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.
- Gel layer
- The layer that the poor-solubility high molecular weight solutes (proteins, polysaccharides, etc.) in the undiluted solution precipitate on the surface of membrane because of increase in concentration by concentration polarization and become gel during treatment of membrane. When the gel layer grows, a distinctive phenomenon that the flux becomes hardly dependent on the pressure but becomes dependent on the concentration of the dissolved matter is observed. It occurs because the amount of dissolved matter which is transferred from the solution to the gel layer proportionally to the flux becomes equilibrium with the amount of dissolved matter which reversibly returns from the gel layer by the concentration gradient decided by the concentration and the flow condition (gel layer model). A similar phenomenon is observed when fouling substances such as colloids and minute solids in the undiluted solution deposit on the membrane surface and form non-reversible resistive layer. Since there is no actual liquid which does not include any fouling substance, it can be said that "gel layer" is a very universal phenomenon during membrane filtration.
- Giardia
- It is a protozoan which belongs to Mastigophora, which lives in guts of human and other animals.
- Gram-negative bacteria
- Bacteria stained with safranine in the Gram's stain. Colon bacilli, salmonella, pseudomonas aeruginosa, etc. are included in it. In general, these are a bacterial group which produces endotoxins, and many of them are aquatic bacteria.
- Gram-positive bacteria
- Bacteria stained with crystal purple in the Gram's stain. Staphylococci, streptococci, Bacillus subtilis, etc. are included in it. In general, these are a bacterial group which produces exotoxin which causes food poisoning, etc.
- Gram's stain
- This is a staining method essential for identification of a bacterium. The cell nucleus is stained in deep purple (crystal purple) with a Gram-positive bacterium, and rose pink (safranine) with a Gram-negative bacterium. It is stained in the following order in this staining method: crystal purple -> Lugol's solution -> alcohol decolorization -> safranine.
- Hand-washing water for surgery
- The water used for sterilizing and washing hands, fingers and arms before surgery for prevention of infection at operating rooms of hospitals. 20 to 30L of hot water is normally used for washing. Its water quality is required to be germ-free, and various types of aseptic water supply equipment is used. ultraviolet sterilization type equipment used to be used often, but since complete sterilization is extremely difficult with this method, equipment of disinfection methods using membrane is adopted more often recently.
- Hardness
- The amount of calcium ions and magnesium ions in the water is converted to corresponding amount of calcium carbonate, and expressed in mg/L. The water whose content of the salts of calcium and magnesium is relatively high is called hard water, and the water whose content of them is relatively low is called soft water.
- Heat sterilization
- This is a sterilization method which kills microbes and spores by applying heat.
- Hollow fiber membrane
- This is thready tubular semipermeable membrane whose diameter is up to 2mm. If the membrane thickness is uniform, the smaller the diameter is, the higher the resistance to pressure becomes. Hollow fiber membrane whose inner diameter is 0.5mm or more is used for the UF membrane operated under low pressure, but the inner diameter of the RO membrane which is used under high pressure is as thin as 0.1mm or less. Hollow fiber membrane has advantages that its membrane itself is resistant to pressure, no support is required, and it is possible to contain the membrane at the highest packing density among various modules.
- Homogeneous membrane
- Membrane whose structure is uniform like general plastic film. To be precise, it is not as dense as plastic film and it has fine porous structure. However, it is called as above because there is no difference in the direction of thickness, and it looks uniform. Permeable membrane and ion exchange membrane are included in homogeneous membrane.
- Hydrophobic adsorption
- Adsorption which occurs between substances whose affinities for water are small. In specific, adsorption which occurs by interaction between chemical structures whose affinities for water are small.
- Internal pressure type
- This is a filtration method which uses a hollow fiber module or a tubular module into which pressurized undiluted solution is poured, and the liquid which passes through the module and comes out to outside of it is collected. The activated layer of membrane exist inside which contacts the undiluted solution. It has an advantage that the membrane performance is fully exerted because there is not unevenness in the flow condition of the undiluted solution.