 minutes;

The fourth step of the twelfth water production cycle: Ultrafiltration strengthens backwashing, closes all valves and soaks for 12.5 minutes,

The fifth step of the twelfth water production cycle: Ultrafiltration strengthens the backwashing flushing, and the backwashing water inlet valve and the backwashing drain valve are opened for flushing, and the flushing time is 2.5 minutes;

After reaching the twelfth water-making cycle, it will automatically enter the first water-making cycle and cycle.

Example 3

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 3 minutes;

The second step of the first water production cycle: the ultrafiltration operation produces water, and the water inlet valve and the water production valve are opened for 50 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 3 minutes;

The second step of the sixth water production cycle: ultrafiltration operation produces water, open the water inlet valve and water production valve, and the time is 50 minutes;

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwashing water inlet valve, backwashing drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, the dosage of hydrochloric acid in backwashing water is 100mg/L, time 2 minutes;

The fourth step of the sixth water production cycle: ultrafiltration and acid soaking, close all valves, and soak for 10 minutes;

Step 5 of the sixth water production cycle: flushing with ultrafiltration and acid backwash, open the backwash inlet valve and backwash drain valve for flushing, and the flushing time is 2 minutes;

The seventh water control cycle to the eleventh water control cycle are the same as the first water control cycle to the fifth water control cycle above;

The first step of the twelfth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 3 minutes;

The second step of the twelfth water production cycle: the ultrafiltration operation produces water, and the water inlet valve and the water production valve are opened for 50 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite in the backwash water is 100mg/L, the dosage of sodium hydroxide is 100mg/L, and the time is 2 minutes;

The fourth step of the twelfth water production cycle: Ultrafiltration strengthens backwashing, closes all valves and soaks for 10 minutes,

The fifth step of the twelfth water production cycle: Ultrafiltration strengthens the backwash flushing, and the backwash water inlet valve and the backwash drain valve are opened for flushing, and the flushing time is 2 minutes;

After reaching the twelfth water-making cycle, it will automatically enter the first water-making cycle and cycle.

Example 4

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwash water inlet valve, backwash drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, add hydrochloric acid to the backwash water to make the pH value 2.2, time 3 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite in the backwash water is 50mg/L, and sodium hydroxide is added to make the pH value at 9.8 for 3 minutes;

All the other steps are the same as in Example 1.

Example 5

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwash water inlet valve, backwash drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, add hydrochloric acid to the backwash water to make the pH value 2.0, Time 2.5 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosing amount of sodium hypochlorite in the backwash water is 75mg/L, add sodium hydroxide to make the pH value at 10.0, and the time is 2.5 minutes;

All the other steps are the same as in Example 2.

Example 6

The third step of the sixth water production cycle: ultrafiltration and acid backwashing, open the backwash water inlet valve, backwash drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, add hydrochloric acid to the backwash water to make the pH value 1.8, time 2 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosing amount of sodium hypochlorite in the backwash water is 100mg/L, add sodium hydroxide to make the pH value at 10.2, and the time is 2 minutes;

All the other steps are the same as in Example 3.

The effect of the present invention will be further described below by way of test examples.

A 2×300MW unit in a power generation company applies the ultrafiltration device to the desalinated water treatment system. The desalinated water production process is: tap water—frequency conversion pump—safety filter (pore size is 130 microns)—ultrafiltration device—clean water tank—clear water Water pump - ion exchanger. The ultrafiltration device uses tap water as the water source and adopts the cross-flow method, that is, the concentrated water is discharged at the same time during operation, and the pollutants in the membrane cylinder are removed by regular sodium hypochlorite backwash and chemical cleaning. The operation steps are: operation - backwash - operation - backwash - operation - backwash, chlorine backwash - operation, automatic backwashing every 30 minutes during operation, each backwashing time is 1 minute, and every 3 water production cycles add Chlorine backwash once. During the operation, it mainly monitors the turbidity of influent and effluent water, backwash residual chlorine, effluent residual chlorine, oxidative reduction potential of effluent water, filter membrane cartridge pressure difference and flow rate. The maximum water inlet pressure of the device design is 500 kPa, the normal water inlet pressure is 30~80kPa, the maximum transmembrane pressure difference is 200kPa, the normal transmembrane pressure difference is between 30~60kPa, the rated output is 100t/h, and the maximum output is 120t /h.

