How Water Treatment Plants Purify Water？

Water treatment equipment of water plant

Ultrafiltration technology is a pressure-driven membrane filtration technology. Under the action of pressure, water and low molecular substances can pass through the ultrafiltration membrane, while particles, colloids and macromolecular substances are retained. The removal principle of ultrafiltration is primarily size exclusion (mechanical filtration), although particles or membranes with charge and surface chemistry may affect purification efficiency. The pore size range of ultrafiltration is about 1000 to 500,000 Daltons, which is larger than that of nanofiltration (200 to 1000 Daltons). The materials of ultrafiltration membranes are mainly polymers such as polysulfone or polyamide. According to specific application requirements, ultrafiltration membranes can be made into sheets, hollow fibers or cut into discs. In many practical applications, a small piece of ultrafiltration membrane can be quickly blocked by filtering impurities and cause a rapid drop in the filtration flow rate. Therefore, ultrafiltration membranes are usually made into large filtration areas, and the filtration direction is tangential to the membrane surface to minimize the possibility of membrane fouling, such as a large sheet (several square feet) of ultrafiltration membranes spirally wound in the center Rolled membrane elements made on tubes, or hollow fiber ultrafiltration membrane elements containing many fine ultrafiltration membrane fibers.

The role of ultrafiltration in water purification process

Ultrafiltration effectively removes colloids, proteins, bacteria, pyrogens (eg, gram-negative bacterial endotoxins), and other organics with a molecular weight larger than the membrane pore size. Ultrafiltration can be used as reverse osmosis pretreatment or terminal filtration of deionized water. When first-grade water is required, it is particularly important to minimize the precipitation of raw material ions in the ultrafiltration membrane and reduce the dead angle of the water flow to prevent bacterial and organic pollution. In this case, the hollow fiber ultrafiltration membrane can be used as an ideal ultrapure water filter element. The hollow fiber ultrafiltration membrane element used in the ultrapure water system is encapsulated in a high-purity plastic container with low ions and organic matter dissolution. The deionized water of 18.2MΩ.cm enters the ultrafiltration container and contacts the outer wall of the hollow fiber membrane for filtration. Entering the inside of the membrane, the filtered water is collected at a high speed and flows out as product water, thereby minimizing the impact of precipitates and pollutants on water quality. Due to the continuous purification of water and the concentration of solutes, the ultrafiltration membrane may be fouled and blocked. In order to ensure the flow rate of the produced water and the purity of the water quality, it is necessary to periodically perform pressure flushing on the membrane surface of the concentrated water side of the ultrafiltration membrane.The filtration efficiency of an ultrafiltration membrane can be expressed as its log reduction value (LRV) as follows: Log=[contaminant content in feed water]/[contaminant content in produced water} Evaluating the endotoxin removal efficiency of hollow fiber ultrafiltration depends on the endotoxin content in the feed water range and LRV value. The endotoxin removal rate LRV of the hollow fiber ultrafiltration membrane was 3.7 and 6.6, respectively. Measuring feed and product water contaminants to ensure final product water quality is extremely important in practical applications. A complete ultrafiltration unit must ensure correct working parameters and pass quality tests, including direct working tests and air pressure leak tests. Ultrafiltration deionized water is used for biological applications that are highly sensitive to bacteria, proteins, metal ions, or dissolved organic matter. With continuous filtration, the build-up of contaminants can negatively impact water quality and experimental results. Chemical disinfection is an effective method to destroy bacteria and organic pollutants in ultrafiltration membranes. However, regular routine disinfection can cause the resistivity of ultrapure water to drop due to the high ionic concentration of the disinfectant. The well-designed ultrafiltration can effectively clean the ion residue after disinfection, make the water quickly restore the best resistivity and ensure that the organic matter is effectively removed.

Reagent grade sodium hydroxide has been shown to be an effective cleaning agent with the following benefits.

Low-clean ultrafiltration membranes are sterilized without the need for hand-prepared sanitizers. In some applications, terminal ultrafiltration units are an effective method of treating small amounts of water. This ultrafiltration unit provides efficient filtration while reducing maintenance and water consumption.

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