How does the waterworks purify water?

Water treatment equipment in waterworks: using ultrafiltration technology to purify water. Ultrafiltration technology is a pressure-driven membrane filtration technology. Under pressure, water and low molecular substances can pass through the ultrafiltration membrane, while particles, colloids and macromolecules are trapped. The removal principle of ultrafiltration is mainly size exclusion (mechanical filtration), although charged particles or membranes with surface chemical properties may affect the purification efficiency. The pore size of ultrafiltration is about 65,438+0,000 to 500,000 daltons, which is larger than that of nanofiltration (200-65,438+0,000 daltons). Ultrafiltration membranes are mainly made of polymers such as polysulfone or polyamide. According to the 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 will be quickly blocked by filtered impurities, resulting in a rapid decline in filtration speed. Therefore, ultrafiltration membranes are usually made with large filtration area and the filtration direction tangent to the membrane surface, so as to minimize the possibility of membrane pollution, such as coiled membrane elements made of large (several square feet) ultrafiltration membranes spirally wound on the central tube, or hollow fiber ultrafiltration membrane elements containing many fine ultrafiltration membrane fibers. The Role of Ultrafiltration in the Process of Water Purification Ultrafiltration can effectively remove colloids, protein, bacteria, pyrogens (such as Gram-negative bacterial endotoxin), and other organic substances with molecular weight larger than membrane pore size. Ultrafiltration can be used as pretreatment of reverse osmosis or as terminal filtration of deionized water. When the first-class water is needed, it is particularly important to minimize the ion precipitation of raw materials of ultrafiltration membrane, reduce the dead angle of water flow and prevent bacterial and organic pollution. In this case, hollow fiber ultrafiltration membrane can be used as an ideal ultra-pure water filtration element. A hollow fiber ultrafiltration membrane element for ultra-pure water system, in which the membrane filaments are encapsulated in a high-purity plastic container, and low ions and organic substances are dissolved out. After entering the ultrafiltration container, 18.2mω. Cm of deionized water contacts with the outer wall of the hollow fiber membrane and is filtered into the membrane filaments, and the filtered water is collected as product water at high speed, thus minimizing the impact of sediments and pollutants on water quality (see figure 1). Due to the continuous purification of water and the concentration of solute, the ultrafiltration membrane may be blocked. In order to ensure the water yield and water quality purity, it is necessary to wash the membrane surface on the concentrated water side of ultrafiltration membrane regularly. The filtration efficiency of ultrafiltration membrane can be expressed by its logarithmic decline value (LRV) as follows: Log=[ water pollutant content]/[water pollutant content] Figure 2 The evaluation of endotoxin removal efficiency of hollow fiber ultrafiltration depends on the range of endotoxin content and LRV value in feed water. Figure 2. The endotoxin removal rate LRV of hollow fiber ultrafiltration membrane is 3.7 and 6.6 respectively. In practical application, it is very important to measure the pollutant content of water supply and water production to ensure the final water quality. A perfect ultrafiltration device must ensure the correct working parameters and pass the quality test, including direct working test and air pressure leakage test. Ultrafiltration deionized water is mainly used for biological applications that are highly sensitive to bacteria, protein, metal ions or dissolved organic matter. With the continuous filtration, the deposition of pollutants will have a negative impact on water quality and experimental results. Chemical disinfection is an effective method to remove bacteria and organic pollutants in ultrafiltration membrane. However, regular routine disinfection will lead to the decrease of resistivity of ultra-pure water because of the high ion concentration of disinfectant. Well-designed ultrafiltration can effectively clean the ion residue after disinfection, make the produced water quickly recover the optimal resistivity and ensure the effective removal of organic matter (see Figure 3 and Figure 4). Reagent-grade sodium hydroxide has been proved to be an effective cleaning agent, which has the following advantages: effectively killing bacteria, effectively reducing endotoxin, effectively killing organic pollutants, reducing the formation of chemical disinfection by-products, minimizing chemical residues, and being an economical and easy-to-use disinfectant. The latest water treatment system is equipped with regular automatic cleaning function, which can clean low concentration ultrafiltration membrane simply and effectively without manual preparation of disinfectant for disinfection. In some applications, small terminal ultrafiltration device is an effective method to treat a small amount of water. This ultrafiltration device can provide effective filtration while reducing maintenance and water consumption.