25 common solutions of reverse osmosis membrane technology problem (Part 3)
- What are particle and colloid pollution? How to measure?
Once particle and colloid contamination occurs in reverse osmosis or nanofiltration systems, it can seriously affect the membrane's water production and sometimes reduce the desalination rate. The early symptoms of colloidal fouling are an increase in system pressure difference, and the sources of particles or colloids in the membrane inlet water source vary from place to place, often including bacteria, sludge, colloidal silicon, iron corrosion products, etc. The drugs used in the pre-treatment part, such as polyaluminum and ferric chloride or cationic polyelectrolyte, may also cause fouling if they cannot be effectively removed in the clarification tank or medium filter. In addition, cationic polymeric dielectrics can also react with anionic scale inhibitors, and their precipitates can contaminate membrane components. SDI15 is used to evaluate the tendency of such fouling or pre-treatment in water. Please refer to the detailed introduction in relevant chapters.
- How long is the maximum allowed shutdown without system flushing?
If the system uses scale inhibitors, when the water temperature is between 20-38 ℃, it takes about 4 hours; Approximately 8 hours below 20 ℃; If the system is not using scale inhibitors, it will take about 1 day.
- How can the energy consumption of the membrane system be reduced?
Low energy consumption membrane elements are sufficient, but it should be noted that their desalination rate is slightly lower than that of standard membrane elements.
It can freely pass through the microfiltration membrane, which is used to remove bacteria, micro flocs, or total suspended solids (TSS). The typical pressure on both sides of the membrane is 1-3 bar
16.Can the reverse osmosis pure water system frequently start and stop?
The membrane system is designed based on continuous operation, but in actual operation, there will always be a certain frequency of startup and shutdown. When the membrane system is shut down, it is necessary to use its produced water or pre treated qualified water for low-pressure flushing to replace high concentration concentrated water containing scale inhibitors from the membrane components. Measures should also be taken to prevent water leakage in the system and the introduction of air, as if the component leaks and dries up, it may result in irreversible loss of water production flux. If the shutdown is less than 24 hours, there is no need to take measures to prevent microbial growth. But if the shutdown time exceeds the above regulations, protective liquid should be used for system preservation or timed flushing of the membrane system.
17.How to determine the direction of installing salt water sealing rings on membrane components?
The salt water sealing ring on the membrane element is required to be installed at the inlet end of the element, with the opening facing the inlet direction. When the pressure vessel is filled with water, its opening (lip edge) will further open, completely sealing the side flow of water from the membrane element to the inner wall of the pressure vessel.
18.How to remove silicon from water?
Silicon in water exists in two forms: active silicon (monomeric silicon) and colloidal silicon (polysilicon): colloidal silicon does not have the characteristics of ions, but has a relatively large scale. Colloidal silicon can be intercepted by fine physical filtration processes, such as reverse osmosis, and the content of water can be reduced through coagulation technology, such as coagulation clarification tanks. However, separation technologies that rely on ion charge characteristics, such as ion exchange resins and continuous electrodeionization processes (CDI), have limited effectiveness in removing colloidal silicon.
The size of activated silicon is much smaller than that of colloidal silicon, so most physical filtration technologies such as coagulation clarification, filtration, and air flotation cannot remove activated silicon. The processes that can effectively remove activated silicon include reverse osmosis, ion exchange, and continuous electrodeionization.