After 1.5 months of operation of No. 1, No. 2 and No. 3 ultrafiltration devices, the inlet water pressure increased from 30 to 80 kPa under normal conditions to 160 to 180 kPa, and the transmembrane pressure difference was greater than 100 kPa. The outlet water pressure of the membrane device was 40 kPa, and the outlet water The flow rate is reduced from 100t/h to 62t/h, and the membrane permeability is reduced from 105 L/(m ² ·h) to 64 L/(m ² ·h). Since the water temperature basically does not change, the temperature has little effect on the operating parameters. When the ultrafiltration device was turned on, it was found that the membrane was seriously fouled and chemical cleaning was required. Considering that the normal chemical cleaning cycle of the ultrafiltration device should be once every 5 to 6 months, the quality of the influent water of the ultrafiltration device is unqualified or the enhanced backwash effect of the ultrafiltration device is not good, but the water quality analysis confirms that the influent water quality meets the requirements. It shows that the cause of the fouling of the ultrafiltration device is the poor effect of enhanced backwashing.

Take the inventive method to carry out cross-flow ultrafiltration membrane backwash afterwards:

The dosing backwashing system has been modified, and the backwashing of single sodium hypochlorite is changed to hydrochloric acid, sodium hypochlorite plus sodium hydroxide to strengthen backwashing, and a hydrochloric acid dosing box, dosing pump and related pipelines are newly added. In the sodium hypochlorite solution tank Add sodium hydroxide solution. After the transformation, the running operation is:

The first step of the first water production cycle: the ultrafiltration exhaust is full of water, open the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve. After both sides are full of water, this step is completed, and the time is 2.5 minutes. ;

The second step of the first water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, and the water production time is 50 minutes;

The third step of the first water production cycle: ultrafiltration backwash, open the backwash water inlet valve and backwash drain valve for 1 minute;

Carry out the second water-making cycle, the third water-making cycle, the fourth water-making cycle and the fifth water-making cycle in the same way as above;

The first step of the sixth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the exhaust valve side of the produced water, and the water inlet valve are opened for 3 minutes;

The second step of the sixth water production cycle: ultrafiltration operation produces water, open the water inlet valve and water production valve, and the time is 50 minutes;

The third step of the sixth water production cycle: ultrafiltration and acid backwash, open the backwash water inlet valve, backwash drain valve, hydrochloric acid inlet valve, hydrochloric acid dosing pump, and the dosage of hydrochloric acid in the backwash water is 75mg/L;

The fourth step of the sixth water production cycle: ultrafiltration and acid soaking, close all valves, and soak for 12.5 minutes;

The fifth step of the sixth water production cycle: flushing with ultrafiltration and acid backwash, open the backwash water inlet valve and backwash drain valve for flushing, and the flushing time is 2.5 minutes;

The seventh water control cycle to the eleventh water control cycle are the same as the first water control cycle to the fifth water control cycle above;

The first step of the twelfth water production cycle: the ultrafiltration exhaust is full of water, and the exhaust valve on the water inlet side, the produced water exhaust valve side, and the water inlet valve are opened for 2.5 minutes;

The second step of the twelfth water production cycle: ultrafiltration operation to produce water, open the water inlet valve and water production valve, the time is 47.5 minutes;

The third step of the twelfth water production cycle: ultrafiltration to strengthen backwashing, add sodium hypochlorite and sodium hydroxide, open backwashing water inlet valve, backwashing drain valve, sodium hypochlorite inlet valve, sodium hydroxide inlet valve, sodium hypochlorite dosing pump , Sodium hydroxide dosing pump, the dosage of sodium hypochlorite and sodium hydroxide in the backwash water is 75mg/L, and the dosage of sodium hydroxide is 75mg/L, and the time is 2.5 minutes;

The fourth step of the twelfth water production cycle: Ultrafiltration strengthens backwashing, closes all valves and soaks for 12.5 minutes,

The fifth step of the twelfth water production cycle: Ultrafiltration strengthens the backwashing flushing, and the backwashing water inlet valve and the backwashing drain valve are opened for flushing, and the flushing time is 2.5 minutes;

After reaching the twelfth water-making cycle, it will automatically enter the first water-making cycle and cycle.

