Introduction
Ultrafiltration equipment plays an important role in many fields, such as drinking water treatment, industrial wastewater reuse, separation and purification in the food and pharmaceutical industries. In order to ensure the long-term stable operation of ultrafiltration equipment, effective maintenance measures are essential.
Daily operation and maintenance
Pressure and flow monitoring
During the operation of ultrafiltration equipment, it is necessary to regularly monitor the inlet and outlet pressures and the filtration flow. Under normal circumstances, the operating pressure should be kept within the range specified by the equipment. For example, for a certain type of hollow fiber ultrafiltration equipment, the operating pressure is generally between 0.1 and 0.6MPa. If the pressure is found to be abnormally high, it may be that the membrane component is blocked or there is a problem with the pipeline system.
The stability of the flow rate also directly reflects the operating status of the equipment. If the filtration flow rate gradually decreases, after excluding the factors of the change in the inlet flow rate, it may be that the membrane contamination causes the membrane flux to decrease. By daily or weekly monitoring of pressure and flow, potential problems can be discovered in time and corresponding measures can be taken.
Water quality monitoring
Regular testing of the quality of influent and produced water is an essential maintenance work. The test items of influent water quality include turbidity, suspended matter, organic matter content, microbial indicators, etc. If the turbidity of the inlet water suddenly increases and exceeds the designed inlet turbidity of the equipment (such as more than 5NTU), it may be necessary to strengthen the pretreatment link.
The water quality test of the produced water mainly focuses on the filtration effect of the ultrafiltration equipment. For example, in drinking water treatment, the bacteria and virus removal rate and turbidity of the produced water meet the standard requirements (such as the turbidity of the produced water is less than 0.1NTU). Once the water quality of the produced water does not meet the requirements, it is necessary to promptly check whether the membrane components are damaged and whether the seal is good.
Equipment appearance inspection
During daily maintenance, the appearance of the ultrafiltration equipment should be inspected. Check whether the shell of the equipment is corroded, deformed or leaking. For equipment with metal shells, if rust spots are found, rust removal and anti-corrosion treatment should be carried out in time.
Check the sealing of the connecting pipes and valves to ensure that there is no water leakage or air leakage. If a slight leakage is found at the pipe connection, the connecting parts should be tightened in time or the sealing gasket should be replaced to prevent the problem from worsening.
Membrane component maintenance
Cleaning
Membrane fouling is a common problem in the operation of ultrafiltration equipment, so it is very important to clean the membrane components regularly.
Physical cleaning:
Backwashing is a commonly used physical cleaning method. Generally, backwashing is performed regularly (such as every week or every two weeks) according to the operating manual of the equipment. During backwashing, the water flow direction is opposite to the normal filtration direction, and some pollutants on the membrane surface are removed by the scouring effect of a larger water flow. The pressure and time of backwashing need to be reasonably set according to the type and specification of the membrane assembly. For example, for some hollow fiber ultrafiltration membrane assemblies, the backwashing pressure can be set at 0.1-0.2MPa, and the backwashing time is 30-60 seconds.
Air scrubbing is also an effective physical cleaning method. By introducing compressed air into the membrane assembly, air bubbles are formed between the membrane fibers, and the bubbles scrub the pollutants on the membrane surface during the rising process. Air scrubbing can be used in combination with backwashing to improve the cleaning effect.
Chemical cleaning:
When physical cleaning cannot effectively restore the membrane flux, chemical cleaning is required. Select the appropriate chemical cleaning agent according to the type of membrane contamination. If it is organic contamination, sodium hydroxide solution can be used for cleaning. For microbial contamination, sodium hypochlorite solution can be used for disinfection and cleaning. When performing chemical cleaning, the specified concentration, temperature and cleaning time must be strictly followed. For example, use 0.5% – 1% sodium hydroxide solution, control the cleaning temperature at 30 – 40°C, and the cleaning time is 30 – 90 minutes.
Membrane integrity inspection
Regularly checking the integrity of the membrane can promptly detect whether the membrane is damaged, leaking, etc. A common method is the pressure decay test. Fill the membrane assembly with water and pressurize it to a certain pressure (such as 0.3MPa), then close the inlet and outlet valves, and observe the pressure decay within a certain period of time (such as 10 – 15 minutes). If the pressure decays too quickly and exceeds the specified range, it may indicate that the membrane is damaged or poorly sealed.
The bubble observation method can also be used. For hollow fiber membrane assemblies, gas is introduced into one side of the membrane, and whether continuous bubbles emerge on the other side. If so, it means that the membrane has a damaged point.
Maintenance of other components
Pump maintenance
The inlet pump, outlet pump, etc. in the ultrafiltration equipment need regular maintenance. Check whether the impeller of the pump is worn and whether the seal is intact. If the flow and head of the pump drop abnormally, it may be caused by impeller wear or blockage.
Lubricate and maintain the pump regularly, and add lubricating oil or grease according to the requirements of the equipment manual. For centrifugal pumps, it is also necessary to check the leakage of the shaft seal. If the leakage exceeds the specified value, the shaft seal should be replaced in time.
Valve maintenance
Check various valves in the equipment, such as water inlet valve, water outlet valve, backwash valve, etc. Ensure that the valve opens and closes flexibly without jamming. If the valve is not sealed tightly, it will cause water leakage or air leakage, affecting the normal operation of the equipment.
For electric valves, check whether the electrical control system is normal and regularly maintain the motor of the valve, such as cleaning the motor surface and checking whether the motor wiring is loose.
Long-term shutdown maintenance
Equipment emptying
If the ultrafiltration equipment needs to be shut down for a long time (such as more than one week), the equipment must be emptied first. Drain all the water in the equipment to prevent the growth of microorganisms in the water during the shutdown period or ice formation in a low temperature environment, which will damage the equipment.
Membrane component protection
After emptying the equipment, the membrane component can be soaked in protective liquid. Choose the appropriate protective liquid according to the material of the membrane. For example, for polyethersulfone membrane, 1% sodium sulfite solution can be used as the protective liquid. The protective liquid can prevent the membrane from being damaged by oxidation, microbial erosion, etc. during downtime.
Equipment rust prevention
The metal parts of the equipment are treated with rust prevention. Anti-rust oil or anti-rust paint can be applied for protection to ensure that the equipment can operate normally when it is restarted after a long-term shutdown.
Conclusion
The maintenance of ultrafiltration equipment is a systematic and meticulous work involving all aspects of equipment operation. Through daily operation maintenance, membrane component maintenance, other component maintenance, and long-term shutdown maintenance, the service life of the ultrafiltration equipment can be effectively extended to ensure that it is always in good operating condition, thereby providing stable and reliable filtration services for various application fields.
