Views: 1491 Author: Kevin Chen Publish Time: 2020-06-05 Origin: Site
The lifespan of the membrane is reflected in two aspects:
The membrane itself is permanently damaged, and it can no longer produce sufficient quantity and quality water.
The membrane is temporarily damaged after being severely contaminated. It needs frequent cleaning to restore water production capacity. The actual use time and cleaning cycle are short, making it difficult to adapt to production requirements. This problem can be solved from the process design, such as improving the quality of the membrane itself, while strengthening the environment, manufacturing construction and operation management.
Inadequate protective design can cause unrecoverable damage to the membrane. For different type of damage, the solution is also different. For example: in order to avoid fibers or sheet scratching damaged, we can choose reinforced PVDF membrane, and a pre-filtration is needed. For preventing the RO membrane from being oxidized by oxidizing substances, an ORP instrument and a reducing agent are added Device. In order to prevent overpressure physical damage, pressure protection facilities can be installed.
Lack of designing experience or reduce material cost will cause serious shortage of the membrane area. The unit area is overloaded, the pollution is serious, and frequent cleaning is also required. For this reason, the membrane area needs to be designed according to the stable membrane flux selection. For inexperienced water quality, the design data must be verified by a pilot test.
For the RO system, the excessive number of membranes connected in series will also cause serious membrane pollution in the rear section and it is difficult to clean and recover. The solution is to rationally design the number of RO membranes connected in series. A two – stage RO design shall be used for cleaning in sections.
In addition, the pretreatment capacity is too small may resulting in poor quality inlet water, it will also shorten the lifespan of the membrane. Regard this, the pretreatment process needs to be improved to ensure that the inlet water meets the requirements.
If the UF / MBR membranes are using bad quality fibers, it is easy to break, has poor pollution resistance and aging resistance, and has low efficiency in backwashing and low tensile strength. It is recommended to use reinforced PVDF membrane.
If the RO membranes have low flux and bad anti-pollution function. We can choose the model with bigger flux. And anti-pollution membranes can also be considered according to water quality.
During the manufacture and installation of the system, failure to clean up the debris in time will result in excessive impurities remaining, which will affect the water production performance. In particular, welding slag, sharp or filament object, etc., will cause damage to the fibers or the films. For MBR membranes, the impurities in the tank must be cleaned before entering the water; for UF and RO systems, the front pipeline system should be rinsed first, the pre-filter should be operated, and then comes the inlet water.
If not dosing timely, especially when the RO system’s scale inhibitor is not added in time, it can cause serious membrane blockage. We should make sure the design is correct and the operation and maintenance should be according to the procedures.
If working under high TMP (Trans – Membrane Pressure), it will cause the ultrafiltration fiber broken and the RO membrane sheet damaged. So, it is necessary to inspect the transmembrane pressure difference and the pressure drop of the membrane, and carry out restorative cleaning in time according to the working conditions to prevent excessive pressure difference operation.
During chemical cleaning, strong acids, strong bases and strong oxidizing agents will cause irreversible chemical damage to the membrane. Therefore, operators need to be proficient in chemical cleaning process to avoid strong acid and strong alkali environment; RO membrane is strictly prohibited to use strong oxidizing chemicals for cleaning.
If the water temperature is higher than 45 ℃, it will shorten the lifespan of the membrane. Generally, the water temperature should be controlled below 40 ° C, and cooling measures should be taken if necessary.
For RO systems, wastewater contains strong oxidizing substances or easily precipitated substances, which will lead to shortened membrane life cycle. When designing the system, from the perspective of its safety, prepare the proper pre-treatment and add a protective shutdown design to avoid causing such problems.