Looking for information on the production of desalinated water using reverse osmosis

You can add my QQ: 99310839

I’ve been warned several times, so I dare not speak casually anymore :( I have information on this topic, but unfortunately I can’t upload it. 　Due to its many advantages such as low equipment investment, low energy consumption, and short construction time, the reverse osmosis seawater desalination process has seen rapid development in recent years, with extensive practical applications; it is increasingly becoming the dominant technology for seawater desalination. The key to reverse osmosis seawater desalination technology is the reverse osmosis membrane. Although the production of these membranes and related components is quite advanced, with a desalination efficiency of > 99.3%, the average service life of these membranes is only 5 years. This is one of the main reasons for the high costs associated with seawater desalination. Membrane fouling is the primary cause of the short service life of these membranes. Pre-treatment of seawater is key to reducing membrane fouling, extending the service life of membranes, and ensuring the long-term stable operation of reverse osmosis systems. 1 　Quality requirements for water entering the reverse osmosis system: The quality standards that the water entering the reverse osmosis system must meet, as well as the objectives to be achieved through pretreatment, are shown in Table 1. Table 1 Quality requirements for water fed into reverse osmosis systems Parameter Target value Water temperature (°C): 20–35 pH value: 3–11 Turbidity (NTU): < 0.3 Colority (units): Clear Pollution index: FI < 4 Residual chlorine (mg/L): < 0.1 CODMn (mg/L): < 2 Fe (mg/L): < 0.1 Note: All values are applicable to polyamide membranes. 　　Pre-treatment is intended to remove suspended solids, organic matter, colloidal substances, microorganisms, bacteria, and certain harmful substances such as iron, manganese, and calcium. Suspended solids, colloidal substances, and soluble organic polymers in water accumulate on the surface of the membrane, causing it to become contaminated; microorganisms and bacteria can erode the membrane, and their residues may precipitate in solid form, further deteriorating the membrane’s performance. Degradation in parameters such as water temperature, pH value, residual chlorine content, and pressure can lead to the hydrolysis and oxidation of the membrane, while changes in the membrane’s structure caused by solutes can also result in a decrease in its water permeability. 2 　Pre-treatment process 211 　Small seawater desalination units: These units produce a small amount of fresh water, are compact in size and light in weight. They are typically used on civilian ships, vessels, islands, etc., as an additional source of fresh water, and are not usually used on a continuous basis over long periods of time. Since the location of use is far from the mainland, the seawater quality remains stable, it is less polluted, and thus of good quality. The main substances to be removed through pre-treatment are suspended solids and colloids; therefore, a relatively simple pre-treatment process can be employed: seawater → bag filter or sand filter → safety filter → reverse osmosis unit. Among them, bag filters can be made from materials such as non-woven fabric and are used to remove suspended particles of larger size; after being in use for a certain period of time, they can be taken out and cleaned manually. Sand filters offer better performance and greater adaptability, but they require backwashing after operating for a certain period of time, and an additional backwashing water pump is needed. The filter elements of security filters can be wound filters or spun-fused filters with a particle size range of 5–22 μm, which are used to remove small-sized suspended particles and colloids; the filter elements can be replaced after being in use for a certain period of time. 212 Pretreatment for mobile seawater desalination units: Mobile seawater desalination units can be designed in container form, trailer form, or mounted on vehicles to serve as specialized desalination vehicles, for use by organizations that need to operate in coastal areas. Furthermore, as a supplementary source for freshwater supply, it is generally not used continuously for long periods. Such devices are subject to space and mass constraints; the equipment used must be small in size and light in weight, and the water source should be seawater from near the coast. Since seawater near the coast is prone to pollution, it contains suspended particles, colloids, and dissolved substances, as well as a large amount of organic matter, microorganisms, bacteria, algae, and other pollutants. Moreover, water quality varies significantly between different regions and seasons. To meet the water quality requirements for feedwater in reverse osmosis processes, it is necessary to enhance pre-treatment and employ more complex treatment processes (see Figure 1). The purpose of adding coagulants is to destabilize the colloidal particles in water and cause them to aggregate into flocs. Since precipitators can only remove larger suspended particles, in order to improve the removal of smaller ones, Figure 1a shows two-stage safety filters, while Figure 1b shows a multimedia filter and a safety filter respectively. In Figure 1a, the filter elements are used in large quantities in the process flow, and the operation is relatively simple; in Figure 1b, the process flow has greater adaptability, but the multi-media filters are heavy, require backwashing, necessitate the use of a backwashing pump as well as storage of water for backwashing, making the operation more complex. Disinfectors are installed in both the processes a and b shown in Figure 1 to kill bacteria and viruses, ensuring that the bacterial count in the water fed into the reverse osmosis system does not exceed the specified limits. Disinfection can be achieved using ultraviolet light, ozone, or chlorine disinfectants. If the latter two methods are used, a de-gassing device is required to remove excess ozone or residual chlorine, thereby preventing the reverse osmosis membrane from being oxidized.

