Nanofiltration technology, high value future development prospects

Nanofiltration technology due to its characteristics are widely used in water treatment field, one of the largest application areas is the softening of drinking water. In addition, drinking water purification and ultrapure water preparation, or industrial and agricultural waste disposal and reuse. As a new type of membrane separation technology, which has a high value, so the industry believes that the development of nanofiltration technology is also very broad prospects.

Nanofiltration technology, high value future development prospects

1 Introduction

Nanofiltration (NF) is a membrane separation technique between ultrafiltration and reverse osmosis. The nanofiltration membrane has a pore size of a few nanometers, hence the name nanofiltration. Nanofiltration research began with the JE Cado tte NS-300 Membrane Study in the late 1970s. After that, nanofiltration developed rapidly and the membrane module was commercialized in the mid-1980s. Nanofiltration process and reverse osmosis and ultrafiltration process with the pressure-driven membrane process, but the mass transfer mechanism is different. Generally considered nanofiltration membrane for the dissolution - diffusion mode; the same time, most of the nanofiltration membrane charged type, the separation of inorganic salts not only by the chemical gradient control, but also by the potential gradient. Nanofiltration technology without any chemical reaction, without heating, no phase change, will not destroy the biological activity, does not change the flavor, fragrance, which is more and more widely used in water treatment, food, pharmaceutical industry in a variety of separation, refining And concentration process. NF technology in water treatment applications include: purification of drinking water, softening, electronics, semiconductors, biological and pharmaceutical production of ultrapure water preparation, contaminated surface water and groundwater and industrial wastewater purification treatment. This paper systematically introduces the application status of nanofiltration technology in water treatment from the aspects of membrane softened water, industrial water and domestic sewage treatment, and prospects the application prospects of the technology.

2 drinking water treatment and preparation of ultrapure water

2. 1 nanofiltration method demineralized water: NF membrane one of the largest areas of application is the softening of drinking water. In water, sulfuric acid and calcium carbonate, magnesium salt to produce water hardness. Film - tech company NF70 film is the main application of water softening, which is called "water softening film," its operating pressure of 0. 5MPa - 0. 7MPa, 85% - 95% to remove the hardness And 70% monovalent ions. Membrane demineralized water main factors considered feed water quality, infiltration water quality and recovery rate. Acid and scale inhibitors are added depending on feed water quality and recovery, depending on the quality and quantity of water infiltrated, the choice of membrane module, the number and arrangement of components, and the associated operating conditions.

Membrane-based demineralized water is common in the United States. Florida's new demineralized water softener plants have been softened by membrane methods over the last 10 years 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, etc., but are similar to the conventional method in terms of investment, operation and maintenance, and price. According to the data of NF - 70 membrane demineralized water in the literature, the TH MFP (Potential Trihalomethazine), TOXFP (Potential Organic Organotrifluoride Potential), SO2 -4 and CaH ( Hardness) removal rate of more than 90%, and TH (total hardness), TDS and DOC index removal rate as high as 80% or more, in addition to other ions (such as N a +, C l-, Fe2 +, etc.) Removal rate is also high. In northern China, water has a high water hardness. For this reason, a long-distance water filtration device was used in Long Island, Shandong Province to build a 140-tonne brackish water demonstration project. Water production in line with national drinking water standards, power consumption is only 1.43kWh / t. In addition, a demonstration project of 24t of brackish water desalination was completed with Shengnan Island, Zhoushan, Zhejiang, using a hollow nanofiltration membrane device. The production of water completely conformed to the standard of drinking water.

2. 2 Purification of Drinking Water: Drinking water pollution is getting more and more attention. Some developed countries in the United States, Europe, Japan and other developed countries have plans to improve their water quality. For example, Japan's MAC-21 and the new MAC-21 plan, Membrane technology as the most effective means of water purification. Europe, the United States and other countries also support many membranes (NF) water purification test, the effect is obvious. Pollutants in groundwater or surface water are mainly pesticides, herbicides, and excess organic halides caused by disinfection, which are toxic and even carcinogenic. Nanofiltration separates disinfection byproducts, trace amounts of herbicides, pesticides, heavy metals, natural organic matter, and partial hardness, SO2-4 and NO3, and is therefore a technologically and economically viable alternative The traditional method of activated carbon adsorption separation method. The general process is: water → pretreatment (flocculation, filtration, etc.) → MF (UF) → NF → effluent (spare). Its advantage is good and stable water quality, chemical dosage less, less land, energy saving, labor-saving, easy management and maintenance, basically zero discharge. The removal rate of most pesticides can be over 99% using NF membranes to remove pesticides in water, such as A trazine, Bzntazone, Dichlorvcs, Diuron (D iuron) and so on. At present, a water treatment plant producing drinking water with a membrane capacity of 140,000 m3 / d in the suburbs of Paris, France, has been successfully operated for more than two years. Its effluent can fully meet the newly-issued EU guidelines on disinfection by-products, The effluent organic carbon (TOC) is less than 0.2mg / L - 0.3mg / L, which has good biological stability and can effectively prevent the bacteria from propagating in the water pipe network. China's Li Lingzhi and other nanofiltration membrane recycling process using heavily polluted Huaihe River as the source of water for advanced treatment tests showed that the process can effectively remove the water NH + 4, N, N 0-2, TOC, mutagens And other impurities, access to safe, qualified drinking water.

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