| critical point drying | <procedure> A method for preparing specimens for the scanning electron microscope that avoids the problems of shrinkage caused by normal drying procedures. Water in the specimen is replaced by an intermediate fluid, for example liquid carbon dioxide, avoiding setting up a liquid/gas interface and then the second fluid is allowed to vaporise by raising the temperature above the critical point, the temperature at which the liquid state no longer occurs. (18 Nov 1997) |
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| freeze-drying | <technique> Method commonly adopted to produce a dry and stable form of biological material that has not been seriously denatured. By freezing the specimen, often with liquid nitrogen and then subliming water from the specimen under vacuum, proteins are left in reasonably native form and can usually be rehydrated to an active state. Since the freeze dried material will store without refrigeration for long periods, it is a convenient method for holding back up or reference material or for the distribution of antibiotics, vaccines etc. Synonym: lyophilization. (18 Sep 2002) |
| activated sludge | See: activated sludge method. (05 Mar 2000) |
| activated sludge method | A method of sewage disposal in which the sewage is treated with 15% bacterially active, liquid sludge, which is produced by repeated vigorous aeration of fresh sewage to form floccules or sediment; when this flocculation process is complete, the resulting activated sludge contains large numbers of bacteria, together with yeasts, molds, and protozoa, which actively effect the oxidation of organic compounds; this mixture is piped to a sedimentation tank, the effluent from which is completely treated sewage. (05 Mar 2000) |
| activated sludge process | <procedure> A method of treating sewage and wastewater through microbial oxidation. Sewage previously treated in settling tanks is aerated to encourage the growth of nonpathogenic aerobic microorganisms (bacteria, yeasts, moulds and protozoans) which break the organic matter down into carbon dioxide, water and simple salts. After this activated sludge is produced, the wastewater undergoes further processing through anaerobic digestion, filtering and chlorination. (29 Dec 1997) |
| sludge | 1. Mud; mire; soft mud; slush. 2. Small floating pieces of ice, or masses of saturated snow. 3. <chemical> See Slime. Sludge hole, the hand-hole, or manhole, in a steam boiler, by means of which sediment can be removed. Origin: CF. Slush. Source: Websters Dictionary (01 Mar 1998) |
| upflow sludge blanket | <apparatus> An apparatus for anaerobic digestion in which the microbes form thick flocculations that are kept suspended near the bottom of the reaction tank. (09 Oct 1997) |