213 Pretreatment in desalination plants Desalination plants supply potable water to the residents of coastal cities or islands; they are large-scale facilities, and the equipment used there is generally not subject to space or quality constraints, allowing for continuous operation over long periods of time. Since the source water used is coastal seawater, its quality is similar to that of the source water treated by mobile units (though affected by tides); the only difference is that the water intake location is fixed. Its process flow is similar to that of mobile units (see Figure 2). In the processes shown in Figures 2a and 2b, the addition of disinfectant serves to kill bacteria and algae. If disinfection is carried out using liquid chlorine or NaClO generators, a reducing agent such as NaHSO3 must be added before seawater enters the reverse osmosis unit to remove chlorine, thereby ensuring the appropriate residual chlorine level in the water fed into the reverse osmosis system and preventing the membranes from being oxidized. The purpose of adding scale inhibitors in the process flow is to prevent the formation of insoluble inorganic salts as seawater is concentrated during desalination, which could otherwise lead to scaling and deposition on the surface of the reverse osmosis membranes and within the system’s pipelines. Common scale inhibitors include H2SO4, (NaPO3)6, and polymer resins. Figure 2b is suitable for areas with low seawater turbidity, while Figure 2c is suitable for areas where seawater turbidity varies greatly and higher turbidity levels may occur. The caisson in Figure 2a takes advantage of the natural filtering effect of the sand layer on the shore, which gives it good adaptability. An activated carbon filter is installed to absorb and remove organic substances as well as unpleasant odors, but the activated carbon needs to be regenerated after being used for a while; it is suitable for areas with high levels of organic substances or unpleasant odors in the seawater. The safety filter in the above process flow can be replaced by ultrafiltration, microfiltration, or nanofiltration, which also allows for the elimination of some chemical reagents (such as disinfectants), thereby further improving the quality of water entering the reverse osmosis unit and ensuring that FI < 1. However, the service life of ultrafiltration, microfiltration, and nanofiltration membranes is relatively short, and their economic viability compared to traditional pretreatment methods still requires further investigation. 3 　It is recommended that when selecting the pretreatment process for seawater desalination, priority should be given to the quality of the seawater to be treated. At the same time, factors such as the location of use, the method employed, the level of management, and the performance of the desalination membranes should also be taken into account, so as to reduce costs and simplify operations while still meeting the water quality requirements for feedwater in reverse osmosis processes.

This is information on the pretreatment section of seawater desalination reverse osmosis systems. For reference only. There are quite a number of units and systems involved in the desalination process using reverse osmosis. There are also many requirements and options regarding membranes. I’ll upload it when I have time. Ugh, I’m worried that if I post too much, people will say I’m spamming... and delete my posts. :L

By the way, there are already some materials on reverse osmosis desalination on the forum; you can search for them as a reference. The link below explains the principle of reverse osmosis; it’s quite easy to understand. You can refer to http://bbs.hcbbs.com/viewthread.php?tid=483408&highlight=%B7%B4%C9%F8%CD%B8