(1) Softening: Membrane softening water mainly uses nanofiltration membrane to selectively permeate ions with different valence states to soften water. Membrane softening can not only remove hardness, but also remove turbidity, chromaticity and organic matter, and its effluent quality is obviously superior to other softening processes. In addition, membrane softening has the advantages of no regeneration, no pollution, simple operation, less occupied area and so on, and has obvious social and economic benefits.
Membrane softening is very common in the United States. In recent 10 years, the new softened water plant in Florida adopted membrane softening instead of traditional lime softening and ion exchange processes. In recent years, with the continuous improvement of nanofiltration performance, the price of nanofiltration membrane components has been declining, and membrane softening method has been superior to or close to conventional methods in investment, operation and maintenance.
② Used to remove organics in water: Besides softening, nanofiltration membrane is mostly used to decolorize and remove natural organics and synthetic organics (such as pesticides), carcinogens, disinfection by-products (trihalomethane and haloacetic acid), their precursors and volatile organics in drinking water treatment, so as to ensure the biological stability of drinking water.
Nano-membrane separation technology is a membrane separation technology developed in recent years, which refers to the nano-scale separation process of membranes. It is separated and purified by intercepting a membrane with a relative molecular weight of 300 ~ 10000 (the particle size of the separated substance is equivalent to 0.3~ 100 nm), which includes the range that nanofiltration and partial ultrafiltration can separate, and it is also a pressure-driven membrane separation process. Because the relative molecular weight range of intercepted substances in nanofiltration technology is larger than that in reverse osmosis, but smaller than that in partial ultrafiltration, nanofiltration technology can intercept some solutes that can pass through ultrafiltration membrane and let substances that cannot pass through reverse osmosis membrane, thus helping to reduce the loss of solute intercepted for this purpose. This technology has the advantages of convenient operation, high treatment efficiency, no pollution, safety and energy saving.