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A tank in which sewage that is settled on a bed of stone, cementasbestos, or other surfaces is treated by aeration with compressed air.

Related Terms


A semiliquid mass removed from the liquid flow of sewage and subjected to aeration and aerobic microbial action; the end product is dark to golden brown, partially decomposed, granular, and flocculent, and has an earthy odor when activated-sludge effluent fresh.


A holding tank that discharges sewage at a rate required by treatment processes.


Inerting means: (i) the introduction of inert gas into an aerated tank with the object of attaining an inert condition suited to a safe gassing-up operation. (ii) the introduction of inert gas into a tank after cargo discharge and warming-up with the object of:— (a) reducing existing vapor content to a level below which combustion cannot be supported if aeration takes place (b) reducing existing vapor content to a level suited to gassing-up prior to the next cargo (c) reducing existing vapor content to a level stipulated by local authorities if a special gas-free certificate for hot work is required — see gas-free condition.


A sewage tank installed below the level of the lowest floor, with a submersibletype centrifugal pump that is used to pump the sewage into the public sewer main.


  1. A tank in which water or sewage is retained for periodic release through a sewer. 2. A small water-filled tank for flushing a water closet.


A tank in which heavy suspended matter is removed in sewage treatment.


Gas-free condition describes the full gas-freeing process carried out in order to achieve a safe atmosphere. It therefore includes two distinct operations: Inerting and Aeration. (Note: — In some gas trades the expression ‘Gas-free’ is used to denote a tank which is just Inerted. Some gas carrier operations can stop at this stage; for example prior to special dry dockings or cargo grade changes).


An underground tank for raw sewage collection; used where there is no sewage system. Also known as cesspit.


A tank used for batch washing of precipitates which cannot be leached satisfactorily in a tank; equipped with a slowly rotating rake at the bottom, which moves settled solids to the center, and an air lift that lifts slurry to the launders. Also known as Dorr thickener.


A sewage treatment tank in which digestion and settlement take place in separate compartments, one below the other.

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