Glossary
The technical terms used in this site and the general terms of water treatment are explained on this page. The terms are listed in alphabetic order. Select the term you are looking for from the index on the left.
- Permeability
- This is a percentage which indicates how much the specific dissolved matter passes through the membrane in the membrane filtration. The value acquired by subtracting the permeability from 100% is the rejection rate.
- Permeate
- Water which passed through membrane. It is also called filtered water.
- Pleated module
- This is a module for raw water watercourse in which flat membrane is folded with spacers inserted between it, and it has almost the same characteristics as the spiral module.
- Pore size
- The size of holes on the part which is responsible for separation of semipermeable membrane (the surface of membrane in most of the cases). It is possible to observe several µm to 0.1µm holes with an electron microscope on MF membrane. The pore sizes of RO membrane and UF membrane are said to be around 10Å and several tens of Å respectively. However, it is almost impossible to actually observe the holes directly, and the rejection rate of salt and the molecular cutoff are used to represent it.
- Pore size distribution
- The pore sizes of semipermeable membrane are distributed in a certain way, and if it is just called "pore size", it indicates the average pore size. If the pore size distribution is narrow, the membrane shows sharp separation performance, but if it is wide, the accuracy of separation decreases. The pore size distribution is measured by the mercury press-in method, etc., but it is very difficult with RO membrane and UF membrane.
- porous structure
- A structure which contains many holes. The porous structure observed in the base layer of ROM membrane and UF membrane and in MF membrane can be observed with an electron microscope. It is categorized into the sponge layer in which small holes without directional properties exist continuously and reticulately and the finger structure in which there are finger-shaped large holes. The active layers in RO membrane and UF membrane are closely packed and their holes are not observed with an electron microscope. However, since separation characteristics can be calculated assuming that there are paths equivalent of pore sizes of around 10Å to several tens of Å, and they are also considered to be porous structures.
- Pressure drop
- When a fluid is poured into watercourse, the energy of the current is partially lost in the form of heat and sound by frictional resistance in the watercourse, and the pressure at the exit becomes lower than the pressure at the entrance. The differential pressure between the entrance and the exit is the pressure drop at that time. In a straight watercourse, the pressure drop is proportional to the length, and inversely proportional to the fourth power of the pipe diameter. It is also proportional to viscosity of the fluid, and proportional to the 1~2 power of the flow velocity.
- purified water
- This is one of standards of the Japanese Pharmacopoeia, and it indicates water of high purity acquired by distilling common water or performing ion exchange. It is used for preparation of pharmaceutical preparations or reagent, but since it contains germs and pyrogen, it cannot be used for manufacturing injections.
- Pyrogen
- A foreign substance which causes fever. Endotoxin derived from Gram-negative bacteria is a representative substance. If any drug polluted with pyrogens is administered by injection, infusion, etc., it induces various biological reactions (fever, chills, vomiting, complement fixation, etc.), and endangers the life of the patient depending on the patient's conditions and the dosage.
- Pyrogenic test
- Whether there is any pyrogen in the injection is tested using a rabbit.
- Rejection rate
- This is the value which indicates the percentage a specific dissolved matter is stopped by the membrane in membrane filtration.
If the rejection rate is 100%, the membrane does not pass the dissolved matter at all. On the contrary, if it is 0%, the dissolved matter passes through the membrane at the same concentration as the undiluted solution.
- Residual chlorine
- The chlorine effective for disinfection which remains in the water after chlorination is called residual chlorine. Among them, hypochlorous acid and hypochlorite are called free residual chlorine, and chloramine is called combined residual chlorine.
- Reverse osmosis membrane (RO membrane)
- When concentrated aqueous solution and dilute aqueous solution (e.g., sea water and water) contact through semipermeable membrane, water moves from the side of dilute aqueous solution to the side of concentrated aqueous solution to make the concentrations of the two solutions reach a state of equilibrium, and creates the differential pressure. The differential pressure is the osmotic pressure, and when a pressure larger than the osmotic pressure is applied to the side of concentrated aqueous solution side, water moves to the side of dilute aqueous solution side through the semipermeable membrane, and if the semipermeable membrane is dense, it is possible to take out pure water. Such a phenomenon is called reverse osmosis, and the membrane used for reverse osmosis is called reverse osmosis membrane. It is said that reverse osmosis membrane has holes of approx. 10Å (0.001µm) on the surface, but in general, the separation characteristics is expressed using the rejection rate of salt. It is used for purification of water such as desalination of sea water, manufacturing of ultrapure water, concentration of fruit juice, etc., and it is also used for manufacturing of aseptic pyrogen-free pure water in hospitals.