1. Softening: The softening of membrane water is mainly achieved by the selective permeability of nanofiltration membranes to different valence ions. Membrane softening can remove turbidity, chroma and organic matter while removing hardness. Its effluent quality is obviously superior to other softening processes. Moreover, membrane softening has the advantages of no regeneration, no pollution, simple operation and less land occupation, and has obvious social and economic benefits.
Membrane softening has been common in the United States. In recent 10 years, new softening water plants in Florida have adopted membrane softening instead of conventional lime softening and ion exchange processes. In recent years, with the continuous improvement of nanofiltration performance, the price of nanofiltration membrane module has been declining. Membrane softening method has been superior to or close to the conventional method in investment, operation and maintenance.
2. Removal of organic compounds from drinking water: In addition to softening, nanofiltration membranes are used to decolorize, remove natural and synthetic organic compounds (such as pesticides), trigenic substances, disinfection by-products (trihalomethane and haloacetic acid), their precursors and volatile organic compounds, and ensure the biological stability of drinking water.
Removal of the three toxic substances: The results showed that nanofiltration membrane could remove most of the toxic and harmful organic substances and Ames mutagens in the water, so that the MR values of TA98 and TA100 strains were less than 2 at all test doses, and the Ames test results were negative. Further research will investigate the retention characteristics of endocrine disrupting substances in drinking water by nanofiltration technology, and provide a basis for safe and high-quality drinking water.
Removal of disinfection by-products and their precursors: Disinfection by-products mainly include trihalomethane (THMs), haloacetic acid (HAAs) and possible Trichloroacetaldehyde hydroxide (CH). Foreign scientists and technicians have carried out extensive research in this field. The average retention rates of the precursors of the three disinfection by-products by nanofiltration membranes are 97%, 94% and 86% respectively. By choosing appropriate nanofiltration membranes, the drinking water quality can meet higher safety and quality drinking water quality standards.
In addition, the nanofiltration water is low corrosive, has a positive impact on the service life of drinking water pipe network and the dissolution of metal ions in the pipeline, and is conducive to the protection of all materials in the water distribution system. The experiment shows that the solution of lead in pipe network can be reduced by 50% and the concentration of other metal ions can meet the drinking water quality standard by using the necessary post-treatment nanofiltration membrane system.
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