Application of ultrafiltration technology in water treatment

The past 30 years is a period of rapid development of ultrafiltration technology. Ultrafiltration separation technology is widely used in drinking water preparation, food industry, pharmaceutical industry, industrial wastewater treatment, metal processing coatings, biological product processing, petroleum processing and other fields. Large-scale water treatment usually focuses on the following aspects: drinking water supply terminals, surface water treatment, seawater treatment and sewage reuse.

(1) Drinking water treatment

As the quality requirements of drinking water become more and more strict, water treatment companies invest more and more energy to control the amount of microorganisms present in the water supply network. In order to do this, one method is to carry out expensive and frequent water quality inspections, or install a barrier to prevent the entry of bacteria and viruses at the water supply terminal.

Using UF system, it is very convenient to build such a barrier. The removal rate of bacteria by ultrafiltration membrane can reach 6log, and the removal rate of virus can reach 4log, so water plants and water users do not have to worry about bacteria and viruses. Because the quality of drinking water itself is very high (turbidity and suspended solids are very low), the membrane system at this time can use a very high membrane flux, which can reach 135 liters / square meter.hour. At the same time, the water inlet condition is high, so the frequency of backflushing and chemically enhanced backwashing can be very low, and the water production can reach 99%. If necessary, a two-stage ultrafiltration system can be set up to reuse the first-stage backwash water.

(2) Surface water treatment

The system is widely used in surface water treatment. The treated water is used for irrigation or as reverse osmosis inlet water to prepare industrial water. In the Netherlands, there are more and more such factories. This technology provides a new way of industrial water, that is, it is not necessary to purchase more and more expensive drinking water, but to use the surface water nearby for treatment.

(3) Seawater desalination

The Middle East is the place with the most severe water shortage. In order to solve this problem, the earliest people usually used distillation technology. From the 1860s, membrane technology was used to solve the water shortage problem in these countries. However, many reverse osmosis seawater desalination systems are facing serious problems of membrane pollution. Mainly because the traditional pretreatment method of the reverse osmosis system cannot provide reliable influent water quality. Therefore, the vast majority of desalination plants work under conditions that are far below their designed water output, and even the water output of some plants is less than 30% of the original design. The research of the small desalination device clearly shows that the ultrafiltration system can control the water quality of seawater with great confidence, and provide high-quality influent for reverse osmosis system. Long-term tests have also shown that the effluent SDI value of the ultrafiltration system can be controlled very well below 2. These tests do not require any pretreatment before the ultrafiltration system, and are suitable for various seawater quality.

(4) Reuse of sewage

Western countries have spent a lot of energy to treat wastewater. After treatment, it is really just to discharge it to the surface water source through the drainage pipe network. This kind of behavior is very unreasonable. Again, because of its price advantages, ultrafiltration provides an attractive solution for wastewater reuse. In fact, the wastewater discharged from urban sewage treatment plants and factories is a very good water resource for industrial water and even drinking water. This is technically completely achievable, but Western users are very difficult to believe this practice. This is more a technical problem than a psychological problem. However, at present in Windhoek, Namibia, a 850-ton / hour water plant is already being built, which uses membrane technology to reuse the effluent from the wastewater treatment plant as drinking water.

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