ANSI AWWA B116-19 pdf download.Electrodialysis and Ion-Exchange Membrane Systems
32. Langelier saturation index (LSI): A calculated index indicating the tendency of a solution to dissolve (negative value), precipitate (positive value), or be at equilibrium (value equal to zero) with calcium carbonate. LSI = pH a – pH s , where pH a is the actual solution pH and pH s is the pH if the solution was at saturation with calcium carbonate. The value of pH s is calculated based on the concentrations of calcium, alkalinity, and dissolved ions, and temperature.
35. Membrane: An engineered material designed to remove solids (dissolved or suspended) that are rejected from the system as either backwash or a concentrate stream, and that produces a stream containing less solute or particles (the product or filtrate stream). This standard focuses on treatment processes that employ IEMs, which selectively allow or restrict ionic transport. Membrane types in pressure-driven standards include low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF), as well as higher-pressure membranes such as nanofiltration (NF) and reverse osmosis (RO). Other definitions are more restrictive including the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), which defines membrane filtration as “a pressure- or vacuum-driven separation process in which particulate matter larger than 1 micron is rejected by a non-fibrous engineered barrier.”
37. Microfiltration (MF): Membrane filtration process with pore diameter nominally at least 0.1 µm that provides at least 3-log removal of Giardia cysts or Cryptosporidium oocysts or similar-sized 3 µm and larger surrogate materials based on challenge testing in accordance with the USEPA Membrane Filtration Guidance Manual.
38. Nanofiltration (NF): Membrane filtration process that removes dissolved constituents from water—such as dissolved organics, color, calcium and magnesium (hardness) ions, and other ions. NF membrane elements provide a nominal organic molecular weight cutoff in the range of about 200 to >500 Daltons and sodium chloride rejection of 0 to 95 percent. NF is like RO with the key difference being that NF has lower sodium chloride rejection than RO, and it exhibits more selectivity in the types of ions that are removed such that NF allows a comparatively higher percentage of monovalent ions to pass to the permeate than multivalent ions.ANSI AWWA B116-19 pdf download.