What is the current status of nanofiltration technology in water treatment?

What is the current status of nanofiltration technology in water treatment?

Nanofiltration membrane softening water: One of the largest applications of NF membranes is softening of drinking water. In water, calcium and magnesium salts of sulfuric acid and carbonic acid produce water hardness. The main application of the film-tech NF70 film is the softening of the water, so called the "water-softening film", its operating pressure is 0. 5MPa ~ 0. 7MPa, can remove 85% ~ 95% hardness and 70 % of monovalent ions. The main considerations for membrane softening water are feed water quality, infiltration water quality and recovery rate. Whether acid and scale inhibitors are added depends on the feed water quality and recovery rate. Depending on the water quality and quantity of the permeate, the membrane modules, the number and arrangement of the components, and the relevant operating conditions are selected. The basic process is shown in Figure 1.

Membrane softening water is common in the United States. In the past 10 years, Florida's new softened water plants have used membrane softening to replace conventional lime softening and ion exchange processes. The main advantages are no sludge, no regeneration, complete removal of suspended solids and organic matter, easy operation and land occupation, and similar to conventional methods in terms of investment, operation and maintenance and price. According to the data of NF-70 membrane softening water in the literature, it is known that the nanofiltration membrane is used to soften water, TH MFP (trihalomethane latent product), TOXFP (total organic halogen potential product), SO2 -4 and CaH in water ( The removal rate of hardness is above 90%, and the removal rate of TH (total hardness), TDS and DOC is as high as 80% or more, and other ions (such as N a+, C l-, Fe2 +, etc.) The removal rate is also high. The water hardness in northern China is relatively high. To this end, Shandong Changdao has adopted a roll-type nanofiltration device to build a demonstration project of brackish water with a daily output of 140 tons. The water production meets the national drinking water standards, and the power consumption is only 1.43 kWh / t. In addition, a brackish water desalination demonstration project with a daily output of 24t was established in Kunshan, Zhoushan, Zhejiang Province with a hollow nanofiltration membrane device. The water production is in full compliance with drinking water standards.

The problem of drinking water pollution has attracted more and more people's attention. The developed countries such as the United States, Europe and Japan have plans to improve water quality, such as Japan's MAC-2 l plan and the new MAC- 21 plan, using membrane technology as water purification. The most effective means. Europe, the United States and other countries have also supported many membrane (NF) water purification tests with obvious results. Contaminants in groundwater or surface water are mainly pesticides, herbicides and excessive organic halides caused by disinfection. They are both toxic and even carcinogenic. Nanofiltration membrane separation removes disinfection by-products, traces of herbicides, pesticides, heavy metals, natural organic matter and partial hardness, SO2 -4 and NO -3, making it a technically and economically viable alternative. A suitable method for conventional activated carbon adsorption separation. The general process is: water infusion → pretreatment (flocculation, filtration, etc.) → MF (UF) → NF → effluent (standby). The advantages are that the water quality is good and stable, the chemical dosage is small, the land occupation is small, the energy saving, the labor saving, the management and the maintenance are basically zero emissions. Using NF membrane to remove pesticides in water, the removal rate of most pesticides can reach more than 99%, such as: Atrazine, Bzntazone, Dichlorvs, Diuron (D) Iuron) and so on. At present, a water plant producing drinking water with a water production capacity of 140,000 m3 /d on the outskirts of Paris, France, has been successfully operated for more than 2 years, and its effluent can fully meet the requirements of the European Union for the release of disinfection by-products. The effluent organic carbon (TOC) is less than 0.2 mg / L ~ 0. 3 mg / L, good biological stability, can effectively prevent the proliferation of bacteria in the water pipe network. China's Li Lingzhi and others used the nanofiltration membrane circulation process to conduct deep treatment experiments with the heavily polluted Huaihe River as the source water. The results show that the process can effectively remove NH+4, N, N 0-2, TOC and mutagens in water. Obtain impurities and obtain safe, qualified drinking water.