What do you know about the cleaning solutions for ultrafiltration machines?

Physical cleaning mainly includes: washing, backwashing, and air washing (mainly including air scrubbing and air water washing). Periodic physical cleaning mainly refers to a cleaning method that sets the system to run for a period of time, performing brief positive washing, backwashing, and gas washing, or combining these three methods.

1. Positive washing: Positive washing is achieved by opening the inlet valve and closing the production water valve, allowing the flushing solution to flow out at a high flow rate from the concentrated water discharge valve, thereby performing high-speed flushing on the membrane surface and reducing the accumulation of pollutants on the membrane surface.

Backwashing: This operation is opposite to filtration, where the backwash water enters the ultrafiltration fiber from the clear liquid side and flows through the membrane to the concentrated water side. Through a large flow of backwash water, the pollutants on the membrane pores and the surface of the hollow fiber membrane are washed away, and the washed pollutants are discharged through the lower discharge valve.

2. Gas scrubbing: Remove pollutants from the surface of the membrane by shaking the membrane filaments with gas.

3. Air water washing: The backwash water is pumped through ultrafiltration to enter the concentration side of the ultrafiltration membrane tube and discharged from the clear liquid side. At the same time, compressed air is intermittently introduced from the filtration inlet of the ultrafiltration membrane tube. The combination of air and water for backwashing can effectively cause shear force and more effectively remove particles contaminated on the membrane surface, and take some particles out of the ultrafiltration membrane tube.

Control each process through PLC, and after running for a period of time, cooperate with certain washing, backwashing, and gas washing to timely and effectively remove pollutants on the membrane surface. This not only ensures stable system operation, but also extends the chemical cleaning cycle.

4. Disperse chemical cleaning

Adding chemical agents to backwashing (also known as "dispersed drug washing" or "chemically enhanced backwashing" in this system)

After each system has been running for a certain amount of time, it will undergo dosing backwashing, which means adding a certain proportion of backwashing agent to the backwash solution through a dosing pump and soaking the membrane for a short period of time. The operation of this process is automatic, but it is necessary to confirm that the agent in the dosing box is sufficient. The amount of backwashing agent added depends on the treated water quality. For detailed information, please consult Kaimo Company.

5. Chemical cleaning

Chemical cleaning: After a period of normal operation, the ultrafiltration membrane components are contaminated by suspended particles, organic matter, and other substances in the wastewater, resulting in a decrease in the production water flow rate and an increase in membrane pressure difference (i.e. a decrease in the production water pressure coefficient). And this phenomenon cannot be restored through physical methods and dispersed chemical cleaning. In order to restore the original performance of the membrane components, regular chemical cleaning is necessary. The specific cleaning plan should be determined by the characteristics and degree of pollution of the pollutants.

5.1 Preparation before chemical cleaning

5.1.1 Selection of cleaning plan

Acid washing scheme: Use an acidic solution to clean the ultrafiltration device.

This cleaning plan is suitable for non organic pollution caused by the inorganic salt content in the inlet water exceeding the design standards, or the suspended solids in the inlet water of the ultrafiltration membrane module being particularly high, resulting in non organic pollution on the inlet side of the membrane.

Alkaline washing scheme: Use alkaline oxidant solution to clean the ultrafiltration device.

When the organic content in the influent is high, it may cause organic contamination of the filter membrane. And when conditions are favorable for biological survival, some bacteria and algae will also be generated in the ultrafiltration membrane components, causing biological pollution.

5.1.2 Quality requirements for chemical cleaning agents

Citric acid, sodium hypochlorite, and sodium hydroxide are all industrial grade.

5.1.3 Safety precautions

1) Avoid direct contact with agents such as NaOH and NaClO, which have varying degrees of corrosiveness, and NaClO is also a strong oxidizing agent.

2) During cleaning, the pressure of the pipeline should be controlled to prevent excessive pressure from causing chemical splashing.

5.2 Chemical cleaning process

5.2.1 Precautions during chemical cleaning

1) Before chemical cleaning of the ultrafiltration device, it is necessary to first perform gas water backwashing.

2) The entire cleaning process of the ultrafiltration device takes at least 2-4 hours.

3) If the ultrafiltration device is shut down for more than three days after cleaning, maintenance must be carried out according to the requirement of long-term shutdown.

4) The cleaning solution must be prepared with ultrafiltration produced water or higher quality water.

5) The cleaning agent must go through 50 cycles before circulating into the membrane components μ The filter element of m is used for filtration to remove possible pollutants from the cleaning agent.

6) The temperature of the cleaning solution should be controlled between 25 ℃ and 40 ℃. Increasing the temperature of the cleaning solution can improve the cleaning efficiency, but pH exceeding 12 is strictly prohibited.

7) When necessary, multiple cleaning agents can be used for cleaning, but cleaning agents and disinfectants should not cause damage to the membrane and component materials. After each cleaning, the cleaning agent should be drained and the system should be rinsed clean with ultrafiltration produced water before using another cleaning agent for cleaning.

8) When using chemical cleaning solution for cleaning, the initial 10-15% dirty cleaning solution is not circulated and is discharged through the discharge valve on the membrane frame.

5.2.2 Pickling operation steps

A 1-2% citric acid solution with ammonia solution adjusted to pH 2-4 or 0.3% HCl solution, suitable for iron pollution and carbonate crystallization pollution blockage.

1) Preparation work

a) Press the shutdown program to shut down the ultrafiltration system.

b) Close all valves of the ultrafiltration system.

c) Prepare 1-2% citric acid in the cleaning solution tank and adjust the pH to 2-4 or 0.3% HCl solution with ammonia water. Stir thoroughly to mix evenly.

2) Cleaning

a) Start the cleaning water pump, slowly open the outlet valve of the cleaning water pump and the inlet and outlet valves of the ultrafiltration device's cleaning solution, control the flow rate of each membrane component at 4-6 m3/h to allow the cleaning solution to enter the membrane components and return to the cleaning solution tank. The cycle cleaning time is 30 minutes.

b) Turn off the cleaning pump and let it soak for 60 minutes.

c) Empty the cleaning solution tank and cleaning filter, and rinse thoroughly with ultrafiltration produced water.

After cleaning, it is necessary to rinse the ultrafiltration membrane components with ultrafiltration produced water to remove residual chemical solutions from the ultrafiltration device.

5.2.3 Alkali washing operation steps

A 0.1% NaClO+0.05% NaOH solution is used to clean the fouling of ultrafiltration membrane components caused by organic matter and active organisms.

Refer to the pickling steps.

5.3 Evaluation of the effectiveness of chemical cleaning

To evaluate the effectiveness of chemical cleaning, the main observation is the production water pressure coefficient. If the production water pressure coefficient can recover to more than 95% after the last chemical cleaning, it is considered that the chemical cleaning has achieved the desired effect. Otherwise, it is necessary to extend the soaking time of the chemical cleaning agent or increase the effective concentration of the chemical cleaning agent.

5.4 Regular sterilization of pressure ultrafiltration system

To prevent microbial contamination on the ultrafiltration membrane, it is necessary to regularly add bactericides to the ultrafiltration system, and the type of bactericide added should be determined according to the process conditions. A commonly used method is to use sodium hypochlorite.

Generally, it should be done once every two weeks, and the addition method can be shock addition before pre-treatment. The concentration of addition is about 50ppm, and the addition time is 2.0 hours. It can also be done through long-term continuous small amount addition.

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