After the transformation, the operation time of the ultrafiltration device is about 7 months, and the water production cycle of the three sets of ultrafiltration devices has been increased from 30 minutes to 50 minutes, which greatly improves the utilization rate of the equipment. The water inlet pressure of the three ultrafiltration devices is between 50 and 80kPa, the transmembrane pressure difference is less than 60kPa, the maximum effluent turbidity is 0.27 NTU, which is less than the design value (<1NTU), and the SDI is less than 2, which is less than the design value ( SDI < 3), the three sets of ultrafiltration devices have not been chemically cleaned during the period, and the average product water flow rates of No. 1, No. 2, and No. 3 ultrafiltration devices reached 89.8%, 88.5%, and 90.2% of the rated flow rate, respectively. The reason why the design flow rate was not reached In winter, although the water entering the ultrafiltration device passes through the heater, the water temperature (actually 12-16°C) is still 18-25°C lower than the optimum temperature. This is a normal phenomenon and a measure to protect the ultrafiltration device. After deducting the influence of temperature factors, the output of the three sets of ultrafiltration all reached the rated output. Therefore, judging from the operation of the three sets of ultrafiltration after the transformation, the equipment is in good condition and the effluent water quality is excellent, which fully meets the design requirements and the reverse osmosis influent water quality requirements, and the operating parameters are stable and all within the design range.

Claims (1)

1. a cross-current type milipore filter back-washing method is characterized in that comprising the following steps:

First makes the water cycle first step: ultrafiltration exhaust full water, and open the influent side air bleeding valve, produce water exhaust valve side, water intaking valve, 2～3 minutes time;

First second step of system water cycle: water is produced in the ultrafiltration operation, opens water intaking valve, produces water valve, 45～50 minutes time;

First the 3rd step of system water cycle: hyperfiltration reverse-rinsing, open backwash water intaking valve, backwash draining valve, 1 minute time;

As above same procedure is carried out second system water cycle, the 3rd system water cycle, the 4th system water cycle and the 5th system water cycle;

The 6th the system water cycle first step: ultrafiltration exhaust full water, open the influent side air bleeding valve, produce water exhaust valve side, water intaking valve, 2～3 minutes time;

The 6th second step of system water cycle: water is produced in the ultrafiltration operation, opens water intaking valve, produces water valve, 45～50 minutes time;

The 6th step in system water cycle the 3rd: ultrafiltration adds sour backwash, opens backwash water intaking valve, backwash draining valve, advances hydrochloric acid valve, hydrochloric acid dosing pump, and hydrochloric acid adds dose 50～100mg/L or pH value 1.8 ~ 2.2 in the backwash water, 2～3 minutes time;

The 6th the 4th step of system water cycle: ultrafiltration adds soak, closes all valves, soak time 10～15 minutes;

The 6th the 5th step of system water cycle: ultrafiltration adds the flushing of sour backwash, and unlatching backwash water intaking valve, backwash draining valve wash washing time 2～3 minutes;

11 system water cycles of the 7th system water cycle to the are identical with five system water cycles of first system water cycle to the as above;

The 12 the system water cycle first step: ultrafiltration exhaust full water, open the influent side air bleeding valve, produce water exhaust valve side, water intaking valve, 2～3 minutes time;

The 12 second step of system water cycle: water is produced in the ultrafiltration operation, opens water intaking valve, produces water valve, 45～50 minutes time;

The 12 the 3rd step of system water cycle: backwash is strengthened in ultrafiltration; Add clorox and NaOH; Open backwash water intaking valve, backwash draining valve, advance the hypochlorous acid sodium valves, advance the hydroxide sodium valves, clorox dosing pump, NaOH dosing pump; Clorox adds dose 50～100mg/L, NaOH and adds dose 50～100mg/L or pH value 9.8 ~ 10.2,2～3 minutes time in the backwash water;

The 12 the 4th step of system water cycle: backwash is strengthened in ultrafiltration, and close all valves and soak, soak time 10～15 minutes,

The 12 the 5th step of system water cycle: the flushing of backwash is strengthened in ultrafiltration, and unlatching backwash water intaking valve, backwash draining valve wash washing time 2～3 minutes;

Reach the 12 system water week after date and get into first system water cycle automatically, circulation.