Research hotspot and progress of membrane separation technology in water treatment

2.2 Reverse Osmosis

Reverse osmosis technology is applied to the advanced treatment of domestic sewage, which can separate and remove the organic substances and salts contained in the water to ensure that the water quality meets the water standard. In the process of practical application, reverse osmosis membrane has the characteristics of high selection and high permeability, and the selective membrane is a membrane treatment method that the operating pressure is higher than that of solution osmosis. Although this method itself has a better effect of purifying water, but affected by technical factors, the application effect of reverse osmosis technology in China can not be compared with Western developed countries, and it still needs to be further improved in the future, making the application of reverse osmosis equipment more efficient. In California, the United States has set up a sewage plant, and has a daily sewage treatment capacity of 37.8m3 reverse osmosis equipment, so that domestic sewage can be better treated, and it is re-applied to the water supply system.

2.3 Chemical wastewater

In order to prevent the environmental impact of chemical wastewater discharge, it is necessary to treat it before discharge. The combination of nanofiltration osmosis and reverse osmosis can effectively treat industrial wastewater containing ammonia molybdate, and the recovery rate of molybdenum ions in water can exceed 96%, which can not only effectively recover molybdenum ions, but also achieve efficient purification of wastewater. At the same time, the membrane separation technology is green and pollution-free, and is very suitable for application in the treatment of industrial wastewater, with specific pretreatment methods, recovery of reusable substances, wastewater purification and resource recovery and other treatment goals. Treatment of drinking water, the use of membrane separation treatment technology has a good effect. At present, people's living standards are gradually improving, so the water quality requirements for drinking water are higher. Compared with the traditional treatment process, the application of membrane separation can effectively remove suspended substances and bacteria in water and improve the purification effect of drinking water. Ultrafiltration, microfiltration and nanofiltration processes can be used in the treatment process to achieve micron level particles in drinking water. At the same time, it can also remove some particles that do not reach the micron level, and remove dissolved gases, inorganic substances and pesticides in water to improve the quality of drinking water.

2.4 Introduction and application of microfiltration membrane technology

Compared with other membrane technologies, microfiltration membrane technology is the first proposed and applied, and the most widely used membrane technology, which is mainly used in the pre-treatment and primary treatment of drinking water production, and can effectively remove solid particles, suspended solids, bacteria and other substances in raw water. In the application of microfiltration membrane technology for drinking water treatment, in order to achieve a good treatment effect, it is often necessary to combine microfiltration membrane technology with other membrane technologies and other water treatment methods to jointly treat water, such as ultrafiltration membrane, nanofiltration membrane, adsorbent, coagulant, etc. On the basis of microfiltration membrane technology, some researchers have tried to use different coagulants to remove humic acid in drinking water and different coagulants to study the membrane pollution, and obtained the coagulant conditions under the optimal effluent quality of drinking water and the type and dosage of coagulants under the condition of minimal membrane pollution. Some researchers take river water as test objects, using different particle size activated carbon to treat river water samples, and the test found that the pollution caused by large particle size activated carbon is more serious than that of small particle size activated carbon.

2.5 Chemical precipitation pretreatment

Chemical precipitation method is a pretreatment method by adding chemical agents to transform the dissolved substances that may cause membrane pollution into difficult soluble substances and precipitate out. Amaral et al. used chemical precipitation as a microfilter-nanofiltration (MF-NF) pretreatment process to treat stable landfill leachate. This process has been proved to be effective in removing organic matter and inorganic matter in waste liquid, and the results show that precipitation as a microfiltration pretreatment can ensure low membrane pollution. Cao et al. used Ruth filter cake filtration theory to analyze the flux decline of Ca2+ in the filtration process of formation of suspension in alginate solution, and the results showed that the addition of Ca2+ reduced membrane contamination. In addition, the mixed precipitation-nanofiltration method was used to recover phosphorus and remove heavy metals from industrial phosphoric acid wastewater, and good purification and recovery efficiency was obtained. It can be seen that chemical precipitation pretreatment can effectively alleviate membrane pollution, and this method has the advantages of low input cost and simple operation, but it still has problems such as low treatment efficiency and secondary pollution to the environment caused by the treated solution.