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.
- Activated sludge
- It is sludge which has excellent adsorptivity and precipitability acquired by applying aeration to sewage. It is an aggregate of the living things such as aerobic bacteria, protozoa, etc. which increase using the organic matter as the nutrient source and organic/ inorganic abiotic sludge, and it has ability to clean sewage.
- Active layer
- Extremely thin and dense layer whose thickness is 0.1µm or less on the surface of nonuniform membrane such as RO membrane and UF membrane. It has an important role of deciding selective permeability of the membrane. No hole is observed on the surface of the active layer even when it is magnified by 20 thousand times or so by an electron microscope, but it is said that there are holes whose pore sizes are around several tens of Å on UF membrane and around 10Å on RO membrane.
- Adsorption
- The phenomenon that specific components in a gas or a liquid selectively adhere to the solid material which contacts them, and the composition ratio becomes higher than the original gas or the original liquid. There are chemical adsorption by chemical bonding strength and physical adsorption by van der Waals forces. If the separation membrane continuously adsorbs components in the solution, the water permeation rate decreases and the separation performance changes in general.
- Aerobic bacteria
- They are bacteria which cannot grow or whose growth is inhibited in an environment where oxygen does not exist. The bacteria which cannot grow at all if here is no oxygen are called strictly aerobic bacteria, and those which grow well in an environment where the oxygen concentration is considerably low are called slightly aerobic bacteria.
- Anaerobic bacteria
- They are bacteria which do not use oxygen as the final electron acceptor for acquiring the energy for growing. In other words, it is a general term of bacteria which can grow under the condition there is no free oxygen, and it is categorized into facultative anaerobe which can grow even if oxygen exists, and obligate anaerobe which becomes difficult to grow if even a small amount of oxygen exists.
- Aquatic bacteria
- These are bacteria which live in water, and a lot of them live even in oligotrophic ion-exchanged water.
- Aseptic test
- This is a test to judge whether there is any live microbes in the material, tools and so forth used for pharmaceutical preparations, medical care, etc.
- Asymmetric membrane
- This is a membrane structure developed for increasing the water permeation rate without losing the separation characteristics and mechanical strength of semipermeable membrane, and the pore size changes in the direction of thickness of membrane. Only the surface of membrane (active layer, the thickness is normally 0.1µm or less) on the side which contacts the solution has holes required for separation characteristics, and the other part (base layer) has large pore sizes and low permeation resistance, which play roles in securing the watercourse for pore size and retaining the membrane strength.
- Back contamination
- The case that the germs which entered from the outlet of sterilized water settle on the sterilized water side and they exist in the sterilized water although the function of manufacturing sterilized water from raw water is functioning normally on a sterilization system, e.g., an aseptic water making apparatus. Adoption of a special valve, utilization of a slow-release germicide and a bacteriostatic agent, incorporation of an ultraviolet germicidal lamp, etc. are conducted as preventive measures against back contamination.
- Back washing
- This is a membrane surface cleaning method, which, contrary to the normal liquid passing method, pours liquid from the permeate side to the undiluted solution side to remove the deposits such as the fouling layer formed on the surface of membrane on the undiluted solution side for recovering the performance of membrane.
- Biochemical oxygen demand (BOD)
- The amount of oxygen required for biologically decomposing organic pollutants in water with dissolved oxygen indicated in mg/L. One of water pollution indicators.
- Chemical oxygen demand (COD)
- The amount of oxygen required for oxidizing the underwater organic matter which easily be oxidized with potassium permanganate is indicated in mg/L. It is one of water pollution indicators.
- Color value
- Color value means the degree of yellowish or tan color of the water indicated with numeric values. The color value when 1L of purified water contains 1mg of platinum and 0.5mg of cobalt in the color standard solution is defined to be 1 degree.
- Common water
- It is one of water standards of the Japanese Pharmacopoeia, and its water quality is almost the same as tap water. Tap water and well water are applicable, but tap water may require removal of residual chlorine. By further treatment of common water, purified water or other high-quality water is acquired.
- Compaction
- It is one of the causes of performance degradation of semipermeable membrane, especially RO membrane. The phenomenon that the highly pressurized membrane is compressed in the direction of thickness and becomes closely packed, and the speed of permeation of water decreases is called compaction. In such a case, the rejection rate of dissolved matter does not change or rather improves. It is known that the exponential law holds between the time of pressurization and the decrease in rejection rate of dissolved matter In order to avoid compaction, it is necessary to pay attention not to apply unnecessarily high pressure to the membrane.
- Composite membrane
- This is semipermeable membrane composed of the base membrane and an active layer which is formed on it with another membrane material. The membrane materials which is possible to create an asymmetric membrane (especially ROM membrane) composed of the same polymer are limited. Therefore, development of composite membranes which have extremely thin active layer formed on the UF membrane surface by various methods started, and more variety of membrane materials are used now.
- Concentrate
- This is water which has not passed membrane, and in which dissolved matter, suspended substances, etc. are concentrated.
- Cross flow filtration method
- This is a method which pours the feed water along the membrane surface, and the permeate which passes the membrane flows in the direction which is different from the feed water by 90 degree. Its merit is that decrease in the rate of filtration by clogging is small.
- Cryptosporidium
- It is a protozoan which belongs to Sporozoa. It lives parasitically upon cells of the gastrointestinal tract and respiratory organs of many animals including mammals, birds and fish.