The molecular weight cut-off of NF membranes is between RO membranes and UF membranes, approximately 200-800 daltons. Retention characteristics: preferential retention of divalent and multivalent anions, and the retention rate of monovalent ions is related to the concentration and composition of the solution. NF is generally used to remove organic matter and pigments from surface water, hardness from groundwater, and partially remove dissolved salts. It is also used for substance extraction and concentration in food and biopharmaceuticals production. The operating pressure of NF membranes is generally 3.5-30 bar.